JP2003516491A - Method of treating exhaust gas containing SOx - Google Patents

Abstract

(57) A method for treating exhaust gas from a lean burn internal combustion engine containing sulfur oxides (SOx) and at least one other air pollutant selected from HC, CO, NO and soot. Wherein the gas is untreated or has undergone some type of chemical and / or catalytic treatment, wherein the method comprises the steps of absorbing a sulfate-forming SOx component in a solid absorbent. And a step of releasing the SO ₂ -containing gas into the atmosphere, and a step of periodically exchanging the absorbing material. A system for performing the method comprises an exhaust passage and a sulfate absorber (26) comprising a substrate supporting a solid material for absorbing sulfate forming components from SOx in the exhaust gas. Wherein the sulfate absorber is adapted to be replaceable.

Description

Detailed Description of the Invention

The present invention provides a method of treating exhaust gas containing sulfur oxides (SOx) and an exhaust system for carrying out this method.

There are regulations on exhaust emissions from internal combustion engines, and these regulations have become increasingly stringent over the last few years. In order to meet current regulatory requirements and control emissions, vehicle exhaust systems typically include major pollutants emitted from the engine, such as unburned hydrocarbons (HC), CO, soot and nitrogen oxides. It comprises a catalytic treatment to control the amount of (NOx). In order to bring the amount of major pollutants emitted from the exhaust system into the legally specified amount range, catalytic converters should help convert these pollutants to less harmful species. Is designed.

One of the other pollutants found in exhaust gases, SOx, is derived from sulfur in engine fuels and / or lubricating oils, which is very difficult to treat. SO ₂ in the exhaust gas is oxidized to SO ₃ on the catalytic converter,
It is converted to "sulfate," which then reacts with water to form sulfuric acid. Sulfuric acid not only poses potential health and environmental damage, but also forms fog and is measured as particulate matter (PM) in legally prescribed emissions testing procedures. The amount of sulfur in fuels and lubricating oils is set low to meet future emission regulations, but for the time being the problem that sulfur causes during exhaust gas aftertreatment remains. SOx reduces the efficiency of components for controlling exhaust gases, such as Johnson Matthey's Continuous Regeneration Trap CRT ™ technology.

The method used in CRT (trade name) is described in EP-A-0341382 and US Pat. No. 4,902,487, both of which are incorporated herein by reference. This method treats NO and soot-containing exhaust gas originating from an internal combustion engine, in particular a diesel engine, which passes unfiltered exhaust gas over an oxidation catalyst and converts NO into NO ₂ . The method comprises collecting soot on a filter and reacting the collected soot with NO ₂ to burn it.

A number of methods have been proposed to remove SOx. EP 0582917 A1 discloses an exhaust system comprising a NOx trap and an SOx trap located upstream. NOx traps generally generate NO
It comprises a component for oxidizing to O ₂ , eg platinum. This NO ₂ is then absorbed by components of the NOx trap composition, such as BaO, and stored as nitrates. Then, the engine is controlled to operate in rich, the stored NO ₂ is released (thereby reproducing the NOx trap), it is typically reduced to N ₂ over a catalyst reducing component, such as rhodium. However, components for oxidizing NO also is also intended to oxidize SO ₂ to SO _3, this SO ₃ is absorbed by BaO, are stored as the sulphate. Sulfate is more stable than nitrate even under rich operating conditions, and the NOx storage capacity of the NOx trap gradually decreases due to the sulfate blocking the storage site. To remove SO, EP0582917A1 includes a SOx trap upstream of the NOx trap, similar to the formulation of NOx traps. In column 5, line 2 of this specification, "all SOx emitted from the engine is absorbed by the SOx absorber, and this SOx is absorbed.
The SOx absorbed by the absorber is not released until the air-fuel mixture supplied to the combustion chamber is rich. " To solve this problem, Johnson Matthey, among others, uses SOx traps in situ (in situ).
) Proposed a method of intermittent regeneration (see EP814242A).

We have now found that by absorbing only the sulfate-forming components of SOx originating from the exhaust gas and releasing the SO ₂ -containing gas into the atmosphere, the amount of particulate matter detected increases. It has been found that the problems of can be reduced or overcome.

According to a first aspect, the invention relates to sulfur oxides (SOx) and HC, CO, NO
And a method for treating exhaust gas originating from a lean-burning internal combustion engine, which contains at least one other air pollutant selected from soot, said gas being untreated or of a certain type Which has been subjected to a chemical treatment and / or a catalytic treatment, and which absorbs an SOx component forming a sulfate in a solid absorbent material, a step of releasing a SO ₂ -containing gas into the atmosphere, and the absorbent material And periodically exchanging.

The term “periodically” means that the absorbent material is removed from the exhaust system and replaced with fresh absorbent material at certain intervals. The length of this interval depends, inter alia, on the capacity of the substance for absorbing the sulphate-forming SOx components and the amount of sulphate-forming SOx components in the exhaust gas flowing in the exhaust system. Sulfate formation S
The capacity remaining in the sulfate trap to absorb the Ox component is evaluated using standard techniques. These techniques use preset "maps" to approximate the cumulative formation of sulfate forming SOx components in the exhaust system resulting from the use of the engine since the last refreshment of the absorbent material. It encompasses the use of sensors and / or programming of the engine management system used.

The most convenient length of the interval is the service period for a typical passenger car including a light duty diesel engine, that is, a period of one year or up to 12,000 miles. This allows the absorbent material to be replaced at the same time as other components, such as spark plugs and oil filters. Of course, a situation may be tolerated in which the absorbent material is replaced only at intervals of several times the normal service period, for example 2-3 times. Nevertheless, the length of this interval can be extended to the useful life of the vehicle in which it is loaded without having to replace it. Alternatively, the vehicle may be scrapped at the end of the period when the absorbent material needs to be replaced.

The term “replace” means to remove the absorber from the exhaust system and load a new absorber. The removed absorber can be regenerated off-engine, depending on the composition, using measures to avoid unacceptable sulfate emissions.

The gas to be treated may be unprocessed, ie untreated,
Alternatively, it may be subjected to some kind of chemical treatment and / or catalytic treatment prior to the step of absorbing the sulfate-forming SOx component. In a preferred form of the invention, such prior treatment comprises oxidizing NO to NO ₂ . Such a process typically oxidizes HC and CO, and possibly some soot components, which may be desirably carried out in several steps, the first of which mainly It oxidizes CO and soot as much as possible, and in the second stage oxidizes mainly NO. As will be appreciated, the process of oxidizing NO to NO ₂ can also facilitate the oxidation of SO ₂ to SO ₃ . However, in order to limit the gas-phase oxidation of SO ₂ by oxidation and NO ₂ in the SO _2, it can be adjusted catalytic select, and / or the temperature.

Alternatively or additionally, the gas may be treated by the introduction of ozone as described in WO99 / 36162 or by the action of a plasma generator as described in WO00 / 21646. This is because such method steps are carried out without substantially oxidizing SO ₂ to SO ₃ .

One of ordinary skill in the art will be aware of a number of ways to reduce the formation of sulfate forming SOx components in an exhaust system. One way is to keep the temperature of the exhaust gas as low as possible. This is, for example, an exhaust gas recirculation device (E
GR) or by placing the oxidation catalyst in a cooler part of the exhaust system away from the exhaust manifold, eg under the floor. However, when a person skilled in the art wants to design a vehicle exhaust system, reducing the amount of SO ₂ oxidation is not the only concern, and is usually the case for hydrocarbon oxidation or NO emission, for example in CRTs. One should consider the oxidation to NO ₂ to be the second important concern. Further, heavy duty diesel (HDD) vehicle engines operate at higher temperatures than passenger vehicle light duty diesel (LDD) engines. In addition, Transit (which can be classified as LDD
The engines of vehicles such as vans often operate at much higher temperatures than similar engines in passenger cars. This is because HDD vehicle engines are designed to haul larger loads and are fitted with transmissions accordingly. Thus, the problem of reducing or avoiding the formation of sulfate forming SOx components in exhaust systems that include exhaust treatment components, such as oxidation catalysts, is difficult.

European HDD vehicles are defined as vehicles having a gross weight greater than 3.5 tons. In most of the United States, HDDs have a total weight of 8500 lbs (38
56 kg) is defined as a larger vehicle. In California, vehicles with a total weight of more than 6000 lbs (2722 kg) are non-light duty, those of 6000 to 14000 lbs (2722 to 6350 kg) are medium duty diesels, and those of more than 14000 lbs (6350 kg) are heavy duty diesel. We are convinced that it is classified. For purposes of this specification, the definition "heavy duty diesel" is intended to encompass both medium duty and heavy duty diesel, as provided by California law.

In the sulphate absorption step, SO ₃ may be adsorbed as it is, or the product of further reactions, especially the reaction with water vapor normally present in the exhaust gas originating from hydrocarbon fuel consuming engines. May be absorbed as.

According to a particular aspect of the invention, the gas is for example before the removal of sulphate,
However, after catalytic oxidation of NO or ozone introduction or plasma action, it is treated, for example by filtration, to remove soot. Such methods typically use the CRT (trade name) technology described above. If the filter is catalyzed, with or without a separate NO oxidation, the catalytic oxidation of SO ₂ on the filter is limited by the choice of catalytic material and / or temperature control.

In a second aspect, the present invention is a system for treating exhaust gas originating from a lean-burn internal combustion engine, said method absorbing sulphate-forming components from an exhaust passage and SOx in the exhaust gas. A sulphate absorber comprising a substrate supporting a solid substance for the sulphate absorber, the sulphate absorber being adapted to be exchangeable.

In a third aspect, the invention provides a lean-burn internal combustion engine, preferably a diesel engine, most preferably a heavy duty diesel engine, in combination with a system according to the invention. In order to prolong the life of the sulphate absorber before replacement and / or to limit its capacity and pressure drop, this engine preferably has a low sulfur content, eg less than 50 ppm w / w, especially 10 ppm.
Operates on fuels containing less than ppm w / w of sulfur.

In a fourth aspect, the present invention provides a vehicle comprising an engine according to the present invention.

In a fifth aspect, the present invention provides that the solid absorbent material comprises barium oxide (10-2
0% w / w), ceria (15-40% W / W), and a balance washcoat containing 2-5 g per cubic inch of a mixed washcoat, according to the invention. I will provide a.

In a sixth aspect, the present invention provides that the solid absorbent comprises a high surface area alumina (50-1
50 m ² g ⁻¹ ) and zeolite β in a 2: 1 to 1: 2 mixture of 0.5 to 4.0 g per cubic inch, and the washcoat is from 0.1 to 0 per cubic inch. There is provided a sulphate absorber according to the invention, comprising 0.5 g of calcium oxide (as calcium metal).

The absorbent is preferably supported on the surface of the ceramic or metal honeycomb. Conventional washcoat layers may be used. Absorbent may be applied to uncoated honeycombs to increase absorbent loading and / or limit coating thickness. The absorbent is in a vessel adapted to be joined alternately between the exhaust treatment reactor or its upstream and downstream portions; or at such a central portion or at the open end of the upstream or downstream portion. And may be in a cassette adapted to be located. The reactor or reactor section may be constructed to removably accommodate such cassettes or coated honeycombs.

In a seventh aspect, the invention comprises removing spent absorbent from the surface of the substrate, preferably by washing, and applying fresh absorbent to this surface. There is provided a method of regenerating an absorber filled with sulfate according to the present invention. For such washing, an additive such as a detergent or a means such as a pH adjusting agent may be used. Therefore, the expensive honeycomb can be reused. Washing may be treated to recover the spent absorbent component, if economical.

The honeycomb substrates for the absorbers, catalysts and filters used in the method or system according to the invention are structurally ceramic, such as cordierite, alumina, mullite, silicon carbide, zirconia or sodium phosphate / It may be made of zirconia or a metal, for example, a heat resistant alloy such as Fecraloy (trade name). Typically, the honeycomb is at least 50 cells per square inch (cpsi) for ceramics, and possibly more, for example up to 800 cp.
si, and even more for metals, for example up to 1200 cpsi. Generally, a range of 100-900 cpsi is preferred.

In the case of catalysts and absorbers, the honeycomb walls are substantially gas impermeable and are preferably of alumina, ceria, zirconia, silicon carbide or other materials, typically oxides. Preferably, a surface area-enhancing washcoat comprising one or more of Absorbent and / or catalytic material is present in one or more layers in and / or on the washcoat. The gas impermeability of this wall may be intrinsic or it may be imparted by using a filter grade honeycomb and blocking its pores by wash coating.

[0026]   The constituent material of the filter honeycomb is the same as the material used for the catalyst honeycomb
May be selected from If the filter honeycomb is ceramic, its honeycomb
The system contains a substantially non-fugitive substance in which the required pores are removed by firing or the like.
The product formed (e.g., by extrusion) of the composition. Honeycomb
Form and bake powder with foam whenever possible, whether lamic or metallic.
It may be a product obtained by binding. Other filters are metal mesh or wire
It may consist of Filter grade honeycomb is preferably 0.1 x 10 ^-3 ~ 20 x 10^-3It has an average pore size of inches (0.25 to 50 μm). This
Filters can be coated with one or more of the washcoats described above and / or
PGM above, for example Pt + MgO, or La / Cs / V_TwoO₅Touch like
A medium may be supported, provided that its fluid permeability is not significantly impaired and
SO at a temperature at which such a catalyst can be used_TwoFormulated to avoid or limit oxidation
The condition is that

In the oxidation catalyst and any final catalyst, the active substance may be, for example, a platinum group metal (PGM), in particular Pt and / or Pd, if necessary other PGM (eg Rh) and other catalyst components or Containing with a facilitating ingredient. The exact composition and composition of these catalysts may vary depending on the requirements of the situation. For oxidation catalysts, low temperature ignitable formulations are generally preferred.

The oxidation catalyst and filter may be provided on a single brick of filter grade honeycomb, the pores in the catalyst area being plugged with a washcoat.

In sulphate sorbents, chemically active coatings include, for example: (a) compounds of alkali metals, alkaline earth metals, rare earth metals and transition metals capable of forming sufficiently stable sulphates; And (b) may comprise absorbent materials such as zeolites, carbon and high area oxides.

The compound (a) is, for example, a composite oxide of an alkaline earth metal and copper, such as Ba.
-Cu-O and _{MnO 2} -BaCuO 2, made with a Ce oxide unless added as possible, or Y-Ba-Cu-O and Y-Sr-Co-O or rare earth mixed oxides, for example CeO ₂ / ZrO ₂ (before absorption). Absorber materials, on the other hand, have been specified with respect to oxides, and during the performance of the method of the invention, this absorbent material may be, for example, hydroxides compatible with the gas in contact with them,
It will be appreciated that it may be present as carbonate and nitrate.

If either compound is used, the absorber is preferably free of materials to catalyze SO ₂ oxidation. This absorber may be provided in one unit or in separate units in series.

The sulphate absorber may contain substances selected for economic reasons as they are not regenerated in situ but have a limited life due to their chemical absorption capacity. .

Suitable SOx absorbers are preparations which contain at least one alkaline earth oxide, in particular calcium oxide, and possibly others, such as magnesium oxide, eg dolomite, or containing SrO or BaO. Comprises. Such oxides may be deposited directly on the honeycomb, or with the aid of a sulfate-enhanced washcoat. Preferably, the oxide is applied as a carbonate, as a mechanically or chemically formed dispersion, or by settling onto the honeycomb surface.

[0034]   Among the preferable sulfate absorbers, the following can be mentioned.

(A) Barium oxide (eg 10 to 20% w / w) and ceria (15 to 40%)
% W / w) and a honeycomb carrying a mixed washcoat containing 2-5 g per cubic inch of alumina (the balance); and (b) high surface area alumina (50-150 m ² g ⁻¹ ) and zeolite β. Two
A honeycomb carrying a washcoat layer comprising from 0.5 to 4.0 g of the mixture from 1 to 1: 2 per cubic inch, the washcoat having a total loading of from 0.1 to 0.5 g per cubic inch. Those that carry calcium oxide in the amount (calculated as calcium metal).

A method for making a sulfate absorber is a washcoat suspension containing a sulfate-reactive substance, a high surface area oxide such as alumina, and optionally an auxiliary material such as a rare earth oxide. And applying it to the honeycomb. According to another method, washcoat suspensions containing high surface area oxides such as alumina and / or zeolites are applied to the honeycomb and then impregnated with sulphate-reactive substances (possibly as solutions). In any method of preparing a sulfate absorber, one or more components are applied as precursor compounds that can be converted to the required active or high surface area materials, for example by heating or contact with hot exhaust gas. can do. Examples of such precursors include the alkaline earth metal and hydrated alumina bicarbonates, acetates and nitrates.

The present invention is illustrated by the accompanying drawings, which show, in cross-sectional elevation view, an exhaust gas treatment reactor containing a catalyst and an absorber corresponding to the process steps of the present invention. In the drawings, member items are indicated by solid lines, and flows of information and control force are indicated by dotted lines.

In the drawing, the reactor comprises a can having an inlet part 10, an outlet part 12 and a central part 14, the three parts being fastened together by a flange 16. The inlet 18 is connected to the exhaust pipe of the engine cylinder block. Entrance 18
Closest to is an oxidation catalyst 22 supported on a ceramic honeycomb. Next is the filter 24, which is a filter grade ceramic honeycomb. The next stage 26 is located in the separable center 14 of the reactor and is an alkaline earth carbonate sulphate absorber supported on a ceramic honeycomb. The treated gas is discharged from the portion 12 through the outlet 20 to the atmosphere.

The reactor contains sensors 28, 30 and 32 for temperature and gas composition. Sensors 28 and 30 measure the pressure drop across filter 24. The value sensed by the sensor is reported to computer 42 for processing and provides, for example, a control signal indicating the need to replace sulfate absorber 26. For convenience when exchanging
Portion 14 does not include the control gear.

In carrying out the method of the present invention, the exhaust gas first strikes the oxidation catalyst 22, which, if the oxidation of HC or NO is optimized separately, will result in two or more series. May be placed in the part connected to. Oxidation of SO ₂ to SO ₃ by O ₂ and NO ₂ is limited by catalyst selection and temperature control. The gas containing soot and NO ₂ enters the filter 24 where the collected soot is burned by NO ₂ . Here, the gas enters the central portion 14 of the reactor and, in the absorber 26, its sulphate-forming constituents are removed. The gas may then be released to the atmosphere or further processed (not shown in the figure).

When a preset time period has elapsed or the sensor 32 reports the presence of sulfate,
The engine is stopped and the exhaust system is cooled. Thereafter, the flange 16 is opened, the central part 14 of the reactor is removed and replaced, and the flange 16 is closed again. The sulfate absorber 26 is extracted from the central portion and sent for regeneration or material recovery. As an example, a vehicle that uses diesel fuel with a sulfur content of 10 ppm at a rate of 20 mpg will be 20,000 miles (assuming an air fuel cost of approximately 30: 1) and at most 80 g of sulfate (SO _{As 3} ). Diesel fuel of 50 ppm is about 1.6 in the exhaust gas.
This produces ppm SO ₂ . Assuming 20% of the SO ₂ is oxidized and the resulting sulfate-forming SOx component is absorbed, the exchangeable trap also has a 200
Accumulate approximately 80 g of sulfate at 00 miles. Therefore, a reasonably sized sulfate absorber for medium to heavy vehicles will hold up during after-sales service.

[0042]

【Example】

  For a full understanding of the invention, the following examples are provided by way of illustration only.

Example 1 A 12 liter, 318 kW direct injection diesel engine with a turbocharger aftercooler was run using a series of fuels derived from Swedish class 1 diesel fuel with thiophene added and thiophene added. Untreated fuel and fuels containing 10, 20, 30 and 40 ppm w / w sulfur were each provided to three samples.

The engine was run on a standard European Steady State (ESC) test cycle and contained 10.5 inches diameter x 6 inches long (267 x 152 mm) containing 400 cells per square inch (65 cells cm ^-2 ). Of platinum on alumina having a platinum loading of 75 gft ^-3 and a platinum-containing oxidation catalyst (22) and a diameter of 100 cells per square inch (16 cells cm ^-2 ). .5 inches x
After passing the gas through a cordierite wall fluidized particle filter (24) having a length of 12 inches (267 x 304 mm), the particulate matter in the exhaust gas (
PM) was measured.

[0045]   The results of PM measurement were as follows.

[0046]   Fuel S ppm w / w 3 10 20 30 40   Outlet PM mg / k Wh 8 10 16 20 20 25

The outlet PM has proven to be a linear function of the sulfur content of the fuel, with certain contributory factors mainly due to the sulfur present in the lubricating oil burned in the engine. These experiments have shown that the sulphates produced by the combustion of sulfur compounds in internal combustion engines are a clear contributor to PM measured by standard methods. Analysis of PM showed that this PM consisted almost entirely of sulfate, with a small amount of nitrate.

Example 2 In order to demonstrate the principle that a solid absorbent material according to the present invention is capable of passing SO ₂ , but absorbing sulfate-forming SOx components, such as SO ₃ , that originate from the gas stream. The SCAT rig was tested indoors. Packing density is about 2.5
g inch ^-3 (41.0 gcm ^-3 ), 400 cell inch ^-2 (65 cell cm ^-2 ), wall thickness 6 × 10 ^-3 inch (0.0015 cm) ceramic honeycomb substrate, calcium oxide wash By applying a coat, the sulfate "
A "trap" was prepared. A 1.5 inch (3.8 cm) long core was obtained for testing.
By oxidizing the SO ₂ by using a platinum on alumina catalyst in the upstream portion of the core, to produce the SO ₃ in the gas stream.

[0049]   Three test cores were tested for steady state performance at a temperature of 300 ° C for 10 minutes.
It was The synthesis gas mixture entering the oxidation catalyst is 40,000 hours for the whole system.^-1of
200 ppm CO at space velocity_Two, 200ppm NO_Two, 20 ppm SO _Two (Diesel fuel containing about 500 ppm sulfur), 100 ppm charcoal water
Elementary (C_Three), 12% O_Two, 4.5% H_TwoO, 4.5% CO_TwoAnd N_TwoThe rest
It had a composition of parts. Mass spectrometric measurement of the gas leaving the core
Was used to analyze in real time.

12 ppm SO ₂ was detected in the gas composition exiting the core. The results showed that some SO ₂ was oxidized by the oxidation catalyst, which was absorbed by the sulfate trap. The presence of SO ₂ in the gas composition exiting the core indicated the ability of the sulfate trap to “escape” SO ₂ .

Example 3 Platinum at 1.4 g / l and washcoat at 150 g / l 400 cells / inch ² (65 cells cm ^-2 ), wall thickness 8 1/100
0 inch (0.02 cm) cordierite monolith substrate (diameter 4.66 "(
A standard oxidation catalyst comprising platinum on alumina covering 11.84 cm) and a length of 3 "(7.62 cm)), 1.7 liter direct supercharge in accordance with European Stage 3 emission regulations. It was installed in the underfloor position of a 1999 vehicle equipped with an injection diesel engine, using diesel fuel containing 350ppm of sulfur at a typical exhaust gas temperature in a light duty Transit (trade name) van, and using the European stage The vehicle was run for 3 driving cycles, and the measured particulate emissions were 0.1.
It was 46 g / km.

The catalyst was then removed and replaced with a bare monolith substrate of the same dimensions as the previous catalyst and the vehicle was run under the same conditions in a European Stage 3 test cycle. The particulate exhaust was 0.77 g / km means that at least 0.069 g / km of sulphate was produced on the catalyst, which also removed some hydrocarbons from the particulate exhaust. I showed that. The same catalyst used in the first test was prepared by adding MgO equivalent to 18 g / l, then the catalyst was loaded into the vehicle and the vehicle was tested in the European Stage 3 test cycle as before. I ran it. The amount of particulate exhaust was 0.056 g / km, which means that the amount of sulfate absorber is 0.090 g / km.
It shows that the sulfate of km was removed.

Example 4 Platinum at 2.8 g / l and washcoat at 150 g / l, 400 cells / inch ² (65 cells cm ^-2 ), wall thickness 8 1/100
0 inch (0.02 cm) cordierite monolith substrate (diameter 4.66 "(
A standard oxidation catalyst comprising platinum on alumina covering 11.84 cm) and a length of 3 "(7.62 cm), 1.7 liter direct unsupercharged according to European Stage 3 emission regulations. It was installed in the underfloor position of a 1999 vehicle equipped with an injection diesel engine.A bare monolith substrate of the same dimensions as this catalyst was placed at the rear of the catalyst.Typical in a light duty Transit (trade name) van The vehicle was run at a typical exhaust gas temperature using diesel fuel containing 350 ppm of sulfur and in a European Stage 3 driving cycle with a measured particulate emission of 0.120 g / k.
It was m.

The catalyst was then removed and replaced with a bare monolith substrate of the same dimensions as the previous catalyst and the vehicle was run under the same conditions in a European Stage 3 test cycle. A particulate exhaust of 0.077 g / km means at least 0.043 g / km.
Sulphate catalyst (this catalyst also removed some hydrocarbons from the particulate exhaust)
Indicates that it was generated above. A substrate coated with alumina containing 24.5 g / l of CaO equivalent was placed behind the platinum on the alumina catalyst from the first test and the vehicle was tested in a European stage 3 test cycle as before. Was run. The amount of particulate exhaust was 0.046 g / km, which means that the sulfate absorber had 0.0
It shows that 74 g / km of sulfate was removed.

[Brief description of drawings]

FIG. 1 is a cross-sectional elevational view of an exhaust gas treatment reactor containing a catalyst and an absorber corresponding to the process steps of the present invention.

[Procedure for Amendment] Submission for translation of Article 34 Amendment of Patent Cooperation Treaty

[Submission date] December 11, 2001 (2001.12.11)

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be amended] Claims

[Correction method] Change

[Contents of correction]

[Claims]

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0007

[Correction method] Change

[Contents of correction]

According to a first aspect, the invention relates to sulfur oxides (SOx) and HC, CO, NO
And a method for treating exhaust gas originating from a lean-burning internal combustion engine, which contains at least one other air pollutant selected from soot, said gas being untreated or of a certain type Of the SOx forming a sulphate of the gas in a solid absorbent material that is substantially free of catalyst feed for SO ₂ oxidation. There is provided a process comprising the steps of absorbing components, releasing the SO ₂ component of the gas to the atmosphere, and exchanging the absorbent material when its sulfate absorbing capacity is exhausted.

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0008

[Correction method] Change

[Contents of correction]

According to a further feature of the invention, the absorbent material may be removed from the exhaust system and replaced at intervals with fresh absorbent material. The length of this interval depends, inter alia, on the capacity of the substance for absorbing the sulphate-forming SOx components and the amount of sulphate-forming SOx components in the exhaust gas flowing in the exhaust system. The remaining capacity in the sulfate trap for absorbing the sulfate forming SOx components is evaluated using standard techniques. These techniques use preset "maps" to approximate the cumulative formation of sulfate forming SOx components in the exhaust system resulting from the use of the engine since the last refreshment of the absorbent material. It encompasses the use of sensors and / or programming of the engine management system used.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0009

[Correction method] Change

[Contents of correction]

The most convenient interval length is during the service period, ie for one year or up to 12,000 miles, for a typical passenger car including a light duty diesel engine. This allows the absorbent material to be replaced at the same time as other components, such as spark plugs and oil filters. Of course, a situation may be tolerated in which the absorbent material is replaced only at intervals of several times the normal service period, for example 2-3 times.

[Procedure Amendment 5]

[Document name to be amended] Statement

[Correction target item name] 0017

[Correction method] Change

[Contents of correction]

In a second aspect, the present invention is an exhaust system for a lean burn internal combustion engine, wherein the system optionally further comprises chemical pretreatment or catalyst pretreatment means. Wherein the sulfate absorber comprises a base material supporting a solid substance for absorbing a SOx component forming a sulfate generated from exhaust gas, wherein the solid substance is , Substantially free of substances that catalyze SO ₂ oxidation, but wherein the sulfate absorbent is adapted to be replaced when its sulfate absorbing capacity is exhausted.

[Procedure correction 6]

[Document name to be amended] Statement

[Correction target item name] 0018

[Correction method] Change

[Contents of correction]

In a third aspect, the invention provides a lean-burn internal combustion engine, preferably a diesel engine, most preferably a heavy duty diesel engine, in combination with an exhaust gas system according to the invention. In order to prolong the life of the sulphate absorber before replacement and / or to limit its capacity and pressure drop, the engine preferably has a low sulfur content, eg less than 50 ppm w / w,
In particular, it operates on fuels containing less than 10 ppm w / w of sulfur.

[Procedure Amendment 7]

[Document name to be amended] Statement

[Name of item to be corrected] 0023

[Correction method] Change

[Contents of correction]

In a seventh aspect, the invention provides for separating an absorbent from an exhaust system;
Removing spent absorbent from the surface of the absorbent substrate, preferably by washing, and applying fresh absorbent to this surface,
There is provided a method of regenerating an absorber filled with sulfate according to the present invention. For such washing, an additive such as a detergent or a means such as a pH adjusting agent may be used. Therefore, the expensive honeycomb can be reused. Washing may be treated to recover the spent absorbent component, if economical.

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Claims (31)

[Claims] 1. A method for treating exhaust gas originating from a lean burning internal combustion engine containing sulfur oxides (SOx) and at least one other air pollutant selected from HC, CO, NO and soot. Wherein the gas is untreated or has been subjected to some kind of chemical and / or catalytic treatment, the SOx component forming a sulfate salt in the solid absorbent material being absorbed. If, comprising the steps of releasing the sO ₂ containing gas to the atmosphere, and a step of periodically replacing the absorbent material, method. 2. The solid sulphate absorbent is substantially free of SO ₂ oxidation catalyst material,
The method of claim 1. 3. The method of claim 1 or 2, wherein the step of pretreating the gas comprises the step of oxidizing NO to NO ₂ . 4. The method according to claim 3, wherein the NO is oxidized by utilizing ozone and / or plasma. 5. The method of claim 3 or 4 comprising the step of treating the gas to remove soot prior to removing the sulfate-forming components. 6. The method of claim 3 or 4 comprising the step of treating the gas to remove soot after removing the sulfate-forming components. 7. The soot treatment step comprises filtering soot from a gas.
The method described in. 8. The method according to claim 7, wherein the soot captured by the filter is combusted in a NO ₂ containing gas at a temperature lower than 400 ° C. 9. The lean burn internal combustion engine of claim 1 wherein the lean burn internal combustion engine is operated with a sulfur containing fuel having less than 50 ppm w / w sulfur and the exhaust gas is a product resulting therefrom. The method according to any one of claims. 10. A system for treating exhaust gas generated from a lean-burn internal combustion engine, the method comprising treating an exhaust passage and a solid for absorbing a component forming a sulfate salt from SOx in the exhaust gas. A sulphate absorber comprising a substrate supporting a substance, wherein the sulphate absorber is adapted to be replaceable. 11. The system of claim 10, wherein the sulfate absorber is substantially free of substances to catalyze SO ₂ oxidation. 12. The method further comprising means for producing and / or introducing ozone and / or plasma for oxidizing NO to NO ₂ upstream of the sulfate absorber and in the exhaust passage. Item 12. The system according to Item 10 or 11. 13. The method according to claim 12, wherein the ozone and / or plasma generating means comprises a UV light source and / or a corona discharge device. 14. The oxidation catalyst for oxidizing NO to NO ₂ is further included, and the oxidation catalyst is located upstream of the sulfate absorber and arranged in the exhaust passage.
13. The system according to any one of 13. 15. A soot filter disposed between the means for oxidizing NO to NO ₂ and the sulfate absorber and disposed in the exhaust passage, thereby providing the filter with soot. captured soot, formed by the combustible in NO ₂ containing gas at a temperature lower than 400 ° C., the system according to any one of claims 12 to 14. 16. The method further comprises means for oxidizing the NO to NO ₂ and a soot filter located downstream of the sulfate absorber and disposed in the exhaust passage, thereby trapping in the filter. soot is formed by a combustible at a temperature lower than 400 ° C. in NO ₂ containing gas, the system according to any one of claims 12 to 14. 17. The system according to claim 15 or 16, wherein the filter is catalyzed. 18. The sulfate absorber comprises: (a) at least one compound of an alkali metal, alkaline earth metal, rare earth metal or transition metal, and / or (b) at least one zeolite, carbon or high surface area oxidation. 18. A system according to any one of claims 10 to 17, comprising a product, or a mixture of two or more thereof. 19. The system according to claim 18, wherein the sulfate absorber comprises a complex oxide or a mixed metal oxide containing at least one metal according to (a) above. 20. The complex oxide is an alkaline earth metal and copper, preferably Ba—Cu—O,
MnO ₂ -BaCuO is _2, optionally further comprising a _{CeO 2, Y-Ba-Cu} -O or Y-Sr-Co-O, the system according to claim 19. 21. The system of claim 19, wherein the mixed metal oxide is CeO ₂ / ZrO ₂ . 22. The system of claim 18, wherein the alkaline earth metal compound is CaO, MgO, SrO or BaO. 23. The system of any of claims 10-22, wherein the substrate is ceramic. 24. A lean-burn internal combustion engine, preferably a diesel engine, in combination with a system according to any one of claims 10-23. 25. The engine of claim 24, wherein the lean burn internal combustion engine is a heavy duty diesel engine. 26. The sulfur is operated with a sulfur-containing fuel having a sulfur content of less than 50 ppm w / w.
Or the engine according to 25. 27.   A vehicle comprising the engine according to any one of claims 24 to 26. 28. The solid absorbent comprises barium oxide (10-20% w / w) and ceria (15-4).
1% of a mixed washcoat containing 0% w / w) and alumina (the balance).
The sulfate absorbent according to any one of claims 10 to 23, which comprises 2 to 5 g per cubic inch. 29. The solid absorbent comprises 0.5 to 4.0 g per cubic inch of a 2: 1 to 1: 2 mixture of high surface area alumina (50 to 150 m ² g ⁻¹ ) and zeolite β. The sulfate absorber according to any one of claims 10 to 23, wherein the washcoat comprises 0.1 to 0.5 g of calcium oxide (as calcium metal) per cubic inch. . 30. The sulphate absorbent of claim 28 or 29 in a can or shell adapted to be removably inserted within an exhaust system. 31. Removing the used absorbent from the surface of the absorbent substrate, preferably by washing, and applying fresh absorbent to the surface. Item 31. A method for regenerating an absorber filled with the sulfate according to any one of items 10 to 30.