WO2016024902A1

WO2016024902A1 - System for exhaust treatment comprising pilc-element for adsorbing catalyst poisons

Info

Publication number: WO2016024902A1
Application number: PCT/SE2015/050846
Authority: WO
Inventors: Ulf NYLÉN; Ali SARAMAT; Sandra DAHLIN; Hanna Lind; Henrik Eriksson; Marita Nilsson
Original assignee: Scania CV AB
Current assignee: Scania CV AB
Priority date: 2014-08-14
Filing date: 2015-08-05
Publication date: 2016-02-18
Anticipated expiration: 2017-02-14
Also published as: DE112015003193T5; SE539895C2; SE1450942A1; CN106574532A

Abstract

The exhaust aftertreatment system (1) according to the present invention comprises a poison trap in the form of an element arranged upstream of an exhaust aftertreatment device (3), in an exhaust channel (4) between an exhaust outlet (5) from a combustion engine and an exhaust inlet (6) of the exhaust aftertreatment device. The element comprises a surface (14), which is intended to be exposed to the exhausts in the exhaust channel, and adapted to adsorb chemical toxins in the exhausts. In this manner, a large amount of chemical toxins may be caught from the exhaust flow already before it reaches the first catalyst in an exhaust aftertreatment device.

Description

SYSTEM FOR EXHAUST TREATMENT COMPRISING PILC-ELEMENT FOR

ADSORBING CATALYST POISONS

TECHNICAL FIELD

The present invention relates to an exhaust aftertreatment system for exhausts from a combustion engine, such exhaust aftertreatment system comprising an exhaust

aftertreatment device comprising at least one catalyst adapted to purify exhausts, for example an exhaust aftertreatment device comprising at least one diesel oxidation catalyst (DOC) and one selective catalytic reduction catalyst (SCR). The invention also relates to a vehicle comprising a combustion engine and an exhaust aftertreatment system.

BACKGROUND A combustion engine burns a mix of air and fuel in order to generate a driving torque. The combustion process generates exhausts, which are emitted from the combustion engine. These exhausts are led via an exhaust conduit to an exhaust outlet arranged at the

downstream end of the exhaust conduit, from which the exhausts are emitted into the environment. The exhausts from the combustion engine contain among others nitrous exhausts (NO_x), carbon dioxide (C0₂), carbon monoxide (CO) and particles. NO_x is a generally accepted generic name for describing the nitrous exhausts, which primarily comprise nitrogen oxide (NO) and nitrogen dioxide (N0₂). Before the exhaust gas is emitted into the environment via the exhaust conduit's exhaust outlet, the exhaust gas is made to pass through an exhaust aftertreatment device arranged in the exhaust conduit, which aftertreatment device usually comprises one or several catalysts, one or several particulate filters for the purification of the exhausts and potentially a silencing agent, which dampens the noise caused by the exhausts. The exhausts are led from the combustion engine to the exhaust aftertreatment device via an exhaust channel. The exhaust aftertreatment device usually comprises a diesel oxidation catalyst (DOC-catalyst) mainly adapted to oxidise hydrocarbons, but also carbon monoxide and nitrogen monoxide. Further, the exhaust treatment system usually comprises a selective catalytic reduction catalyst (SCR-catalyst), in which a reductant and NO_x may react and be converted into nitrogen and water, and thus reduce the amount of NO_x emitted into the atmosphere. The reductant is usually an urea-based solution, such as Adblue^®, and is injected into the exhaust conduit upstream of the SCR-catalyst.

The exhaust aftertreatment device usually also comprises one or several diesel particulate filters (for example a catalytically coated soot filter CSF (Catalysed Soot Filter), to catch and oxidise for example soot particles. Other types of catalysts may also be used in an exhaust aftertreatment device, such as an ammonia slip catalyst (ASC).

The various components of the exhaust aftertreatment device are arranged inside a joint house which is gas-proof, except for one exhaust inlet arranged in the house, to which the exhaust channel from the combustion engine is connected, one exhaust outlet from which the purified exhausts are allowed to be led further into the surrounding atmosphere via the exhaust conduit outlet, and potential connections for supply and removal of compositions used in the various components, such as for example a urea-based solution for the SCR.

The diesel oxidation catalyst is often arranged upstream of an SCR-catalyst, in order thus to oxidise hydrocarbons, carbon monoxide and nitrogen monoxide before these reach the SCR- catalyst, since they may otherwise impact the efficiency of the SCR-catalyst. It is actually common for the diesel oxidation catalyst to be the first component in the exhaust

aftertreatment device. The diesel oxidation catalyst is thus often exposed to a large amount of substances and compounds that may cause poisoning and deactivation of the diesel oxidation catalyst. In exhaust aftertreatment devices where the diesel oxidation catalyst is not the first catalyst in the device, the first catalyst exposed to the exhausts will naturally be the one exposed to the greatest load of chemical toxins in the exhausts.

Sulphur poisoning of the diesel oxidation catalyst is a known problem within the technical area. The solution to this problem is usually to temporarily increase the temperature of the exhausts, so that the sulphur coating dissolves or disintegrates. Prior art also provides for trying to catch sulphur before it reaches the diesel oxidation catalyst, by arranging a suitable component for this purpose in the exhaust aftertreatment device.

US 2009/0107121 Al describes an exhaust aftertreatment system comprising a catalyst that functions like an SO_x-trap, an oxidation catalyst, a particulate filter and an NO_x SCR-catalyst. The catalyst functioning like an SO_x-trap consists of a honeycomb structure with several passages extending in the axial direction of the catalyst. Furthermore, this catalyst has a coating, comprising for example an alkali metal, on which a precious metal is arranged. This means that the cost of SO_x-trap is relatively high. I n addition, it may be difficult to replace if the SO_x-trap as such is deactivated in such a way that it is no longer able to adsorb chemical toxins.

In addition to sulphur, other substances that may accumulate in the first catalyst in the exhaust aftertreatment device also occur, which may not be removed by way of an increased temperature. It has become apparent that phosphor in particular is problematic in prior art exhaust aftertreatment systems, since compounds containing phosphor poison and/or deactivate the catalyst. Phosphor is, for example, present in certain fuels such as bio-fuels, or is used as an addition in certain motor oils, and may therefore also be present in the exhausts from the combustion engine. Post-mortem analyses of diesel oxidation catalysts that had been arranged first in an exhaust aftertreatment device, and where bio-fuels had been used for the combustion engine, show that large amounts of toxins, such as phosphor, had accumulated in the diesel oxidation catalyst.

Poisoning and/or deactivation of the diesel oxidation catalyst leads to a deteriorated efficiency of the diesel oxidation catalyst, and in the longer run it also impacts subsequent components in the exhaust aftertreatment system.

US 2002/0064491 Al describes a method wherein volatile phosphor compounds in exhausts are removed through a reaction with metal or metal containing compounds, which form solid compounds with the volatile phosphor compounds in the exhausts. This may occur by way of administering the metal or metal compound upstream of the catalyst, as an additive to the motor oil or the fuel in the combustion engine, or by way of an adsorbing device that may remove phosphor from the exhausts before they reach the catalyst and is arranged in an exhaust conduit between an engine and a catalyst.

EP 0638349 Al describes a method to protect catalysts for purification of exhausts from toxins with an adsorbent, which may consist of zeolite or mixtures of different zeolites. The adsorbent is arranged in the exhaust stream upstream of the catalyst and may be in honeycomb form. It may also be coated on the catalytic coating of the catalyst.

Since the different catalysts are often in-built with additional components in a joint unit, i.e. an exhaust aftertreatment device as described above, it is not easy to remove one individual catalyst separately from a vehicle in order to clean, regenerate or replace the same. Replacing the entire exhaust aftertreatment device also entails a significant cost. A replacement of a catalyst, for example a diesel oxidation catalyst, in exhaust aftertreatment devices permitting this, also entails a significant cost since such catalysts are expensive. It is therefore desirable to minimise the poisoning or at least substantially delaying the poisoning of a catalyst, in particular in the catalyst that is arranged first in the direction of the exhaust flow, in the exhaust aftertreatment device.

Apart from this, there are currently also statutory requirements in some states, unions of states or regions requiring that the exhaust aftertreatment device have a minimum life expressed as a period of time and/or an accumulated driving distance for the vehicle, such as for example 7 years or 700 000 kilometres, without exceeding the emission requirements. This means that an exhaust aftertreatment system for vehicles must be built in such a manner that it either has such a life or may easily be regenerated, so that an exhaust aftertreatment device does not need to be replaced with a new one within the statutory period/driving distance.

SUMMARY OF THE INVENTION

One objective of the present invention is to reduce the risk of, or alternatively delay deactivation of a catalyst, such as a diesel oxidation catalyst, in an exhaust aftertreatment system in a cost effective manner and preferably without substantially impacting the pressure of the exhausts in the exhaust aftertreatment system. This objective is achieved with the help of the exhaust aftertreatment system according to the independent claim 1. The exemplified embodiments are defined by the independent claims. The exhaust aftertreatment system according to the present invention comprises a poison trap in the form of an exhaust aftertreatment device in an exhaust channel, arranged between an exhaust outlet from a combustion engine and an exhaust inlet in the exhaust

aftertreatment device. The element comprises a surface, which is intended to be exposed to the exhausts in the exhaust channel, and adapted to adsorb chemical toxins in the exhausts. In this manner, a large amount of chemical toxins may be caught from the exhaust flow already before it reaches the first catalyst in an exhaust aftertreatment device. Furthermore, the element's placement means it may easily be removed for replacement or regeneration, without any need for removing the exhaust aftertreatment device from the vehicle and dismantling it.

The exhaust aftertreatment system according to the present invention comprises an exhaust aftertreatment device and an exhaust channel, adapted to be arranged between an exhaust outlet in a combustion engine and an exhaust inlet in the exhaust aftertreatment device. The exhaust aftertreatment device comprises at least one catalyst adapted to purify the exhausts. An element having a surface adapted to adsorb at least one substance that may deactivate the catalyst in the exhaust aftertreatment device, is arranged in the exhaust channel. Said surface comprises a material consisting of PILC, pillared layered clay. Suitably, the entire surface of the element that is exposed to the exhausts is made of PILC. The element is preferably detachably arranged in relation to the exhaust channel, and may in this way be removed from the exhaust treatment system for cleaning or regeneration or alternatively be replaced. This may, for example, be achieved by releasing the exhaust channel rom the exhaust aftertreatment device and the exhaust outlet of the combustion engine, and the element being pushed or pulled out of the exhaust channel. Another alternative is that the exhaust channel comprises a hatch, through which the element may be inserted into and removed from the exhaust channel, respectively. Another alternative is to arrange the element in a first exhaust channel section, which is detachably arranged in relation to a second, adjacent exhaust channel section in the exhaust channel's axial direction, whereby the exhaust channel section may either be replaced, or the element therein may be cleaned or regenerated. The element may suitably comprise several channels, through which the exhausts may flow, whose axial extensions are arranged in the axial extension of the exhaust channel. This reduces the risk that the element may cause a pressure drop, for example compared to if the element's channels had an angled extension in relation to the main flow through the exhaust channel. Furthermore, it is preferable that the element has an open area, in the exhaust channel's radial cross section, which area is larger than the open area of the first catalyst in the exhaust purification device. Thus, there is no risk that the element may be clogged by, for example, particles in the exhausts or that it may impact the pressure of the exhausts in the exhaust channel. In order to achieve this, the element may, for example, be designed as a honeycomb structure, a net-shaped structure or at least a partly pleated structure, where said pleats are arranged so that they extend in the axial direction of the exhaust channel. These structures also have the advantage that they have a large surface coming into contact with the exhausts, and may accordingly have a large adsorbing surface.

According to one exemplifying embodiment, the PILC material is selected from a PILC comprising pillars made of aluminium oxide, silica, titanium oxide or a mixture of at least two of said oxides. These PILC generally have good thermal properties and are stable at temperatures over 500 °C.

The PILC material may suitably be doped to increase the affinity for at least one substance or compound, preferably phosphor or phosphor containing compounds, which may deactivate said catalyst in the exhaust aftertreatment device.

According to one exemplifying embodiment PILC is selected from PCH, a Porous Clay

Heterostructure, preferably a PCH comprising pillars of silica, titanium oxide or a mixture of silica and titanium oxide and is doped with iron or aluminium. These materials have turned out to have very good thermal properties and a particularly good ability to adsorb phosphor and its compounds. The PILC-material may be arranged as a coating on a load carrier, in such a way that the coating and the load carrier jointly form the element. It is also conceivable that the entire element may consist of PILC.

For cost reasons, it is preferred that the surface of the element, preferably the entire element, is free of precious metals. The element is also not intended to be a catalyst for purification of exhausts, but only to adsorb toxins from the exhausts that may deactivate the catalysts arranged downstream, and thus need not function as a catalyst.

The element is preferably arranged at or in the vicinity of a downstream end of the exhaust channel. For example, it may be arranged in the immediate vicinity of the exhaust inlet to the exhaust aftertreatment device. In this manner, for example mechanic stress on the element, caused by vibrations during the operation of the combustion engine, may be minimised.

Furthermore, this placement of the element is preferred since the flow of exhausts in this part of the exhaust channel is turbulent, which promotes mass transport of toxins and deposition of these on a surface exposed to the exhausts.

The element may have a limited extension in the exhaust channel's axial extension, since it has turned out that the interception of chemical toxins may be achieved effectively on a relatively short surface, in particular when there is a turbulent flow of exhausts. A relatively small axial extension is also advantageous, since the risk that the element substantially impacts the pressure of the exhausts in the exhaust channel is minimised. Suitably, the element's axial extension in the exhaust channel's axial extension may be between 1 and 10 cm, preferably up to and including 5 cm.

The present invention also relates to a vehicle comprising a combustion engine and an exhaust aftertreatment system as described above. The vehicle may for example be a truck, a bus or a passenger car. The vehicle may also be a marine vehicle or a terrain vehicle.

DESCRIPTION OF DRAWINGS Fig. la shows a schematic side view of a vehicle comprising a combustion engine and an exhaust aftertreatment device.

Fig. lb shows a perspective view of an exhaust aftertreatment system comprising an exhaust aftertreatment device and an exhaust channel.

Fig. lc schematically shows an example of an exhaust aftertreatment device.

Fig. 2 shows a part of a radial cross section of an element adapted to be arranged in an exhaust aftertreatment system, in accordance with an exemplifying embodiment of the present invention.

Fig. 3 shows a part of a radial cross section of an element adapted to be arranged in an exhaust aftertreatment system, in accordance with another exemplifying embodiment of the present invention.

Fig. 4 shows a part of a radial cross section of an element adapted to be arranged in an exhaust aftertreatment system, in accordance with another embodiment of the present invention.

DETAILED DESCRIPTION

Below, the invention is described in further detail with reference to the enclosed figures. The invention is not limited to the embodiments described and displayed in the figures, but may be modified within the framework of the enclosed claims. Furthermore, the figures should not be deemed drawn to scale, since certain features may be exaggerated in order to further illustrate the invention.

The present invention is intended to overcome the problems caused by chemical toxins in exhausts. Toxins in this context means elements or compounds thereof, which may poison or deactivate at least one catalyst in an exhaust aftertreatment device, in particular a diesel oxidation catalyst in an exhaust aftertreatment device. Such toxins may be present either in gaseous form, in particulate form or in some cases even in liquid form, without departing from the invention. Poisoning of such a catalyst usually takes place through toxins accumulating in the catalyst and leading to a so-called fouling (coating) on the catalytic surfaces of the catalyst. Toxins may also accumulate in the catalyst via selective adsorption on the catalytic surfaces of the catalyst. In this manner, the toxins may finally deactivate the catalyst, since the catalytic reaction is prevented or at least significantly deteriorated. Examples of toxins are sulphur, phosphor, zinc, calcium, magnesium or alkali metals, or compounds comprising one or several of these elements In accordance with the present invention, an element with a surface adapted to catch substances or compounds in the exhausts from the combustion engine is arranged in the exhaust channel, arranged between an exhaust outlet in the combustion engine and an inlet of an exhaust aftertreatment device, the latter comprising one or several catalysts arranged for purification of the exhausts. In this manner, said surface catches at least one substance or compound that may poison or deactivate the components in the exhaust aftertreatment device, in particular the diesel oxidation catalyst in the exhaust aftertreatment device, in cases where this is arranged first of the catalysts in the exhaust aftertreatment device. The exhaust channel usually constitutes an unused part of an exhaust aftertreatment system and functions primarily as a transport distance for the exhausts, from the combustion engine (more specifically from the turbine in the turbo charger of the combustion engine) to the exhaust aftertreatment device. By arranging an element with a surface adapted to catch one or several substances or compounds that may poison or deactivate the diesel oxidation catalyst in this exhaust channel, the exhaust channel is used efficiently. In addition, the life of the exhaust aftertreatment device in the exhaust aftertreatment system is prolonged, since it may be used for a longer period of time before the exhaust aftertreatment device needs to be replaced or otherwise regenerated. Furthermore, the fact that said element is arranged in the exhaust channel instead of in the exhaust aftertreatment device means that said element may easily be replaced or removed for regeneration, for example at an ordinary service of the vehicle, without the exhaust aftertreatment device as such having to be removed from the vehicle and dismantled. Another advantage of the present invention is that the exhaust aftertreatment device does not need to be rebuilt to facilitate the advantages of the invention, but only the exhaust channel needs to be adapted. In this manner, existing vehicles may also use the advantages of the invention by only replacing the exhaust channel with an exhaust channel adapted to contain said element.

Interception of toxins from the exhausts from the combustion engine through said element arranged in the exhaust channel takes place by way of adsorption on a surface of the element. Adsorption means retaining of a substance, which may be an atom, an ion, a molecule or a compound from a gas or liquid, on a surface of a solid body. Adsorption may be divided into chemisorption, which comprises a chemical reaction between the surface and the adsorbing substance, or physiosorption, in which the interacting forces between the surface and the substance are relatively weak and may be caused by for example van der Waal-forces.

The exhaust channel constitutes a pipe shaped element, which may comprise several bends or similar, and may thus have a central axis that is not straight. The exhaust channel may be divided into several exhaust channel sections. At least one exhaust channel section may be adapted, in a conventional manner, to allow absorption of vibrations in the exhaust channel, in order thus to minimise the mechanical stress on the exhaust channel.

The exhaust aftertreatment device comprises at least one catalyst intended to purify the exhausts from the combustion engine. Usually, the exhaust aftertreatment device comprises several different catalysts, such as a DOC, SCR, ASC, and/or CSF. It may also comprise other types of filters and/or silencing means. The exhaust aftertreatment device comprises a house, in which the various components thereof are arranged as one joint entity. The house comprises an exhaust inlet connected to the exhaust channel, which extends from the combustion engine to the exhaust aftertreatment device, and an outlet from which purified exhausts may be led further to the surrounding atmosphere. The exhaust aftertreatment device is built in such a manner that exhausts are not permitted to leave the exhaust aftertreatment device otherwise than through the outlet.

In accordance with the present invention, said element consists of an element with a surface adapted to catch one or several substances or compounds that may poison or deactivate a catalyst. The surface comprises a material consisting of a pillar-equipped clay, PILC, which facilitates adsorption of said substance(s) or compound(s). The element may, for example, be substantially cylinder shaped and have a honeycomb structure, a net shaped structure or a pleated structure, in such a manner that the structure (that is to say the construction) of the element creates axial channels through which the exhausts may flow. Such a cylinder shaped element is suitably arranged coaxially with the exhaust channel. Furthermore, the element is preferably in the form of a monolithic structure.

In order to minimise the risk that the element may create a pressure drop in the exhaust channel during the operation of the combustion engine, it is preferable that it has a relatively open structure, i.e. a large open area in the exhaust channel's radial cross section. The open area for the element consists of the sum of the area of the channels in the exhaust channel's radial cross section. However, the element should have a sufficiently large surface area to be able to adsorb as much of the chemical toxins in the exhausts as possible, in order thus to minimise the risks that a catalyst in the exhaust aftertreatment device may be poisoned.

The element may have a relatively short axial extension in the exhaust channel's axial extension. A short axial extension is advantageous, in order to minimise the pressure drop in the exhaust channel caused by the element, i.e. to ensure that the element does not contribute to a significant pressure drop increase. At post-mortem analyses of diesel oxidation catalysts arranged first in an exhaust purification device, it has been shown that deposition of chemical toxins occurs primarily in the first centimetre of the catalyst, where the exhaust flow is turbulent. For this reason, an axial extension of the element in the exhaust channel could be as short as around 1 cm, in particular if the element is arranged in a part of the exhaust channel where the exhaust flow is turbulent, for example in the vicinity of the inlet to the exhaust aftertreatment device. For the same reason, the element does not need to have an axial extension which is greater than 10 cm, even if it is possible to adapt elements with a longer extension. Preferably, the element could have an axial extension in the exhaust channel's axial extension of around 1-5 cm.

As opposed to prior art poison traps, such as conventional precious metal containing honeycomb structures to catch sulphur containing compounds, the element to catch toxins is arranged, in accordance with the present invention, in the exhaust channel, is made of a relatively cheap material, preferably has a large open area and a relatively short axial extension, and is preferably detachably arranged in the exhaust channel. Thus, a cost effective solution to the problem with deactivation of a catalyst in the exhaust aftertreatment device is achieved, without any substantial impact on the pressure of the exhausts in the exhaust channel or in the exhaust aftertreatment device, which in turn, for example, could impact the load on the combustion engine and/or the efficiency of subsequent components in the exhaust aftertreatment device.

Fig. la shows a schematic side view of a vehicle 100 in the form of a truck. The vehicle 100 is equipped with a combustion engine 2 arranged to operate the vehicle's driving wheels 17 via a gearbox and a cardan shaft (not displayed). The combustion engine 2 is operated by a fuel, which is fed to the combustion engine with the help of a fuel system comprising a fuel tank 16. The exhausts from the combustion engine 2 are transported via an exhaust channel 4 to an exhaust aftertreatment device 3. Fig. lb shows a perspective view of an exhaust aftertreatment system 1 comprising an exhaust aftertreatment device 3 and an exhaust channel 4. The exhaust channel 4 is arranged between an exhaust outlet 5 of a combustion engine 2 (only displayed schematically) and an exhaust inlet 6 of the exhaust aftertreatment device 3. The exhaust channel is thus arranged for transport of exhausts from the combustion engine to the exhaust aftertreatment device.

Fig. lc schematically shows an exemplified exhaust aftertreatment device 3, comprising a diesel oxidation catalyst (DOC) 7, a selective catalytic reduction catalyst (SCR) 8 arranged downstream of the DOC, and a particulate filter 9 arranged downstream of the SCR-catalyst. The different components of the exhaust aftertreatment device may be arranged in different ways and additional components may be present. For example, the exhaust aftertreatment device may also comprise silencing means, additional particulate filters, and additional catalysts, if needed for specific application. Any type of exhaust aftertreatment device may be used according to the invention, provided it comprises at least one catalyst for purification of exhausts. Preferably, the exhaust aftertreatment device comprises at least one diesel oxidation catalyst and one SCR-catalyst, and potentially a catalytically coated particulate filter, however not necessarily arranged in the order displayed in Fig. lc. Since the element is arranged upstream of the exhaust aftertreatment device, it will be subjected to a large load in the form of chemical toxins in the exhausts, and will thus be saturated long before the exhaust aftertreatment device. It is therefore desirable to arrange the element in a detachable manner in the exhaust channel, in order thus to facilitate an easy replacement or removal of the element for cleaning or regeneration. The element according to the present invention may therefore be arranged in the exhaust channel either in the form of an exhaust channel section, which is detachably attached to at least one adjacent exhaust channel section, or another exhaust channel section, or to an inlet to the exhaust

aftertreatment device. Another alternative is to arrange an opening, which may preferably be closed with a hatch or similar, in the exhaust channel, through which the element may be inserted into the exhaust channel and removed from the exhaust channel, respectively.

In accordance with the present invention, the element has a surface, which is intended to be exposed to the exhausts in the exhaust channel, which surface comprises a material consisting of a pillared clay, PILC. The PILC-material is arranged in such a manner that chemical toxins in the exhausts may be adsorbed with the help of this material. The element may consist entirely of the PILC-material, or the PILC-material may be present in the form of a coating on a surface of the element, which surface is intended to be exposed to the exhausts. In the latter case, the element comprises a load carrier and a coating of PILC. Preferably, all the surfaces which are intended to be exposed to the exhausts are made of the PILC material. Furthermore, the PILC material constitutes the outermost surface of the element, that is to say there is no additional coating on the PILC-material on the side of the PILC-material opposite to a potential load carrier. On the other hand, it is possible to arrange a coating between the load carrier and the coating of PILC if desired, for example to improve the adhesion of PILC to the load carrier.

PILC consists of a zeolite-like material with modified layers, which are separated from each other at controlled distances and contain a two-dimensional network of pores. PILC is made of synthetic or natural clays, for example smectites (in particular montmorillonite), vermiculites, or bentonite. The PILC-material is made by replacing cations in the silicate of the clay with for example hydroxy cations, preferably large hydroxy cations, which are formed by hydrolysis of metal oxides or salt. This may, for example, be achieved by swelling the clay with a suspension substance, for example water, and adding the desired cation to the suspension. At heating, the metal hydroxy cations are subject to dehydration and dehydroxylation, forming a stable metal oxide or other metal salts. The formed metal oxide or salt constitutes a nano particle, functioning like a pillar that keeps the thin silicate layers separate from each other. This creates space of molecular size between the layers in the material, usually 1-20 A, even though it is possible to create also larger distances. Examples of oxides that are used as pillars are oxides of titanium, zirconium, aluminium, iron, silica or chrome. If the cation, which is added to the clay to form the pillars, is catalytically active, the resulting material may be used as a catalyst. PILC may, if desired, be doped with metal or metal ions. Examples of dopants that may be used in PILC are alkaline earth metals or transition metals (incl. lanthanids), or ions thereof. Prior art also provides for doping with other substances, such as aluminium and gallium.

PILC was developed the first time in the 1970s and is currently used, for example, as catalysts when cracking hydrocarbons, and as catalysts or adsorbents at soil and water remediation. PILC has also been suggested as a catalyst in SCR-processes to reduce nitrogen oxides, for example in coal-fired boilers, as described in US 5,415,850.

A novel class of PILC was developed in the 1990s, referred to as PCH, Porous Clay

Heterostructures. The preparation thereof is based on the introduction of silicon oxide pillars in between the layers of clays through a method using a surfactant. Titanium oxide, for example, may also form pillars in PCH. PCH is characterised by a high surface area, a structure comprising micro and meso pores, surface acidity, and cation-exchange properties. The structure of PCH is stable up to high temperatures and PCH may therefore be used in high temperature processes.

The affinity of PILC (and PCH) to toxins, such as phosphor and others, and/or the catalytic effect of PILC, may be increased further, if desired, by introducing a suitable dopant. In this manner, the ability of the material to adsorb toxins may be further improved.

PILC has the advantage of being a relatively cost effective material, compared with traditional precious metal containing materials used as catalysts or, for example, sulphur traps in exhaust aftertreatment systems. PILC also has a large specific surface area, which makes this material suitable for applications where one or several substances are adsorbed. Furthermore, PILC generally has a good ability to catch phosphor and phosphor containing compounds, as well as other chemical toxins in the exhausts and may, if desired, be doped to further improve this ability. PILC also have the advantage of containing large pores of different sizes, and may thus accumulate pollutants in the larger pores, without hampering the catalytic ability in cases where a catalytic effect is desired.

In accordance with the present invention, the PILC-material is used to adsorb chemical toxins, primarily phosphor and phosphor containing compounds, from the exhausts before they reach the exhaust aftertreatment device, with its catalysts arranged for purification of the exhausts. In order to do so, the PILC-material is arranged as a surface in an element in the exhaust channel connecting the combustion engine with the exhaust aftertreatment device. In order to adsorb toxins from the exhausts said surface is exposed to the exhausts when they flow through the exhaust channel towards the exhaust aftertreatment device. Depending on the substance or substances that must be adsorbed, and on which PILC-material that is used, the adsorption may occur by way of chemisorption or physiosorption.

In order to ensure that the material copes with the temperature conditions in the exhaust channel, typically up to at least 500 °C, the PILC-material for the surface of the element is suitably selected from a PILC that is thermally stable up to at least 500 °C, preferably up to at least 550 °C. PILC containing pillars of silica, so called Si-PILC, or pillars of silica and titanium oxide, have been shown to be stable up to temperatures of at least 800 °C, and are therefore examples of suitable alternatives. PILC with only titanium oxide as pillars, so-called Ti-PILC, or PILC with pillars made of aluminium oxides, so-called AI-PILC, are also conceivable. PILC- materials with pillars of several different types, so-called "mixed pillars" have been shown to have particularly good thermal properties.

According to one exemplifying embodiment, PILC is selected from a PCH with pillars made of silica, or silica and titanium oxide. This material may, if desired, be doped to achieve a better affinity for certain substances or pollutants, in particular phosphor and/or phosphor containing compounds, or for additionally improved thermal stability. According to one exemplifying embodiment, the PCH-material with pillars made of silica, or silica and titanium oxide, is doped with iron, vanadium or aluminium.

Furthermore, it is preferable that a PILC material with a high affinity to phosphor is used, in order thus to ensure that as high an amount of phosphor and phosphor containing

compounds as possible is caught before they reach the exhaust aftertreatment device.

Dopants that have been shown to be efficient to catch phosphor and/or phosphor containing compounds comprise for example aluminium, zirconium, titanium, gallium, calcium, chrome, lanthanum or iron.

According to one exemplifying embodiment, the PILC-material consists of an PCH with pillars made of silica, or silica and titanium oxide, and doped with iron or aluminium. Such a material is stable at high temperatures and has a good ability to catch phosphor and phosphor containing compounds.

According to another exemplifying embodiment, the PILC-material consists of a PILC with pillars made of aluminium oxide, a so-called AI-PILC, preferably made of bentonite. Such a material has a good affinity to phosphate in particular.

The PILC-material may be prepared in a conventional manner and adapted to the element or to a part thereof. For example, it could be extruded to a monolithic element, for example with a honeycomb structure or similar as described above, or alternatively be added to a load carrier in the form of a wash coat.

Since the element has the objective of catching toxins from the exhausts before they reach the exhaust aftertreatment device, which is intended to carry out the purification of the exhausts so that they may be released into the atmosphere, the element should be adapted in such a way that there is no risk that it may be clogged by particles in the exhausts. It is therefore desirable that it has a relatively large open area as described above. Preferably, it has an open area which is larger than the open area of each one of the catalysts in the exhaust

aftertreatment device. This also has the effect of minimising the risk of a pressure drop in the exhaust channel, which may otherwise impact the combustion engine and thus the fuel consumption.

However, the element should have as large a surface area as possible, in order to adsorb as much chemical toxins as possible without any risk of causing a pressure drop in the exhaust channel. For this reason, it is preferable for the element to be adapted in such a manner that, seen in a radial cross section of the exhaust channel, it has a honeycomb structure, a net- shaped structure or alternatively a pleated structure. Fig. 2 schematically shows a radial cross section of a part of a honeycomb structure 10 in an element, where each surface 14 of the channels 13 comprises PILC. In a similar manner, Fig. 3 shows a cross section of a part of a net-shaped structure 11, where each surface 14 of the channels 13 comprises PILC and Fig. 4 shows a cross section of a part of a pleated structure 12, where each surface 14 of the channels 13 comprises PILC. The structure displayed in Fig. 4 also comprises distance elements 15, for example in the form of disc elements, which support the pleated structure and/or increase the mechanic strength of the element. The channels 13 displayed in Figs. 2 to 4 are arranged in such a manner that their axial extension is arranged in the exhaust channel's axial extension. The invention according to the present description is not limit to the embodiments displayed and described above, but may be modified within the framework of the enclosed claims. For example, the vehicle is not limited to a truck as displayed in Fig. la, but may be any vehicle comprising a combustion engine and an exhaust aftertreatment system as described above. Furthermore, the element does not need to have such a structure as displayed in Figs. 2-4, as long as it allows passage of exhausts through the element over a surface thereof.

Claims

1. Exhaust aftertreatment system (1) for treatment of exhausts from a combustion engine (2), said exhaust aftertreatment system comprising an exhaust aftertreatment device (3) and an exhaust channel (4), arranged between an exhaust outlet (5) in a combustion engine and an exhaust inlet (6) in the exhaust aftertreatment device, wherein the exhaust aftertreatment device comprises at least one catalyst adapted to purify the exhausts, characterised in that an element with a surface (14) adapted to adsorb at least one substance or compound that may deactivate a catalyst in the exhaust aftertreatment device, is arranged in the exhaust channel (4), wherein said surface (14) comprises a material consisting of a pillar equipped clay, PILC.

2. Exhaust aftertreatment system according to claim 1, wherein said element is

detachably arranged in relation to the exhaust channel.

3. Exhaust aftertreatment system according to claim 2, wherein a wall in the exhaust channel comprises a hatch, through which the element may be inserted into and removed from, respectively, the exhaust channel.

4. Exhaust aftertreatment system according to claim 2, wherein the element is arranged in a first exhaust channel section, which is detachably arranged in relation to an adjacent second exhaust channel section in the exhaust channel's axial direction.

5. Exhaust aftertreatment system according to one of the previous claims, wherein the element comprises several channels, whose axial extension is arranged in the exhaust channel's axial extension and wherein the element has an open area in the exhaust channels' radial cross section, which area is larger than the open area in said catalyst.

6. Exhaust aftertreatment system according to any of the previous claims, wherein the element has a honeycomb structure, a net-shaped structure or an at least partly pleated structure.

7. Exhaust aftertreatment system according to any of the previous claims, wherein the PILC-material is selected from a PILC comprising pillars of aluminium oxide, silica, titanium oxide or at least two of these.

8. Exhaust aftertreatment system according to any of the previous claims, wherein the PILC-material is doped, in order to increase the affinity for the at least one substance or compound that may deactivate the at least one catalyst in the exhaust purification device, preferably to increase the affinity for phosphor and/or phosphor containing compounds.

9. Exhaust aftertreatment system according to any of the previous claims, wherein the PILC-material is selected from a porous clay heterostructure, PCH.

10. Exhaust aftertreatment system according to claim 8, wherein the PILC-material is a PCH comprising pillars of silica, titanium oxide, or alternatively silica and titanium oxide, and is doped with iron, vanadium or aluminium.

11. Exhaust aftertreatment system according to any of the previous claims, wherein the PILC-material is arranged as a coating on a load carried, wherein the coating and the load carrier jointly form this element.

12. Exhaust aftertreatment system according to any of claims 1-10, wherein the entire element consists of the PILC-material.

13. Exhaust aftertreatment system according to any of the previous claims, wherein the surface is free of precious metals, and preferably wherein the entire element is free of precious metals.

14. Exhaust aftertreatment system according to any of the previous claims, wherein the element is arranged at or in the vicinity of a downstream end of the exhaust channel.

15. Exhaust aftertreatment system in accordance with claim 14, wherein the element is arranged in the immediate vicinity of the exhaust inlet of the exhaust aftertreatment device.

16. Vehicle (100) comprising a combustion engine (2) and an exhaust aftertreatment system (1) according to any of the previous claims, said exhaust aftertreatment system being adapted for aftertreatment of exhausts from the combustion engine.

17. Vehicle according to claim 16, wherein the vehicle is a truck, a bus or a car.