FR2904656A1 - Pollutant treating device for motor vehicle, has photocatalysts in dielectric material covering external and internal electrodes and having elimination and reception surface for receiving and eliminating pollutants - Google Patents

Abstract

Device for treating pollutants contained in gaseous effluents of a motor vehicle, characterized in that it comprises at least one elementary element 12 for eliminating pollutants internally defining a conduit 14 for gaseous effluents and provided with a first electrode external 22, a second internal electrode 24 between which is applied an electrical pulse, and at least one photocatalyst 34, 36 of dielectric material covering one of the two electrodes and comprising a receiving surface and elimination 40 pollutants.

Description

 Device for treating pollutants contained in gaseous effluents of a motor vehicle and associated method

The invention relates to the treatment of pollutant components contained in a gaseous medium and, in particular, to the field of devices for filtering gaseous effluents from a motor vehicle.

More particularly, the invention relates to a device for treating pollutants, in particular by means of photocatalytic elimination of the pollutant components contained in gaseous effluents.

A first interesting application of the device relates to the treatment of a gas mixture intended to be drawn from inside the passenger compartment of a motor vehicle.

Indeed, the European anti-pollution standards are at the moment more and more restrictive with regard to the treatment of pollutants, such as volatile organic compounds (VOCs) and the release of unpleasant odors.

VOCs can be released from the products and materials used to draw air from inside the cabin. Odors can, for their part, develop in a heating / air conditioning system used in the vehicle. Indeed, within such a device, microorganisms can proliferate, resulting in the formation of unpleasant odors that are then conveyed inside the cabin during its operation. A second interesting application of the device relates to the purification of exhaust gases from the internal combustion engine of the motor vehicle.

This application is interesting insofar as it is known that the heterogeneity of the combustion processes in the engines, in particularly in diesel engines, has the effect of generating polluting carbon particles which should be reduced in the atmosphere.

Among the systems known to considerably reduce the quantity of particles, dust and other soot, emitted into the atmosphere, and meet the antipollution standards, mention may be made of the particulate filter mounted in the exhaust line of the engine.

Indeed, such a filter is designed so as to retain the particles contained in the exhaust gas flowing through it. However, as the engine is used, the particles accumulate in the filter and eventually cause significant backpressure to the engine exhaust, which significantly reduces its performance.

In this respect, controlled regeneration devices make it possible to periodically burn the particles trapped in the filter and thus to avoid a significant rise in the exhaust back pressure and possible clogging of the filter.

This regeneration is carried out by raising the temperature at the particle filter to a temperature of the order of 570 ° C to 650 ° C, at which temperatures the carbon particles retained in the filter burn instantly.

To do this, we can proceed to a delayed injection of fuel, or post-injection, into the combustion chambers of the engine. In particular, fuel can be injected after the top dead center during the expansion phase, which has the effect of increasing the temperature of the exhaust gas.

However, such a delayed injection has the disadvantage of raising the temperature of the exhaust gas very far upstream of the particulate filter, which is likely to cause mechanical fatigue. and to cause a phenomenon of dilution of the gas oil in the lubricating oil of the engine.

In addition, in order to reduce the amount of pollutant emitted into the atmosphere, it is also possible to provide an exhaust treatment device mounted on the exhaust line. Such a treatment device may be provided with an oxidation catalyst and a fuel injector disposed upstream of the oxidation catalyst, considering the flow direction of the exhaust gas. An oxidation catalyst makes it possible to oxidize the residual combustion products of the HC / CO type to CO ₂ and H ₂ O. The oxidation catalyst is effective when its temperature is high. However, cold, it does not work satisfactorily. There is therefore a risk of pollution all the higher as the average journey of a vehicle is generally short.

In order to avoid such pollution, it is desirable to allow, from the start of the vehicle or during congested urban situations, a treatment of residual products of the HC / CO type that is effective. In this respect, the patent application US 2003/0140622 describes a system for treating the exhaust gases of a diesel-type combustion engine, the system being provided with an oxidation catalyst positioned in the exhaust line. engine, and a plasma reactor connected to a pipe opening into the exhaust line upstream of said oxidation catalyst, considering the flow direction of the exhaust gas. The plasma reactor allows an injection of gas into the exhaust line so as to obtain a prior conversion of NO _x before entering the oxidation catalyst. This system has the disadvantage of not allowing a significant increase in the temperature of the exhaust gas, which reduces the efficiency of the oxidation catalyst.

For an application relating to the purification of a gaseous mixture intended to be drawn inside the passenger compartment of the motor vehicle, similar treatment devices have also been proposed which comprise in particular a plasma generator and a photocatalyst arranged downstream. said generator, considering the flow direction of the gas mixture. For more details, reference may be made to the device described in document US 2005/0142047.

Also known from US 2005/0058582, a heating / air conditioning device comprising an electrostatic filter, a plasma generator and an oxidation catalyst, arranged from upstream to downstream, considering the gas flow direction.

These devices have the disadvantage of not allowing a satisfactory activation of the catalyst in order to obtain a good treatment efficiency of the pollutants carried by the gases. In view of the foregoing, the object of the invention is to overcome the disadvantages associated with the production of prior treatment devices.

In particular, the object of the invention is to provide a device for treating pollutants contained in gaseous effluents which is particularly effective.

The present invention also aims to provide a device that can be used for the treatment of a mixture of gases intended to be drawn inside the passenger compartment of the motor vehicle. The present invention also aims to provide a device adapted to treat exhaust gases from the internal combustion engine of the vehicle.

The present invention finally aims to provide a pollutant treatment device that is particularly compact.

According to a first aspect, the subject of the invention is therefore a device for treating pollutants contained in gaseous effluents of a motor vehicle, which comprises at least one elementary elimination module internally delimiting a conduit for the gaseous effluents.

The module is provided with a first external electrode, a second internal electrode between which an electrical pulse is applied, and at least one photocatalyst of dielectric material covering one of the two electrodes and comprising a receiving surface and a elimination of pollutants.

With such a device, it becomes possible to obtain a treatment of pollutants that is particularly simple and effective, with only one means.

The applicant has determined that the use of a photocatalyst of dielectric material inside a dielectric barrier discharge makes it possible to increase the treatment efficiency of the pollutants contained in the gaseous effluents.

Indeed, the use of a photocatalyst arranged radially and axially between the electrodes makes it possible to lower the activation temperature thereof. The electrical pulse created between the two electrodes promotes the excitation of the photocatalyst, which further decreases the temperature at which it is particularly effective. Moreover, with this arrangement in which the photocatalyst constitutes the dielectric material of the dielectric barrier discharge, the axial dimension of the catalytic surface is relatively large. Thus, a large axial dimension active elimination surface is obtained without increasing the size of the device.

Advantageously, the device comprising first and second photocatalysts covering the first and second electrodes, respectively. The use of two photocatalysts each covering one of the electrodes makes it possible to increase the reliability of the device. Indeed, with this arrangement, in operation, the state of the two electrodes is preserved for a longer period.

In addition, the use of two photocatalysts makes it possible to increase the active surface area for receiving, absorbing and eliminating pollutants.

Preferably, the photocatalyst (s) are of tubular general shape.

In a preferred embodiment, the first and second electrodes are coaxial.

The device may further comprise an additional radiation source arranged radially between the first external electrode and the second internal electrode.

Advantageously, the axial dimension of the photocatalyst (s) is substantially equal to that of the first and second electrodes.

The device may further comprise an absorbent disposed downstream of the first and second electrodes, considering the flow direction of the gaseous effluents inside the module. In one embodiment, a plurality of elementary pollutant removal modules are connected in parallel to the flue gas stream.

According to a second aspect, the subject of the invention is also a process for treating pollutants contained in gaseous effluents from a motor vehicle, in which an electrical impulse is applied across two electrodes of a dielectric barrier discharge comprising at least two electrodes. less a photocatalyst of dielectric material covering one of the two electrodes and comprising a surface for receiving and removing pollutants.

The gaseous effluents may be the exhaust gas of the internal combustion engine of the motor vehicle, or the gas mixture intended to be drawn from inside the passenger compartment of the vehicle. The present invention will be better understood on studying the detailed description of embodiments taken by way of non-limiting examples and illustrated by the appended drawings, in which: FIG. 1 is a sectional view of a treatment device of pollutants contained in gaseous effluents according to a first embodiment of the invention, Figure 2 is a sectional view along the line II-II of Figure 1, and Figure 3 is a sectional view of a processing device according to a second embodiment of the invention. FIGS. 1 and 2 show a device for treating pollutants contained in gaseous effluents of a motor vehicle, designated by the general reference numeral 10. This device can be used for the treatment of pollutants, such as VOCs and odors, contained in a mixture of gases intended to be drawn from inside a passenger compartment of a motor vehicle. This device can also be used for the treatment of pollutants contained in the exhaust gas of the internal combustion engine of the vehicle, and in particular for the treatment of carbon particles.

This device 10 essentially comprises an elementary treatment module 12 internally delimiting a conduit 14 for gaseous effluents, inside which the pollutants conveyed by said effluents will be removed.

The duct 14, delimited by a cylindrical general wall, of axial general axis 16, is provided with two mutually opposite open ends 18 and 20 for fixing the device to a pipe in which the gaseous effluents to be treated circulate.

More precisely, the open end 18 is intended, in the case of an application for the treatment of the engine exhaust gases, to be directly connected at the outlet of the exhaust manifold of the internal combustion engine, the end 20 being, meanwhile, intended to be connected to an exhaust pipe exhaust.

In order to allow the elimination of the pollutants carried by the gaseous effluents entering the conduit 14 through the end 18, the device 10 comprises in particular first and second electrodes, referenced respectively 22 and 24.

The first outer electrode 22 has a generally tubular shape and is coaxial with the axis 16. The first electrode 22 is fixed against the outer wall of the conduit 14, by any appropriate means. It extends over most of it. The second internal electrode 24 also has a generally tubular shape, coaxial with the axis 16. The first and second electrodes 22 and 24 are coaxial with each other.

The second internal electrode 24 is here mounted on the inner wall of a tube 26 closed at each of its ends and mounted inside the conduit 14. The second electrode 24 has an axial dimension equal to that of the first electrode 22. and is aligned axially with respect thereto.

In other words, the first external electrode 22 radially surrounds the second internal electrode 24.

The tube 26 is coaxial with the axis 16 of the duct 14. It has a relatively small radial dimension compared to that of the duct

14 so as to provide a tubular radial space between the outer wall thereof and the inner wall of the conduit 14 for the flow of gaseous effluents. The tube 26 is fixed relative to the conduit 14.

The first external electrode 22 is electrically connected to an alternating voltage power source, symbolized by the reference 28, via a connection 30. The power source 28 is also connected to the second internal electrode 24. via a connection 32 extending radially in the conduit 14.

Insulators (not shown) are arranged on the conduit 14 and the tube 26 so as to electrically isolate the wall of these two elements from the internal electrode 24. For the elimination of the pollutants carried by the gaseous effluents, the device 10 also comprises first and second photocatalysts 34, 36 associated with the first and second electrodes 22, 24, respectively. The first external photocatalyst 34 has a generally tubular shape and is coaxial with the axis 16. It is fixed against the inner wall of the conduit 14 by any appropriate means. The photocatalyst 34 comprises an axial dimension substantially equal to that of the first external electrode 22, and is axially aligned therewith. The photocatalyst 34 is thus located entirely inside the conduit 14. It comprises mutually opposite open ends so as to allow the passage of gaseous effluents. In a similar manner, the second internal photocatalyst 36 has an axial dimension substantially equal to that of the second internal electrode 24, and is fixed on the outer wall of the tube 26. The second photocatalyst 36 thus has a generally tubular shape. It is aligned axially with respect to the second internal electrode 24. The first photocatalyst 34 thus radially surrounds the second photocatalyst 36 and the second internal electrode 24. The second photocatalyst 36 radially surrounds the second internal electrode 24. Advantageously, the photocatalysts 34 and 36 comprise titanium dioxide (TiO ₂ ). In operation, the gaseous effluents charged with pollutants enter the conduit 14 through the open end 18, and flow substantially axially inside thereof to the vicinity of the first and second electrodes 22 and 24. From of these, the gaseous effluents are ionized, the pollutants thus being electrically charged. The pollutants are then deflected radially inwards or outwards towards the second photocatalyst 36 or the first photocatalyst 34.

In order to allow an outward deviation of the pollutants, the first external electrode 22 is maintained at a n zero potential, the second internal electrode 24 is brought to a positive or negative potential.

The potential difference created between the first and second electrodes 22 and 24 induces the presence of an electric field in the duct 14. If this electric field has a sufficient intensity, in particular in the very near vicinity of the internal electrode 24, it a partial or total ionization of the gases, comprised axially and radially between the internal and external electrodes 24, is then produced. The use of photocatalysts 34 and 36, respectively covering the first electrode 22 and the second electrode 24, enables the current to be cut off. thus created between said electrodes, so as to limit the losses necessary for the ionization of the gases, and avoid the transition to the arc while maintaining a strong electric field. Such an arc passage could damage the outer and inner electrodes 22 and 24.

Under these conditions, the almost homogeneous electric field in the inter-electrode space deflects the charged pollutants that migrate radially towards the first photocatalyst 34 at a pollutant receiving and elimination surface 40 constituted by the internal wall or bore. Photocatalyst 34. This cylindrical surface 40 thus has an axial dimension substantially equivalent to that of the first electrode 22.

Of course, it is also conceivable to provide a supply of the first and second electrodes 22 and 24 so that the charged pollutants are directed radially inward towards the second photocatalyst 36. Under these conditions, a receiving surface 42 and elimination of pollutants is constituted by the cylindrical outer wall thereof. The electric field is heterogeneous only in the vicinity of the first and second electrodes 22 and 24. The pollutants charged and deposited on the surface 40 agglomerate by electrostatic interaction and by Van der Waals forces, and are then removed by the reaction reactions. oxidation-reduction occurring at this surface of the first photocatalyst 34.

In fact, the discharge created between the first and second electrodes 22 and 24 creates a plasma comprising electrons which by an energy exchange process cause the production of highly reactive radicals capable of initiating, at the level of the surfaces 40 and 42. photocatalysts 34 and 36, oxidation reactions with the pollutants to be eliminated.

In addition, the creation of the plasma also generates ultraviolet (UV) radiation between the electrodes 22 and 24, which makes it possible to locally increase the temperature between them and to excite the photocatalysts 34 and 36. In other words the temperature of the photocatalysts 34 and 36 increases and their efficiency increases.

In other words, after obtaining the capture at the receiving surfaces 40, 42 of the first and second photocatalysts 34 and 36 of dielectric material, via an electrical pulse collection between the first and second electrodes 22 and 24, the photocatalysts 34 and 36 allow the establishment of oxidation - reduction reactions between the pollutants to be eliminated and the active species of the medium generated by the electrical pulse of collection, which are reactions occurring on the surface of the surfaces 40 and 42. Thus, at the open end, gaseous effluents are obtained in which the pollutants have been substantially reduced. The receiving surfaces 40, 42 of the first and second photocatalysts 34 and 36 thus form pollutant absorption surfaces.

The provision of an electric barrier discharge which is provided with photocatalysts 34, 36 acting as a dielectric material of the discharge makes it possible to obtain a treatment of the pollutants carried by the gaseous effluents with a single device, in a particularly efficient and economical manner.

In fact, the Applicant has determined that with photocatalysts 34 and 36 which are thus arranged inside the dielectric discharge barrier, the removal efficiency of the pollutants is substantially increased.

In order to increase the thermal activation of the photocatalysts 34 and 36, the device 10 also comprises a plurality of plasma filaments 38 arranged radially between said first and second photocatalysts 34 and 36. The plasma filaments 38 are distributed over most of the the axial length of these photocatalysts 34 and 36. The plasma filaments thus constitute a source of radiation, here ultraviolet, additional. In the embodiment illustrated in FIG. 3, in which the identical elements bear the same references, an absorbent 42 is fixed on the inner wall of the duct 14, close to the open end 20. This absorbent 44 may for example be a catalyst made of manganese dioxide (MnO ₂ ) or a layer of zeolyte.

This absorbent 44 disposed downstream of the electrodes 22 and 24, considering the flow direction of the gaseous effluents inside the conduit 14, further increases the efficiency of the device 10. Although in the previously described embodiments, a single elementary treatment module 12 has been shown, it is easy to see that the device 10 may comprise a plurality of modules 12 connected in parallel with the flow of gaseous effluents to be treated, in such a way that to increase the overall efficiency of the device.

Thanks to the invention, a pollutant treatment device is obtained which comprises at least one elementary elimination module, internally delimiting a conduit for the gaseous effluents to be treated, which is provided with a plasma reactor comprising a first external electrode. , a second internal electrode between which is applied an electrical pulse, and at least one photocatalyst of dielectric material covering at least one of the two electrodes for the removal of pollutants.

Claims (10)

1. A device for treating pollutants contained in gaseous effluents from a motor vehicle, characterized in that it comprises at least one element (12) for eliminating pollutants internally defining a conduit (14) for gaseous effluents and provided with a first external electrode (22), a second internal electrode (24) between which an electric pulse is applied, and at least one photocatalyst (34, 36) of dielectric material covering one of the two electrodes and comprising a surface for receiving and removing (40) pollutants. 2. Device according to claim 1, comprising first and second photocatalysts (34, 36) covering the first and second electrodes, respectively. 3. Device according to claim 1 or 2, wherein the one or more photocatalysts (34, 36) are of tubular general shape. 4. Device according to any one of the preceding claims, wherein the first and second electrodes are coaxial. 5. Device according to any one of the preceding claims, further comprising an additional radiation source arranged radially between the first outer electrode and the second inner electrode. 6. Device according to any one of the preceding claims, wherein the axial dimension of the photocatalyst or photocatalysts is substantially equal to that of the first and second electrodes. 7. Device according to any one of the preceding claims, further comprising an absorbent (44) disposed downstream. first and second electrodes, considering the flow direction of the gaseous effluents inside the module. 8. Device according to any one of the preceding claims, comprising a plurality of elementary modules for eliminating pollutants connected in parallel with the flow of gaseous effluents. 9. A process for treating pollutants contained in gaseous effluents from a motor vehicle, characterized in that an electrical impulse is applied across two electrodes of a dielectric barrier discharge comprising at least one photocatalyst of dielectric material covering one of the two electrodes and comprising a surface for receiving and removing (40) pollutants. 10. The method of claim 9, wherein the gaseous effluents are the exhaust gas of an internal combustion engine of the motor vehicle. 1. Process according to claim 9, in which the gaseous effluents are the mixture of gases intended to be drawn from inside the passenger compartment of the motor vehicle.