Classifications

• • C—CHEMISTRY; METALLURGY
  • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
  • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
  • C04B38/00—Porous mortars, concrete, artificial stone or ceramic ware; Preparation thereof
  • C04B38/0006—Honeycomb structures
  • C04B38/0012—Honeycomb structures characterised by the material used for sealing or plugging (some of) the channels of the honeycombs
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J35/00—Catalysts, in general, characterised by their form or physical properties
  • B01J35/50—Catalysts, in general, characterised by their form or physical properties characterised by their shape or configuration
  • B01J35/56—Foraminous structures having flow-through passages or channels, e.g. grids or three-dimensional monoliths
  • B01J35/57—Honeycombs
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
  • B01J37/02—Impregnation, coating or precipitation
  • B01J37/0201—Impregnation
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
  • B01J37/02—Impregnation, coating or precipitation
  • B01J37/0215—Coating
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2279/00—Filters adapted for separating dispersed particles from gases or vapours specially modified for specific uses
  • B01D2279/30—Filters adapted for separating dispersed particles from gases or vapours specially modified for specific uses for treatment of exhaust gases from IC Engines
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
  • B01J23/38—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals
  • B01J23/40—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals of the platinum group metals
  • B01J23/42—Platinum
• • C—CHEMISTRY; METALLURGY
  • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
  • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
  • C04B2111/00—Mortars, concrete or artificial stone or mixtures to prepare them, characterised by specific function, property or use
  • C04B2111/00474—Uses not provided for elsewhere in C04B2111/00
  • C04B2111/00793—Uses not provided for elsewhere in C04B2111/00 as filters or diaphragms
• • C—CHEMISTRY; METALLURGY
  • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
  • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
  • C04B2111/00—Mortars, concrete or artificial stone or mixtures to prepare them, characterised by specific function, property or use
  • C04B2111/00474—Uses not provided for elsewhere in C04B2111/00
  • C04B2111/0081—Uses not provided for elsewhere in C04B2111/00 as catalysts or catalyst carriers
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
  • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL-COMBUSTION ENGINES
  • F01N2550/00—Monitoring or diagnosing the deterioration of exhaust systems
  • F01N2550/06—By-pass systems

Definitions

• the invention relates to the field of particulate filters used in an exhaust line of an engine for the removal of soot typically produced by combustion of a diesel fuel in an internal combustion engine. More specifically, the invention relates to a particulate filter, said filter further comprising a material conferring catalytic properties, and a method of preparing it.
• Filtration structures for soot contained in the exhaust gas of an internal combustion engine are well known in the prior art. These structures most often have a honeycomb structure, one of the faces of the structure for the admission of the exhaust gases to be filtered and the other side the exhaust of the filtered exhaust gases.
• the structure comprises, between the intake and discharge faces, a set of adjacent ducts or channels of axes parallel to each other separated by porous filtration walls, which ducts are closed to one or the other of their ends for delimiting input chambers s 'opening according to the inlet face and outlet chambers s' opening according to the discharge face.
• the peripheral part of the structure is surrounded by a cement, called coating cement in the following description.
• the channels are alternately closed in an order such that the exhaust gases, during the crossing of the honeycomb body, are forced to cross the walls side of the input channels to join the output channels. In this way, the particles or soot are deposited and accumulate on the porous walls of the filter body.
• the filter bodies are porous ceramic material, for example cordierite or silicon carbide.
• the particulate filter is subjected to a succession of filtration phases (accumulation of soot) and regeneration (removal of soot).
• filtration phases the soot particles emitted by the engine are retained and are deposited inside the filter.
• regeneration phases the soot particles are burned inside the filter, in order to restore its filtration properties.
• the porous structure is then subjected to intense thermal and mechanical stresses, which can cause micro-cracking likely over time to cause a severe loss of filtration capacity of the unit, or even its complete deactivation. This phenomenon is particularly observed on monolithic filters of large diameter.
• said parts are synthesized on the basis of the same material, most often silicon carbide SiC or cordierite. This choice also makes it possible to homogenize the distribution of heat during the regeneration of the filter.
• the expression "at the base of the same material” is meant in the sense of the present description that the material consists of at least 25% by weight, preferably at least 45% by weight and very preferably at least 70% by weight of said material.
• the filters or porous soot filtration structures as previously described are mainly used on a large scale in the exhaust gas pollution control devices of a diesel engine.
• the exhaust line of the internal combustion engine comprises, in series, a catalytic purification member and a particulate filter.
• the catalytic purification unit generally of open honeycomb structure, is adapted for treatment of pollutants in the gas phase, while the particulate filter is adapted to remove soot particles emitted by the engine.
• the succession of filter elements on the exhaust line is however responsible for a significant loss of load on said line, which may affect the engine performance .
• the honeycomb structure is impregnated with a solution comprising the catalyst or a precursor of the catalyst.
• Such methods generally include an immersion step in either a solution containing a catalyst precursor or a catalyst solubilized in water (or other solvent), or a suspension in water of catalytic particles.
• a solution containing a catalyst precursor or a catalyst solubilized in water (or other solvent), or a suspension in water of catalytic particles An example of such a process is described in US Pat. No. 5,866,210.
• the application at the other end of the filter of a vacuum allows in a second time the rise of the solution in the structure and consequently the coating of the internal walls of the honeycomb structure.
• said impregnations can be obtained by pumping, by applying a vacuum or under the pressure of the liquid comprising the impregnation solution, on at least one end of the monolith.
• the processes described are characterized by a combination of these different techniques, in successive steps, the final step allowing the removal of the excess solution in the filter by introduction of air under pressure or by suction.
• One of the essential goals sought by the implementation of these methods is to obtain a uniform coating of the catalyst on or even inside at least a portion of the porous walls of the channels constituting the internal part of the structure and traversed by the gases exhaust.
• the catalyst is deposited uniformly on the walls of the filter channels, but also that a minimum portion thereof is deposited on the parts of the honeycomb structure which do not come into direct contact with the gases to be filtered or the soot.
• Said parts are essentially the coating cement for a monolithic structure, added with the joint cement in the case of a filter block as previously described, that is to say combining several monolithic elements in honeycomb and in to a lesser extent the cement used for plugs alternately obstructing the channels.
• the present invention relates to a process for obtaining a filter for the filtration of a gas loaded with soot particles and gas phase pollutants such as carbon monoxide CO, oxides nitrogen NOx, SOx sulfur oxides, HC hydrocarbons, said process comprising the steps of: a) manufacturing a first structure comprising:
• a central part comprising a plurality of honeycomb filter elements interconnected by a joint cement, the one or more elements comprising a set of adjacent ducts or channels with axes parallel to one another separated by porous walls, which conduits being closed by plugs at one or the other of their ends to define inlet chambers opening on a gas inlet face and outlet chambers opening on a discharge face of gas, such that the gas passes through the porous walls and a peripheral portion constituted by a coating cement protecting the said element or elements, the porosity of the joint cement and / or the coating cement and / or the cement constituting the plugs being less than the porosity of the material constituting said walls, b) impregnating said structure with a solution containing a precursor of the catalyst or the solubilized catalyst in a solvent such as water, a suspension in a solvent such as water of catalytic particles.
• said elements, the coating cement, the joint cement and the plugs are based on the same ceramic material, preferably based on silicon carbide SiC.
• the porosity of the cement used for the coating and / or for the seal and / or for the plugs is less than 5%, preferably at least 10%, and very preferably at least 10%. 15% or even 20%, to the porosity of the filter elements.
• this difference of 5, 10, 15 or 20% is calculated on the basis of the percentage difference in porosity between the filter element (s) and the coating or joint cement, based on the percentage of porosity of the filter element (s) in question.
• the porosity of the honeycomb filter elements is between 30% and 70%, preferably between 35% and 60%.
• the porosity of the cement used for the coating and / or for the seal and / or for the plugs is between 20% and 60%, preferably between 25% and 45%.
• the impregnation of the structure can be carried out by any method known in the art and in particular by pumping the solution through the structure, by applying a vacuum or a vacuum or under pressure liquid comprising the impregnating solution on at least one end of the structure.
• a vacuum or a vacuum or under pressure liquid comprising the impregnating solution on at least one end of the structure.
• Better impregnation is generally achieved by a combination of these different techniques, in successive steps, usually a final step allowing the removal of the excess solution in the filter by suction or by introduction of pressurized air .
• the impregnation step may be implemented according to the methods and / or devices known from the prior art and in particular according to one of the methods or devices described in the patents or patent applications mentioned above.
• the porosity of the cement used for the coating and / or for the seal and / or for the plugs can be adjusted according to several methods of preparation:
• the cement composition and / or the particle size distribution of the grains entering into the cement composition and / or the quantity of cement are adjusted. water mixed with grains as well as that of the other liquid ingredients, to obtain the desired porosity.
• the porosity of the coating cements and / or seal and / or plugs is adjusted by the introduction, during the preparation step, of a charge or filler according to the English term, whose size is adjusted to that of the pores of the cement.
• the filler by occupying at least part of the pores of the cement, thus prevents catalyst precursors or the catalyst from infiltrating the porosity.
• the charges are, for example, organic or inorganic molecules, the size of which is substantially identical to or smaller than that of said precursors or said catalysts.
• the invention relates to a catalytic filter that can be obtained by the process ⁇
• the manufacturing method as just described and characterized by a lower porosity of the cement constituting the coating and / or the joints and / or plugs relative to the porosity of the filter element or elements, as well as by the presence of a minimal amount of catalyst on said cement.
• a minor amount is understood to mean a smaller amount of catalyst relative to the theoretical amount of the catalyst contained in a cement of the same porosity as that of the filtering elements.
• the catalytic filter is characterized in that the porosity of the cement constituting the coating and / or the joints and / or plugs is less than 5%, preferably at least 10%, and very preferably at least 15% to the porosity of the filter element or elements.
• a filtering structure comprising an assembly of silicon carbide filter elements bonded with a joint cement was synthesized according to the techniques described in patent EP 1 142 619.
• a quantity of water corresponding to 10% of the weight of this mixture is added to obtain a cement of adequate viscosity.
• the assembly is annealed at a temperature sufficient to ensure satisfactory cohesion of the filter and its elements.
• This crude structure is then immersed in a bath of an aqueous solution containing the appropriate proportions of a platinum precursor in the form of H 2 PtClO, and a precursor of cerium oxide CeO 2 (in the nitrate form of cerium) and a precursor of zirconium oxide ZrO 2 (in the form of zirconyl nitrate) according to the principles described in publication EP 1 338 322 A1.
• the filter is impregnated with the solution according to an implementation method. similar to that described in US Patent 5,866,210.
• the filter is then dried at about 150 ° C. and then heated to a temperature of about 600 ° C.
• Table 2 The main characteristics of the catalytic filter thus obtained are summarized in Table 2.
• 0.25% weight of platinum in the monolithic elements ie 4.0 grams, of which 3.8 grams in the porosity of the walls of the honeycomb elements and 0.2 grams in the plugs.
• 0.13% weight of platinum in the coating cement ie 0.25 gram, over a thickness of a few tens of ⁇ m from the external surface of the cement, 0.08% weight of platinum in the cement joint, ie 0.25 gram, the platinum being homogeneously distributed throughout the thickness of the cement.
• a catalytic filter was manufactured by repeating the same steps as those of Example 1, except that the cement used for the coating and the seal was prepared from the following proportions of the various constituents:
• the porosity of the joint and coating cements in the raw structure is 36.5%, which corresponds to a difference in porosity between the porosity of the filter elements and the porosity of the cement of 22.3%.
• the porosity of the seal and coating cements in the filter (after impregnation) is this time 35%, which corresponds to a difference in porosity between the porosity of the filter elements and the porosity of the cement of 18.6%.
• the chemical analysis shows a total concentration of Pt of 48 g / ft 3 (1.68 kg / m 3 ), ie 4.2 grams distributed over the different parts of the filter.
• a catalytic filter was manufactured by repeating the same steps as those of Example 2, with the difference that the material used to make the caps is not identical to the extrusion paste used for the synthesis of the elements but is a specific mixture leading after cooking to a lower porosity.
• the proportions of the various constituents of the mixture used are as follows:
• the characteristics of the raw structure and the filter obtained after impregnation according to this example are substantially the same as those obtained for Example 1 and listed in Tables 1 and 2.
• the chemical analysis shows a total Pt concentration of 47 g / ft 3 , ie 4.1 grams, distributed over the different parts of the filter.
• the present invention is not limited to this simple embodiment and that any known means of acting on the porosities of the cement and / or filter elements and / or their plugs, such as the introduction of fillers or sintering additives, should be considered as part of the present invention. Without departing from the scope thereof, it is also possible to use a combination of such means to exert even better control of said porosity.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Organic Chemistry (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Ceramic Engineering (AREA)
• Structural Engineering (AREA)
• Filtering Materials (AREA)
• Catalysts (AREA)
• Exhaust Gas After Treatment (AREA)
• Filtering Of Dispersed Particles In Gases (AREA)

Applications Claiming Priority (3)

Publications (1)

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• 2006
  • 2006-04-07 EP EP06726320A patent/EP1871525A2/fr not_active Withdrawn
  • 2006-04-07 US US11/910,528 patent/US20080170973A1/en not_active Abandoned
  • 2006-04-07 WO PCT/FR2006/050314 patent/WO2006106275A2/fr not_active Ceased
  • 2006-04-07 JP JP2008504819A patent/JP2008537510A/ja active Pending

Non-Patent Citations (1)

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