CS198119B2 - Catalyser carrier for cleaning the exhaust gases from the motors and method of making the carrier - Google Patents

Abstract

1406903 Catalyst support element and method of preparing such an element SOC GENERALE DES PRODUITS REFRACTAIRES 2 Feb 1973 [4 Feb 1972] 5362/73 Heading B1F A catalyst support element for a catalyzer apparatus for purification of motor exhaust gases comprises a porous rigid unitary element composed of interwoven ceramic fibres and refractory binding material, the bonded fibre composition having an apparent density of not more than 0.6, an open porosity of at least 70%, a compressive strength of at least 100% by weight, a shrinkage when heated from ambient temperature to 1,000‹C of not more than 2%, and a specific surface area of at least 10 m<SP>2</SP>/g, and shows substantially no deterioration after at least 100 thermal shocks, where a thermal shock is the effect occurring on the catalyst support of the sudden introduction thereof into an enclosure at 800‹C, maintaining it therein for 15 minutes, and thereafter cooling the catalyst support element in air at ambient temperature. A method of making the element comprises forming a paste of refractory ceramic fibres and a refractory binder material, introducing the paste into a mould, drying the formed shape and thereafter firing the shape at a temperature of from 1200-1300‹C, impregnating the resulting product with a gel or mol of at least one refractory oxide or a mixture of at least one refractory oxide with metals that form refractory oxides, drying the impregnated product and then firing the dried product at a temperature of 600-800‹C.

Description

The subject of the invention is a carrier. Catalyst for the purification of engine exhaust gases and a process for its production.

The purification of the exhaust gases depends mainly on the oxidation of carbon monoxide to carbon dioxide and on the reduction of nitric oxide. For this purpose, the type of catalytic converter through which the exhaust gases are guided must be carefully selected. Beads or pellets of porous ceramic are usually used as supports for catalysts. masses, as well as rigid thin-walled ceramic bodies in the form of honeycomb mesh or balls or rolls of felt from ceramic fibers. These bodies are housed in a metal container or container where they are retained, for example, by a metal net.

These devices have been found to be damaged during operation. They are subject to the effects of passing hot gases, vehicle shocks, resonances caused by engine pulsation, severe temperature changes when the engine starts and stops, as well as other changes while the engine is running.

Bulk supported catalyst supports of porous ceramic or fiber are damaged by abrasion. The metal nets which hold them are then deformed by the temperature of the gases (800 ° C) as well as by the temperature of the gas. by vigorously heating and cooling, thereby further increasing the vibration movement of the catalyst supports.

Rigid ceramic honeycomb mesh supports are subjected to the same severe conditions and do not resist better than other supports because their resistance to thermal shock is at best average.

BACKGROUND OF THE INVENTION The present invention relates to catalyst supports better suited to the particular conditions of exhaust pots and to their installation in an exhaust gas purification system from an engine.

In the accompanying drawings, FIGS. 1 and 2 show the catalyst support according to FIG. The invention, in the form of a monoblock, of a circular plate in FIG. FIG. 2 is a transverse vertical section. FIG. 3 shows one embodiment of an exhaust purifying device. engine gases comprising the catalyst supports of the invention. The graph in Fig. 4 shows curves showing the dependence of the degree of conversion of carbon monoxide to carbon dioxide on the engine speed.

The catalyst support of the invention for the purification of engine exhaust gases, consisting of a solid monoblock of braided ceramic fibers and a refractory binder, is characterized in that the monoblock material has a density expressed as a proportion of the mass of the monoblock. and its volume, not more than 0,6.10 ³ kg / / m3, total open pore volume not less than 70 ·% 70%, compressive strength not less than 3.10 ⁵ Pa, water adsorption capacity not less than 100% and additional shrinkage at 1000 ° G not more than 2 o / and is formed in the form of a circular plate 2 with axial holes 3, which is extended at its periphery by an unperforated ring 1 having a height greater than the height of the circular plate 2.

In one variation of the carrier according to the invention, the density of the axial holes 3 in the plate 2 adjacent to the ring 1 is zero. That is, only the central portion of the plate 2 comprises axial openings 3 and is surrounded by an edge portion that is free of holes.

According to another embodiment of the support according to the invention, the circular plate 2 is provided in its central part with axial holes 3 more densely than at its edge, the density of the axial holes 3 being greatest in the central part of the circular plate 2. The average number of axial holes 3 thus substantially lower in the peripheral portion than in the central portion. Parts. It is preferred that the mean density of the holes in the edge portion gradually decrease towards the outer edge.

The term "plate" means both a prism and a cylinder in which the dimensions of the base are considerably greater than the height. The non-perforated ring 1 extending the unperforated peripheral portion of the circular plate 2 forms a continuous whole therewith, either by co-molding with the circular plate or by being manufactured separately and later rigidly bonded thereto by refractory cement.

The diameter of these parts is preferably 50 to 250 mm when the cylinder is in the range of 20 to 60 mm.

The axial holes have a diameter of from 1 to 8 mm, preferably 1.5 to. 3 mm, but may also have any other geometric shape with equivalent cross-section. Sum of cross-section of axial holes 3. ve. the central portion is at least 25%, preferably at least 35% of the surface area of the central portion. circular plates 2.

The circumferential ring 1 has a height in the range of up to 20 mm, preferably about 3 mm. The thickness of the ring depends on the material from which it is made and on the conditions of use, as follows.

The catalyst-forming fibers are preferably based on active alumina, or ceramic fibers containing 40 to 50% alumina, but may also be asbestos, mineral wool or slag. The condition is that the linear shrinkage does not exceed 2% at the maximum gas temperature, ie about · 800 ° C. Mixtures of the various fibers may also be used.

The binders which the fibers are bonded to each other and which give the monoblock the necessary stiffness to resist erosion by gases are preferably aluminum phosphate, refractory clays, bentonites, silica gel, gels or salts of refractory metal oxides such as silicon, aluminum, zirconium or chromium, individually or in mixtures. A gel or sol of alumina and / or boehmite is preferred, characterized in addition to the ability to bond the fibers to high heat resistance, and reacts readily with the fibrous substrate to form a monoblock with good mechanical strength. The proportion of refractory binder is 10 to 60% by weight, preferably 30 to 40% by weight, based on the weight of the monoblock.

The most effective catalyst is a platinum catalyst. However, it is also possible to use less salts or oxides. rare transition metals which are equally effective when used in larger amounts by weight.

A process for producing a catalyst support according to the invention, wherein a suspension of fibers and binder is prepared in a suitable ratio, which is shaped in a mold and then dried and fired, characterized in that the shaped support is after its first firing at a temperature within 1200 to 1300 ° C impregnated with a gel or sol of refractory metal oxide, such as silicon, aluminum, zirconium, chromium or mixtures of these metal oxides, after which it is baked again at a temperature in the range of 600 to 800 ° C.

In a variation of the process for producing the carrier of the invention, the fiber and binder suspension is shaped in a suitable ratio during filtration. All fibers remain on the filter while the binder is only partially adsorbed and the rest flows through the filter into the filtrate. This part of the binder in the filtrate is reused in the preparation of a further slurry, which is re-applied to the fibers, possibly adding the binder. The filtering is followed by drying.

If fibers of sufficient heat resistance are used, it is sufficient to burn the bodies thus obtained at a temperature of at least 600 ° C to react with the fibers to form a monoblock of a new, rigid, partially crystalline and dimensionally stable material.

When less thermally stable fibers are used, the shaped and dried carrier is fired at 1200 to 1300 ° C to achieve good stability by the refractory binder reaction with the fibers. The carrier thus fired is then impregnated with a gel or sol of a refractory metal oxide such as silicon, aluminum, zirconium, chromium, or with a gel or sol of a mixture of these oxides, and then baked again at 600 to 800 ° C after drying. By this second operation, the catalyst support is solidified and activated to increase the specific surface area.

The carrier thus produced should, without taking into account the axial holes, have the following characteristics: a density of at most 0.6.103 kg / m ³ , preferably at most 0.4. 10 ³ kg./m ³ , total open pore volume · at least 70 percent, preferably above 80 ° / o, compressive strength at room temperature up to · 800 ° C. Celsius at least 0.3 MPa, preferably at least 0.4 MPa, water adsorption capacity of at least 100%, without damage after 100 thermal shocks (abrupt insertion into the oven at 800 ° C, left in the oven for 15 minutes and air cooling to room temperature], a shrinkage at 1000 ° C of at most 2 ° / o, preferably below 1%, a specific surface area of at least 10 m ² / g, preferably at least 30 m 2 / g.

The carrier according to the invention and the process for its preparation are illustrated by the following examples.

Example 1

An example of a catalyst support according to the invention is shown in FIG. 1 in a horizontal section and - in FIG. 2 in a side section along line a-a. In the slurry plant, a slurry is prepared comprising 3 wt% alumina fibers, 3 wt% ceramic fibers, 1.5 wt% asbestos fibers, 1 wt% silica sol, 6 wt% colloidal boehmite powder, 40 wt% aluminum phosphate and 45.5% water by weight.

Active alumina fibers having a diameter of 4 to 20 μπι and a specific surface area of 70 m2 / g have the following composition by weight:

silicon dioxide 14.5% alumina 85.0% titanium dioxide 0.1% ferric oxide 0.2% calcium oxide tracks magnesium oxide 0.1% natron 0.1% potassium oxide tracks

Ceramic fibers with a mean diameter of μΐη and a specific surface area of 1,5 m ² / g have the following mass composition:

silicon dioxide 53.6% alumina 45% ferric oxide 0.5% titanium dioxide 0,5 -% calcium oxide 0.1% magnesium oxide tracks natron 0.3% potassium oxide tracks

Medium diameter asbestos fibers

μτα and a specific surface area of 1 m2 / g have the following mass composition: silicon dioxide 60,4 -% alumina 1.5% ferric oxide 28.1% calcium oxide tracks magnesium oxide 7% Natron . 2% potassium oxide 1%

Aluminum phosphate having a density of 1.48.103 kg / m 3 contains 34% by weight of phosphorus pentoxide, 6.8% by weight alumina and 59.2% by weight of water. The silica sol, containing 40 wt% silica and 60 wt% water, has a density of 1.3. . 103 kg / m ³ . Boehmit contains 70 wt% alumina and 30 wt% water.

The suspension is filtered in a mold to obtain the monoblock shown in Figures 1 and 2 having the following dimensions:

monoblock diameter 140 mm ring thickness 115 mm height of perforated center plate 2 '30mm ring height 1 10mm

107 axial holes 3 with a diameter of 6mm the total area of the holes represents 25% of the surface of the central part of the monoblock.

After drying and firing at 800 ° C, the monoblock has the following composition by weight and has the following characteristics:

silicon dioxide 26% alumina 45 -% titanium dioxide 0.1% ferric oxide 3.8% calcium oxide tracks magnesium oxide 0.8% natron 0.3% potassium oxide 0.1% Phosphorus pentoxide 23.9 o / o apparent density 0.42.103 kg / m3 total open pore volume 85% adsoprce vody 150% compressive strength 0,9 MPa specific surface. 12 m2 / g additional shrinkage- at temperature 1000 ° C 0.5% specific thermal conductivity at a mean temperature of 400 ° C 0.163 W / m.K coefficient of extensibility in 20 to 800 ° C 5.2: 10-0

thermal shock resistance (20 ° - 800 ° - 20 ° C) - more than gas permeable cycles. Ю ^-7 ml дд gas viscosity _{p., And} - _having, at one wale of 1 cm ² cross-section of the body under a pressure difference of 0.1 Pa, measured at a distance of 1 cm

Example 2

In the slurry plant, a slurry is prepared comprising 13 wt% alumina fibers, 23 wt% colloidal boehmite powder, 4 wt% silica sol and 60 wt% water. These are similar to those used in Example 1.

The slurry is filtered in the mold to give a monoblock having the same outer dimensions as the monoblock of Example 1 but containing 600 axial channels of 3 mm diameter. The total cross-section of the apertures represents 35% of the central portion of the monoblock surface.

After drying and firing at 800 ° C

The monoblock material has the following characteristics: weight composition: silicon dioxide 13.0 ° / o alumina 86.5% ferric oxide 0,25 0/0 titanium dioxide tracks calcium oxide tracks magnesium oxide tracks natron 0.25% potassium oxide stopv apparent density: 0.35.10 ³ kg / m ³ total volume open pores 88% water adsorption 200% specific surface 85 m ² / g compressive strength 0,6 MPa additional shrinkage at temperature 1000 ° C 0.8% specific thermal conductivity at a mean temperature of 400 ° C .039 W / m. К coefficient of expansion between 20 ° C to 800 ° C 5.ΙΟ “ ⁸ thermal resistance impacts (20 ° - 800 ° C) of more than 200 cycles gas permeability 1,2. * ⁶ ml

[measured as in Example 1)

Example 3

In the slurry production plant, a slurry is prepared comprising 5 wt% ceramic fibers with 45 wt% alumina, 36 wt% aluminum oxide sol containing 20% Al2O5, 2 wt%, silica sol containing 40% SiO2 and 57 wt% % water.

The suspension is filtered in a mold to give a monoblock in the form of a disk perforated in the central part and having a ring of the following dimensions on the periphery:

outer diameter 120mm ring thickness 1 15mm height of center punched part 27mm ring height 1 3mm

613 holes 3 with 2mm diameter

The total cross-section of the axial holes is 26 percent of the surface of the central portion of the monoblock.

After drying and firing at 1250 ° C the monoblock material has the following composition by weight:

silicon dioxide 46,25% aluminum oxide 53% iron oxide 0,35%

titanium dioxide tracks calcium oxide tracks magnesium oxide tracks natron 0.35% potassium oxide 0.05% and having the following characteristics: density 0.28.10 ³ kg / m ³ total volume of open pores 90% specific surface 3 m ² / g compressive strength 0.4 MPa The carrier thus prepared is impregnated into a suspension comprising 36 wt. % of an aluminum oxide sol containing 20% Al 2 O 3, 2 wt % sol- to silica content 40% SiO2 and 62 % by weight of water. After drying and firing at 800 ° C the monoblock material has the following characteristics: Features: Weight composition: silicon dioxide 39.1% alumina 60.1 ° / o ferric oxide 0.3% titanium dioxide tracks calcium oxide tracks magnesium oxide tracks natron 0.4% potassium oxide 0.05% density 0.35.10 ³ kg / m ³ total volume of open pores 88% adsoprce vody 220% specific surface 40 m ² / g compressive strength 0,6 MPa additional shrinkage (at 1000 ° C) 0.8% specific thermal conductivity at a mean temperature of 400 ° C 0.139 W / m. К

thermal shock resistance (20 ° - 800 ° C) more than 200 cycles gas permeability 1.10 ~ ⁶ ml (measured as in Example 1)

The exhaust gas purifying apparatus using the above-described catalyst support of the present invention comprises a substantially metal casing having gas inlet and outlet openings, with internally supported catalyst supports, positioned on top of each other and fixedly connected to each other such that an empty space is formed between the central portions of two successive monoblocks, a material having elastic properties being interposed between said monoblocks and the metal casing.

The rings allow the individual monoblocks to be spatially separated so that a vortex chamber is formed between them, in which combustion takes place, thereby improving the cleaning result. On the other hand, the pressure loss is reduced.

The peripheral non-perforated portion as well as the ring, which is a pure composition of thermal insulators, are of sufficient thickness that the temperature of the outer surface of the carrier does not exceed 400 ° C under the operating conditions of the device, i.e.. using gases of about 800 ° C. It is . very important because there are numerous materials. to a flexible insert between the monoblocks and the casing, the elasticity of which is permanently maintained at temperatures above 400 ° C. Preferred materials are asbestos, glass fibers, metal fibers, asbestos fabric, glass fabric, metal fabric or fine metal mesh. '

The stacked monoblocks are rigidly joined together, for example, by refractory cement applied to the periphery of the ring, which thereby joins the peripheral portion of the adjacent plate 2. This provides a rigid monoblock having a perforated portion where catalytic processes take place and an uninterrupted outer a wall providing thermal insulation; the monoblock is resiliently housed in a metal casing thanks to an insert of resilient material. Because there is no mutual displacement between catalytic and insulating. With parts having an outer surface temperature of less than 400 ° C, elasticity problems occur only in the low temperature region instead of the central hot region.

The combination of the flexible bearing and its placement in the temperate area ensures a long service life of the entire device.

It should be noted that:. Although the strength of the catalyst supports according to the invention is sufficient to ensure that the erosion induced by the flowing gases does not have undesirable consequences, it is nevertheless not too high, so that it guarantees good thermal shock resistance to all monoblocks.

The disc-shaped carriers of the invention shown in Figures 1 and 2 have been used in the exhaust gas cleaning apparatus shown in vertical section in Figure 3, which consists of a steel sheet casing 4 having an inner diameter of 150 mm which it comprises three discs 5, 6, 7 according to example 2 (discs produced according to the first variation). The discs were impregnated with a solution of hexachloroplatinic acid such that the platinum coating was 1% of its weight. Activation was performed by heating at 450 ° C for four hours. The monoblocks are bonded to each other by a cement containing 70% of very fine alumina and 30% of aluminum phosphate similar to that of Example 2.

After firing, the tensile strength of the joints is higher than the strength of the catalyst support itself. The resilient fit is achieved by compressing the loose asbestos 8 into a 5 mm empty space between the sheath and the monoblocks themselves. The side walls are also provided with a flexible 5 mm thick asbestos board that is secured against slipping by metal rings.

The apparatus was connected to a 1200 cm ³ cylinder engine with a 1 m long manifold. Additional air at 8 m 3 / h for maximum post-combustion of carbon monoxide to carbon dioxide was introduced by suitable equipment at the engine outlet pipes.

At the highest engine speed of 4500 rpm, the heat inside the scrubber is 670 ° C. The hot surface temperature of the asbestos layer is only 220 ° C. The total pressure drop in the plant is only 14.7 kPa.

After 200 hours of operation, no damage to the catalyst support was found or the elasticity was not reduced. layers of asbestos. The cleaning results obtained are graphically represented by the graph in FIG. 4, where the curves represent the rate of conversion of carbon monoxide to carbon dioxide at engine speed (revolutions per minute when gears are included, curves 11, 12, 13, 14, and). in free running, curve 10). The results show that cleaning is very good 1 at low speed.

In many cases, the monoblocks with the non-perforated edge portion of the first are suitable. design. However, under certain circumstances, when the engine is running, especially in winter, sudden ignition of the hydrocarbons condensed in these monoblocks may cause an almost instantaneous temperature rise to 800 ° C 1 more in their central part. Tension caused by different expansion of the central and peripheral parts may cause one to break. monoblock in the area. Tomuto. the danger can be avoided by using monoblocks according to the second embodiment described above, in which they are peripheral. area holes, but in larger. distance from each other than in the center. Said apertured edge region is generally thicker compared to the non-apertured edge region of the monoblocks of the first embodiment. The total number of apertures is substantially the same for monoblocks according to both embodiments, intended for the same engines, to maintain the same. cross section for gas passage.

For comparison, two rows of discs having a diameter of 101.6 mm and a height of 30 mm with a ring of height were produced under conditions similar to those of Example 3. 3 mm on one side.

First of all, the disks had a central band of 81.6 mm in diameter, perforated by 888 axial ducts with a diameter of 1.7 mm (i.e. 17 ducts per 1 cm ² ), and an unperforated edge insulating portion of 10 mm thickness.

In the second row, the discs comprised a 61.6 mm central perforated portion with 516 axial channels of 1.7 mm diameter (i.e. 17 holes per cm 2), and a peripheral region of lower thermal conductivity and a thickness of 20 mm perforated by 372 axial . channels with a diameter of 1.7 mm (ie 7 channels per cm2), the greater the distance from each other, the more they were from the center of the plate. . The overall cross-section of the channels was therefore the same as in the first replacement, only their distribution was altered.

The exhaust gases are passed through a cleaning apparatus which, in the first case, comprises first-row discs, and in the second case, second-row discs. In the first case, the temperature of the monoblock was found to decrease almost linearly from 700 ° C at the end of the punched portion to 300 ° C on the outer surface, with a sudden change in the intermediate region. In the second case, the temperature drops from 700 ° C

Claims (8)

SUBJECT An engine exhaust catalytic converter catalyst support consisting of a solid monoblock of entangled ceramic fibers and a refractory inorganic binder, characterized in that the monoblock material has a density expressed as a proportion of the monoblock mass and its volume of at most 0.6. . 103 kg / m ³ , total open pore volume of at least 70%, compressive strength of at least 3X105 p _a , water adsorption capacity of at least 100 o / ₀ and additional shrinkage at 1000 ° C of at most 2%, and is circular-shaped (2) with axial holes (3), which is extended at its periphery by an unperforated ring (1) having a height greater than that of the annular plate (2). Carrier according to Claim 1, characterized in that the proportion of refractory binder is 10 to 60% by weight, in particular 30 to 40% by weight. 3. Carrier according to claim 1, characterized in that the material from which it is made has a specific surface area of at least 10 m ² / g. Carrier according to claim 1, characterized in that the ring (1), pressed together with the circular plate (2), forms a single continuous whole therewith. 25 mm from the center up to 300 ° C on the outer surface without a sharp temperature change in the intermediate area. A sharp temperature change inside the monoblock is very undesirable if the highest temperature in the center is reached very quickly. However, the material can withstand it if the cleaner is put into continuous operation gradually. OF THE INVENTION Carrier according to Claim 1, characterized in that the density of the axial holes (3) is zero in the vicinity of the ring (1). Carrier according to claim 1, characterized in that the circular plate (2j) has axial holes (3) in its central part more densely than at its edge, the density of the axial holes (3) being greatest in the central part of the circular plate (2) . Carrier according to Claim 6, characterized in that the total cross-section of the axial holes (3) in the central part of the circular plate (2) is at least 25%, in particular at least 35% of the surface area of the central part of the circular plate (2). 8. A process for producing a catalyst support as claimed in any one of claims 1 to 5, wherein a suspension of fibers and a binder is prepared which is shaped in a mold and then dried and fired, characterized in that the shaped support is first fired at 1200 up to 1300 ° C is impregnated with a gel or sol of a refractory metal oxide, such as silicon, aluminum, zirconium, chromium, or mixtures of these metal oxides, after which it is baked again at a temperature in the range of 600 to 800 ° C. 3 sheets of drawings