SE441982B - DEVICE FOR USE IN THE TREATMENT OF A GAS THROUGH CATALYST - Google Patents

Description

7806996-0 the surface area of the plates, only the surface area that is likely to be contacted by the gases to be treated is useful and that the part of the surface area of the plates which is in contact with other plates cannot be used to support a catalyst. Up to 30% of the total surface area of the plates can be lost in this way and this results in the need to increase the total size of the catalyst substrate to obtain a given effective surface area. In some applications, however, it is desirable to reduce the total volume of catalyst support material contained in a given volume of a catalyst device, without reducing the total surface area available to support a catalyst. It is also desirable to find a cheaper, alternative way of manufacturing the catalyst substrate than that of producing the same sheet metal or strip material.

It has now been found that the ideas behind the invention according to G3-P5 1 472 138 can be extended by selecting and regulating the configuration and the coating of the supporting substrate.

Thus, if the substrate is made in wire form in a special, open, three-dimensional configuration, which is more fully defined below, with which contact between adjacent wires or parts of a wire is avoided at least until the coating has been performed, and if the wire surface is smooth and in mainly free from interruptions (except at the ends), such as in a wire with a circular cross-section, this entails a number of important advantages. Within a particularly wide range, regulation of important parameters, such as exposed surface area, resistance to gaseous or liquid flow, mass and thermal conductivity properties of the substrate, can be achieved without the limitation that normally arises from difficulties in coating a substrate with wire configuration by contact with material, which is dispersed in a liquid medium. Furthermore, by using a metal substrate, a high degree of corrosion resistance at high temperature can be achieved, so that, for example, a substrate of an aluminum-containing, ferritic alloy without the yttrium additive can give a satisfactory effect, and service life in the harsh environment of an exhaust system. in a motor vehicle.

It has further been found that these advantages, while of fundamental importance in the manufacture and use of supported catalysts for satisfactory performance and service life in the catalytic purification of exhaust gases for motor vehicles, are also significant in every other systems (whether it applies catalysis or not), where fluids, ie liquids and gases, are to be treated by passing over and interacting with a solid surface and regulation of the above parameters is important. Examples of other such systems where devices made in accordance with the present invention may be useful are chromatographic separations, processes in which the solid surface material has affinity for a component of the fluid flowing over it, and is used to separate it. component from the fluid, and flame arresters.

Thus, in one aspect of the present invention there is provided an apparatus for use in the treatment of a gas by catalysis, the gas being passed over a solid surface consisting of a catalytically active material with which the gas interacts, which apparatus is characterized in that it comprises a container with an associated gas inlet duct and a gas outlet duct extending therefrom, a plurality of separate components mounted in the container, each component comprising a three-dimensional wire assembly, the wire of which delimits open spaces in the outermost parts , which are small enough to at least limit the penetration by entangling one component with another of the components, at least a substantial number of the components being free to entangle with each other, unless this was prevented by their inherent configuration, and a solid coating of a catalytically active material for the interaction between the gas and the solid material.

The filamentary substrate preferably defines at the periphery of the open three-dimensional configuration open spaces at the periphery which are sufficiently small in relation to the shape and diameter of the filamentary substrate to avoid or limit penetration of a component into the inner open space. of another component in the plurality of components brought together.

In other words, contact between adjacent parts of the wire is avoided in each component.

It is preferred to manufacture the wire-shaped substrate in a helical configuration, in which the space between adjacent windings is smaller than the diameter of the wire mold. The wire-shaped substrate 7806996-0 The IP base can be manufactured in a helical configuration from corrugated wire-shaped base. Preferably, the helical configuration is a helical coil with its windings extending progressively along a common axis. The corrugation can be applied along the length of the wire form, so that in each revolution of the coil the space between adjacent parts of the wire-shaped substrate varies as a consequence of the corrugation. The pitch of the corrugation can be arranged in relation to the diameter of the spool and the pitch of the revolution of the spool so that the peaks or ridges of the corrugation in each revolution appear adjacent to a peak in the next subsequent revolution of the spool.

The preferred use of the device is thus in the treatment of a gas by catalysis, in which case at least one surface of the component or each component consists of a catalytically active material.

A plurality of components may be combined to form a gas permeable body through which the gas to be treated may flow into contact with the surfaces of the components. Preferably, these components are distributed randomly in a container and retained within the container to form it. gas permeable bodies. Alternatively, the component, or any such, may be laid (folded or wound) on itself, or on other such components, to form the gas permeable body through which the gas to be treated may flow in contact with the surface of the component. or the components.

Preferably, the wire is made of an aluminum-containing iron alloy (available in the United Kingdom under GB-registered trademark FECRALLOY). Such a metal alloy suitable for use in the present invention can be found within the alloy specification of a composition, expressed in% by weight: 10-30% Cr, 1-10% Al, 0-0.5% C and the residue Fe .

When resistance to hot embrittlement is important, such alloys are prepared within a composition specification in% by weight of: up to 20% Cr, 1-10% Al, 0.1-3.0% Y and the balance Fc. Here a certain hot embrittlement can be tolerated, such as when a helically coiled wire is used, higher chromium content up to 25% by weight can be used. The especially preferred composition is a FECRALLOY alloy with 15.50-16.50% Cr, 4.6-5.6% Al, 0.3-1.0% Y and the balance Fe.

The above alloys may include additives of Co and / or Ni, and it is recommended that such additives be limited to 0-3% by weight of each element. However, acceptable efficacy can be achieved with these additives in the range of 0-5% Co and 0-53 Ni.

An alternative alloy is the one sold under the GB brand KANTHAL DSD.

A typical example of such an alloy has an approximate composition in% by weight of 22.5% Cr, 4.5% Al, 2.0% Co, 0.1% C and the residue Fe.

Preferably, the aluminum-containing alloy has a ceramic layer on its surface. Preferably, the ceramic material is bonded to the surface of the wire mold by heat treatment. The ceramics may include alumina, ceria, yttria, oxides of Groups 4-6 and silicic acids. The preferred ceramic material consists of alumina, which is bonded to the wire form by heat treatment.

Preferably, heat treatment is performed, either before or after or both before and after coating with the porous ceramic material, in the presence of oxygen to form a layer mainly consisting of alumina on the surface of the alloy wire from aluminum coming from inside the alloy. .

Catalytically active material can be deposited or precipitated on a plurality of components, which are then combined to form a catalyst device. The catalytically active material can be deposited either after a previous coating of the substrate alloy with porous ceramic material or it can be deposited simultaneously with the porous ceramic material.

There are many ways to apply the catalytic materials to a substrate, such as spraying using gas discharge, plasma spraying, flame spraying, wet coating, vapor deposition and sintering. The preferred method of depositing a catalyst on the coil is that described in DE-A-26 47 702. Examples of embodiments of the present invention will now be described with reference to the accompanying drawings, in which: Figs. 1, 2 and Fig. 4 shows three components for use in a catalyst device constructed in accordance with the present invention; Fig. 3 shows the wire mold used to make the components of Fig. 2; Figs. 5 and 6 show two catalyst device numbers; made from a number of components of the type shown in Figs. 1, 2 or 4, arranged relative to each other to define a body through which a gas to be treated can flow, and Figs. 7 and 8 shows two further forms of catalyst device, made of a single component similar to that shown in Figs. 1, 2 or 4.

In the following embodiments of the invention, the finished product is to be used for the treatment of exhaust gases from internal combustion engines by catalysis. It should be understood, however, that the catalyst devices of the present invention may be useful in other industrial processes that require supported, catalytically active material.

Pig. 1 shows a component, consisting of a helical spool 10, made of a wire 11 of 1.0 mm diameter and circular cross-section wound along an axis to form a spool 76.2 mm long X 6.4 mm outer diameter. The pitch of the yards is about 1.0 mm.

The wire is made of FECRALLOY alloy (In GB registered trademark) with a composition in weight% of 4.6-5.6% Al, 15.50-16.50% Cr, 0.3-1.0 % Y and residue Fe. A predominantly alumina layer is formed on the surface of the wire and a catalyst is deposited on the alumina layer, as described in DE-A-26 47 702.

In a particular example, described in the DE-A suitable for use in the preparation of catalyst devices according to the present invention, alumina, prepared by a steam condensation method, is prepared into a sol by mixing with water and the sol is mixed with a solution of yttrium nitrate in water to to form a "mixed sun". A platinum salt is added to the mixed sole to form a dispersion which is applied to a pre-oxidized substrate of FECRALLOY alloy. The substrate thus coated is then fired to provide a coating containing platinum as the catalytically active material. Other techniques for applying a catalyst to coil 10 may be used.

Fig. 2 shows an alternative form of coiled wire form, made from the same type of alloy wire 0.5 mm in diameter and wound into a coil 3.0 mm in diameter and 40 mm long with a pitch of 2.8 mm. The wire used to make the spool 10 in Fig. 2 is shown in Fig. 3. From Fig. 3 it can be seen that the wire 11 along its length is applied to a corrugation 12 before it is wound into a spool. The corrugation 12 has a pitch of normally 3.5 mm and the dimension, measured from top to top 14, is normally 1.0 mm. The corrugations 12 impart strength to the thin wire 11 and the peaks 13, 14 of the corrugation 12 of each turn are arranged to coincide with peaks 13, or 14, in the next adjacent turn to prevent adjacent coiled portions from creeping into each other. . In this case, a coating and a catalytically active material are applied to the wire 11 in exactly the same manner as described in connection with Fig. 1.

The components shown in Figures 1 and 2 may have a uniform pitch, as shown in Figures 1 and 2, or the pitch may vary along the length of the coil as shown in Figure 4. In the case of the component shown in Figure 2 the pitch of the corrugations can be changed so that the peaks 13, 14 of each revolution coincide.

Figs. 5 and 6 show a number of coils 10 of the type shown in Figs. 1-4, brought together in a suitable holder 15 to form different catalyst devices. In Fig. 5, for example, a number of layers 16, 17 of coils 10 are used. The longitudinal axis of each coil 10 in each layer 16, 17 extends in a common direction, but each layer 16 is arranged in relation to adjacent layers 17. , so that the longitudinal axes of the spools 10 of each layer 16 form an angle to the longitudinal axes of the spools 10 in adjacent layers 17. Wires 18 are used to prevent the spools from falling out of the holder 15.

In Fig. 6, all the coils 10 are collected in a holder 15 with their longitudinal axes extending in a common direction. The cross-sectional shape of the holder 15 may be rectangular (as shown) or circular, elliptical or have any other shape which may accommodate the coils 10. The gas to be treated is caused to flow in a direction substantially parallel to the longitudinal axes of the coils 10 (arrow A). Alternatively, another holder 15 may be used, which allows the gas to flow perpendicular to the longitudinal axes of the coils 10.

Wires 18 were used to retain the bundle of coils 10 in the holder 15 of the catalyst device of Figures 5 and 6.

Instead of laying a plurality of coils 10 to form the catalyst device shown in Fig. 5 or 6, one or more long lengths of coil of the type shown in Figs. 1, 2 or 4 may optionally be folded on top of itself to achieve a similar, layered effect. A continuous length of coiled wire, as shown in any of Figs. 1, 2 or 4, can be wound on itself to form a catalyst device. Two examples of such a device are shown in Figs. 7 and 8. The catalyst device of Fig. 7 is formed by winding the coiled part 10 on a bobbin or coil sleeve 19 to provide one or more layers. The catalyst device of Fig. 8 is formed by winding the coiled portion 10 into a helical shape.

A number of helically wound layers can be stacked side by side to form a complete catalyst system.

Instead of mounting a plurality of coils 10 of the type shown in Figs. 1, 2 and 4, in an ordered pattern, as shown in Figs. 5 and 6, the coils can be poured randomly into a container. More specifically, a 0.25 mm diameter FECRALLOY alloy wire is wound into a coil having a total diameter of 2.7 mm and a continuous length. The coil thus formed is then chopped to give coils with a length of 6.4 mm and a plurality of the coils are poured into a container with an open end or a tube, which has a fine net at one end. The container or tube can have any shape. The container can be shaken to ensure that the coils sink into the container and form a gas-permeable body, and when the container is filled with the chopped coils, a second wire mesh is attached to retain the coils in the container. During operation, the exhaust gases to be treated are caused to flow through the gas-permeable body thus formed. The coils 10 of the catalyst devices according to Figs. 5-8 preferably have a surface coating and a catalyst, applied to them, before they are collected in the container 15. In some cases it may be possible to coat them after they have been collected in the holder 15.

The diameter of the thread and the size of the spools 10 (ie length, diameter and pitch of the spool) may vary to suit each particular process. In particular, these parameters can be varied to meet the desired pressure drop specifications for the intended use of the catalyst device. By varying these parameters, one can effectively vary the total, effective surface area available to support a catalyst.

The cross-sectional shape of the hole of the coils is preferably circular, although it may be of any desired shape, e.g. triangular, rectangular or polygonal, obtained by winding the wire form helically along any suitably shaped mandrel. The terms "helical" and "helical" as used herein are intended to include coils wound along a shaft regardless of the shape of the hole of the coil. The coils can be formed on a standard spring winding machine.

The coils may have a uniform diameter or be tapered.

It is preferred to make the wire form of a metal, e.g. steel, refractory metal carbides, WC, TiC, TaC, stainless steel and stainless iron. The wire form can be drawn wire or an extruded wire.

It may be possible in some cases to use a ceramic fiber, although it is considered that such a manufacturing path would not be as easy as manufacturing the components of metal wire due to the need to fabricate the components in a raw (plastic) state and then burn them to achieve the finished shape.

Catalyst devices, prepared according to the present invention, are useful for the treatment of exhaust gases from internal combustion engines by catalysis and in particular for the entrapment and treatment of soot products in the exhaust gases from diesel engines by catalysis, and the catalytic reduction of nitrogen oxides and the catalyst. lytic oxidation of hydrocarbons and carbon monoxide in the exhaust gases of an engine.

An important advantage obtained by manufacturing the catalyst devices in the form of a number of coils in accordance with the present invention is that it is possible to apply different catalytically active materials to different coils, if desired. For example, a composite catalyst device can be provided using two or more sets of identical coils, combined to form a body of different catalytically active materials, deposited on each set of coils. For example, a catalyst device similar to that shown in any of Figs. completely different metal from the platinum group.

In a specific example, a catalyst device, prepared in accordance with the present invention for treating exhaust gases from internal combustion engines by catalytic converter, may have some coils coated with platinum and the others coated with rhodium. a common coating with platinum positions close to the rhodium positions. The present inventors have observed that after prolonged use, platinum becomes less efficient in catalyzing the oxidation of the hydrocarbons. Examination of the surface of the catalyst reveals that active platinum positions have been lost, but it was found that this loss does not occur to the same extent when the rhodium and platinum are deposited on separate coils.

Tests, including the oxidation of propane, were performed by flowing a mixture of propane / oxygen, carried in a nitrogen flow, over two types of supported catalyst. One supported catalyst was a Pt / Rh mixed catalyst on a ceramic coated substrate of FECRALLOY alloy (shown as Catalyst A below), the other consisting of separate Pt and Rh catalysts on separate coils, made of ceramic-coated FECRÅLLOY alloy, combined to form a common catalyst (shown as catalyst B below). The catalyst volume is passed through 100,000 times per hour of the propane / oxygen mixture. The results are shown below.

Temperature required for Type of supported 100% oxidation of propane ïïšaåšïïïor New catalyst Catalyst after heating in air at 1000 C for 12 hours.

A 35o ° c 5oo ° c B o 4oo ° c 4oo ° c 7806996-0 11 It should be noted that the problem of deteriorating the efficiency of platinum as a catalyst may also exist in the commercial production of nitric acid from ammonia, where pla thaw and rhodium were used as the catalysts. Therefore, a catalyst bed made of two sets of coils, each set of either platinum or rhodium, can be valuable for the production of nitric acid.

The present invention can, of course, find use in a variety of chemical processes, including the treatment of gases and liquids by interaction with a solid surface.

Claims (7)

-7806996-0 12 Patent claims Device for use in the treatment of a gas by catalysis, the gas being passed over a solid surface consisting of a catalytically active material with which the gas interacts, characterized in that it comprises a container (15) with a an associated gas inlet duct and a gas outlet duct extending therefrom, a plurality of separate components (10) mounted in the container (15), each component (10) comprising a three-dimensional wire assembly, the wire (11) of which in the outermost parts (13, 14) delimiting open spaces small enough to at least limit penetration by entangling one component (10) with another of the components (10), at least a substantial number of the components (10) being free to entangle with each other, unless this was prevented by their inherent configuration, as well as a solid coating of a catalytically active material for the interaction between the gas and the solid material. Device according to claim 1, characterized in that contact between adjacent parts of the wire (II) is avoided in each component (10). Device according to claim 1 or 2, characterized in that each component (10) has a spiral configuration, in which the space between adjacent turns is less than the diameter of the trees (II). Device according to one or more of the preceding claims, characterized in that each of the components (10) is manufactured in a spiral configuration of a wavy wire shape, whereby in each revolution of the spiral configuration the space between adjacent parts of the wire (11) ) varies as a result of the corrugation. Device according to one or more of the preceding claims, characterized in that the components (10) are randomly distributed in the container (15). 7806996-0 15 Device according to one or more of claims 3-5, characterized in that a corrugation is superimposed along the length (ll) of each wire. Device according to claim 6, characterized in that the pitch of the corrugation is arranged in relation to the diameter of the spiral configuration and the pitch of the winding of the spiral configuration so that the axes of the corrugation in each revolution appear adjacent one ridge in the next subsequent revolution of the spiral configuration.