WO2010099970A1

WO2010099970A1 - Method and apparatus for holding down catalyst particles flowing thereagainst

Info

Publication number: WO2010099970A1
Application number: PCT/EP2010/001377
Authority: WO
Inventors: Stefan Hamel; Domenico Pavone
Original assignee: Uhde Gmbh
Priority date: 2009-03-05
Filing date: 2010-03-05
Publication date: 2010-09-10
Also published as: AR075787A1

Abstract

The invention relates to a method for performing reactions in the gaseous phase, which are conducted over a catalyst bed comprising catalyst particles, wherein a layer of elements is arranged above the catalyst bed in the gas conducting direction so that said layer of elements prevents the catalyst particles from flowing back and swirling, and wherein the layer elements are resistant to corrosion and temperature, thus representing a failure-free retaining apparatus even at high temperatures. The invention also relates to an apparatus comprising gas-permeable layer elements, suitable for covering a catalyst bed comprising catalyst particles, so that said bed is impermeable for catalyst particles.

Description

Method and device for holding down streamed catalyst particles

[0001] The invention relates to a process for holding down solid particles of catalyst in a reactor for carrying out catalyzed gas-phase reactions. The invention also relates to a device for fixing solid catalyst particles in a catalyst bed of a reactor for carrying out chemical reactions in the gas phase. Without this device, the catalyst particles are fluidized in the reactor, so that there is an undesirable backflow and turbulence of the catalyst particles opposite to the gas flow direction in the reactor. The holding device is preferably made of individual elements which form a closed but gas-permeable layer over the catalyst charge.

The aim of the invention is to retain the catalyst particles, which are present in a fixed bed flowed through in the direction of reaction gas, and to prevent unwanted particle movement. If the catalyst particles move excessively, this means long-term wear of the catalyst particles and abrasion or loss through fragmentation into smaller fragments. This can already lead to increased pressure loss in the catalyst bed itself. The particle fragments discharged with the gas stream or the dust produced during the fragmentation can also cause problems in subsequent parts of the plant. For this purpose, the catalyst particles, which are designed for fixed bed operation, must be secured against movement.

[0003] DE 10359744 A1 describes a process for the injection of oxygen or an oxygen-containing gas into a synthesis reactor, for example for dehydrogenation, with a substantially axial flow through the gas mixture through a catalyst packing. The oxygen-containing gas stream is sprayed at an oblique angle in the direction of the catalyst surface by a special device having a ring manifold having specially arranged outlet openings. This achieves a mixing of the oxygen or the oxygen-containing gas mixture with the reaction gas, which is passed through the catalyst after mixing with the oxygen. To ensure short residence times of the gas mixture before entering the catalyst bed, the distance between the mixing nozzles and the catalyst surface is kept low. The oblique flow of the bed surface and the short distance between the mixing nozzles and the Catalyst surface cause turbulence can form in the inflowing gas flow, which lead to local turbulence and backflow, so that the catalyst particles set in undesirable motion. However, this is undesirable since it can lead to long-term abrasion or breakage of the particles.

DE 10 2008 006 560 A1 relates to a purification process for a column. This document mentions a holding jig with a support bottom for a packed bed. Through the grate flow gases and liquids, while neither the structural implementation nor the procedural significance of the gratings is shown.

DE 101 44 891 A1 describes the production of hydrocyanic acid, while a Niederhalterost and a Auflagerost are arranged in a reactor to confine the catalyst bed.

In US 5 073 236 A, a distillation column is disclosed, in the column, the catalysts were embedded in a corrugated, provided with lattice plate pairs of plates, thus here is no support to detect a catalyst bed.

A ceramic packing element made of foamed ceramic has been proposed in DE 102 08 711 B4, although the packing element may be formed from catalytic materials and act as a catalyst, but has identical parallel flow channels with defined angles in which the fluid to be reacted is to flow , The catalytic substance is either contained in the packing element or applied to the packing element, for this no retainer was needed.

Likewise, a packing element in EP 1 658 134 B1 disclosed, the packing element is made of ceramic, has a polygonal structure. In EP 0 531 148 A1, the packing element has honeycomb structure with open passages. In DE 37 05 476 A1 a column packing of packing elements in the form of gratings is shown. All the packing elements mentioned here have the same defined flow channels, do not form a closed plane and also do not provide a retention function for the catalyst particles.

From GB 1 349 757 A a water boiler with a gas distributor plate is known. Between the primary and secondary bed through the gas distributor plate, the gas is intended to flow from bottom to top for fluidization by means of the flared geometrically identical holes. DE 20 13 615 C3 discloses a reactor for carrying out catalytic reactions with liquids and gases. In this case, a grid is arranged in the reactor, on the grid first forms a layer of large balls of inert material with a diameter that the balls can not roll through the grid, a barrier layer. On top of this, further layers are deposited with relatively smaller spheres, after which the catalyst is layered. Such an occupancy greatly prolongs the residence time of the gas before it enters the catalyst bed, and it also causes turbulence of the bulk material.

Known is the maintenance of catalyst particles by a layer of ceramic balls, which are larger and heavier than the catalyst particles or by a perforated plate. By the flow through the ball bed, the residence time of the gas mixture is greatly increased. In addition, the application of large spheres to a bed of catalyst particles results in a random bed, thereby increasing the risk of local vortexes and recirculation zones which adversely affect the gas mixture residence time. The installation of perforated sheets is also problematic because the operation of the pinhole can reduce the catalyst bed. As a result, cavities, which represent circulation zones and can lead to an undesired movement of the catalyst particles, form below the metal sheet. The perforated sheets may undergo corrosion over time by the flow of the reaction gas, whereby a regular replacement of the perforated plates is required. This leads to increased operating costs.

There is therefore the object to provide a method and an apparatus available that allow effective retention of catalyst particles in a fixed bed reactor and in an atmosphere of an oxygen-containing gas in mixture with the reaction gas have no tendency to corrosion. The holding device should be resistant even at high temperatures and show no signs of softening by melting processes. The gas permeation resistance should also be as variable as possible.

[0013] The invention achieves this object by means of a device which is constructed from layer elements in such a way that these elements can be placed next to one another and thereby form a flush layer. This is deposited on the catalyst particles, the catalyst particles are prevented from swirling and flowing back. Due to the production, the ceramic elements and the metal foams have an arbitrarily adjustable pore size, so that the gas passage resistance can be set as desired. Both the ceramic elements and the metal foams are very temperature resistant and have no tendency to corrosion in the oxygen-containing atmosphere. The ceramic elements and metal foams are further characterized by a very low coefficient of thermal expansion. In addition, less unwanted particles are added to the process gas in the reactor.

The layer elements may have any geometric shape that allows the formation of a closed, but gas-permeable layer. The layer elements are preferably designed in the form of cuboids, which have shapes on the sides, which allow an interlocking of the layer elements. These can be, for example, bevelled sides, so that the layer elements in adjacent rows have a reversed lying-around sense. As a result, the rows engage with one another and close the catalyst layer upwards in the gas flow direction. The parallelepiped cuboids are arranged in rows, with the adjacent rows each having an inverted horizontal sense of the chamfered sides so that these elements intermesh in adjacent rows to form a closed but gas-permeable layer.

[0015] The lateral shaping can also comprise mutual indentations and bulges, which in each case intermesh and thus have a flush closing of the catalyst layer upwards. These indentations and bulges are also commonly referred to as "tongue-and-groove connections." T-pieces, which are lined up in rows in the opposite direction, are also possible for lateral shaping, so that they finish flush the catalyst layer upwards.

In particular, a method is claimed for holding down catalyst particles in a reactor for carrying out chemical reactions, wherein

The gas to be reacted is passed into a reactor having a catalyst bed charged with solid catalyst particles or with particles of a solid support material containing a catalyst or coated with a catalytically active material, and

The catalyst particles are retained in the reactor by means of a holding device,

and that is characterized in that The catalyst particle is retained in the gas flow direction in front of the catalyst bed by a holding device of layer element material and the layer element material consists of a solid body of open-pore porous material with random pores,

• and the holding device is impermeable to catalyst particles and permeable to gas.

The holding device is preferably made of flat laminate element material. The layer element material should consist of a solid and be open-pored, porous and provided with random pores. The layer elements of the layer element material form a holding device, which is impermeable to catalyst particles and permeable to gas.

Depending on the size of the catalyst particles, the layer element may be designed during manufacture in such a way that the layer element has smaller pores on the side facing the catalyst charge than the smallest cross section of the catalyst particles provided. As a result, the catalyst particles are held in the catalyst bed bounded by the holding device made up of composite layer elements. At high speed, the reaction gas dusts through the holding device and then enters the catalyst bed. Larger pores on the side facing away from the catalyst bed or the gas-flowing side of the layer element cause a reduced pressure loss and favor the flow through the gas.

In one embodiment of the invention, the layer elements are chamfered on the sides, so that they form an enclosed, but gas-permeable layer in an arrangement in adjacent rows in opposite horizontal sense of direction. This layer still contains columns that are formed by the opposite edges. These gaps are such that they have a smaller gap width than the catalyst particles, so that turbulence and backflow of the catalyst is prevented. In order to keep the radial movement and the gap formation of the holding device in a predetermined tolerant range, the layer elements can be designed to be connectable: the layer elements are already configured with connectivity during manufacture, or they are connected during connection of the holding device. The holding device is preferably made of elements with a rectangular or square plan. The elements that make up this layer can also be round or irregular in shape. It is only important that a closed layer of this layer element material can be formed, and no gaps arise between the layer elements through which catalyst particles can escape. The layer is gas permeable. The layer elements are designed to be connectable. The compound of the layer elements can be configured in many ways, for example, a layer element may already contain the possibility of connection such as indentation or bulge, of course, the layer elements can also be connected to each other by aids such as pen or wire. All reasonable functional connection possibilities are applicable. Of course, the elements can also be fitted to the walls of the walls for fitting into the reactor in the mold.

The layer elements may also have a geometric shape, which facilitates an interlocking of the layer elements and thus the formation of the layer according to the invention. Thus, the layer elements may be exemplified as widened T-pieces and these layer elements are arranged in rows, wherein the adjacent rows each have a reverse vertical sense of the T-pieces, so that these elements interlock in adjacent rows and a closed, but form gas-permeable layer. As a result, the protrusions of the T-pieces form an offset gap, thereby increasing the strength of the layer and lowering the particle permeability of the gaps. These elements are arranged in rows, with the adjacent rows each having a reversed vertical sense of the T-pieces so that these elements interlock in adjacent rows to form a closed but gas-permeable layer.

The layer elements can also have lateral bulges, by means of which, when stored in rows next to one another in a reversed horizontal direction, interlocking of the layer elements is made possible, whereby the strength of the layer is increased and the particle permeability of the gaps is lowered. In this way, also forms a closed, but gas-permeable layer. The layer elements have in this embodiment on two adjacent sides bulges and two other adjacent side indentations. In a lay-up in layers, the bulges and indentations of the sides of the layer elements interlock, so that one obtains a layer with increased strength and reduced particle permeability. In a further embodiment of the invention, the layer elements are made of an open-cell porous porous ceramic with random pores. The foamed ceramic can be produced by the known methods of the prior art. A preferred method is that of molding through a polyurethane foam. In this case, a polyurethane foam (PUR foam) is dipped with the desired geometry in an aqueous dispersion of a ceramic fine material, then dried and fired. During the firing process, the PUR foam burns, leaving a ceramic foam. An exemplary method for this teaches the EP 260826 B1. The pore density and the pore size of the foams can be arbitrary for the implementation of the device according to the invention. Preferably, this is in the range of 8 to 100 ppi ("pores per inch").

The elements made of ceramic foam can be made of any ceramic materials. So this can be made of oxidic ceramic materials, for example. These can be used as single components or as a mixture. Examples of oxidic ceramic materials are the chemical compounds Al ₂ O ₃ , CaO, CeO, Cr ₂ O ₃ , Fe ₂ O ₃ , HfO ₂ , MgO, SiO ₂ , SnO ₂ , TiO ₂ , Y ₂ O ₃ or ZnO. The foamed ceramic may also contain zirconium dioxide ZrO ₂ in admixture with CaO ₁ CeO, MgO or Y ₂ O ₃ for stabilization. Also admixtures of ZnAIO ₄ , CaAIO ₄ , V ₂ O ₅ or MoO _{3 are possible} . The elements made of ceramic foam can also be made of non-oxide ceramic materials. Examples of non-oxidic ceramic materials are the chemical compounds AIN ₁ BN ₁ BC, MoSi ₂ , SiC or SiN. These can also be used as single components or as a mixture. Finally, it is also possible to produce the elements from a mixture of oxidic and non-oxidic ceramic materials.

A further embodiment of the invention relates to the use of the metal foam as a layer element. Due to the property of the metal foam, it is particularly suitable as a layer element for the holding device. Layered open-pore porous metal foam with random pores can be produced by the known methods of the prior art. An organic foam such. B. Polyurethane can be coated with metal powder, water and binder suspension, and then processed by heat treatment to metal foam. Or by means of the SRSS process (Schlickerreaktionsschaumsintern) also the desired metal foam can be produced. Therefore, when manufacturing the metal foam, the appropriate method can be used at the discretion of the skilled person. Like the ceramic elements, the metal foam segments can also be arranged so that a closed gas-permeable layer is formed. However, compared to the rigid and brittle ceramic element, the metal foam has high specific rigidity and strength, and is slightly flexible. In the case of the locally different laying of the catalyst bed, the segments of the metal foams follow the catalyst surface, in each case independently of the other segments, therefore there is no free space between the catalyst bed and the covering metal foams, despite the unevenness of the catalyst bed. As a result of the property of the metal foam per se, the individual segments of the metal foams can be assembled like the ceramic elements; moreover, the metal foams can still be assembled via further joining methods. In an advantageous embodiment, the metal foam contains guide grooves which serve as a connection to one another, the metal foams can be easily installed and removed via the guide grooves. The metal foam can be formed with hooks or eyelets during manufacture in order to form the individual segments into a flush layer connect, as well as the metal foam can also be provided connectable with screws, in addition, the metal foam can also be made connectable by welding or gluing.

A holding device made of metal foam layer elements can also be used in radial reactors. A flush layer of metal foams with the catalyst bed to be held is placed parallel to the reactor wall, the reaction gases flow radially through the holding device and the catalyst bed.

To prevent creeping currents in the edge area of the catalyst cover, it is possible, for example, to position balls made of ceramic with matched diameters. Due to the increased flow resistance unwanted flow through the edge area is reliably prevented. The balls or particles can be placed on the catalyst bed, for example, between the layer elements and the reactor wall. As a result, the residual volume which forms between the wall of the reactor and the holding device is sealed with particles which are permeable to gas. The particles for sealing the residual volume are formed by way of example from spheres, granules, or any kind of shaped pieces. For this purpose, suitable gas-permeable parts of the layer element can be used for sealing. Any form of particle that can be used for the particles to seal the remaining volume between the wall of the reactor and the holding device is possible. Due to the particle bed in the gap between layer elements and wall and the associated higher flow resistance is An undesirably high "bypass" flow of the gas mixture into the catalyst layer is reduced or prevented altogether.For the introduction and assembly of the layer elements on the catalyst bed, suction cups can be used by way of example.

The layer of individual elements for retaining the catalyst may have any desired layer thickness in the reactor. The thickness of the layer elements depends on the permissible residence time of the gas mixture outside the catalyst bed. Together with the porosity of the elements and the thickness of the layer results in a residence time of the gas mixture, which can be adapted to the reaction-technical requirements. The thickness of the elements or the layer in the reactor can be arbitrary. However, the layer is preferably 1 to 10 cm high.

The device according to the invention offers the advantage of a simple but effective barrier for catalyst particles in a reactor for gas reactions. As a result, in the gas flow direction, rearward turbulences and backflow of catalyst particles can be prevented. The device is resistant to high temperatures, it is resistant to corrosive gases or an oxygen-containing atmosphere. It can be adjusted well in terms of their Gasdurchströmungswiderstandes and in terms of their pore size and thus in their retention capacity for catalyst particles. Finally, the device according to the invention also has the advantage of a low weight, so that it can not lead to particle breakage and abrasion of the catalyst particles.

It is conceivable that the holding device according to the invention is suitable for carrying out reactions in the liquid phase. However, it is preferred to carry out reactions in the gas phase.

In principle, the device according to the invention can be used in any gas phase reaction which is carried out with a particulate catalyst. Examples are oxydehydrogenations, hydrogenations, oxidation reactions, isomerizations or alkylations. However, oxydehydrogenations are preferably carried out with the device according to the invention. A preferred temperature range for carrying out the oxidative dehydrogenation is 500 to 1000 ⁰ C.

The inventive design of a device for flow guidance of synthesis gas is explained in more detail with reference to three drawings, wherein the inventive method is not limited to these embodiments. FIG. FIG. 1 shows the device according to the invention, which are arranged in adjacent rows of layer elements with beveled sides, each having a horizontally opposite sense of direction. These form a closed, but gas-permeable layer for catalyst particles. FIG. 2 shows the device according to the invention, which are arranged in adjacent rows of widened T-pieces, each with horizontally opposite sense of direction. FIG. 3 shows the device according to the invention with indentations and indentations ("tongue and groove connection") on respective opposite sides. [FIG FIG] FIG. 4 shows an embodiment of the metal foam as a holding device for the catalyst bed.

FIG. 1 shows the device according to the invention made of gas-permeable ceramic elements, wherein the individual elements in the form of layer elements (1) with bevelled sides (1a, 1b) are formed and placed next to one another in rows. These cover the catalyst bed (2). The layer elements cover the catalyst bed in the gas flow direction (3) upwards. As a result, the catalyst particles from the catalyst bed can not be swirled or flow back. The layer elements are located laterally on the reactor wall (4). The catalyst particles are retained in the gas flow direction by a gas-permeable support device (5). The support device (5) is a gas-permeable device which prevents the leakage of catalyst particles. These may be, for example, the layer elements (1) according to the invention or simply a grid, of course, the support device (5) may consist of ceramic elements or metal foams.

FIG. 2 shows the device according to the invention made of gas-permeable ceramic elements, wherein the individual elements in the form of layer elements (1), which are formed as widened T-pieces, are placed in rows next to one another. The bulges of the T-pieces (1c, 1d) can be seen here, which mesh with a reverse sense of direction of the installation of the tees. The formed layer (1) covers the catalyst bed (2). The layer elements (1) cover the catalyst bed (2) in the gas flow direction (3) upwards. As a result, the catalyst particles from the catalyst bed (2) can not swirl or flow back. The layer elements lie laterally on the reactor wall (4). The catalyst particles are retained in the gas flow direction by a gas-permeable support device (5). The support device (5) here is the same as in FIG. 1.

FIG. 3 shows the device according to the invention made of gas-permeable ceramic elements, wherein the individual elements in the form of layer elements (1) are provided with indentations and indentations (1e, 1f) on opposite sides are arranged. The elements are here arranged in rows, the indentations and recesses (also called "tongue and groove connection") interlocking with one another The layer (1) thus formed covers the catalyst bed (2). As a result, the catalyst particles from the catalyst bed (2) can not swirl or flow back The laminar elements are located laterally on the reactor wall 4. The catalyst particles are retained in the gas flow direction by a gas-permeable support device (5) Support device (5) here is the same as in FIG. 1.

In FIG. 4, the individual segments of metal foams lie loosely next to one another on the catalyst bed, forming a flush layer over the catalyst bed. Each metal foam segment is provided with a central bore through which a cylindrical pin passes, the pin having a flat plate at one end and a threaded end at the other end, and the plate has a larger diameter than the bore. With the help of the plate, a metal foam segment can be easily pulled out of the holding device, for example, to fill the catalyst bed or to change the catalyst bed. The pin can be hollow or solid and made of the same material as the holding device. The diameter of the hole is so large that the pin fits through the bore, and the pin additionally has play for the axial and radial movement, moreover, the play in the bore around the pin must not be greater than the cross section of the smallest catalyst particles so that no catalyst particles can escape through the hole. The pin should be so long that it is present between the plate and the metal foam as well as between the metal foam and the screwed nut each game. The game allows the holding device to be made of metal foams on the catalyst bed. Each pin has a connectivity, which is located above or below the threaded nut, with which all pins can be connected together. The connection possibility can be, for example, a grid, a wire, rods or a template. Of course, only those connection options are used that make sense for the purpose of this connection. The connection of the pins should prevent the transverse movement of the metal foams, so that no gap formation between the metal foams, and thus the holding device can retain the catalyst bed from the metal foams. In this embodiment, you can even dispense with the holes, the pins can be welded or glued directly to the Metallschäu- me. [0039] List of Reference Numerals

1 layer of foam ceramic

1a beveled side of a layer element

1b Beveled side of a layer element

1c T overhang of a layer element

1d T overhang of a layer element

1e bulge of a layer element

1f indentation of a layer element

2 catalyst bed

3 gas flow

4 reactor wall

5 support device

Claims

claims

1. A method for holding down catalyst particles in a reactor for carrying out chemical reactions, wherein

characterized in that

The catalyst particle is retained in the gas flow direction in front of the catalyst bed by a holding device of layer element material and the layer element material consists of a solid body of open-pore porous material with random pores,

• and the holding device is impermeable to catalyst particles and permeable to reaction gas.

2. A method for holding down catalyst particles in a reactor for carrying out chemical reactions according to claim 1, characterized in that the pores in the laminate material on the side facing the catalyst bed side are smaller than the smallest cross section of the catalyst particles.

3. A method for holding down catalyst particles in a reactor for carrying out chemical reactions according to any one of claims 1 or 2, characterized in that the pore size of the layer element material on the side facing the catalyst bulk is smaller than that of the opposite side.

4. A method for holding down catalyst particles in a reactor for carrying out chemical reactions according to any one of claims 1 to 3, characterized in that the pore size in the laminate material increases, from the catalyst bed facing the opposite side.

5. A method for holding down catalyst particles in a reactor for carrying out chemical reactions according to any one of claims 1 to 4, characterized in that the residual volume, which forms between the wall of the reactor and the holding device, sealed from matching, gas-permeable parts of the laminate material becomes.

6. A method for holding down catalyst particles in a reactor for carrying out chemical reactions according to any one of claims 1 to 4, characterized in that the residual volume of balls, pellets, rings, ellipsoids, rods, irregularly shaped particles or fragments is formed.

7. A method for holding down catalyst particles in a reactor for carrying out chemical reactions according to any one of claims 1 to 6, characterized in that it is the porous layer material porous porous element with random pores.

8. A method for holding down catalyst particles in a reactor for carrying out chemical reactions according to any one of claims 1 to 6, characterized in that it is the porous layer material porous porous foam with random pores.

9. A device for holding down catalyst particles in a reactor for carrying out chemical reactions according to claim 1, characterized in that the holding device of laminated material consists of a solid body of porous porous material with random pores, which is designed to be connected to each other, which has any geometry which allows the formation of a closed, but gas-permeable layer.

10. A device for holding down catalyst particles in a reactor for carrying out chemical reactions according to claims 1 and 9, characterized in that the holding device consists of laminar material having the geometry of in the sides bevelled cuboids, and these elements are arranged in rows wherein the juxtaposed rows each have a reversed horizontal sense of the chamfered sides so that these elements intermesh in juxtaposed rows to form a closed but gas permeable layer.

11. A device for holding down catalyst particles in a reactor for carrying out chemical reactions according to claims 1 and 9, characterized in that the holding device consists of laminated material having the geometry of tees, and these elements are arranged in rows, wherein the juxtaposed rows each have a reverse vertical sense of the T-pieces, so that these elements interlock in adjacent rows and form a closed, but gas-permeable layer.

12. A device for holding down catalyst particles in a reactor for carrying out chemical reactions according to claims 1 and 9, characterized in that the holding device consists of laminar material having the geometry of cuboids having on one side a lateral bulge, and on the opposite side have a lateral indentation and these elements are arranged in rows, so that these elements interlock in adjacent rows and form a closed, but gas-permeable layer.

13. A device for holding down catalyst particles in a reactor for carrying out chemical reactions according to any one of claims 1 to 12, characterized in that the holding device consists of layered open-pore porous ceramic elements with random pores.

14. A device for holding down catalyst particles in a reactor for carrying out chemical reactions according to any one of claims 1 to 12, characterized in that the holding device consists of layered open-cell porous metal foams with random pores.

15. A device for holding down catalyst particles in a reactor for carrying out chemical reactions according to any one of claims 1 to 13, characterized in that it is the layer-shaped ceramic element is an open-cell porous porous ceramic with random pores.

16. A device for holding down catalyst particles in a reactor for carrying out chemical reactions according to claim 15, characterized in that the ceramic elements or the foamed ceramics oxidic ceramics, taken from the group of chemical compounds Al ₂ O ₃ , CaO, CeO ₁ Cr ₂ O. ₃ , Fe ₂ O ₃ , HfO ₂ , MgO, SiO ₂ , SnO ₂ , TiO ₂ , Y ₂ O ₃ or ZnO as single components or in a mixture.

17. Device for holding down catalyst particles in a reactor for carrying out chemical reactions according to claim 16, characterized in that the foamed ceramic zirconium dioxide ZrO ₂ in admixture with CaO, CeO, MgO or Y ₂ O ₃ for stabilization.

18. A device for holding down of catalyst particles in a reactor for carrying out chemical reactions according to one of claims 15 to 17, characterized in that the ceramic elements or the expanded ceramics non-oxide ceramics, taken from the group of chemical compounds AIN, BN, BC, MoSi ₂ , SiC or SiN as single components or in a mixture.

19. A device for holding down catalyst particles in a reactor for carrying out chemical reactions according to any one of claims 15 to 18, characterized in that the ceramic elements or the foamed ceramics consist of oxidic and non-oxide ceramics in the mixture.

20. Device for holding down catalyst particles in a reactor for carrying out chemical reactions according to claim 14, characterized in that the metal foam contains guide grooves, which serve as connections to each other.

21. A device for holding down catalyst particles in a reactor for carrying out chemical reactions according to claim 14, characterized in that the metal foam is designed to be connectable with hooks or eyes.

22. Device for holding down catalyst particles in a reactor for carrying out chemical reactions according to claim 14, characterized in that the metal foam is designed to be connectable with screws.

23. Device for holding down catalyst particles in a reactor for carrying out chemical reactions according to claim 14, characterized in that the metal foam is designed to be connectable by welding.

24. An apparatus for holding down catalyst particles in a reactor for carrying out chemical reactions according to claim 14, characterized in that the metal foam is designed to be connectable by gluing.

25. Use of the layer element made of metal foam for holding down catalyst particles in a reactor for carrying out chemical reactions according to any one of claims 1 to 24 in a radial reactor.

26. Use of the holding device for holding down catalyst particles in a reactor for carrying out chemical reactions according to any one of claims 1 to 25, characterized in that it is the gas phase reaction to a reaction for the oxidative dehydrogenation of alkanes.

27. Use of the holding device for holding down catalyst particles in a reactor for carrying out chemical reactions according to one of claims 1 to 26, characterized in that it is carried out at a temperature of 500 to 1000 0C.