RU2417840C1 - Catalytic element - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to catalytic elements. Described is a catalytic element having a regular structure, characterised by that the element consists of two structurally merged components, the first component being a bearing matrix, made from one or more types of highly porous permeable cellular materials in which space is formed, and the second component being discrete granules of one or more types, which completely or partly lie in the formed space at least in one of the matrices.

EFFECT: described catalytic element enables to regulate heat- and mass-exchange parametres of processes by combining catalyst components of one or more different types; avoiding loss of the catalytic element due to wearing.

13 cl, 13 dwg, 3 ex

Description

The invention relates to catalytic elements of regular structure, which may find application in various catalytic processes.

The most common and simplest type of catalysts to manufacture is catalysts made in the form of various granules. The sizes of the molded granules of the catalysts range from fractions of millimeters, but, as a rule, not less than 0.5 mm to several tens of millimeters, as a rule, not more than 100 mm in the largest size, for example, length.

Granular catalysts can be prepared both by extrusion and by other methods, for example by pressing or rolling. All molding methods are highly productive and allow you to get a wide range of formulations and forms of catalysts. The shape of the granular catalysts is determined by the production method, for example, extrudates by compression through dies, tablets or more complex forms obtained by compression, spherical bodies obtained by rolling. Granules of more complex shapes can have different cross-sectional geometry - trefoils, finned or otherwise, as well as one or more through channels.

Examples of some of the most common granular catalysts are shown in FIG. 2.

But granular catalysts have their disadvantages during operation:

high flow resistance; catalyst wear associated with abrasion, which leads to the loss of valuable components, such as precious metals; dust emission; and increase in layer resistance; low heat transfer parameters inside the layer. In the apparatus, the catalyst is stratified by the size of the granules, and the apparatus becomes clogged with dust from abrasion.

Partially, the disadvantages of granular catalysts are eliminated by another type of catalyst, namely cell blocks. The use of cell blocks provides low flow resistance. Cellular units are technologically advanced in operation, practically have no abrasion and entrainment associated with friction and vibration.

However, the cellular blocks are inherent and significant disadvantages associated with both the manufacture and operation of the blocks. When forming blocks, complex and expensive equipment is used, molding performance is low, molding of honeycomb structures is possible for a limited number of ceramic compositions, most formulations either do not provide high-quality channels or crack during drying and heat treatment. It is impossible to make a block from the most common carrier - gamma-alumina and ceramic-modifying additives, most often the block monolith and the active layer are two different materials, which creates complexity in the manufacturing process of the block catalyst and can lead to peeling of the active layer during operation.

Honeycomb blocks are very sensitive to thermal shock - temperature drops during operation, they have low thermal stability, i.e. cracking at high and variable temperatures, poor heat transfer of ceramics and the possibility of heat dissipation of the reaction in the stream inside the channel.

The honeycomb structure of the catalyst always has two distinct geometric components: the channel and the channel wall.

The presence of channels of great length and small in comparison with the length of the diameter always creates a danger of clogging of the channels with reagents or reaction products, or soot. In addition, there is a strong difference in the flow structure in the channel along the axis and in the wall layer, which creates additional diffusion restrictions. Mass transfer between adjacent channels is not possible.

To prevent bypasses, that is, the flow of reagents along the outer surface of the unit past the channels, requires the use of high-temperature sealing devices. The device of the automobile converter, consisting of a ceramic block of a metal housing and heat-resistant seals, is shown in Fig.13.

Cellular catalytic elements are known (RU 2128081, B01J 35/04, 1999; JP 62-191048, B01J 35/04, 1987; DE 3430886, B01J 35/04, 1986; JP 53-137866, B01D 53/34, 1978. JP 54-141382, B01J 1/00, 1979; EP 0260704, B01J 21/04, 1988, etc.).

In the patent RU 2209117, B01J 35/04, 07.27.2003 a catalytic element of a regular honeycomb structure is described, which is made in the form of a layer of separate prisms connected by side faces and having honeycomb channels, individual prisms having a gap between the side prisms faces 0.1-1.0 diameter of the honeycomb channel. For laying along the perimeter of the layer, triangular and trapezoidal blocks truncated to the diameter of the contact apparatus are used. These catalysts are used when carrying out high-temperature processes in the gas phase, for example, the oxidation of ammonia.

Cellular catalysts for the production of sulfuric acid, a process for the oxidation of sulfur dioxide, are proposed. Block cellular catalysts are most widely used in the processes of gas purification from harmful impurities.

In all of the above processes, cellular block catalysts exhibit their positive qualities, while retaining the disadvantages, primarily low thermal stability - cracking, peeling of the active catalytic layer from the block monolith, clogging of channels.

A known catalytic element, which is a cassette (assembly), in which individual catalytic elements obtained by standard granulation methods are combined by a common block design (RU 2362624, B01J 35/04, 07.27.09). The catalytic elements are rods or pellets of a catalyst of circular or other cross-section and are assembled using a spacer device in a single unit. The spacer device can be made in the form of a grid in which the catalyst block is assembled, in the form of pins on which the catalytic elements are fixed, or in the form of plates in which the catalytic elements can be mechanically fixed. The catalytic element can be formed from parallel or angled layers of catalyst rods, the same is possible when loading the blocks into the reactor. The catalytic elements in the reactor will be oriented in the direction of “flow along”, “flow perpendicularly”, “flow at an angle” to the rods, while the degree of turbulization of the flow will vary significantly. The element can be formed from heterogeneous catalyst rods, that is, from various catalysts having the same shape. The element may be formed from catalyst rods of different diameters. The geometry of the rod itself can be not only round, but also different in cross section, which makes it possible to increase the geometric surface.

Advantages of the proposed item. Simple and productive, as with extrudates, molding of catalytic rods from a wide range of ceramic compositions, including active aluminum oxides. Low flow resistance. Constant "frontal run-in" of the flow on the catalytic element. The stream is not closed in the channel, like a cell unit. Constant changes in the direction and mixing of the flow through the layers of the element. Good mixing and turbulization of the flow of reagents from layer to layer. High mass and heat transfer characteristics. Lack of contact between the rods and, as a consequence, wear by friction. No dust during operation of the catalyst bed. Heat resistance. The absence of thermal expansion-contraction, since the catalytic element is thermally compensated by the structure itself and is not a monolith. No cracking occurs. There is no danger of “clogging” the catalyst layer with dust, reagents, soot.

The disadvantage of this combined catalyst is the need to develop and manufacture complex fastening and placement elements of the granules themselves and structures spacing the granules from each other.

Another known type of catalyst is catalysts in which highly porous permeable cellular materials (HPMP) are used as a carrier. These catalysts can be made of metals, alloys of carbon materials, or ceramic. Another common name for highly porous cellular materials is foam metals and ceramic foam (metal foam, porous metal, open cell foam).

HPLM carriers and catalysts possess a number of inherent advantages only to them, including in comparison with cellular and granular catalysts.

The catalysts from HPMP have no rubbing parts, and therefore, wear and dust during operation, which is characteristic, for example, of discrete granules.

The total porosity of HPMP can reach 95% of their volume. As a result, they have a very low flow resistance, which allows them to be used even in the mode of natural convection of reagents, which is difficult to achieve for catalysts made of granules and blocks.

The mesh structure of the solid skeleton and freely accessible open pores make this material equally permeable to flow in any direction, which is not the case, for example, in block catalysts, where there is a clear separation of surfaces into an impermeable side and open front surface, channels and walls. The flow of reagents in HPLC is not closed in a single channel, as in blocks. There is practically no phenomenon of clogging of the channels with soot or reaction products for catalysts from HPMP.

A constant change in the direction of flow in macropores eliminates stagnant zones, turbulizes the flow of reagents and ensures their constant mixing. More thermally conductive than ceramic, the foam metal from which HPLM is made, and a turbulent flow provide mixing and high mass and heat transfer characteristics.

The large volume of free space of the cellular metal leads to a low volumetric weight of the catalyst. Therefore, catalysts based on HPLM have low thermal inertia, quickly warm up with the reaction heat, and enter the operating mode.

Since the water absorption of HPLM is much lower than that of porous granules, and the thermal inertia of the metal is practically absent and the catalyst quickly heats up, the formation of condensate films from reaction products, for example, water, is practically excluded on its surface. This is a significant advantage of HPLC catalysts over both granular catalysts and ceramic blocks with their low thermal conductivity.

Foam metal (HPLM) is the only material available for carriers and catalysts, which can be very simple to directly heat the catalyst, for example, to start the catalytic reaction or to maintain it.

A very important positive quality for the design of catalysts from HPMP is their mechanical properties. These materials better than others withstand shock or prolonged deforming loads. Even when deformed, foam-based catalysts retain their performance.

Catalysts made of metal HPMP are much smaller than block catalysts, they are susceptible to sudden changes in temperature - thermal shock.

At the same time, catalysts made of highly porous cellular materials are not without their drawbacks.

Advantages of low density: the absence of thermal inertia and high thermal conductivity turn into a disadvantage of this type of catalysts during unsteady supply of reagents. If the concentration of reagents entering the catalyst decreases, or even for a short time, drops to zero, then it cools down as quickly as it heats up. When the supply of reagents is restored, the cooled catalyst may not “ignite”, and a breakdown of unreacted substances occurs, which is unacceptable with explosive or toxic substances. In this case, a granular catalyst having a large mass and thermal inertia is preferable.

Catalysts made of ceramic cellular materials, unlike their metal counterparts, as a rule, do not have sufficient mechanical strength. They are fragile, do not withstand loads and impacts and, despite the presence of a number of patents, have not found application in industrial processes.

Adhesion (adhesion) of the intermediate active layer, which is applied to metal HPMP, is weaker than metal block ceramics due to the large difference in thermal expansion of metal than ceramics, and complex technological processes are used for high-quality metal-substrate adhesion.

A known synthesis gas catalyst (Application RU 2006125733/04, B01J 35/04, 01/27/08), in which the catalyst carrier contains a porous body, which is made of at least a substance selected from ceramic foam and ceramic honeycomb coating. Possessing the above advantages, it also has a significant drawback - it is fragile and can be completely destroyed when a shock wave hits the front in an emergency.

A known system for controlling and removing hydrogen (Application RU 2002129113, C01B 3/58, 04/10/04), in which metal catalyst is used as a catalyst carrier. However, the catalyst must be placed in a heat insulating support, which complicates the design of the hydrogen recombiner. In addition, the pilot operation of these catalysts confirmed the disadvantage associated with the rapid cooling of the catalyst, with a decrease in the concentration of incoming hydrogen in the stream, after the explosive concentration was again reached, this catalyst began to work with a significant delay.

This invention solves the problem of creating such a catalytic element, which combines the advantages of block-structure catalysts and granular, but devoid of their disadvantages.

EFFECT: almost complete elimination of losses from abrasion and entrainment even of the most fragile granular catalysts, including in processes with high or variable flow rates and vibration;

ensuring more stable operation in processes with unsteady or intermittent supply of reagents; the ability to control and improve the hydrodynamic characteristics of flows in catalytic reactors (apparatuses); the ability to control heat and mass transfer process parameters;

steady work in the conditions of high humidity and low temperatures; free shaping and orientation of catalytic devices (devices) in space; technological flexibility and the ability to create “smart” catalytic systems that adapt to the actual conditions of the reaction.

The invention is illustrated in figure 1, which presents the principle of formation of the proposed new catalytic element.

In a matrix of highly porous cellular material of HPLM by known methods they form spaces - cavities, channels, nests.

Then, any necessary catalysts of a discrete granular form are taken. Discrete granules are placed in cavities formed in HPM. The granules inside the matrix of HPLC are fixed by any known technological methods, for example, plastic deformation of the matrix itself, locking devices or even freely fall asleep in the cavities, channels or nests intended for this.

The result is a catalytic element according to this invention, characterized by new properties and opening up technological capabilities that do not exist separately from its components.

In figure 1, 1, discrete granules are indicated; pos.2 - highly porous cellular material with nests (holes) for granules formed in it; pos.3 indicates the result of the proposed technical solution - a new catalytic element.

Some of the possible types of discrete granular catalyst (granules) are presented in Figure 2, and the structure and general view of the HPLM are shown in Figure 3.

Examples (photos) of the finished catalytic elements according to this invention are shown in Fig.4.

There are a number of granular catalysts based on carriers of high activity gamma alumina. They have very high catalytic properties. But their significant drawback is the fragility and abrasion of soft gamma oxide. Placed in a matrix of HPLM, as proposed in this invention, the catalyst granules will retain all their advantages, and the mechanical properties of the granules protected by the matrix will not matter.

Without the proposed technical solution, these catalysts are practically not used, for example, on moving objects, and in stationary devices during operation they lose from abrasion up to 50% of their mass, including active precious metals deposited on the catalyst carrier.

A matrix from HPLC, even without catalytic properties, can be useful, for example, when it plays the role of a heat radiator - quickly removing heat of reaction, or, conversely, quickly warming up the inertial mass of ceramic granules. Such an application can be critical for reactions and processes with explosive reagents when it is necessary to prevent rapid local overheating of the catalyst or reactor, which can cause ignition or explosion. An example of such a process is the catalytic recombination (“cold” burning) of hydrogen in hydrogen safety systems.

Figure 5 shows two variants of the catalytic device. The first (item 4) consists only of a granular catalyst - rods of regular shape containing platinum on an oxide ceramic support. The second (item 5) is a catalytic element according to this invention, in which the same granules (rods) are fixed in a foam-honey matrix.

In the third (item 6) figure of Figure 5 is a graph of local temperatures along the length of the rods of the ceramic catalyst, that is, along the flow of reagents. In the graph, curve 7 corresponds to the temperature distribution along the length of the catalytic rod without a foam metal radiator, and curve 8 for the variant with a copper HPLC matrix according to this invention.

It can be seen that the use of the proposed catalytic element due to good heat dissipation on a matrix of copper HPMP allowed eliminating local (up to 600 ° C) ceramic overheating and equalizing the temperature of the catalyst. This not only extends the life of the catalyst itself, but also reduces the risk of explosion.

The catalyst can only be a matrix of HPLC, and the granules inside it play the role of a thermal brake or thermal inert. This property will be important for processes with the danger of rapid heating or, conversely, with rapid cooling. For example, due to the low inertia of the foam metal, the catalytic process can quickly and uncontrolledly enter dangerous high-temperature parameters, or, conversely, due to the rapid cooling of the HPLC, the catalytic reaction can stop - “collapse”.

A technical solution based on this invention will be useful, for example, for the operation of catalytic reactors in the purification of harmful emissions from non-stationary sources of pollution. So, when cleaning emissions from printing machines, the concentration of pollution in the air changes dozens of times during the working day, sometimes falling to zero. The granular catalyst in the HPLC matrix is able to smooth out these vibrations with its mass and thermal inertia. And, on the contrary, with a sharp increase in concentrations, the foam matrix will quickly distribute the temperature in the apparatus, increased by several hundred degrees, and prevent dangerous overheating of the catalyst and apparatus assemblies.

It is possible to use in the composition of the proposed catalytic element both granules and a VPNM matrix having catalytic properties, but being different catalysts. For example, differing in the composition of their active metals or their concentration. This technique will be useful for reactions that require more active (concentrated) catalysts for their “start”, and subsequently less active, but also less expensive, can “work” on a heated stream.

There are conditions when the catalyst is required to maintain operability at high humidity of gaseous reactants entering the catalyst, or during the formation of water as a product of a chemical reaction. In this case, highly porous active granules quickly and in large quantities adsorb water in the pores and capillaries, a blocking film of condensate forms, and the catalyst loses its activity or completely stops working. Foam catalysts - HPLM are less susceptible to condensing liquid vapors. However, in most cases they are inferior in activity to highly porous granules.

The combination of two components in one catalytic element: the matrix of foam metal and granules allows us to solve the problem of the operation of the catalysts in low temperature and high humidity conditions. Having a very thin active layer deposited on a metal base, HPLM is practically devoid of water absorption and dries quickly from the heat of reaction. Low heat capacity and good thermal conductivity of the metal allow it to warm up almost instantly and serve for the granules placed in it - the “starter” of the catalytic process.

The catalytic properties of the constituents of the proposed catalytic element themselves — the HPMP matrix and granules — in the composition of even one element can be different.

When the flow of reagents through the catalyst bed occurs, they chemically interact with the formation of reaction products. As a result of the reaction, almost all of its basic properties change along the flow. The chemical composition, temperature, molar and volume ratio of products and reagents are changing. As a result, the flow volume and density, and, as a result, the velocity and especially the hydraulic resistance of the layer, which grows in proportion to the square of the velocity, can change. Particularly significant changes occur during gas phase processes.

That is, all the way through the catalyst from the entrance to the bed to the exit from it, the flow properties at each subsequent level differ from the previous one. This is true for all types of catalysts - granular, block, foam-metal, even for catalysts in the form of a thin (several millimeters) packet of platinum chains. In conventional catalysts, this variable flow constantly interacts with the same medium, for example, a layer of identical granules or an extended channel of a block. If almost all the properties of the flow change with the passage of the catalyst bed, then having the same catalyst along the entire length of the bed is in any case not optimal. It is desirable to have an optimized catalyst for changing composition, temperature, speed, and other parameters.

The catalytic element according to this invention opens up the possibility of constructing a “smart” catalyst, in which the properties change along the flow (process), adapting to the actual conditions of the chemical reaction. It is possible to achieve this by collecting in the catalytic element the HPLC matrix and the granules enclosed in them with properties optimized for the actual flow.

As part of one catalytic element, discrete catalyst granules of different characteristics can be used inside the HPMP matrix.

So, at the beginning of the reaction, in the first layers of the catalyst (frontal layer), the concentration of reagents in the stream is maximum, and a less active, for example, catalyst containing less precious metal, can be used. Downstream, the concentration of reagents decreases due to a chemical reaction, and a catalyst with a high content of active components is required. In this case, components of one catalytic element can be used, for example granules or with catalytic properties that vary along the flow.

Figure 6 shows a fragment of a catalytic element in which the concentration of palladium in the granules (rods) of the catalyst from the frontal layer to the exit of the stream from the catalytic element changes, increasing by 10 times. The numbers in Fig. 6 indicate the percentage of active precious metal - palladium in a discrete catalyst, increasing along the flow and providing the most complete reaction (conversion) even with a decrease in the concentration of reagents during the reaction. That is, in the composition of one catalytic element different granular catalysts are used inside the same catalyst matrix from HPLM.

In this case, the concentration of palladium is optimal for the reaction conditions at each discrete level. A variant of such an “intelligent” catalytic element can significantly reduce the mass of the precious metal used, which is unattainable using only granules or only HPMP catalysts separately.

The same technique can be used when heating the reagent stream with reaction heat. If at the inlet to the catalytic element the flow temperature is not sufficient to start the reaction, the use of more active catalysts is required, then the heated reaction mixture can also react on a catalyst with a lower content of active components. Such an application of the proposed catalytic element can significantly reduce the consumption of expensive components - precious metals.

For example, in catalytic processes for the neutralization of harmful emissions, the use of expensive platinum metals in comparison with nickel, copper and chromium counterparts can reduce the temperature of the onset of the reaction (ignition) by several hundred degrees. This gives serious technical advantages to platinum catalysts, but their cost is very high. Using the catalytic element of this invention, it is possible to construct it from an HPMP metal coated with platinoids and granules placed therein from a cheap catalyst (for example, nickel-chromium-copper). In this case, the platinized matrix will ignite at low temperature, and the cheaper (without platinum metals) granular ceramic catalysts “come into operation” after heating the reaction on the matrix with heat.

The catalytic element may contain highly porous cellular material of more than one type, for example, it can be made of different HPLC, differing in geometric, catalytic, chemical, structural, thermal, acoustic, or other characteristics.

Combining the composition of the proposed catalytic element VPNM or granules with different geometric characteristics, you can adjust the hydrodynamic parameters of the catalytic reactors.

So, at high flow rates of reagents, especially gas, in the catalytic apparatus, there are always uneven speeds along the length or, more often, over the cross section. This leads to an uneven working load on the catalyst bed. The part of the catalyst, to which the reagent flow arrives at a higher speed, works with overload, while other sections may be underloaded.

Figure 7 shows the photos of HPLM, significantly different in pore size, and, accordingly, in hydrodynamic resistance to flow.

On Fig shows a variant of the finished catalytic element with different pore sizes of foam matrices. The central part has pores with a diameter of 1-1.5 mm and has 4 times greater gas-dynamic resistance than the peripheral one with pores of 3-4 mm. The use of such a catalytic element allows you to equalize the velocity plot along the cross section of the apparatus and create a uniform load on the entire catalyst. In the same way, using catalytic elements with different resistances over the cross section of the apparatus, it is possible to equalize the flow of reagents at speeds not only along the axis of the reactor, but also if the flow is “pressed” to one of the walls due to the design of the reactor, for example, non-optimal input reagents in the apparatus. Such a technical solution is especially effective at high speeds and gas flows.

Another option of an “intelligent” catalytic element may be a design in which the HPLC matrix with granules at the inlet of the stream has pores of a minimum size, and further along the stream, the pore size of the foam metal increases. This allows a flexible response, for example, to a rapid increase in flow temperature, leading to an increase in volume and, therefore, speed. Such conditions exist in adiabatic, that is, processes that occur at constant pressure. The large-pore matrix has a significantly lower resistance and will be optimal for increased flow rates through the catalyst.

The technological capabilities of the proposed catalytic element allow you to create from it spatial structures of complex and diverse shapes. The matrix of highly porous VPNM cellular material can have a non-linear or arbitrary shape, which can be easily given, for example, by galvanic molding, plastic deformation, stamping, welding, cutting and other known techniques. Some variants of the geometric shape of the bearing matrix of HPLC is illustrated in Fig.9. It can be seen from the figure that foam metal is not just a catalyst, but a self-supporting matrix of any necessary shape for placement of catalyst granules.

It is known that catalytic apparatuses with granular charge catalysts predominantly have a vertical position, and the catalyst is filled up on special shelves, grids or in baskets. The horizontal version of the reactor with a granular catalyst is a complex and not sufficiently reliable design, especially if there is vibration, shock, or other shock, for example, in vehicles.

The complex design and unreliability of horizontal catalytic devices has led to the almost complete cessation of the use of granular catalysts in automotive exhaust gas converters. Nevertheless, the potential of such catalysts is far from exhausted, and granules in comparison with ceramic blocks in this process have their positive qualities.

The use of the catalyst “HPLC plus granules” according to this invention makes it possible to create catalytic reactors of any geometric shape, including complex, curved, variable cross-section and with a variable composition of the catalysts during the catalytic assembly. In this case, the catalytic elements themselves can be oriented in the desired direction (or in different directions) and enclosed in any geometric volume in accordance with the design requirements for the catalytic reactor.

There are engineering problems when during design there is a shortage of free space to accommodate the catalytic apparatus. For example, confined conditions often arise for marine, space or aviation technology products and very little space remains to accommodate a catalytic reactor, or even free space is generally curved. This difficult task is quite easily solved using the proposed catalytic element.

Figure 10 shows an example of the shaping of the catalytic reactor in the annular gap, remaining free around the conditional unit. The numbers in the figure denote: item 9 - free annular space "provided" by the design of the unit; Pos.10 - catalytic elements of the desired shape according to this invention, located in free space; POS 11 - flow of reagents to the catalytic elements.

Placing the catalytic elements in the free gap created the desired effect — the free geometry of the catalyst, regardless of the location “provided” by the structure, shape or size.

Thus, from several catalytic elements, collecting them sequentially, it is possible to create catalytic assemblies for conducting multi-stage processes, to assemble flexible modular systems. The performance of the granules and the catalyst matrix constituting the catalytic element does not depend on the shape of the element, and the catalyst granules fixed in the HPLC are not subject to friction or wear even when operating under conditions of strong vibration or shock.

There are technical problems when the state of the catalyst must be maintained constant even without the flow of a stream of chemical reagents. For example, the catalyst should have a temperature above ambient temperature. Moreover, sometimes this condition should be maintained for a long time, for hours or sometimes for days.

Such requirements may be imposed on catalytic devices of “constant readiness”. For example, in explosion and fire safety systems and other similar ones. In these cases, to maintain the desired temperature, usually additional continuous heating devices are placed inside the catalytic device.

The proposed embodiment of the catalytic element has a matrix of foam metal, which can play the role of a direct heater for the granules placed in it, without even being a catalyst. To do this, just connect the electrical voltage directly to the metal HPM. In this case, direct heating of the granules with the heat of the ohmic resistance of the foam metal matrix will be more efficient and economical than with an additional heater placed, for example, in air.

Both discrete granules during normal use in the form of filling layers in catalytic apparatuses, and HPMP-based catalysts are randomly oriented media that do not have any preferred direction. Cellular block catalysts, on the contrary, have unidirectional regular channels, which create diffusion and thermal difficulties in separating the flow into the wall and central (along the channel axis).

The proposed catalytic element allows you to achieve the effect of the predominant flow direction, the most beneficial for specific conditions of the process. For example, by intensifying mixing or, conversely, reducing the turbulization of the flow.

So, the granules inside the HPLC matrix can have a consistent spatial orientation, i.e. be specially arranged relative to each other in a regular manner, for the best interaction with the flow of reagents.

Figure 11 shows an example of the organization of the flow of reagents in the catalytic element according to the schemes: "flow-across" pos.12 and "flow-along" pos.13 relative to the granular catalyst.

12 schematically shows a catalytic reactor device (for example, for purifying harmful gas emissions) in which two catalytic elements of the present invention with catalyst granules inside the HPMP are rotated 90 ° relative to each other. On Fig pos.14 indicated: oriented at an angle to each other catalytic elements; pos.-15 conditional reactor vessel.

Such techniques can intensify the catalytic process, providing flow turbulization and constant “frontal run-up” of the flow on the catalyst, as well as better mixing and mass and heat transfer characteristics.

Also, if necessary, it is possible, on the contrary, to reduce the reaction rate by orienting the granular catalyst accordingly. For example, to exclude the frontal flow of reagents to the catalyst, orienting the granules along the flow. Such technical solutions are effective primarily for processes with the free (convective) movement of reagents, when any reduction in resistance is desirable and significant.

Thus, not being a separate catalyst with regular geometric properties, discrete granules and catalysts based on HPLC combined in the composition of the proposed catalytic element acquire an important property in the catalysis technology - the regularity of the medium and orientation with respect to the flow of reagents. Moreover, unlike cellular block catalysts, in which the flow and channel coincide in direction, the proposed catalytic element makes it possible to create any desired combinations in the orientation of the flow and catalyst.

During the operation of a conventional block catalyst enclosed in a housing, or pellets, sprinkled on a shelf (in a basket) of a reactor, there is always a danger of bypass - reagent leakage past the catalyst through voids, gaps or cracks formed. To eliminate bypasses, the use of special seals or other technical methods is required.

So, during the operation of an automobile converter, the rapid temperature difference in it can reach 500-800 ° C. This requires the installation of special seals between the ceramic block and the metal casing. Seals must remain operational at high and variable temperatures, compensate for the very different thermal expansions of the metal and ceramics, and at the same time be airtight and prevent gaps.

The proposed catalytic element does not have the concept itself - lateral or closed surfaces. There is no advantageous direction, for example, an extended channel, for the movement of the flow. The pellets are placed in a supporting catalytic matrix, they cannot be poured to some edge and create a bypass. Even cracked, the catalyst granules remain in their nests and continue to work.

An example of the formation of bypasses in a catalytic converter with a standard ceramic block catalyst and a solution to this technical problem using the proposed element is illustrated in Fig. 13. A standard automobile catalytic converter is shown on the left, and a catalyst variant using the proposed catalytic element is shown on the right.

The numbers in Fig. 13 are schematically indicated: pos. 16 is a longitudinal section through the body of a catalytic reactor (for example, an automobile exhaust gas neutralizer); 17 - gas bypass past the catalytic unit through a defect in the seal; 18 - damaged high temperature seal; on pos.19 - standard block ceramic catalyst; 20 - catalytic elements according to this invention, rotated at an angle of 90 relative to each other; 21 - housing conventional catalytic reactor.

From the figure of Fig. 13 it can be seen that with this technical solution, when the ceramic granules and the foam metal matrix (foam ceramics) are permeable to gas from all sides, there is no possibility of gas bypasses, and even cracking of ceramic granules placed in the matrix VLYAM, does not reduce the health of the device.

The catalytic element according to this invention is thermally compensated in its construction, that is, indifferent to any variable temperatures. This property is given to him by the combination of an elastic compressible HPLC matrix and discrete granules fixed in it.

Example 1. A group of granular catalysts is known for the conversion (oxidation) of toxic carbon monoxide (carbon monoxide) to safe dioxide. The carrier (base) of this catalyst is highly porous gamma-alumina, and the catalytically active metal is palladium. The carrier of this catalyst has very low mechanical properties, especially hardness and abrasion resistance. So, the loss of catalyst in the form of dust from abrasion, including the ablation of a precious metal, amounted to 40-50% of the mass during the actual operation. Especially this phenomenon was present on moving objects in the presence of vibrations. Replacing a granular catalyst with a block one is impossible in this case, because of poor adhesion it is not possible to form a high-quality active layer-substrate on the ceramic (or metal) surface of the block for subsequent deposition of a catalytically active metal - palladium.

A catalytic element according to this invention was created and tested in which granules of a “soft” catalyst - palladium on gamma-alumina, were enclosed in a matrix of highly porous foam nickel.

The granules were obtained by standard technology - by extrusion on a screw granulator and had a cylindrical shape with a cylinder diameter of 2.8 mm and a height of 20 mm. The structure of the granules is highly porous, the total volume of at least 80%. For this reason, the granules have low mechanical properties. "Abrasion resistance" by the standard method for catalysts is not higher than 59%. The applied active ingredient was dispersed palladium — the average crystallite size was 2–5 nanometers, in an amount of 2.4% by weight.

In the matrix of foam metal by the method of deformation (extrusion) with a calibrated tool - a rod with a diameter of 3 mm, cavities (nests) were formed into which the catalyst granules freely entered. After the ceramic granules were placed in the formed nests, the catalytic element was pressed (compressed in two directions) on a hydraulic hand press. As a result of this, the granules were rigidly fixed in their nests. In the future, for their study, the granules could be removed only with the destruction of the matrix.

These catalytic elements were subjected to vibration test and shock tests. No abrasion losses were observed, part of the granules in the foam nickel cavities cracked due to shock loads, but this did not affect the performance of the catalytic element. Thus, the new catalytic element, possessing the advantages of two catalysts, was spared from their main disadvantages.

Example 2. In hydrogen safety systems, catalysts for the "flameless burning" of hydrogen in oxygen in the air with the formation of water, the so-called hydrogen recombiners, are used. The task of these catalysts and devices is to prevent the creation of explosive concentrations of hydrogen (explosive gas) in the air of enclosed spaces. For these purposes, both granular and foam metal catalysts containing platinum metals are used.

Granular oxide-based catalysts, having good activity, have a serious drawback: at room temperature and lower temperatures, the formed water film (reaction product) does not evaporate, remains in the pores of the carrier and blocks the gas-phase reaction of oxygen with hydrogen. Granular ceramic catalyst stops working.

Catalysts from HPLM with supported platinum group active metals are not much affected by the condensate formed, since their porosity and layer thickness are much smaller than that of alumina pellets. That is, water absorption is practically absent. In this case, the thermal inertia of the thin metal, which is practically zero in comparison with ceramics, is sufficient for rapid evaporation of the water film formed by the heat of a chemical reaction. However, the low thermal inertia of the foam metal leads to almost instantaneous cooling of the catalyst with a sharp decrease in the concentration of hydrogen in the room, since the heat of the chemical reaction ceases to be released. If the hydrogen content in the air rises again, the cold catalyst does not “ignite”, that is, it does not start working much longer than the safe period.

Catalytic elements were manufactured on the basis of active ceramic granules placed in matrices from a foam-based catalyst.

The granular catalyst was a special ceramic structure based on alumina with a bimodal porous structure. The number of micropores (10-15 nanometers) was at least 80%, and transport macropores (more than 5000 nanometers) amounted to 20%. The active component was platinum with the addition of ruthenium (a total of 1.3% by weight of platinum metals). The shape of the granules of the catalyst is cylindrical, 12 mm in diameter, 12 mm high. Photos of the granules of this catalytic element are shown in figure 2 - photograph on the right.

The matrix was a foam nickel catalyst coated with platinum in an amount of up to 1.3 g per liter of HPLM. The holes (nests) for the catalyst of the required size were laid in advance, during the manufacture of HPLC, for the operation of galvanic formation of foam metal.

In such a catalytic element, due to the much higher activity of the granular catalyst, the reaction on the granules began already at 0 ° C, the metal matrix from the foam metal was quickly (in 5-6 seconds) heated by the heat generated and “picked up” the reaction with the entire volume of the catalytic element. When the hydrogen supply ceased, the catalytic element heated to 90 ° C, due to the thermal inertia of the ceramic mass of the granules, kept the operating temperature for 25-30 minutes and immediately turned on when the hydrogen supply was resumed. Thus, the catalytic element proposed according to this invention eliminated the disadvantages inherent in its components, became practically inertialess and allowed to significantly increase the explosion safety of the protected objects.

Example 3. Exothermic, that is, catalytic reactions occurring with a large heat release on a granular catalyst often lead to local, overheating of the reaction zones inside the apparatus. The main reason is the low thermal conductivity of ceramic carriers and the high starting concentrations of reagents that “run” onto the frontal layer of granules in the apparatus. In a number of processes, it is necessary to use less active than desired catalysts only to maintain the thermal conditions inside the apparatus at acceptable parameters. To overcome the contradiction between the necessary activity and possible local overheating of the catalyst, a catalytic element was manufactured containing highly active platinum-plated ceramic rods placed in a foamomed matrix.

Rods made of high-temperature ceramics were molded on a special piston hydraulic bench by extrusion of a ceramic mass through a die. The size of the rods after firing is 6 mm in diameter and 60 mm in length. The rods (granules) have a through hole with a diameter of 2 mm.

The foamomed matrix had an average open pore size of 1.5-2.5 mm. The thickness of the foam metal is 10 mm. The holes for the granular rod catalyst were carried out on a drilling machine along a conductor to a depth of 8 mm.

Before placing the catalyst rods, the matrix was heated to 250 ° C, after which the rods entered the drilled blind holes with a tight fit. From the cooled matrix, the rods could subsequently be removed only with a breakdown punch. The method of placement of granular rods and the appearance of such a catalytic element is illustrated in figure 5, position 5.

Thus, the foamed HPMN only came into contact with the ends of the granular catalytic rods, on which the maximum temperature developed during the reaction, that is, served as a heat sink. Figure 5 shows photographs of two catalytic elements - with and without HPLM, as well as a graph of temperatures along the length of the catalytic rod. The temperature graph along the reagents along the catalyst rod clearly shows that there is no local overheating of the catalyst and reagents on the catalytic element “core catalyst plus HPMP”. For catalytic reactions in which the reactants create explosive mixtures, the absence of local overheating is crucial for the safety of the process. This catalytic element was tested according to the standard method for catalytic hydrogen recombiners at the existing Kalinin NPP and showed higher activity than the standard catalyst.

Claims (13)

1. A catalytic element of a regular structure, characterized in that it consists of two structurally combined components, the first component is a carrier matrix made of one or more types of highly porous permeable cellular materials in which space is formed, and the second component is discrete granules of one or more types that are fully or partially placed in the formed space in at least one of the matrices. 2. The catalytic element according to claim 1, characterized in that the highly porous cellular material of the carrier matrix and the discrete granules disposed therein have catalytic properties. 3. The catalytic element according to claim 1, characterized in that only discrete granules have catalytic properties in it, and the highly porous cellular material is a carrier matrix or serves to impart the desired thermal, hydrodynamic, or other characteristics to the catalytic element. 4. The catalytic element according to claim 1, characterized in that only highly porous cellular material has catalytic properties, and discrete granules are designed to give the catalytic element the desired thermal, hydrodynamic or other characteristics. 5. The catalytic element according to claim 1, characterized in that the highly porous cellular material and discrete granules placed in it have the same catalytic properties, that is, they themselves are catalysts of the same type or the same catalytically active component is deposited on them. 6. The catalytic element according to claim 1, characterized in that the highly porous cellular material and discrete granules placed in it have different catalytic properties, that is, they themselves are different catalysts or various catalytically active components are deposited on them. 7. The catalytic element according to claim 1, characterized in that it contains discrete granules of more than one type, for example, consists of different materials according to geometric, chemical, structural or catalytic characteristics. 8. The catalytic element according to claim 1, characterized in that it contains highly porous cellular material of more than one type, for example, consists of different materials according to geometric, catalytic, chemical, structural, thermal or acoustic characteristics. 9. The catalytic element according to claim 1, characterized in that the matrix of highly porous cellular material has an indirect or arbitrary shape, which is given to it by any known technological methods, such as: electrochemical molding, plastic deformation, stamping or cutting. 10. The catalytic element according to claim 1, characterized in that the discrete granules inside the matrix of highly porous cellular material are fixed in the formed spaces by any known technological methods, for example, plastic deformation of the matrix itself, locking devices or tight fit of the granules. 11. The catalytic element according to claim 1, characterized in that the discrete granules inside the matrix of highly porous cellular material are not fixed, but are freely filled into the formed spaces intended for this purpose - cavities, channels or nests. 12. The catalytic element according to claim 1, characterized in that one or more matrices can be heated to the temperature necessary to start the catalytic process, due to its own ohmic resistance when an electric current is passed through it. 13. The catalytic element according to claim 1, characterized in that the granules placed in a highly porous cellular material have a coordinated spatial orientation, i.e. specially oriented relative to each other in a regular way.

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