FR2811589A1 - Device for conducting catalytic reaction on solid with at least one reactant in liquid state under normal conditions - Google Patents

Abstract

A catalyst unit (1) contains an evaporation unit (2) and a reaction unit (3) assembled with a connector conducting heat from the solid. The evaporation unit is movable relative to the reaction unit. The evaporation unit is porous in at least some zones and is placed over all or part of the surface of the reaction unit. Several catalyst units are stacked on top of each other at a distance, each having at least one crossing which forms a channel.

Description

The present invention relates to a device for carrying out a reaction to

  catalysis on solid, for which at least one educt is present in the liquid state under normal conditions, comprising a catalysis unit, comprising an evaporation unit and a reaction unit 4 - placed together in conductive bond of the

heat of the solid.

  Solid-state catalysis reactions are currently of increasing importance in the most different fields, for example in the field of fuel cells, the generation of hydrogen from hydrocarbons, among which conventionally fall into this category. also in the field of alcohols, aldehydes, ketones and the like, and water, comprising 1-5 the reforming of hydrocarbons (Ullmann's Encyklopâdie der technischen Chemie, Band 12, pages 113 to 116, Verlag Chemie, Weinheim 1976). A mixture consisting of hydrocarbons, in particular methanol and water, is then converted on the surface of a corresponding solid catalyst.

  which most often contains copper.

  Other examples are the conversion of carbon monoxide to carbon dioxide by a reaction with hydrogen, in what is called the "hydrogen shift reaction", the oxidation of carbon monoxide, during from which a gas, containing CO, is reacted with a gas containing oxygen on a catalyst, as well as the combustion (oxidation) of a combustible educt with the addition of a gas containing oxygen, in this that one

calls a "catalytic burner".

  The fuel cells mentioned above are increasingly used also in motor vehicles and obtain the hydrogen necessary for combustion from the on-board hydrocarbon in the form

  liquid, knowing that methanol is used in particular.

  This reaction, in practice, is carried out so that a mixture, containing water vapor and hydrocarbon, is brought into contact, with the addition of heat at an appropriate temperature, with an appropriate catalyst in order to generate hydrogen, in a process of

  reactions usually taking place in several stages.

  Liquid educts must then either be supplied in extremely finely sprayed form to the surface of the catalyst, or they must at least partially present themselves in the vapor phase before coming into contact with the surface of the catalyst. The last variant can

  then be performed using different devices.

  By DE 44 26 692 CI, we know what is called a reforming reactor, for which an evaporator device is installed spatially separate upstream of the catalytically effective layer, heat transfer, from the elevator to the catalytically effective layer, made by a fluid heat transfer medium. The structure is however complex, in particular due to

  the use of an additional heat transfer medium.

  Furthermore, in DE 197 20 294 Cl and the non-prepublished patent application DE 199 0G 672.8 is described a reforming reactor with an upstream coupling between the evaporator and the reaction zone. The evaporator then consists of a porous heat conducting structure which is bordered on the surface to the reaction zone, that is to say to the catalytically effective layer, and which is rigidly connected thereto. . This can be done by a common sintering of the evaporator structure with the catalytically effective layer, so that the coupling, thus established in the zone of

  reaction with the evaporator, is carried out in one piece.

  The heat transfer then takes place via a

solid heat.

  The reactor systems mentioned above, using a rigid connection or coupling between the evaporator and the reaction zone, however have the disadvantage that the heat, which is released during evaporation, due to the thermal gradient establishing between the evaporator and the reaction zone, causes mechanical stresses, thermally induced, which for short is called "thermal stresses", in the reaction zone. This often leads to ruptures and warping of the physical structure of the reaction zone, but also on the structure of the evaporator which can even

partially fragment.

  Starting from this, the invention aims to shout a coupling between the evaporator and the reaction zone, coupling avoiding the drawbacks mentioned above of the prior art and proving insensitive to the

thermal constraints.

  This problem is solved by a device for carrying out a catalysis reaction on solid, characterized in that the evaporation unit is movable relative to the reaction unit Due to the mobile arrangement of the unit of evaporation compared to the unit of reaction, there is transfer and evacuation of the thermal stresses in a translational energy, so that the structures of the two units remain not influenced by that and undergo therefore no damage, for example

  cracks, warping and ablations.

  The concept "mobile" in this regard means any arrangement which allows the evaporation unit, in the presence or temperature gradients between the evaporation unit and the reaction unit, to carry out translational displacements with respect to the reaction unit, which produce a transfer of technical constraints into kinetic energy. This can, for example, be obtained by the fact that a mattress of metallic fiber is chosen as the evaporation unit, which is fixed movably on the reaction unit, using suitable means. Similarly, the evaporation unit can also be made of sintered ceramic or sintered metal, which is then fixed, mechanically or by pressing,

on the reaction unit.

  The arrangement of the evaporation zone into a reaction zone can be made according to a free choice, as long as there is a connection which conducts the heat of the solid bodies, that is to say that the zone of evaporation can be arranged in accordance with DE 197 20 294 CI, above or

next to the reaction zone.

  Advantageously, the evaporation unit is porous, so that the educts can arrive in a controlled manner on the reaction unit. Depending on the size of the pores and any pressure applied, the quantity of educts arriving at the reaction unit can be measured,

  so that the reaction can be optimized.

  Naturally, the use of a metallic mattress, for example of special steel, or else of an appropriate alloy, is conceivable, however the width, often too large,

  mesh should be taken into consideration.

  According to a preferred embodiment, the evaporation unit is arranged over the entire surface of the reaction unit. This ensures regular heating of the reaction unit. This is further advantageous if the reaction mixture is discharged into the evaporation unit and the reaction unit which is often

also porous.

  However, it is also advantageous to have the evaporation unit on a partial area of the surface of the reaction unit. This is particularly preferred when the reaction products are not discharged, as in some cases, through the evaporation and reaction unit, but are added in a metered manner, using mechanical devices, only in an area of the reaction unit which is covered by the evaporation unit. This however depends on the choice of reactor and the catalytic reaction. For example, it is also conceivable that what is called a stacking reactor, of modular structure, is made up of several catalytic units arranged one after the other and one above the other, units which have reaction units alternated regularly or irregularly, on the surface of which is at least partially arranged an evaporation unit. According to a preferred embodiment of the device according to the invention, provision is made for having several catalysis units stacked one above the other, units the form of which can be freely chosen. Each catalysis unit has at least one crossing, the respective crossings being in alignment to form an inlet channel for the supply of the educt mixture and, between the different layers, being made distribution channels which branch out from the input channel. The reaction mixture is now guided on the surface of the evaporation units, knowing that the necessary heat of evaporation is produced by an exothermic reaction of the liquid or, if necessary, by the supply of an additional fuel, for example oxygen. The reaction mixture now reacts on the reaction unit and the thermal stresses which occur if necessary, for example in the case of rapid addition of the reaction mixture, are evacuated by being converted into translational energy, thanks to the mobile evaporation unit with respect to the reaction unit, so that stacked reactors of expensive construction can also be operated for a longer period of time, without risking damage by thermal stresses Obviously, too, it is possible to consider other concepts, in particular stack reactors with modular structure, for which the invention can be implemented, A device according to the invention is used for catalytic reactions for which at least one reaction product is in liquid form which, before the catalytic reaction takes place on a solid which, more often than not, is exothermic, must be transferred to a reactor. r, in vapor or gaseous state. A preferred example is the obtaining of hydrogen from a mixture constituted

  a hydrocarbon, as defined at the beginning, and water.

  Other advantages and embodiments of

  the invention results from the description and the drawing

Annex.

  It is obvious that the characteristics mentioned above

  above and those which will be explained further below can be used not only in the combination each time indicated but also in other combinations or else alone, without leaving the framework of the

present invention.

  The invention will be represented schematically using an embodiment in the drawing and will

  be described in detail with reference to the drawings.

  Figure 1 shows a device section according to the invention. FIG. 2 represents another device according to the invention. FIG. 1 shows a catalysis unit 1 which consists of an evaporation unit 2 and a reaction unit 3. The evaporation unit 2 is then placed on the common surface of the reaction 3, in a mobile manner with the heat conduction effect of the solid with respect thereto. The catalysis unit 1 also represents at least one crossing (not shown in the drawing) The surface of the catalysis unit can be freely structured, for example in the form of meander bosses to increase the surface area reactive, both for the evaporation process and for the reaction process In the present case, however, for the sake of

  simplicity, with a practically flat surface.

  The evaporation unit 2 comprises a porous body, conductive of heat, having a wettable surface of large area which, if necessary, can be swept by the passage of a gaseous oxidizing agent, for example air or oxygen. The reaction unit 3 consists of a gas permeable body containing a catalytically active, porous material, preferably sintered. In another embodiment, the reaction unit 3 is formed on its inner face, by means of suitable arrangements, also so as to be impermeable to gas, The evaporation unit 2 is either pressed on the reaction 3, knowing that the pressing pressure is chosen such that, upon the occurrence of thermal stresses, the evaporation unit 2 can move relative to the reaction unit 3 which is rigidly fixed, or is disposed of mobile way with heat conduction of the solid, thanks to suitable mechanical means, for example frames, grooves, clamps and

  analogues, on the reaction unit 3.

  The liquid to be evaporated is brought to the surface of the reaction unit 2 in the direction of the arrows shown in the figure. The necessary evaporation energy is provided by an exothermic reaction of a fuel with the oxidizing agent having penetrated by diffusion into the evaporation unit 2 and the reaction unit 3, onto the catalyst material. The fuel, for which it may also be the liquid to be evaporated, can be present both in liquid form, and also partially or

  completely in vapor or gaseous form.

  Depending on the type of reactor, the gas formed is for example returned to the evaporation unit and is evacuated together with the oxidizing agent, if necessary, out of the reactor. However, in the case where it is a stacking reactor of modular structure of the type in which the reaction educts with, if necessary, the necessary oxidizing agents are forced through all the catalysis units arranged one on the others, there is a reaction of the educt mixture through all of the reaction units and the products are then taken off at the lower end of the

stacking reactor.

  FIG. 2 represents a catalysis unit 6 which also consists of an evaporation unit 7 and a reaction unit 8. The evaporation unit 7 is then placed only on part of the surface of reaction unit, mounting

  being mobile with a conduction of the heat of the solid.

  The materials of the reaction and unit unit

  corresponding to those described above

  above about Figure 1. Likewise, the movable arrangement of the evaporation unit 7 on the reaction unit 8

  is carried out with the arrangements mentioned above.

  As mentioned in connection with FIG. 1, the evaporation of the educt mixture takes place in the evaporation unit 7. The mixture consisting of the educts, of the products and of an oxidizing agent which is, in the case if necessary, is then directed, in the direction symbolized by the arrows, onto the surface, covered by the evaporation unit 7, of the catalysis unit 8, there where the mixture of educt continues to react. The conversion of the educt mixture can then be controlled more quickly, however less well. Those skilled in the art will choose between the concepts, represented in FIGS. 1 and 2, of the device according to the invention, depending on the reaction to be carried out and the

type of reactor to be used.

Claims (5)

REVENDI CATIONS   1. Device for carrying out a catalysis reaction on solid, for which at least one educt is present in the liquid state under normal conditions, comprising a catalysis unit (1), comprising an evaporation unit (2) and a reaction unit (3), placed together in conductive connection of the heat of the solid, cara'c-t-ri4 Aen that the evaporation unit (2) is movable relative to the reaction unit (3).   2. Device according to any one of   previous claims, characterized in that the unit   evaporation (3) is porous at least by areas.   3. Device according to claim 1 or 2, characterized in that the evaporation unit (2) is arranged on the overall surface of the reaction unit (3), 4. Device according to claim 1 or 2, characterized in that the evaporation unit (2) is arranged on a partial area of the surface of the unit reaction (3) -   5. Device according to any one of   previous claims, characterized in that are   provided with several catalysis units (1) stacked one on top of the other, each of which has at least one passage to form a channel, and the catalysis units (1) which are sealed are arranged at a distance from each other others.