Catalytic device for carrying out a reaction within a gaseous medium, reactor, reaction process and process for producing the catalytic device

Catalytic apparatus for carrying out the reaction in a gaseous medium, reactor, reaction process and process for producing the catalyst apparatus

Technical field

The present invention relates to catalytic reactions in a gaseous medium at high temperature, for example ammonia oxidation and HCN synthesis. A certain object of the invention is an improved catalytic apparatus that can be used in this type of reaction and a reactor containing it.

BACKGROUND OF THE INVENTION

Ammonia oxidation is widely used in nitric acid production. The method, known as the Ostwald process, comprises an operation in which a preheated ammonia / air mixture, typically containing 5-15% by volume, in particular 10-12% by volume air, is passed at a high linear velocity, measured at standard temperature and pressure conditions through a catalytic apparatus. arranged over the cross section of the reactor.

Synthesis of hydrocyanic acid - HCN in a single operation from ammonia and gaseous hydrocarbon, in which the heat required for the endothermic reaction is generated by the simultaneous combustion reaction with oxygen or air containing gas in the presence of a catalyst, is an operation known for many years - see U.S. Pat. No. 1,934,838. It is known as the Andruss process.

These two types of reaction employ platinum group catalysts, usually in the form of a flat woven mesh. The working cross-section of these catalysts is limited by the reactor dimensions.

In order to increase the productivity of these reactors, it is possible to increase the number of catalytic tissues. However, beyond a certain thickness, the pressure drop thus produced counteracts the increase in the flow of the reactant and abolishes the effects of a better conversion yield. In addition, side reactions may occur by increasing the thickness. Therefore, difficulties in increasing production result in the prior art from the pressure drop, from the number of catalyst active sites - the contact surface area, from the contact of the catalyst with the reactants.

In order to increase the effective surface area of ​​the catalyst, U.S. Pat. Nos. 5,160,722 and 5,356,603 disclose the use of catalytic meshes having transverse undulations. Although the surface area is thus increased, these undulations have low amplitudes, maintaining the shape of the system is only possible for temperatures below 800 ° C. In addition, the mechanical properties of the metal become inadequate and tend to penetrate due to pressure drop, creases or undulations. The service life of such a device is therefore very short, which is incompatible with industrial production.

The patent application EP931 585 describes in its part the use of catalytic mesh in the form of radially undulating discs or cones so that the rotating burner can follow the undulation as it rotates about its axis. However, the above problems remain.

It is therefore an object of the present invention to provide a catalyst apparatus comprising a catalyst having a larger geometric surface area and which resists reaction conditions without substantially increasing the pressure drop or side reaction.

SUMMARY OF THE INVENTION

Said drawbacks of the prior art are overcome by a catalytic apparatus for carrying out the reaction in a gaseous medium at a temperature between 800 ° C and 1400 ° C, such as the synthesis of HCN or the oxidation of ammonia according to the invention, which comprises at least one structured material.

Which acts as a catalyst for this reaction and a support comprising at least one ceramic part whose structure permits passage of gases, said part of the support having a corrugated end face whose enlarged surface area β formed by the undulation with respect to the planar surface is greater, or equal to a value calculated for the sawtooth ripple, is between 1.1 and 3, wherein the structured material is positioned and held on the wavy face of the shape-following portion of the carrier.

Further, the means for retaining the structured material on the corrugated end face of the support portion is formed from a second portion of the ceramic support whose structure permits gas passage, wherein said second portion having a corrugated end face corresponding to and complementing the corrugated end face of the support portion is placed that the corrugated faces face towards each other and the structured material is disposed therebetween and follows a shape ripple to produce a homogeneous pressure drop across the catalytic device and also that the carrier has a honeycomb structure or that the ripple has a sawtooth where the surface area increase β equals an increase in surface area α as well as an increase in surface area β] ε of about 1.4, or that the structured material is a mesh.

The drawbacks of the prior art are also overcome by an exothermic reaction reactor at a temperature of between 800 ° C and 1400 ° C in a gaseous medium having a substantially circular cross-section comprising the above-mentioned catalytic apparatus extending over the cross-section of the reactor, the exothermic reaction is the synthesis of HCN or that the catalytic device is located on hollow bricks forming the base of the reactor and is covered by a heat shield.

Further, the shortcomings of the prior art are eliminated by a reaction process in a gaseous medium at a temperature between 800 ° C and 1400 ° C, which is based on the use of the above-mentioned catalytic apparatus or reactor, which process is HCN synthesis or a gas mixture The hydrocarbon-containing hydrocarbon, preferably methane, ammonia and oxygen are passed through the above catalytic apparatus at a temperature between 800 and 1400 ° C to obtain a gas stream containing at least 5% by volume HCN.

Last but not least, the shortcomings of the state of the art are also eliminated by the method of manufacturing the catalytic apparatus, which is based on the fact that the structured material is not rolled onto the face of the support to follow its shape and subsequently attached by the restraining means or and are formed by a second carrier portion, the face of which is applied to the opposite surface of the structured material against the face of the carrier portion.

An advantage of the invention is that the pressure drop is substantially homogeneous over the entire catalytic apparatus thus formed.

Other conventional means for retaining the structured material on the corrugated faces of the first portion of the support may be used.

For the purposes of the present invention, the term "structured material" means any set of strips or wires that are linear and / or in the form of spiral parts through which gases can pass. This assembly is, for example, of mesh, woven fabric, knitted fabric or as a felt and can be obtained by various techniques such as weaving, knitting, sewing, embroidery, etc. Preferably, it is a mesh.

For the purposes of the present invention, the term "two wavy faces of substantially coincident and complementary shape" means any combination of two faces having a corrugation of similar size and shape, i.e. having the same magnification in the surface area β, which is designed such that the corrugations complement each other, i.e. they are complementary.

Other objects of the invention and its advantages will be apparent to those skilled in the art from the detailed description and reference to the accompanying drawings.

-2GB 304571 B6

Overview of the drawings

An exemplary embodiment of the present invention is shown in the accompanying drawings, in which Fig. 1 is a schematic representation of a catalytic apparatus according to the invention; Fig. 2 is a parameter which allows to calculate the increase in surface area (a) produced by sawtooth corrugations.

DETAILED DESCRIPTION OF THE INVENTION

The carrier 2 according to the present invention is made of a ceramic whose structure allows the passage of gases. Examples of such ceramics are, without limitation, ceramic foams or ceramic composites. The term "ceramic" preferably means within the meaning of the present invention any refractory material capable of withstanding the temperatures to which the catalytic platinum mesh reaches in the reaction of a medium containing, inter alia, steam. When used in the synthesis of HCN according to the Andrussow process, this temperature can reach up to 1200 ° C. The materials that are suitable are therefore based on alumina and may contain varying amounts of silica - 10 to 60 wt. and magnesium, zirconium, titanium and cerium oxide - 1 to 20 wt. for each of these components. These materials may include, but are not limited to, one or more of the following compounds: silicon dioxide-silica SiO₂, silicon carbide SiC, silicon nitride Si₃N₄, silicon boride, silicon boron nitride, aluminum oxide A1₂O₃, aluminosilicate, carbon fibers, zirconium oxide ZrO₂, Yttrium oxide Y₂O₃, calcium oxide CaO, magnesium oxide MgO and cordierite MgO A1₂O₃ - SiO₂.

Preferably, a Stetta® G29 ceramic is used, the characteristics of which are as follows:

<td>Poréz- nost</td><td>Relati- in her density in kg / cm³</td><td>Flexural strength N / mm²</td><td>Linear koefic. of extensibility i / K.io⁶at 20</td><td>Linear coefficient. of extensibility í / K.io '⁶</td><td>Thermal conductivity W / (mK)</td><td>Durability against thermal rázům ° C</td><td>Maximál. traffic. temperature in ° C</td><td>Volume. resistance- nost at 800 [deg.] C</td>

<td> &gt; 3</td><td> 2</td><td> 4,5</td><td> 1,5-3</td><td> 2-4</td><td> 1,3 1,7</td><td> 380</td><td> 1000</td><td> 10^with</td>

Prior to use, the materials used to form the carrier 2 are usually made by known techniques of molding, pressing, agglomeration, and the like. They are then calcined at a high temperature &amp; gt; 1300 ° C to obtain mechanical properties comparable to their future operating conditions. These combined operations must impart to them a structure that can be passed through gases, which may be, for example, in the form of cells interconnected in three directions - foam or honeycomb with a circular or polyglonal - square, rectangular, hexagonal, etc. cross-section.

In particular, the structured material I which is effective as a catalyst is a platinum group catalytic metal and can be prepared from platinum, rhodium, iridium, palladium, osmium, ruthenium or a mixture or alloy of two or more of these metals. Preferably, it is a platinum or platinum / rhodium alloy. Alternatively, the catalyst may be of the platinum group as described above and of at least one material containing, but not limited to, cerium, cobalt, manganese, magnesium and ceramics.

The undulations of the faces 6 and 7 of the carrier 2 can be of any type, in particular in the form of saw teeth.

The sawtooth wave will be defined by the height "h" of each waveform and the distance "d" between the two waves. The increase in surface area created by the ripple of this type can therefore be calculated from these three parameters (Fig. 2) as follows:

a = sl (4h² + d²) / d

-3GB 304571 B6

The surface area increase β produced by any type of waveform according to the invention will be at least equal to a and will be selected in the range of about 1.1 to about 3. This is because a = 1.1 corresponds to a surface area increase of 10%. Below this value, the benefits of this wave are not very obvious. Above β = 3, the use of such a device becomes difficult. The sawtooth waves of the invention preferably have an isosceles triangle profile with a distance d = 2h, resulting in a ratio of about 1.40 and therefore an increase in surface area of ​​about 40%.

The present invention also relates to a high temperature exothermic reactor in a gaseous medium having a substantially circular cross-section and comprising a catalytic device according to the invention extending across its cross-section.

It also relates to a reaction process in a gaseous medium at high temperature, such as ammonia oxidation or HCN synthesis, using a catalyst device or reactor according to the invention.

In a certain embodiment of the invention, the process of the present invention is the synthesis of HCN and comprises the operation of passing a gaseous mixture containing a hydrocarbon, preferably methane, ammonia and oxygen, through a catalytic device of the invention at a temperature between 800-1400 ° C. has obtained a gas stream containing at least 5% vol. HCN.

The hydrocarbon used in the process for the synthesis of HCN of the invention may be substituted or unsubstituted, and an aliphatic, cyclic or aromatic hydrocarbon, or a mixture thereof. Examples of these hydrocarbons include, but are not limited to, methane, ethylene, ethane, propylene, propane, butane, methanol, and toluene. The hydrocarbon is preferably methane.

The present invention also relates to a process for the production of the catalytic apparatus according to the invention, in which the structured material 1 is unfolded on the corrugated face 6 of part 3 of the support 2 by following its shape and retained thereon by restraining means.

These restraining means are preferably mechanical and consist of a second part 4 of the support 2, whose corrugated face 7 covers the front surface of the structured material 1, which lies on the opposite side to the corrugated face 6 of part 3 of the carrier 2.

More preferably, the combination thus formed produces a small pressure drop that is substantially homogeneous across the reactor cross-section.

A certain schematic embodiment of the device according to the invention - see Fig. 1, consists of:

- combination of corrugated tissue - structured material i,

- a corrugated ceramic support 2 composed of two parts 3 and 4, each having a corrugated face 6 and 7.

Mesh-structured material 1 is embedded between the end faces 6 and 7 of both parts 3 and 4 of the carrier 2.

The parts 3 and 4 of the carrier 2 are made of ceramic having a honeycomb structure with a circular or polygonal - square, rectangular, hexagonal and the like cross-section.

Example of preparation of catalytic apparatus according to the invention:

The carrier 2 according to the present invention can be given a wavy shape, either before calcination, i.e. during the forming operation, or after calcination, folding and gluing together of triangular prisms.

-4GB 304571 B6

The combination of the platinum mesh of the structured material 1 forming the catalyst charge is then sandwiched between the two portions 3 and 4 of the corrugated carrier 2. This positioning operation is performed by rolling the combination of elliptical mesh of the structured material 1 to be deposited on the corrugated portion 3 of the carrier 2 of elliptical-shaped webs that will be applied to the corrugated portion 3 of the support 2, the support 2 is previously placed on the hollow bricks 11 forming the base of the reactor with a circular cross-section. The width of the elliptical meshes corresponds to the internal diameter of the reactor. The length is equal to the width multiplied by the previously determined coefficient β. The topsheet, i.e. the second portion 4 of the corrugated material support 2, allows the mesh to be immobilized mechanically, contributing to a homogeneous pressure drop across the combination over the entire exposed surface. A heat shield is then placed on the catalytic device thus formed

10. This allows the reaction and all activation energy to be kept at the lowest point of the tissue surface. The hollow bricks 11 are themselves placed on the tubes 12 of the reactor boiler, which are composed of refractory cement 13.

Performance

The use of the catalyst apparatus of the present invention allows, for the same reactor, to increase the surface area for contact between the catalyst and the reagents. That is, for all reagents, increased productivity and a minimal and substantially constant pressure drop, which allows for much longer production campaigns when this device resists reaction conditions, is not substantially susceptible to mechanical deformation.

The table below allows the technical data of a representative prior art system to be compared with the catalyst apparatus of the invention.

<td></td><td>State of the art: Flat system</td><td>Invention: Corrugated system</td>

<td>Coefficient a</td><td> 1,0</td><td> 1,4</td>

<td>Productivity: kg of HCN per tonne of air and kg of catalyst</td><td> 2,00</td><td> 2,16</td>

<td>Increase in pressure drop: % per month of initial pressure drop</td><td> 29</td><td> 5</td>

<td>Test duration: hours of production</td><td> 995</td><td> 3138</td>

PATENT CLAIMS