DK144996B - PROCEDURE FOR CARRYING OUT THE CATALYTIC EXOTHERMY GAS PHASE PROCESS AND PROCEDURE FOR THE PREPARATION OF A CATALYST - Google Patents

Description

1 144996 #

The present invention relates to a process for carrying out catalytic exothermic gas phase processes in a cooled reactor containing a bed of a porous particulate catalyst active for the desired reaction.

5 A wide range of gas-phase catalytic processes provide high heat generation and in many cases result in significant temperature increases. Examples of this are the catalytic conversion of alcohols by the so-called Mobile synthesis to hydrocarbons, of carbon oxides by methanisation to methane or by Fischer.

Tropsch synthesis for gasoline and / or define (processes accompanied by the so-called water gas reaction); further, ammonia synthesis, preparation of formaldehyde from methanol, natural gas or other hydrocarbons and preparation of sulfuric acid 5 "steam and sulfur trioxide from sulfur dioxide.

The high temperatures can cause a number of disadvantages. In many cases, they can cause damage or destruction of the catalyst, for example, by sintering the catalyst material or the catalyst's pore system. Frequently, undesirable side reactions can occur by producing hydrocarbons from carbon oxides or alcohols, thus decomposing into coal that can block and destroy the catalyst. In many cases, the higher temperatures can shift the reaction equilibrium and selectivity in the undesirable direction; Thus, at Fischer-Tropsch, high temperature syntheses favor methane formation at the expense of the desired products, e.g., ethane, ether or other olefins or gasoline.

Exothermic catalytic processes are often carried out in adiabatic reactors, and in such cases, in many cases, an attempt is made to limit the rise in temperature by diluting the reaction components, either with gases which are inactive under the reaction conditions or by recirculating product gas. Dilution with inert gases gives costs to the gases and separates them from the final product, and product gas recirculation results in energy losses in recirculation compressors.

In other cases, therefore, the exothermic processes have been carried out in refrigerated reactors, thereby avoiding dilution and use of recirculation compressors. The cooling medium is used, among other things. air, salt baths, mixtures of biphenyl and biphenyloxide, for example "Dowtherm", and in the aforementioned hydrocarbon formation reactions frequently boiling water. In refrigerated reactors, it is possible to achieve a low outlet temperature for the product gases and thus a favorable reaction equilibrium in cases where the desired product is favored by low temperature. However, it cannot be avoided in cooled catalyst bed reactors that shortly after the "ignition" of the reaction, ie. a short distance inside the catalyst bed is a hot zone, a so-called "hot spot", where the temperature will often be close to temperature thermodynamically determined by the adiabatic temperature rise. Only then is the reaction gas cooled, that is, further up in the catalyst bed. Accordingly, the same problems as mentioned above will arise with regard to catalyst stability, possibly selectivity, and in the case of hydrocarbon reactions, carbon formation.

10 The problems surrounding the hot spot temperature are in the lit. treated by van Welsenaere and Froment (Chemical Engineering Science, vol. 25, pp. 1503-1516, 1970), and it appears that hot spot is unavoidable in constant wall temperature tube reactors and that hot spot temperature is very sensitive to small variations in the process variables such as input temperature, reactant concentrations and wall temperature. Therefore, there is a risk that the temperature may rise in an uncontrollable manner so that the so-called "runaway" occurs. Welsenaere and Froment indicate how the reactions can be controlled under given conditions, for example, when carried out in a solid catalyst bed arranged in tubes surrounded by a refrigerant; a critical factor here is the pipe diameter. In this thesis, Welsenaere and Froment state results for the oxidation of p-xylene to phthalic anhydride at atmospheric pressure and with large excess air.

25 The calculations have been made for an irreversible first order reaction, but can also be transferred to non-first order reversible reactions without significant changes. Thus, for example, for the methanization reactions (1) CO + 3H2 <? = * CH4 + H2O + 49 kcal / mol, 30 (2) 2CO + 2H2 f = ^ CH4 + CO2 + 59 kcal / mol and (3) CO2 + 4H2i = ^ CH4 + 2H20 + 39 kcal / mol that the diameter of the catalyst tubes cannot exceed a few millimeters if full safety against runaway is required in all conditions. Such a small pipe diameter is unusable in 35 industrial operations. The major difference between Welsenaere and Froment's example and the methanization reactions appears to be the high pressure and the high molar concentration at the latter and the resulting large heat production per unit volume. volume unit catalyst. Similar conditions apply to other hydrocarbon-forming reactions, such as the Fischer-Tropsch 5 synthesis to form gasoline and / or olefins:

(4) nCO + 2nH2 f - (CH2) n + H2O + ca. 40 kcal / g atom C

or the so-called Mobile synthesis to form hydrocarbons from alcohols, e.g.

(5) nCH-, ΟΗ - (CHO) + nH-O + ca. 12 kcal / g atom C

Thus, it is not possible, without special precautions, to prevent the temperature from rising to or to a value close to that determined by such adiabatic temperature rise for such reactions. Welsenaere and Froment propose to dilute the catalyst charge in the catalyst bed, for example with catalytically inert filler bodies, thereby producing the amount of heat produced per minute. reactor volume is reduced. However, it turns out that a relatively strong dilution of the catalyst is required, which requires an increase in the catalyst volume itself to "turn on" the reaction. Thus, the method has the disadvantage of assuming an enlargement of the reactor and thus an increase in the cost of capital; what will often be more significant is the dilution having the disadvantage of reducing the catalyst filling resistance or the adsorption capacity of catalyst poisons entailed in the reaction stream. Therefore, such a dilution of the catalyst is not a satisfactory solution to the temperature control problems of chilled exothermic catalytic processes.

To further study the conditions, experiments were carried out in an air-cooled methanization reactor with a catalyst 30 with the designation MCR-2X. It is a microporous temperature stable, mechanically strong catalyst with nickel crystal liters of the same order of magnitude as the pore diameter, on a γ-alumina support (see Karsten Pedersen, Allan Skov and J.R. Rostrup-Nielsen, ACS Symposium, Houston, March 1980).

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The catalyst was used in the form of cylinders with a height and diameter of 4.3 mm. In some of the experiments, the catalyst was diluted with catalytically inactive cylinders of the same geometric design. The pressure in the reactor was maintained at 26 kg / cm and a feed gas having the composition was 70% Hg, 9% CO, 10% CO 2 and 11% CH 2. These test conditions will give thermodynamically determined adiabatic temperature increases of between 380 and 400 ° C, regardless of the dilution rate of the catalyst.

It was found that without dilution of catalyst 10, it was not possible to limit the temperature rise, thus being stated at 380-400 ° C. At dilution ratios of 1: 3 and 1: 5 (ie 3 and 5 times the volume of inert cylinders as catalyst bodies, respectively), actual temperature increases that were up to 50 ° C were lower than the expected adiabatic temperature increases of 380-400 ° C. . In these experiments, the pipe wall temperature in the hot spot area was approx. 600 ° C or more, which in industrial operation will be an unrealistically high pipe wall temperature; in an industrially cooled reactor, the highest pipe wall temperature will not exceed 400 ° C. The resulting limitation of the temperature rise must be said to be substantial, although it is of no great practical industrial importance in itself, and although catalyst dilution in this way is, for the reasons stated above, not very appropriate.

However, a closer analysis of the decreased temperature rise 25 showed that the reduced temperature rise was due to the reaction rate not having increased as strongly as would be expected according to the reaction kinetics, and surprisingly, this decreased reaction rate was due to the calculated reaction rate at high temperature 30 exceeding the rate of reaction. diffusing the reactants through the gas film surrounding the catalyst particles. Since the gas phase diffusion is almost independent of the temperature (activation energy 1-2 kcal / mol), the reaction rate encountered a barrier due to the absence of reactants 35 at the actual reaction sites, the interior of the catalyst bodies, and therefore the reaction is prevented from running.

It is the object of the invention to utilize this surprising observation to indicate how one can generally prevent U4996 runaway in catalyzed exothermic gas phase reactions in cooled reactors. This is achieved according to the invention by using a catalyst whose individual particles have a zone of reduced catalytic activity for the reaction.

Thus, according to the invention, the outermost portion of each catalyst particle may comprise a zone inactive for the reaction; or it may be a zone of reduced activity for that highly exothermic reaction. In cases where at the same time a highly exothermic main reaction occurs and one or more side reactions (which may be less exothermic, or even thermally neutral or endothermic), the outer layer may optionally be catalytically active for the side reaction, but not for the main reaction; By way of example, the reactions (1), (2) and (4) catalyzed by 15 nickel are accompanied by the water gas reaction, also referred to as the shift reaction: (6) CO + H2 O v - '- =?> CO 2 + H2 + 10 kcal / mol catalyzed by, inter alia, copper.

Whether catalytically inert, or catalytically active for a side reaction but inactive for the main reaction, the above film diffusion is extended to include diffusion through the inert outer layer of the catalyst.

Therefore, it becomes possible to determine the maximum reaction rate in the reactor since it is determined by the thickness of the inert layer. In practice, the thickness of the inert reaction layer will be one to a few orders of magnitude greater than the thickness of the surrounding gas film; the thickness of this gas film can be estimated from approx. 1 μ under normal industrial conditions; According to the invention, the said outer zone of the catalyst particles may therefore suitably have a thickness of 0.01-2 mm. Thicknesses of said layers of over approx. In practice, 0.5 or 1 mm will only be used when using relatively large catalyst particles.

In general, the explanation of the invention as defined is that a given catalyst body with homogeneous activity and homogeneous pore system subjected to a given mixture of reactants is subjected to various reaction restrictions as the reaction temperature changes (increases).

At low temperature, the reaction rate of the catalyst material is limited. The reaction is here in the so-called intrinsic state, where there is almost no concentration gradient of the reaction participants through the pore system of the catalyst body. As the temperature rises, the catalyst activity increases, causing the reactants to increase in gradient through the catalyst bodies. At a time point, a temperature range is reached where the diffusion of the reactants through the catalyst bodies becomes the limiting parameter of the reaction rate; this means that not all the catalyst material is used in the reaction; the efficiency factor becomes <1.

If the temperature is further increased, the parameter determining the rate of reaction will be the rate at which the reactants are transported through the gas film surrounding the catalyst bodies. Under normal conditions, this speed is too large for the reactor's cooling surface to limit the hot spot temperature to a level substantially below that of the adiaba. tical temperature rise, which in many cases means that thermal sintering cannot be avoided or, for some methanation reactions, that coal formation cannot be averted.

However, in the invention, a restrictive surface is incorporated into the individual catalyst bodies by increasing the gas film or in some way reducing the permeability of the reactants, thereby limiting the reaction rate and, consequently, the rise in temperature.

30 One might expect that incorporation of such an inert layer, "delay layer", will cause difficulty initiating or "igniting" the exoteric reactions. However, this does not happen because the reaction rate in the ignition zone is in any case low, so the gas diffusion through the inert layer will not be limiting (determining) the reaction rate. This layer first becomes a limiting factor, ie. in fact, it only begins to work when the reaction rate becomes so large that you want it to slow down.

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Since the inert layer forms only a small part of the catalyst pellet, the catalyst's resistance to poisoning is maintained.

In this connection, it may be mentioned that the outer layer of the catalyst pellets in question can exceed 50% of their volume; but usually the proportion will be substantially smaller, so for cylindrical catalyst bodies having a height and diameter of 4.2 mm typically 1-10%, especially 2-10% and frequently 2-5% of the volume.

The reactor can be any type of cooled reactor for exothermic reactions, for example a tube reactor or a reactor with a larger space of any shape, through which cooling pipes flow into which a refrigerant flows. The catalyst bed will most often be a so-called fixed bed, but the invention can also be utilized in connection with catalysts in fluid bed.

As mentioned, the outer layer must have decreased catalytic activity, and although it will often be appropriate to use a catalyst whose individual particles have a highly inactive zone (or main reaction) for the desired reaction (or main reaction), it may be appropriate to use in some cases. a catalyst in which this outer zone has only one activity which is impaired for the reaction (or the main reaction).

The outer zone can be produced in a variety of ways, often in analogy with the prior art of the pharmaceutical industry, where tablets are made with multiple layers of different composition or different concentration of active substance.

Thus, one can first produce normal catalyst bodies consisting of a porous support with the catalytically active material. They can be prepared by known techniques, for example by coalescing or by first preparing porous support bodies which are then impregnated with the catalytically active material. The catalyst thus produced is then dipped into a gel or sol of inert carrier material, of the same kind as the catalyst carrier or other species itself. If the outer layer is not to be catalytically completely inert but has limited catalytic activity, it can then be impregnated, but ensure that the concentration of catalytically active material U4996 9 is lower than in the inner layer. Alternating impregnations, leaches and chemical treatments can be combined to achieve the desired structure and combination of structures. On a finished catalyst, for example, by electrolysis or precipitation from the vapor phase, one can apply an inert layer or even a catalytically active layer which partially clogs the pore openings, thereby reducing the catalyst activity in the outer layer and the rate of diffusion to the interior of the catalyst. A particular structure can be obtained by tableting a mixture of divided catalyst particles with an inert carrier material. In this way, the diffusion effect is combined with a dilution of the catalyst, which can significantly reduce the dilution rate.

Practical embodiments of these methods and combinations thereof will be apparent to those skilled in the art.

As mentioned, the stated principle can be utilized not only in the case of a single exothermic reaction, but also in cases where a catalytic exothermic main reaction and one or more catalytic side reactions take place simultaneously in the same reactor. In that case, according to the invention, a catalyst active for the main reaction 20 can be used whose individual particles have a zone of material which is at least partially inactive with respect to the main reaction, but catalytically active for one or more side reactions.

A practical embodiment of such a catalyst, or the whole of catalysts designed according to the principles of the invention, is a catalyst consisting of particles of a porous support which is catalytically inactive for the desired reaction or main reaction (but optionally catalytically active for a side reaction). ), and zone of the pore system contains a catalytically active material for the desired reaction or main reaction in such a way that the pores in the outer zone of the carrier particles are free of the catalytically active material for the reactions or the main reaction. For example, the pores content of catalytically active material may be provided by co-precipitation, by electrolysis, by precipitation from the vapor phase or by impregnation from the liquid phase. The design may also be as claimed in claim 6.

The catalyst may further be configured as claimed in claim 7.

U4996 ίο

Catalysts designed according to the principles described can be used with particular advantage for hydrocarbon reactions such as those shown above, especially methanation reactions. The catalyst can hereby consist of a known support material, for example γ-alumina, magnesium aluminum spinel, silicic anhydride, zirconia, titanium dioxide or combinations of two or more of these materials, together with catalytically active nickel, having a zone without nickel or with decreased nickel concentration. Hereby the desired scale effect 10 is obtained immediately.

However, the principle can be utilized in an even more elegant way; As mentioned above, reactions (1), (2) and (4) are accompanied by the water gas reaction (6). Reactions (1) - (4) and also the water gas reaction are catalyzed by nickel, while the water gas reaction is also catalyzed by e.g. copper. It is advantageous to have methanization reactions accompanied by the water gas or shift reaction in such a way that the partial pressure of carbon monoxide is reduced before it comes into excessive contact with the catalyst nickel, since CO is to some extent a catalyst poison for 20 nickel and the poisoning can be reduced. by reducing the C0 partial pressure. It is noted that it is nickel metal and copper metal that catalyze the reactions, but that the catalyst metal is applied in the form of a compound, often a nitrate or hydroxide which is later oxidized, for example by calcination, and finally reduced to the free metal, often at the beginning of the reaction. the desired reaction by hydrogen present among the reaction participants; these conditions are disregarded in the following, and the description will only operate with the free metals.

It is known that copper and nickel alloys over a certain copper content exhibit very little activity for methanization (see M. Araki and V. Ponec, J. Catalysis 44, 439 (1976)); it is further elucidated in the above Example 1. The Ni / Cu catalyst, on the other hand, still has activity for converting carbon monoxide to carbon dioxide in the aqueous gas reaction (6). This can now be utilized in connection with the present invention in that a nickel catalyst having a shell of nickel-copper alloy is prepared. This is achieved partly by slowing down the highly heat-generating methanization reaction, but also reducing the partial pressure of the carbon monoxide at the aqueous gas reacton, thereby protecting the nickel-containing catalyst core from the so-called β deactivation (see the aforementioned treatise by Karsten Pedersen, Allan Skrup and JR -sympo-Sium). Upon β-deactivation, adsorbed carbon monoxide is slowly converted to low reactivity coal deposits which deactivate the catalyst, but this is avoided when the invention proceeds according to claim 8.

The outer copper-containing catalyst film can be formed in various ways. For example, first, in known manner, for example, by impregnation or co-precipitation, particles of a nickel catalyst can be prepared and then dipped the particles in water or other liquid and then in an impregnating liquid containing a copper compound, for example copper nitrate or copper hydroxide.

Another method consists of precipitating copper hydroxide from copper nitrate into the outer portions of the pore system of the catalyst 20. It is advantageous in this process if the carrier material is basic, for example, contains free magnesium oxide.

This can be achieved, for example, by using a magnesium-aluminum spinel support burned at such a temperature (approx.

1100 ° C) that unreacted magnesium oxide still has some reactivity. Also, the pore system can first be filled with slurried magnesium oxide or another base such as calcium oxide or solutions of an alkali metal hydroxide. Copper hydroxide will be precipitated in the outer part of the pore system according to the reaction 30 (7) Cu (NO3) 2 + MgO + H2O- »Cu (OH) 2 + Mg (NO3) 2 ·

The described method can be used with nickel catalysts where the nickel has been evenly distributed in other ways, as mentioned for example co-precipitation, impregnation with nickel nitrate without the presence of MgO or other alkaline compounds in the pore system. If the catalyst support contains free magnesium oxide or other alkaline compounds, nickel may be applied before or after copper by impregnation with nickel hexamine formate, which itself is alkaline but does not cause the precipitation of nickel upon contact with basic substances.

In this way, it is possible to regulate the ratio of nickel to copper in the outer zone of the catalyst and at the same time achieve an even distribution of the nickel content.

The invention also relates to a process for producing the catalyst as claimed in claim 8, which is characterized by the characterizing part of claim 9.

The reaction rate of methanization and thus the reaction temperature can be controlled by similar principles using a vanadium- or molybdenum-based catalyst in sulfur-containing atmosphere as described in Danish Patent Application No. 5396/79 of December 18, 1979.

It may be particularly valuable to utilize the principle 15 of the present invention in connection with the process of producing a gas mixture of high content of C2 hydrocarbons as described in Danish Patent Application No. 5395/79 by reacting a feed gas mixture containing hydrogen and carbon oxides. by means of a catalyst containing molybdenum and / or vanadium and iron and / or nickel in the presence of gaseous sulfur compounds. This is a Fischer-Tropsch synthesis and there is a great deal of emphasis on keeping the temperature relatively low because higher temperature will shift the equilibrium towards 25 methane formation. Therefore, in accordance with the present invention, the catalyst bodies may be provided with a shell of inert carrier or a shell containing copper for the synthesis of the concurrent water-gas reaction.

The process according to the invention will be explained in more detail by some examples.

Example 1 A. A series of catalysts were prepared by precipitation of sodium silicate and varying amounts of copper and nickel nitrate with sodium hydrogen carbonate.

The precipitate was formed into particles leached for sodium compounds, dried at 120 ° C, calcined at 500 ° C and reduced in hydrogen at 500 ° C. The methanization activity was measured at 1 atm and 250 ° C by passing a 40 gas of 1% CO in an amount of 100 Nl / h over the catalyst in the form of irregular bodies having a size of 0.3-0.5 mm (measured by sieve-mesh width). The following results were obtained:

Catalyst Weight% Atomic ratio Activity, 5 No. Ni Cu Ni / Cu + Ni 10 ~ 3 mol / g / h 1 68.5 0 1.0 93.75 2 54.2 14.6 0.8 22.32 3 40 , 2 29.0 0.6 8.93 4 26.5 43.0 0.4 3.57 10 5 13.1 56.7 0.2 0.89 6 0 70.1 0 0

It is seen that even a small amount of copper drastically reduces the mechanization activity.

B. 3 catalysts were prepared by a carrier of - 2 15 γ-alumina having an inner surface area of about 2 40 m / g were impregnated in solutions of copper nitrate, nickel nitrate and a mixture of nickel nitrate and copper nitrate, respectively. The impregnated carriers were calcined at 550 ° C and reduced in hydrogen at 720 ° C. The catalysts are tested in a reactor at a pressure of 1 atm with 53.5 Nl / h gas consisting of 61.8 volume% >2> 18.2 volume% H 2 O and 20.0 volume% CO, over 0.2 g catalyst as 0.3-0.5 mm particles. Hereby, the following rates of carbon oxide conversion (the water gas reaction, the shift reaction) and the methanation were measured: reaction rate at 375 ° C 3 mol / g / h shift methanization

Cu 1.05 0 30 Ni, Cu 73 5.2

Ni +) - 43

Ni ++ 1431 1608 +) measured at 311 ° C as reactor temperature could not be controlled at 375 ° C.

35 ++) measured on the catalyst MCR-2X mentioned above.

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It is seen that the Ni, Cu catalyst has good activity for the water-gas reaction, while none of the Cu-containing catalysts has significant activity for methanization.

Example 2 A carrier consisting of magnesium oxide with a smaller content of alumina (ratio Mg / Al 7: 1) is impregnated in the form of cylinders of height and diameter 4.5 mm with a saturated aqueous solution of copper nitrate. The impregnated support was calcined at 550 ° C.

By breaking the particles, it was clearly seen that copper 10 had accumulated like a thin black shell on the outside of the support. Microscopic examination showed that the layer had a thickness of approx. 50 µ.

The copper impregnated support was impregnated with a saturated aqueous solution of nickel hexamine formate prepared by dissolving 23 g of nickel formate in 50 ml of concentrated ammonia water. The impregnated catalyst was calcined at 300 ° C.

In breaking the particles, even staining and consequent distribution of nickel was observed. By analysis, 0.6% by weight was found

Cu and 2.7% by weight Ni.

A similar catalyst is prepared by impregnating first in nickel hexamine formate and then copper nitrate. The copper shell was seen as dark staining of the outer zone of the particles. This catalyst is referred to as Catalyst A, and as a reference, a copper-free methanization catalyst, designated Catalyst B, is prepared by impregnating the support in nickel hexamine formate.

Example 3

A methanization catalyst containing approx. 25% by weight of nickel on a stabilized alumina support was impregnated in the form of 4.2 x 4.2 mm cylinders in an alumina gel prepared by slurrying 11 g of alumina in 180 ml of water and gelled with 5.6 ml of concentrated nitric acid. . The impregnated catalyst was calcined at 550 ° C.

A similar preparation was made with the difference that 1Q ml of the alumina gel was previously mixed with a solution of copper nitrate. The impregnated and calcined catalyst showed an outer shell containing copper, by microscopic examination estimated at a thickness of approx.

0.5 mm. Smaller amounts of copper nitrate had penetrated into the catalyst interior, but the ratio of copper content in the outer zone to the interior could be estimated at approx. 3: 1. This catalyst is designated C.

Example 4

This experiment shows how a coating on a catalyst applied by a gel can limit the reaction rate at high temperature.

A nickel methanization catalyst in the form of 4.2 x 4.2 mm cylinders was coated with an alumina gel and then dried. Then, the catalyst was reduced in pure hydrogen at 800 ° C for 2 hours. This catalyst is called D.

A catalyst without such a coating was activated (reduced) in the same way. It is designated E and is identical to the aforementioned catalyst MCR-2X.

Example 5

This example shows testing of the catalysts A-E referred to in Examples 20 2-4.

The catalyst pellet being tested was clamped between two thermocouples in a 6 mm internal diameter reactor. It was then heated in pure hydrogen to ca. 300 ° C to remove any traces of nickel oxide.

The hydrogen supply was then stopped and the system was fed with a synthesis gas of 9% CO in Hg at a rate of approx.

100 Nl / h throughout the experiment. At about. At 300 ° C, the product gas stream was analyzed on a gas chromatograph and the amount of methane produced was determined. The temperature was then raised stepwise and the rate of methanization determined each time.

The following table shows that inactive outer layer catalysts applied with the gel have limited high temperature reaction rate compared to the homogeneous reference catalyst.

X

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Table 3

Catalyst Test Temp. Methanization Action Millimol / g / h A 300 1.4

Al 2 O 3, Mg0 support 360 4 5 impregnated with 417 6 copper nitrate and 518 12 nickel hexamine formate 603 11 678 12 B 346 18 10 Al 2 O 3.Mg0 support 389 60 impregnated with 482 180 nickel hexamine formate 577 250 715 240 C 330 55 15 Ni0.Al202 catalyst with Al2 O3 570 130 741 95 D 243 3.5

Ni0.Al203 catalyst 295 30 20 coated with a shell 336 50 containing copper oxide 440 65 and A1203 597 60 E 274 80

NiO.Al 2 O 3 catalyst 323 180 25 (aforementioned known catalyst 379 250 catalyst MCR-2X without 438 270 restrictions) 508 315 569 310

The reason why the catalysts B and E have maximum activity in the temperature range considered is the thickness of the gas film during the test, where the gas velocities have been substantially lower than in industrial operation; under normal industrial operation with the higher gas velocities, the gas film would become thinner and thus slow down the diffusion. The mass transition number for the gas film o is estimated at approx. 7 kmol / h / m, where under industrial conditions it will be about 100 kmol / h / m. This means that the difference in high temperature activity with and without shell will be greater than that shown in Table 3.

Claims (6)

144996 A process for carrying out catalytic exothermic gas phase processes in a cooled reactor containing a bed of a porous, particulate catalyst which is active for the desired reaction, characterized in that a catalyst is used whose individual particles have an extremely catalytically reduced reaction zone. activity. Process according to claim 1, characterized in that a catalyst is used whose individual particles 10 have a highly inert reaction zone for the reaction. Process according to claim 1 or 2, characterized in that said outer zone of said catalyst particles has a thickness of 0.01-2 mm. A process according to any one of the preceding claims, wherein a catalytic exothermic main reaction and one or more catalytic side reactions take place substantially simultaneously in the same reactor containing a bed of a reaction active particulate catalyst characterized by a catalyst whose single particles have a zone of material which is at least partially inactive with respect to the main reaction and catalytically active for one or more side reactions. Process according to any one of the preceding claims, characterized in that a catalyst is used which consists of particles of a porous support which is catalytically inactive for the desired reaction or main reaction and which contains in part of the pore system a the desired reaction or main reaction catalytically active material, in such a way that the pores in the outer zone of the carrier particles are free of that of the desired reaction or main reaction catalytically active material. Process according to any one of claims 1-3, characterized in that a catalyst consisting of particles of a porous, inert carrier material is used which contains in a part of the pore system a catalytically active material for the desired reaction. such that the pores in the outer zone of the support are partially blocked by catalysts.