Catalyst for the production of aromatic amines having a defined fine fraction

Abstract

A catalyst suitable for the hydrogenation of aromatic nitro compounds to the corresponding aromatic amines containing copper and optionally one or more additional metals on a carrier material, the catalyst having a particle size distribution in the range of from 10 to 1000 µm, wherein the fine fraction of particles with particle sizes ≤ 45 µm is from 10 to 20 % by weight, the d50 value of the particle size distribution is from 80 to 180 µm.

Description

[0001] Catalyst for the production of aromatic amines having a defined fine fraction

[0002] Description

[0003] The invention relates to a catalyst that is suitable for the production of aromatic amines from the corresponding aromatic nitro compounds, to a process for producing aromatic amines using this catalyst, and to the use of the catalyst for producing aromatic amines.

[0004] Catalysts suitable for the production of aromatic amines, for example aniline, through hydrogenation of the parent nitro compounds, and processes for the production thereof, are known.

[0005] CN-A 1 657 162 relates for example to a fluidized-bed catalyst for producing aniline through hydrogenation of nitrobenzene. The catalyst comprises silica (SiOz) as support material and also copper, chromium, molybdenum, and a further metal selected from nickel, zinc, barium, vanadium, bismuth, lead or palladium.

[0006] A process for producing aromatic amines such as aniline through hydrogenation of the corresponding nitroaromatics with hydrogen on immobilized catalysts under adiabatic conditions is described in EP-A 1 882 681 . All catalysts that can be used for the gas-phase hydrogenation of nitro compounds are in principle suitable as catalysts. The metal component of the catalysts may be present either in the form of an alloy or as a mixed oxide and the catalyst may optionally be produced using an inert support material. Examples of suitable support materials are alumina (a- and y-modification), silica (SiOz), titanium dioxide (TiOz), red earth, water glass or graphite. The metals used are preferably Pd, Te, V, Nb, Ta, Cr, Mo, W, Pb or Bi.

[0007] The reaction of aromatic nitro compounds R-(NOz)n(I) with hydrogen on a catalyst usually leads to the corresponding aromatic amines R-(NHz)n(II).

[0008] In addition to the fixed-bed process, a highly suitable process variant for the hydrogenation of aromatic nitro compounds, for example nitrobenzene, to aromatic amines, for example aniline, on solid catalysts is the so-called fluidized-bed process described for example in Ullmann's Encyclopedia of Industrial Chemistry vol. 15, pp. 319-366 and in particular for the production of aniline in DE 1114820 B. Here the particulate supported catalyst forms a fluidized bed.

[0009] Process requirements for such a solid catalyst, especially for a fluidized-bed catalyst, include for example good fluidity in order that a stable fluidized bed can be formed, good mechanical stability, and good thermal conductivity of the solid catalyst in order to dissipate the relatively high heat of reaction of the hydrogenation reaction from the solid catalyst to the cooling devices of the reaction vessel, for example heat exchangers. The property profile of catalysts of the prior art suitable for the hydrogenation of aromatic nitro compounds to aromatic amines is still in need of further improvement, particularly as regards heat transfer to a cooling device, for example a heat exchanger.

[0010] The object is solved by a catalyst suitable for the hydrogenation of aromatic nitro compounds to the corresponding aromatic amines containing copper and optionally one or more additional metals on a carrier material, the catalyst having a particle size distribution in the range of from 10 to 1000 pm, wherein the fine fraction of particles with particle sizes < 45 pm is from 10 to 25 % by weight, based on the total weight of the catalyst, the d50 value of the particle size distribution is from 80 to 180 pm.

[0011] In general, the d90 value of the particle size distribution is from 300 to 1000 pm.

[0012] Preferably, the fine fraction of particles with particle sizes < 45 pm is from 15 to 20 % by weight, based on the total weight of the catalyst. The particle size distribution is determined according to ISO13320.

[0013] Preferably, the d50 value of the particle size distribution is from 100 to 130 pm.

[0014] The d50 and d90 values are given for the mass-related particle size distribution. The d50 value is the mass-based median (50%) particle size. The d90 value is the mass-based 90% particle size.

[0015] The d50 and the d90 values are determined by laser diffraction according to ISO13320.

[0016] The desired amount of fine fraction and the desired d50 and d90 values of the particle size distribution of the final catalyst can be adjusted by milling and / or by sieving steps in the preparation process of the catalyst.

[0017] Aromatic nitro compounds in the context of the present invention are those of the general formula R-(NO2)n (I).

[0018] Aromatic amines in the context of the present invention are those of the general formula R- (NH2)n (II).

[0019] In formulas (I) and (II), R and n are defined as follows:

[0020] R is a substituted or unsubstituted aromatic Ce to C radical, for example such unsubstituted radicals are phenyl or naphthyl, very particularly preferably phenyl. Optionally, the aromatic Ce to C radical, preferably the phenyl radical, may contain at least one additional substituent, for example an alkyl group such as methyl, ethyl, propyl or higher-chain alkyl substituents and / or one or more halogen substituents such as fluorine, chlorine, bromine, and iodine and / or alkyl or aryl groups substituted with heteroatoms such as N, O, S or halogen. When there are two substituents on the phenyl radical, including -NO2 or -NH2 -groups, these substituents may be in the ortho (1 ,2), meta (1 ,3) or para (1 ,4) -position relative to one another; when there are three substituents on the phenyl ring, including -NO2 or -NH2 -groups, these substituents may be in the (1 ,2,4)-, (1 ,2,5)-, (1 ,2,6)-, (1 ,3,5)-, (1 ,3,4)- or (1 ,3,6)-position relative to one another. n is an integer from 1 to 5, preferably 1 or 2.

[0021] Examples of aromatic nitro compounds (I) in the context of the present invention are mononitrobenzene (nitrobenzene), ortho-, meta- or para-dinitrobenzene, ortho-, meta- or para-mononitro- toluene, dinitrotoluene in all its isomeric forms, including by way of example those listed above for three substituents on the phenyl ring, trinitrotoluene in all its isomeric forms, preference being given to 2,4,5-trinitrotoluene and particular preference to mononitrobenzene (nitrobenzene).

[0022] The inventive catalytic hydrogenation of aromatic nitro compounds of the formula (I) leads to the corresponding aromatic amines (II), for example mononitrobenzene to monoaminobenzene, the latter also known as aniline.

[0023] Examples of aromatic amines (II) in the context of the present invention are the amines corresponding to the aromatic nitro compounds (I) mentioned above by way of example, preferably monoaminobenzene (aniline), ortho-, meta- or para-diaminobenzene, ortho-, meta- or paramonoaminotoluene, diaminotoluene (toluylene diamine) in all its isomeric forms, triaminotoluene in all its isomeric forms, preference being given to 2,4,5-triaminotoluene and particular preference to aniline (monoaminobenzene).

[0024] The catalyst of the invention comprises a support material selected from the group consisting of porous silica (SiC>2), gamma-, delta- or theta-alumina (AI2O3), titanium dioxide, zirconium dioxide, and graphite. The support material is usually porous and capable of being impregnated. The support material preferably comprises silica.

[0025] The support of the copper catalyst preferably comprises more than 95% by weight, especially more than 98% by weight of S iC>2 , based on the support as such without taking account of the catalytically active metal components.

[0026] Copper is the catalytically active metal in the catalyst of the invention, usually after calcining, generally present in non-elemental form, for example as an oxide or carbonate or hydroxide. These compounds are however usually reduced during the hydrogenation, that is to say in the presence of hydrogen. The content of copper, calculated in elemental form, as active agent for the hydrogenation reaction based on the total mass of the catalyst system of the invention is usually within a range from 5% to 30% by weight, preferably 10% to 25% by weight. Copper may be present in any oxidation state, for example in oxidation state +l and / or +II (e.g. for copper in the form of copper oxides); oxidation state 0 (e.g. metallic copper) is also possible. The catalyst of the invention optionally comprises one or more further metals, also referred to herein as “dopants”, as the pure element or in the form of a compound, for example as an oxide. The further metal is selected from the group consisting of at least one metal selected from main group I, main group II, main group IV, and subgroups II, V, VI, and VIII of the periodic table of the elements, preferably at least one metal selected from the group consisting of potassium (K), sodium (Na), barium (Ba), lead (Pb), zinc (Zn), vanadium (V), chromium (Cr), molybdenum (Mo), tungsten (W), and iron (Fe).

[0027] The further metals may be present in any oxidation state, for example in oxidation state 0 as elemental metals and / or for example in oxidation states +l to +VI, for example in the form of oxides or halides or oxohalides and the like.

[0028] The further metals may be present in the catalyst of the invention in any concentration, but the cumulative weight of the further metals is preferably less than the weight of copper.

[0029] The process for producing the catalyst system of the invention is executed such that a support material comprising a component selected from the group consisting of silica, gamma-, delta- or theta-alumina AI2O3, titanium dioxide, zirconium dioxide and graphite, preferably silica, is produced and this support material, preferably silica, is contacted with copper, usually in the form of chemical compounds thereof such as salts in complexed and / or uncomplexed form, for example carbonates, oxides, hydroxides, nitrates, nitrites, and halides such as fluoride, chloride, bromide, and iodide, and optionally with one or more further metals selected from the group consisting of at least one metal selected from main group I, main group II, main group IV and subgroups II, V, VI, and VIII of the periodic table of the elements, usually in the form of chemical compounds thereof such as salts in complexed and / or uncomplexed form, for example carbonates, oxides, hydroxides, nitrates, nitrites, and halides such as fluoride, chloride, bromide, and iodide.

[0030] The desired amount of fine fraction and the desired d50 and d90 values of the particle size distribution of the final catalyst are adjusted by suitable milling and / or by sieving steps in the preparation of the catalyst.

[0031] The invention also concerns a process for improving the performance of a catalyst suitable for the hydrogenation of aromatic nitro compounds to the corresponding aromatic amines with regard to run time and / or heat transfer coefficient, wherein the catalyst contains copper and optionally one or more additional metals on a carrier material, and the catalyst has a particle size distribution in the range of from 10 to 1000 pm, comprising the step of adjusting the particle size distribution of the catalyst such that the fine fraction of particles with particle sizes < 45 pm is from 10 to 20 % by weight, and the d50 value of the particle size distribution is from 80 to 180 pm.

[0032] Preferably, the fine fraction of particles with particle sizes < 45 pm is adjusted to be from 15 to 20 % by weight. Preferably, the d50 value of the particle size distribution is adjusted to be from 100 to 130 m.

[0033] The particle size distribution of the catalyst is in general adjusted by milling and / or sieving steps in the preparation of the catalyst.

[0034] A preferred process for producing the support material is spray-drying, wherein in a preferred embodiment the support material essentially consists of silica, i.e. it comprises more than 95% by weight, especially more than 98% by weight, of SiO2, based on the support as such without taking account of the catalytically active metal components.

[0035] The silica of the invention that is used is known in principle and may be produced for example as described in DE 102004 006 104 A or purchased as a commercial product under the name D11-20 Hydrogel (BASF SE).

[0036] In a highly suitable process, the silica of the invention is produced by the sol-gel process, which is known in principle to those skilled in the art. For example, sodium silicate, e.g. Na2SiO3, can here be reacted with acid, for example sulfuric acid. This generally gives a hydrogel (silica hydrogel) that can be treated further, for example washed with aqueous ammonia solution and / or with water containing dissolved carbon dioxide. The hydrogel material thereby obtained is usually coarse-grained and is generally then fed into a comminution process, in particular a milling process, for example in order to achieve a certain particle size.

[0037] In the context of the present invention, wet milling to a finely particulate hydrogel is particularly preferred for comminution of the hydrogel material, but the hydrogel material may also be comminuted by dry milling. It is possible to add an aqueous alkali metal hydroxide solution during or after wet milling of the hydrogel material, for example in order to increase the abrasion resistance of the finely particulate hydrogel obtained, as described in more detail in WO 2010 / 130604. Wet milling for example takes place in a pin mill or impact-plate mill, in particular a stirred ball mill. For spray-drying, the hydrogel material to be comminuted is usually added to a liquid. This mixture generally has a solids content of 10% to 15% by weight and a pH of 5 to 10.

[0038] A suspension of the finely particulate hydrogel described above, is then usually spray-dried to obtain the support material. The suspending agent is for example water, organic solvents or mixtures of water and organic solvents such as lower alcohols, and is preferably water.

[0039] The method of spray-drying is known in principle to those skilled in the art. It is customary to do this in a spray tower into which the suspension to be dried (also referred to as the “slurry” or “spray slurry”) is sprayed, usually with nozzles. Typical conditions for this are: Temperature in the spray tower inlet within a range from 250 to 350° C, temperature in the spray tower outlet within a range from 100 to 140° C, nozzle pressure within a range from 1 .5 to 2 bar. The support produced from silica during spray-drying of the finely particulate hydrogel described above preferably has a BET surface area, measured using the DIN 66131 method, of 400 to 620 m2 / g.

[0040] The supporting of copper and optionally the one or more further metals on the support material is usually carried out by impregnating the support material using the processes known to those skilled in the art for heterogeneous catalysts.

[0041] This is preferably done by applying an aqueous solution or suspension comprising copper and optionally at least one further metal selected from the group consisting of at least one metal selected from main group I, main group II, main group IV, and subgroups II, V, VI, and VIII of the periodic table of the elements, preferably at least one further metal selected from the group consisting of potassium (K), sodium (Na), barium (Ba), lead (Pb), zinc (Zn), vanadium (V), chromium (Cr), molybdenum (Mo), tungsten (W), and iron (Fe), to the formed support, preferably comprising silica, by means of the impregnation process.

[0042] Copper, and the optionally further metals may be added for example in the form of carbonate solutions, in particular ammoniacal carbonate solutions, or nitrate solutions. The addition may be carried out a little at a time for each metal component or else in a single step.

[0043] The catalyst obtained by impregnation is then dried in the usual manner and calcined in the usual manner, for example in air within a temperature range from 150 to 550° C. Impregnation, drying, and calcination processes are known to those skilled in the art.

[0044] The copper-containing catalyst of the invention has improved heat transfer properties expressed by the k value, which is within a range of from 500 to 1100 W / m2K, preferably within a range of from 700 to 1000 W / m2K.

[0045] The k value is determined using the method as described in the examples and here indicates how much heat the catalyst system of the invention is able to transfer per heat exchanger surface and per Kelvin difference in temperature. The higher the k value, the more heat the fluidized catalyst system is able to release, for example to a heat exchanger, or absorb.

[0046] The catalysts of the invention in general belong to "Geldart type A", regarding their fluidization behavior. For this group the particle size is between 20 and 300 pm, and the particle density is typically less than 1 .5 g / cm3. Prior to the initiation of a bubbling bed phase, beds from these particles will expand by a factor of 1 .2 to 3 at incipient fluidization with a corresponding decreased bulk density.

[0047] The process for producing aromatic amines (II) through catalytic hydrogenation of the parent aromatic nitro compounds (I) is described in more detail below. The process of the invention uses as starting materials the aromatic nitro compounds (I) corresponding to the aromatic amines (II). This means that the process of the invention replaces the nitro groups (-NO2) present in the starting materials by the corresponding amino groups (-NH2). In the process of the invention, it is accordingly possible to use the corresponding aromatic nitro compounds (I) containing at least one nitro substituent, with the preferred or exemplary compounds mentioned above in the definition of the aromatic nitro compounds (I) and aromatic amines (II) also explicitly included here. Particularly preferred starting materials are mononitrobenzene (nitrobenzene), nitrotoluene (o-, m- or p-nitrotoluene) or dinitrotoluene in all its isomeric forms. Very particular preference is given to using mononitrobenzene (nitrobenzene) and dinitrotoluene as starting material in the process of the invention.

[0048] Catalytic hydrogenation in the context of the present invention means the reaction of the aromatic nitro compounds (I) with hydrogen in the presence of the catalyst system of the invention to afford the corresponding aromatic amines (II). This catalytic hydrogenation can here be carried out by methods known to those skilled in the art. For example, the pressure may be 1 to 50 bar, preferably 2 to 20 bar, more preferably 2 to 10 bar. The hydrogenation temperature is for example 150 to 400 °C, preferably 200 to 300 °C, more preferably 270 to 300 °C.

[0049] In general, the catalyst described above is used in a fluidized-bed reactor in a fluidized-bed process for the reaction of aromatic nitro compounds (I) with hydrogen to afford the corresponding aromatic amines (II). In this fluidized-bed process, a flow of e.g. hydrogen passes through a distributor tray in the fluidized-bed reactor from below and through the catalyst system of the invention, preferably the copper-containing catalyst system of the invention, which is generally present in the form of a fluidized bed. The aromatic nitro compound (I), preferably nitrobenzene, may for example likewise be introduced into the fluidized bed formed from the catalyst system of the invention, preferably the copper-containing catalyst system of the invention from below and / or from the side, in gaseous or preferably liquid form. Such fluidized-bed processes, for example for the catalytic hydrogenation of nitrobenzene to aniline are known in principle and are described for example in DE-B 1 114 820 and DE-B 1 133 394.

[0050] In one embodiment of the fluidized-bed process for the reaction of the aromatic nitro compounds (I) with hydrogen in the presence of the catalyst system of the invention to afford the corresponding aromatic amines (II), the fluidized bed is for example provided with internals that divide the fluidized bed into a plurality of cells arranged horizontally and also a plurality of cells arranged vertically in the fluidized-bed reactor. Such fluidized-bed reactors are described for example in WO 2008 / 034770, the disclosure of which is explicitly incorporated herein. The cell walls of the cells are generally gas-permeable and have openings ensuring that the exchange value of the catalyst system of the invention, preferably of the copper-containing catalyst system of the invention, in the vertical direction is within a range from 1 to 100 liter / h per liter reactor volume. In a further embodiment of the fluidized-bed process for producing aromatic amines (II) through catalytic hydrogenation of the parent aromatic nitro compounds (I) using the catalyst of the invention, the process is carried out in a fluidized-bed reactor fitted with a gas distributor. Such gas distributors are known to those skilled in the art; they are described for example in CN-A 1 634 860, the disclosure of which is explicitly incorporated herein.

[0051] The aromatic amines (II) produced in the process of the invention may optionally be subjected to one or more purification steps following the catalytic hydrogenation. For example, purification by distillation may be carried out. This allows the water present in the reaction to be removed from the aromatic amine (II) obtained from the reaction mixture by distillation, in which the water content of the aromatic amine (II) can in a single distillation step be lowered to less than 20% by weight based on the mixture of aromatic amine (II) and water. The heat of reaction evolved during the hydrogenation can be used to heat the above-described distillation or used to generate steam used in other chemical processes. The distillation column is preferably operated at an absolute head pressure of less than 1 bar. In addition, any low boilers that arise may also be removed by distillation.

[0052] The aromatic amine (II) (crude amine (II)) obtained in the hydrogenation may optionally be extracted with an aqueous alkali metal hydroxide solution, with subsequent separation of the aqueous and organic phases. The concentration of the employed alkali metal hydroxide solution and the temperature during the extraction are set such that, in the separation of the aqueous and organic phases, the aqueous phase is the lower phase. The extraction is preferably carried out at temperatures from 30 to 50° C.

[0053] The process of the invention has the advantage that aromatic amines (II), in particular aniline and toluene diamine, can be produced in high yield and / or high chemical purity, with the improved heat-transfer properties of the catalyst system of the invention in this highly exothermic hydrogenation reaction making it possible to achieve an increased space-time yield of aromatic amines (II).

[0054] The invention is further illustrated by the examples that follow.

[0055] Examples

[0056] The parameters were determined as follows:

[0057] Particle size distributions were measured by laser diffraction on a Malvern Mastersizer 2000 in accordance with ISO 13320.

[0058] Average particle diameters (d50 values) were calculated from the particle size distributions.

[0059] The heat transfer in the form of the k value was measured for the catalyst of the invention and for comparative catalysts as follows: One liter of catalyst is fluidized with nitrogen in a fluidized- bed reactor. A heating probe having a known surface area A is used to heat the fluidized catalyst to a defined temperature difference AT relative to the heating probe. The k value of the catalyst sample can then be determined via the electrical heating power P required as k = P / (A x AT).

[0060] Run time

[0061] The run time of the catalyst is defined as the hours of reactor operation attained until the product quality was out of specification.

[0062] Preparation of the reference catalyst (according to the invention)

[0063] The method of spray-drying is known in principle to those skilled in the art. It is customary to do this in a spray tower into which the suspension to be dried (also referred to as the “slurry” or “spray slurry”) is sprayed, usually with nozzles. Typical conditions for this are: Temperature in the spray tower inlet within a range from 250 to 350 °C, temperature in the spray tower outlet within a range from 100 to 140 °C, nozzle pressure within a range from 1 .5 to 2 bar.

[0064] A support material consisting of silica was sprayed to a solid pulverulent product by spray-drying a 13.5% by weight aqueous suspension of SiCh (Hydrogel D11-20, BASF, milled to 10 pm) with addition of 0.5% by weight of NaOH in a spray tower at a nozzle pressure of 1 .8 bar.

[0065] 150 g of the pulverulent silica was placed in a rotary evaporator. 50 g of an ammoniacal solution of Cu (15% by weight CuO, density d = 1 .244 g / l) was added to the support at 120°C and 480 mbar. A further 240.3 g of the Cu solution was added in six further impregnation steps. After each impregnation step, the material was dried for 1 h at 120 °C and 480 mbar and in the final two impregnation steps it was dried for 2 h at 120 °C and 300 mbar. The product was forced through a 250 pm sieve in order to break up agglomerates that had formed. The catalyst was then finally heated to 390 °C in a muffle furnace at 1 K / min and calcined at 390 °C for 2 h.

[0066] The catalyst had a CuO content of 22.2% by weight, a particle size distribution between 10 and 600 pm and comprised particles with an average particle diameter (d50 value) of 114 pm. The fine fraction of particles with particle sizes < 45 pm amounted to 18 % by weight based on the total weight of the catalyst.

[0067] Example 1 (according to the invention)

[0068] The reference catalyst was transferred to a fluidized bed reactor and the gas space rendered inert by flushing with nitrogen. The temperature in the reactor was adjusted to the range between 220 and 260 °C and the activation of the catalyst started by metering in hydrogen. As soon as unchanged temperature conditions and a stable fluidization were established, the reaction was started by metering in mononitobenzene (MNB). The hydrogenation reaction was operated in the range of 260 and 310 °C. The amount of MNB was adjusted in accordance with a target load of 0.6 to 0.9 kg(MNB) x kg (catalyst)-1x IT1. Hydrogen was added in excess of MN B in a hydrogen : MNB-ratio between 5 : 1 and 10 : 1. The heat that was produced during the reaction was removed via heat exchangers. As soon as complete conversion was not achieved any more, the reaction was stopped.

[0069] The heat exchange coefficient (k value) determined at complete conversion after a run time of 1080 h was 880 W / m2K.

[0070] Example 2 (for comparison)

[0071] The catalyst was prepared as the reference catalyst of example 1 , with the exception that after the calcination the catalyst was again sieved in order to obtain a catalyst with a fine fraction (< 45 pm) of below 7 % by weight. The catalyst still had a particle size distribution between 10 and 600 pm, but the average particle diameter (d50 value) was 140 pm.

[0072] The heat exchange coefficient (k value) determined according to example 1 at complete conversion after a run time of 110 h was 650 W / m2K.

[0073] Example 3 (for comparison)

[0074] The catalyst was prepared as the reference catalyst of example 1 , with the exception that after the calcination part of the catalyst was milled. The obtained catalyst mixture was again sieved in order to obtain a catalyst with a fine fraction (< 45 pm) of above 30 % by weight. The catalyst still had a particle size distribution between 10 and 600 pm, but the average particle diameter (d50 value) was 85 pm.

[0075] The heat exchange coefficient (k value) determined according to example 1 at complete conversion after a run time of 570 h was 650 W / m2K.

[0076] Discussion of results:

[0077] The examples were all performed until the product quality was out of specification, therefore a longer run time with a high heat transfer coefficient means a better performing catalyst. Low performing catalysts are indicated by a shorter run time and lower heat transfer coefficients.

[0078] In Example 1 , both a longer runtime and a higher heat transfer coefficient were obtained. In Example 2, on-spec product could not be produced after only 110 hours. In Example 3, both run time and heat transfer coefficient were significantly lower than in Example 1 .

Claims

Claims1 . A catalyst suitable for the hydrogenation of aromatic nitro compounds to the corresponding aromatic amines containing copper and optionally one or more additional metals on a carrier material, the catalyst having a particle size distribution in the range of from 10 to 1000 pm, wherein the fine fraction of particles with particle sizes < 45 pm is from 10 to 20 % by weight, the d50 value of the particle size distribution is from 80 to 180 pm.

2. The copper containing catalyst according to claim 1 , wherein the fine fraction of particles with particle sizes < 45 pm is from 15 to 20 % by weight.

3. The copper containing catalyst according to claim 1 or 2, wherein the d50 value of the particle size distribution is from 100 to 130 pm.

4. The copper containing catalyst according to any one of claims 1 to 3, wherein the carrier material is silica.

5. The copper containing catalyst according to any one of claims 1 to 4, containing one or more additional metals selected from main group I, main group II, main group IV, and subgroups II, V, VI, and VIII of the periodic table of the elements.

6. The copper containing catalyst according to claim 5, containing one or more further metals selected from the group consisting of potassium (K), sodium (Na), barium (Ba), lead (Pb), zinc (Zn), vanadium (V), chromium (Cr), molybdenum (Mo), tungsten (W), and iron (Fe).

7. A process for preparing aromatic amines, comprising the step of catalytic hydrogenation of the corresponding aromatic nitro compounds in the presence of a fluidized bed of the catalyst as defined in any one of claims 1 to 6.

8. The process according to claim 7, wherein aniline is prepared by catalytic hydrogenation of nitrobenzene.

9. The process according to claim 7, wherein toluene diamine is prepared by catalytic hydrogenation of dinitrotoluene.

10. The use of the catalyst as defined in any one of claims 1 to 6 for preparing aromatic amines through catalytic hydrogenation of the corresponding aromatic nitro compounds.

11. A process for improving the performance of a catalyst suitable for the hydrogenation of aromatic nitro compounds to the corresponding aromatic amines with regard to run time and / or heat transfer coefficient, wherein the catalyst contains copper and optionally one or more additional metals on a carrier material, and the catalyst has a particle size distribution in the range of from 10 to 1000 pm, comprising the step of adjusting the particle size distribution of the catalyst such that the fine fraction of particles with particle sizes < 45 pm is from 10 to 20 % by weight, and the d50 value of the particle size distribution is from 80 to 180 pm.

12. The process according to claim 11 , wherein the fine fraction of particles with particle sizes < 45 pm is adjusted to be from 15 to 20 % by weight.

13. The process according to claim 11 or 12, wherein the d50 value of the particle size distribution is adjusted to be from 100 to 130 pm.

14. The process according to any one of claims 11 to 13, wherein the particle size distribution of the catalyst is adjusted by milling and / or sieving steps in the preparation of the catalyst.