Organic compounds -- part of the class 532-570 series – Organic compounds – Amino nitrogen containing
Patent
1999-10-07
2000-06-27
Barts, Samuel
Organic compounds -- part of the class 532-570 series
Organic compounds
Amino nitrogen containing
564423, 502308, C07C20900
Patent
active
06080890&
DESCRIPTION:
BRIEF SUMMARY
This application is a 371 of PCT/EP98/01985 filed Apr. 6, 1998.
the present invention relates to the production of aromatic amines by catalytic hydrogenation of corresponding aromatic nitro compounds in the gas phase by means of new palladium-containing supported catalysts.
The hydrogenation of nitrobenzene to the corresponding aromatic amines in the gas phase on fixed palladium catalysts on ceramic supports is known. Thus a process for the reduction of nitro compounds in the presence of palladium-containing multicomponent supported catalysts in cooled tubular reactors is described in DE-A 2 849 002. The contact consists substantially of 1 to 20 g palladium, 1 to 20 g vanadium and 1 to 20 g lead per liter of .alpha.-Al.sub.2 O.sub.3. A disadvantage of the gas phase hydrogenations described in the cited patent publication is the low loading (specific loading) of the catalysts. The loadings given are approximately 0.4 to 0.5 kg/l.times.h. Here the loadings is defined as the quantity of nitroaromatics in kg which is reacted per liter of catalyst bed within one hour. Associated with the low catalyst loading is an unsatisfactory space-time yield in large-scale processes for the production of aromatic amines. Furthermore, the selectivities at the beginning of an operating period are significantly lower than the are towards the end, which results in losses in yield and problems in working up the crude product.
It was the object of the present invention to provide a process for the production of aromatic amines by catalytic hydrogenation of corresponding aromatic nitro compounds, which can be carried out on a large scale without problems, which renders possible a high space-time yield and which has a selectivity with regard to the required amines of .gtoreq.90% even at the beginning of an operating period.
The present invention accordingly provides a process for the production of aromatic amines by catalytic hydrogenation of corresponding aromatic nitro compounds in the gas phase, which is characterised in that the hydrogenation is carried out in the presence of catalysts which, besides palladium, vandium and lead, contain in addition molybdenum, tungsten and/or rhenium on a ceramic support material having a BET surface area of less than 40 m.sup.3 /g, at temperatures of from 180.degree. C. to 500.degree. C. in a catalyst bed and in a molar ratio of hydrogen to the nitro group or nitro groups of from 3:1 to 30:1.
Aromatic nitro compounds which can be hydrogenated by the process according to the invention are in particular those corresponding to the following formula: ##STR1## wherein R.sup.1 and R.sup.2 are identical or different and represent hydrogen or C.sub.1 -C.sub.4 -alkyl, in particular methyl and ethyl, and
Preferably nitrobenzene or the isomeric nitrotoluenes are hydrogenated by the process according to the invention.
Suitable ceramic support materials for the catalysts according to the invention include in principle all ceramic solids having BET surface areas of less than 40 m.sup.2 /g, preferably of less than 20 m.sup.2 /g, in particular of less than 10 m.sup.2 /g. The following compounds in particular are suitable as ceramic solids: metal oxides and/or mixed metal oxides of the elements magnesium, aluminium, silicon, germanium, zirconium and titanium: .alpha.-aluminium oxide is preferably used as support material.
Surprisingly, it has been found that contacts which, besides palladium, vanadium and lead, also contain Mo, W and/or Re deposited in the form of a shell on the above-mentioned support materials, in particular .alpha.-aluminium oxide, are particularly stable, highly loadable and selective catalysts. Special emphasis is therefore placed on catalysts which contain a) from 1 to 50 g palladium, b) from 1 to 50 g vanadium, c) from 1 to 20 g lead and d) from 1 to 20 g molybdenum, tungsten and/or rhenium per liter of oxide support material, the support material having a surface area of less than 40 m.sup.2 /g, preferably of less than 20 m.sup.2 /g and in particular of less than 10 m.sup.2 /g. Catalys
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Buysch Hans-Josef
Gallus Manfred
Jentsch Joerg-Dietrich
Langer Reinhard
Barts Samuel
Bayer Aktiengesellschaft
Gil Joseph C.
Whalen Lyndanne M.
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