Method for starting a reaction during the production of aromatic amines from nitroaromatics
The present invention relates to a method of producing aromatic amines by hydrogenation of aromatic nitro compounds. This method provides a reactor containing a hydrogenation catalyst; supplies aromatic nitro compounds and hydrogen to the reactor and contacts them with a hydrogenation catalyst, in which the hydrogen which is supplied to the reactor is by a compressor and the compressor contains an operating fluid which at least partially contacts the hydrogen; and regenerates the hydrogenation catalyst by heating and contacting it with oxygen. Particular operating liquids are subsequently exchanged.
1. A process for preparing aromatic amines by hydrogenation of aromatic nitro compounds, which comprises:
A) providing a reactor with hydrogenation catalyst present therein;
B) introducing aromatic nitro compounds and hydrogen into said reactor contacting with said hydrogenation catalyst, wherein at least said hydrogen is fed into the reactor by means of a compressor and said compressor contains an operating liquid which at least partially contacts said hydrogen;
C) regenerating said hydrogenation catalyst by heating and contacting with oxygen;
wherein
D1) at least partially removing liquids which are present in said reactor and/or in plant parts fluidically connected downstream to said reactor and which were at least partly present in said reactor and/or in said plant parts during step C);
and/or:
D2) at least partially replacing said operating liquid of said compressor which was present in said compressor and/or in recirculation facilities connected to said compressor during step C) by an operating liquid which was not present in said compressor and/or in recirculation facilities connected to said compressor during step C);
are carried out after C).
2. The process as claimed in claim 1 , wherein said compressor is a liquid ring compressor.
3. The process as claimed in claim 1 , wherein said operating liquid in said compressor is water or an aqueous solution containing more than 90% by weight of water.
4. The process as claimed in claim 1 , wherein said reactor is additionally filled or flushed with an inert gas after step C).
5. The process as claimed in claim 1 , wherein step D1) is carried out by flushing said reactor and/or plant parts fluidically connected downstream to said reactor with water and/or an aqueous solution containing more than 90% by weight of water.
6. The process as claimed in claim 1 , wherein the molar ratio of hydrogen to nitro groups of said aromatic nitro compounds in step B) is from ≧3:1 to ≦100:1.
7. The process as claimed in claim 1 , wherein aromatic nitro compounds having the general formula (I):
in which:
R1 and R2 are each, independently of one another, hydrogen, methyl or ethyl, with the proviso that R2 can also be NO 2 , are used in step B).
8. The process as claimed in claim 1 , wherein said aromatic nitro compounds in step B) are nitrobenzene and/or dinitrotoluene.
9. The process as claimed in claim 1 , wherein the catalyst in said reactor is arranged in a fixed catalyst bed.
10. The process as claimed in claim 1 , wherein the interior of said reactor and/or the interior of plant parts fluidically connected to said reactor is/are heated to a temperature of more than 58° C. of step D1) and/or D2) and before renewed introduction of aromatic nitro compounds and hydrogen into said reactor and contacting with said hydrogenation catalyst.