Method for producing aromatic amines or aliphatic amino alcohols

Abstract

The invention relates to a process for preparing aromatic amines by hydrogenation of nitroaromatics in the presence of catalysts, in which a fluid reaction mixture which comprises amines and from which the catalysts are separated off is formed in a reactor. After the catalysts have been separated off, a measurement of the absorption of UV/VIS radiation by the reaction mixture is carried out to determine the concentration of nitro and nitroso compounds in the reaction mixture.

1 . An apparatus for carrying out a process for the preparation of aromatic amines by hydrogenation of nitroaromatics or of aliphatic amino alcohols by hydrogenation of nitro alcohols comprising hydrogenating nitroaromatics or nitro alcohols in the presence of catalysts, the apparatus comprising:
 a reactor for the hydrogenation of nitroaromatics or of nitro alcohols in the presence of catalysts to form a reaction mixture,   a separation element for separating off the catalysts from the reaction mixture, and   a UV/VIS spectrometer for measuring the absorption of UV/VIS radiation by the reaction mixture to determine the concentration of nitro and nitroso compounds in the reaction mixture   wherein said separation element is disposed between said reactor and said UV/VIS spectrometer.   
   
   
       2 . The apparatus according to  claim 1 , wherein the reactor is selected from the group consisting of a stirred tank; a fluidized-bed reactor; a monolithic, catalytic hydrogenation reactor; a shell-and-tube reactor; a bubble column; and a loop reactor. 
   
   
       3 . The apparatus according to  claim 1 , wherein the separation element is a centrifuge or a filter. 
   
   
       4 . The apparatus according to  claim 1 , wherein the UV/VIS spectrometer comprises a UV/VIS light source, a detector, and a vessel, the vessel being located between the UV/VIS light source and the detector and wherein reaction mixture flows through the vessel. 
   
   
       5 . The apparatus according to  claim 4 , wherein the UV/VIS light source radiates in a wide spectral range for the recordation of an absorption spectrum, or radiates in a narrow spectral range for the measurement of an absorption at a single wavelength. 
   
   
       6 . The apparatus according to  claim 5 , wherein the measurement of absorption is carried out at a wavelength in the range from 450 to 550 nm or the absorption spectrum is recorded in a wavelength range from 350 to 750 nm. 
   
   
       7 . The apparatus according to  claim 4 , wherein a distance (path length) which the light emitted by the UV/VIS light source travels during the measurement of the absorption through the reaction mixture in the vessel before it leaves the vessel and is detected by the detector is in the range from 0.5 to 1.5 cm. 
   
   
       8 . The apparatus according to  claim 4 , wherein the UV/VIS light source and the detector are mounted in a flow cell that is connected to substream lines conveying the reaction mixture. 
   
   
       9 . The apparatus according to  claim 4 , wherein the UV/VIS light source comprises one or two lamps selected from the group consisting of a tungsten filament lamp, a hydrogen lamp, and a deuterium lamp. 
   
   
       10 . The apparatus according to  claim 4 , wherein the detector comprises one or more components selected from the group consisting of a vacuum photocell, a photomultiplier, and a silicon photodiodes. 
   
   
       11 . The apparatus according to  claim 4 , wherein the UV/VIS spectrometer further comprises one or more components selected from the group consisting of a monochromator, an amplifier, an evaluation unit, and a display. 
   
   
       12 . The apparatus according to  claim 1 , further comprising a regulator for regulating the concentrations of the nitro and nitroso compounds. 
   
   
       13 . The apparatus according to  claim 1 , wherein said apparatus performs automatic on-line measurement of the concentration of the nitro and nitroso compounds in the reaction mixture. 
   
   
       14 . The apparatus according to  claim 1 , further comprising nitroaromatics or nitro alcohols, and catalyst.