| 摘要 |
The present invention relates to a continuously operated adiabatic process for the preparation of nitrobenzene by nitration of benzene with nitric acid and sulfuric acid, in which the dilute sulfuric acid obtained after the nitration has taken place and the crude nitrobenzene has been separated off from the aqueous phase is concentrated for the purpose of re-use in the nitration, and after its concentration, at least one minute before it comes into contact with fresh nitric acid again an oxidizing agent is added such that a concentration of the oxidizing agent of from 10 ppm to 5,000 ppm, based on the total weight of the concentrated sulfuric acid to be recycled into the nitration, is established. |
| 主权项 |
1. A continuously operated adiabatic process for the preparation of nitrobenzene by nitration of benzene, comprising:
a) reacting a benzene-containing stream (a1) in a reactor with sulfuric acid (a.2) and nitric acid (a.3) under adiabatic conditions, wherein benzene is employed in a stoichiometric excess, based on nitric acid (a.3), separating the process product obtained in step a) in a phase separation apparatus into an aqueous phase (b.1) comprising sulfuric acid and an organic phase (b.2) comprising nitrobenzene, c) concentrating the aqueous phase (b.1) obtained in step b) by evaporation of water to give an aqueous phase (c.1) having an increased sulfuric acid concentration compared with (b.1), wherein phase (c.1) is returned into step a) and is used as a component of (a.2), and d) working up the organic phase (b.2) obtained in step b) to give pure nitrobenzene (d.1),whereinan oxidizing agent (c.2) is added to the concentrated aqueous phase (c.1) comprising sulfuric acid at least 1 minute before the phase (c.1) comes into contact with the nitric acid stream (a.3), to an extent such that a concentration of the oxidizing agent (c.2) of from 10 ppm to 5,000 ppm, based on the total weight of the concentrated aqueous phase (c.1) comprising sulfuric acid to be returned into step a), is established. |
