Process for producing nitrobenzene

Patent metadata

Field	Value
Publication number	US-10023524-B2
Application number	US-201515320804-A
Country	US
Kind code	B2
Filing date	Jun 22, 2015
Priority date	Jun 24, 2014
Publication date	Jul 17, 2018
Grant date	Jul 17, 2018

Abstract

The present invention relates to a process for the continuous production of nitrobenzene by the nitration of benzene with nitric acid and sulphuric acid under adiabatic conditions, not the entire production plant being shut down during a production stop, but the production plant being entirely or at least partly operated in recirculation mode. The invention further relates to a plant for producing nitrobenzene and to a method for operating a plant for producing nitrobenzene.

First claim

The invention claimed is:

1. A process for preparing nitrobenzene, comprising
(I) nitrating benzene with nitric acid in sulfuric acid to form nitrobenzene in a reactor, with introduction of a mass flow of benzene (m 1 ), a mass flow of nitric acid (m 2 ), and a mass flow of sulfuric acid (m 3 ), into the reactor, thereby obtaining a reaction mixture comprising an organic nitrobenzene-containing phase and an aqueous sulfuric acid-containing phase;
(II) separating the organic nitrobenzene-containing phase and the aqueous sulfuric acid-containing phases of the reaction mixture from (I) in a phase separation apparatus;
and optionally (III) to (VII):
(III) concentrating the aqueous sulfuric acid-containing phase separated in (II) by evaporating water in an evaporation apparatus to give an aqueous sulfuric acid-containing phase having elevated sulfuric acid concentration, with recycling of the concentrated sulfuric acid-containing aqueous phase via a sulfuric acid tank into (I) and use thereof as a constituent of the mass flow m 3 ;
(IV) washing the organic nitrobenzene-containing phase obtained in (II) in at least two stages and separating off an aqueous phase after each stage, using a wash vessel having a phase separation unit or a wash vessel and a separate phase separation apparatus in each stage,
(V) distilling the organic nitrobenzene-containing phase obtained in the last stage of (IV) in a distillation apparatus, and
(VI) working up the aqueous phase from the first wash stage of (IV), comprising collecting the aqueous phase in a wastewater collection vessel and cleaning said aqueous phase in an apparatus for distillation or stripping,
and
(VII) working up the aqueous phase from the second wash stage of the at least two wash stages of (IV), comprising collecting the aqueous phase in a wastewater collection vessel and cleaning said aqueous phase in an apparatus for distillation or stripping, where the apparatus for distillation or stripping may be connected up- and/or downstream of an apparatus for thermal pressure decomposition,
wherein
the process is interrupted, the interruption comprising the steps of shutting down one or more, but not all, plant sections from (I) to (VII), reducing the mass flow m 1 and the mass flow m 2 to zero and, in at least one of the plant sections that has not been shut down, using an output stream of said at least one plant section that has not been shut down as an input stream for the respective plant section or an upstream plant section, thereby operating said at least one plant section that has not been shut down in circulation mode.

2. The process as claimed in claim 1 , additionally comprising (III) to (VII).

3. The process as claimed in claim 2 , wherein (IV) comprises
(IVa) washing the organic nitrobenzene-containing phase obtained in (II) in at least one wash stage, and separating phases into a first aqueous phase and a first organic nitrobenzene-containing phase,
(IVb) washing the first organic nitrobenzene-containing phase obtained in (IVa) in at least one alkaline wash with an aqueous solution of a base selected from the group consisting of sodium hydroxide, sodium carbonate and sodium hydrogencarbonate, and separating phases into a second aqueous phase and a second organic nitrobenzene-containing phase,
and
(IVc) washing the second organic nitrobenzene-containing phase obtained in (IVb) in at least one neutral wash with water, and separating phases into a third aqueous phase and a third organic nitrobenzene-containing phase.

4. The process as claimed in claim 1 , wherein an output stream in every plant section that has not been shut down is used again as an input stream for the corresponding plant section or an upstream plant section.

5. The process as claimed in claim 2 , wherein an output stream from the plant section from (V) is used as an input stream for the plant section from (IV).

6. The process of claim 1 , additionally comprising
(1) at least one of:
(a) conducting an inspection, repair, cleaning or maintenance measure in the one or more plant sections that have been shut down,
and
(b) compensating for a lack of feedstocks or auxiliaries,
during the interruption of the process;

and
(2) restarting the process again after completion of said inspection, repair, cleaning or maintenance measure, or after the lack of feedstocks or auxiliaries has been overcome.

Assignees

• Covestro Deutschland Ag

Inventors

• Knauf Thomas
• Drinda Peter

Classifications

• B01J19/2465

  externally, i.e. the mixture leaving the vessel and subsequently re-entering it · CPC title

• B01J19/002

  Avoiding undesirable reactions or side-effects, e.g. avoiding explosions, or improving the yield by suppressing side-reactions · CPC title

• B01J2219/00268

  Detecting faulty operations · CPC title

• C07C201/08 Primary

  by substitution of hydrogen atoms by nitro groups · CPC title

• B01J19/1881

  externally, i.e. the mixture leaving the vessel and subsequently re-entering it · CPC title