Process for producing nitrobenzene

Patent metadata

Field	Value
Publication number	US-11136285-B2
Application number	US-201816009396-A
Country	US
Kind code	B2
Filing date	Jun 15, 2018
Priority date	Jun 24, 2014
Publication date	Oct 5, 2021
Grant date	Oct 5, 2021

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

What is claimed is:

1. A plant configured, when in operation, to prepare nitrobenzene by nitration of benzene in the presence of sulfuric acid,
the plant comprising the following plant sections:
(I) a reactor for nitration of benzene with a mixture of nitric acid and sulfuric acid to form nitrobenzene,
(II) a phase separation apparatus for phase separation of the reaction mixture obtained in the reactor (I) into an aqueous sulfuric acid-containing phase and an organic nitrobenzene-containing phase,
(III) an evaporator (III.a) for concentration of the aqueous sulfuric acid-containing phase and a sulfuric acid reservoir tank (III.b) for accommodation of the concentrated aqueous sulfuric acid-containing phase and the provision thereof for the reactor (I),
(IV) a wash vessel with phase separation unit per wash stage or a wash vessel and a separate phase separation apparatus per wash stage for at least two-stage washing of the organic nitrobenzene-containing phase from (II),
(V) a distillation apparatus for purification of the organic nitrobenzene-containing phase from (IV),
(VI) a wastewater collection vessel and an apparatus for distillation or stripping for collection and subsequent cleaning of the wastewater from the first wash stage from (IV),
and
(VII) a wastewater collection vessel and an apparatus for distillation or stripping for collection and subsequent cleaning of the wastewater from the second wash stage from (IV),
wherein the plant further comprises a process control unit,
wherein in the plant is configured such that
during an interruption lasting from 1 hour to 1 day in the preparation of nitrobenzene forced by requirements for inspection, repair, maintenance or cleaning, which requirements affect one or more, but not all plant sections (I) to (VII), the interruption proceeding from the plant being in operation,

not the entire plant is shut down, but instead only the plant sections affected by the requirements are shut down, which interruption comprises
(A) stopping charging the reactor with benzene and nitric acid, the stopping being implemented by the process control unit, the process control unit being configured to automatically interrupt the supply of benzene and nitric acid on shutdown of the plant sections affected by the requirements, and
(B) in at least one of the plant sections that have not been shut down, establishing a circulation mode by
(i) recycling an output stream of the at least one plant section which has not been shut down into the respective plant section,
or by
(ii) conducting an output stream of the at least one plant section which has not been shut down into a plant section which is upstream or downstream and thence, optionally via further plant sections that have not been shut down, recycling said output stream into the plant section said output stream originated from,
wherein a barrier circuit enables the setting to circulation mode only after the process control unit has automatically shut down the supply of benzene and nitric acid,
wherein the plant is further configured to start up the overall plant again immediately after the interruption ends.

2. The plant as claimed in claim 1 , plant section (IV) comprising:
(IVa) a wash vessel with phase separation unit or a wash vessel and a separate phase separation apparatus for washing and subsequent phase separation of the organic nitrobenzene-containing phase from (II),
(IVb) a wash vessel with phase separation unit or a wash vessel and a separate phase separation apparatus for washing and subsequent phase separation of the organic nitrobenzene-containing phase from (Iva),
and
(IVc) a wash vessel with phase separation unit or a wash vessel and a separate phase separation apparatus for washing and subsequent phase separation of the organic nitrobenzene-containing phase from (Ivb).

3. The plant as claimed in claim 1 , wherein, independently of one another or simultaneously, the output stream in every plant section that has not been shut down can be recycled and again used as an input stream for the respective plant section or an upstream plant section.

4. The plant as claimed in claim 1 , wherein the plant is configured such that the output stream from plant section (V) can be used as an input stream for plant section (IV).

5. The plant as claimed in claim 1 , wherein an apparatus for thermal pressure decomposition is arranged upstream and/or downstream of the apparatus for distillation or stripping.

6. A method of operating a plant for preparation of nitrobenzene, the plant comprising the following plant sections:
(I) a reactor for nitration of benezene with a mixture of nitric acid and sulfuric acid to form nitrobenzene,
(II) a phase separation apparatus for phase separation of the reaction mixture obtained in the reactor (I) into an aqueous sulfuric acid-containing phase and an organic nitrobenzene-containing phase,
(III) an evaporator (III.a) for concentration of the aqueous sulfuric acid-containing phase and a sulfuric acid reservoir tank (III.b) for accommodation of the concentrated aqueous sulfuric acid-containing phase and the provision thereof for the reactor (I),
(IV) a wash vessel with phase separation unit per wash stage or a wash vessel and a separate phase separation apparatus per wash stage for at least two-stage washing of the organic nitrobenzene-containing phase from (II),
(V) a distillation apparatus for purification of the organic nitrobenzene-containing phase from (IV),
(VI) a wastewater collection vessel and an apparatus for distillation or stripping for collection and subsequent cleaning of the wastewater from the first wash stage from (IV),
and
(VII) a wastewater collection vessel and an apparatus for distillation or stripping which may be connected up- and/or downstream of an apparatus for thermal pressure decomposition, for collection and subsequent cleaning of the wastewater from the second wash stage from (IV),
wherein the plant further comprises a process control unit,
wherein, when the plant is in operation, the preparation of nitrobenzene is interrupted from 1 hour to 1 day forced by requirements for inspection, repair, maintenance or cleaning, which requirements affect one or more, but not all plant sections (I) to (VII), the interruption comprising shutting down not the entire plant, but instead only the plant sections affected by the requirements, the method further comprising:
(A) stopping the supply of benzene and nitric acid, and optionally sulfuric acid, into the reactor (I), the stopping being implemented by the process control unit, the process control unit being configured to automatically interrupt the supply of benzene and nitric acid on shutdown of the plant sections affected by the requirements;
(B)
(i) recycling an output stream from at least one plant section that has not been shut down into the respective plant section
or
(ii) conducting an output stream from at least one plant section that has not been shut down into a plant section which is upstream or downstream and thence, optionally via further plant sections that have not been shut down, recycling said output stream into the plant section said output stream originated from;
thereby setting said at least one plant section that has not been shut down to circulation mode, wherein a barrier circuit enables the setting to circulation mode only after the process control unit has automatically stopped the supply of benzene and nitric acid;

(C) optionally opening at least one of the plant sections affected by the requirements;
(D) conducting an inspection, repair, maintenance or cleaning measure in at least one of the plant sections affected by the requirements;
(E) optionally closing and optionally inertizing the at least one plant section from (D);
(F) starting up

Assignees

• Covestro Deutschland Ag

Inventors

• Knauf Thomas
• Drinda Peter

Classifications

• C07C201/08 Primary

  by substitution of hydrogen atoms by nitro groups · CPC title

• B01J19/0006

  Controlling or regulating processes (controlling or regulating in general G05) · CPC title

• C07C201/16

  Separation; Purification; Stabilisation; Use of additives · CPC title

• B01J19/2465

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

• B01J19/24

  Stationary reactors without moving elements inside (B01J19/08, B01J19/26 take precedence; with stationary particles B01J8/02) · CPC title