Process for producing nitrobenzene

Patent metadata

Field	Value
Publication number	US-2018346405-A1
Application number	US-201816009396-A
Country	US
Kind code	A1
Filing date	Jun 15, 2018
Priority date	Jun 24, 2014
Publication date	Dec 6, 2018
Grant date	—

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

1 . A process, preferably operated adiabatically, for preparing nitrobenzene, comprising the steps of
(I) nitrating benzene with nitric acid in sulfuric acid to form nitrobenzene in a reactor, with introduction of benzene with a mass flow rate of m 1 , nitric acid with a mass flow rate of m 2 and sulfuric acid with a mass flow rate of m 3 into the reactor; (II) separating the phases of the reaction mixture from step (I) in a phase separation apparatus into an aqueous sulfuric acid-containing phase and an organic nitrobenzene-containing phase; and optionally (and preferably) steps (III) to (V): (III) concentrating the aqueous phase obtained in step (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 step (I) and use thereof as a constituent of mass flow m 3 ; (IV) washing the organic nitrobenzene-containing phase obtained in step (II) in at least two stages and separating off the 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, preferably rectifying, the organic nitrobenzene-containing phase obtained in the last stage of step (IV) in a distillation apparatus, and (VI) working up the wastewater from the first wash stage of step (IV), comprising collecting the wastewater in a wastewater collection vessel and cleaning this wastewater in an apparatus for distillation or stripping, (VII) working up the wastewater from the second wash stage of step (IV), comprising collecting the wastewater in a wastewater collection vessel and cleaning this wastewater 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, characterized in that in the event of shutdown of one or more plant sections from steps (I) to (VII), if they are conducted, the mass flow mi and the mass flow m 2 are reduced to zero and, in at least one of the plant sections that has not been shut down, the output stream is used again as input stream for the respective plant section or an upstream plant section.

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

3 . The process as claimed in claim 2 , wherein step (IV) comprises the steps of
(IVa) washing the organic nitrobenzene-containing phase obtained in step (II) in at least one wash, preferably one or two washes, more preferably one wash, then separating the phases into an aqueous phase and an organic nitrobenzene-containing phase, (IVb) washing the organic nitrobenzene-containing phase obtained in step (IVa) in at least one alkaline wash, preferably one or two alkaline washes, more preferably one alkaline wash, with an aqueous solution of a base selected from the group consisting of sodium hydroxide, sodium carbonate and sodium hydrogencarbonate, then separating the phases into an aqueous phase and an organic nitrobenzene-containing phase, (IVc) washing the organic nitrobenzene-containing phase obtained in step (IVb) in at least one neutral wash, preferably two to four neutral washes, more preferably two or three neutral washes, most preferably two neutral washes, with water, then separating the phases into an aqueous phase and an organic nitrobenzene-containing phase.

4 . The process as claimed in at least one of the preceding claims, wherein the output stream in every plant section that has not been shut down is used again as input stream for the corresponding plant section or an upstream plant section.

5 . The process as claimed in at least one of the preceding claims, wherein the output stream from the plant section from step (V) is used as input stream for the plant section from step (IV).

6 . A plant for preparation of nitrobenzene, 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, and optionally (and preferably) plant sections (III) to (VII): (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 is configured to reduce to zero the introduction of the mass flow of benzene and of the mass flow of nitric acid into the reactor (I) during an interruption of the process that comprises a shutdown of one or more, but not all, plant sections (I) to (VII), such that at least one plant section is unaffected by the shutdown, and the plant is configured to use an output stream of said at least one plant section unaffected by the shutdown, as an input stream for the respective plant section or an upstream plant section, thus operating said at least one plant section unaffected by the shutdown in circulation mode.

7 . The plant as claimed in claim 6 , comprising plant sections (III) to (VII).

8 . The plant as claimed in claim 7 , 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).

9 . The plant as claimed in claim 6 , 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.

10 . The plant as claimed in claim 6 , 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).

11 . A method of operating a plant for preparation of nitrobenzene, 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 phas

Assignees

• Covestro Deutschland Ag

Inventors

• Knauf Thomas
• Drinda Peter

Classifications

• B01J2219/0004

  Processes in series · CPC title

• C07C201/08 Primary

  by substitution of hydrogen atoms by nitro groups · CPC title

• C07C201/16

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

• B01J19/1881

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

• B01J2219/00268

  Detecting faulty operations · CPC title