Process for the continuous production of nitrobenzene

Patent metadata

Field	Value
Publication number	US-12180135-B2
Application number	US-202017602366-A
Country	US
Kind code	B2
Filing date	Apr 14, 2020
Priority date	Apr 17, 2019
Publication date	Dec 31, 2024
Grant date	Dec 31, 2024

Abstract

The invention relates to a continuously operating process for producing nitrobenzene, comprising the following steps: a) nitriding benzene in adiabatic conditions with sulfuric acid and nitric acid, using a stoichiometric excess of benzene in relation to the nitric acid; b) first separating a gaseous phase containing benzene and gaseous secondary components from the raw process product of the nitridation in a gas separator provided specifically for this purpose, then separating, in a downstream phase-separating apparatus, the resulting liquid phase, which is depleted in gaseous components and contains nitrobenzene and sulfuric acid, into a sulfuric acid phase and a nitrobenzene phase; and c) processing the nitrobenzene phase, obtaining nitrobenzene. The invention also relates to a production plant suitable for carrying out the claimed process.

First claim

The invention claimed is:

1. A process for the continuous preparation of nitrobenzene, comprising:
a) adiabatically reacting a benzene-containing stream in a reactor with sulfuric acid and nitric acid using a, based on nitric acid, stoichiometric excess of benzene, to obtain a process product containing nitrobenzene, benzene and sulfuric acid;
b) (i) passing the process product containing nitrobenzene, benzene and sulfuric acid into a gas separator in which a gaseous phase comprising benzene and gaseous secondary components is removed from the process product, leaving a liquid phase comprising nitrobenzene and sulfuric acid and depleted of gaseous constituents;
 (ii) passing the liquid phase produced in step b)(i) into a phase separation apparatus in which the liquid phase is subjected to a phase separation, wherein a liquid aqueous, sulfuric acid-comprising phase and a liquid organic, nitrobenzene-comprising phase are withdrawn from the phase separation apparatus; and
c) working up the liquid organic, nitrobenzene comprising phase to obtain the nitrobenzene.

2. The process as claimed in claim 1 , further comprising:
d) concentrating the liquid aqueous, sulfuric acid-comprising phase by evaporation of water to give a concentrated liquid aqueous phase comprising a higher concentration of sulfuric acid as compared to the liquid aqueous, sulfuric acid-comprising phase, wherein the concentrated liquid aqueous phase is recycled into step a) and used as constituent of the sulfuric acid.

3. The process as claimed in claim 1 , in which the workup of the liquid organic, nitrobenzene-comprising phase comprises:
(i) washing the liquid organic, nitrobenzene-comprising phase and removing unconverted benzene, and
(ii) using removed benzene as a constituent of the benzene used in step a).

4. The process as claimed in claim 1 , in which the stoichiometric excess of benzene based on nitric acid in step a) is set to a value in the range from 2.0% to 40% of theory.

5. The process as claimed in claim 1 , in which the temperature in the reactor of step a) is maintained in the range from 98° C. to 140° C.

6. The process as claimed in claim 1 , in which step a) is performed in a plurality of reactors operated in parallel and
(α) the process products containing nitrobenzene, benzene and sulfuric acid that are obtained in each of the plurality of reactors are combined prior to performing step b)(i); or
(β) the process products containing nitrobenzene, benzene and sulfuric acid that are obtained in each of the plurality of reactors are each passed in step b)(i) into a dedicated gas separator and the liquid phases comprising nitrobenzene and sulfuric acid and depleted of gaseous constituents that are obtained in the gas separators are combined
 (β)( 1 ) in the phase separation apparatus of step b)(ii) or
 (β)( 2 ) prior to performing step b)(ii);

or
(γ) the process products containing nitrobenzene, benzene and sulfuric acid that are obtained in each of the plurality of reactors are passed in step b)(i) into a common gas separator without prior combining.

7. The process as claimed in claim 1 , in which the gas separator used comprises a gravitational separator or a centrifugal separator.

8. The process as claimed in claim 7 , in which the gas separator comprises a gravitational separator.

9. The process as claimed in claim 8 , in which the gravitational separator comprises a horizontally or vertically arranged gravitational separator to which the process product containing nitrobenzene, benzene and sulfuric acid
is fed from the side or from the bottom, wherein the gaseous phase comprising benzene and gaseous secondary components is withdrawn from the gravitational separator as a top stream and the liquid phase comprising nitrobenzene and sulfuric acid and depleted of gaseous constituents is withdrawn from the gravitational separator as a bottom stream at the bottom or from the side, or
is fed from the top, wherein the gaseous phase comprising benzene and gaseous secondary components is withdrawn from the gravitational separator from the side and the liquid phase comprising nitrobenzene and sulfuric acid and depleted of gaseous constituents is withdrawn from the gravitational separator at the bottom.

10. The process as claimed in claim 7 , in which the gas separator comprises a centrifugal separator.

11. The process as claimed in claim 10 , in which the centrifugal separator comprises a vertically arranged, cylindrical, conical or cylindrical-conical cyclone through which the process product containing nitrobenzene, benzene and sulfuric acid is guided with the generation of swirl, wherein the gaseous phase comprising benzene and gaseous secondary components is discharged towards the top and the liquid phase comprising nitrobenzene and sulfuric acid and depleted of gaseous constituents is discharged towards the bottom.

12. The process as claimed in claim 1 , in which the reactor used in step a) comprises a tubular reactor.

13. A production plant for performing the process for the continuous preparation of nitrobenzene as claimed in claim 1 , comprising:
a) a reactor configured to adiabatically react a benzene-containing stream with sulfuric acid and nitric acid using a, based on nitric acid, stoichiometric excess of benzene;
b) (i) a gas separator arranged downstream of the reactor, the gas separator being configured to separate the process product from the reactor into a gaseous phase comprising benzene and gaseous secondary components and a liquid phase comprising nitrobenzene and sulfuric acid and depleted of gaseous constituents;
 (ii) a phase separation apparatus arranged downstream of the gas separator, the phase separation apparatus being configured to separate the process product from the gas separator into a liquid aqueous, sulfuric acid-comprising phase and a liquid organic, nitrobenzene-comprising phase; and
c) an apparatus configured to work up the liquid organic, nitrobenzene-comprising phase from the phase separation apparatus to give the nitrobenzene; and
d) optionally, devices configured to concentrate the liquid aqueous, sulfuric acid-comprising phase from the phase separation apparatus by evaporation of water and devices configured to recycle the liquid aqueous phase thus obtained comprising a higher concentration of sulfuric acid compared to the liquid aqueous, sulfuric acid-comprising phase into the reactor as a constituent of the sulfuric acid.

14. The production plant as claimed in claim 13 , comprising
a) a plurality of reactors configured to operate in parallel for the adiabatic reaction of a benzene-containing stream with sulfuric acid and nitric acid using a, based on nitric acid, stoichiometric excess of benzene; and
in a variant (α),
b) (i- 0 ) arranged downstream of the reactors, devices configured to combine the process products containing nitrobenzene, benzene and sulfuric acid that are obtained in the reactors to form a mixed stream and configured to introduce the mixed stream into
 (i) a gas separator, arranged downstream of the devices configured to combine the process products containing nitrobenzene, benzene and sulfuric acid that are obtained in the reactors, the gas separator being configured to separate the mixed stream into a gaseous phase comprising benzene and gaseous secondary components and a liquid phase comprising nitrobenzene and sulfuric acid and depleted of gaseous constituents, and
 (ii) a phase separation apparatus, arranged downstream of the gas separator, the phase separation apparatus being configured to separate the liquid phase comprising nitrobenzene and sulfuric acid and deplete

Assignees

• Covestro Deutschland Ag
• Covestro Intellectual Property Gmbh & Co Kg

Inventors

• Knauf Thomas
• Kalem Murat
• Drumm Christian
• Racoes Alexandre

Classifications

• C07C201/16

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

• B01J2219/00033

  Continuous processes · CPC title

• B01J19/2425

  in parallel · CPC title

• B01D19/0057

  the centrifugal movement being caused by a vortex, e.g. using a cyclone, or by a tangential inlet · CPC title

• B01D17/02

  Separation of non-miscible liquids · CPC title