Method for producing nitrobenzene by adiabatic nitriding

Patent metadata

Field	Value
Publication number	US-9260377-B2
Application number	US-201314415788-A
Country	US
Kind code	B2
Filing date	Jul 23, 2013
Priority date	Jul 27, 2012
Publication date	Feb 16, 2016
Grant date	Feb 16, 2016

Abstract

The invention provides a continuous adiabatic process for the preparation of nitrobenzene by nitrating benzene with mixtures of sulfuric and nitric acids using a stoichiometric excess of benzene, wherein the content of organic compounds in the circulating sulfuric acid, at least during the start-up period of the production plant, is always kept below 1.0 mass percent, based on the total mass of circulating sulfuric acid. This is preferably achieved by a procedure in which, either after the end or before the beginning of a production cycle, the circulating sulfuric acid is circulated at elevated temperature so that the organics contained in the sulfuric acid, preferably comprising nitrobenzene and traces of benzene, dinitrobenzene and nitrophenols, are separated off in the evaporation apparatus for concentrating the sulfuric acid.

First claim

The invention claimed is:

1. A continuous process for the preparation of nitrobenzene by the nitration of benzene, comprising:
a) reacting a benzene-containing stream (a.1) in a reactor with a mixture of sulfuric acid (a.2) and nitric acid (a.3) under adiabatic conditions, wherein the benzene is used in a stoichiometric excess, based on nitric acid (a.3), and the quantity M′ of the benzene-containing stream (a.1) fed into the reactor per hour is increased over a period of time t from the beginning of the nitration until a preset target value for M′ is achieved,
b) 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 the water in an evaporation apparatus to give an aqueous phase (c.1) comprising sulfuric acid and having a higher sulfuric acid concentration than (b.1), wherein the phase (c.1) is recycled into step a) via a sulfuric acid tank and used as a component of (a.2), and
d) working up the organic phase (b.2) obtained in step b) to pure nitrobenzene (d.1),
wherein at least during the period of time t, only a sulfuric acid stream (a.2) having a content of organic compounds of less than 1.0 mass percent, based on the total mass of (a.2), is fed into the reactor.

2. The process according to claim 1 wherein the organic compounds are selected from the group consisting of benzene, nitrobenzene, the isomers of dinitrobenzene and the isomers of nitrophenol.

3. The process according to claim 2 wherein the organic compound comprises nitrobenzene.

4. The process according to claim 1 wherein the continuous reaction is interrupted by stopping the addition of the benzene-containing stream (a.1) and nitric acid (a.3) and, after complete conversion to nitrobenzene of the residual nitric acid present in the reactor, after removal of the organic phase (b.2) from the phase separation apparatus and after concentrating (b.1) to (c.1), the remaining sulfuric acid-containing phase (c.1) is circulated through the reactor, the phase separation apparatus, the evaporation apparatus and the sulfuric acid tank at a temperature of 60° C. to 140° C. until the content of organic compounds in (c.1) is lower than 1.0 mass percent, based on the total mass of the sulfuric acid-containing phase (c.1), and wherein the so purified sulfuric acid-containing phase (c.1) is used as a component of (a.2) in the next production cycle.

5. The process according to claim 1 wherein, starting from a production plant that is not in operation, before the introduction of the benzene-containing stream (a.1) and nitric acid (a.3), the sulfuric acid-containing phase (c.1) which is still present from the previous production cycle is circulated through the reactor, the phase separation apparatus, the evaporation apparatus and the sulfuric acid tank at a temperature of 60° C. to 140° C. until the content of organic compounds in (c.1) is lower than 1.0 mass percent, based on the total mass of the sulfuric acid-containing phase (c.1), and wherein the so purified sulfuric acid-containing phase (c.1) is used as a component of (a.2) in the next production cycle.

6. The process according to claim 4 wherein the absolute pressure in the evaporation apparatus is adjusted to 50 mbar to 300 mbar, while the sulfuric acid-containing phase (c.1) is circulated, in order to bring the content of organic compounds in (c.1) to a value of less than 1.0 mass percent, based on the total mass of the sulfuric acid-containing phase (c.1).

7. The process according to claim 1 wherein benzene is used in step a) in an excess of 2.0% to 20% of theory.

8. The process according to claim 5 , wherein the absolute pressure in the evaporation apparatus is adjusted to 50 mbar to 300 mbar, while the sulfuric acid-containing phase (c.1) is circulated, in order to bring the content of organic compounds in (c.1) to a value of less than 1.0 mass percent, based on the total mass of the sulfuric acid-containing phase (c.1).

9. The process according to claim 2 , wherein benzene is used in step a) in an excess of 2.0% to 20% of theory.

10. The process according to claim 3 , wherein benzene is used in step a) in an excess of 2.0% to 20% of theory.

11. The process according to claim 4 , wherein benzene is used in step a) in an excess of 2.0% to 20% of theory.

12. The process according to claim 5 , wherein benzene is used in step a) in an excess of 2.0% to 20% of theory.

13. The process according to claim 6 , wherein benzene is used in step a) in an excess of 2.0% to 20% of theory.

14. The process according to claim 8 , wherein benzene is used in step a) in an excess of 2.0% to 20% of theory.

Assignees

• Bayer Materialscience Ag

Inventors

• Knauf Thomas
• Merkel Michael
• Mairata Antoni

Classifications

• C07C201/06 Primary

  Preparation of nitro compounds · CPC title

• C07C201/08 Primary

  by substitution of hydrogen atoms by nitro groups · CPC title

• C07C205/06

  having nitro groups bound to carbon atoms of six-membered aromatic rings · CPC title

• C07C201/16

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