Process for working up waste water from nitrobenzene preparation

Patent metadata

Field	Value
Publication number	US-9771290-B2
Application number	US-201414784443-A
Country	US
Kind code	B2
Filing date	Apr 15, 2014
Priority date	Apr 18, 2013
Publication date	Sep 26, 2017
Grant date	Sep 26, 2017

Abstract

The present invention provides a process for working up alkaline waste water which is formed during washing of crude nitrobenzene obtained by nitration of benzene, wherein
(i) the alkaline waste water is heated to a temperature of from 150° C. to 500° C. under an increased pressure with respect to atmospheric pressure with exclusion of oxygen; (ii) a base is added to the waste water obtained in (i); and (iii) the waste water obtained in (ii) is purified further by stripping with a stripping gas and the stripping gas stream loaded with impurities is then cooled to a temperature of from 10° C. to 60° C.

First claim

The invention claimed is:

1. A process for working up alkaline waste water which is formed during washing of crude nitrobenzene obtained by nitration of benzene, comprising:
(i) heating the alkaline waste water to a temperature of from 150° C. to 500° C. under an increased pressure with respect to atmospheric pressure with exclusion of oxygen;
(ii) adding a base to the waste water obtained in (i); and
(iii) further purifying the waste water obtained in (ii) by stripping with a stripping gas and then cooling the stripping gas stream loaded with impurities to a temperature of from 10° C. to 60° C.

2. The process of claim 1 , comprising in heating the alkaline waste water in step (i) under an absolute pressure of from 50 bar to 350 bar.

3. The process of claim 1 , comprising heating the alkaline waste water in step (i) for a period of from 5 minutes to 120 minutes.

4. The process of claim 3 , comprising, after the heating, cooling the alkaline waste water to a temperature of from 60° C. to 100° C.

5. The process of claim 1 , in which the base used in step (ii) is an aqueous solution of a base selected from the group consisting of lithium hydroxide, sodium hydroxide, potassium hydroxide and rubidium hydroxide.

6. The process of claim 1 , comprising adding the base in step (ii) such that a pH of at least 12 is established.

7. The process of claim 1 , in which the stripping in step (iii) is carried out under an absolute pressure of from 0.5 bar to 2 bar and at a temperature of from 80° C. to 120° C.

8. The process of claim 1 , in which the stripping gas is steam.

9. The process of claim 1 , comprising purging organic constituents out of the stream obtained in step (iii) after cooling of the stripping gas stream loaded with impurities to a temperature of 10° C. to 60° C., to obtain a stream depleted in organic constituents.

10. The process of claim 9 , comprising partially to completely returning the stream depleted in organic constituents to the stripping (iii).

11. The process of claim 9 , comprising sending the stream depleted in organic constituents, where it is not returned to the stripping (iii), directly to a waste water treatment.

12. The process of claim 1 , comprising sending the stripped waste water obtained in step (iii) directly to a waste water treatment.

13. The process of claim 1 , in which the alkaline waste water used in step (i) originates from step c) or step d) or step e) the following process steps:
a) nitration of benzene with nitric acid or a mixture of nitric acid and sulfuric acid and separating off of the aqueous phase;
b) washing of the organic process product obtained in step a);
c) alkaline washing of the washed organic process product obtained in step b);
d) optional separation of benzene and/or nitrobenzene out of the alkaline waste water obtained in step c); and
e) optional stripping of the alkaline waste water obtained in step c) or step d).

Assignees

• Bayer Materialscience Ag
• Covestro Deutschland Ag

Inventors

• Knauf Thomas
• Mairata Antoni
• Sluyts Erik
• Van Tricht Jan

Classifications

• C02F2103/36

  from the manufacture of organic compounds · CPC title

• C07C205/06

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

• C07C201/08

  by substitution of hydrogen atoms by nitro groups · CPC title

• C07C201/16

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

• C02F2101/38

  containing nitrogen · CPC title