Process for scrubbing dinitrotoluene

Patent metadata

Field	Value
Publication number	US-9249083-B2
Application number	US-201313870506-A
Country	US
Kind code	B2
Filing date	Apr 25, 2013
Priority date	Apr 25, 2012
Publication date	Feb 2, 2016
Grant date	Feb 2, 2016

Abstract

The invention relates to a process for scrubbing a crude mixture comprising dinitrotoluene, nitric acid, nitrogen oxides and sulfuric acid obtained in the nitration of toluene after the nitrating acid has been separated off, which comprises two scrubbing steps (SS-I) and (SS-II), wherein
i) in a first scrubbing step (SS-I), the crude mixture is extracted with a scrubbing acid I comprising nitric acid, nitrogen oxides and sulfuric acid in a scrub comprising at least one extraction stage, where the scrubbing acid discharged from the first extraction stage (SS-I-1) of the first scrubbing step (SS-I) has a total acid content of from 20 to 40% by weight and a prescrubbed crude mixture is obtained, ii) in a second scrubbing step (SS-II), the prescrubbed crude mixture comprising dinitrotoluene is extracted with a scrubbing acid II in a scrub comprising at least one extraction stage, where the scrubbing acid discharged from the first extraction stage (SS-II-1) of the second scrubbing step (SS-II) has a pH of less than or equal to 4 and a mixture comprising dinitrotoluene which is essentially free of nitric acid, sulfuric acid and nitrogen oxides is obtained.

First claim

The invention claimed is:

1. A process for scrubbing a crude mixture comprising dinitrotoluene, nitric acid, nitrogen oxides and sulfuric acid obtained in the nitration of toluene after the nitrating acid has been separated off, the process comprising:
i) extracting in countercurrent a crude mixture with a scrubbing acid I comprising nitric acid, nitrogen oxides and sulfuric acid in a scrub comprising at least two extraction stages, such that scrubbing acid discharged from a first extraction stage (SS-I-1) of the extraction of stage i) has a total acid content of from 20 to 40% by weight, to obtain a prescrubbed crude mixture;
ii) extracting in countercurrent the prescrubbed crude mixture comprising dinitroluene with a scrubbing acid II in a scrub comprising at least two extraction stages, such that scrubbing acid discharged from a first extraction stage (SS-II-1) of the extraction of stage ii) has a pH of less than or equal to 4 and has a content of sulfate of not more than 100 ppm, a content of nitric acid of not more than 2000 ppm and a content of nitrogen oxides (calculated as HNO 2 ) of not more than 50 ppm, to obtain a mixture comprising dinitrotoluene which is essentially free of nitric acid, sulfuric acid and nitrogen oxides.

2. The process according to claim 1 , wherein the extracting i) comprises from 2 to 4 extraction stages.

3. The process according to claim 1 , wherein the extracting ii) comprises from 2 to 4 extraction stages.

4. The process according to claim 1 , wherein the scrubbing acid discharged from the first extraction stage (SS-II-1) of the extraction of stage ii) has a pH of from 0 to 3.

5. The process according to claim 1 , wherein the scrubbing acid discharged from the first extraction stage (SS-II-1) of the extraction of stage ii) has a pH of from 0.5 to 2.

6. The process according to claim 1 , wherein water or a scrubbing acid having a total acid content of from 0.2 to 1.5% by weight is fed to a last extraction stage (SS-I-n) of the extraction of stage i).

7. The process according to claim 1 , wherein water is fed to a last extraction stage (SS-II-n) of the extraction of stage ii).

8. The process according to claim 1 , wherein:
I) in the first extraction stage (SS-I-1) of the extraction of stage i), the crude mixture comprising dinitrotoluene, nitric acid, nitrogen oxides and sulfuric acid is fed into a first mixer (M-I-1) together with circulated scrubbing acid (SA-I-1) from a first phase separation apparatus (S-I-1) belonging to this first extraction stage and excess scrubbing acid (SA-I-2) from the subsequent extraction stage (SS-I-2), and a scrubbing emulsion formed in the mixer is separated in the first phase separation apparatus (S-I-1) into the scrubbing acid (SA-I-1) and crude mixture which has been scrubbed once (DNT-I-1); and
II) the crude mixture which has been scrubbed once (DNT-I-1) is, in the subsequent extraction stage (SS-I-2) of the extraction of stage i), fed into a second mixer (M-I-2) belonging to this extraction stage together with the circulated scrubbing acid (SA-I-2) from a second phase separation apparatus (S-I-2) belonging to this extraction stage and, if the extraction of stage i) comprises more than 2 extraction stages, with excess scrubbing acid (SA-I-3) from the subsequent extraction stage (SS-I-3) or, if the extraction of stage i) comprises precisely 2 extraction stages, with fresh water or scrubbing acid.

9. The process according to claim 1 , wherein:
I) in the first extraction stage (SS-II-1) of the extraction of stage ii), the prescrubbed crude mixture comprising dinitrotoluene is fed into a first mixer (M-II-1) belonging to this extraction stage together with circulated scrubbing acid (SA-II-1) from a first phase separation apparatus (S-II-1) belonging to this extraction stage and excess scrubbing acid (SA-II-2) from the subsequent extraction stage (SS-II-2), the scrubbing emulsion formed in the first mixer is separated in the first phase separation apparatus (S-II-1) into the scrubbing acid (SA-II-1) and crude mixture which has been scrubbed once (DNT-II-1); and
II) the crude mixture which has been scrubbed once (DNT-II-1) is, in the subsequent extraction stage (SS-II-2) of the extraction of stage ii), fed into a second mixer (M-II-2) belonging to this extraction stage together with the circulated scrubbing acid (SA-II-2) from a second phase separation apparatus (S-II-2) belonging to this second extraction stage and, if the extraction of stage ii) comprises more than 2 extraction stages, with excess scrubbing acid (SA-I-3) from the subsequent extraction stage (SS-I-3) or, if the extraction of stage ii) comprises precisely 2 extraction stages, with fresh water.

10. The process according to claim 1 , wherein the volume ratio of dinitrotoluene-comprising crude mixture to scrubbing acid in the extraction stages of the extraction of stage i) and the extraction of stage ii) is from 1:4 to 10:1.

11. The process according to claim 1 , wherein the volume ratio of dinitrotoluene-comprising crude mixture to fresh water in the last extraction stage (S-II-n) of the extraction of stage ii) is from 1:2 to 15:1.

12. The process according to claim 1 , wherein a dinitrotoluene-comprising mixture comprising a total of not more than 800 ppm of nitrocresols and nitrophenols, not more than 600 ppm of nitrobenzoic acids, not more than 300 ppm of nitric acid and nitrogen oxides, and not more than 3 ppm of sulfate is taken off from the last extraction stage (SS-II-n) of the extraction of stage ii).

13. The process according to claim 1 , wherein the scrubbing acid discharged from the first extraction stage (SS-II-1) of the extraction of stage ii) has a total content of nitrocresols and nitrophenols of less than 5 ppm and a content of nitrobenzoic acids of less than 50 ppm.

14. The process according to claim 1 , wherein the scrubbing acid discharged from the first extraction stage (SS-II-1) of the extraction of stage ii) is neutralized and, optionally after removal of dinitrotoluene dissolved therein by extraction and removal of the extractant, fed without further pretreatment to the biological treatment stage of a water treatment plant.

Assignees

• Basf Se
• Meissner Gmbh & Co Kg Josef

Inventors

• Neto Samuel
• Fritz Ruediger
• Hempel Renate
• Allardt Holger
• Becker Barbara
• Leschinski Julia
• Ahrens Sebastian
• Hermann Heinrich
• Haendel Mirko
• Poehlmann Juergen

Classifications

• C07C201/06 Primary

  Preparation of nitro compounds · CPC title

• C07C205/06 Primary

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