Process for acidic scrubbing of dinitrotoluene in the presence of hydrocyanic acid

Patent metadata

Field	Value
Publication number	US-9688606-B2
Application number	US-201415031100-A
Country	US
Kind code	B2
Filing date	Oct 22, 2014
Priority date	Oct 22, 2013
Publication date	Jun 27, 2017
Grant date	Jun 27, 2017

Abstract

Process for scrubbing a crude mixture which is obtained in the nitration of toluene after separating off the nitrating acid and comprises dinitrotoluene, nitric acid, nitrogen oxides and sulfuric acid, which comprises two scrubbing steps (WS-I) and (WS-II), wherein
i) in a first scrubbing step (WS-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 (WS-I-1) of the first scrubbing step (WS-I) has a total acid content of from 10 to 40% by weight and a content of from 80 to 350 ppm of hydrocyanic acid, giving a prescrubbed crude mixture,
ii) in a second scrubbing step (WS-II), the prescrubbed crude mixture comprising dinitrotoluene is extracted with a scrubbing acid II in a scrub comprising at least one, preferably at least 2, extraction stage(s), where the scrubbing acid discharged from the first extraction stage (WS-II-1) of the second scrubbing step (WS-II) has a pH of less than or equal to 4, giving a dinitrotoluene-comprising mixture which is essentially free of nitric acid, sulfuric acid, nitrogen oxides and hydrocyanic acid and has a content of not more than 300 ppm of nitric acid and nitrogen oxides, not more than 3 ppm of sulfate and not more than 50 ppm of hydrocyanic acid.

First claim

The invention claimed is:

1. A process for scrubbing a crude mixture which is obtained in the nitration of toluene after separating off the nitrating acid and comprises dinitrotoluene, nitric acid, nitrogen oxides and sulfuric acid, which comprises two scrubbing steps (WS-I) and (WS-II), wherein
i) in a first scrubbing step (WS-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 (WS-I-1) of the first scrubbing step (WS-I) has a total acid content of from 10 to 40% by weight and a content of from 80 to 350 ppm of hydrocyanic acid, giving a prescrubbed crude mixture,
ii) in a second scrubbing step (WS-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 (WS-II-1) of the second scrubbing step (WS-II) has a pH of less than or equal to 4 and a content of sulfate of not more than 100 ppm, a content of nitric acid of not more than 2000 ppm, a content of nitrogen oxides (calculated as HNO 2 ) of not more than 50 ppm and a content of hydrocyanic acid of not more than 120 ppm, giving a dinitrotoluene-comprising mixture which is essentially free of nitric acid, sulfuric acid, nitrogen oxides and hydrocyanic acid and has a content of not more than 300 ppm of nitric acid and nitrogen oxides, not more than 3 ppm of sulfate and not more than 50 ppm of hydrocyanic acid.

2. The process according to claim 1 , wherein the first scrubbing step (WS-I) comprises from 2 to 4 extraction stages and is carried out in countercurrent.

3. The process according to claim 1 , wherein the second scrubbing step (WS-II) comprises from 2 to 6 extraction stages and is carried out in countercurrent.

4. The process according to claim 1 , wherein the scrubbing acid discharged from the first extraction stage (WS-II-1) of the second scrubbing step (WS-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 (WS-II-1) of the second scrubbing step (WS-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 the last extraction stage (WS-I-n) of the first scrubbing step (WS-I).

7. The process according to claim 1 , wherein water is fed to the last extraction stage (WS-II-n) of the second scrubbing step (WS-II).

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

9. The process according to claim 1 , wherein
I) in the first extraction stage (WS-II-1) of the second scrubbing step (WS-II), the prescrubbed crude mixture comprising dinitrotoluene is fed together with circulating scrubbing acid (WSR-II-1) from a first phase separation apparatus (S-II-1) belonging to this extraction stage and excess scrubbing acid (WSR-II-2) from the subsequent extraction stage (WS-II-2) into a first mixer (M-II-1) belonging to this extraction stage, the scrubbing emulsion formed in the first mixer is separated in the first phase separation apparatus (S-II-1) into the scrubbing acid (WSR-II-1) and crude mixture (DNT-II-1) which has been scrubbed once, and
II) the crude mixture (DNT-II-1) which has been scrubbed once is, in the subsequent extraction stage (WS-II-2) of the second scrubbing step (WS-II), fed together with the circulated scrubbing acid (WSR-II-2) from a second phase separation apparatus (S-II-2) belonging to this second extraction stage and, when the second scrubbing step (WS-II) comprises more than 2 extraction stages to (WS-II-m), with excess scrubbing acid (WSR-II-3) to (WSR-II-m) from the subsequent extraction stage (WS-II-3) to (WS-II-m) or, when the scrubbing step comprises precisely two extraction stages, with freshly introduced water (W-II-1) into a second mixer (M-II-2) belonging to this extraction stage of the second scrubbing step (WS-II).

10. The process according to claim 1 , wherein the volume ratio of dinitrotoluene-comprising crude mixture and scrubbing acid in the extraction stages of the scrubbing steps (W-I) and (W-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 freshly introduced water in the last extraction stage (W-II-m) of the second scrubbing step (W-II) is from 1:2 to 15:1.

12. The process according to claim 1 , wherein a dinitrotoluene-comprising mixture which comprises a total of not more than 800 ppm of nitrocresols and nitrophenols, not more than 600ppm of nitrobenzoic acids, not more than 300 ppm of nitric acid, not more than 50 ppm of hydrocyanic acid and not more than 3 ppm of sulfate is taken off from the last extraction stage (WS-II-m) of the second scrubbing step (WS-II).

13. The process according to claim 1 , wherein the scrubbing acid discharged from the first extraction stage (WS-II-1) of the second scrubbing step (WS-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 12 , wherein the scrubbing acid discharged from the first extraction stage (WS-II-1) of the second scrubbing step (WS-II) is after dinitrotoluene dissolved therein has been separated off by extraction and the extractant has been separated off and after neutralization, fed without further pretreatment to the biological treatment stage of a water treatment plant.

15. The process according to claim 14 , wherein the scrubbing acid which has been separated off from the first extraction stage (WS-II-1) of the second scrubbing step (WS-II) is extracted with toluene and the extracted scrubbing acid is stripped with a stripping gas, giving a wastewater having a hydrocyanic acid content of less than 1 ppm.

Assignees

• Basf Se
• Meissner Gmbh & Co Kg Josef

Inventors

• Neto Samuel
• Fritz Rüdiger
• Hempel Renate
• Allardt Holger
• Dai Yuan Shen
• Becker Barbara
• Ahrens Sebastian
• Leschinski Julia
• Hermann Henrich
• Haendel Mirko
• Pöhlmann Jürgen

Classifications

• B01D2011/002

  Counter-current extraction · CPC title

• B01D11/0488

  Flow sheets · CPC title

• C07C201/16 Primary

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

• C02F1/26

  by extraction · CPC title

• C02F2101/18

  Cyanides · CPC title