Process for workup of NOx-containing offgases from wastewater streams of nitration plants

• US 9,630,866 B2
• Filed: 12/13/2010
• Issued: 04/25/2017
• Est. Priority Date: 12/16/2009
• Status: Expired due to Fees

• Current Assignee: BASF SE
• Original Assignee: BASF SE
• Inventors: Fritz, Ruediger, Hempel, Renate, Zoellinger, Michael, Allardt, Holger, Reetz, Reiner
• Primary Examiner(s): Nguyen, Nam
• Assistant Examiner(s): Norris, Claire
• Application Number:
  US13/511,256
• Publication Number:
  US 20120228218A1
• Time in Patent Office: 2,325 Days
• Field of Search: 210665, 210612, 210631, 210749, 435262, 4352625
• CPC Class Codes: C01B 21/40 Preparation by absorption of oxides of nitrogen C01B21/26 takes precedence
• CPC Class Codes: C02F 1/20 by degassing, i.e. liberation of dissolved gases degasification of liquids in general B01D19/00; arrangement of degassing apparatus in boiler feed supply F22D
• CPC Class Codes: C02F 1/78 with ozone C02F1/4672 takes precedence
• CPC Class Codes: C02F 2103/36 from the manufacture of organic compounds
• CPC Class Codes: C02F 2209/008 comprising telecommunication features, e.g. modems or antennas
• CPC Class Codes: C02F 2209/02 Temperature
• CPC Class Codes: C02F 2209/06 pH
• CPC Class Codes: C02F 9/00 Multistage treatment of water, waste water or sewage
• CPC Class Codes: C07C 201/08 by substitution of hydrogen atoms by nitro groups
• CPC Class Codes: C07C 205/06 having nitro groups bound to carbon atoms of six-membered aromatic rings

Abstract

The present invention relates to a process for workup of nitrite-comprising alkaline process wastewaters from the nitration of aromatic compounds, wherein the alkaline process wastewater is acidified by addition of acids and the offgas which comprises nitrogen oxides and escapes from the acidified process wastewater is worked up, comprising the steps of

• • a) acidifying the process wastewater by adding acid to a pH below 5, which forms an organic phase which separates out, an acidic aqueous phase and a gaseous NO_x-containing phase, and
  • b) removing the gaseous NO_x-containing phase.

Claims

1. A process for workup of an alkaline process wastewater obtained from a nitration of an aromatic compound to produce mono-, di- and tri-nitroaromatics, comprising:

(a) acidifying the alkaline process wastewater by adding acid to obtain a mixture with a pH below 5, which forms an organic phase which separates out, an acidic aqueous phase, and a gaseous NO_x-containing phase, and

(b) removing the gaseous NO_x-containing phase,

wherein the acid in (a) is a concentrated sulfuric acid obtained from the workup of an aqueous sulfuric acid-containing phase obtained in the nitration, wherein the concentrated sulfuric acid has a sulfuric acid concentration of 85% to 95% by weight.

2. The process of claim 1, wherein the NO_x formed in the course of acidification in step (a) are stripped out of the organic and acidic aqueous phases by an inert gas and converted to the gaseous phase.

3. The process of claim 1, wherein the NO_x formed in the course of acidification in (a) are stripped out of the organic and acidic aqueous phases by nitrogen, mixtures of nitrogen and oxygen, air or carbon dioxide and converted to the gaseous NO_x-containing phase.

4. The process of claim 1, wherein the alkaline process wastewater originates from the scrubbing of a crude product from the nitration with aqueous alkali metal carbonate or alkali metal hydrogencarhonate solution, and nitrogen oxides are stripped out of the organic and acidic aqueous phases by the carbon dioxide formed in the course of acidification of the alkaline process wastewater and converted to the gaseous NO_x-containing phase.

5. The process of claim 1, wherein the aromatic compound to be nitrated is benzene, toluene, xylene, chlorobenzene or dichlorobenzene.

6. The process of claim 1, wherein the alkaline process wastewater is acidified at a temperature of 20 to 90°

C.

7. The process of claim 6, wherein the temperature is from 55 to 70°

C.

8. The process of claim 1, wherein (b) is performed before further treatment of the organic and aqueous phases.

9. The process of claim 1, wherein the acidic aqueous phase is extracted with a solvent after removal of the organic phase.

10. The process of claim 1, wherein the acidic aqueous phase, after removal of the organic phase, is sent to an ozonolysis, a thermolysis or a biological wastewater treatment.

11. The process of claim 1, further comprising, after (b):

(c) further processing of the NO_x present in the gaseous NO_x-containing phase removed to produce nitric acid.

12. The process of claim 11, wherein the gaseous NO_x-containing phase removed is supplied in (c), without prior purification and removal of other gas constituents, directly to an absorption column for nitric acid production.

13. The process of claim 11, wherein the nitric acid obtained in (c) is recycled into the nitration of the aromatic compounds.

14. The process of claim 1, wherein the NO_x-containing phase removed after (b) is sent to an incineration.

15. The process of claim 1, wherein the alkaline process wastewater contains nitrites and the amount of nitrites is lowered by 90% to 99% after (a) and (b).

16. The process of claim 1, wherein the concentrated sulfuric acid has a sulfuric acid concentration of 90% to 93% by weight.

17. In a process of nitrating an aromatic compound, wherein an alkaline process wastewater is obtained from the nitration and a concentrated sulfuric acid phase is obtained from a distillation of an aqueous phase produced in the nitration, the improvement comprising (a) acidifying the alkaline process wastewater with the concentrated sulfuric acid phase to produce an aqueous phase, an organic phase and a gaseous NO_x-containing phase and (b) removing the gaseous NO_x-containing phase.