Method of cleaning an apparatus used in the concentration of a mineral acid

Patent metadata

Field	Value
Publication number	US-12441614-B2
Application number	US-202017783375-A
Country	US
Kind code	B2
Filing date	Dec 16, 2020
Priority date	Dec 18, 2019
Publication date	Oct 14, 2025
Grant date	Oct 14, 2025

Abstract

The present invention relates to a method for preparing an apparatus (or a plant comprising a plurality of apparatuses), for example a heat exchanger, a vaporizer or a distillation column, for use in a process (in particular a continuously operated process) for concentrating a mineral acid by evaporation of water, wherein the apparatus or the plant comprises (at least) a device which is resistant to the mineral acid and the device is flushed with an aqueous alkali metal hydroxide solution having a concentration by mass of alkali metal hydroxide in the range from 1% to 30% at a temperature in the range from 40° C. to 90° C. for a time of from 2 hours to 7 days.

First claim

The invention claimed is:

1. A method for preparing and using an apparatus comprising an acid-resistant device,
wherein the acid-resistant device has a coating comprising steel enamel, silicon carbide, glass, tantalum, niobium, a perfluorinated polymer, or a composite of two or more thereof,
or
wherein the acid-resistant device is made of one of steel enamel, silicon carbide, glass, tantalum, niobium, a perfluorinated polymer, or a composite of two or more thereof,
the method comprising:
(a) flushing the acid-resistant device with an aqueous alkali metal hydroxide solution having a concentration by mass of alkali metal in the range from 1% to 30% at a temperature in the range from 40° C. to 90° C. for a time of from 2 hours to 7 days; and then subsequently
(b) using the apparatus comprising the acid-resistant device flushed in step (a) in a process of concentrating a mineral acid by evaporation of water, wherein said process comprises contacting the acid-resistant device with the mineral acid during the concentrating of the mineral acid or wherein said process comprises contacting the acid-resistant device with the mineral acid while the mineral acid has a concentration that was increased as a result of said concentrating of the mineral acid.

2. The method as claimed in claim 1 , wherein the alkali metal hydroxide solution comprises sodium hydroxide solution, potassium hydroxide solution, or a mixture thereof.

3. The method as claimed in claim 1 , wherein the flushing is carried out for a time of from 8 hours to 30 hours.

4. The method as claimed in claim 1 , wherein the acid-resistant device comprises a heat exchanger for heating the mineral acid, a distillation apparatus for removing organic compounds from the mineral acid, a vaporization apparatus, a heat exchanger for cooling the mineral acid after the mineral acid has been concentrated and/or a vessel for accommodating the mineral acid after the mineral acid has been concentrated.

5. The method as claimed in claim 4 , wherein the acid-resistant device is a heat exchanger which is designed for heating the mineral acid and/or for cooling the mineral acid after the mineral acid has been concentrated.

6. The method as claimed in claim 4 , wherein the acid-resistant device comprises a heat exchanger for cooling the mineral acid after the mineral acid has been concentrated and a vessel downstream thereof for accommodating the mineral acid after the mineral acid has been concentrated.

7. The method as claimed in claim 1 , wherein the mineral acid comprises sulfuric acid, nitric acid, or a mixture thereof.

8. The method as claimed in claim 7 , wherein the process of concentrating the mineral acid by evaporation of water comprises concentrating sulfuric acid that is used as a catalyst and diluent in a nitration of an aromatic compound with nitric acid to obtain an aromatic nitro compound.

9. The method as claimed in claim 8 , wherein the aromatic nitro compound comprises nitrobenzene or dinitrotoluene.

10. The method as claimed in claim 7 , wherein the process of concentrating the mineral acid by evaporation of water is used for concentrating sulfuric acid that has been diluted by use of the sulfuric acid as a desiccant for drying a gas.

11. The method as claimed in claim 10 , wherein the gas comprises chlorine.

12. The method as claimed in claim 1 , wherein the acid-resistant device comprises a coating comprising a perfluorinated polymer or wherein the acid-resistant device is made at least partly of a perfluorinated polymer, where the perfluorinated polymer is mechanically stabilized with an inert material.

13. The method as claimed in claim 1 , wherein the acid-resistant device comprises a coating comprising steel enamel, silicon carbide, glass, niobium and/or tantalum or wherein the acid-resistant device is made at least partly of steel enamel, silicon carbide, glass, niobium and/or tantalum.

14. The method as claimed in claim 1 , wherein the acid-resistant device is not disassembled for the purpose of carrying out the flushing.

15. The method as claimed in claim 14 , wherein the apparatus is not disassembled for the purpose of carrying out the flushing of the acid-resistant device.

Assignees

• Covestro Intellectual Property Gmbh & Co Kg
• Covestro Deutschland Ag

Inventors

• Pennemann Bernd
• Tajvidi Kameh

Classifications

• F28G9/00

  Cleaning by flushing or washing, e.g. with chemical solvents (appliances using jets of fluid for removing debris F28G1/16, F28G3/16) · CPC title

• C07C201/08

  by substitution of hydrogen atoms by nitro groups · CPC title

• C01B21/44

  Concentration {(C01B21/40 takes precedence)} · CPC title

• B01D53/28

  Selection of materials for use as drying agents · CPC title

• B01D53/263

  by absorption · CPC title