Process for separating an isocyanate prepared by phosgenation of a primary amine in the gas phase from the gaseous crude product of the phosgenation

Patent metadata

Field	Value
Publication number	US-9932299-B2
Application number	US-201414765870-A
Country	US
Kind code	B2
Filing date	Feb 5, 2014
Priority date	Feb 8, 2013
Publication date	Apr 3, 2018
Grant date	Apr 3, 2018

Abstract

The present invention relates to a process for separating an isocyanate prepared by reaction of a primary amine with an excess of phosgene in the gas phase from the gaseous crude product obtained in the reaction, wherein
(i) the gaseous crude product is partially liquefied by contacting with a quenching liquid, (ii) the gas phase obtained in step (i) is partially condensed, (iii) the condensate obtained in step (ii) is used as the quenching liquid in step (i), (iv) the portions of the gas phase that were not condensed in step (ii) are at least partially liquefied, (v) the liquid phase obtained in step (iv) is likewise used as the quenching liquid in step (i), and (vi) the liquid phase obtained in step (i) is worked up to the pure isocyanate without previously being used as quenching liquid.

First claim

What is claimed:

1. A process for separating an isocyanate prepared by reaction of a primary amine with an excess of phosgene, comprising:
(i) converting a gaseous crude product obtained by a gas phase reaction of the primary amine with the excess of phosgene and that comprises at least isocyanate, hydrogen chloride and unreacted phosgene, into a liquid phase comprising at least quenching liquid and isocyanate and a gas phase comprising at least hydrogen chloride and phosgene by contacting the gaseous crude product with at least one quenching liquid;
(ii) partially condensing the gas phase obtained in step (i) to obtain a condensate and a portion of the gas phase that is not condensed;
(iii) using the condensate obtained in step (ii) as at least one quenching liquid in step (i);
(iv) at least partially liquefying the portion of the gas phase not condensed in step (ii) to obtain a liquid phase;
(v) using the liquid phase obtained in step (iv) as at least one quenching liquid in step (i); and
(vi) working up the liquid phase obtained in step (i) to pure isocyanate without previously using it as quenching liquid.

2. The process according to claim 1 , comprising using a condenser in step (ii) in which the gas phase and the condensate are guided co-currently.

3. The process according to claim 1 , wherein the at least partial liquefaction of the portion of the gas phase not condensed in step (ii) is carried out in step (iv) in a washing column having at least one separator stage, wherein at least one solvent stream is fed to the washing column as a washing liquid.

4. The process according to claim 3 , comprising removing a gaseous top stream from the washing column and condensing the gaseous top stream in a condenser to obtain a condensate, and feeding the condensate so obtained back into the washing column as additional washing liquid.

5. The process according to claim 3 , comprising feeding exactly one solvent stream to the washing column.

6. The process according to claim 3 , comprising feeding a solvent stream to the washing column above the separator stage where a single separator stage is present or, where a plurality of separator stages are present, above the uppermost separator stage, wherein the solvent stream comprises isocyanate to be separated off in an amount by mass of from 0 ppm to 100 ppm, based on the total mass of the solvent stream.

7. The process according to claim 3 , comprising feeding a solvent stream to the washing column beneath the separator stage where a single separator stage is present or, where a plurality of separator stages are present, beneath the lowermost separator stage, wherein the solvent stream comprises isocyanate to be separated off in an amount by mass of from 0 to 20%, based on the total mass of the solvent stream.

8. The process according to claim 1 , comprising obtaining steam by step (ii).

9. The process according to claim 1 , comprising bringing the quenching liquid of step (iii) and the quenching liquid of step (v) into contact with the gaseous crude product separately from one another in step (i).

10. The process according to claim 9 , comprising bringing the quenching liquid of step (v) into contact with the gaseous crude product above the quenching liquid of step (iii).

11. The process according to claim 1 , comprising combining the quenching liquid of step (iii) and the quenching liquid of step (v) and bringing them into contact with the gaseous crude product in step (i) together as a quenching liquid stream.

12. The process according to claim 1 , wherein comprising passing:
(a) a portion of the condensate obtained in step (ii),
(b) a solvent stream, or
(c) stream (a) and stream (b)
into a condenser in addition to the gas phase obtained in step (i).

13. The process according to claim 1 , comprising carrying out the contacting of the gaseous crude product with the at least one quenching liquid by injecting the at least one quenching liquid into the gaseous crude product.

14. The process according to claim 1 , wherein the primary amine comprises an isomer of toluylenediamnine, an isomer of diphenylmethanediamine, 1,6-hexamethylenediamine, an isomer of isophoronediamine or an isomer of diaminodicyclohexylmethane.

Assignees

• Bayer Materialscience Ag
• Covestro Deutschland Ag

Inventors

• Steffens Friedhelm
• Mahr Bastian

Classifications

• C07C263/20 Primary

  Separation; Purification · CPC title

• C07C265/14

  containing at least two isocyanate groups bound to the same carbon skeleton · CPC title

• C07C253/00

  Preparation of carboxylic acid nitriles (of cyanogen or compounds thereof C01C3/00) · CPC title

• C07C263/18

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

• B01D3/009

  in combination with chemical reactions · CPC title