Method for producing isocyanates

Patent metadata

Field	Value
Publication number	US-9593075-B2
Application number	US-201314385270-A
Country	US
Kind code	B2
Filing date	Mar 15, 2013
Priority date	Mar 19, 2012
Publication date	Mar 14, 2017
Grant date	Mar 14, 2017

Abstract

The invention relates to a method for preparing isocyanates by phosgenating the corresponding amines, wherein low-boiling secondary components, excess phosgene, and the co-product hydrogen chloride are separated from the crude liquid isocyanate stream, which is obtained after the phosgenation has occurred, within a maximum of 60 minutes, and wherein the crude liquid isocyanate stream is not exposed to temperatures above 250° C. until said separation.

First claim

What is claimed is:

1. A continuous method for preparing an isocyanate by
(i) reacting the corresponding primary amine with phosgene in stoichiometric excess in a reaction chamber, wherein the reaction is carded out either in the liquid phase in the presence of an inert solvent or in the gas phase, wherein a stream comprising a liquid inert solvent is added to the process product after leaving the reaction chamber,

such that a crude product 1 is obtained comprising the desired isocyanate, inert solvent, secondary components having a boiling point below that of the isocyanate (low boilers), secondary components having a boiling point above that of the isocyanate (high boilers), hydrogen chloride and unreacted phosgene,
(ii) separating the crude product 1 into a liquid product stream 2 containing the desired isocyanate and into a gaseous product stream 3,
(iii) working-up the liquid product stream 2, wherein inert solvent, low boilers, high boilers, hydrogen chloride and phosgene are removed from the desired isocyanate,

characterized in that
the low boilers, the hydrogen chloride and the phosgene are removed in step (iii) within a period of 30 second to 60 minutes following the separation of the crude product 1 in step (ii) into the product streams 2 and 3, and the temperature of the product stream 2 is always maintained below or equal to 250° C.

2. The method as claimed in claim 1 , in which the workup step (iii) is carried out in more than one stage, wherein inert solvent, low boilers, hydrogen chloride and phosgene are removed from the product stream 2 by distillation in a first stage (iii.a), such that a product stream 4 depleted in inert solvent, low boilers, hydrogen chloride and phosgene is obtained, and in at least one further stage (iii.b) pure isocyanate 5 is obtained from the product stream 4 by distillation.

3. The method as claimed in claim 2 , in which step (iii.a) is carried out in a dephosgenation column and step (iii.b) is carried out in a column for final purification, and in which the residence time of isocyanate formed in step (i) after the separation of the crude product 1 in step (ii) up to the effluent of the product stream 4 depleted in inert solvent, low boilers, hydrogen chloride and phosgene from the dephosgenation column in step (iii.a) is 30 seconds to 60 minutes.

4. The method as claimed in any of claims 1 to 3 , in which the reaction of the primary amine with phosgene in the reaction chamber in step (i) is carried out in the gas phase.

5. The method of claim 1 , in which the primary amine used is toluylenediamine.

6. A continuous method for preparing an isocyanate by
(i) reacting the corresponding primary amine with phosgene in stoichiometric excess in a reaction chamber, wherein the reaction is carried out in the gas phase, wherein a stream comprising a liquid inert solvent is added to the process product after leaving the reaction chamber,

such that a crude product 1 is obtained comprising the desired isocyanate, inert solvent, secondary components having a boiling point below that of the isocyanate (low boilers), secondary components having a boiling point above that of the isocyanate (high boilers), hydrogen chloride and unreacted phosgene,
(ii) separating the crude product 1 into a liquid product stream 2 containing the desired isocyanate and into a gaseous product stream 3,
(iii) working-up the liquid product stream 2, wherein inert solvent, low boilers, high boilers, hydrogen chloride and phosgene are removed from the desired isocyanate,

characterized in that
the low boilers, the hydrogen chloride and the phosgene are removed in step (iii) within a period of 30 second to 60 minutes following the separation of the crude product 1 in step (ii) into the product streams 2 and 3, and the temperature of the product stream 2 is always maintained below or equal to 250° C.

7. The method of claim 6 , in which the workup step (iii) is carried out in more than one stage, wherein inert solvent, low boilers, hydrogen chloride and phosgene are removed from the product stream 2 by distillation in a first stage (iii.a), such that a product stream 4 depleted in inert solvent, low boilers, hydrogen chloride and phosgene is obtained, and in at least one further stage (iii.b) pure isocyanate 5 is obtained from the product stream 4 by distillation.

8. The method of claim 7 , in which step (iii.a) is carried out in a dephosgenation column and step (iii.b) is carried out in a column for final purification, and in which the residence time of isocyanate formed in step (i) after the separation of the crude product 1 in step (ii) up to the effluent of the product stream 4 depleted in inert solvent, low boilers, hydrogen chloride and phosgene from the dephosgenation column in step (iii.a) is 30 seconds to 60 minutes.

9. The method of claim 6 , in which the primary amine used is toluylenediamine.

Assignees

• Bayer Ip Gmbh
• Covestro Deutschland Ag

Inventors

• Bruns Rainer
• Lorenz Wolfgang
• Rausch Andreas Karl
• Wershofen Stefan
• Loddenkemper Tim

Classifications

• C07C263/10 Primary

  by reaction of amines with carbonyl halides, e.g. with phosgene · CPC title

• C07C263/20

  Separation; Purification · CPC title

• Y02P20/582

  Recycling of unreacted starting or intermediate materials · CPC title

• C07C265/14

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