Method for producing isocyanates

Patent metadata

Field	Value
Publication number	US-10577311-B2
Application number	US-201615762224-A
Country	US
Kind code	B2
Filing date	Sep 20, 2016
Priority date	Sep 24, 2015
Publication date	Mar 3, 2020
Grant date	Mar 3, 2020

Abstract

The invention relates to a method for an economically and technically improved embodiment of a production interruption in a production method for isocyanates by phosgenation of the corresponding amines, in which the entire production plant is not closed while one or more parts of the plant is taken out of operation, rather the input materials and/or reaction products available in the production plant are recirculated through at least one part of the plant that has not been taken out of operation. The invention further relates to a plant for producing isocyanates and to a method for operating a plant for producing isocyanates.

First claim

The invention claimed is:

1. A process for preparing isocyanates, comprising:
I) reacting an amine with phosgene in the liquid phase in a reaction zone comprising
I.1) a unit for providing an amine in the form of an amine solution in a solvent,
I.2) a unit for providing phosgene in the form of a phosgene solution in a solvent,
I.3) a unit for providing a solvent,
I.4) a mixing unit for mixing the amine solution in the solvent with the phosgene solution in the solvent and optionally further solvent, the mixing unit being configured to be continuously charged with the amine solution in the solvent, the phosgene solution in the solvent, and optionally further solvent, and
I.5) a reaction space arranged downstream of the mixing unit, for conducting a phosgenation reaction, with a separator unit optionally connected downstream, wherein the reaction space and/or the separator unit have outlet conduits for a liquid stream and a gaseous stream;
wherein
the amine, in the form of the amine solution with a mass flow rate m 2 from the unit for providing an amine, and
the phosgene, in the form of the phosgene solution with a mass flow rate m 3 from the unit for providing phosgene, and optionally solvent from the unit for providing a solvent with a mass flow rate m 4 are conducted into the mixing unit and mixed therein, and
the mixture obtained is converted in the downstream reaction space and separated into a liquid stream comprising crude isocyanate and solvent, and a gaseous stream comprising phosgene and hydrogen chloride;

II) separating the liquid stream from step I) into a liquid stream comprising solvent and crude isocyanate, and a gaseous stream comprising phosgene and hydrogen chloride in a distillation apparatus;
III) separating the liquid stream obtained in II) into a gaseous stream comprising solvent and a liquid stream comprising crude isocyanate in a distillation apparatus;
IV) separating the gaseous stream obtained in III), into a liquid stream comprising solvent and a gaseous stream comprising phosgene in a distillation apparatus;
V) obtaining a liquid isocyanate stream from the liquid stream obtained in III), resulting in a gaseous stream comprising secondary components and optionally solvent, in a distillation apparatus, and which optionally comprises removing polymeric isocyanate fractions in an upstream unit for polymer removal as a separate stream;
VI) absorbing the gaseous streams obtained in steps I), II) and IV) in solvent to obtain a liquid stream comprising solvent and phosgene, and a gaseous stream comprising hydrogen chloride in an absorption apparatus;
VII) optionally, absorbing the gaseous stream obtained in VI) in water or dilute hydrochloric acid in an absorption apparatus with formation of an offgas stream;
VIII) optionally, cleaning offgas streams at least from VII), in a workup apparatus configured to work-up offgas obtained from at least step VII);
IX) optionally, preparing phosgene from carbon monoxide and chlorine in an apparatus configured to prepare phosgene, and which is connected to the unit for provision of phosgene;
wherein
the process is interrupted, the interruption comprising shutting down one or more, but not all, plant sections from (I) to (IX), reducing the mass flow rate m 2 to zero and, in at least one of the plant sections that has not been shut down,
(i) recycling the output stream from this at least one plant section which has not been shut down into the respective plant section,
or
(ii) conducting the output stream from this at least one plant section which has not been shut down into a plant section which is upstream or downstream and thence, optionally via further plant sections that have not been shut down, recycling said output stream into the plant section said output stream originated from.

2. The process as claimed in claim 1 , comprising step (IX).

3. The process as claimed in claim 1 , in which the gaseous output stream from the reaction space or, if present, from the separation unit in step I) is used as input stream for the absorption apparatus in VI), wherein the liquid output stream from the absorption apparatus in VI) is conducted via the units for providing phosgene and for mixing into the reaction space and thence, if present, into the separation unit in step I).

4. The process as claimed in claim 1 , in which the liquid output stream from the reaction space or, if present, from the separation unit in step I) is used as input stream for the distillation apparatus in step II), wherein the gaseous output stream from the distillation apparatus in step II) is used as input stream for the absorption apparatus in step VI), wherein the liquid output stream from the absorption apparatus in step VI) is conducted via the units for providing phogene and for mixing into the reaction space and thence, if present, into the separation unit in step I).

5. The process as claimed in claim 1 , in which the liquid output stream from the reaction space or, if present, from the separation unit in step I) is used as input stream for the distillation apparatus in step II), wherein the liquid output stream from the distillation apparatus in step II) is used as input stream for the distillation apparatus in step III), wherein the gaseous output stream from the distillation apparatus in step III), optionally after condensation in a condenser, is used as input stream for the distillation apparatus in step IV), wherein the liquid output stream from the distillation apparatus in step IV) is conducted via the units for providing solvent, for providing an amine and for mixing into the reaction space and thence, if present, into the separation unit in step I).

6. The process as claimed in claim 1 , which additionally comprises a unit for polymer removal in V) wherein the bottoms output stream from the unit for polymer removal, optionally via a storage tank, is used as input stream for the distillation apparatus in step III), wherein the liquid output stream from the distillation apparatus in step III) is recycled into the unit for polymer removal.

7. The process as claimed in claim 1 , additionally comprising step (VII) wherein the liquid output stream from the absorption apparatus in step VII), optionally via a storage tank, is recycled back into the absorption apparatus in step VII).

8. The process as claimed in claim 1 , in which the amine comprises at least one of methylenediphenyldiamine, polymethylenepolyphenylenepolyamine, a mixture of methylenediphenyldiamine and polymethylenepolyphenylenepolyamine, tolylenediamine, xylylenediamine, hexamethylenediamine, isophoronediamine and naphthyldiamine.

9. A plant for preparation of isocyanates in the liquid phase, comprising the following plant sections:
I) a reaction zone comprising
I.1) a unit for providing an amine in the form of an amine solution in a solvent,
1.2) a unit for providing phosgene in the form of a phosgene solution in a solvent,
1.3) a unit for providing a solvent,
1.4) a mixing unit for mixing the amine solution in the solvent with the phosgene solution in the solvent and optionally further solvent, the mixing unit being configured to be continuously charged with the amine solution in the solvent, the phosgene solution in the solvent, and optionally further solvent, and
1.5) a reaction space arranged downstream of the mixing unit, for conducting a phosgenation reaction, with a separator unit optionally connected downstream, wherein the reaction space and/or the separator unit have outlet conduits for a liquid stream and a gaseous stream;

II) a distillation apparatus configured to separate the liquid stream from I) into a liquid stream and a gaseous stream;
III) a distillation apparatus configured to separate the

Assignees

• Covestro Deutschland Ag

Inventors

• Knauf Thomas
• Manzel Dirk
• Plathen Peter
• Spriewald Jürgen

Classifications

• C07C263/10 Primary

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

• B01J2219/00225

  stopping the system or generating an alarm · CPC title

• C07C263/20

  Separation; Purification · CPC title

• B01J19/24

  Stationary reactors without moving elements inside (B01J19/08, B01J19/26 take precedence; with stationary particles B01J8/02) · CPC title

• B01J2219/00222

  taking actions · CPC title