Process for preparing an isocyanate by partly adiabatically operated phosgenation of the corresponding amine

Patent metadata

Field	Value
Publication number	US-10851048-B2
Application number	US-201916677744-A
Country	US
Kind code	B2
Filing date	Nov 8, 2019
Priority date	Nov 13, 2018
Publication date	Dec 1, 2020
Grant date	Dec 1, 2020

Abstract

A process for preparing an isocyanate by reacting a primary amine with phosgene. The process includes providing an amine solution and adjusting its temperature in a heat exchanger, providing a phosgene solution and adjusting its temperature in a heat exchanger, mixing the amine solution with the phosgene solution, further conversion in an adiabatically operated reaction zone and the removing of the gas phase formed as a result of the chemical reaction in a separation zone, expanding the remaining liquid phase, further conversion of the liquid phase remaining after expansion in an indirectly heated reaction zone, and isolating the isocyanate from the obtained reaction solution. The temperature in the reaction zone and the temperature in the separation zone is adjusted by fixing a target value of 110° C. to 145° C. for the temperature of the reaction mixture and using the actual temperature of the reaction mixture for closed-loop control of the temperature of the solution of the primary amine and/or of the temperature of the solution of phosgene.

First claim

The invention claimed is:

1. A process for preparing an isocyanate by reacting a primary amine with phosgene, comprising:
I) providing a solution of the primary amine in a solvent and adjusting the temperature of the solution of the primary amine by indirect heat transfer in a heat exchanger operated with a heat carrier medium;
II) providing a solution of phosgene in a solvent and adjusting the temperature of the solution of phosgene by indirect heat transfer in a heat exchanger operated with a heat carrier medium;
III) mixing the solution of the primary amine and the solution of phosgene in a mixing unit to give a reaction mixture having a stoichiometric excess of phosgene based on the amino groups of the primary amine in the range from 40% to 200% of theory;
IV) running the reaction mixture through a reaction zone and through a separation zone that is arranged downstream in the flow direction of the reaction zone to form a gas phase under a pressure of 8.0 bar (abs.) to 50.0 bar (abs.) , wherein the reaction zone and the separation zone are not heated and are not cooled, and wherein the gas phase and remaining liquid phase from the separation zone are removed separately from one another;
V) expanding the liquid phase withdrawn from the separation zone with partial conversion of the liquid phase to the gas phase;
VI) running the liquid phase that remains after the expansion through an indirectly heated reaction zone, thereby forming:
(a) a hydrogen chloride and phosgene-containing gas phase which is removed, and
(b) an isocyanate- and solvent-containing liquid phase which is withdrawn from the indirectly heated reaction zone; and

VII) working up the isocyanate- and solvent-containing liquid phase to recover the solvent and obtain the isocyanate;
where the process comprises adjusting the temperature in the reaction zone and the temperature in the separation zone by fixing a target temperature of 110° C. to 145° C. for the temperature of the reaction mixture and using the actual temperature of the reaction mixture, measured continuously or at intervals, for closed-loop control of at least one of:
(a) the temperature of the solution of the primary amine to a temperature of 30° C. to 130° C. by means of the heat exchanger used in step I); and
(b) the temperature of the solution of phosgene to a temperature of −20° C. to 120° C. by means of the heat exchanger used in step II).

2. The process of claim 1 , in which the solution of the primary amine provided in step I) has a proportion by mass of primary amine based on the total mass of thereof of 25% to 50% and the solution of phosgene provided in step II) has a proportion by mass of phosgene based on the total mass of thereof of 45% to 90%.

3. The process of claim 1 , in which the gas phases obtained in steps IV), V) and VI) are worked up to obtain hydrogen chloride and phosgene and optionally solvent.

4. The process of claim 3 , in which the gas phases obtained in steps IV), V) and VI) are, prior to the workup, adjusted to a common pressure and combined.

5. The process of claim 1 , in which the mixing unit from step III) is not heated and not cooled.

6. The process of claim 1 , in which the mixing unit used in step III) comprises one or more dynamic mixers.

7. The process of claim 1 , in which reaction zone and separation zone from step IV) are disposed in a common reactor.

8. The process of claim 7 , in which the reactor is a tubular reactor in an upright arrangement.

9. The process of claim 8 , in which the reaction mixture obtained in step III) flows through the reactor from the bottom upward.

10. The process of claim 1 , in which the indirectly heated reaction zone from step VI) is part of a shell and tube reactor, the liquid phase remaining after the expansion in step V) is run through the tube interior thereof and a heating medium is run through the tube exterior thereof, or the liquid phase remaining after the expansion in step V) is run through the tube exterior thereof and a heating medium is run through the tube interior thereof.

11. The process of claim 1 , in which the heat exchangers used in step I) and in step II) are independently selected from the group consisting of shell and tube heat exchangers and plate heat exchangers.

12. The process of claim 1 , in which the heat exchangers used in step I) and in step II) are independently operated with a heat carrier medium selected from the group consisting of oil, salt melts, organic solvents and water.

13. The process of claim 1 , in which a pressure-retaining valve for the gas phase that forms and a closed-loop liquid level controller for the liquid phase are disposed in the separation zone from step IV), by means of which the pressure of the gas phase is kept constant.

14. The process of claim 1 , in which:
(i) methylene diphenylene diisocyanate and/or polymethylene polyphenylene polyisocyanate is prepared by reacting methylene diphenylene diamine and/or polymethylene polyphenylene polyamine with phosgene, or
(ii) tolylene diisocyanate is prepared by reacting tolylenediamine with phosgene.

15. The process of claim 1 , in which adjusting the temperature in the reaction zone and the temperature in the separation zone comprises closed-loop control of
(a) the temperature of the solution of the primary amine; and
(b) the temperature of the solution of phosgene.

16. The process of claim 15 , in which adjusting the temperature in the reaction zone and the temperature in the separation zone comprises:
entering the target value for the temperature of the reaction mixture from step III) into an electronic data processing system;
providing the measured values of the actual temperature of the reaction mixture from step III) in electronic form;
transmitting the measured values provided in electronic form to the electronic data processing system;
comparing the target value with the actual temperature in the electronic data processing system;
if a deviation in the actual temperature from the target value by more than 1.0° C. is found, then:
in the event of an upward deviation reducing, or
in the event of a downward deviation increasing
the temperature of the heat carrier medium used in the heat exchangers by transmitting a corresponding command from the electronic data processing system to the temperature control device used to adjust the temperature of
(a) the heat carrier medium used to operate the heat exchanger used in step I); and
(b) the heat carrier medium used to operate the heat exchanger used in step II).

Assignees

• Covestro Deutschland Ag

Inventors

• Knauf Thomas
• Steffens Christian
• Hielscher Anke
• Wastian Dietmar
• Spriewald Juergen

Classifications

• B01J19/1812

  Tubular reactors · CPC title

• C07C263/10 Primary

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

• B01J19/0013

  Controlling the temperature of the process · CPC title

• C07C263/20

  Separation; Purification · CPC title

• B01J2219/00051

  Controlling the temperature · CPC title