PROCESS FOR PRODUCING ISOCYANATES

Abstract

The invention relates to a process for producing isocyanates by reacting the corresponding amines with phosgene in the liquid phase, comprising: (a) mixing an amine comprising feed stream, a phosgene comprising feed stream and optionally an inert solvent; (b) reacting the amine with phosgene in a first reaction section to obtain an intermediate reaction mixture comprising isocyanate, carbamoyl chlorides, amine hydrochlorides and unreacted phosgene; (c) cleaving the carbamoyl chlorides and remove phosgene from the intermediate reaction mixture in a second reaction section to obtain an isocyanate comprising crude product, (d) optionally working-up the crude product; wherein reacting (b) is carried out such that the intermediate reaction mixture comprises 1.7 to 5 mol-% solid amine hydrochlorides based on the molar amount of amine fed into the process.

Claims

1.-11. (canceled)

12. A process for producing isocyanates by reacting the corresponding amines with phosgene in the liquid phase, comprising: (a) mixing an amine comprising feed stream, a phosgene comprising feed stream and optionally an inert solvent; (b) reacting the amine with phosgene in a first reaction section to obtain an intermediate reaction mixture comprising isocyanate, carbamoyl chlorides, amine hydrochlorides and unreacted phosgene; (c) cleaving the carbamoyl chlorides and remove phosgene from the intermediate reaction mixture in a second reaction section to obtain an isocyanate comprising crude product, (d) optionally working-up the crude product; wherein reacting (b) is carried out such that the intermediate reaction mixture comprises 1.7 to 5 mol-% solid amine hydrochlorides based on the molar amount of amine fed into the process.

13. The process according to claim 12, wherein the amount of amine hydrochlorides in the intermediate reaction mixture is adjusted by controlling the excess of phosgene fed into the reaction.

14. The process according to claim 12, wherein the amount of amine hydrochlorides in the intermediate reaction mixture is adjusted by controlling the amount of inert solvent.

15. The process according to claim 12, wherein the inert solvent is selected such that the solubility of the amine is reduced if the amount of solid amine hydrochlorides falls below a predetermined value and the solubility of the amine is increased if the amount of solid amine hydrochlorides rises above a predetermined value.

16. The process according to claim 12, wherein the amount of amine hydrochlorides in the intermediate reaction mixture is adjusted by controlling the temperature of the feed streams into the first reaction section and/or the reaction in the first reaction section.

17. The process according to claim 12, wherein the amount of amine hydrochloride in the intermediate reaction mixture is adjusted by controlling the amount of hydrogen chloride in the phosgene comprising feed stream.

18. The process according to claim 12, wherein the amount of amine hydrochloride in the intermediate reaction mixture is adjusted by controlling the mixing rate of the feed streams.

19. The process according to claim 12, wherein the amount of amine hydrochloride in the intermediate reaction mixture is adjusted by controlling the pressure during the reaction (b).

20. The process according to claim 12, wherein the amount of solid amine hydrochloride in the intermediate reaction mixture is determined by diluting a partial stream of the intermediate reaction mixture with solvent and counting the particles in the diluted partial stream.

21. The process according to claim 12, wherein the amine is diphenylmethanediamine (MDA), polyphenylene-polymethylene polyamine (PMDA), toluene diamine (TDA), hexamethylenediamine (HDA) or isophorone diamine (IPDA).

22. The process according to claim 12, wherein the first reaction section is operated in a residence time reactor.

Description

EXAMPLES

Example 1

[0044] In a plant for producing TDI as described in WO-A 2004056756 with a tube reactor as residence time reactor as described in example 1 of the international application, a 19.5% solution of TDA in chlorobenzene is mixed with a 90% solution of phosgene in chlorobenzene in a mixing device as described in WO-A 2010/015667, the molar phosgene excess being 500%. The amount and size of solid particles in the intermediate reaction mixture withdrawn at the end of the reaction tube was determined by a photographical method and subsequent image evaluation. For this, a partial stream of the intermediate reaction mixture was withdrawn and diluted with chlorobenzene. The thus obtained mixture was fed through a cuvette for taking transmitted light photos.

[0045] The particle concentration in the intermediate reaction mixture determined by this process was 0.23% by volume which corresponds to a molar concentration of 2.7 mol-% based on the amount of TDA fed into the process. The loss in yield which was determined by the amount of TDI produced in the total process and the amount of TDA fed into the process was 3.01%.

Comparative Example 1

[0046] TDI was produced in the same way as described in example 1. However, a modified mixing nozzle was used by which the amount of amine hydrochloride in the intermediate reaction mixture could be reduced to 0.04% by volume, corresponding to 0.47 mol-% based on the amount of TDA fed into the process. Even though the amount of solid amine hydrochlorides 35 was reduced, the loss in yield increased to 3.26%.

Example 2

[0047] MDI was produced by phosgenation of MDA in a 2-stage process according to WO-A 99/54289 (EP1073628 ?). Thereby 50 kg/h MDA are mixed with solvent chlorobenzene at a mass ratio chlorobenzene:MDA of 1.4. In a reaction mixing nozzle a phosgene containing feed (65% phosgene, 32% chlorobenzene, 3% HCl) is mixed with the amine containing feed. The reaction product is fed to a series of stirred vessels acting as residence time reactors and running at 100° C. and 5.5 bar, 4.5 bara, 2.8 bara and 2.5 bara respectively. Gas phase separated at each reactor and liquid phase from last reactor are fed to a distillation column operating at about 1.2 bara and a sump temperature of 172° C. to get a MDI-solvent mixture at the bottom. A partial stream of the liquid feed to the column is withdrawn, mixed with chlorobenzene and the size distribution and amount of solid particles was determined in a particle counter of Markus Klotz GmbH. Solvent is removed out of the sump product in a distillation to get a crude MDI product.

[0048] By carrying out the process in such a way, the amount of solid particles, particularly amine hydrochloride was 0.55% by volume, corresponding to 2.27 mol-% based on the amount of MDA fed into the process. The total yield was determined by the NCO-value of the crude MDI and was 32.1 g NCO/100 g.

Example 3

[0049] MDI was produced according to the process of Example 2 but the temperature of the second stirred tank reactor was set to 110° C. The solids concentration decreased on 0.35% by volume which corresponds to 1.7 mol-% based on the amount of MDA fed into the process. The NCO-value was 31.75 g/100 g.

Comparative Example 2

[0050] MDI was produced according to the process of Example 2 but the temperature of the second stirred tank reactor was set to 120° C. The solids concentration decreased on 0.2% by volume which corresponds to 1.0 mol-% based on the amount of MDA fed into the process. The NCO-value was 31.6 g/100 g.

Example 4

[0051] MDI was produced according to the process of Example 2 but the temperature of the second stirred tank reactor was set to 90° C. The solids concentration increased on 0.7% by volume which corresponds to 3.5 mol-% based on the amount of MDA fed into the process. The NCO-value was 31.74 g/100 g.

Comparative Example 3

[0052] MDI was produced according to the process of Example 2 but the amount of solvent was decreased to get a mass flow ratio of chlorobenzene to MDA of 1.0. The solids concentration increased on 1.05% by volume which corresponds to 5.1 mol-% based on amount of MDA fed into the process. The NCO-value was 31.54 g/100 g.