Method for Producing Isocyanates

Abstract

The invention relates to a process for preparing isocyanates by reacting amines with phosgene in the gas phase in a reaction zone, with the reaction mixture being passed through a zone into which a liquid is sprayed to stop the reaction, wherein the reaction mixture is passed through a zone having a reduced flow cross section between the reaction zone and the zone into which the liquid is sprayed.

Description

EXAMPLE 1

67.5 kg/h of reaction gas comprising tolylene diisocyanate isomers, phosgene and hydrochloric acid were produced in a tube reactor (diameter: 8 mm) with upstream mixing device. The reaction gas was then conveyed via a constriction of the cross section having a diameter of 3.0 mm to the quenching zone. The mach number in the narrowest cross section was about 0.85. Two individual single-fluid nozzles having a spray cone opening angle of 80° were located in the quenching zone. The nozzles produced droplets having a Sauter diameter of about 100 μm. The amount of liquid sprayed in was 100 kg/h. The quenching liquid sprayed in consisted of monochlorobenzene. The temperature of the reaction gas on entering the quenching zone was 363° C. and the pressure of the gas was 6.8 bar. The entry temperature of the quenching liquid was 100° C., and the exit velocity of the liquid droplets from the spray nozzle was about 50 m/s. The residence time of the reaction gas in the quenching zone was about 0.01 second. The temperature of the quenched gas dropped to 156° C. in the quenching zone. The desired temperature decrease thus occurred in less than 0.01 second. The amount of tolylene diisocyanate in the reaction gas mixture decreased by 80% relative to the concentration on entering the quenching zone.

Claims

1. A process for preparing isocyanates by reacting amines with phosgene in the gas phase in a reaction zone, with the reaction mixture being passed through a zone into which a liquid is sprayed to stop the reaction, wherein the reaction mixture is passed through a zone having a reduced flow cross section between the reaction zone and the zone into which the liquid is sprayed.

2. The process according to claim 1, wherein tube reactors, flow tubes with or without internals or plate reactors are used as reaction zone.

3. The process according to claim 1, wherein the ratio of the flow cross section in the constriction to the flow cross section in the reaction zone is from 1/1.2 to 1/10.

4. The process according to claim 1, wherein the ratio of the flow cross section in the constriction to the flow cross section in the reaction zone is from 1/2 to 1/10.

5. The process according to claim 1, wherein the ratio of the flow cross section in the constriction to the flow cross section in the reaction zone is from 1/3 to 1/10.

6. The process according to claim 1, wherein the liquid droplets sprayed in have a Sauter diameter of from 5 to 5000 μm.

7. The process according to claim 1, wherein the liquid droplets sprayed in have a Sauter diameter of from 5 to 500 μm.

8. The process according to claim 1, wherein the liquid droplets sprayed in have a Sauter diameter of from 5 to 250 μm.

9. The process according to claim 1, wherein the temperature of the liquid sprayed in is from 0 to 300° C.

10. The process according to claim 1, wherein the temperature of the liquid sprayed in is from 50 to 250° C.

11. The process according to claim 1, wherein the temperature of the liquid sprayed in is from 70 to 200° C.

12. The process according to claim 1, wherein the liquid sprayed in is an organic solvent.

13. The process according to claim 1, wherein the liquid sprayed in is an aromatic solvent which may be substituted by halogen atoms.

14. The process according to claim 1, wherein the liquid sprayed in is an isocyanate.