Process for the preparation of isocyanates in the gas phase

1. A process for the production of an isocyanate comprising reacting in the gas phase a primary amine with phosgene at a temperature above the amine's boiling point over an average contact time of 0.05 to 15 seconds under adiabatic conditions.

2. The process of claim 1 further comprising: (i) condensing the isocyanate in the primary amine and phosgene reaction mixture by cooling the isocyanate-containing gas stream to a temperature above the corresponding carbamyl chloride's decomposition point, (ii) removing excess phosgene from the primary amine and phosgene reaction mixture, and (iii) recycling hydrogen chloride gas to recover chlorine for use in phosgene synthesis.

3. The process of claim 1 in which the amine is vaporized and optionally diluted with an inert gas or with vapors of an inert solvent and heated to a temperature of from 200 to 600° C. to form vaporized amine containing essentially no droplets of unvaporized amine, prior to reaction with the phosgene.

4. The process of claim 1 further comprising:

a) heating the amine gas, optionally diluted with an inert gas or with vapors of an inert solvent, and phosgene separately to temperatures of from 200 to 600° C. and continuously mixing the amine and phosgene to produce a gaseous reaction mixture,

b) continuously passing the gaseous mixture produced in step a) through a reaction chamber without back-mixing, and reacting the amine and phosgene therein over an average contact time of from 0.05 to 15 seconds under adiabatic conditions to form an isocyanate-containing gas stream,

c) cooling the isocyanate-containing gas stream leaving the reaction chamber to a temperature greater than decomposition point of the amine's corresponding carbamyl chloride to condense the isocyanate, and

d) separating uncondensed isocyanate from the gas stream by scrubbing with a liquid.

5. The process of claim 4 in which the reaction chamber has a rotationally symmetric geometry with a constant or increasing flow area in the reaction mixture's direction of flow.

6. The process of claim 4 in which the reaction chamber has sections of constant and increasing flow area in the direction of flow.

7. The process of claim 4 in which the gaseous mixture leaving the reaction chamber comprises at least one isocyanate, phosgene and hydrogen chloride, and the gaseous mixture is cooled in step c) by having at least one liquid stream sprayed into it.

8. The process of claim 7 in which at least part of the scrubbing liquid obtained in step d) after use in the gas scrubber is used in step c) for cooling the gaseous mixture leaving the reaction chamber.

9. The process of claim 7 in which at least part of the mixture obtained after condensation in step c) is used in step c) for cooling the gaseous mixture leaving the reaction chamber.

10. The process of claim 1 in which the isocyanate is toluene diisocyanate, methylenediphenyl diisocyanate, dicyclohexylmethane diisocyanate, hexamethylene diisocyanate and/or isophorone diisocyanate.

11. The process of claim 3 in which the vaporized amine does not contain any droplets of unvaporized amine.