Covestro Deutschland Ag

Thomas Bludowsky

Joachim Zechlin

Tim Loddenkemper

Volker Michele

Wolfgang Taube

Qiang Wei

Zhangyong Ming

Yuguo Gai

The present invention relates to a process for preparing an isocyanate comprising the steps of (A) reacting an amine with a stoichiometric excess of phosgene using an aromatic solvent of formula CHCl, wherein X=1 or 2, (a) as a diluent during the reaction and/or (b) as a means for cooling the reaction mixture formed from the reaction of the amine with phosgene (so-called quench) to obtain (optionally after a decompression) a liquid product mixture comprising the isocyanate and the aromatic solvent employed and a gaseous product mixture containing phosgene and hydrogen chloride; followed by (B) isolating the isocyanate from the liquid product mixture obtained in step (A) comprising the step of a final distillation in which the isolated isocyanate is obtained as a product stream, wherein in the final distillation or in a distillation step upstream of the final distillation at least one stream comprising aromatic solvent of formula CHCl, wherein Y=X+1, is (at intervals or continuously) discharged such that the isolated isocyanate has a mass fraction, based on its total mass, of aromatic solvent of formula CHClin the range from 0.0 ppm to 9.9 ppm, preferably 0.0 ppm to 5.0 ppm, particularly preferably 0.0 ppm to 3.0 ppm.

Method for producing isocyanates

A process for quenching, in a quenching zone, a gaseous reaction mixture that includes a diisocyanate, phosgene and hydrogen chloride that is obtained in a reaction zone upstream of the quenching zone by phosgenation of a diamine in the gas phase. The process includes injecting a deposit preventing liquid in a deposit preventing zone located between the reaction zone and the quenching zone by passing the deposit preventing liquid through spray nozzles for the deposit preventing liquid at the entrance to the deposit preventing zone. Each spray nozzle for the deposit preventing liquid sprays the deposit preventing liquid (i) onto a wall segment of the deposit preventing zone that is adjacent to said spray nozzle for the deposit preventing liquid to produce a film of the deposit preventing liquid flowing along the wall, and/or (ii) to areas in a cross-sectional plane of the deposit preventing zone before the entrance to the quenching zone.

Process for quenching a gaseous reaction mixture obtained in the gas phase phosgenation of diamines

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Ratingen, Germany

Thomas Bludowsky