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US 10,239,826 B2Granted
Method for producing isocyanates
AssigneeCovestro Deutschland AG
InventorsFriedhelm Steffens, Bastian Mahr
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Abstract
A method for producing isocyanates by reacting primary amines with phosgene in a stoichiometric excess in the gas phase, wherein the excess phosgene is subsequently recovered and recirculated back into the reaction. particular a method for the feedback-controlled recirculation of the recovered phosgene, particularly when the phosgene stream that should be recovered is distributed between multiple gas-phase reactors operated in parallel.
Claims16
A continuous process for preparing an isocyanate by gas phase phosgenation of the corresponding primary amine, comprising:
- (i) reacting the primary amine with an excess of phosgene to obtain a process product;
- (ii) treating the process product with a solvent at a temperature which is below the boiling point of the isocyanate and above the decomposition temperature of the corresponding carbamoyl chloride to give a gaseous stream (ii-1) containing hydrogen chloride and unreacted phosgene and a liquid stream (ii-2) containing solvent and isocyanate;
- (iii) separating the hydrogen chloride and phosgene present in the stream (ii-1) to give a liquid phosgene-containing stream (iii-1) and a gaseous stream (iii-2) containing hydrogen chloride;
- (iv) partially vaporizing the liquid phosgene-containing stream (iii-1) to give a two-phase process product;
- (v) introducing the two-phase process product at the top of a distillation column, from which a gaseous phosgene-containing stream is taken off at the top;
- (vi) recirculating the gaseous phosgene-containing stream to step (i);
- and
- (vii) working up the liquid stream (ii-2) containing solvent and isocyanate to isolate the isocyanate.
5 more elements
Dependencies are inferred from the claim text.