PROCESS FOR PREPARING ISOCYANATES

摘要

The present invention relates to gas phase phosgenation of amines for preparation of isocyanates. In the present invention, phosgene is prepared by reacting chlorine with an excess of carbon monoxide in a gas phase. The obtained phosgene-containing reaction mixture is divided into two streams by a thermal and/or a membrane separating process. The first stream is a low-carbon monoxide stream of no more than 1% by weight of carbon monoxide, based on a total weight of the first stream. The second stream is a carbon monoxide-rich stream of more than 10% by weight of carbon monoxide, based on a total weight of the second stream. The first stream is used as the phosgene-containing reactant stream in the gas phase phosgenation of amines to prepare isocyanates. The second stream can be recycled into the phosgene synthesis.

主权项

1. A process for preparing an isocyanate via a gas phase phosgenation of a corresponding amine, the process comprising:
reacting carbon monoxide with chlorine with a stoichiometric carbon monoxide excess over chlorine in a gas phase, thereby obtaining a phosgene-comprising reaction mixture; dividing the phosgene-comprising reaction mixture into a low-carbon monoxide stream and a carbon monoxide-rich stream by at least one separating process of a thermal separating process and a membrane separating process, wherein the low-carbon monoxide stream comprises not more than 1% by weight of carbon monoxide, based on a total weight of the low-carbon monoxide stream, and the carbon monoxide-rich stream comprises more than 10% by weight of carbon monoxide, based on a total weight of the carbon monoxide-rich stream; and introducing the low-carbon monoxide stream as a phosgene-comprising reactant stream into the gas phase phosgenation of the corresponding amine, thereby obtaining the isocyanate and hydrogen chloride as a coproduct.