METHOD OF PRODUCING ISOCYANATE Russian patent published in 2012 - IPC C07C263/10 

FIELD: chemistry.

SUBSTANCE: method comprises the following steps: a) reaction of a primary aliphatic or aromatic amine with phosgene in the presence of a solvent to obtain the corresponding isocyanate and a stream containing hydrogen chloride, phosgene and solvent, low-boiling compounds and inert substances; b) separation of the stream containing hydrogen chloride, phosgene and solvent, low-boiling compounds and inert substances in at least a two-step sequence of absorption steps, comprising at least one isothermic absorption step and at least one adiabatic absorption step, to obtain (i) a stream of hydrogen chloride containing not more than 0.5 wt % phosgene in terms of the total weight of the stream of hydrogen chloride, and (ii) a stream of liquid phosgene; and c) recycling the stream of liquid phosgene (ii) to step (a). The phosgene is partially condensed from the stream containing hydrogen chloride, phosgene and solvent, low-boiling compounds and inert substances before said separation in at least a two-step sequence of absorption steps. The method enables to clean the stream which contains hydrogen chloride, phosgene and solvent, low-boiling compounds and inert substances coming from the amine phosgenation process such that the residual concentration of phosgene in the stream of hydrogen chloride remains not higher than 0.5 wt %, thereby minimising the loss of initial phosgene.

EFFECT: improved method.

8 cl, 4 dwg, 1 ex