Process for the preparation of isocyanates

摘要

The invention relates to a process for the preparation of isocyanates in a system network comprising an isocyanate production plant, a chlorine production plant and a phosgene production plant, in which carbon dioxide formed as a by-product is partially to completely condensed out with the gaseous chlorine formed in the chlorine production plant and enters into the phosgene preparation process and, after the preparation of phosgene, the predominant part of the carbon dioxide formed is thereby sluiced out of the system network in gaseous form.

主权项

1. A process for preparing an isocyanate comprising the steps of
(i) reacting a stream E1 comprising a primary amine with a phosgene-comprising stream P16 to form a product stream P1, which comprises said isocyanate, hydrogen chloride, unreacted phosgene, and carbon oxides; (ii) separating the product stream P1 into a liquid product stream P2 comprising said isocyanate and a gaseous product stream P3 comprising hydrogen chloride, unreacted phosgene, and carbon oxides; (iii) mixing the product stream P3 with a gaseous product stream P4 comprising oxygen to form a gaseous mixed stream P5; (iv) oxidizing the gaseous mixed stream P5 on a catalyst to form a gaseous product stream P6 comprising hydrogen chloride, carbon dioxide, excess oxygen, chlorine, and water; (v) partially to completely removing the hydrogen chloride and water from stream P6 as a stream P7 comprising hydrochloric acid to form a product stream P8 depleted in hydrogen chloride and water; (vi) separating the product stream P8 into a liquid chlorine-rich product stream P9, which comprises chlorine, carbon dioxide, and oxygen, and a gaseous, low-chlorine product stream P10, which comprises the residual amount of chlorine from P8 not contained in P9, carbon dioxide, and oxygen; (vii) dividing the gaseous product stream P10 into a gaseous purge stream P11 and a gaseous product stream P12; (viii) treating the purge stream P11 with an aqueous base E3 to form a gaseous purge stream P13 and a liquid waste water stream P14; (ix) mixing the gaseous stream P12 with a gaseous stream E4 comprising oxygen to form the gaseous product stream P4 which comprises oxygen and is employed in step (iii); (x) evaporating the liquid chlorine-rich product stream P9 to form a gaseous chlorine-rich product stream and mixing the gaseous chlorine-rich product stream with carbon monoxide E5 and with chlorine E6 to give a mixture, and reacting said mixture to give a gaseous product stream P15 comprising phosgene and carbon oxides; (xi) separating the gaseous product stream P15 in a separating device I into a phosgene-rich product stream P16, which is employed in step (i) and comprises phosgene and carbon oxides, and into a low-phosgene purge stream P17 which comprises the residual amount of the phosgene from P15 which is not contained in P16 and carbon oxides;whereinin step (vi) the separation of the product stream P8 into a liquid chlorine-rich product stream P9 and into a gaseous low-chlorine product stream P10 is carried out by cooling P8 to a temperature of from −10° C. to −80° C. under an absolute pressure of from 1 bar to 30 bar without subsequent distillation.