| 摘要 |
This invention relates to a process for operating a gas phase phosgenation plant (100) to form an isocyanate (4) by reacting an amine (2) with phosgene (1), in which the gas phase phosgenation plant is started up by first charging the plant with phosgene. At the same time as, or after the first charge of phosgene, the amine supply devices are rendered inert using a hot inert gas stream (30). Then, amine is admixed for the first time. In this way and by maintaining a pressure drop in the amine and phosgene devices to the mixing zone, the back mixing of phosgene into the amine-containing reactant stream during start-up is prevented. |
| 主权项 |
1. A method of operating a gas has phosgenation plant (100) for producing an isocyanate (4) comprising reacting an amine (2) with phosgene (1), in which said gas phase phosgenation plant (100) comprises at least
(i) an apparatus 1000 for providing a gaseous phosgene stream (10), (ii) apparatus 2000 for providing a gaseous amine stream (20), (iii) a mixing zone (3100) for mixing the streams (10) and (20), with the mixing zone being connected by connecting devices (1100, 2100) to the apparatus 1000 and the apparatus 2000, (iv) a reaction zone (3200) arranged downstream of the mixing zone (3100) for further conversion of the previously mixed streams (10) and (20), (v) a reaction stopping zone (4000) arranged downstream of the reaction zone (3200) to end the reaction, and optionally (vi) a workup section (5000), which comprises devices for recovery and recycling of unconverted phosgene (1″) (5100) and devices for obtaining the isocyanate prepared in pure form (5200), wherein the gas phase phosgenation plant (100) is started up by: (I) providing a gaseous phosgene stream (10) at a temperature T10 of 200° C. to 600° C. with an absolute pressure p10 of 100 mbar to 3000 mbar in the apparatus 1000 and continuously introducing this gaseous phosgene stream (10) through the connecting device 1100 into the mixing zone (3100), the reaction zone (3200) and the reaction stopping zone (4000), the pressure p10 being greater than the pressure p3100 in the mixing zone (3100); (II) either simultaneously with or after step (I),
(a) introducing an inert substance (3), at a temperature T3<200° C. into the apparatus 2000, heating the inert substance (3) in the apparatus 2000 to obtain an inert gas stream (30) which is passed through the connecting device 2100, the mixing zone (3100), the reaction zone (3200) and the reaction stopping zone (4000)or(b) introducing an inert gas stream (30)
(b.1) into the connecting device 2100 and thence through the mixing zone (3100), the reaction zone (3200) and the reaction stopping zone (4000)or(b.2) into the apparatus 2000 and thence through the connecting device 2100, the mixing zone (3100), the reaction zone (3200) and the reaction stopping zone (4000),where the inert gas stream (30) in variant (a) and in variant (b) has a temperature of 200° C. to 600° C. and an absolute pressure p30 of 100 mbar to 3000 mbar,andwhere the pressure p30 in variant (a) and in variant (b) is greater than the pressure p3100 in the mixing zone (3100): and (III) after step (H), providing a gaseous amine stream (20) at a temperature T20 of 200° C. to 600° C. with an absolute pressure p20 of 100 mbar to 3000 mbar in the apparatus 2000 and continuously introducing this gaseous amine stream (20) through the connecting device 2100 into the mixing zone (3100), where the pressure p20 is greater than the pressure p3100 in the mixing zone (3100), and where the composition and the mass flow rate of the stream (20) are matched to the composition and the mass flow rate of stream (10) such that, in the mixing zone (3100), phosgene (1) is present in a stoichiometric excess in relation to the primary amino groups of the amine (2). |
