Phosgene removing method for TDI production

Abstract

A phosgene removal method used for manufacturing TDI relates to a method for removing poisonous gas from a gas-liquid mixture. The method comprises the following steps that a reaction liquid which contains TDI, a solvent isophthalic acid diethylester and superfluous phosgene and is discharged from a phosgenation reactor undergoes high-pressure phosgene removal treatment at first and then undergoes low-pressure phosgene removal treatment; moreover, the reaction liquid is reheated during low-pressure phosgene removal treatment so as to reboil the phosgene; then, the reaction liquid enters a negative-pressure phosgene removal stage so as to remove the phosgene in the material through negative-pressure phosgene removal treatment; and finally, final product TDI can be obtained after the reaction liquid is treated by a residue removal tower and a solvent removal tower.

Description

technical field [0001] The present invention relates to a method for removing toxic gases from gas-liquid mixtures. Background technique [0002] In the industrial production of TDI (toluene diisocyanate), toluene diamine is used for phosgenation reaction with excess phosgene in an inert solvent, and the reaction produces the target product TDI and by-product hydrogen chloride, and then undergoes dehydrochlorination, dephosgenation, residue removal and removal Solvent and other steps to finally obtain the product TDI, the excess phosgene and inert solvents in the reaction process are recovered and recycled. Phosgene, one of the reactants, is a highly toxic substance and must be completely removed from the product to ensure the safety of the product TDI. The removal of phosgene in TDI industrial production generally goes through a three-stage removal process of high-pressure, low-pressure and negative-pressure dephosgene towers to ensure that the product does not contain pho...

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Problems solved by technology

[0003] In the traditional phosgene removal process, the low-pressure dephosphorization tower relies on the heat provided by the material flashing from the bottom of the high-pressure dephosphorization tower to achieve the removal of phosgene at low pressure. When the high-pressure dephosphorization tower is operating abnormally, the low-pressure dephosphorization tower The tower does not have the necessary adjustment means to remedy, but directly transmits the problem to the negative pressure dephosphorization tower, causing the vacuum system of the negative pressure dephosphorization tower to be unstable; in addition, the removal of heavy components such as TDI to the vacuum system will cause waste. It still contains phosgene, which affects the normal operation of the follow-up residue removal and solvent removal systems. When the phosgene removed by the low-pressure dephosphorization tower is sent to the phosgene recovery system, the load on the phosgene recovery system is relatively large

The low-pressure degassing tower is operated at a pressure of 0.17MPa. On the one hand, pressure control is required, which increases the complexity of the operation; on the other hand, since TDI is easy to polymerize and generate residue at high temperature, it is necessary to control the temperature at the bottom of the tower at 170°C Below, and also contain more phosgene in the tower bottom material at this temperature, make the removal effect of final product TDI phosgene not good

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