Refining and reclaiming technology of tail gas absorption solvent in production of toluene diisocyanate

Abstract

The invention relates to a refining and reclaiming technology of a tail gas absorption solvent in the production of toluene diisocyanate (TDI). The solvent containing little phosgene, toluene diisocyanate and di-Et-1,3-benzenedicarboxylate (DEIP) performs two-stage refinement in an atmospheric refining tower and a vacuum refining tower, and a falling-film evaporator and a storage tank are arranged between the two towers. The overhead non-condensable gas phase of the atmospheric refining tower is returned to a phosgene absorption tower to recycle phosgene, the refined solvent is drawn from theside of the atmospheric refining tower, the temperature of the tower bottom is controlled to be 3-8 DEG C higher than the boiling point of the solvent, the discharged material of the tower bottom enters the falling-film evaporator, the evaporating temperature is 20-30 DEG C higher than the boiling point of the solvent, the unevaporated material enters the storage tank for storage, the material inthe storage tank performs batch vacuum rectification under the absolute pressure of 0.1-0.25bar, and the unevaporated residual material enters the residue evaporator of a TDI device to recycle TDI and DEIP. By using the solvent refining technology provided by the invention, the useful components in the solvent can be completely recycled, and the technology has the advantages of simple and stable operation and lower cost and energy consumption.

Description

Technical field: [0001] The invention relates to a process for refining and recovering tail gas absorption solvents in the production of toluene diisocyanate (TDI), and belongs to the technical field of solvent recovery. Background technique: [0002] The solvent used in the TDI production process of the heavy solvent method is diethyl isophthalate (DEIP), and the boiling point is higher than TDI. The quality of the TDI product produced by this process is better, but the freezing point of the heavy solvent is high, and the solubility of phosgene in it is low. Therefore, light solvents such as toluene and chlorobenzene need to be used to absorb the phosgene in the production tail gas. The vacuum system produced by TDI also needs toluene or chlorobenzene, so the heavy solvent method has a separate light solvent system. The main function of this system is to absorb the phosgene in the production tail gas with light solvent, recover the phosgene absorbed by the light solvent and...

AI Technical Summary

Problems solved by technology

The current process has caused the loss of useful substances such as phosgene, solvent, TDI, DEIP, etc., and has adverse effects on the environment

[0004] In the actual operation process, by increasing the evaporation temperature of the refining tower reboiler, the solvent content in the bottom discharge can be reduced, and the loss of solvent can be reduced, but it cannot fundamentally solve the problem of loss of useful components, and it will also bring some other questions

Increasing the evaporation temperature will lead to a decrease in the discharge volume at the bottom of the tower, making it difficult to achieve continuous discharge and unstable operation; it is necessary to increase the heat medium temperature of the reboiler accordingly, and the energy utilization efficiency is reduced; the gasification rate of the material is low, and the reboiler at the bottom of the tower can only The forced circulation method can be used, the amount of circulating material is large, and the operating cost of the pump is high

Moreover, the evaporation temperature at the bottom of the tower should not be too high, because TDI will self-polymerize at high temperature and block the pipeline.

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