Method for recycling phosgene in continuous production process of toluene di-isocyanate

Abstract

The invention discloses a method for recycling phosgene in a continuous production process of toluene di-isocyanate, comprising the following steps: importing a gas stream rich in phosgene, hydrogen chloride and less impurities, which is generated in a preparation process of the toluene di-isocyanate, to a first phosgene absorption tower and leading in inert organic solvent to absorb; lifting pressure of the gas streams exhausted from the top of the first phosgene absorption tower by a compressor, lifting the pressure of part of tower bottom absorption liquid of the first phosgene absorption tower by the tower bottom liquid pump and then entering a second phosgene absorption tower, importing another gas stream rich in phosgene, hydrogen chloride and less impurities to the second phosgene absorption tower and supplementing the inert organic solvent to keep absorbing; reusing the phosgene inert organic solvent solution acquired from the bottom of the second phosgene absorption tower in the continuous production process of the toluene di-isocyanate. The method can obviously decrease the loading of the compressor, thereby reducing the cost on investment, operation and maintenance, improving the operation stability, and achieving the purpose of recycling the phosgene at a lower cost.

Description

technical field [0001] The invention relates to a method for recovering phosgene in the continuous production process of toluene diisocyanate. Background technique [0002] Polyurethane materials have the characteristics of convenient modification, easy processing and molding, and simple construction, and are extremely widely used in various fields such as heat insulation, shockproof, sound insulation, cushion materials, packaging, and light structures. Isocyanate is an important monomer raw material in the polyurethane industry. The method of preparing isocyanate by phosgenation of primary amine has been reported many times in patents, and has been carried out on a large scale in industry, especially aromatic isocyanate TDI (toluene diisocyanate), The reactions that may occur during its preparation are as follows: [0003] [0004] [0005] TDI+urea→TDI biuret (7) [0006] TDI+TDI biuret → polyurea (8) [0007] Reaction (1), (2) is the main reaction to generate iso...

AI Technical Summary

Problems solved by technology

[0009] When the existing process recycles phosgene, since the amount of gas stream d to be compressed in actual production is large, it is necessary to use a large compressor to pressurize the gas stream d and send it to the absorption tower 6; coupled with the phosgenation reaction The complexity of the system and the high toxicity of phosgene itself impose strict requirements on the selection and operation of large compressors, making the phosgene recovery process costly, poor in operation stability, and highly dangerous

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