Method for continuously preparing toluene diisocynate

Abstract

The invention relates to a method for continuously preparing toluene diisocynate, in particular to a method for preparing coarse toluene diisocynate by a phosgene method. The method comprises the following steps: mixing toluene diamine and DEIP solvent, performing low-temperature photochemical reaction on the mixture and excessive liquid phosgene in a jet reactor, heating and cracking a reaction product in a photochemical reaction tower to further decompose toluene dicarbamic chloride serving as an intermediate product to form the toluene diisocynate, recycling the reclaimed phosgene and the DEIP solvent, and delivering the hydrogen chloride gas serving as a side product to a hydrogen chloride absorption system.

Description

technical field [0001] The invention relates to a method for continuously preparing toluene diisocyanate, in particular to a method for preparing crude toluene diisocyanate by a phosgene method. In this method, toluene diamine is mixed with solvent DEIP, and the low-temperature photochemical reaction is carried out with excess liquid phosgene in the jet reactor, and then heated and cracked in the photochemical reaction tower to further decompose the intermediate product toluene dicarbamoyl chloride to generate toluene For diisocyanate, the recovered phosgene and solvent DEIP are recycled, and the by-product hydrogen chloride gas is sent to the hydrogen chloride absorption system. Background technique [0002] Toluene diisocyanate (TDI) is one of the most used isocyanate products in the world and one of the main raw materials of polyurethane. The TDI production process is mainly to generate phosgene (COCL) by the reaction of carbon monoxide provided by gas purification and c...

AI Technical Summary

Problems solved by technology

[0005] The production of toluene diisocyanate (TDI) generally adopts following two kinds of processes in the world at present: the first kind is to use diethyl isophthalate (DEIP) as solvent, carry out photochemical reaction under high pressure condition, namely The so-called "heavy solvent production process"; but in the photochemical reaction of this process, the solvent diethyl isophthalate (DEIP) easily reacts with phosgene to generate m-ethyl benzoyl chloride (CBC), which The substance is easy to cause blockage of the reactor; in addition, because DEIP is expensive, its large consumption will increase the cost of the final product TDI; moreover, there is another defect in this process, in order to recover the residual phosgene in the system, it is necessary to add A phosgene recovery unit uses toluene as a solvent for phosgene recovery, which adds difficulties to the production control of TDI

The second is to use o-dichlorobenzene (ODCB) as a solvent to carry out photochemical reaction under low pressure conditions, which is commonly called "light solvent production process"; the photochemical reaction of this process is in a reactor with agitator Carrying out, it is difficult to avoid the reaction of toluene diamine (TDA) and toluene diisocyanate (TDI) in the reaction process, because the generation of this reaction reduces the yield of TDT product, produces a large amount of residue simultaneously to the slag removal system to afford; another defect of this process is that a large amount of solvent o-dichlorobenzene is used to circulate in the system, which increases the consumption of raw materials and power energy of the equipment, and improves the production cost of TDI

[0006] 1. Many residues. Most of the residues are urea components. They not only reduce the product yield, but also erode the pipeline equipment and increase the production cost; in addition, the residues are easy to cause blockage and need to stop production to clean up the blockage;

[0007] 2. The complex phosgene separation process will increase the chance of phosgene leakage

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