Method for refining crude toluene diisocynate

Abstract

The invention relates to an improvement of a method of refining crude toluene diisocynate (TDI), in particular to the improvement of the method of refining crude toluene diisocynate by a phosgene method. A large amount of phosgene is desorbed from the crude toluene diisocynate and is recycled, then the crude toluene diisocynate is processed by a residue desorption tower and a solvent desorption tower to obtain the crude toluene diisocynate with higher TDI purity after rectification, and finally the refined toluene diisocynate is barrelled.

Description

technical field [0001] The present invention relates to the improvement of the refining method of crude toluene diisocyanate, in particular to the improvement of the refining method of preparing crude toluene diisocyanate by phosgene method. After removing and recovering a large amount of phosgene from the crude toluene diisocyanate, in the present invention, the crude toluene diisocyanate is rectified to reach a relatively high TDI purity through a residue removal tower and a solvent removal tower, and then loaded into drums. 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 chlorine gas provided by hydrochloric acid electrolysis. 2 ), composed of toluenediamine (TDA) and COCL 2 Reaction, and then through the steps of dehydrochl...

AI Technical Summary

Problems solved by technology

At present, there are two kinds of inert solvents: the first one is diethyl isophthalate (DEIP), which performs photochemical reaction under high pressure conditions, which is commonly called "heavy solvent production process"; but the photochemical reaction of this process Among them, the solvent diethyl isophthalate (DEIP) reacts easily with phosgene to generate m-ethyl benzoyl chloride (CBC), which easily causes the clogging of the reactor; in addition, due to the high price of DEIP, its large amount The consumption of will increase the cost of final product TDI; Furthermore, there is another defect in this process, in order to reclaim the residual phosgene in the system, need to add a set of phosgene recovery device, use toluene as the solvent of reclaiming phosgene, give TDI Increased difficulty in production control

The second is o-dichlorobenzene (ODCB), which carries out photochemical reaction under low pressure conditions, which is commonly called "light solvent production process"; the photochemical reaction of this process is carried out in a reactor with agitator, 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 TDI products, and produces a large amount of residues to bring burden to the slag removal system at the same time; 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 increases the production cost of TDI

[0003] 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;

[0004] 2. The complex phosgene separation process will increase the chance of phosgene leakage

Additionally, prolonged exposure of the isocyanate and residue to the heated zone results in a higher rate of residue formation

Finally, it is energy inefficient to condense the overhead stream from the pre-evaporator before sending it to the isocyanate column

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