Preparation method and system of mono-isocyanate

Abstract

The invention relates to a preparation method and system of mono-isocyanate. According to the method, an excessive amount of phosgene is subjected to phosgenation reaction with corresponding amine, and after obtained reaction liquid is subjected to gas stripping through hydrogen chloride and phosgene is removed, the fact that the phosgene is completely separated with isocyanate is realized, and the purpose that the excessive amount of phosgene can be recycled is achieved. Pyrolysis gas obtained by performing pyrolysis on reaction liquid with phosgene being stripped is captured through an inertsolvent, solution of corresponding isocyanate is obtained, and qualified isocyanate can be obtained through subsequent separation. A process for preparing mono-isocyanate through the method has the characteristics of high yield and low solid waste amount.

Description

technical field [0001] The invention relates to a method and system for preparing monoisocyanate. The process of preparing monoisocyanate by using the method and system has the characteristics of high yield and no solid waste. Background technique [0002] Monoisocyanates are widely used in pesticides, pharmaceutical intermediates and organic synthesis. [0003] Methyl isocyanate and butyl isocyanate are a kind of important pesticide intermediates, wherein methyl isocyanate is mainly used in the synthesis of carbamate pesticides, such as: Kebaiqi, methadone, medox, isoprocarb (leafhopper San), Zhongdingwei (Sisha), Jiatuqi, Shashaqi, Haoanqi, Thiodimethodil, Prothiocarbafuran, and Dingsialon, etc.; Butyl isocyanate is used in the phosgenation method to prepare benzoyl It can be used as a catalyst for urea herbicides, and it can also be used for the synthesis of pesticide fungicide benomyl. [0004] In addition, ethyl isocyanate is an important pharmaceutical intermediate, ...

AI Technical Summary

Problems solved by technology

Although this scheme can obtain isocyanate with low boiling point, because the cracking temperature of carbamate is higher than that of carbamoyl chloride, this process is more likely to lead to an increase in the polymer of monoisocyanate, resulting in a decline in the overall yield

[0010] At the same time, in the process of preparing monoisocyanate by phosgenation method, excessive phosgene is generally used to promote the complete reaction, so as to avoid further reaction of unreacted amine with photochemical product hydrogen chloride or isocyanate and its carbamoyl chloride to form urea species or hydrochlorides, resulting in reduced yield and equipment blockage

If this part of excess phosgene is to be recovered, due to the relatively low boiling point of monoisocyanate, a small amount of isocyanate will be entrained in the reaction tail gas and dephosgene tail gas, and these monoisocyanates will often bring great difficulties to the subsequent recovery of phosgene

If this part of phosgene is not recovered, on the one hand, the economy of the whole process is poor, and in addition, because the entrained monoisocyanate enters the phosgene decomposition system, it is easy to cause the increase of the total organic matter in the phosgene decomposition wastewater, resulting in the difficulty of subsequent wastewater treatment and cost increase

Therefore, in the traditional process of preparing monoisocyanate, the molar ratio of phosgene to amine is often low, which easily leads to the generation of urea or hydrochloride, thereby affecting the overall yield and device operating efficiency

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