Process for preparing toluene diisocyanate (TDI) by using toluenediamine and dimethyl carbonate

Abstract

The invention relates to a process for preparing toluene diisocyanate (TDI) by using toluenediamine and dimethyl carbonate. According to the process, a deactivation catalyst, namely zinc oxide (ZnO), of a reaction, which is used for synthesizing toluene dicarbamate (TDC) through catalyzing toluenediamine and dimethyl carbonate by zinc acetate, is used as a catalyst of a reaction for TDC decomposed TDI preparation, the deactivation catalyst, namely ZnO, of the reaction is not required to be separated from the product TDC and is directly applied to the reaction for TDC decomposition catalyzed TDI preparation, and a TDC decomposed TDI preparation process adopts that decomposition reactors of two stages are in series connection and a fractional condenser is arranged between the decomposition reactors of two stages. According to the process, TDC is synthesized through catalyzing toluenediamine and dimethyl carbonate by zinc acetate, and the deactivation catalyst, namely ZnO, of TDC synthesis is selected as an efficient catalyst for TDC decomposition reaction, so that the catalysis effect is good, and the yield of TDI is high; and the temperature of the TDC decomposition reaction is low, so that the total production cost can be greatly reduced.

Description

technical field [0001] The invention uses toluene diamine and dimethyl carbonate as raw materials to synthesize methyl toluene dicarbamate, and then prepares toluene diisocyanate through catalytic decomposition. Background technique [0002] Toluene diisocyanate (TDI) is an important organic chemical intermediate and one of the important raw materials for the polyurethane industry. At present, the phosgene method is used in the industrial production of TDI, but the raw material phosgene is highly toxic, and the by-product HCl is easy to cause corrosion of equipment. Therefore, the research on the synthesis of TDI by non-phosgene method has been paid much attention at home and abroad. Among them, the process of synthesizing methyl toluene dicarbamate (TDC) by reacting toluene diamine (TDA) with dimethyl carbonate (DMC), and decomposing TDC to obtain TDI has considerable industrial potential. [0003] There have been many reports in the literature about the synthesis of carba...

AI Technical Summary

Problems solved by technology

That is, there must be a catalyst separation step, and the comprehensive and reasonable utilization of the catalyst in the process of synthesizing isocyanate is not considered

[0010] (2) For the process of carbamate decomposition to prepare isocyanate: most documents are carried out under the action of catalysts, and the catalysts used are not related to carbamate synthesis catalysts, and the decomposition temperature is high; although there are documents that do not use catalysts for decomposition reactions, However, it needs to be carried out at a very high temperature. The temperature of the first-stage reactor has reached 230-380°C, and the decomposition temperature of the second-stage reactor has reached 300-600°C. Such a high reaction temperature is prone to side reactions, resulting in product yield. The rate is low, and it will greatly increase the equipment cost and production cost

[0012] At present, there is no research report about the deactivated catalyst for the synthesis of carbamate by reacting amine with organic carbonate to directly catalyze the reaction of carbamate to prepare isocyanate, and there is no report on the two-stage process of carbamate to prepare isocyanate. Introduction to the Process of Decomposition Reactors Operated in Series with Partial Condenser

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