In Situ Preparation of Nanometer-Scale Zinc Oxide from Zinc Acetate in the Reaction for the Synthesis of Dimethyl Toluene Dicarbamate and Its Catalytic Decomposition Performance

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• 作者：Guirong Wang ; Dan Ma ; Xiaoqiang Jia ; Xuexia Cui ; Xinqiang Zhao ; Yanji Wang
• 刊名：Industrial & Engineering Chemistry Research
• 出版年：2016
• 出版时间：July 27, 2016
• 年：2016
• 卷：55
• 期：29
• 页码：8011-8017
• 全文大小：308K
• 年卷期：0
• ISSN：1520-5045

文摘

The synthesis of toluene diisocyanate (TDI) starting from dimethyl carbonate (DMC) instead of phosgene is a green and safe reaction process. In the first reaction step of the process, i.e., the reaction of toluene diamine (TDA) with DMC to dimethyl toluene dicarbamate (TDC), zinc acetate shows excellent catalytic performance. However, zinc acetate gradually transforms to nanometer-scale zinc oxide and loses its catalytic activity. Fortunately, the nanometer-scale zinc oxide can be used as a catalyst for the second step of the process, i.e., decomposition of TDC to TDI. In this work, a novel catalytic process was realized for the synthesis of TDC together with in situ preparation of the nanometer-scale zinc oxide and for the synthesis of TDI from decomposition of TDC catalyzed by the nanometer-scale zinc oxide. The experimental results show that TDC yield reached 98.9%, and a ZnO yield of 90.1% was simultaneously obtained under the reaction conditions of molar ratio of TDA/DMC = 1/30, mass ratio of TDA/Zn(OAc)₂ = 1/0.16, reaction temperature of 160 °C, and reaction time of 7 h. The obtained zinc oxide was characterized by XRD, TEM, and BET, and the results show that it was nanoscale and possessed a wurtzite structure and a specific surface area of 60 m²/g. Furthermore, the zinc oxide showed a high catalytic performance for TDC decomposition reaction, and the yield of TDI and toluene monoisocyanate (TMI) separately reached 87.5% and 12.4% under the reaction conditions of zinc oxide concentration of 3.2 × 10^–3 g/mL, reaction temperature of 240 °C, reaction pressure of 7.33 kPa, and reaction time of 1.5 h. The resultant reaction mixture, mainly including TDC and the nanometer-sized zinc oxide, could be directly introduced into the second step reactor for the decomposition of TDC, saving the cost for separation and purification.