Study On Synthesis Of Toluene Diisocyanate By Catalyic Decomposition Of Toluene Dicarbamate

The synthesis of toluene diisocyanate?TDI?by non-phosgene route has became a word-wide research topic.Especially carbonate method with advantages of non-toxic materials and mild reaction conditions is a value method.The method includes two steps of synthesis and decomposition of toluene dicarbamate?TDC?.Because of self-polymerization of TDI easily at a high temperature the decomposition step has been a critical step.Hence the experimental study on the decomposition reaction of toluene dicarbamate has a great theoretical and applied significance.Firstly,Fe₂O₃ was prepared by different methods and its catalytic performance was investigated separately.The Fe₂O₃ catalysts were characterized by a series of characterization methods.BET and SEM of the catalyst were carried out,and the results show that the pore diameter of catalyst has effect on catalytic performance,and the bigger the pore diameter,the higher the catalytic performance.Besides,it was also found that Fe₂O₃-0 contains impurities by the characterization of XRD.Combined with the result of XRD,FTIR,ICP and dissolution method,it was discovered that Fe₂O₃-0 contains SiO₂about 30⁴0%.Further study of the catalytic properties of SiO2,Fe2O3-SiO2 on the decomposition of TDC was carried out and the results show that crystal SiO₂ has catalytic performance on the decomposition of TDC,and the catalytic activity of Fe₂O₃-SiO₂ is higher than Fe₂O₃ or SiO₂ solely.Secondly,React-IR was employed to track and monitor the reaction of decomposition of TDC.The di-n-octyl-o-phthalate?DOP?was used as the suitable solvent,and the best treatment of solvent is that the absorbance of solvent as background is subtracted as reaching the reaction temperature.Based on Lambert-Beer's theorem and quantitative relationship of the components,the concentration of each component in the reaction process was determined by the absorbance as time.Then the kinetic model of TDC decomposition reaction was established and the kinetic model parameters were determined.The experimental values are in good agreement with the predicted values.Kinetic equations were obtained as follows:???Finally,the thermal decomposition reaction and catalytic decomposition reaction of different toluene dicarbamate were studied.It can be obtained from the characterization of TGA that the thermal decomposition temperature of different toluene dicarbamate from low to high is TDC?Ph?<TDC?Me?<TDC?Pr?<TDC?Bu?.The decomposition experiment of different toluene dicarbamate was studied with DOP as a solvent and Fe₂O₃ as a catalyst.The results show that catalytic decomposition from easy to difficult successively is TDC?Ph?,TDC?Bu?,TDC?Pr?,TDC?Me?.The reason of different results of catalytic decomposition and thermal decomposition is that with solvent and catalyst during catalytic decomposition reaction,but without solvent and catalyst during the characterization of TGA.The mixtures of TDC and the solvent as well as TDC and the catalyst were deal with different manners,and then were characterized by FTIR.Combined with analysis of FTIR,the reaction mechanism of the decomposition of TDC catalyzed by Fe₂O₃ was speculated.