Study On Liquid-Phase Decomposition Reaction Of Aromatic (Alkyl) Carbamate

The synthesis of isocyanate using dimethyl carbonate instead of phosgene is a non-phosgene route which is clean, mild, and has the most industrialized potential. This technology consists of the synthesis of aromatic (alkyl) carbamate and it's decomposition reaction. In this paper, decomposition reaction of aromatic (alkyl) carbamate was studied.Firstly, the reaction of toluene dicarbamate (TDC) cleavage to toluene diisocyanate (TDI) was studied. The effects of reaction temperature, reaction pressure, concentration of catalyst, reuse of catalyst and heat carrier on the yield of TDI were investigated. When heat carrier and solvent were different, the optimum reaction conditions: 260℃, 6.7 kPa, and the yield of TDI was 91.3%; the reuse of catalyst was well, but the yield of TDI decreased slowly when heat carrier was reused. When heat carrier and solvent were the same substance. The experiment showed that di-n-octylphthalate (DOP) was the best solvent. The optimum reaction conditions was obtained as following: temperature 260℃, pressure 5.4kPa, temperature of distillation 165℃, the yield of TDI reached 99%; the reuse of catalyst and heat carrier was well.Secondly, the reaction of 1,6-hexamethylene dimethylurethane cleavage to 1,6-hexam ethylene diisocyanate was studied. The effects of catalysts, heat carriers, reaction conditions on the yield of HDI were investigated, naphthenic oil which was as optimal carrier and zinc which was as optimal catalyst were determined, The highest yield of HDI was 80.3%. But comprehend sively considered from temperature controlling, heat carrier carryover, stability and so on, optimal conditions: temperature 260℃, pressure 8.0kPa, the yield of HDI was 71.3%. The reuse of catalyst and heat carrier on the yield of HDI were investigated, catalyst and heat carrier could reuse, but yield of HDI decreased slowly, when heat carrier was reused.Finally, the vapor-liquid equilibrium data for binary system of TDI-DOP at 8.0kPa were determined. With the software of ASPEN PLUS, Taking 5000t/a as an example, the separating process of solvent and toluene diisocynate was simulated calculated, The optimum conditions was obtained by simulation as following: ideal stage 7, the feed stream stage 4, reflux ratio 1.2, tower diameter of rectification section 0.93m, tower diameter of stripping section 1.63m, power of evaporator 5.9×10~5 kcal/h, power of condensator -1.2×10~5 kcal/h, the concentration of TDI fulfilled requirement.