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

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.