Hydrolysis of Toluene Diisocyanate Residue at Atmosphere Pressure for Toluene Diamine Recovery
Abstract: Toluene diisocyanate (TDI) is an important organic compound, usually manufactured from toluene diamine (TDA) as the main raw material through phosgenation. The purification of the phos-genation products by distillation results in high molecular weight and insoluble waste materials in quite a large amount. This residue, often called TDI distillery residue, has been an environment threat and different strategies have been set up for their processing. The most common process currently employed is its hydrolysis under high pressure and high temperature, which also allows recovery of TDA in considerable amount. This paper provides a novel and simple process for the hydrolysis of TDI residue without need for high pressure, and toluene diamine, the important raw material in the production of TDI, was also recovered at the same time. In this process, TDI residue was dispersed in either ethylene glycol, triethylene tetramine or their mixture, along with sodium hydroxide as a catalyst. Heated to the refluxing temperature of the mixture, the hydrolysis was conducted by refluxing at temperature varied from 140˚C to 290˚C under atmosphere pressure. Experimental conditions, including the medium solvent and its amount, reflux time and tempera-ture as well as the amount of alkali solution for the hydrolysis, were studied, and the hydrolysis was optimized with regard to the yield of TDA. Under the optimized conditions, a TDA yield of 54.44% based on the residue mass was achieved. This work therefore presents a reliable and facile process for the hydrolysis of TDI residue. Based on the results, mechanism of the hydrolysis is proposed.
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