Between Toluene Diisocyanate Green Synthesis Process Research

At present,the industrial production of isocyanate uses phosgene as raw material.This process is harmful for environment and difficult to control.Dimethyl carbonate(DMC), which is called "Green Chemical",can substitute phosgene for the synthesis of methyl N-(m-tolyl)carbamate,and then m-Toluene isocyanate can be prepared by the decomposition of methyl N-(m-tolyl)carbamate.This route has distinct advantages,such as moderate conditions,inexpensive catalyst and unique by-product-methanol.If it is combined with the synthesis of DMC by gas-phase oxidative carbonylation of methanol,the high economical process can be acquired.So it is a prospective route for further development in clean production.As for the process of methyl N-(m-tolyl)carbamate preparation.The kinds of catalysts and reaction conditions were investigated.Zn(OAC)₂ and PbO were found to be high activity catalysts.The influences of reaction factors were discussed.The temperature is a major factor. Using orthogonal testing method,the optimum condition:When Zn(OAC)₂ was used as catalyst of the reaction,94.23%yield of methyl N-(m-tolyl)carbamate was attained at 413K in 2.5h.n(DMC):n(3-aminetoluene)= 8:1,n(catalyst):n(3-aminetoluene)=7.8%.When PbO was used as catalyst of the reaction,91.37%yield of methyl N-(m-tolyl)carbamate was attained at 433K in 3h.n(DMC):n(3-aminetoluene)= 8∶1,n(catalyst):n(3-aminetoluene) = 12%.The cleavage of methyl N-(m-tolyl)carbamate was studied using TGA and DSC.It was found that the cleavage of methyl N-(m-tolyl)carbamate begun from the melting point and was an endothermic reaction.Effects of solvents and heat-carriers were investigated,the optimal compages was dibutyl phthalate as solvent,paraffin liquid as heat-cartier and zinc powder as catalyst.On this condition,orthogonal layout was arranged to optimize the experiments.The optimal operating conditions:220℃,degree of vacuum 0.095MPa,3h, 3.0g/100mL solvent,m(catalyst):m(methyl N-(m-tolyl)carbamate)= 6%,the yield of m-Toluene isocyanate was 92.05%.Based on the feasibility analysis of the continuous process to product m-Toluene isocyanate,the yield of the continuous process was 78.92%.So a set of continuous apparatus draft was made.