Study On Synthesis Of 2,4-toluene Diisocyanate From 2,4-toluene Dicarbamate

2, 4-Toluene diisocyanate(TDI) is an important organic medium,which is used mostly as raw material for preparing Poly Urethane(PU).At present,the industrial production of TDI uses phosgene as raw material,which is a poisonous substance.This process is harmful to environment and difficult to control.Dimethyl carbonate (DMC),which is called"Green Chemical",can substitute phosgene for the synthesis of 2,4-toluene dicarbamate (TDC).And then TDI can be prepared by the decomposition of TDC.This route have 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 method,the high atom economics process can be acquired.So it is a prospective route for further development in clean production.The following research concerning about the process of TDI synthesis from TDC has been systematically done in this thesis.Firstly, the material (TDC) was prepared through the reaction of TDI with methanol and purified through crystallization.Its purity was determined by HPLC.Secondly, the apparatus used for liquid-phase cleavage reaction was designed and assembled.The principle of solvent and heat-carrier empolied was concluded,and effect of reaction solvents,heat-carriers on the cleavage reaction were investigated.The most high yield of TDI was 77.76% using dimethyl-o-phthalate as solvent and Di-(2-Ethylhexyl)phthalate as heat-carrier. Lg(34) orthogonal lay out was arranged to optimize the experiments.The optimal operating conditions were:270癈,2.666kPa, 3h,3.5gTDC/100ml solvent,the yield of TDI was 78.43%.Then the liquid-phase catalytic cleavage reaction of TDC was studied.Zinc powder,aluminium powder,reduced iron powder,uranul zinc acetate,zinc oxide and zinc chloride ware found to be better with high activity among 18 catalysts we studied. The highest yield was 99.38% using Dimethyl-o-phthalate as solvent, Di-(2-Ethylhexyl)phthalate as heat-carrier and zinc powder as catalyst.Thirdly, the apparatus used for gas-phase cleavage reaction was investigated and assembled. The cleavage of TDC was studied using TGA and DSC for the first time.It was found that the cleavage of TDC begun from the melting point.Effects ofdifferent temperature on the thermal cleavage reaction were investigated.The yield of TDI was more higher while the temperature rising.The yield of TDI has a step chage between 350-400C .It was concluded that there was a energe mount .Crossing the energe mount, the reaction would be carry out more effective .Zn^ ZnCK Cu and CuO were found to be better with high activities under the reaction condition we studied. The activities of Zn and ZnO were higher than that of Cu and CuO.It was found for the first time that II-A metal and their oxides have catalytic activity towards the cleavage of TDC.The yield of TDI was 96.72% using Mg as catalyst and 94.85% using MgO as catalyst at 450C.As the metal oxides of II-A,the activity of CaO was lower than that of MgO.The yield of TDI was 90.30% using CaO as catalyst at 450"C.Fourthly ,non-isothermal kinetic study of the process of TDI synthesis from TDC has been performed.In the range of practical interest investigated in this work,the reaction order was derived as N=1.09 .The apparent activation energy Ea=23.05kJ/mol and the rate of this process may be described by rTDC=4.380X 105exp(-2.305X104/RT) PTDC1.09.