Study On The Green Process Of Synthesizing Diphenyl Methane Diisocyanate

MDI is one of the most important raw materials for producing polyurethane.Currently, the phosgene method was adopted to produce MDI all over the worldand then to produce polyurethane. However, phosgene is the noxious gas. It isvery dangerous at the processes of transportation and storage. So varieties of safemeasures should be required to avoid the catastrophic accidents occurred. Withthe development of chemistry and technology, looking for the green of chemicalmaterials to manufacture MDI is necessary.In this paper dimethylcarbonate and diphenylmethanediamine(MDA) wereused as materials to produce diphenylmethanedicarbam(MDC), and the yields ofMDC reached94%. Then, by using IR and1HNMR the structure of MDC wasidentified. Through putting the MDC into the ionic liquids at high temperature,the final production, which is diphenylmethanediisocyanate (MDI) could beobtained. In this work, the technology of synthesizing MDC optimiting ionicliquid and pyrolysizing MDC was studyed. The process of this reaction is notonly mild but also the by-product methanol can be used for makingdimethylcarbonate. Besides, ionic liquids as solvents are non-toxic, no corrodingequipment and easy to remove.In these work,24ionic liquids have been synthesized by usingN-methylmorpholine and N-methylimidazole as raw materials and two stableionic liquids (for example N-methyl-N-ethylestermorpholinium tetrafluoroborateand1-ethylester-3-methyl-imidazolium tetrafluoroborate) were obtained throughthe thermal analysing method. The temperatures of thermal decomposition are310and290℃. Respectively between the temperature of310and320℃, theweight of the former had a slight loss; Between the temperature of320and340 ℃, the weight dropped by13%; Between the temperature of340and410℃, theweight dropped by85%. By the temperature of320℃, the weight of latter had aslight loss; between the temperature of320and340℃, the weight dropped by67%; Between the temperature of340and410℃, the weight dropped by32%.Furthermore, by improving the methods of this two ionic liquid, the productscould reach good yields such as92%and94%. By using IR and1HNMR thestructure of the ils can be identified.when using N-methyl-N-ethylestermorpholinium tetrafluoroborate and1-et-hylester-3-methylimidazolium tetrafluoroborate as solvents, and zinc acetate ascatalyst, at the conditions of220-230℃and1.9Pa, the MDI was obtained andthe yield reached88%. The product was proved to be very good by using IR and1HNMR. After the experiments the solvents could be recycled three times and therecovery of the ILs may be up to80%, from which the cost of production can bereduced greatly.