Phosgene free route to methyl diphenyl diisocyanate (MDI)

An alternative production process for MDI, in which no toxic phosgene is used, was designed. The plant should produce MDI at a rate of 300 kton/yr at market specifications and using methylelenedianiline (MDA) as a raw material, which has to be converted to MDI for at least 98%. Seven published routes were studied and compared on process conditions, technical and economical feasibility, and safety. Three routes remained, which all involved the reaction of MDA to a carbamate intermediate and the successive thermolysis of this intermediate to MDI and side-products. For these routes, a systematic design procedure was applied. The design for the promising route using urea and 3-methyl-1-butanol was completed. Heat integration studies showed that the savings for the process designed were limited to ∼ 4 Mw leading to 21 Mw hot utility and 90 Mw cold utility. This is an abstract of a paper presented at the CHISA 2012 - 20th International Congress of Chemical and Process Engineering and PRES 2012 - 15th Conference on Process Integration, Modelling and Optimisation for Energy Saving and Pollution Reduction (Prague, Czech Republic 8/25-29/2012).