Interest remains in non-phosgene routes to toluene diisocyanate (TDI) owing
to safety and environmental issues. The carbonylation of dinitrotoluene (DNT)
has been studied and was presented in PEP Report 1E (1992). More recently,
as the use of dimethylcarbonate (DMC) has been considered as a gasoline additive,
routes have been examined that might use cheap DMC from methanol and urea
produced in large capacity facilities. The key reaction for one such potential
route is described in US 6,034,265. This patent describes the reaction of
toluenediamine (TDA) with DMC to form a biscarbamate intermediate that can
be taken to TDI. In addition, there has been research on the reaction of TDA
with urea to give toluenediurethane, which can subsequently be decomposed
to TDI.
In this review we present the process economics for the integrated production
of TDI from DNT via TDA and DMC. We also present a cost estimate for the production
of TDI via TDA and urea. We compare the economics of both of these processes
to those for the traditional route via phosgene as well as for TDI by the
reductive carbonylation of DNT.
