Published December 2006
A recent patent (US 6,992,214 B2, Jan. 31, 2006) assigned to Dow Global Technologies discloses an integrated process for producing toluene diisocyanate (TDI) from toluene diamine (TDA) and dimethyl carbonate (DMC). The process chemistry is not new involving the intermediate production of the toluene diurethane (TDU) via reaction of TDA with DMC in the presence of a zinc catalyst followed by thermal decomposition of the TDU to TDI and methanol.
The novelty is in the methodology used to prevent the zinc catalyst from being carried over into the TDU pyrolysis step which is performed in the gas phase. Relatively high yields of TDI based on converted TDA and DMC are obtained following the teachings in the patent. This review includes development of a conceptual flow scheme based on the patent information, simulation of the process scheme, development of a process design for a base case plant producing 200 MMlb/yr TDI starting with purchased TDA and DMC, and development of capital cost and production cost estimates. Estimated TDI Product Value (25% BFT ROI included) produced by this technology is approximately 95 cents/lb. Historical US prices for TDI have been in the $1 range indicating that the TDA/DMC route to TDI is a viable alternative to the phosgene based route.
