Published February 2004
While all current MDI production uses phosgene, interest in non-phosgene routes continues for environmental and safety considerations. A number of non-phosgene processes to MDI were developed some twenty years ago. The best of these was a process by Asahi that produced MDI via the oxidative carbonylation of aniline. Asahi used a PdCl2 catalyst suspended in liquid and subsequently recovered by filtration. This process was described in detail in PEP Report 1E (1992). Earlier this year a patent (US 6,541,653) issued that describes the vapor phase oxidative carbonylation of aniline. The catalyst is PdCl2 on zeolite. In this review we present a speculative design for a new route to MDI via vapor phase oxidative carbonylation of aniline. We compare the economics of this process (at 50 million lb/yr capacity) with those of the Asahi process as well as with the conventional phosgene route.