PEP Review 2004-2
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.
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