Manufacturing of MDI
Manufacturing of MDI
MDI (diphenylmethane di-isocyanate) is a di-isocyanate used in certain specific slabstock applications, such as some specialized high resilience foams. MDI is manufactured commercially from aniline. Aniline is reacted with formaldehyde to give a mixture of aromatic amines containing 2 or more aromatic rings. These amines are then phosgenated to give a mixture of MDI’s, sometimes called “crude” MDI. Crude MDI is then distilled to separate pure MDI (containing 2 aromatic rings, which themselves can exist as several isomers) from “polymeric” MDI (which contains 3 or more aromatic rings):
The chemistry of MDI manufacture
Aniline + Formaldehyde = Mixture of aromatic amines (Phosgenation) = Crude MDI = Polymeric MDI
Aniline + Formaldehyde = Mixture of aromatic amines (Phosgenation) = Crude MDI (Distillation) = Pure MDI
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MDI production accounted for 73% of world aniline consumption; other large applications include use as a chemical intermediate for rubber processing chemicals, dyes and pigments. Since most MDI producers are captive in aniline and its precursor nitrobenzene, typically in integrated units, nearly all MDI expansions result in increased production and consumption of nitrobenzene/aniline. MDI has been the driving force behind world growth in aniline demand since 1982. Future demand for aniline will continue to depend largely on MDI requirements.
MDI is consumed in polyurethane (PU) foam, both rigid and flexible. Most rigid PU foam is used in construction and appliances while flexible PU foam is used primarily in furniture and transportation. As a result, consumption of nitrobenzene/aniline/MDI largely follows the patterns of the leading world economies and depends heavily on construction/remodeling activity (residential and nonresidential), automotive production and original equipment manufacture (OEM).
The following pie chart shows world consumption of aniline:
Between 2003 and 2006, world capacity for aniline grew at an average annual rate of 6.2%, trailing world consumption, which grew at an average annual rate of 8.4% during that period. Rapid demand growth in all regions during 2003–2006, particularly in Asia (11.3% per year) and Europe (7.8% per year) was balanced by slower yet significant growth in the United States (3.6% per year). World trade in aniline accounted for less than 10% of production in 2006 since most aniline produced is converted to MDI, typically in adjacent plants.
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