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Going with the flow: material use in the new PMDI plants: more than 6 million tonnes of materials need to be moved annually in just one of tomorrow's pMDI plants.

Article Excerpt
In recent months, a number of companies have announced construction plans for new world-scale manufacturing units for polymeric MDI (methylene diphenyl diisocyanate, pMDI), both in Europe and in China.

Companies such as BASF, Bayer MaterialScience, Huntsman and Chinese group Yantai Wanhua, as well as Hungarian isocyanates producer BorsodChem, have announced pMDI capacity additions.

And these organisations are claiming new, better efficiencies of these yet-to-be-built units. Generally, they have revealed few details of the chemistry and technology behind such advances.

To make pMDI, the starting point is benzene, nitrated to nitrobenzene and then hydrogenated to produce aniline. This is then condensed with formaldehyde under acid catalysis yielding polymeric methylene dianiline (pMDA). The process then requires generation of phosgene, and finally phosgenation of this pMDA, usually dissolved in monochlorobenzene (MCB), to make pMDI, with MCB then removed by distillation.

Gas-phase boost for TDI

Bayer MaterialScience has been forthcoming about its new gas-phase process to phosgenate TDA (toluene diamine) and make TDI (toluene diisocyanate). This minimises solvent use, reducing the complications this introduces.

The German firm has exploited this approach in its new process, which it will roll out in a 300 ktpa TDI plant at Caojing, near Shanghai in China, planned for start up in 2010.

Unfortunately, manufacture of pMDI requires phosgenation of polymeric methylene dianiline (pMDA), which cannot be done...

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