MDI – Methylenediphenyl diisocyanate


Flowsheet MDI

MDI is produced from Benzene by nitration to Nitrobenzene (NB) followed by hydrogenation of NB to produce Aniline (AN). The Aniline is condensed with formaldehyde to produce a diamine, MDA (Methylene diphenyl diamine). MDA is finally phosgenated to produce the end product, MDI. The crude MDI consists of several different isomers and oligomers which are separated into two ring MDI (pure MDI and OMDI) and oligomeric MDI’s, PMI.


Aniline (CAS No. 62-53-3) is produced in a continuous high efficiency liquid phase hydrogenation process. The process utilizes a proprietary catalyst for maximum economy and selectivity. The heat of reaction is used to produce steam for internal use as well as for export. The process is safe, easy to control and it gives excellent quality.


Methylene dianiline (4,4-MDA, CAS No 101-77-9) and oligomeric MDA (PMA, CAS No. 25214-70-4) is produced by condensation of Aniline with formaldehyde in acidic environment. The overall process is continuous but it uses a combination of tank and batch reactors. The by-product brine (NaCl) solution is purified so it can be used as raw material in a chlor-alkali plant or be released to a suitable recipient.


MDI Mixed isomers (MDI, CAS No. 26447-40-5) and oligomeric MDI (PMI, CAS No. 32055-14-4) is produced by reacting PMA with phosgene in a solvent. The solvent and the excess phosgene is recovered and recycled. The by-product HCl is purified and either oxidized to produce chlorine which is used in the phosgene synthesis or sent outside the plant area for use in e.g. a VCM plant. Part of the HCl gas is absorbed in water to give hydrochloric acid which is used in the MDA synthesis. The crude PMI mixture is further purified and separated into 2-ring MDI (CAS No. 26447-40-5) from which pure 4,4’-MDI (CAS No. 101-68-8) and a 2,4’-MDI rich fraction (OMDI, CAS No. 5873-54-1) is produced. The remaining oligomeric fraction is PMI and it is, together with the 2-ring material, either sold as it is or blended and/or modified into various MDI based products.

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