Abstract:
PROBLEM TO BE SOLVED: To provide a method for producing methylenedianiline (MDA) by reacting aniline with formaldehyde in the presence of acid catalysts while minimizing the N-methyl-MDA content as an undesirable by-product. SOLUTION: The semicontinuous method for producing MDA includes: introducing aniline with or without the acid catalyst; feeding formaldehyde with or without the acid catalyst through a mixing means into a circuit in which aniline with or without the acid catalyst and with or without previously added formaldehyde is circulated; and heating a reaction mixture to a temperature above 75°C after feeding in at least 50% of the total amount of formaldehyde to be fed. There is also provided a method for producing polyisocyanates by phosgenation of amines obtainable in such a manner. MDA is used for production of methylene-bis(phenyl isocyanate) (MDI) having a low chlorine content and/or a light color. COPYRIGHT: (C)2011,JPO&INPIT