PRODUCTION OF METHYLENE-CROSSLINKED POLYPHENYLENE POLYISOCYANATE

PURPOSE:To obtain highly reactive poly-MDI and high-purity 4,4'-MDI simultaneously by separating the product obtained by reaction of a polyamine with phosgene into a MDI isomer mixture and poly-MDI through distillation and by further separating the isomer mixture through crystallization. CONSTITUTION:A product obtained by reaction with phosgene of a polyamine formed by condensation between aniline and formalin in the presence of an acid catalyst, is distilled and separated into (A) a mixture of various isomers of diphenylmethane diisocyanate (MDI) and (B) a methylene-crosslinked polyphenylene polyisocyanate (poly-MDI) containing 20-60wt.% of MDI. The mixture A is then separated, through a crystallization process, into (C) 10-40wt.% of a uncrystallized portion with acid and hydrolyzable chlorine highly concentrated, (D) 10-40wt.% of an initial soluble portion and (E) 40-60wt.% of the main soluble portion comprising high-purity 4,4'-MDI, and an inert gas is introduced into the component C followed by treatment under heating at 80-120 deg.C and then mixing with the component B at an arbitrary proportion.