| 摘要 |
A method for the production of di- and poly-isocyanates of the diphenylmethane series involves making crude MDI by reaction of aniline and formaldehyde followed by phosgenation and distillation as usual, then determining the acidity of the fractions obtained and adjusting their acidity to the required level by treatment with an acid compound. - A method for the production of di- and poly-isocyanates of the diphenylmethane series (I) involves (a) acid-catalysed reaction of aniline and formaldehyde to give di- and poly-amines, (b) phosgenation of the amines (optionally in solvent) to give crude di-/poly-isocyanate, (c) distillation to give a fraction containing at least 5 wt% tri- and poly-nuclear MDI and fraction(s) containing at least 95 wt% dinuclear MDI, (d) analytical determination of the acidities of these fractions and (e) addition of an acid compound to one or more of these fractions to obtained the required acidity.
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