| 摘要 |
<p>A method for the production of 4,4'-diphenylmethanedi-isocyanate (4,4'-MDI) by reacting aniline with formaldehyde and then reacting the amine mixture with phosgene, involves separating the resulting mixture by distillation and/or crystallisation to give a first fraction containing at least 97 wt% 4,4'-MDI and not more than 3 wt% 2,4'-MDI and a second fraction containing 30-60 wt% 4,4'-MDI, 1-12 wt% 2,4'-MDI, not more than 2 wt% 2,2'-MDI and 35-65 wt% tri- and higher-functional polyisocyanates. A method for the production of 4,4'-diphenylmethanedi-isocyanate (4,4'-MDI) involves (a) reacting aniline and formaldehyde in the mol ratio (1.7-4):1 in presence of an acid catalyst to give di- and poly-amines, (b) reacting with phosgene to give a mixture containing 44-80 wt% 4,4'-MDI plus 1-12 wt% 2,4'- and/or 2,2'-MDI and 10-55 wt% tri- and higher-functional polyisocyanates (PMDI), and (c) separating the mixture into two fractions by distillation and/or crystallisation, comprising F1 (5-40 wt% of the mixture) and F2 (60-95 wt%), in which F1 contains at least 97 wt% 4,4'-MDI and not more than 3 wt% 2,4'-MDI, and F2 contains 30-60 wt% 4,4'-MDI, 1-12 wt% 2,4'-MDI, not more than 2 wt% 2,2'-MDI and 35-65 wt% PMDI.</p> |
