| 摘要 |
The instant invention is directed to a process for the production of diisocyanatodiphenyl methane isomers having an adjusted content of chlorine compounds comprising: (a) separating diisocyanatodiphenyl methane isomers from a polyisocyanate mixture of the diphenyl methane series in a first distillation stage, (b) subjecting said separated isomers to a second distillation stage using a recycle ratio of from 0.1 to 10 and wherein from 0.5 to 10% by weight of the feed into said second distillation stage is run off as the sump product, (c) subjecting the head product of said second distillation stage to a third distillation stage whereby readily volatile impurities are freed therefrom, and (d) working up the sump product of said third distillation stage to obtain purified 4,4'-diisocyanatodiphenyl methane and, optionally, purified 2,4'-diisocyanatodiphenyl methane. |
