| 摘要 |
1325286 Separation of polyisocyanate mixtures GOTTFRIED REUTER GmbH 3 Feb 1972 [4 Feb 1971] 5046/72 Heading C2C [Also in Divisions B2 and C3] An organic polyisocyanate mixture which contains, in preponderant amount, diphenylmethane diisocyanate isomers and higher functional polyisocyanates with more than two benzene rings in the molecule is separated by first separating the mixture by a short path distillation into a first fraction which contains a residue of diphenylmethane diisocyanate isomers together with the higher functional polyisocyanates and into a second fraction which, of the polyisocyanates, contains practically only the diphenylmethane diisocyanate isomers and secondly separating the second fraction by fractional crystallization into a third fraction, which predominantly comprises 4,4<SP>1 </SP>- diphenylmethane diisocyanate, and into a fourth fraction, in which the 2,2<SP>1</SP>- and 2,4<SP>1</SP>- isomers of the diphenylmethane diisocyanate are enriched in the 4,4<SP>1</SP>-diphenylmethane diisocyanate. The second fraction may be freed from volatile substances and sparingly volatile, chlorine-containing compounds by a fractional distillation prior to the crystallization step. The fractional crystallization is preferably combined with a wash process in which the wash liquid is a diphenylmethane-diisocyanate mixture with a high content of 4,4<SP>1</SP>-isomer. |
