| 摘要 |
1. A process for the recovery of pure diisocyanates selected from the group consisting of (i) 2,4-diisocyanatotoluene and mixtures thereof with up to 35 % by weight, based on the mixture as a whole, of 2,6-diisocyanatotoluene, (ii) 1,6-diisocyanatohexane and (iii) 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethyl-cycloh- exane from concentrated solutions of the phosgenation products of the diamines on which the diisocyanates are based in technical chlorobenzene and/or technical ortho-dichlorobenzene, characterized in that the solutions of the phosgenation products which accumulate in the phosgenation of the diamines forming the basis of the diisocyanates in the solvents mentioned and which have a solvent content of 40 to 98 % by weight are freed by distillation from most of the solvent to a residual content of 2 to 15 % by weight and, optionally, a partial amount of the diisocyanate formed, the concentrates thus obtained are throughly mixed at temperature of from -20 degrees C to 130 degrees C with aliphatic hydrocarbons liquid at room temperature and/or with aliphatic ethers liquid at romm temperature as extractants, the ratio by weight of extractant to concentrate being kept at 0.5:1 to 30:1, to form a liquid two-phase mixture, the liquid phases formed are separated from one another after phase separation, the pure diisocyanate is recovered from the liquid phase of lower specific gravity by removal of the solvent or extractant present therein by distillation and the phase of higher specific gravity separated off is optionally delivered to another extraction. |
