摘要 |
A process for the production of a mixture of 2,4-toluene diisocyanate and 2,6-toluene diisocyanate containing 65/sB3% by weight of the former from a starting mixture of the two diisocyanates containing 70-90% by weight of a formula comprises freezing the starting mixture under substantially static conditions and bringing its temperature to 5-8 DEG C. so as to form a mixture of mother liquor and a coherent crystalline deposit rich in 2,4-toluene diisocyanate, and separating the mother liquor, while raising the temperature of the mixture by 0.5-3 DEG C., to produce a liquid fraction containing 65/sB3% by weight of 2,4-toluene-diisocyanate, and a crystalline residue containing 90-95% by weight of 2,4-toluene diisocyanate. In another feature of the invention a method of producing substantially pure 2,4-toluene diisocyanate from a starting mixture of 2,4-toluene diisocyanate and 2,6-toluene diisocyanate containing 90-95% by weight of the former prepared as above comprises freezing the starting mixture under substantially static conditions and bringing its temperature to 8-11 DEG C. so as to form a mixture of mother liquor and a coherent crystalline deposit, and separating the mother liquor while raising the temperature of the mixture to 18-21.5 DEG C. when the substantially pure 2,4-toluene disisocyanate is obtained as a crystalline residue. |