Patent ID: 7521576

Claim:
A process for preparing 2,4′-MDI which contains very little 2,2′-MDI comprising distilling an isomeric starting mixture of diisocyanatodiphenylmethanes comprising 2,2′-diisocyanatodiphenylmethane, 2,4′-diisocyanatodiphenylmethane and 4,4′-diisocyanatodiphenylmethane in a separating wall column to obtain at least one product mixture comprising 85 to 99 wt. % of 2,4′-diisocyanatodiphenylmethane, up to 15 wt. % of 4,4′-diisocyanatodiphenylmethane and up to 0.2 wt. % of 2,2′-diisocyanatodiphenylmethane.