Patent ID: 9090540
Filing Date: 2015-07-28
Classification: C07C

Abstract:
1. A process for the production of a mixture of methylene diphenyl diisocyanate (MDI) isomers, comprising: forming methylene diphenyl diamines and polyamines of the diphenylmethane series by reacting aniline and formaldehyde in the presence of an acid catalyst; phosgenating the methylene diphenyl diamines and polyamines of the diphenylmethane series to produce a mixture of the MDI isomers and polymeric MDI; heating the mixture of the MDI isomers and polymeric MDI to a temperature between about 170° C. to about 260° C. separating from the heated mixture of the MDI isomers and the polymeric MDI a first fraction containing at least 98% by weight of the MDI isomers comprising at least 52% by weight of 2,4′-MDI and 2,2′-MDI based on the total weight of the first fraction, of which a content of 4,4′-MDI in the first fraction is from 5% to 48% by weight, a content of 2,4′-MDI in the first fraction is from 52% to 95% by weight, and a content of 2,2′-MDI in the first fraction is from 0.01% to 20% by weight; heating the first fraction to a temperature between about 150° C. and about 190° C.; separating from the heated first fraction a second fraction containing at least 99% by weight of the MDI isomers comprising at least 52% by weight of 2,4′-MDI based on the total weight of the second fraction, of which a content of 4,4′-MDI in the second fraction is from 5% to 48% by weight, a content of 2,4′-MDI in the second fraction is from 52% to 95% by weight, and a content of 2,2′-MDI in the second fraction is from 0.00% to 0.80% by weight; and after removing the first fraction, a third fraction is separated from the heated mixture of MDI isomers and polymeric MDI using an evaporative reboiler and a side rectifier, the third fraction having a content of 4,4′-MDI in the third fraction of at least 98.5% by weight based on the total weight of the third fraction.