Patent ID: 9505711
Filing Date: 2016-11-29
CPC Classification: C07C

Claim Text:
1. A method for purifying 4,4′-methylene diphenyl diisocyanate, the method comprising purifying a mixture by distillation through a distillation column, such that a first gaseous stream comprising the mixture contacts at least one liquid compound within the distillation column, to obtain a second gaseous stream at a top of the distillation column, which is removed to obtain purified 4,4′-methylene diphenyl diisocyanate, wherein: the mixture comprises 4,4′-methylenediphenyl diisocyanate having a hydrolyzable chlorine content of greater than 100 ppm as determined by ASTM D4663-10; the second gaseous stream comprises the purified 4,4′-methylenediphenyl diisocyanate having a maximum hydrolyzable chlorine content of 100 ppm as determined by ASTM D4663-10; wherein said distillation column comprises ordered packing elements and wherein said first gaseous stream is fed into said distillation column at a point below said ordered packing elements; and said first gaseous stream is taken off as a side stream from a first column, and a product obtained from a bottom phase of said distillation column is recirculated to said first column.