Patent ID: 8907124

Claim:
A process for preparing a methylene diphenyl isocyanate), the process comprising: (a) phosgenation of a crude MDA mixture to form a crude MDI mixture; (b) fractionation of the crude MDI mixture to give at least one crude two-ring MDI mixture M and at least one polymeric MDI mixture P; (c) purification and/or fractionation of at least one mixture M to give at least one mixture F comprising at least one selected from the group consisting of 2,2′-MDI, 2,4′-MDI and 4,4′-MDI; and (d) independent storage of the mixture F obtained in step (c) and the mixture P obtained in step (b), to obtain a stored mixture F and a stored mixture P, wherein 1 to 30% by weight of the stored mixture F and/or part of the stored mixture P based on a total amount of the mixture F and/or the mixture P independently stored is, independently, recirculated to at least one of the steps (b) or (c).