Process for the preparation of polypropylene with improved productivity

摘要

The present invention relates to a process for the preparation of a polypropylene in a sequential polymerization process comprising least two polymerization reactors connected in series, wherein the polymerization in the at least two polymerization reactors takes place in the presence of a Ziegler-Natta catalyst, and said Ziegler-Natta catalyst comprises (a) a pro-catalyst comprising (a1) a compound of a transition metal, (a2) a compound of a metal which metal is selected from one of the groups 1 to 3 of the periodic table (IUPAC), (a3) an internal electron donor, (b) a co-catalyst, and (c) an external donor, whereinthe ratio of catalyst feed rate to propylene (C3) feed rate in the first polymerization reactor (R1) is 1.0 to 4.5 g/t.