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 a pre-polymerization reactor and at 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, wherein said Ziegler-Natta catalyst is present in the pre-polymerization reactor and ethylene (C2) in addition to propylene (C3) is fed to said pre-polymerization reactor in a C2/C3 feed ratio of 0.5 to 10.0 g/kg.