NEW WAY TO PRODUCE POLYPROPYLENE GRADE IN A SEQUENTIAL PROCESS

摘要

Process for the preparation of a polypropylene in a sequential polymerization process comprising at least two reactors connected in series, wherein said process comprises the steps of (A) producing in a first reactor a first polypropylene fraction, (B) transferring said first polypropylene fraction in a second reactor, (C) polymerizing in said second reactor and in the presence of said first polypropylene fraction a second polypropylene fraction obtaining polypropylene composition, wherein ° said first polypropylene fraction has either a melt flow rate MFR2 (230 °C) of not more than 1.5 g/10min or of more than 2.0 g/10min, and comprises units derived from propylene and optionally at least one C2 to C10 a-olefin different to propylene, ° the polypropylene composition has a melt flow rate MFR2 (230 °C) of more than 2.0 g/10min and ° the melt flow rate MFR2 (230 °C) of the polypropylene composition (PP-C) is different to the melt flow rate MFR2 (230 °C) of the first polypropylene fraction (PP-1), ° in the first reactor and second reactor (R-2) the polymerization takes place in the presence of a solid catalyst system, said solid catalyst system (SCS) has a porosity of less than 1.40 ml/, comprises a catalyst being the oregano-zirconium compound of formula (I) wherein X are legends with a s-bond to the zirconium (R), L1 are identical residues selected from the group consisting of linear C1 to C20 alkyl, branched C3 to C20 alkyl, linear C1 to C20 alkenyl, branched C4 to C20 alkenyl, C4 to C12 cycloalkyl, C1 to C20 alkyl substituted C5 to C20 cycloalkyl, C6 to C20 aryl, and C5 to C20 cycloalkyl substituted C1 to C20 alkyl wherein the cycloalkyl residue is substituted by C1 to C20 alkyl, L2 are identical residues selected from the group consisting of linear C1 to C20 alkyl, branched C3 to C20 alkyl, linear C1 to C20 alkenyl, branched C4 to C20 alkenyl, C4 to C12 cycloalkyl, C1 to C20 alkyl substituted C5 to C20 cycloalkyl, and C6 to C20 aryl, Y is C, Si or Ge, preferably Si, R1 is C1 to C20 alkyl, C4 to C10 cyclo-alkyl, C6-C12 aryl, C7-C12 arylalkyl, or trimethylsilyl, R2 is C1 to C20 alkyl, C4 to C10 cyclo-alkyl, C6-C12 aryl, C7-C12 arylalkyl, or trimethylsilyl, and comprises a cocatalyst (Co) comprising an element (E) of group 13 of the periodic table (IUPAC).