Self-limiting catalyst system with controlled aluminum to SCA ratio and method
A catalyst composition for the polymerization of propylene is provided. The catalyst composition includes one or more Ziegler-Natta procatalyst compositions having one or more transition metal compounds and one or more esters of aromatic dicarboxylic acid internal electron donors, one or more aluminum containing cocatalysts and a selectivity control agent (SCA). The SCA is a mixture of an activity limiting agent and a silane composition. The catalyst composition has a molar ratio of aluminum to total SCA from 0.5:1 to 4:1. This aluminum/SCA ratio improves polymerization productivity and the polymer production rate. The catalyst composition is self-extinguishing.
1. A catalyst composition for use in a propylene polymerization process comprising:
one or more Ziegler-Natta procatalyst compositions comprising a transition metal compound containing magnesium and titanium, and one or more esters of aromatic dicarboxylic acid internal electron donors;
one or more aluminum containing cocatalysts; and
a selectivity control agent (SCA) comprising a mixture of: (A) a mixed silane composition comprising a mixture of:
(i) a first alkoxysilane that is a dimethoxysilane selected from the group consisting of dimethyldimethoxysilane, diisopropyldimethoxysilane, dicyclopentyldimethoxysilane, and bis(perhydroisoquinolino)dimethoxysilane; and
(ii) a second alkoxysilane that is an ethoxysilane selected from the group consisting of ethyltriethoxysilane, n-propyltriethoxysilane, diisobutyldiethoxysilane, methylcyclohexyldiethoxysilane, and tetraethoxysilane; and (B) an activity limiting agent (ALA) comprising an alkyl ester of C 4 -C 3 o aliphatic acid;
wherein:
(1) the molar ratio between the dimethoxysilane to the ethoxysilane in the SCA mixture is from 9:1 to 1:9;
(2) the SCA includes 60-97 mole percent of ALA and 3-40 mole percent mixed silane composition;
(3) the catalyst composition having a normalized activity ratio Air/A6 7 from 1% to 5%, wherein the normalized activity ratio is defined as Aii5/A6 7 , where A 1 s is the activity at temperature 115° C. and A6 7 is the activity at 67° C.;
(4) a molar ratio of aluminum to total moles of SCA comprising the mixture of the mixed sane composition and the ALA is from 0.5:1 to 4:1; and
(5) wherein a molar ratio of aluminum to Ti is 35-50.
2. The catalyst composition of claim 1 wherein the first alkoxysilane is diisopropyldimethoxysilane and the second alkoxysilane is tetraethoxysilane.
3. The catalyst composition of claim 1 wherein the first alkoxysilane is dicyclopentyldimethoxysilane and the second alkoxysilane is tetraethoxysilane.
4. The catalyst composition of claim 1 wherein the first alkoxysilane is bis(perhydroisoquinolino)dimethoxysilane and the second alkoxysilane is n-propyltriethoxysilane.
5. The catalyst composition of claim 1 wherein the first alkoxysilane is dicyclopentyldimethoxysilane, the second alkoxysilane is n-propyltriethoxysilane, and the ALA is isopropyl myristate.
6. The catalyst composition of claim 1 , wherein the ALA comprises isopropyl myristate.
7. The catalyst composition of claim 1 , wherein a molar ratio of aluminum to ALA is 0.5-6.7.
8. The catalyst composition of claim 1 , wherein a molar ratio of aluminum to the mixed silane composition is 1.25-80.
9. The catalyst composition of claim 1 , wherein a molar ratio of aluminum to total SCA is 0.5-4.