Olefin polymerization process
A multi-reactor solution process for polymerizing ethylene is disclosed. Ethylene is polymerized in a first reaction zone in two parallel reactors and the polyethylene is transferred to a second reaction zone to continue or complete the polymerization. Ethylene is contacted with a mixture of a titanium halide and a vanadium halide in the first parallel reactor and with a magnesium-titanium based Ziegler-Natta catalyst at a lower temperature in the second parallel reactor. The process gives improved catalyst activity.
1 . A multi-reactor solution process which comprises polymerizing ethylene in a first reaction zone in first and second parallel reactors and transferring the polyethylene from each reactor to a second reaction zone to continue or complete the polymerization; wherein ethylene is contacted in the first parallel reactor with a first catalyst comprising a mixture of a titanium halide and a vanadium halide and ethylene is contacted in the second parallel reactor with a second catalyst comprising a magnesium-titanium based Ziegler-Natta catalyst and wherein the temperature in the second parallel reactor is lower than the temperature in the first parallel reactor.
2 . The process of claim 1 wherein the first catalyst comprises a mixture of titanium tetrachloride and vanadium oxytrichloride.
3 . The process of claim 1 wherein the second catalyst comprises the product formed by contacting a titanium compound with a magnesium halide or an organomagnesium compound.
4 . The process of claim 3 wherein the second catalyst comprises the product formed by contacting titanium tetrachloride with an alkyl magnesium compound.
5 . The process of claim 4 wherein the alkyl magnesium compound is an alkyl magnesium silylamide.
6 . The process of claim 1 further comprising the addition of an α-olefin in the first reaction zone.
7 . The process of claim 6 wherein greater than 60% by weight of the α-olefin is added to the second parallel reactor and the α-olefin is selected from the group consisting of 1-butene, 1-hexene, and 1-octene.
8 . The process of claim 1 wherein the first catalyst is additionally added to the second reaction zone.
9 . The process of claim 1 further comprising a third reaction zone wherein the third reaction zone is a tubular reactor.
10 . The process of claim 1 wherein an aluminum compound selected from the group consisting of trialkylaluminums, dialkylaluminum halides, dialkylaluminum alkoxides, dialkyl aluminum siloxides, alkylaluminum dihalides, and tetraalkyl aluminum oxides is added to the first and second parallel reactors.
11 . The process of claim 1 wherein the temperature in the second parallel reactor is at least 2° C. less than the temperature in the first parallel reactor.