US 7,514,508 B2
Process for the polymerization of ethylene
Gerben Meier, Frankfurt (Germany); Massimo Covezzi, Ferrara (Italy); Pietro Baita, Rovigo (Italy); and Gabriele Mei, Ferrara (Italy)
Assigned to Basell Poliolefine Italia s.r.l., Milan (Italy)
Appl. No. 10/568,739
PCT Filed Jul. 19, 2004, PCT No. PCT/EP2004/008063
§ 371(c)(1), (2), (4) Date Feb. 17, 2006,
PCT Pub. No. WO2005/019280, PCT Pub. Date Mar. 03, 2005.
Claims priority of provisional application 60/497900, filed on Aug. 25, 2003.
Claims priority of application No. 03077645 (EP), filed on Aug. 20, 2003.
Prior Publication US 2007/0093621 A1, Apr. 26, 2007
Int. Cl. C08F 2/38 (2006.01); C08F 2/34 (2006.01); C08F 210/02 (2006.01)
U.S. Cl. 526—65  [526/88; 526/348.5; 526/905] 20 Claims
OG exemplary drawing
 
1. A process for preparing a broad molecular weight polyethylene by polymerizing ethylene in the presence of a polymerization catalyst, the process comprising the following steps, in any mutual order:
a) polymerizing ethylene monomer, optionally together with at least one first α-olefinic comonomer having from 3 to 12 carbon atoms, in a first gas-phase reactor in the presence of a first amount of hydrogen, thereby forming an ethylene polymer;
b) copolymerizing ethylene with at least one second α-olefinic comonomer having from 3 to 12 carbon atoms in a second gas-phase reactor in the presence of a second amount of hydrogen, wherein the second amount of hydrogen is less than the first amount of hydrogen;
where in at least one of said gas-phase reactors growing polymer particles flow upward through a first polymerization zone (riser) under fast fluidization or transport conditions, leave said riser and enter a second polymerization zone (downcomer) through which they flow downward under the action of gravity, leave said downcomer and are reintroduced into the riser, thus establishing a circulation of polymer between said two polymerization zones,
wherein the ethylene polymer obtained from step a) represents from 40 to 65% by weight of a total ethylene polymer produced in the overall process.