Patent ID: 6716936
Filing Date: 2004-04-06
Classification: C08F,Y10S

Abstract:
A process for the production of low to medium density polyethylene homo and copolymers, said process comprisinga) introducing ethylene, hydrogen, a light aliphatic solvent, optionally one or more further olefin monomers, and an ethylene polymerization catalyst into a first reactor; b) operating said first reactor at the bubble point of the reactor contents, such that heat generated by the polymerization reaction is removed via the heat of vaporization of a boiling light solvent mixture; c) condensing a vapor comprising light solvent from said first reactor to form a light solvent condensate, optionally subcooling said light solvent condensate, and returning said light solvent condensate or a portion thereof to said first reactor, such that return of said light solvent condensate to said reactor maintains the reactor at a desired first reactor pressure and first reactor temperature; d) removing a polyethylene slurry stream from said first reactor containing light solvent and polyethylene polymer of number average molecular weight Mn, and directing said polyethylene slurry stream to a hydrogen removal system to form a hydrogen depleted polyethylene slurry stream; e) directing said hydrogen depleted polyethylene slurry stream to a second reactor; f) introducing one or more reactant stream(s) comprising ethylene, the same light aliphatic solvent as said first reactor, optionally hydrogen, optionally one or more further olefin monomers, and optionally further ethylene polymerization catalyst into said second reactor; g) operating said second reactor at the bubble point of the reactor contents, such that heat generated by the polymerization reaction is removed via the heat of vaporization of a boiling light solvent mixture; h) condensing a vapor comprising light solvent from said second reactor to form a light solvent condensate, optionally subcooling said light solvent condensate, and returning said light solvent condensate or a portion thereof to said second reactor, such that return of said light solvent condensate to said reactor maintains the reactor at a desired second reactor pressure and second reactor temperature; i) polymerizing ethylene and optional further comonomer(s) in said second reactor to produce a polyethylene polymer with a number average molecular weight Mn2, Mn2 and Mn, being different; and j) removing a bimodal polyethylene slurry stream from said second reactor and removing light solvent and unreacted monomer(s) from said bimodal polyethylene slurry stream to obtain a solid bimodal polyethylene product.