Process for removal of intermediate hydrogen from cascaded polyolefin slurry reactors
AssigneeEquistar Chemicals, LP
InventorPatrick J. McGrath
Life of this patent
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Abstract
Multimodal polyolefin polymers may be prepared in series-connected polymerization reactors where a prior reactor is a slurry reactor employing light solvent as the slurry medium and hydrogen to limit polymer molecular weight, the polymer product from the prior reactor being substantially freed of hydrogen prior to entry into a subsequent polymerization reactor operating at low hydrogen pressure to produce a high molecular weight olefin. The economics and operating performance of such a series slurry reactor polyethylene process can be significantly improved through the use of an intermediate slurry transfer system and hydrogen removal apparatus that employs flash drums in series in conjunction with a warm recycle solvent slurry diluent.
Claims11
An interstitially mixed, multimodal polyethylene copolymer containing a low molecular weight portion comprising a copolymer of ethylene and at least one other copolymerizable olefin monomer, and a higher molecular weight portion comprising a polyethylene homo- or copolymer, prepared by the process of
- a) polymerizing at least two olefin monomers in the presence of hydrogen in a prior slurry reactor employing light solvent as a slurry medium to form a first polyolefin polymer of a first molecular weight;
- and
- b) removing said first polyolefin polymer from said prior slurry reactor as a hydrogen-containing polymer slurry in light solvent and introducing said hydrogen-containing polymer slurry into a subsequent slurry reactor containing ethylene and optionally one or more olefin monomers other than ethylene, and employing a low concentration of hydrogen, polymerizing to form an ethylene homo- or copolymer, and recovering a polyolefin polymer therefrom,
- wherein the hydrogen concentration in the hydrogen-containing polymer slurry is lower than the hydrogen concentration in said prior slurry reactor, the hydrogen mass flow from the hydrogen-containing polymer slurry fed to the subsequent reactor is less than a fresh hydrogen mass flow feed to the subsequent reactor by a factor of at least 10, and wherein a rapidly hydrogen-consuming catalyst is not employed in said subsequent slurry reactor.
Dependencies are inferred from the claim text.