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A Method for Increasing Catalyst Productivity in A Staged Metallocene Reactor System To Reduce Effects Of Hydrogen Generation

IP.com Disclosure Number: IPCOM000033626D
Publication Date: 2004-Dec-20
Document File: 7 page(s) / 634K

Publishing Venue

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Abstract

This invention describes a method to enable the production of higher molecular weight polymers in a metallocene catalyzed staged reactor system. The production of higher molecular weight polymers is made possible by the addition of any catalyst activity increasing agent(s) to the second or subsequent reactor(s). Metallocene catalysts can become limited in the highest molecular weight achievable by producing low levels of hydrogen, a polymer chain transfer agent, during polymer chain growth. These low levels of hydrogen can limit the maximum molecular weight produced by inflating the hydrogen-to-ethylene concentration that controls molecular weight. This phenomenon becomes an even greater limitation in the first reactor of a staged reactor system, where the ethylene concentration is held low to retain catalyst activity for later reactors. By the addition of a catalyst activity enhancing agent in the second (or subsequent) reactor(s), the ethylene concentration in the first reactor can be increased. This decreases the hydrogen-to-ethylene concentration in this reactor and allows the production of higher molecular weight polymers normally not achievable in a staged reactor system.

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A Method for Increasing Catalyst Productivity in A Staged Metallocene Reactor System To Reduce Effects Of Hydrogen Generation

This invention describes a method to enable the production of higher molecular weight polymers in a metallocene catalyzed staged reactor system.  The production of higher molecular weight polymers is made possible by the addition of any catalyst activity increasing agent(s) to the second or subsequent reactor(s).  Metallocene catalysts can become limited in the highest molecular weight achievable by producing low levels of hydrogen, a polymer chain transfer agent, during polymer chain growth.  These low levels of hydrogen can limit the maximum molecular weight produced by inflating the hydrogen-to-ethylene concentration that controls molecular weight.  This phenomenon becomes an even greater limitation in the first reactor of a staged reactor system, where the ethylene concentration is held low to retain catalyst activity for later reactors.  By the addition of a catalyst activity enhancing agent in the second (or subsequent) reactor(s), the ethylene concentration in the first reactor can be increased.  This decreases the hydrogen-to-ethylene concentration in this reactor and allows the production of higher molecular weight polymers normally not achievable in a staged reactor system.

Staged polyethylene reactors typically operate by feeding catalyst to only the first reactor in a series of reactors.  The discharge of the first reactor is then sent to one or more reactor(s) where an additional polymer is made under a different set of reactor conditions on and in the polymer particles produced in the first reactor.

Staged polyethylene reactors typically operate by feeding catalyst to only the first reactor in a series of reactors.  The discharge of the first reactor is then sent to one or more reactor(s) where an additional polymer is made under a different set of reactor conditions on the same resin particles.  Since catalyst feed is only usually to the first reactor of the series, the ethylene concentration in the first reactor is held relatively low (30-150 PSI ethylene) and catalyst inventory is high in order to save some catalyst activity for the subsequent reactors.  At the same time, the last reactor of a series is normally operated at the highest pressure and ethylene concentration possible to maximize productivity of the partially used catalyst entering that reactor.  Additionally, catalyst decay can also require higher catalyst residues in the first reactor in order to maintain full polymerization activity in the second reactor.  This invention describes a method for enabling the production of higher molecular weight polymers while producing polyethylene with a metallocene catalyst in a staged reactor system, particularly for those catalytic systems that generate Hydrogen during polymerization.

Some metallocene catalysts liberate hydrogen during polymer chain growth.  Because of the extreme sensiti...