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IMPROVED SCAVENGER FOR EXPERIMENTAL OLEFIN POLYMERIZATION REACTORS

IP.com Disclosure Number: IPCOM000029778D
Publication Date: 2004-Jul-12
Document File: 1 page(s) / 33K

Publishing Venue

The IP.com Prior Art Database

Abstract

Experimental olefin polymerization reactors are typically opened to the atmosphere for cleaning and preparation and then charged with a pre-bed before every experimental run or at other times such as for maintenance or substantial product change over. Despite subsequent heating and purging with inert gas to passivate the reactor, residual impurities, such as water or oxygen, will still be present on the reactor walls or in the pre-bed, or in other places in the reaction system. These impurities may be in sufficient quantity to poison the small amounts of catalyst (micromolar quantities) used in experimental polymerizations. These impurities may also be in sufficient quantity to prevent re-start of the system unless a chemical scavenger is added to the reactor prior to adding catalyst. A small amount of an aluminum alkyl solution is normally used for this purpose. However, despite efforts to remove residual alkyl, most catalysts are not inert to these scavengers, which can act as a co-catalyst for the polymerization, a poison for the catalyst or can alter the results of the experiments, such as activity, molecular weight and kinetic constants. It would thus be advantageous to be able to passivate reactor systems with a material that would scavenge impurities on the walls and in any material charged as a pre-bed without having significant impact on the subsequent polymerization reaction. By anchoring the scavenger to a support, the interactions with catalyst sites can be avoided and thus accomplish this objective.

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IMPROVED SCAVENGER FOR EXPERIMENTAL OLEFIN POLYMERIZATION REACTORS

Experimental olefin polymerization reactors are typically opened to the atmosphere for cleaning and preparation and then charged with a pre-bed before every experimental run or at other times such as for maintenance or substantial product change over.  Olefin polymerization includes the manufacture of polyethylene, polypropylene and copolymers of ethylene and propylene.  Despite subsequent heating and purging with inert gas to passivate the reactor, residual impurities, such as water or oxygen, will still be present on the reactor walls or in the pre-bed, or in other places in the reaction system.  These impurities may be in sufficient quantity to poison the small amounts of catalyst (micromolar quantities) used in experimental polymerizations.  These impurities may also be in sufficient quantity to prevent re-start of the system unless a chemical scavenger is added to the reactor prior to adding catalyst.  A small amount of an aluminum alkyl solution is normally used for this purpose.  However, despite efforts to remove residual alkyl, most catalysts are not inert to these scavengers, which can act as a co-catalyst for the polymerization, a poison for the catalyst or can alter the results of the experiments, such as activity, molecular weight and kinetic constants.  It would thus be advantageous to be able to passivate reactor systems with a material that would scavenge impurities on the walls and in any material charged as a pre-bed without having significant impact on the subsequent polymerization reaction.  By anchoring the scavenger to a support, the interactions with catalyst sites can be avoided and thus accomplish this objective.  Enabling examples include:

·         the use of supported methylalumoxane (SMAO) as a scavenger for single-site catalysts (including metallocene catalysts)

·         the use of SMAO as a scavenger for Ziegler-Natta catalysts

·         the use of triethyl aluminum (TEAL) on silica as a scavenger for chromium catalysts

·         the use of methylalumoxane (MAO) on functionalized polystyrene as a scavenger for vanadium, Ziegler-Natta or single-site catalysts.

Metallocene catalysts are known to be very susceptible to trace levels of impurities and residual alkyl from passivation can poison the catal...