Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymerizing in tubular or loop reactor
Reexamination Certificate
2000-05-15
2001-12-04
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymerizing in tubular or loop reactor
C526S066000, C526S068000, C526S069000, C526S070000, C526S079000, C526S351000, C526S160000, C422S132000, C422S134000
Reexamination Certificate
active
06326442
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a process for polymerizing olefins to polyolefins. More particularly, the invention relates to a process for polymerizing dilute olefin feeds using a multistage reactor system in which the freshest catalyst is used to process the most dilute feeds.
BACKGROUND OF THE INVENTION
Most of the current processes for producing polyolefins are co-current in nature and require a highly concentrated and purified olefin feedstock, which results in increased complexity and cost for polyolefin production. As the catalyst and olefin streams proceed through a series of reactors, increasingly dilute olefin is contacted with increasingly less active catalyst. As a consequence, incomplete conversion of the olefin is achievable in a single pass through the reactor. The unconverted olefin must be recycled to the beginning of the process. Unless a portion of this recycled stream is purged, the concentration of diluents in the polymerization reactors builds to unacceptable levels. In many current polymerization processes, the amount of purge ultimately is determined by the content of diluents in the fresh feed. High diluent concentrations in the feed demand high purge rates and concomitant olefin loss. In order to avoid such loss, extensive and complex separation schemes are required, which greatly increase the complexity, investment, and operational cost while reducing the reliability of the polymerization process.
An effective, efficient process is needed for handling dilute olefin feeds.
SUMMARY OF THE INVENTION
The present invention provides a method for substantially continuously polymerizing olefins comprising: introducing into a first reaction zone a fresh olefin polymerization catalyst; contacting said fresh olefin polymerization catalyst in said first reaction zone with a first vent mixture at a first feed rate and under conditions sufficient to form and avoid melting a polyolefin, wherein first vent mixture comprises unreacted olefins and a diluent vented from a second reaction zone; withdrawing a vent product of unreacted olefins and diluent from said first reaction zone; withdrawing from said first reaction zone a first product mixture comprising said catalyst and said polyolefin; passing said first product mixture to said second reaction zone; contacting said first product mixture in said second reaction zone with a second vent mixture at a second feed rate and under conditions sufficient to form and avoid melting said polyolefin, wherein said second vent mixture comprises a material selected from the group consisting of a fresh feed and a mixture comprising unreacted olefins and diluent from a third reaction zone; and, withdrawing from said second reaction zone a second product mixture comprising said catalyst and said polyolefin.
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Brinen Jeffrey Lawrence
Koveal Russell John
McAlpin James John
Exxon Mobil Chemical, Inc.
Harlan R.
Wu David W.
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