Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2001-11-06
2003-05-13
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S068000, C526S128000, C526S159000, C526S160000, C526S170000, C526S348200, C526S348500, C526S348600, C526S088000
Reexamination Certificate
active
06562924
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a process for the gas-phase (co-)polymerization of olefins in a fluidized bed reactor using a metallocene catalyst.
The present invention also relates to a process for preventing fouling during the gas-phase (co-)polymerization of olefins in a fluidized bed reactor using a metallocene catalyst.
The present invention further relates to a process for improving the polymer flowability and the fluidization characteristics during the gas-phase (co-)polymerization of olefins in a fluidized bed reactor using a metallocene catalyst.
Processes for the co-polymerization of olefins in the gas phase are well known in the art. Such processes can be conducted for example by introducing the gaseous monomer and comonomer into a stirred and/or gas fluidized bed comprising polyolefin and a catalyst for the polymerization.
In the gas fluidized bed polymerization of olefins, the polymerization is conducted in a fluidized bed reactor wherein a bed of polymer particles is maintained in a fluidized state by means of an ascending gas stream comprising the gaseous reaction monomer. The start-up of such a polymerization generally employs a bed of polymer particles similar to the polymer which it is desired to manufacture. During the course of polymerization, fresh polymer is generated by the catalytic polymerization of the monomer, and polymer product is withdrawn to maintain the bed at more or less constant volume. An industrially favoured process employs a fluidization grid to distribute the fluidizing gas to the bed, and to act as a support for the bed when the supply of gas is cut off. The polymer produced is generally withdrawn from the reactor via a discharge conduit arranged in the lower portion of the reactor, near the fluidization grid. The fluidized bed consists in a bed of growing polymer particles. This bed is maintained in a fluidized condition by the continuous upward flow from the base of the reactor of a fluidizing gas.
The polymerization of olefins is an exothermic reaction and it is therefore necessary to provide means to cool the bed to remove the heat of polymerization. In the absence of such cooling the bed would increase in temperature and, for example, the catalyst becomes inactive or the bed commences to fuse. In the fluidized bed polymerization of olefins, the preferred method for removing the heat of polymerization is by supplying to the polymerization reactor a gas, the fluidizing gas, which is at a temperature lower than the desired polymerization temperature, passing the gas through the fluidized bed to conduct away the heat of polymerization, removing the gas from the reactor and cooling it by passage through an external heat exchanger, and recycling it to the bed. The temperature of the recycle gas can be adjusted in the heat exchanger to maintain the fluidized bed at the desired polymerization temperature. In this method of polymerizing alpha olefins, the recycle gas generally comprises the monomer and comonomer olefins, optionally together with, for example, an inert diluent gas such as nitrogen or a gaseous chain transfer agent such as hydrogen. Thus, the recycle gas serves to supply the monomer to the bed, to fluidize the bed, and to maintain the bed at the desired temperature. Monomers consumed by the polymerization reaction are normally replaced by adding make up gas or liquid to the polymerization zone or reaction loop.
It is also well known that metallocene catalysts can advantageously be used for the (co-)polymerization of olefins. In particular, it has been reported that metallocene catalysts can now be successfully used in slurry or liquid phase polymerization process in industrial plants. This is unfortunately not the case for the gas phase process where many problems still remain. For example, metallocene catalysts have a tendency toward fouling in gas phase polymerization process. It would appear that non uniform fluidization as well as poor heat transfer in the polymerization process are more frequently encountered in gas phase when metallocene catalysts are used. An explanation might be that metallocene polymer particles have a higher tendency to adhere together or to the walls of the reactor and to continue to polymerize and often fuse together and form chunks, which can be detrimental to a continuous process, particularly a fluidized bed process. Another problem linked to the use of metallocene catalysts in a fluidized bed process lies in the very particular activity kinetic profile exhibited by this catalyst; indeed it is reported in the literature that the metallocene activity kinetic profile is responsible for most of the polymerization troubles faced when this type of catalyst is introduced into the reactor, problems even more exacerbated during the polymerization start-up. There is thus a need in the art to find a process for producing successfully polyolefins on gas phase industrial plants using a metallocene catalyst.
The Applicants have now unexpectedly found a simple and efficient process which overcomes the problems encountered with the gas phase polymerization of olefins using a metallocene catalyst.
SUMMARY OF THE INVENTION
In accordance with the present invention, there has now been found a process for the gas-phase (co-)polymerization of olefins in a fluidized bed reactor using a metallocene catalyst in the presence of a process aid additive characterised in that the additive comprises at least one of the components selected from:
(1) a polysulfone copolymer,
(2) a polymeric polyamine, and
(3) an oil-soluble sulfonic acid.
Preferably, the process aid additive comprises at least two components selected from above components (1), (2) and (3). More preferably, the process aid additive comprises a mixture of (1), (2) and (3).
DETAILED DESCRIPTION OF THE INVENTION
The process aid additive can be added at any location of the fluidized bed polymerization system, e.g. in the reactor itself, below the fluidization grid or above the grid in the fluidized bed, above the fluidized bed, in the powder disengagement zone of the reactor, anywhere in the reaction loop or recycle line, in the fines recycle line (when a fines separator, preferably a cyclone, is used) etc . . . According to a preferred embodiment of the present invention, the process aid additive is directly added into the fines recycle line (when a fines separator, preferably a cyclone, is used) or directly into the polymerization zone, more preferably directly into the fluidized bed, ideally into the lower part of the bed (below half bed height). For the purposes of the present invention and appended claims, the polymerization zone means the reaction zone consisting of the fluidized bed itself, and the region above the fluidized bed which consists of the powder disengagement zone and/or the velocity reduction zone. The process aid additive is preferably directly added into the fluidized bed polymerization reaction zone. It is also particularly preferred according to the present invention that the process aid additive is not added in admixture with a catalyst component like the catalyst itself or the cocatalyst. According to another preferred embodiment, the process aid additive is added into the fluidized bed polymerization system through the well known BP high productivity nozzles which protrude through the fluidization grid directly into the fluidized bed (see e.g. WO9428032, the content of which is incorporated hereby by reference).
According to the present invention, the polysulfone copolymer component of the process aid additive (often designated as olefin-sulfur dioxide copolymer, olefin polysulfones, or poly(olefin sulfone)) is a polymer, preferably a linear polymer, wherein the structure is considered to be that of alternating copolymers of the olefins and sulfur dioxide, having a one-to-one molar ratio of the comonomers with the olefins in head to tail arrangement. Preferably, the polysulfone copolymer consists essentially of about 50 mole percent of units of sulfur dioxide, about 40 to 50 mole percent of units derived fr
Benazouzz Gacem
Camoin Michel
Coupier Laurent
Isnard Jean-Pierre
McNally John Paul
BP Chemicals Limited
Cheung William K
Finnegan, Henderson Farabow, Garrett and Dunner L.L.P.
Wu David W.
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