Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2002-03-08
2003-10-28
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, C526S140000, C526S141000, C526S138000, C526S105000, C526S348200, C526S348600, C526S201000
Reexamination Certificate
active
06639028
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a process for the continuous gas-phase (co-)polymerisation of olefins in a fluidised bed reactor using a chromium oxide catalyst.
The present invention also relates to a process for preventing fouling during the continuous gas-phase (co-)polymerisation of olefins in a fluidised bed reactor using a chromium oxide catalyst.
Processes for the co-polymerisation 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 fluidised bed comprising polyolefin and a catalyst for polymerisation.
In the gas fluidised bed polymerisation of olefins, the polymerisation is conducted in a fluidised bed reactor wherein a bed of polymer particles is maintained in a fluidised state by means of an ascending gas stream comprising the gaseous reaction monomer. The start-up of such a polymerisation generally employs a bed of polymer particles similar to the polymer which it is desired to manufacture. During the course of polymerisation, fresh polymer is generated by the catalytic polymerisation of the monomer, and polymer product is withdrawn to maintain the bed at more or less constant volume. An industrially favoured process employs a fluidisation grid to distribute the fluidising 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 The polymer produced is generally withdrawn from the reactor via a discharge conduit arranged in the lower portion of the reactor, near the fluidisation grid. The fluidised bed consists in a bed of growing polymer particles. This bed is maintained in a fluidised condition by the continuous upward flow from the base of the reactor of a fluidising gas.
The polymerisation of olefins is an exothermic reaction and it is therefore necessary to provide means to cool the bed to remove the heat of polymerisation. In the absence of such cooling the bed would increase in temperature and, for example, the catalyst would become inactive or the bed would begin to melt. In the fluidised bed polymerisation of olefins, the preferred method for removing the heat of polymerisation is by supplying to the polymerisation reactor a gas, the fluidising gas, which is at a temperature lower than the desired polymerisation temperature, passing the gas through the fluidised bed to conduct away the heat of polymerisation, removing the gas from the reactor and cooling it by passage through an external beat exchanger, and recycling it to the bed. The temperature of the recycle gas can be adjusted in the heat exchanger to maintain the fluidised bed at the desired polymerisation temperature. In this method of polymerising 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 is used to supply the monomer to the bed, to fluidise the bed, and to maintain the bed at the desired temperature. Monomers consumed by the polymerisation reaction are normally replaced by adding make up gas or liquid to the polymerisation zone or reaction loop.
It is also well known that chromium oxide or “Phillips” catalysts can advantageously be used for the (co-)polymerisation of olefins, particularly in slurry processes as well as in gas phase processes. It is even reported in the literature that chromium oxide catalysts are much less or even not prone to fouling problems in olefin gas phase polymerisation processes in comparison with Ziegler-Natta catalysts which exhibit many fouling problems.
While the man in the art specialised in olefin gas phase polymerisation is still pursuing his understanding of the fouling phenomena associated with the use of Ziegler-Natta catalysts, in particular metallocene based catalysts, there is still a need in the art to find a process for producing more successfully polyolefins on gas phase industrial plants using a chromium oxide catalyst.
The Applicants have now unexpectedly found a simple and efficient process which allows us to improve the gas phase polymerisation of olefins using a chromium oxide catalyst. This was done through a detailed analysis of the rare problems occurring during the olefin gas phase polymerisation using a chromium oxide catalyst. Amongst those problems, one can recite slight fouling which can repeatedly occur during polymerisation and provoke periods of off specification materials, fouled lumps, . . . ; hot spot phenomena related to points of higher than average temperature within the polymerisation zone; static phenomena measured with static probes within the polymerisation zone were also part of the detailed analysis and study.
Surprisingly, the very simple process of the Applicants provides an industrial solution to all these problems, in particular to the fouling problems that could affect gas phase polymerisation of olefins with chromium oxide catalysts.
SUMMARY OF THE INVENTION
In accordance with the present invention, there has now been found a process for the gas-phase (co-)polymerisation of olefins in a fluidised bed reactor using a chromium oxide catalyst in the presence of a process aid additive wherein the additive comprises at least one of the components selected from:
(1) a polysulphone copolymer,
(2) a polymeric polyamine, and
(3) an oil-soluble sulphonic 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).
The process aid additive can be added at any location of the fluidised bed polymerisation system, e.g. in the reactor itself, below the fluidisation grid or above the grid in the fluidised bed, above the fluidised bed, in the powder disengagement zone of the reactor (also named velocity reduction zone), 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 added directly into the fines recycle line (when a fines separator, preferably a cyclone, is used), or directly into the polymerisation zone, more preferably directly into the fluidised bed, ideally into the lower part of the bed (below half bed height). For the purposes of the present invention and appended claims, the polymerisation zone means the reaction zone consisting of the fluidised bed itself, and the region above the fluidised bed which consists of the powder disengagement zone and/or the velocity reduction zone. According to another preferred embodiment of the present invention, the process aid additive is added at at least two different locations of the fluidised bed polymerisation system. 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 fluidised bed polymerisation system through the well known BP high productivity nozzles which protrude through the fluidisation grid directly into the fluidised bed (see e.g. W09428032, the content of which is incorporated hereby). It is also particularly preferred that the process aid additive is not added in admixture with a liquid comonomer used for the copolymerisation.
According to the present invention, the polysulphone copolymer component of the process aid additive (often designated as olefin-sulphur dioxide copolymer, olefin polysulphones, or poly(olefin sulphone)), is a polymer, preferably a linear polymer, wherein the structure is considered to be that of alternating copolymers of the olefins and sulphur dioxide, having a one-to-one molar ratio of the comonomers with the olefins in head to tail arrangement. Preferably, the polysulphone copolymer consists essentially of about 50 mole percent of units of sul
Heslop David
Isnard Jean-Pierre
Shin Myung-Je
BP Chemicals Limited
Cheung William
Finnegan, Henderson Farabow, Garrett and Dunner L.L.P.
Wu David W.
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