Process for polymerizing one or more 1-olefins in the gas phase

Details Process for polymerizing one or more 1-olefins in the gas phase Process for polymerizing one or more 1-olefins in the gas phase

1988-05-12

1990-11-13

Schofer, Joseph L.

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Polymerizing in presence of inert solid masses so as to...

526 88, 526106, 526129, 526901, 526904, C08F 234, C08F 1002, C08F 244

Patent

active

049702793

DESCRIPTION:

BRIEF SUMMARY
The invention relates to a process for the polymerisation or copolymerisation of alpha-olefins and optionally dienes in the gaseous phase, in a fluidised and/or mechnically agitated reactor, in the presence of a Ziegler-Natta type catalytic system or a catalyst based on activated chromium oxide by a thermal treatment in a non-reducing atmosphere. Such catalytic system or catalyst can if desired be employed in the form of a prepolymer prepared therefrom.
It is known to polymerise alpha-olefins in the gaseous phase, for example, using a fluidised bed reactor in which solid particles of polymer in the course of formation are maintained in the fluidised condition by an ascending as flow containing in particular the alpha-olefins to be polymerised. As it passes through the fluidised bed, a portion only of the alpha-olefins is polymerised in contact with the particles of polymer in course of formation. That fraction of the alpha-olefins which has not reacted leaves the fluidised bed and passes through a cooling device adapted to dissipate the heat evolved during polymerisation, before being recycled into the fluidised bed reactor. Polymerisation is generally performed continuously, i.e, by introducing into the fluidised bed reactor, continuously or semi-continuously, solid particles of catalyst from which the polymer particles will develop, the resulting polymer powder being withdrawn from the reactor, also continuously or semi-continuously.
The polymerisation of alpha-olefins in the gaseous phase is performed in the presence of a Ziegler-Natta type catalytic system formed by a combination of a solid catalyst based on at least one compound of a transition metal belonging to Groups IV, V or VI of the Periodic Table of Elements, and a co-catalyst comprising at least one organometallic compound of a metal of Groups I to III of this Table, or in the presence of a solid catalyst containing a chromium oxide compound activated by a thermal treatment in a non-reducing atmosphere.
It is also known that the catalytic system or catalyst can be previously converted into an alpha-olefin prepolymer obtained by bringing the catalytic system or catalyst into contact with one or more alpha-olefins, so as to form a catalytically active prepolymer which can be directly used in the polymerisation of alpha-olefins in the gaseous phase. This prepolymer is formed by solid particles whose size can be controlled as required and which have an activity in the polymerisation of alpha-olefins which is particularly well suited to a process in the gaseous phase.
Whatever the kind of catalyst used in a gas phase polymerisation process may be, the catalyst particles develop during polymerisation into polymer particles of larger dimensions. In a polymerisation process using a fluidised bed reactor, the velocity of the ascending as flow is so selected that the largest polymer particles are kept in the fluidised condition and not deposited on the bottom of the reactor or the fluidisation grid, and the finest particles are not entrained out of the fluidised bed into zones in which the polymerisation reaction is undesirable. More particularly, it is important for the ascending gas flow to give the fluidised bed the best possible homogenisation so as to avoid the appearance of hot spots, which may soften or melt the polymer particles and therefore form agglomerates and finally lead to the stoppage of polymerisation.
It is moreover known that an increase in the polymerisation temperature generally enhances the yield of the poly-alpha-olefins in relation to the catalyst. This is why the polymerisation of alpha-olefins in the gaseous phase is generally performed at the highest possible temperature, although the temperature is substantially lower than that from which onwards the polymer particles begin to soften and agglomerate with one another by sintering. It is moreover known in general that a polyolefin powder has a lower softening temperature and therefore a stronger tendency to agglomerate by sintering at a given temperature, in proportion as the d

REFERENCES:
patent: 2970135 (1961-01-01), Lanning et al.
patent: 3132125 (1964-05-01), Schwander et al.
Int. App. No. PCT/GB87/00697 to Bailly et al., published 10-02-87.

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