Note: Descriptions are shown in the official language in which they were submitted.
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A process and an apparatus for polymerization of olefin monomers
This invention relates in an olefin polymerization process and particularly a
process
for polymerization of olefins in liquid medium. The invention further relates
in
polymerization processes containing a prepolymerization step. This invention
also
relates in an olefin polymerization apparatus.
Various methods for manufacturing solid polymers from hydrocarbons, for
example
from 1-olefins have been developed. In one such method olefins, such as
ethylene,
-- - propylene or butene, are polymerized in the presence of catalysts in
hydrocarbon
diluents or in monomers acting as diluents. The reactants are kept in liquid
phase by
maintaining a proper pressure in the polymerization reactor. When the polymer
is
insoluble or only slightly soluble in the diluent, the polymer product forms
as
particles suspended in the diluent and therefore the process is called a
slurry process.
As batch process the above process has the advantage that all the polymer
particles
have the same residence time in the reactor and therefor the product quality
is even.
However, in commercial high production plants the polymerization reactors tend
to
be large. The operation is labor extensive and the quality of the products
from batch
to batch is not the same. For these reasons the batch reactors are not
commercially
acceptable.
A typical continuous slurry process is carried out in a continuous pipe
reactor
forming a loop, where the polymerization is carried out in a circulating
turbulent
flow. The product containing polymer, diluent and monomers, is taken from the
loop
reactor either continuously, or more usually, periodically through a discharge
valve
and it is introduced to a separator, where the polymer is separated by
lowering the
pressure.
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Another reactor type in olefin polymerization art is a gas phase reactor,
where
polymerization is carried out in the presence of catalysts and gaseous
monomers.
Typically the polymerization is carried out in fluidized bed reactors, where
polymerization is carried out continuouly in a bed formed by polymerizing
polymer
particles. This bed is kept in fluidized state by circulating gaseous flow
from the top
of the reactor to the bottom of the reactor. Polymerization heat is removed by
cooling said circulating gaseous flow.
I1_ is also known continuous multiphase processes, where slurry reactors, such
as
loop reactors are followed by one or more gas phase reactors or where two or
more
gas phase reactors are used in series.
-. - A known problem in continuous processes is that even residence time of
catalyst is
difficult to achieve. Therefore the product quality tends to be more or less
uneven.
This phenomena is exaggerated in multiphase processes. The catalyst is usually
fed
into the first reactor only. Some of the catalyst particles react with the
monomers for
a longer period, whereas part of the catalysts flows straight through the
reactor and
will be removed more or less unreacted. In the next reactor the unreacted
catalyst
particles react differently with monomers and resulting, among others, in
uneven
product quality, gels, lumps and more difficult process control.
It is also known to prepolymerize a small amount of olefin monomer with a
catalyst
before using these catalysts into a main polymerization reactor. Typically
such
prepolymerization reduces catalyst attrition and improves the resulting
polymer
morphology. Prepolymerized catalysts also may suspend more readily in hydrocar-
bon solvents, yield polymers of higher bulk density and reduce formation of
lumps
in gas phase reactor.
Such prepolymerization can be carried out by contacting a solid catalyst
component
with a small amount of olefin monomer in a suitable diluent or monomer in a
vessel
separate from the main polymerization reactor.
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The most convenient way to prepolymerize is a continuous prepolymerization,
but
due to residence time distribution, part of the catalyst will not
prepolymerize enough
and will produce fines in the main polymerization reactor. A batch
prepolymeriz-
ation often reduces the catalyst activity and there is always some difference
between
prepolymerized catalyst batches. Some catalysts have to be prepolymerized so
much
that the amount of polymer may cause the catalyst handling to be too
troublesome.
Some catalyst feeders feed small batches of catalyst with a cycle time of
several
seconds or minutes. This sometimes causes fluctuation in prepolymerization or
in
actual polymerization.
The common problem in all polymerization processes mentioned above is uneven
residence time distribution, which leads to uneven and undesirable product
quality
and more difficult process control. This problem can be to some extent avoided
if
tubular, very long reactors having a very small diameter is used. For example
in EP
0279153 a prepolymerization method is disclosed, where the prepolymerization
is
carried out as a plug flow. However, that kind of reactors are difficult to
control and
they are not suitable for high production rates because of risk of plugging
and low
capacity.
Therefore need exists for olefin polymerization processes where the
polymerization
can be carried out so that more narrow residence time distribution can be
achieved
and the problems arising from the uneven polymerization degree can be avoided.
The object of the present invention is to achieve a polymerization process,
where the
disadvantages described above can be avoided. Another object of the present
invention is to achieve a process for olefin polymerization, which can be
applied as
well in normal polymerization as catalyst prepolymerization. Still another
object of
the invention is to achieve polymerization processes where the catalyst used
is
prepolymerized in certain way.
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Thus the invention concerns a process for polymerization of olefin monomer in
fluid
medium in the presence of olefin polymerizing catalyst, diluent and optional
co-
catalyst and donors, said process comprising the steps:
- forming a fluid stream containing said catalyst,
- continuously feeding said fluid stream into an elongated polymerization
reactor comprising at least two successive chambers separated by dividing
plates having a diameter slightly smaller than that of the polymerization
reactor,
- feeding into said polymerization reactor monomer and optionally cocatalyst
and donor under temperature conditions to polymerize said olefin while
maintaining a mixed flow in said chambers to polymerize the monomer and
-- - optional comonomer in the fluid, and
- removing the resulting polymer slurry from said polymerization reactor.
The invention also concerns an apparatus for polymerization of olefin monomer
and
optionally other monomer in the presence of olefin polymerizing catalyst,
diluent and
optional cocatalyst and donors, said apparatus comprising:
- means for continuously feeding a fluid stream containing said catalyst into
an
elongated polymerization reactor comprising at least two successive chambers
separated by dividing plates having a diameter slightly smaller than that of
the polymerization reactor,
- means for feeding into said polymerization reactor monomer and optionally
cocatalyst and donor under temperature conditions to polymerize said olefin
while maintaining a mixed flow in said chambers to polymerize the monomer
and optional comonomer in the fluid, and
- means for removing the resulting polymer slurry from said polymerization
reactor.
The invention also concerns an apparatus for prepolymerizing olefin
polymerization
catalyst.
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According to the invention the polymerization takes place in an elongated
reactor,
preferably in cylinder-like reactor, which has an inside diameter greater than
that of
the inlet and outlet points. The term "elongated" means that the
length/diameter ratio
of the reactor is greater than 2, preferably more than 2,5.
According to the invention the polymerization reactor comprises at least two
successive chambers separated by dividing plates having a diameter slightly
smaller
than that of the polymerization reactor. Preferably the polymerization reactor
is
divided to several successive chambers.
In such polymerization reactor preferably each part of the chambers can be
equipped
with some mixing device in order to eliminate the deposition of the catalyst
or
- - forming polymer onto the surfaces of the polymerization reactor. As mixer
device
one or more rotating or static mixers can be used. The static mixers may also
be
attached to the walls of the reactor.
The chambers are divided from each other with plate-like members so that a
narrow
gap is situated between the chambers. Therefore the diameter of the plates is
preferably slightly smaller than the inside diameter of the polymerization
reactor.
However, it is also possible that the diameter of the dividing plates is
smaller.
Generally it can be said that the diameter can be 1-25 mm less than the inner
diameter of the reactor. When the polymerization reactor is divided to several
chambers, the diameter of the dividing plates can decrease thereby eliminating
the
risk of plugging. The gap between the diameter of the reactor and the diameter
of
the dividing plate in the last chamber is preferably smaller than the diameter
of the
outlet opening of the reactor.
According to one embodiment of the invention the dividing plates and the
mixers
between the dividing plates are attached to the same shaft.
Liquid and the catalyst particles flow to the next chamber between the
separation
plate and the wall of the reactor. Rotation of the disk keeps the area clean.
In the
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first chamber of the reactor the catalyst mean residence time is of at least 3
times,
preferably 10 times the cycle time of the catalyst feeder to assure that there
is
minimal fluctuation in the catalyst feed to the actual polymerization in the
later
chambers.
The reactor can be vertical or horizontal, although the vertical position is
preferable.
Plug flow behaviour in the reactor according to the invention assures that
every
active catalyst particle has enough prepolymer to prevent the breakage in
later
p~ymerization.
As an additional feature the reactor according to the invention can contain
additional
flow mixing means located in the inner surface of the reactor. Such means can,
for
example, be studs attached to the inner surfaces of the reactor in some or
each
chambers and/or the cover plate of the reactor. Such mixing elements enhance
the
mixing effect by forcing flow from the reactor walls towards the central parts
of the
reactor.
The flow mixing means can also comprise supporting bars, which support a
bearing
block for the central shaft. The bars are preferably locked by friction on the
reactor
walls or by other means.
A fluid carrier stream containing the polymerization catalyst or part of the
polymerization catalyst is formed and fed into this reactor. A second stream
of
polymerizable monomer or monomers is also fed to the reactor. Other components
of the catalyst system can also be fed to this reactor.
As fluid carrier stream inert hydrocarbon diluents can be used. Such diluents
include, among others, propane, butane, pentane, hexane and alike. Also poly-
merizable monomers can be used as the fluid carrier. Such monomers include for
example propylene, butene and hexene. The mixtures of the fluid carriers
mentioned
can also be used.
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The polymerization takes place inside of the reactor as a mixed plug flow.
This term
means that the flow inside of the reactor takes place as mixed flow, the flow
direction of which is, however, generally forward from one end of the reactor
to
other end. No part of the reactor contents flows backwards through the reactor
and
no stagnant flow regions exist where the flow remains in place longer than
other
parts of the flow.
The residence time in the reactor depends on such factors as the catalyst used
or the
polymerization degree desired, but generally the advantages of the invention
are
achieved when the residence time is more than one minute, preferably from two
minutes to 30 minutes. A shorter time is sufficient when the polymerization
reactor
is used as a prepolymerization reactor and longer periods are necessary when
the
- - polymerization reactor is used as the ordinary polymerization reactor.
At least part of the cocatalyst is fed to the first chamber of the reactor
according to
the invention. The monomer or monomers can be fed to any or every chamber of
the
reactor. In case of propylene polymerization also the donor can be fed to any
of the
chambers or along with the catalyst.
The polymerization heat is removed by cooling. The cooling can be carried out
with
a cooling jacket surroundig the polymerization reactor. However, other methods
for
cooling can also be used.
The reaction temperature can be selected within a wide range, for example in
the
range of 0 °C to 90 °C. The pressure can be likewise selected
within a wide range,
for example between 10 bar - 100 bar. The cooling jacket can be divided into
several compartments to make possible to use temperature gradient over the
length
of the reactor.
Use of solid, transition metal-base polymerization catalysts for
polymerization of
olefins is well known. Typically these catalysts are based a complex derived
from a
halide of a transition metals, such as titanium, vanadium, chromium and
zirconium,
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and a cocatalyst, which are typically based on metal alkyls, such as
organoaluminum
compounds. A typical catalyst comprises a titanium halide, which is supported
on a
magnesium halide complexed with an alkyl aluminum. It is also known to use
electron donors or Lewis bases for controlling the stereospecifity of the
polymer.
Examples of such electron donors are, among the others, ethers, esters and
siloxanes. Except of Ziegler-Natta catalysts described above also metallocene
type
catalysts can be used according to the invention.
The catalyst component to be fed to the reactor can also be mixed in
appropriate
medium. Such medium can be for example hydrocarbon wax. The catalyst can also
be prepolymerized in conventional way and further treatment is carried out
according
to the invention.
The process of the invention is particularly advantageous in prepolymerization
of
such catalysts. Every stage of prepolymerization can be carried out in
different
conditions. Eg. temperature, monomer, diluent, cocatalyst and donor
concentrations
can be varied. Different monomers can be used in different stages of
prepolymeriz
ation. Different components can be contacted in certain order to achieve
optimum
performance of the catalyst. Further conventional antistatic agents can be fed
to the
reactor in any desired point.
The design of the reactor according to the invention is easy to manufacture.
No extra
flanges or walls are needed which could plug the reactor. The number of
chambers
can changed simply by reducing or adding separation plates and mixing elements
also afterwards.
The process according to the invention is particularly advantageous applied as
prepolymerization step in various polymerization process. Thus one object of
the
invention is a process for polymerization of olefin monomer in the presence of
olefin
polymerizing catalyst, diluent and optional cocatalyst and donors, by feeding
into at
least one polymerization reactor monomer(s), diluent, catalyst, cocatalyst and
optional hydrogen and/or donor under temperature conditions to polymerize said
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olefins) to olefin polymers and after polymerization removing said polymers
from
the reactor. The process is characterized in that the catalyst fed into the
polymerization reactor is prepolymerized by forming a fluid carrier stream
contain-
ing said catalyst, continuously flowing said carrier stream into an elongated
prepoly-
merization chamber containing at least two successive chambers separated by
dividing plates having a diameter slightly smaller than that of the
prepoiymerization
chamber, feeding into said prepolymerization chamber monomer and optionally
cocatalyst and donor by maintaining a mixed plug flow in said
prepolymerization
chamber for a period of at least one minute under temperature conditions to
prepoly-
merize said olefin onto said catalyst, and feeding said prepolymerized
catalyst into
the first polymerization reactor.
Thus the prepolymerization of the catalyst is carried out first and the
process further
can comprise one or more slurry reactors after said prepolymerization step.
The
slurry reactors can be conventional stirred-tank reactors or loop reactors.
The process according to the invention can also comprise also a process where
the
preceding prepolymerization step is followed by one or more gas phase
reactors.
Further the polymerization process following the preceding prepolymerization
step
can also be a combination of slurry and gas phase polymerization steps. The
slurry
polymerization step is preferably a loop reactor step.
In slurry processes the pressure in the prepolymerization vessel is selected
preferably
so that it is higher than in the following reactor. Thus the transfer of the
prepoly-
merized catalyst from the prepolymerization chamber into the slurry reactor is
as
easy as possible, because the catalyst can be straight moved to the next
reactor. Thus
the pressure can be for instance between 40-90 bar, preferably 50-70 bar,
however
provided that the pressure is higher than in the next slurry reactor. The
transfer of
the prepolymerized catalyst can be carried out also periodically, if desired,
and also
conventional catalyst transfer devices can be used, if necessary.
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It is recommendable that the whole catalyst amount in the process will be fed
to the
prepolymerization according to the invention and no extra catalysts will be
fed to the
slurry reactor or reactors. Instead it is possible to feed the cocatalyst
either only to
the prepolymerization step or partly into the prepolymerization chamber and
partly
S to the slurry polymerization reactor or reactors.
Low boiling inert hydrocarbon is fed to the slurry reactor as polymerizing
medium.
Examples of suitable hydrocarbons are aliphatic hydrocarbons like propane,
butane,
pentane and hexane. Advantageous hydrocarbons are especially propane and iso-
10 butane. It is also possible to use a mixture of one or more hydrocarbons
mentioned
before. In the case of propylene polymerization the polymerization medium is
preferably propylene.
The reaction mixture consisting of a reaction mixture from previous reactor
together
with added fresh monomer, hydrogen, optional comonomer and cocatalyst is
circulated continuously through the slurry reactor, whereby more suspension of
polymer in particle form in a hydrocarbon medium or monomer will be produced.
The conditions of the slurry reactor will be chosen so that at least 12 w-% of
the
whole production will be polymerized in each slurry reactor. The temperature
can be
chosen within the range of 40-110 °C, advantageously within the range
50-100 °C. The reaction pressure can be chosen within the range of 40-
90 bar,
preferably within the range or 50-70 bar, however provided that the reaction
pressure is lower than the pressure of the previous reactor. The residence
time must
be at least 10 minutes, but preferably in the range of 0.5-2 hours.
In slurry polymerization more than one reactors can be used in series. In such
case
the polymer suspension in an inert hydrocarbon or in monomer produced in the
slurry reactor is fed without the separation of inert components and monomers
periodically or continuously directly to the latter slurry reactor, which acts
in lower
pressure than the previous slurry reactor.
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Further it is possible to operate one or more slurry reactors at temperatures
and
pressures that are above the critical temperature and pressure of the
polymerization
medium. The polymerization then takes place under supercritical conditions.
The type of the slurry reactors) can be conventional stirred-tank reactors or
loop
reactors or the combination thereof. Preferably loop reactors are used.
The reactor according to the invention can be used also as a prepolymerization
reactor before one or more gas phase reactors. Gas phase reactor can be an
ordinary
fluidized bed reactor, although other types of gas phase reactors can be used.
In a
fluidized bed reactor the bed consists of the formed and growing polymer
particles
as well as still active catalyst come along with the polymer fraction. The bed
is kept
- - in a fluidized state by introducing gaseous components, for instance
monomer on
such flowing rate which will make the particles act as a fluid. The fluidizing
gas can
contain also inert carrier gases, like nitrogen and also hydrogen as a
modifier.
The gas phase reactor used can operate at temperature region between 50-115
°C,
preferably between 60-110 °C and the reaction pressure between 10-40
bar and
the partial pressure of monomer between 2-30 bar.
According to still another embodiment the reactor of the invention is used as
a
prepolymerization reactor which is followed by a slurry reactor or reactors
and a gas
phase reactor or reactors.
In every polymerization step it is possible to use also comonomers selected
from
ethylene, propylene, butene, pentene, hexene and alike as well as their
mixtures.
The invention is further illustrated by figures, in which
Fig. la illustrates the polymerization device according to the invention,
which can
be applied as a polymerization reactor or as prepolymerization reactor,
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Fig 1b is an enlargened cross-sectional view of the reactor of Fig. la along
the line
A-A, and
Fig. 2 is a schematic flow graph one preferable embodiment of the invention
, comprising a prepolymerization reactor followed by a loop reactor and a gas
phase
reactor.
In Figures la and 1b the polymerization reactor according to the invention is
denoted
by a numeral 1. The polymerization reactor 1 has a generally elongated
cylindrical
form defined by inner surface 2, deck plate 3a and bottom plate 3b. The
length/diameter ratio of the reactor 1 is at least 2, preferably more than
2.5. The
reactor 1 can be cooled by a cooling jacket 4, which can partly or entirely
surround
- the inner wall 2 of the reactor 1. The cooling jacket 4 can be divided to
several
separate cooling chambers by separators 5. Cooling medium is introduced to the
cooling jacket 4 by line 6 and valves 7 and it is removed from the cooling
jacket 4
through valves 8 and line 9. Thus different reaction temperatures can be
applied in
the reactor when needed.
The reactor is equipped with a central shaft 10 extending over the height of
the
reactor 1. The shaft 10 is rotated by suitable means 11. The inside volume of
the
reactor 1 is divided into at least two chambers 12a by dividing plates 12b
attached
to the central shaft 10. The diameter of each dividing plate 12b is slightly
smaller
than the inside diameter of the reactor 1 leaving a gap of 2-25 mm between the
edge
of the dividing plate 12b and the inside wall of the reactor 2. The number of
the
dividing plates 12b can be varied between 1 to 100 thereby allowing two or
more
sequential polymerization chambers 12a inside the reactor 1.
The reactor 1 is further equipped with mixing elements 13 inside of the
chambers
12a. The mixing elements 13 are attached to the central shaft 10 to rotate
along with
it. The mixing elements 13 can be also static elements 14 attached into the
inside
wall 2 of the reactor 1 and extending inside of the chambers 12a. Such static
mixers
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14 can be located in different places in the reactor wall 2 and also in the
deck and
bottom plates 3a,3b of the reactor 1.
The shaft 10 can also be supported by bearing block 15. In such arrangement
the
bearing block 15 is supported to the inside wall 2 of the reactor 1 by bars
16. The
supporting bars 16 give an efficient mixing effect on the circulating flow of
the
polymerization medium in the reactor 1. The ends of the supporting bars 16 can
be
supported on the reactor wall 2 by friction or by other means thereby
preventing the
rotation.
The catalyst from reservoir 17 is fed to the feeding device 18 where it is
mixed
with a diluent from line 19 and is further fed to the reactor 1 through line
20. The
- - same or different monomers can be fed to the reactor 1 through lines 2/a
and/or line
21b and valves 22. Cocatalyst and donors can be fed into the reactor 1 from
reservoir 23 and a feeding device 24 with a diluent from line 25. In the same
wise
same or different cocatalysts and monomers can be fed into the reactor 1 from
line
26 and valves 27.
The polymer or prepolymer is removed from the reactor 1 through line 28. From
line 29 it is possible to feed also antistatic agents to the polymer or
prepolymer.
In Figure 2 it is presented a schematic view of one process where the
prepolymeriz-
ation reactor 1 according to the invention is used combined with loop-gas
phase
sequence.
Catalyst from reservoir 30 is fed to the feeding device 31 together with
diluent from
line 32. The feeding device 31 feeds the catalyst/diluent mixture into the
prepoly-
merization chamber 1 via line 33. Monomer is fed through line 34 and
cocatalyst
and possible donors can be fed into the reactor 1 through lines 35.
From the prepolymerization chamber 1 the prepolymerized catalyst is removed
preferably directly through line 36 to a loop reactor 40. In the loop reactor
40 the
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polymerization is continued by adding a diluent from the line 42, monomer from
line
43, hydrogen from line 44 and an optional comonomer from line 45 through the
line
46. To the loop reactor 40 it can be added also optional cocatalyst in an
ordinary
way (not presented).
From the loop reactor 40 the polymer-hydrocarbon mixture is fed through one or
several exhaust valve 47 and the product transfer line 48 to the flash
separator 50.
The hydrocarbon medium removed from the polymer particles, the remaining
monomer and hydrogen are removed from the flash separator 50 either through
the
line 51 to the recovery unit (not presented) or back to the loop reactor 40
through
the line 46. The polymer particles are removed from the flash separator 50
through
the removing line 52 to the gas phase reactor 60.
In the lower part of the gas phase reactor 60 there is a bed consisted of
polymer
particles, which will be kept in a fiuidized state in an ordinary way by
circulating the
gases removed from the top of the reactor 60 through line 61, compressor 62
and the
heat exchanger (not presented) to the lower part of the reactor 60 in an
ordinary
way. The reactor 60 is advantageously, but not necessarily, equipped by a
mixer
(not presented). To the lower part of the reactor 60 can be led in a well
known way
monomers from line 63, optionally comonomer from line 64 and hydrogen from the
line 65. The product will be removed from the reactor 60 continually or
periodically
through the transfer line 66 to the recovery system (not presented).
Examples
Highly active catalyst and highly active polymerization conditions (e.g.
enough
hydrogen) were used to test the properties of the novel system. For the
examples
1-6 highly isotactic (98~1 %) homopolymer with MFR (2,16 kg 230 °C)
20~1
g/10 min was produced. Normal temperature of 70 °C and higher
temperature of 94
°C were tested in the actual polymerization.
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Example 1
A pilot plant operated continuously was used to produce PP-homopolymer. The
plant
comprises a catalyst, alkyl, donor and propylene feed systems and a small
stirred
tank reactor named as CCSTR due to several compartments. Said components are
fed to the CCSTR.
The catalyst used was a highly active and stereospecific ZN-catalyst made
according
to Finnish Patent No. 88047. The catalyst was contacted with triethylaluminium
(TEA) and dicyclopentyldimethoxysilane (DCPDMS) (Al/Ti ratio was 3 and
Al/donor was 3 (mole)) before feeding to the CCSTR.
The catalyst was fed according to Finnish Patent No. 90540 and was flushed
with
propylene (15 kg/h) to the CCSTR in which also TEA and DCPDMS are fed. The
CCSTR was operated at 40 bar pressure, 20 °C temperature and mean
residence
time of the catalyst at 3 min. Al/Ti (mole) ratio was kept at 150 and Al/donor
ratio
at 5.
The loop reactor was operated at 39 bar pressure, 70 °C temperature
and mean
residence time of the catalyst at 3 h. The solid polymer was separated from
the
polymer slurry by depressurising. The MFR (2.16 kg, 230 °C) of the
produced PP-
homopolymer was controlled to be 20 via hydrogen feed. Product characteristics
is
shown in Table I.
Example 2 (Comparative)
Procedure was the same as Example 1 but the compartmented CCSTR was replaced
with normal continuous stirred-tank reactor (CSTR).
Example 3
Procedure of the Example 1 was repeated.
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Example 4
Procedure was the same as Example 1 but the mean residence time of the
catalyst
was kept at 4 min.
Example 5 (Comparative)
Procedure was the same as Example 4 but the compartmented CCSTR was replaced
with normal CSTR.
Example 6
- - Procedure was the same as Example 1 but the mean residence time of the
catalyst
was kept at 2 min.
Example 7 (Comparative)
Procedure was the same as Example 6 but no continuous prepolymerization was
used. The catalyst was prepolymerized with propylene (the mass ratio of PP/cat
was
10) in batch according to Finnish Patent No. 95387.
The catalyst was mixed with TEA and DCPDMS and flushed with cold propylene to
the loop reactor.
Example 8
Procedure was the same as Example 2 (comparative) but the catalyst was pre-
polymerized with propylene (the mass ratio of PP/cat was 10) in batch
according to
Finnish Patent No. 95387 before continuous prepolymerization.
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Example 9
A pilot plant operated continuously was used to produce PP-homopolymer. The
plant
comprises a catalyst, alkyl, donor and propylene feed systems and a stirred
tank
reactor named as CCSTR due to several compartments. Said components are fed to
the CCSTR.
The catalyst according to Example 1 was fed into the CCSTR-reactor, which was
operated at 51 bar pressure, 20 °C temperature and mean residence time
of the
catalyst at 5 min. Al/Ti (mole) ratio was kept at 75 and Al/donor ratio at 5.
The polymer slurry from the CCSTR was fed to a loop reactor in which also
- - hydrogen and more propylene was fed. The loop reactor was operated at 50
bar
pressure, 94 °C temperature and mean residence time of the catalyst at
30 min. The
solid polymer was separated from the fluid by depressurising. The MFR (2.16
kg,
230 °C) of the produced PP-homopolymer was controlled to be 20 via
hydrogen
feed. Product characteristics is shown in Table II.
Example 10 (Comparative)
Procedure was the same as Example 9 but no continuous prepolymerization was
used. The catalyst was prepolymerized with propylene (the mass ratio of PP/cat
was
10) in batch according to Finnish Patent No. 95387.
The catalyst was mixed with TEA and DCPDMS and flushed with cold propylene to
the slurry reactor.
Example 11 (Comparative)
As Example 7 (comparative} except that the catalyst was prepolymerized to mass
ratio of 7 (PP/cat) in batch according to Finnish Patent No. 95387, cyclohexyl-
methylmethoxysilane (CHMMS) was used as donor, Al/Ti (mole) ratio was kept at
CA 02250264 1998-09-08
WO 97/33920 PCT/FI97/00162
18
100 in the loop reactor, and MFR (2.16 kg, 230 °C) of the produced PP-
homo-
polymer was controlled to be 2.5 via hydrogen feed.
Product characteristics are shown in Table III.
Example 12 (Comparative)
As Example 11 (comparative) except that a small diameter pipe with inner
diameter
of 4 mm was used and the length of the pipe was selected to give 20 second
residence time for the catalyst and the pipe was operated at 0 °C.
Example 13 (Comparative)
As Example 12 (comparative) but the pipe was operated at 20 °C.
Example 14 (Comparative)
As Example 13 (comparative) but the length of the pipe was selected to give to
give
40 second residence time for the catalyst. Line was impossible to operate for
longer
period of time - no product characteristics available.
Example 15
Procedure was the same as Example 1 but the temperature of the upper part of
prepolymerization reactor was 20 °C and the temperature of the lowest
part of
prepolymerization reactor was 40 °C. The mean residence time of the
catalyst was
at 7 min. 50 w-% from total hydrogen feed was fed into the prepolymerization
reactor and 50 w-% into the loop-reactor.
Product characteristics are shown in Table IV.
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WO 97/33920 PCT/FI97/00162
19
Example 16
Procedure was the same as Example 1 but the compartment CCSTR was replaced
with two compartments (separated by one dividing plate) on upper part of
prepol.
reactor and in lowest part with three vertical equalizing grids.
Example 17
Procedure was the same as Example 16 but a metallocene catalyst, rac-dimethyl-
silanediyldiyl-bis-1,1'-{2-methyl-4-phenylindenyl)zirconium dichloride
supported on
porous Si02, was used. The catalyst was flushed into the prepolymerization
reactor
with propane feed. Not any cocatalyst or donor were fed. The mean residence
time
- - of the catalyst was kept at 9 min. The temperature of the upper part of
prepoly-
merization reactor was 15 °C and the temperature of the lowest part of
prepoly-
merization reactor was 13 °C. The morfology of the PP homopolymer was
excellent
(not any fines). Operability of the process was good.
Example 18 (Comparative)
Procedure was the same as Example 17 but not continuous prepolymerization was
used. The catalyst was prepolymerized with propylene (the mass ratio of PP/cat
was
1.3) in batch (dry prepolymerization in gas phase), in the product of the loop
reactor
was lot of fines and loop fouling was observed.
Example 19
As Example 17 but no batch prepolymerization was used.
Example 20 {Comparative)
As Example 19 but no continuous prepolymerization was used.
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WO 97/33920 PCT/FI97/00162
Example 21
Same as Example 19 but the temperature of the prepolymerization was kept at 25
°C
and the residence time of the catalyst was kept at 7 min.
5
Examples show that in polymerization of polyolefin polymer with highly active
and
stereospecific ZN-catalyst the amount of fines can be reduced by using a novel
CCSTR as a prepolymerization system compared to traditional batch-wise pre-
polymerization or a simple CSTR type reactor.
Examples also show that combination or traditional batch-wise
prepolymerization and
a continuos prepolymerization can be useful.
Further more examples show that for fines reduction a short time pipe
prepolymeriz-
ation was not useful even in producing as low MFR as 2.5 g/10 min.
CA 02250264 1998-09-08
WO 97/33920 PCT/FI97/00162
21
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