Note: Descriptions are shown in the official language in which they were submitted.
49
BACKGROUND OF THE INVENTION:
Field of the Invention;
The present invention relates to a process for
continuously preparing polyolefins having widely distributed
molecular weights, and more particularly to a process for
continuously preparing polyolefins having widely distributed
molecular weights employing a highly active Ziegler type
catalyst comprising a transition metal compound supported
on a solid carrier and an organometallic compound and by
the use of a plurality of reactors, each of the first and
second stage reactors being kept in a condition under
which desired polymerization reaction takes place.
Prior Art;
Polyolefins commonly used for forming various
molded articles, e.g. bottles, cable tubes and very thin
films, must fairly adapted to the molding conditions
when they are brought to plasticized states and must be
easily molded in desired shapes. Polyolefins having
high melt indices, i.e. those having low average molecular
weights, have improved moldabilities or workabilities due
to flow characteristics, but they are deteriorated in
their mechanical strengths, such as impact strength
and tensile strength. On the other hand, polyolefins having
low melt indices are improved in their strengths, but
their moldabilities are poor. It is well known in the
~,
V11~2~49
art that this contradictory problem can be solved by using
polyolefins having widely distributed molecular weights.
In recent years, properties required of polyolefins
become manifold, and there is a tendency of decreasing
the amount of resins to be used as small as possible for
saving resources as far as the required properties are
satisfied. For instance, it has been tried to decrease
the wall thicknesses of a bottle or of a film while
retaining satisfactory strengths. Under these circumstances,
there is an increasing demand for polyolefins which have
good workabilities due to flow characteristics, high impact
strengths, high tensile strengths and improved environmental
stress cracking resistance, and which will give molded
articles of good properties even when the amounts of the
resins to be used are small.
Several processes for preparing polyolefins having
widely distributed molecular weights wherein olefins are
polymerized in multi-stage polymerization reactions,
have been known. For example, such processes are disclosed
in Japanese Kohkoku Patent No. 42716/73 (Patent Publication
No. 42716/73) and Japanese Kohkai Patent No. 639/71
(Provisional Patent Publication No. 639/71). Each of these know
processes comprises the first stage wherein the polymerization
is effected by the use of a specific organometallic compound
and in the presence of a large amount of hydrogen for
i~ 49
forming relatively low molecular weight polymers, and the
second stage wherein the polymerization is effected in
the presence of a small amount of hydrogen for forming
relatively high molecular weight polymers. However, this
known process is disadvantageous in that an operation for
separating and recirculating the hydrogen is required
since the amount of hydrogen existing in the first stage
is large. Moreover, the properties of the resin obtained
by this process are not satisfactory in that a gelled mass
tends to form in the molding step to result in poor
molding qualities so that the strengths of the molded
article are inferior.
Japanese Kohkoku Patent No. 11349/71 (Patent Publicati~
No. 11349/71) discloses a process comprising the initial
stage of effecting polymerization by the use of a
predetermined amount of a specific polymerization catalyst
in the presence of a small amount of hydrogen, and the
subsequent stage of effecting polymerization in the
presence of a large amount of hydrogen. However, this
publication only discloses a discontinuous process, i.e.
batch process, for preparing polyolefins, but not specifically
referred to a continuous process for preparing polyolefins
having widely distributed molecular weights, nevertheless
the continuous process is more convenient from the
industrial standpoint of view. In such a batch process
-- 5 --
g
for preparing a polyolefin, the first stage polymerization
reaction is carried out under the predetermined condition
in a single reactor in which a gas phase is normally
existing at the upper portion thereof, and after the
completion of the first stage reaction the condition is
adjusted to suit for the second stage reaction, and
then the second stage reaction is carried out in the same
reactor in which a gas phase is also existing at the
upper portion thereof. This process is disadvantageous
from the industrial standpoint of view in that it
requires complicated operations, that the production
efficiency thereof is lowered and that difficulties are
encountered in delicately controlling the reactions.
The present invention is particularly concerned
with an industrially convenient process for continuously
preparing polyolefins which have widely distributed
molecular weights and superior properties by the use of
a highly active Ziegler type catalyst comprising a
transition metal compound supported on a carrier and
an organometallic compound. The process for polymerizing
olefins using the highly active Ziegler type catalyst
has a very important advantage in that a step of removing the
catalyst from the formed polymers can be avoided
because of the fact that a large amount of polymers are
formed with an extremely small amount of the catalyst.
-- 6 --
2(~9
However, when polyolefins having widely distributed
molecular weights are prepared with the use of the afore-
mentioned highly active Ziegler type catalyst, and particularly
when they are prepared by a generally known process
other than the process of the present invention by the
use of the multi-stage polymerization method which
comprises an initial stage of forming relatively high
molecular weight polymers and a successive stage of forming
relatively low molecular weight polymers, the following
difficulties will arise:
` In order to prepare high molecular weight polymers
in the initial or first polymerization stage, the first
stage polymerization must be carried out in the absence
of hydrogen or the concentration of hydrogen in the first
stage should be low. As a result, a large mount of
polymers is formed in an extremely short period of
time due to the high activity of the catalyst. Particularly,
if a gas phase mainly composed of a monomer is present in .
the polymerization reactor of the first stage, the
concentration of the olefin monomer in the liquid phase
is increased and it becomes difficult to control the
monomer concentration in the liquid phase below the
desired low level. With the increase in monomer concentration,
the polymer formation is further accelerated to give polymers
in short period of time that it becomes extremely difficult to
49
control the reaction. It is, therefore, desirable
to effect polymerization under a condition wherein the
concentration of the monomer in the gas phase is low.
~owever, the decrease in monomer concentration inevitably
causes reaction pressure drop and necessitates provision
of certain forced means such as a transfer pump for
delivering the reaction product to the second stage, which
means would cause fouling or blockage of the transfer
passage.
Also, in the successive or second stage wherein
relatively low molecular weight polymers are formed, the
polymerization must be carried out with an increased
concentration of hydrogen so that the polymer yield per
unit time in the second stage is considerably decreased
as compared to that in the first stage. Although the
presence of a gas phase existing at the upper portion of
the reactor and sufficiently enriched with the monomer is
effective to increase the yield of polymers in the second
stage, it is difficult to increase the monomer concentration
to a satisfactory high level since a large amount of
hydrogen is present in the polymerization reactor of the
second stage. Further, even when a sufficient amount
of the monomer is present in the second stage, the yield
of polymers per unit time is decreased as compared to
that obtainable in the polymerization reactor of the first
1~2~49
stage .
If the yield of polymers in the first stage, i.e.
the stage for forming high molecular weight polymers, is
exceedingly increased and the yield of polymers in the
scond stage, i.e. the stage for forming low molecular
weight polymers, is extremely decreased, the distribution
of molecular weight of the resulting polymer is not
sufficiently wide, and besides the polymer contains
excessive amount of high molecular weight polymers,thus
~/~
10 resulting in poor ~e~q~i~ity.
In order to overcome the aforementioned disadvantages,
it is advisable to use a smaller reactor in the first stage
as compared to the polymerization reactor used in the
second stage. However, when a small polymerization reactor
is used in the first stage, the residence time of the
reaction mixture in the first stage becomes too short
to make the reaction condition uniform so that the
reproducibility of the process might be badly affected.
Furthermore, complicated operations are required for
operating the small and large polymerization reactors mounted
in line with one another in a continuous operation mode.
OBJECTS AND SUMMARY OF THE INVENTION:
An object of the present invention is to provide
a process for continuously preparing polyolefins having
widely distributed molecular weights wherein the reaction
~1~3Z~49
mixture is transferred from the first stage reactor to the second
stage agitating reactor by the pressure difference without using
any forced transfer means.
Another object of the present invention is to provide a
process for preparing polyolefins having widely distributed molec-
ular weights and having good workabili-ties due to flow character-
istics, high impact strengths, high tensile strengths and improved
environmental stress cracking resistances.
A further object of the present invention is to provide
a process for continuously preparing polyolefins having widely
distributed molecular weights, which is simple in operation and
has good producibility and in which it is possible to control the
reactions delicately.
Yet a further object of the present invention is to pro-
vide a process for preparing polyolefins having widely distributed
molecular weights in good yield.
These and other objects of the invention will become
apparent from the following description.
According to the present invention there is provided a
2Q process for preparing polyolefins by polymerizing olefins in the
presence of a solvent, hydrogen and a highly active Ziegler-type
catalyst comprising a transition metal compound on a solid carrier
and an organometallic compound, in a plurality of reactors, to
prepare polyolefins having widely distributed molecular weights,
the improvement comprising: (a) polymerizing olefins in a first
stage reactor at a temperature of from 30 to 100C and a pressure
of from 2 to 100 kg/cm2, in the presence of a gas phase containing
an inert gas in the upper portion of the reactor to form a poly-
merization reaction mixture comprising a dispersion of relatively
high molecular weight polymer particles in the solvent; (b) con-
tinuously effecting the flow of the polymerization reaction mixture
from the first stage reactor to a second stage reactor, the second
-- 10 --
A
~1~2(~49
staye reactor maintained at a pressure lower than that of the
first stage reactor, whereby the flow of polymerization reaction
mixture is driven by J~he pressure difference; (c) subsequently
polymerizing olefins in the second stage reactor, with agitation
and beneath a gas phase containing hydrogen and olefins to form
polymers having a relatively lower molecular weight, the olefin
polymerization in said second stage reactor being effected by
supplying additional hydrogen and additional olefins; and (d)
continuously removing from the second stage reactor a polymeri-
zation reaction mixture containing polyolefins having widely dis-
tributed molecular weights, dispersed in the solvent.
~l~ZQ~Cl
DESCRIPTION OF TIIE INVENTION:
If the first stage polymerization is effected
under a condition wherein a gas phase containing an inert gas
is existing, the polymerization reaction can be readily
controled, for instance the heat of reaction can be easily
removed since the reaction may take place even when the
concentration of hydrogen is low and the concentration
of the monomers is also relatively low, and the internal
pressure in the first stage reactor can be maintained
at a sufficiently high pressure due to the inert gas
pressure so as to make it possible to conveniently transfer
the reaction mixture to the second stage kept at a lower
pressure without using any forced transfer means.
We have also found that the environmental
stress cracking resistance and the impact strength of the
resulting polymers are remarkably improved when one
or more of olefin comonomers is supplied to the first
stage reactor. It is surprising that the properties
just mentioned above are not improved if said one or
more of comonomers is not introduced into the first
stage reactor but is introduced only into the second stage
agitating reactor, as will b6/e described hereinbelow in
~o,. ~
tho Comparative Examples~ It is not essential that the
olefin comonomers be present in the reactors of the
second and subsequent stages, but they may be present if
- 12 -
~1~2~9
it is desired to decrease the density of the prepared
polyolefins to a lower value.
The advantageous features of the process of the
present invention may be summarized as follows:
(1) Polyolefins having widely distributed molecular
weights can be produced thorugh continuous multistage
reactions at high yield.
(2) The production ratio between the high molecular
weight polymers and the low molecular weight polymers
can be accurately controlled within a wide range,
and the distribution range of each of the prepareted
polyolefins may be freely varied as desired.
(3) It is not particularly required to use
small plymerization reactor in the first
stage so that the reaction mixture is held
therein for a residence time enough for forming
polymers in good reproducibility.
(4~ Since the process of the invention is a
continuous process comprising the first stage
of forming relatively high molecular weight
polymers and the successive or second stage of
forming relatively low molecular weight polymers,
the prepared polymer does not contain any gel,
thus uniform molded articles can be molded therefrom.
(5) Since the polymerization reactions can be
- 13 -
z(~`~9
effected under sufficiently controlled condition
through the process wherein the pressure of the
first stage is higher than that of the successive
stage, the reaction product from the first
stage can be continuously transferred to the next
stage without using any forced transfer means.
A Even if the product from the first stage ~ ~
isin the form of a slurry, it does not intcrfc~-
with the continuous operation of the process.
(6) Polyolefins having particularly improved
workabilities due to flow characteristics and
physical properties can be produced when copolymers
of two or more olefins are formed in the first
stage wherein the reaction for forming high
molecular weight polymers takes place in the
continuous multi-stage reaction process.
BRIEE DESCRIPTION OF THE DRAWING:
The present invention will now be described
with reference to the accompanying drawing in which:
a single figure is a flow diagram showing the
process of the invention including the first stage of effecting
polymerization in the presence of an inert gas.
PREFERRED EMBODIMENT OF THE INVENTION:
Referring to the drawing, an upstanding agitating
vessel 1 is provided with an agitator 8 and may be
- 14 -
'- ~ -
.
.
~2~49
employed as an embodiment of the first stage reactor in
the present invention. When an upstanding agitating
vessel is used, the ratio of the height to the diameter
thereof may be generally 1 to 10, preferably 1.5 to 5,
and a pressure vessel having a diameter of generally
about 0.5 to 10 m, preferably 1 to 5 m, may be used.
Also, in the present invention, reactors of other
type, such as tubular reactors and recirculating mixer
reactorsmay be preferably used. In the system, a raw
olefin in a gaseous or liquefied form is fed through a
line 3 to a reaction vessel 1. Usable olefins include
generally those having 2 to 6 carbon atoms, and preferably
lower olefins such as ethylene, propylene, and butene -1.
Alternatively, a main monomer and an olefin comonomer
may be fed through the line 3 to the reaction vessel 1
in gaseous or liquefied form. The olefin comonomer
may be separately fed through another line (not shown)
to the vessel. A single olefin selected from the olefins
having 2 to 6 carbon atoms such as ethylene or propylene
may be used as the main olefin monomer. In the process
of the invention, ethylene is the most preferred main
monomer. Examples of olefins which may be used as the
olefin comonomer are olefins other than the one used
as the main monomer and having 2 to 8 carbon atoms such
as ethylene, propylene, butene-l, pentene-l, 4-methylpentene-1,
- 15 -
11~2~P49
hexene-l, heptene-l and octene-l and preferable being
olefins having 3 to 6 carbon atoms. It is preferred
to feed the comonomer to the first stage reaction vessel
1 in a ratio of 0.1 to 10 mol% per mol of the main monomer.
CO~70,~O,~ f' r of'
A single~or a plurality~comonomers may be used. Incidentally,
in order to improve the properties of the polyolefins
prepared according to the process of the present
f7,~7e,~/~" e
invention, diolefins such as butadiene, isoprene, p,porylonc,
1,4-hexadiene or 5-ethylidenenorbornene may be added in
an amount of 1/10 mol~ based on the amount in mol of the
olefins. The term "polyolefins" according to the
invention include those containing such diolefins.
A liquid polymerization reaction medium is fed
through a line 6. Generally usable liquid reaction medium
are inert organic solvents, and hydrocarbons having 3 to 20
carbon atoms including aliphatic, aromatic and alicyclic
hydrocarbons are preferred, the representative examples of
preferred reaction medium being butane, pentane, hexane,
heptane, benzene, toluene and cyclohexane. A small amount of
hydrogen is fed thorugh a line 4, if desired. As is
mentioned hereinbefore, relatively high molecular wieght
polymers are fomred in the first stage of the process
of the invention, and thus the polymerization in the first
stage may be effected without feeding hydrogen thereto.
However, a small amount of hydrogen may be fed to the first
- 16 -
-
11~2~49
age~ if required, so as to let the concentration
of hydrogen in the first stage be about three quarters or
less, e.g. about one half to one fiftieth, of that in the
second stage. The polymerization in the first stage
reaction vessel 1 is effected generally at 30 to 100C,
preferably at 40 to 95C, at a pressure of generally 2
to 100 kg/cm2, preferably 6 to 70 kg/cm2. The pressure
in the first stage reaction vessel 1 is maintained higher
than that in the second stage agitating vessel 2 by the
value of about 10 kg/cm or less, preferably by about 5
to 0.1 kg/cm2. The concentration of monomers (in the
liquid phase) in the first stage reaction vessel 1 may
be 5 to 200~ of that (in the liquid phase) in the second
stage agitating vessel 2. It is preferred to keep the
lS concentration of monomers in the first stage within the
range of 20 to 100~ as that in the second stage reaction
vessel 2, i.e. the monomer concentration in the first stage
reaction vessel be preferably kept not higher than that
in the second stage reaction vessel.
In the system shown, an inert gas is introduced
through a line 4a and the polymerization is effected
under a condition wherein a gas phase containing the
inert gas is existing at the upper protion of the
reaction vessel 1. The polymerization reaction takes
place under the condition in which the fed monomers and/or
- 17 -
4'9
a small amount of hydrogen are dissolved in the reaction
medium. In the polymerization process according to the
present invention, formed polymer particles are dispersed
in the solvent. The polymerization reaction proceeds
under the condition in which an inert gas, monomers and
optionally a small amount of hydrogen are present in the
gas phase. The concentration of the inert gas in the
gas phase may be 20 to 99 mol%, preferably 40 to 99 mol%,
and most preferably 60 to 99 mol~. If the concentration
of the inert gas is too low, the concentration of monomers
becomes exceedingly high and the object of the present
invention can not be attained. As the inert gases which
may be used in the process of the invention, there
may be mentioned nitrogen, helium, neon, argon and methane,
nitrogen being the most preferred one.
In the embodiment shown in the figure, a catalyst
is fed through a line 5. In general, the catalyst may
be fed to the reaction vessel while being mixed with
and dispersed in said solvent. The catalyst used in the
invention is a highly active Zieger type catalyst comprising
a transition metal compound supported on a solid carrier
and an organometallic compound. The catalyst used in
the present invention will be described in detaïl.
The catalyst which may be used in the process
of the present invention comprises a solid component combined
- 18 -
.
~lf~2~4g
with an organometallic compound from a metal of Group
I - IV of the Periodic Table, preferably with an organoaluminium
or organozinc compound, and has the catalytic activity of
generally higher than 50 g. polymer/g. catalyst-hr-olefin-
pressure (kg per cm ), preferably higher than 100 g. polymer/g.
catalyst-hr-olefin-pressure (kg per cm2). Said solid
component comprises a solid carrier and a transition
metal compound supported on said carrier. Substances which
may be used as the solid carrier include metallic magnesium,
magnesium hydroxide, magnesium carbonate, magnesium oxide,
various alminac, silica, silica-alumina and magnesium
chloride; double salts, double oxides, hydrated carbonate
and hydrated silicates of a metal or metals selected
from the group consisting of magnesium, silicon, aluminium
and calcium; and those obtained by treating or reacting the
substances stated above with an oxygen-containing compound,
a sulfur-containing compound, hydrocarbons or a halogen-
containing compound. As the transition metal compound
which is supported on the solid carrier, there may be
mentioned halides, alkoxy halides, oxides and halogenated
oxides of Ti, V, Zr and Cr. Specific examples of the
catalysts usable in the present invention are those prepared
by combining an organoaluminium or organozinc compound with
a solid component, such as MgO-Rx-TiC14 system ~See Japanese
Kohkai Patent No. 27586/74), A1203-AlX3-0RR'-TiC14
-- 19 --
ll(~Z~?49
system (See Japanese Kohkai Patent No. 86480/74),
RMgX-TiCln(OR)4 n (See Japanese Kohkai Patent Nos. 72384/74
and 86483/74), A12O3-SO3-TiC14 system (See Japanese Kohkai
Patent Nos. 100182/75, 151977/75 and 144794/75),
Mg-SiC14-ROH-TiC14 system (See Japanese Kohkai Patent
No. 86481/74), MgC12-Al(OR)3-TiC14 system (See Japanese
Kohkai Patent Nos. 90386/74 and 64381/75), MgC12-SiC14-
ROH-TiC14 system (See Japanese Xohkai Patent No. 106581/74)
and Mg(OOCR)2-Al(OR)3-TiC14 system (See Japanese Kohkai
Patent No. 120980/74). In the meanwhile, a portion or all
of said organometallic compound may be directly fed to
the reaction vessel through another feeding line while
being dissolved in a solvent separately rather than being
combined with said solid component.
A jacket is provided around the wall of the first
stage reaction vessel 1 for passing a cooling medium
therethrough. A cooler 10 is mounted in line with a
recirculation passage for the polymerization reaction
mixture. The heat of reaction may be removed either by
flowing a cooling medium through the jacket or by
recirculating the reaction mixture through the cooler 10,
or both measures may be taken as occasionaries. The
first stage reaction vessel 1 as shown includes generally
one reactor, but a plurality of reactors (not shown), which
are operated under the substantially same condition, may
- 20 -
2~4~3
be connected in line with or in series with one another.
The polymerization reaction mixture from the
first stage reaction vessel 1 is continuously transferred
through a line 11 to the second stage agitating vessel 2
provided with an agitator 9 by the pressure difference
without using any forced delivering or transfer means
such as a pump. Since no forced transfer means is used,
there is almost no danger of the occurrence of fouling
or blockage.
The process of the present invention is operated
continuously without virtually separating any portion
of the components of the polymerization mixture.
Accordingly, it has an advantage of eliminating a separating
operation of handling a pressurized mixture which contains
polymers and which tends to cause fouling. Hydrogen
and additional monomers are supplied, respectively, through
a line 7 and a line 12, to the polymerization reaction
mixture delivered to the second stage agitating vessel
2, and the polymerization is effected continuously. Hydrogen
is fed in an amount such that the concentration of H2
in the gas phase is in the range of generally from 30
to 95 mol%, preferably from 40 to 90 mol%.
The concentration of the monomer in the gas phase
contained in the second stage agitating vessel 2 may be
varied within the range of from 5 to 70 mol%, preferably
~L~L02~
from 10 to 60 mol%, and the concentration of the monomer
in the liquid phase is correspondingly determined depeding
upon the polymerization temperature and pressure and the
kind of the monomer used.
In case where copolymerization is effected in
the first stage agitating vessel, an additional amount of
a comonomer may be fed through the line 7 or another line
(not shown). The amount of the added comonomer may be
varied such taht the molar ratio thereof is 0.1 to 10 mol%
per mol of the main monomer contained in the second stage
agitating vessel.
An additional catalyst may be fed through a line 13,
as required. The second stage vessel 2 may be substantially
similar in shape as the one employed as the first stage
reactor, and an upstanding agitating vessel may be used
for this purpose. The temperature of the second stage
agitating vessel is kept at generally 50 to 100C, preferably
60 to 95C, and the pressure thereof being kept at the
value lower than that of the first stage reactor, as
described above. The heat of polymerization reaction is
removed by the use of a cooler 14. Although there is shown
a method of recirculating the liquid phase in the
accompanying drawing, cooling may be effected alternatively by
a method of removing the gas phase in the second stage
agitating vessel, and cooling the same to liquefy the
- 22 -
2(~9
portion of the solvent vapor or the monomer which is then
recirculated into the vessel (not shown). In the process
of the present invention, the polymerization reaction in
the second stage is effected in the presence of a gas
phase containing the olefins and hydrogen at the upper
portion of the second stage agitating vessel. For this
reason, the polymerization reaction in the second stage
may be easily controlled by adjusting the temperature
and pressure in the vessel, and the concentrations of
the monomer and hydrogen may be maintained at a higher level.
Similarly as in the first stage, the polymer
particles formed by the second stage polymerization are
dispersed in the solvent.
According to the processs of the invention,
the first stage polymerization further continues in the
second stage. The ratio between the high molecular weight
polymers and the low molecular weight polymers in the
formed reaction product may be freely selected in a wide
range. However, it is generally desirable to prepare
a composition composed of 5 to 70% by weight of the high
molecular weight polymers and 30 to 95% by weight of the
low molecular weight polymers, preferable composition
being composed of 10 to 60% by weight of the high molecular
weight polymers and 40 to 90% by weight of the low molecular
weight polymers.
- 23 -
~1C32~
The polymerization reaction mixture from the
second stage is removed continuously through a line 15,
and the polymers are recovered from the solvent. The
second stage agitating vessel 2 as shown includes generally
one reactor, but two or more of reactors (not shown), which
are operated under the substantially same condition, may be
connected in line with or in series with one another.
The present invention has the characteristic
features as described hereinabove, and provides an advantageous
process for preparing polyolefins having widely distributed
molecular weights on an industrial scale. Polymers may be
recovered from the polymerization reaction mixture removed
from the second stage agitating vessel by any of the conventional
methods for recovering polyolefins. It should be noted
that a step of removing inorganic residues which are derived
from the catalyst may be eliminated since the highly active
Ziegler type catalyst comprising a transition metal
compount supported on a solid carrier and an organometallic
compound is employed in the process of the invention.
Polymers may be, for instance, recovered from the
polymerization reaction mixture by a method of introducing
the reaction mixture through the line 15 into a flashing
vessel 16 into which steam is fed through a line 17 to
distill off the residual hydrogen, unreacted monomers and
solvent. Polymers are recovered through a line 19 in
- 24 -
: .
11~2~g
the form of a water slurry by introducing warm water
through a line 20. The hydrogen, monomers and solvent
distilled off from the reaction ~ixture may be refined
in a refining step (not shown) and returned to the process
for reuse. In the polymer recovery step of the process
of the present invention, two or more of flashing vessels
may be provided in line with one another for perfectly
recovering the unreacted materials and the solvent.
EXAMPLES OF T~IE INVENTION:
The present invention will be further described
in detail with reference to several examples thereof.
Example
Using the system shown in the drawing, polymerization
was effected in accordance with the illustrated polymerization
process. 1.35 m3/hr of hexane, 1.0 mol/hr of triethylaluminium,
- 9.0 g/hr of a catalyst comprising TiC14 supported on a
solid carrier including anhydrous magnesium chloride and
15 kg/hr of ethylene were continuously fed to an agitating
reactor of 0.9 m internal volume which was maintained
at 85C. The upper portion of the reactor was then purged
with pressurized nitrogen gas to form an inert gas
phase, and the reactor was maintained at a gauge pressure
of 17.0 kg/cm2. The polymerization reaction mixture slurry
from the first stage reactor was delivered from the bottom
of the reactor through a conduit to a 2.0 m3 second stage
- 25 -
.- ~
ll~Z(~49
agitating vessel by the pressure difference, and added
wlth ethylene, propylene and hydrogen in the second
stage vessel which was maintained at 85C and at a
total gauge pressure of 16 kg/cm2, the volume of the
liquid phase being kept at 1.5 m . The molar ratio of
ethylene:propylene:hydrogen in the gas phase contained
in the second stage vessel was maintained at 29.0:1.0:70.
This two stage polymerization was operated very stably
- for 100 hours. The reaction mixture was removed, and
the polymers were recovered and dried to obtain 4,850 kg
of a mixture of widely distributed molecular weight
polyethylenes of a bulk density 0.31, a melt index 0.059,
Melt Index at the Loadinq of 21 6 ka
a flow parameter (log Melt Index at the Loading of 2.i6 kg
2.32 and a density 0.9523 g/cm3. The molding qualities
of the polyethylene thus obtained was excellent. A 10
thick film was molded therefrom, and it was found that
the number of gels formed on the film was greatly decreased
to 15/1000 cm2. The properties of the film were also
satisfactory.
Example 2
Using the system shown in the drawing,1.35 m3/hr of
hexane, 1.0 mol/hr of triethylaluminium, 9.0 g of the
Ti-containing solid catalyst which was the same as used in
Example 1, 39 kg/hr of ethylene and 27 g/hr of hydrogen
were continuously fed to a 0.9 m3 first stage reactor which
- 26 -
b;
",,
was maintained at 85C. The upper portion of the reactor
was then purged with nitrogen gas to form an inert gas
phase, and the reactor was maintained at a gauge pressure
of 16.2 kg/c~2. The slurry from the first stage reactor
was delivered through a conduit to a 2.0 m3 second stage
agitating vessel by the pressure dif erence, and added
with ethylene, propylene, and hydrogen in the second stage
vessel which was maintained at 85C and at a total gauge
pressure of 15.8 kg/cm2, the volume of the liquid phase
being kept at 1.5 m3. The molar ratio of ethylene:propylene:
hydrogen in the gas phase contained in the second stage
vessel was maintained at 39.1:1.2:59.7. This two stage
polymerization was operated very stably for 100 hours.
The reaction mixture was continuously removed, and the
polymers were recovered and dried to obtain 9,150 kg of
a mixture of widely distributed molecular weight polyethylenes
of a bulk density 0.33, a melt index 0.36, a flow
param/etfer 2.01 and a density 0.9550 g/cm3. The molding
qualtiticc of the polyethylene thus obtained were excellent,
and the properties of a bottle molded therefrom by means
of the blow molding were also satisfactory.
Example 3
Using the system shown,polymerization was
effected in accordance with the illustrated polymerization
process. 1.35 m3/hr of hexane, 1.0 mol/hr of triethylaluminium,
- 27 -
..
~1~12C~49
9.0 g of the Ti-containing solid catalyst which was the
same as used in Example 1,37 kg/hr of ethylene, 1.3 kg/hr
of butene-l and 25 g/hr of hydrogen were continuously fed
to an agitating reactor of 0.9 m3 internal volume, and
the reactor was maintained at 85C. The upper portion
of the reactor was then purged with nitrogen gas to form
an inert gas phase, and the reactor was maintained at a
gauge pressure of 17.0 kg/cm2. The polymerization
reaction mixture slurry from the first stage reactor was
delivered from the bottom of the reactor through a conduit
to a 2.0 m second stage agitating vessel by the pressure
difference, and added with ethylene and hydrogen in
the second stage vessel which was maintained at 85C and
at a total gauge pressure of 16 kg/cm2, the volume of
the liquid phase being kept at 1.5 m3. The molar
ratio of ethylene:hydrogen in the gas phase contained in
the second stage vessel was maintained at 35:65. This
two stage polymerization was operated very stably for
100 hours. The reaction mixture was continuously removed,
and the polymers were recovered and dried to obtain 9,630
kg of a mixture of widely distributed molecular weight
polyethylenes of a bulk density 0.33, a melt index 0.32,
a flow parameter 2.05 and a density 0.9548 g/cm3. The
stiffness of the polymer thus obtained measured by
the ASTM D747-63 method was 13.1 x 10 psi, the
- 28 -
~1~2~9
environmental stress cracking resistance (ESCR) thereof
measured by the ASTM D-1693-60T method was 128 hr, and
the critical shear rate measured by using an Instron rheometer
was 1710 sec 1. These figures show that the properties
of this polymer are well balanced.
Comparativc Example ~
1.35 m /hr of hexane, 1.0 mol/hr of triethylaluminium,
9.0 g/hr of the Ti-containing solid catalyst,which was the
same as used in Example 1, 39 kg/hr of ethylene and 27 g/hr
of hydrogen were continuously fed to a 0.9 m3 first stage
reactor which was maintained at 85C. The upper.portion
of the reactor was then purged with nitrogen gas to form
an inert gas phase, and the reactor was maintained at a
gauge pressure of 16.5 kg/cm2. The slurry from the
first stage reactor was delivered through a conduit to a 2.0 m3
second stage agitating vessel by pressure difference,
and added with ethylene, butene-l and hydrogen in the
second stage vessel which was maintained at 85C and at
a total gauge pressure of 15.8 kg/cm2, the volume of the
gas phase being kept at 1.5 m3. The molar ratio of
ethylene:butene-l:hydrogen in the gas phase contained
in the second stage vessel was maintained at 33.1:1.9:65.
This two stage polymerization was operated very stably
for 100 hours. The reaction mixture was continuously removed,
and the polymers were recovered and dried to obtain 8,930 kg of
- 29 -
~ (32~9
mixture of widely distributed molecular weight polyethylenes
of a bulk density 0.30, a melt index 0.33, a flow parameter
2.02 and a density 0.9556 g/cm3. The stiffness of the
obtained polymer was 12.0 x 10 psi, the ESCR was 38 hr and the
critical shear rate was 1010 sec 1. These results are
inferior as compared to Example 3.
Example ~
1.35 m3/hr of hexane, 1.0 mol/hr of triethylaluminium,
9.0 g/hr of the Ti-containing solid catalyst which was the
same as used in Example 1, 15 kg/hr of ethylene and 0.7 kg/hr
of propylene were continuously fed to a 0.9 m3 first stage
reactor which was maintained at 85C. The upper portion
of the reactor was then purged with nitrogen gas to form
an inert gas phase, and the reac4tor was maintained at a
gauge pressure of 17.0 kg/cm . The polymerization reaction
mixture slurry from the first stage reactor was delivered
from the bottom of the reactor through a conduit to a second
stage agitating vessel of 2.0 m3 internal volume by
the pressure difference, and added with ethylene
and hydrogen in the second stage vessel which was maintained
at 85C and at a total gauge pressure of 16 kg/cm2,
the volume of the liquid phase in the vessel being kept at
1.5 m . The molar ratio of ethylene:hydrogen in the gas
phase contained in the second stage vessel was maintained
at 30:70. This two-stage polymerization was operated
- 30 -
. ~
Z~9
very stably for 100 hours. The reaction mixture was
continuously removed, and the polymers were recovered and
dried to obtain 5,580 kg of a mixture of widely distributed
molecular weight polyethylenes of a bulk density 0.29,
a melt index 0.061, a flow parameter 2.33 and a density
0.9511 g/cm3. The molding qualities of the polymer thus
obtained were excellent. A 10~ film was molded therefrom,
and it was found that the number of gels formed on the film
was greatly decreased to 9/1000 cm2 The Dart impact
strength measured in accordance with ASTM D1709-62T
was 168 g. The other properties of the film were also
satisfactory.
Comparativc Example ~
1 35 m3/hr of hexane, 1.0 mol/hr of triethylaluminium,
0.9 g of the Ti-containing solid catalyst which was the
same as used in Example 1 and 15 kg/hr of ethylene were
continuously fed to a 0.9 m3 first stage reactor which was
maintained at 85C. The upper portion of the reactor was
then purged with nitrogen gas to form an inert gas phase,
and the reactor was maintained at a gauge pressure of
17.0 kg/cm . The slurry from the first stage reactor was
delivered through a conduit to a second stage agitating
vessel of 2.0 m3 internal volume by the pressure difference
and added with ethylene, propylene and hydrogen in the
second stage vessel which was maintained at 85C and
- 31 -
11~2~49
at a total gauge pressure of 16 kg/cm2, the volume of the
liquid phase being kept at 1.5 m3. The molar ratio
of ethylene:propylene:hydrogen in the gas phase contained
in the second stage agitating vessel was maintained at
29.0:1.0:70. This two stage polymerization was operated
very stably for 100 hours. The reaction mixture was
continuously removed, and the polymers were recovered
and dried to obtain 4,850 kg of a mixture of widely
distributed molecular weight polyethylenes of a bulk
density 0.31, a melt index 0.059, a flow parameter 2.32 and a
density 0.9523 g/cm3. The polymer thus obtained was molded
to a 10~ thick film, the Dart impact strength of which
was 108 g. This result is inferior as compared to that
obtained in Example ~.
While the present invention has been described
with reference to the specific examples, it should be
understood that the invention is not restricted to such
examples, but any change and modification may be
made within the spirit and scope of the present invention
as recited in the appended claims.
