Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to a process for the
purification of an olefin polymer obtained by the
polymerization of one or more olefins with the aid of a ~; ;
catalyst comprising a titanium halide and an organo
aluminium compound. The crude olefin polymers obtained
in this way contain catalyst remnants which may adversely
affect the properties of the polymer. By "catalyst remnants"
is meant the catalyst and any decomposition products or
derivatives thereof which may be formed durin~ the polymer~
ization.
.
The removal of these catalyst remnants is usually
termed "deashing" and the deashing efficiency is generally
denoted by the percentage of titanium which is removed -
from the polymer during the purification. This is given
by the expression
~ 15 Deashing efficiency = 100 x (Tiinitial ~ Tifinal)/(Tiinitial)
- This definition is usually chosen because titanium can be
determined more accurately than, for example, aluminium~
and, moreover, the removal of other elements broadly follows
that of titanium. ~;~
The present invention provides a process for the
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; purification of an olefin polymer obtained by polymerizing
one or more olefins with the aid of a catalyst comprising
a titanium halide and an organo aluminium com~ound, which
~ process comprises
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(a) contacting a slurry of the polymer in a liquid hydrocarbon `
medium with from 0.01 to 20~w (based on the liquid phase) of an ~ i
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alcohol and with at least 0.1 mole of oxygen, or an equivalent ~
amount of a peroxide, per gram atom of titanium present in the ~ ~ ;
slurry, and (b) washing the polymer with a liquid hydrocarbon ;~
medium in the presence of from 0.01 to 20~w (based on t`he wash
liquid) of an alcohol. ~ ~
The olefin polymers may be derived from olefins ~-
having, for example, 2 to 6 carbon atoms, such as ethylene, ~ ;
propylene, 1- or 2-butene, isobutene or l-hexene. The process
of the invention is particularly suitable for the deashing of
polypropylene, to which further reference will be made below. ~ -
Propylene is usually polymerized in the liquid phase
with the aid of a trivalent titanium compound, in particular
TiC13 and an aluminium dialkyl halide activator, as described,
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for example, in United Xingdom Patent Specifications 1,120,079, ~ ?~
1,390,355 and 1,372,440 which issued to Shell Internationale ;~
Research Maatschappij B.V. on July 17, 1968; September 4, 197S
and November 30, 1974, respectively. The polymerization is
generally carried out in the presence of a liquid hydrocarbon ;
diluent in which the propylene is substantially insoluble.
This leads to the formation of the slurry comprising solid
.
polypropylene, the catalyst remanents and the diluent. Suitable
inert diluents are propane, the pentanes, hexanes, iso-octanes
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and/or mixtures of hydrocarbons, e.g. aviation alkylate. The
process of the
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invention is of particular interest for slurries
containing, as the liquid hydrocarbon medium, an excess ;~
of the liquid olefin monomer (propylene), optionally
together with the corresponding saturated hydrocarbon
(propane). The slurry concentration, i.e. the weight
percentage of solid polypropylene present, may be ~rom
10 to 65 % w, preferably from 25 to 55 % w,and ;~
especially ~rom 30 to 50 % w.
The alcohol used in step (a) may be a saturated
aliphatic alcohol having up to 10 carbon atoms, for
example the propanols, butanols, pentanols and nonanols. `~
Alcohols having 3 or 4 carbon atoms especially
; isopropanol, 1-butanol and 2-butanol are preferred.
The use of 2-butanol has proved advantageous in avoiding
corrosion problems in the equipment used for the process.
Mixtures of two or more alcohols may also be used.
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i When the slurry is contacted with the alcohol, the
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catalyst is inactivated and in part solubilized. Contact
times are usually at least 2 minutes, and preferably from
20 3 to 15 minutes. The alcohol is applied in an amount of
at least 0.01 % w and preferably not more than 7 % w -
based on the liquld phase~ for example from 0.1 to 2 % w,
and in particular from 0.1 to 1.0 % w.
I The slurry is also contacted with oxygen or a ;~
; 25 peroxide, in order to achieve a substantially complete
~ decomposition and solubilization of the catalyst ;~
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remnants. The use of oxygen is generally preferrecl, ~ ~
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it being recommended to apply a mixture of 2 and an ;~
inert gas, especially nitrogen. Mixtures may contain
from 0.1 to 25 % v 2~ preferably from 0.3 to 20 % v 2;
particularly preferred are O2fN2 mixtures containing
~ 5 from 0.5 to 10 % v 2 The peroxide preferably has a ;
- half-life time of one hour at a temperature within the
range 50-175C, preferably 60-140C. A particularly
preferred peroxide is dilauroyl peroxide.
The amount of oxygen is suitably from 0.1 to ~
50 mole/gat Ti, preferably from 0.2 to 2.5, and in ?
particular from 0.25 to 2 mole O2/gat Ti. When a
peroxide is used an amount equivalent to those mentioned
above may be applied, for example from 0.25 to 2 mole
of dilauroyl peroxide per gat Ti.
The contacting with oxygen may be carried out
! simultaneously with the introduction of the alcohol,
but is preferably carried out after the introduction of
the alcohol. Effective stirring to provide an intimate
contact between gas and liquid is desirable. The contact
time may vary between wide limits, but generally lies
between 1 and 50 minutes, in particular between 5 and
30 minutes. When a peroxide is used, this may also be
added, for example, together with the alcohol, in one
portion, or gradually over a period of time ranging -~
e.g. from 1 to 50 minutes, preferably from 5 to 30
minutes. ~-~
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Since the decomposition of the cat;alyst may be
accompanied by the formation of hydrogen halide which
could give rise to corrosion problems, a scavenger
for the hydrogen halide, preferably propylene oxide,
may be added together with the alcohol~ The scavenger
is preferably employed in amounts ranging from 0.5 to ~
20 mole per gat Ti, in particular from 1 to 15 mole ~; ;
per gat Ti. -
Preferred temperatures for step (a) are from 20 ~o :
80C, in particular from 20 to 60C.
: In order to keep the reaction medium in the liquid
:,~ state, it may sometimes be desirable to maintain a
pressure above atmospheric pressure, for example, when
propylene, or a propylene~propane mixture, is used as ;~
the diluent.
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After step (a) the slurry is washed with a liquid -~
hydrocarbon medium in the presence of an alcohol
- step (b).
It has been found advantageous to use a similar
hydrocarbon medium to that used in step (a), for
example, the olefin monomer, optionally containing the . :~
corresponding saturated compound, viz. propylene or a `~
propylene/propane mixture.
Surprisingly, it has been found that the deashing ;-
efficiency is increased very considerably by the
presence of the alcohol in the wash liquid. The alcohol ~-
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ls preferably of the same type as that used in step (a~
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especially saturated alcohols having 3 or 4 carbon
atoms, for example iso~ropyl alcohol, 1-butanol or ~-
2-butanol.
The amount of alcohol used in the washing step (b)
is preferably not higher than 7 % w, for example from ~ ; ?~
0.1 to 2.0 % w and in particular from 0.1 to 1.0 % w -
of the wash liquid. The washing may be carried out at
a temperature from 10 to 80C, preferably 30 to 50C.
Preferably the washing is carried out with stirring.
In a batch process the bulk of~ the liquid nhase may be
removed from the slur-ry, for example by filtration, and
the polymer contacted with fresh portions of the liquid
hydrocarbon medium and alcohol. Very few such washings,
usually two, are generally needed to achieve the desired
i 15 purification. Alternatively the slurry may be passed
!
down a column through which a counter-current of the
washing medium is maintained.
While the process of the invention may very conveniently
be conducted batchwise, it is highly suited to be carried
out as a continuous, or semi-continuous operation. i;~`
The purified polypropylene recovered after separation
from the liquid phase, has excellent mechanical properties,
e.g. yield stress of 37.5 MN/m2.
EXAMPLE ~`
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De=a=sh=ing==o=f=a_=saur=r~==of_pQ~ o=g~le~e
The experiments were carried out in a 2~-liter
autoclave of stainless steel (AISI 316) provided with
external heating equipment,stirring and intake facilities
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and a "Hoke" filter (40-55 ~) which was located close
to the bottom of the autoclave to permit filtration
of the slurry and removal of the filtrate through an
outlet in the bottom of the autoclave.
The slurry of polypropylene had been obtained by
mass polymerization of propylene, the catalyst having
been prepared by reduction of TiCl4 with Al(C2H5)3,
: as described for example in UK Patent Specificati.on 1,390,355
~; using pentane as a di.luent. The polymerization had ~)(?~n
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carried out in accordance wi.th thc l-rocedure descIibed
in the UK Patent Specification 1,372,LI40 at 60C for about
6 hours yielding about 3000 g of polypropylene (PP) per g
TiCl3. 600 g of the resulting slurry of polypropylene in propylene
.: monomer was then transferred to the autoclave whi.ch had been .
flushed with nitrogen at 90C for 15 hours and cooled to 20C.
Decomposition of the catalyst
. After having been diluted to the desired concentration :
with propylene, supplied from a cylinder pressurized with
nitrogen, the slurry was heated with stirring to 55C, whereupon
a dosed mixture of 1-butanol ~ROH) and propylene oxide (PO~
was pumped into the autoclave. Stirring was continued at that
temperature for 15 minutes, and an oxy~en/nitrogen mixture .`
containing 0.5 %v 2 was then gradually introduced, e.g.
for 30 minutes. The autoclave was subsequently cooled to 40C
. 25 in about 10 minutes, after which the bulk of the liquid contents ~ .
. was removed therefrom by filtration in about 30 seconds.
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:. Extraction (washing)
:~ Extract;ion of solubilized catalyst remnants from the ~-
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solid polypropylene was effected by addition in about ~;
30 seconds of fresh propylene to the autoclave (kept at - ;
40C) to replace the amount of propylene removed, the ~ ~ ;
required quantity of 1-butanol being pumped in simultaneously~
Subsequently~ the mixture was stirred for another 60 seconds. ~ ;
The wash liquid was then removed by filtration and the ;~
operation was repeated. After a total of two extractions
the remaining propylene was flashed off, and the purified `~ ~
polypropylene was recovered from the autoclave. ~-
From the filtrates obtained, propylene was flashed
off, and the residue worked up for analysis of titanium
which was determined by means Or X-ray fluorescence.
The polypropylene powder obtained was dried ln a
vacuum oven at 60-70C to constant weight, after which
it was analysed for the contents of Ti, Al and Cl by `~
X-ray fluorescence.
;; Experimental conditions and results obtained are
shown in the table below.
Comparison of Experiments 1 and 2 shows the striking
increase in the deashing efficiency when 1-butanol is ;~
added to the wash liquid (propylene), while comparison of
Example 3 with Examples 4, 5 and 6 demonstrates the
dramatic effect of an oxidizing agent in the decomposition
step on the deashing efficiency. From the results obtained ;~
it is clear that both measures are essential for achieving
high deashing efficiencies.
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