CA1060146A

CA1060146A - Process for the purification of olefin polymerizates

Info

Publication number: CA1060146A
Application number: CA000240839A
Authority: CA
Inventors: Abraham Van Mannekes; Ross T. Channon; Jan W. De Beukelaar
Original assignee: Shell Canada Ltd
Current assignee: Basell Technology Co BV
Priority date: 1975-01-07
Filing date: 1975-12-01
Publication date: 1979-08-07
Also published as: ZA7625B; BE837218A; DE2600205C2; FR2297218B1; NL7600033A; JPS5919124B2; DE2600205A1; AU501125B2; AU1005876A; NL180590B; GB1491371A; IT1053281B; NL180590C; BR7600120A; JPS5193987A; FR2297218A1

Abstract

A B S T R A C T

A process for the 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 compound, which process comprises (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 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 or 0.1 to 20 % w (based on the wash liquid) of an alcohol.

Description

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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 :,: ;, :
; 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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i6 (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 :~
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, : , 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 ,. ~

and/or mixtures of hydrocarbons, e.g. aviation alkylate. The process of the ., ' ' A -~ ~

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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.
.' i When the slurry is contacted with the alcohol, the ., .
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 ~-, 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 ~`
,:, :: :-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 ,: - .:
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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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process for the 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 compound, which process comprises (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 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 0.1 to 20%w (based on the wash liquid) of an alcohol.

2. A process as claimed in claim 1 in which the polymer is polypropylene.

3. A process as claimed in claim 1 or 2 in which the liquid hydrocarbon medium used in step (a) or (b) is the liquid olefin monomer.

4. A process as claimed in claim 2 in which the alcohol used in step (a) or (b) is a saturated aliphatic alcohol having 3 or 4 carbon atoms.

5. A process as claimed in claim 4 in which the amount of alcohol used in step (a) or (b) is not above 7%w (based on the liquid phase).

6. A process as claimed in claim 5 in which the oxygen is admixed with an inert gas.

7. A process as claimed in claim 6 in which the slurry is contacted with the oxygen after the alcohol.

8. A process as claimed in claim 1 in which the peroxide is dilauroyl peroxide.

9. A process as claimed in claim 6 or 8 in which the step (a) is carried out in the presence of a scavenger for the hydrogen halide formed.

10. A process as claimed in any one of the claims 1, 6 or 8 in which step (a) is carried out at 20° to 80°C and step (b) at 30° to 50°C.

11. A process according to claim 1 or 2 wherein the liquid hydrocarbon medium used in step (a) or (b) comprises a mixture of the liquid olefin monomer together with the corresponding satuated hydrocarbon.