CA1151140A - Method for producing polyolefines in the form of powder by polymerization in the gaseous phase - Google Patents

Abstract

Abstract of the Disclosure The invention relates to a method of producing polyolefins in powder form, by polymerizing ethylene or copolymerizing ethylene and propylene and/or butylene-(1). The reaction is carried out in the presence of a catalyst comprising a mixture of: (1) a vanadium component obtained by reacting (a) a mixture of vanadyl(V)-chloride and vanadyl(V)-alcoholate in a molar ratio of 1:2 to 2:1, or a reaction product of vanadyl(V)-chloride with a lower alcohol in a molar ratio of 1:2 to 1:1, with (b) ethylaluminum dichloride, diethylaluminum chloride, isobutylaluminum dichloride and/or diisobutylaluminum chloride in a molar ratio V:A1 of 1:3 to 1:1, in an inert solvent, with stirring at a specific stirring power of 0.1 to 20 000 watts/m3, and separating the solid thus obtained;
(2) a finely divided silica xerogel in a weight ratio of from 0.5:1 to 10:1 based on the vanadium component; (3) a polyolefin in powder form possessing trickling ability, having an average particle diameter up to 1 000 µm and being practically free from very fine grained material, in an amount of from 0.5 to 3.0 grams per milligram of the vanadium component, calculated as vanadium peroxide; and (4) an alumino-organic compound of the general formula RnAlX3-n, wherein R signifies a saturated hydrocarbon radical with 2 to 20 carbon atoms, X signifies a halogen atom, and n is a number from 1 to 3, or a product of the reaction between trialkyl aluminum or dialkylaluminum-hydride and a 1.3 diolefin, in an amount of from 0.1 to 3.0Mmole per gram of powdered polyolefin.

Description

The invention relates to a method for producing polyolefins in the form of powder by polymerizing ethylene, or copolyrners thereof, with propylene and/or butylene-~l) in the gaseous phase. The polyolefin powder produced in accordance with the invention is noted ~or the fact tha-t it is particularly suitable for processing into shaped parts, with Lhe machines and equipment nor-mally used in processing synthetic materials, without prior granulation.
It is known that polyolefin powders can be produced from vanadium compounds, with special Ziegler catalysts. The said powders have very good flow-or trickle-properties, high bulk-densities and a narrow particle-size range and, with a suitable choice of co-catalysts, are suitable for processing by extrusion or injection-moulding.
Ho~eyer, these catalysts, developed for suspension processes, cannot be used directly for the technically progressive gaseous-phase processes.
Carrier-catalysts are normally used for gaseous-phase polymerization of ethylene in the fluidized bed. The components of Ziegler catalysts, transition-metal compounds, preferably of the IVth to VIth secondary group of the Periodic ~ystem, such as titanium, vanadium and chromium compounds, and metal-organic compounds, preferably aluminum, are reacted, if necessary in inert h ydrDcar D0115 liquid ~}~x~kfl~ttes as solvents and diluents, with catalyst-carriers such as silica-gel, magnesium oxychloride, magnesium oxide, magnesium hydroxide, or aluminum oxide and t]le like, and are dried. The catalytically active solid thus obtained is suitable for polymerization a~ter the addition of alumino-organic compounds. The solid containing the transition-metal~ and the solid impregnated with the alumino-organic compound, may be introduced separately into the poly-merizing zone of the fluidized-bed reactor.
All of these catalysts containing inorganic carrier-materials have the disadvantage that the pol~ner produced by them has a relatively high ash-content. This may have highly undesirable effects when the polymer is processed into finished articles. ~or example, the catalyst-carriers may act as cracking-catalysts in the melted synthetic material, thus forming volatile components, causing odour problems and forming bubbles in the melt. Furthermore, the synthetic materials may absorb atmospheric humidity during storage, also leading to the forming of bubbles in extrusions, unless the material is subjected to a costly drying process before it is processed. Polymer powders produced by existing methods, also leave much to be desired in the matter of Elow or trickle-properties and bulk-density, and must therefore be granulated before they can be processed into finished parts on conven-tional equipment.
According to the present invention there is provided a method for ~roducing polyolefins in the form of powders, which process comprises polymeriz-` ing ethylene or copolymerizlng ethylene and propylene and/or butylene~ in the gaseous phase, under a pressure of lQ to lOQ bars, at a temperature of about 50 to about 110C, if necessary in the presence of hydrogen, the reaction being carried out in the presence of a catalyst comprising a mixture of:
(1) a vanadium component obtained by reacting (a~ a mixture of vanadyl(V)-chloride and vanadyl~V)-alcoholate in a molar ratio of 1:2 to 2:1~ or a reaction p~odu~t ~ e~ of vanady](V)-chloride with a lower alcohol in a molar ratio of 1:2 to 1:1, with (b~ ethylalu~inum dichloride, diethylaluminum chloride, isobutyl-aluminum dichloride and/or di`isobutylaluminum chloride in a molar ratio V:Al of 1:3 to 1:1, in an inert solvent, with stirrlng at a speci~ic stirring power of Q.l to 20,0Q0 watts~m , and separating the solid thus obtained;
~21 a finely clivided silica xerogel in a weight ratio of from 0.5:1 to 10:1 based on the vanadium component;
(3~ a polyolefin in po~der form possessing trickling ability, having an average particle dla~eter up to l,aOQju~ and being practically free from very ~3L5~0 fine grained material, in an amount of from 0.5 to 3.0 grams per milligram of the vanadium component, calculated as vanadium pentoxide; and (4) an alumino organic compound of the general formula R AlX3 n' wherein R signifies a saturated hydrocarbon radical with 2 to 20 carbon atoms, X
signifies a halogen atom, and n is a number from 1 to 3, or a product of the re-action between trialkyl aluminum or dialkyl-aluminum-hydride and a 1.3 diolefin, in an amount of from 0.1 to 3.0 mMole per gram of powdered polyolefin. The van-adium component (1) is obtained by reacting the claimed initi~l materials with each other, at room temperature or above, in an inert liquid hydrocarbon such as a saturated, straight-chain or branched aliphatic or saturated alicyclic hydro-carbon, for example, n-hexane, 2-methyl-pentane, 3-methyl-pentane, cyclohexane, or mixtures thereof. Suitable alcoholates are those commercially available, and bearing straight-chain or branched radicals, preferably those with 2 to 4 carbon atoms in the alkyl radical. Ethanol, propanol-(l) or butanol-(l) in particular may be used as lower alcohols. In order to obtain catalysts according to the in-vention, which will produce powdered polymers wi~h high bulk-densities and out-standing flow-properties, it is necessary to maintain the claimed molar ratios in reacting the vanadium compounds. More particularly, reaction of the vanadium compound thus obtained with the alumino-organic compound is best carried out with 20 stirring, advantageous stirring-powers being between 0.1 and 20,000, preferably between 1 and 5000J watts/m3. In this case, the vanadium compound occurs as a solid; it may be separated from the hydrocarbon and dried under an inert gas, e.g. carefully cleaned nitrogen or argon. Suitable equipment for this, among others, is, above all~ rotary evaporators or fluidized-bed driers.
Suitable silica-xerogels ~2) according to the invention are preferably those having particle sizes d' (DIN 66 145) of about 50 ~0 150 ~m, specific sur-faces (DIN 66 131) of about 200 to 700 m2/g, and pore volumes of about 0.8 - -to about 1.7 ml/g. These data correspond, for example, to the following commer-cially available products: Ketjensilica~F5 (AKZ0), silicic acid K322 (DEGUSSA), or silica-gel grade 952 ~GRACE~. The silica-xerogels are preferably used with roasting losses of less than 1%. It is clesirable to dry silica-xerogel by roasting prior to use.
Silica-~erogel is preferably used in a weight ratio of between 2:1 and 4:1 in relation to the vanadium component, but lower or higher weight ratios may be used. Weight ratios lower than about 0.5:1 are no longer effective according to the invention, while ratios of above 10:1 result in polymers with an Imdesirably high ash-content.
The silica-xerogel of the vanadium component may be admixed after evaporation or concentration. This breaks up any lumps formed and produces a powder which flows. In many cases, however, it is advantageous to add the finely divided silica-xerogel, in the above-mentioned ratios, to the catalyst component containing vanadium suspended in hydrocarbon, before concentrating. This is a more reliable way of avoiding agglomerations or lumps.
The powdered vanadium component, mixed with silica-xerogel, is then mixed with the claimed, easily flowing ~3~ polyolefin in powder form. The polymer or copolymer which is to be produced is particularly suitable for this 2Q purpose.
The alumino-organic compound ~4) is added to the mixture of components (1), ~2~ and C3~. It is better, however, to incorporate the alumino-organic compound into the powdered polyolefin, before the latter comes into contact with the mixture of components (ll and ~2). The following are particularly suitable as alumino-organic compounds: aluminum-trialkyls, for example triiso-butyl-, tri-n-octyl-, tri-n-dodecyl-, tri-n-tetradecyl- or tri-n-hexadecyl-aluminum.
Also suitable are kno-~n products Qf the reaction between trialkyl-aluminum or .

' dialkyl-aluminum hydride and a 1,3-diolefin, pre~erably triisobutyl-aluminum or diisobutyl-aluminum hydride and isoprene, commercially available as "isoprenylaluminium".
Impregnation of the powdered polyolefin ~ith the alumino-organic component must naturally be carried out under a protective gas, nitrogen or argon, preferably in a ploughshare-mixer or a fluid-mixer.
Because of their satisfactory flow properties, the powdered catalyst mixtures produced according to the invention have outstanding handl-ing properties. For instance, transferring them rom storage containers to metering devices presents no problems and no interruptions. In polymerizing ethylene, or copolymerizing ethylene and propylene and/or butylene-(l), in the gaseous phase, the catalyst-mixtures according to the invention may be used, for example, in the kno~n equipment and processes described in German OS's 16 07 648 and 17 45 114; because of their advantageous properties, they may also be used in other existing equipment.
It is true that it is known from British Patent Application

2 010 870 A to use, in polymerizing ethylene under suspension or solution polymerization conditions~ Ziegler carrier-catalysts mixed with silica-xerogel.
This relates to meth~ds using liquid hydrocarbons as diluents, the purpose being to avoid blockages caused by unduly vigorous polymerization at the point ~here the catalyst enters the reactor. In contrast to this, the new method according to the invention achieves a totally different purpose, for which the said British patent application provides no teaching, namely uninterrupted trouble-free handling of a solid, dry, Ziegler catalyst in the equipment used in the production thereof, during transportation, and during metering into the polymerizing reactor. The new method according to the invention also makes it possible to overcome the above-mentioned disadvantages of "carriered"

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polymerizing catalysts and to produce polymer powders of outstanding quality.
Examples 1 to 8. Catalyst production.
182.8 g ~1.055 moles) of vanadyl~V)~chloride and 257.6 g (1.055 mole) of vanadyl(V)-n-propylate are stirred toge-ther in 1.66 L of a hexane section 63/80C for 1 hour at room temperature. This mixture, and a solution of 535.7 g (4.22 mole) of ethylaluminum-dichloride in 2.30 L of the hexane section 63/80C, are added synchronously, over a period of 2 hours, at 25C, to 2 L of the hexane section, stirring being carried out with a blade-agitator at a specific stirring-power of 1,000 watts/m3. The suspension thus ob~ained is then heated for twomore hours under reflux, stirring being continued at the same power. After cooling, the solid is separated, is washed five times, each time witll 5 L of the hexane section, after which it is suspended in 6 L of the said hexane section.
One part of the suspension is mixed with Ketjensilica F5 (AKZO) silica-xerogel~ previously roasted for 3 hours at 800C (roasting loss at l,000C for 1 hour = 0.7% by weight), the solid: silica-zerogel ratio being as 1:1, 1:2 and 1:4 (as shown in Table 1 - page 9 of the text). The hexane is then distilled in a rotary evaporator at 50C and 113 mbars, after which the residue is dried at 50C and 7 mbars until the weight remains constant.
Dry polyethylene powder is loaded into a ploughshare mixer adapted to 20 be heated and is dried for 5 hours at 50C and at a pressure of 10 mbars. Care-fully cleaned nitrogen is then allowed to flow into the mixer. Over a period of 2 hours, a solution of the above mentioned trialkyl-aluminum in hexane ~shown in Table 1) is dripped. The charge is then mixed for a further 3 hours.
The product, made from the vanadium component and the Ketjensilica F5, is then allowed to trickle into the prepared polyethylene-alkyl-aluminum ,~ ~

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mixture, and mixing is carr~ed out for 15 ~nutes.
Additional details of catalyst production ma~ be gathered from Table I

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-Examples l to 5. Polymerization.
Polymerization is carried out in a cylindrical, horizontally arranged steel autoclave with a capacity of 1.65 L, in which the polymer is kept in motion by rotating s-tirring elements fitted to a shaft (blades and displacing elements). Between 90 and 130 g of polyethylene powder are placed in the auto-clave, the said powder having been dried for ~hours at 50C and 67 mbars and rendered inert by stirring for 3 hours with 7 mMoles of tris-(n-dodecyl)-aluminum per 100 g of polyethylene. The relevant catalyst probe is then in-serted in the nitrogen co-mterflow. After 15 minutes stirring, Eor the purpose of distributing the catalyst in the prepared polyethylene, a hydrogen partial-pressure of 5 bars is established, the charge is heated to the polymerizing temperature of 80~C~ and ethylene is forced in slowly. Polymerizing is then carried out for 5 hours at a pressure of 33 bars. At the end of this time, polymerization is halted by relieving the pressure on the monomers. The relevant polymerization conditions and results appear in Table 2.

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1~ ~ydrogen partial~ressure 5 ~ars; total pressure 33 bars; 80C; 5h.
2~ by treatment ~ith 0,07 m~ol o~ tris-~n-dodec~ alumlnum.
(Example 2: a~o44 mMol) per g PE lnerted polyethylene.
3)~ polyethylene for~ed during polymerization.
) ~ulk-density ~DIN 53 4~): 0,330 g/cm ; ability to trickle ~DIN 53 492): VRlO = 2,4 cm /s; viscocity No . tDIN 53 728): 440 cm /g.
5) bulk-density: Q,370 g/cm3; ability to trickle: VR10 - 6~ cm3/s;
visco~ity No. 560 cm /g.
6) DIN 53 468.
7) DIN 53 492.
) DIN 53 728.
9) DIN 53 735.

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Examples 6 to 8.
Polymerization is carried out as in Exa~lples 1 to 5, but the selected amount of the relevant l-olefin is introduced into the autoclave before the ethylene is added.
The relevant polymerization conditions and results appear in Table 3.

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~ - 15 _ Comparison examples A and B
In contrast to the procedure in Examples 1 to 8, catalysts A and B
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are produced ~ithout the addition of ~e~ge~ i~a F5 (see Table 1). Under the same polymerization conditions as in Examples 1 to 5, no polyethylene is produced in Examples A and B ~see Table 2~.

Example 9.
In producing the catalyst, the procedure is as in Example 1, but tri-n-tetradecyl aluminum is used instead of tri-n-dodecyl aluminum. Polymerization is carried out as in Example 1. Polymerization condi-tions are as in Example 1.
Polymerization results may be gathered from Table 4.
Example 10.
In producing the catalyst, the procedure is as in Example 4. Instead of Ketjensilica F5, silicic acid K 322 (DEGUSSA) is introduced after heating Eor 3 hours at 800C. Polymerization is carried out as in Example 1. Polymerization conditions are as in Example 1. Polymerization results may be gathered from Table 4.
Example 11.
The catalyst is produced as in Example 4, except that Silica-Gel Grade 952 (GRACE) is used instead of Ketjensilica F5, also after heating for 3 hours at 800C. Polymerization is carried out as in Example 1. Polymerization conditions are as in Example 1. Polymerization results may be gathered from Table 4.
Example 12.
In producing the catalyst, 138.6 g ~0.8 mole) of vanadyl(V)-chloride and 293.0 g (1.2 mole) of vanadyl~V)-n-propylate are stirred together in 1.6 L
of a hexane section 63/80C for 1 hour at room temperature. This mixture, and a solution of 507.8 g ~4.0 mole~ of ethylaluminum-dichloride in 2.2 L of the hexane section 63/goQC, are added synchronously, over a period of 2 hours, at 25C, to 2 L of the hexane section, during stirring with a blade-stirrer at a specific stirring po~er of 1 QQ0 ~atts/m3. The suspension thus obtained is then heated for 2 more hours under reflux, using the same stirring power. After cooling, the solid is separated, ~ashed 5 times, each time ~i~h 5 L of ~he ^ ~

hexane section, and suspended in 6 L thereof. Catalyst production is then continucd as in Example 2 (see also Table 1). Polymerization is carried out as in Example 1. Polymerization conditions are as in Example 1. Polymerization results may be gathered from Table 4.
Example 13 In producing the catalyst, 2Q8.0 g (1.2 mole) of vanadyl(V)-chloride and 195.4 g (0.8 mole) of vanadyl(V)-n-propylate are stirred together in 1.6 L
of a hexane section 63/80~C, for 1 hour at room temperature. This mixture, and a solution of 5Q7.8 g (4.0 mole) of ethylaluminum-dichloride in 2.2 L of the hexane section 63/80C, are added synchronously over a period of 2 hours, at 25C, to 2 L of the hexane section, while stirring with a blade-stirrer, using a specific stirring power of 1 ~OQ watts/m3. The suspension thus obtained is then heated for 2 more hours under reflux, while being stirred at the same specific stirring power. After cooling, the solid is separated, washed Eive times, each time with 5 L oE the hexane section, and suspended in 6 L thereof.
The procedure is then as in Example 2. Polymerization is carried out as in Example 1. Polymerization conditions are as in Example 1. Polymerization results may be gathered from Table 4.
Example 14 In producing the catalyst, 183 g Cl.Q6 mole~ of vanadyl(V)-chloride and 258 g (1.06 mole) of vanadyl(Y)-n-propylate are stirred together with 1.77 L
of a hexane section 63t80C, for 1 hour, at room temperature. This mixture, and a solution of 620 g (4 mole~ of isobutylal~uninum-dichloride in 3.45 L of the hexane section 63/80C, are added synchronously, over a period 2 hours, to 2 L
of the hexane section, at 32 to 36C, while stirring with a blade stirrer at a specific stirring power of 78 watts/m3. The suspension thus obtained is then heated for 2 more hours, under reflux, ~hile being stirred at the same specific stirring power. After cooling, the ~ol~d is separated, ~ashed 5 tlmes, each time with 5 L of the hexane section and suspended in 6 L thereof. The procedure thereafter is as in Example 2. Polymerizatlon ~s as in Exanlple 1. Polymeriza-tion conditions are as in Example 1. Polymerization results may be gathered from Table 4.
Example 15.
In producing the catalyst, 122.3 g (705.7 m~lole) oE vanadyl(V)-chloride and 172.3 ~ (705.7 ~h~) of ~anadyl~V)-n-propylate are heated in 1.7 L
of a hexane section 63/80~C, under nitrogen, for 2 hours, at 55C. After cool-ing, at a temperature of between 20 and 25C, a solution of 340.3 g (2 822.6 m~i~
molo) of diethylaluminum-chloride in 1.43 L of the same hexane section is added over a period of 2 hours while stirring with a blade stirrer at a specific stir-ring power of 126 watts/m3. The suspension thus obtained is stirred for 2 more hours, at 55~C, using the same stirring power. After cooling, the solid is separated, washed 5 times, each time with 5 L of the hexane section and is suspended in 6 L thereof. Catalyst production is continued thereafter as des-cribed in Example 2. Polymerization is as in Example 1. Polymerization condi-tions are as in Example 1. Polymerization results may be gathered from Table 4.
xample 16.
In producing the catalyst, 346.6 g (2.0 mole~ o~ vanadyl~V)-chloride and 180.3 g (3.0 mole) of propanol-Cl) are heated with 1.59 L of a hexane sec-tion 63/80QC, for 2 hours, under reflux, whereby hydrogen-chloride escapes. Ihis mixture, and a solution of 507.8 g (~.0 mole~ of ethylaluminum-dichloride in 2~25 L of the hexane section 63/80C, are added synchronously, o~er a period of 2 hours, to 2 L of the hexane $ection, at 28C, under nitrogen~ and while stir-ring with a blade-stirrer at a specific stirring power of 95 watts/m3. The suspension thus obtained is then heated for 1 more hour, under reflux, and with ~L~a~

stirring at the same s.~t~rr~ng power. A~ter cool~n~, t~e sol~d ~.s separated, washed five times, each time ~ith 5 L o the he~ar.e section, and then suspended in 6 L thereof. Catalys* production then proceeds as in Example 2. Polymeri-zation is as in Example 1. Polymerization conditions are as in Example 1.
Polymeri~ation results ~ay be gat~.ered from Table 4.

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--.

Table 4 ~Cont'd.) ) hydrogen partial pressure: 5 bars; total pressure 33 bars; 80C, 5 h.
2) by treatment with 0,07 mMole o~ tris-(n-dodecyl)-aluminum per g PE
inerted polyethylene 3) polyethylene ~ormed during polymerization.

4) bulk-density (DIN 53 468): 0,330 g/cm3, ability to trickle ~DIN 53 492): VR10 = 2,4 cm3/s; viscosity No: (DIN 53 728): 440 cm3/g

5) bulk-density (DIN 53 468): 0,370 g/cm3; ability to trickle (DIN 53 492): VR10 = 6,6 cm3/s; viscosity No. (DIN 53 728): 560 cm3/g.
) DIN 53 468 ) DIN 53 492 ) DIN 53 728 ) DIN 53 735

Claims (6)

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

1. A method for producing polyolefins in the form of powders, which pro-cess comprises polymerizing ethylene or copolymerizing ethylene and propylene and/or butylene-(1) in the gaseous phase, under a pressure of 10 to 100 bars at a temperature of about 50 to about 110°C, if necessary in the presence of hydrogen, the reaction being carried out in the presence of a catalyst comprising a mixture of:
(1) a vanadium component obtained by reacting (a) a mixture of vanadyl(V)-chloride and vanadyl(V)-alcoholate in a molar ratio of 1:2 to 2:1, or a reaction product of vanadyl(V)-chloride with a lower alcohol in a molar ratio of 1:2 to 1:1, with (b) ethylaluminum dichloride, diethylaluminum chloride, isobutyl-aluminum dichloride and/or diisobutylaluminum chloride in a molar ratio V:A1 of 1:3 to 1:1, in an inert solvent, with stirring at a specific stirring power of 0.1 to 20 000 watts/m3, and separating the solid thus obtained;
(2) a finely divided silica xerogel in a weight ratio of from 0.5:1 to 10:1 based on the vanadium component;
(3) a polyolefin in powder form possessing trickling ability, having an average particle diameter up to 1 000 µm and being practically free from very fine grained material, in an amount of from 0.5 to 3.0 grams per milligram of the vanadium component, calculated as vanadium pentoxide; and (4) an alumino-organic compound of the general formula RnA1Xx-n, wherein R
signifies a saturated hydrocarbon radical with 2 to 20 carbon atoms, X signifies a halogen atom, and n is a number from 1 to 3, or a product of the reaction between trialkyl aluminum or dialkyl aluminum-hydride and a 1.3 diolefin, in an amount of from 0.1 to 3.0 mMole per gram of powdered polyolefin.

2. A method for producing catalysts for the polymerization according to claim 1, wherein component (2) is added to suspended component (1).

3. A method according to claim 1 or 2, wherein component (4) is added to component (3) before this mixture is combined with the mixture of components (1) and (2).

4. A method according to claim 1 wherein the polymerization or copolymer-ization is carried out at a pressure of 25 to 50 bars.

5. A method according to claim 1 wherein the specific stirring power is from 1 to 5 000 watts/m3.

6. A catalyst for use in producing polyolefins in the form of powders by polymerizing ethylene or copolymerizing ethylene and propylene and/or butylene-(1) in the gaseous phase, under a pressure of 10 to 100 bars at a temperature of about 50 to about 110°C, which catalyst comprises a mixture of:
(1) a vanadium component obtained by reacting (a) a mixture of vanadyl(V)-chloride and vanadyl(V)-alcoholate in a molar ratio of 1:2 to 2:1, or a reaction product of vanadyl(V)-chloride with a lower alcohol in a molar ratio of 1:2 to 1:1, with (b) ethylaluminum dichloride, diethylaluminum chloride, isobutyl-aluminum dichloride and/or diisobutylaluminum chloride in a molar ratio V:A1 of 1:3 to 1:1, in an inert solvent, with stirring at a specific stirring power of 0.1 to 20 000 watts/m3 and separating the solid thus obtained;
(2) a finely divided silica xerogel in a weight ratio of from 0.5:1 to 10:1 based on the vanadium component;
(3) a polyolefin in powder form possessing a trickling ability, having an average particle diameter up to 1 000 µm and being practically free from very fine grained material, in an amount of from 0.5 to 3.0 grams per milligram of the vanadium component, calculated as vanadium pentoxide; and (4) an alumino-organic compound of the general formula RnA1X3-n, wherein R signifies a saturated hydrocarbon radical with 2 to 20 carbon atoms, X signifies a halogen atom, and n is a number from 1 to 3, or a product of the reaction between trialkyl aluminum or dialkyl aluminum-hydride and a 1.3 diolefin, in an amount of from 0.1 to 3.0 mMole per gram of powdered polyolefin.