CH619241A5 - Catalyst system for olefin polymerisation, process for preparing the system and its use - Google Patents

Abstract

The catalyst system for stereospecific polymerisation of alpha-olefins comprises an organometallic activator and particles of titanium trichlorides. The particles are dried until their liquid content is lower than 0.5 % by weight of TiCL3 which they contain; they are preferably spherical and consist of an agglomerate of porous microspheres. The dried particles exhibit a catalyst activity which is superior to that of the particles which have a higher liquid content and result in polymers with excellent morphology.

Description

The present invention relates to a catalytic system which can be used for the polymerization of olefins, a process for preparing this system, and its use for the stereospecific polymerization of alpha-olefins.

It is known to stereospecifically polymerize alpha-olefins such as propylene by means of a catalytic system comprising a titanium trichloride in the form of solid particles and an activator consisting of an organometallic compound such as diethylaluminum chloride.

In Belgian patent 780 758, the holder described particles of titanium trichlorides whose use in the polymerization of alpha-olefins is particularly advantageous. These particles are characterized by their particular structure. They are in fact made up of an agglomerate of microparticles which are themselves extremely porous. As a result, these particles have a particularly high specific surface and porosity.

This particular structure leads, in polymerization, to exceptional performance. Due to the porosity of the particles, the catalytic activity is so high that the polymerization can be carried out under conditions such that the catalytic residues are so low that they no longer have to be removed. We can therefore do without the conventional alcohol treatment of the polymers obtained. In addition, since these particles have the form of large regular spheres, the polymer obtained is also in the form of regular spherical particles. As a result, it has a high specific gravity and has very good flowability.

Finally, when these particles are prepared according to the particular procedure also described in the aforementioned Belgian patent of the Applicant, the polymers obtained have very good stereoregularity and contain only a very small proportion of amorphous polymer. For the vast majority of applications, they can be implemented as they are, without the conventional purification of the amorphous fraction by washing with a hot solvent.

However, the particles of titanium trichlorides prepared according to the procedure described in the aforementioned Belgian patent have a serious drawback. Indeed, it has been found that, when they are used in the polymerization of propylene at a relatively high temperature (of the order of 70 ° C.), the polymer obtained is no longer an enlarged replica of the starting particles and occurs in a degraded form from the point of view of morphology: there are many fine particles, the shape of the particles is irregular and the apparent specific gravity is low. However, it is very advantageous to carry out the polymerization at a relatively high temperature in order to optimize the productivity of the polymerization installations.

Particles of titanium trichlorides have now been found which have all the advantages of the particles prepared in accordance with the aforementioned Belgian patent and which, moreover, no longer have the disadvantage of giving polymer of poor morphology when the polymerization temperature is relatively high. .

The present invention therefore relates to a catalytic system for the polymerization of olefins, comprising an organometallic compound of metals from groups la, IIa, üb or Dlb of the Periodic Table and particles of titanium trichloride, associated with a liquid, characterized in that these particles of titanium trichloride contain less than 1% of liquid relative to the weight of titanium trichloride present in the particles.

The licensee has found that when the particles are dried until the liquid content is below the limit specified above, there is a phenomenon of hardening or quenching. When the drying is carried out under conditions which do not lead to such low liquid contents, the drawback mentioned above is observed during the polymerization at relatively high temperature. On the other hand, when the drying is carried out so as to obtain the above-mentioned liquid content, the dried particles have the same catalytic activity, or even an activity slightly higher than that of the particles having a higher liquid content and lead to excel polymers

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slow morphology even when polymerizing at relatively high temperature.

Preferably, the particles are dried until their liquid content is less than 0.5%. The best results are obtained when the liquid content of the dried particles is less than 0.3%. It is generally pointless to continue drying when the liquid content of the particles reaches 0.01% because there is no longer any significant improvement in their properties.

The titanium trichloride particles of the catalytic system according to the invention can be associated, before drying, with any compound, or mixture of compounds, which is liquid under normal conditions of temperature and pressure. This compound can for example be titanium tetrachloride which was used for the preparation of trichloride or else a Lewis acid or base used to treat trichloride. However, it is preferred that the liquid associated with the particles of titanium trichlorides subjected to drying is chosen from aliphatic, cycloaliphatic, aromatic hydrocarbons and their mixtures which are liquid under normal conditions of temperature and pressure. The best results are obtained with aliphatic and cycloaliphatic hydrocarbons comprising from 3 to 12 carbon atoms, technical grade hexane being the most commonly used. Other examples of preferred hydrocarbons are pentane, heptane, octane, cyclohexane, benzene, toluene and xylenes.

The titanium trichloride particles subjected to drying are generally associated with at least 1% of liquid counted by weight of liquid relative to the weight of titanium trichloride (TiCb) present in the particles. Preferably, the amount of liquid is at least 2%. The best results are obtained when it is at least 5%.

The preferred operating conditions under which the titanium trichloride particles are dried are specified below. It has been found that the choice of these operating conditions can contribute to reinforcing the hardening phenomenon mentioned above and therefore to give the polymer an even improved morphology.

The drying temperature is below 90 ° C. Drying carried out at a temperature above 90 ° C in fact leads to particles whose polymerization activity is lower than that observed with particles dried at lower temperatures. In addition, drying temperatures below 20 ° C are impractical because they excessively lengthen the drying time.

Preferably, the particles are dried at a temperature between 50 and 80 ° C. The best results are obtained when the temperature is between 60 and 75 ° C.

The drying time depends not only on the temperature but also on many other operating conditions. In any case, the drying is continued until the liquid content of the particles is less than the limit mentioned above. The liquid content of the particles can be determined by difference by heating a sample of the particles at high temperature, for example, until their weight remains constant. The drying time is between 15 minutes and 48 hours and preferably between 30 minutes and 6 hours. All other conditions remaining identical, the drying time is generally shorter the higher the temperature.

The pressure under which the particles are maintained during drying is not critical as long as it is lower than the saturation pressure of the liquid associated with the particles. In general, one operates at atmospheric pressure or at reduced pressure. It may be advantageous to operate at reduced pressure (of the order of the Torr fraction), when the drying temperature is low, close to room temperature for example, in order to accelerate the elimination of the excess liquid.

The particles can be dried under sweeping using an inert gas. To do this, nitrogen is preferably chosen. This inert gas must be purified of any substance capable of inhibiting the catalytic properties of titanium trichloride such as carbon monoxide and oxygen. The inert gas can be heated to provide all or part of the calories required for drying.

The drying of the titanium trichloride particles according to the invention can be carried out in any apparatus suitable for this operation, and for example in movable bed dryers such as trays dryers, rotary drum, pneumatic, of the type tunnel, etc. It is also possible to use dryers with a fixed bed traversed by an inert gas. However, it is preferred to carry out drying in a fluid bed. In this case, the fluidizing gas is an inert gas as defined above. Finally, the drying can be carried out continuously or batchwise.

The particles subjected to drying can be used in the form of a more or less concentrated suspension in the liquid with which they are associated. In this case, at the start of drying, the liquid forming the liquid phase of the suspension is first evaporated before the actual drying begins. Thus it is possible to inject the particles in suspension in a liquid hydrocarbon in a fluid bed.

However, for reasons of economy, it is preferred that the particles are not associated with too large a quantity of liquid, the evaporation of which would require too many calories. Preferably, the amount of liquid associated with the particles does not exceed that which the particles are capable of absorbing while remaining pulverulent and without the formation of a continuous liquid phase. When particles are available in the form of a suspension, it is therefore advantageous, before drying, to get rid of the excess liquid phase, for example by filtration, centrifugation or siphoning.

The particles of titanium trichlorides used as starting materials for preparing the dried particles according to the present invention can be obtained by any method. Thus they can be prepared from a solid complex based on titanium dichloride by oxidoreduction with the intervention of titanium tetrachloride; these dichloride-based complexes are prepared by reduction of tetrachloride using aluminum in a benzene medium.

However, it is preferred to use particles obtained by reduction of titanium tetrachloride. This reduction can be carried out using hydrogen or metals such as magnesium and preferably aluminum. The best results are obtained from particles formed by reduction of titanium tetrachloride with an organometallic compound. This may for example be an organomagnesium compound. However, the best results are obtained with organoaluminum compounds.

The organoaluminum compounds which can preferably be used are those which contain at least one hydrocarbon-based radical attached directly to the aluminum atom. Examples of compounds of this type are mono-, di- and trialkylaluminiums whose alkyl radicals contain from 1 to 12 and preferably from 1 to 6 carbon atoms, such as triethylaluminium, isoprenylaluminiums, diisobutylaluminium hydride and ethoxydiethylaluminum. With compounds of this type, the best results are obtained with dialkyl aluminum chlorides and, in particular, with diethylalumi-nium chloride.

The reduction of titanium tetrachloride by means of an organoaluminum compound can advantageously be carried out under the operating conditions described in Belgian patent 780,758 of the holder. Usually the method of

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preparation involves the use, in particular for washes, of an organic diluent of the same species as the liquids preferred to be associated with the particles of titanium trichlorides subjected to drying in accordance with the present invention which have been defined above. The particles obtained therefore contain such a liquid after their preparation.

Particles of titanium trichlorides which are particularly suitable for being dried in accordance with the present invention are those which are described in Belgian patent 780,758 of the holder. These particles which are spherical generally have a diameter of between 5 and 100 microns and most often between 15 and 50 microns. They consist of an agglomerate of equally spherical microparticles which have a diameter between 0.05 and 1 micron and most often between 0.1 and 0.3 micron. As said, these particles have a particular morphology in the sense that the microparticles are extremely porous. As a result, the particles have a specific surface, measured by the B.E.T. based on nitrogen adsorption, greater than 75 m2 / g and most often between 100 and 250 m2 / g. At the same time, the particles have an internal pore volume greater than 0.15 cm3 / g and most of the time between 0.20 and 0.35 cm3 / g. The internal porosity of the particles can be measured by combining the nitrogen adsorption method with that by mercury penetration. The porosity of the microparticles is attested by the high value of the pore volume measured on the particles and corresponding to the pores of less than 200 Å in diameter. This pore volume is greater than 0.11 cm3 / g and most of the time it is between 0.19 and 0.31 cm3 / g. The apparent specific weight (measured by compaction) of these particles is usually between 0.6 and 1.2 kg / dm3.

The licensee also described in Belgian patent 780 758 a particular method for preparing the particles defined in the preceding paragraph. This method involves the reduction of titanium tetrachloride by means of a reducing agent, which is preferably a dialkylaluminum chloride whose alkyl chains contain from 2 to 6 carbon atoms, under mild conditions. Thereafter, a treatment is carried out by means of a complexing agent which is preferably chosen from organic compounds comprising one or more atoms or groups having one or more pairs of free electrons capable of ensuring coordination with the atoms of titanium or d aluminum present in titanium or aluminum halides. The preferred complexing agents are aliphatic ethers, the aliphatic radicals of which comprise from 4 to 6 carbon atoms. Finally, a treatment is carried out using titanium tetrachloride and the particles are washed using diluents such as those defined above.

The particles prepared according to this procedure by choosing the preferred conditions correspond to the formula TiCb. (AIRCl2) x.Qy where R is an alkyl radical comprising from 2 to 6 carbon atoms, Q is a complexing agent as defined above, x is any number less than 0.20 and y is any number greater than 0.009 and generally less than 0.20.

As a variant of the operating method described above, it is also possible to carry out only the treatment by means of the complexing agent or only that using the tetrachloride or else to carry out both simultaneously. It is also possible to replace the titanium tetrachloride with a chemical equivalent such as vanadium, silicon or carbon tetrachlorides. However, the results obtained according to these variants are less advantageous than those obtained with the method described in the aforementioned Belgian patent. In fact, these variants do not generally lead to particles having as regular a morphology or an internal porosity as high as the preferred operating mode. As a result, the catalytic activity of these particles is less

high and the morphology of the polymer obtained less good. In addition, these variants lead to trichlorides containing relatively large amounts of aluminum chlorides. As a result, the particles lead to less stereospecific catalysts.

The particles of titanium trichlorides subjected to drying do not consist exclusively of the compound of chemical formula TiCb. In general, this compound is combined in the form of a solid solution, co-crystallized or complexed with other compounds generally originating from the preparation of trichloride. In general, these other compounds cannot be removed by washing with hydrocarbons which are preferably associated with the particles subjected to drying. In most cases, the particles contain at least 50% by weight of TiCb relative to the total dry weight. Preferably, they contain at least 65% thereof. The most favorable results are obtained when they contain at least 80%.

Certain methods of preparing titanium trichloride particles lead to perfectly dry particles. These particles can nevertheless be dried in accordance with the invention after having been impregnated beforehand with a suitable liquid and, preferably, the hydrocarbons described above.

The particles obtained are not generally distinguished from the point of view of their structure, from the particles used to prepare them. Thus, when they are prepared from spherical particles consisting of an agglomerate of extremely porous spherical microparticles, they have substantially the same structure, the same dimensions and the same shapes as the starting particles. As a result, they are also characterized by the same high specific surface associated with the same high pore volume. All that has been said in connection with these starting particles is valid for the particles according to the invention to which they lead.

Likewise, the titanium trichloride particles according to the invention contain at least 50% by weight of TiCb relative to the total dry weight. Preferably, they contain at least 65% thereof. The most favorable results are obtained when they contain at least 80%.

After having been dried, and preferably after their temperature has dropped below 30 ° C., the particles according to the invention can be immediately brought back into contact with a liquid and in particular with a hydrocarbon such as those which are associated with preferably before drying and which can also be used as diluents in suspension polymerization. The particles according to the invention can also be subjected to a preactivation and optionally prepolymerization treatment as described in Belgian patent 803,875 filed on August 22, 1973 by the Applicant, and stored under hexane for long periods without losing their qualities.

For the polymerization, the titanium trichloride particles according to the invention are used together with an activator selected from the organometallic compounds of metals from groups la, IIa, üb and mb of the Periodic Table and preferably from the compounds of formula AlR 'mX3-m where

- R 'is a hydrocarbon radical containing from 1 to 18 carbon atoms and preferably from 1 to 12 carbon atoms chosen from alkyl, aryl, arylalkyl, alkylaryl and cycloalkyl radicals; the best results are obtained when R 'is chosen from alkyl radicals containing from 2 to 6 carbon atoms

- X is a halogen chosen from fluorine, chlorine, bromine and iodine; the best results are obtained when X is chlorine

- m is any number such that 0 <mä = 3 and prefe5

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rence such as 1,5âmâ2,5; the best results are obtained when m is equal to 2.

Diethylaluminum chloride (AlEt2Cl) ensures maximum activity and stereospecificity of the catalytic system.

The catalytic systems thus defined apply to the polymerization of olefins with terminal unsaturation, the molecule of which preferably contains 2 to 18 and in particular 2 to 6 carbon atoms such as ethylene, propylene, butene-1, pentene -1, methylbutene, hexene-1, 3- and 4-methylpentenes-1 and vinylcyclohexene. They are particularly advantageous for the stereospecific polymerization of propylene, butene-1 and 4-methylpentene-1 into crystalline, highly isotactic polymers. They also apply to the copolymerization of these alpha-olefins together as well as with diolefins comprising from 4 to 18 carbon atoms. Preferably, the diolefins are unconjugated aliphatic diolefins such as 1,4-hexadiene, unconjugated monocyclic diolefins such as 4-vinylcyclohe-xene, alicyclic diolefins having an endocyclic bridge such as dicyclopentadiene, methylene- and ethylene-norbornene and conjugated aliphatic diolefins such as butadiene or isoprene.

They also apply to the manufacture of so-called block copolymers which are made from alpha-olefins and diolefins. These block copolymers consist of successions of chain segments with variable lengths; each segment consists of a homopolymer of an alpha-olefin or of a random copolymer comprising an alpha-olefin and at least one comonomer chosen from alpha-olefins and diolefins. The alpha-olefins and the diolefins are chosen from those mentioned above.

The titanium trichloride particles are particularly suitable for the manufacture of propylene homopolymers and of copolymers containing in total at least 50% by weight of propylene and preferably 75% by weight of propylene.

The polymerization can be carried out by any known process: in solution or in suspension in a hydrocarbon solvent or diluent which is preferably chosen from aliphatic or cycloaliphatic hydrocarbons such as butane, pentane, hexane, heptane, cyclohexane, methylcyclohexane or mixtures thereof. It is also possible to carry out the polymerization in the monomer or one of the monomers maintained in the liquid state or even in the gas phase.

The polymerization temperature is generally chosen between 20 and 200 ° C and preferably when operating in suspension, between 50 and 80 ° C, the best results being obtained between 65 and 75 ° C. The pressure is generally chosen between atmospheric pressure and 50 atmospheres and preferably between 10 and 30 atmospheres. This pressure is of course a function of the temperature used.

The polymerization can be carried out continuously or batchwise.

The preparation of so-called block copolymers can also be done according to known methods. It is preferred to use a two-step process consisting in polymerizing an alpha-olefin, generally propylene, according to the method described above for the homopolymerization. Then, the other alpha-olefin and / or diolefin, generally ethylene, is poly-merized in the presence of the homopolymer chain which is still active. This second polymerization can be carried out after completely or partially removing the unreacted monomer during the first step.

The organometallic compound and the particles can be added separately to the polymerization medium. They can also be brought into contact, at a temperature between -40 and 80 ° C, for a period of up to 2 hours before introducing them into the polymerization reactor.

The total amount of organometallic compound used is not critical; it is generally greater than 0.1 xmol per liter of diluent, of liquid monomer or of reactor volume, preferably greater than 1 mmol per liter.

The amount of particles used is determined according to their TiCb content. It is generally chosen so that the concentration of the polymerization medium is greater than 0.01 mmol of TiCb per liter of diluent, of liquid monomer or of reactor volume and preferably greater than 0.2 mmol per liter.

The ratio of the amounts of organometallic compound and particles is also not critical. It is generally chosen so that the molar ratio of organometallic compound / TiCb present in the particles is between 0.5 and 20 and preferably between 1 and 15. The best results are obtained when the molar ratio is between 2 and 10.

The molecular weight of the polymers produced according to the use of the invention can be adjusted by adding to the polymerization medium one or more molecular weight adjusting agents such as hydrogen, diethylzinc, alcohols, ethers and alkyl halides.

It is also possible to add, to the polymerization medium, a complexing agent of the same type as the agents which can be used in the preparation of the particles according to the method described in Belgian patent 780,758.

The stereospecificity and the activity of the particles of the catalytic system according to the invention are at least as high and often higher than those of the catalytic complexes described in Belgian patent 780,758, when they are prepared from the latter. Thus, during the homopolymerization of propylene, the proportion of amorphous polypropylene, evaluated by measuring the weight of polypropylene soluble in the inert polymerization and washing solvent relative to the total polypropylene produced during the polymerization is almost always less than 3%. As for the activity, expressed in g of insoluble polypropylene per hour and per g of TiCb contained in the particles, it easily reaches 2500 g of insoluble polypropylene, when the homopolymerization is carried out at around 70 ° C in suspension in hexane .

Finally, the particles make it possible, surprisingly, to obtain polymers of slightly higher specific gravities, all other conditions equal, than those of the polymers obtained by the intervention of catalytic complexes which have not been dried according to the invention. These very high apparent specific weights are advantageous from the point of view of the size reductions of the polymerization installations and of the storage areas which they allow. In addition, the very tight particle size distribution of the polymer powders and the very high average diameter of the particles, combined with this high apparent specific weight facilitates to an appreciable extent the polymer drying operations and its subsequent implementation by current methods of molding.

The following examples serve to illustrate the invention without limiting its scope.

Example 1

A - Preparation of the starting particles

120 ml of dry hexane and 30 ml of pure TiCU are introduced into a 500 ml reactor equipped with a paddle agitator rotating at 140 rpm. This hexane-TiCk solution is cooled to 1 (± 1) ° C. Within 4.5 h s

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a solution consisting of 90 ml of hexane and 34.2 ml of AlEt2Cl is added thereto while maintaining the temperature of 1 (± 1) ° C in the reactor.

After addition of the AeteCl-hexane solution, the reaction medium consisting of a suspension of fine particles is kept stirring at 1 (± 1) ° C for 15 min, then is brought to 1 ° at 23 ° C and maintained for 1 h at this temperature and then brought to 65 ° C. in approximately 1 hour. The medium is kept stirring for 2 h at 65 "C.

The liquid phase is then separated from the solid by filtration and the solid product, called "reduced solid" is washed 5 times with 100 ml of dry hexane, with resuspension of the solid during each washing.

The “reduced solid” is suspended in 300 ml of diluent (hexane) and 48.5 ml of di-isoamyl ether (EDIA) are added thereto. The suspension is stirred for 1 h at 35 ° C. Then, the solid obtained called “treated solid” is separated from the liquid phase.

The “treated solid” is suspended in an amount of 47 g in 95 ml of hexane and 25 ml of TiCk contained in a 500 ml glass reactor with three tubes, equipped with a double envelope for the circulation of water. , a sintered plate, a side tube for filtration and a two-blade stirrer, and the suspension is kept under stirring at 70 ° C for 2 h. The liquid phase is then removed by filtration and the solid obtained is washed 4 times with 100 ml of hexane at 70 ° C.

B - drying

The drying of the washed solid is carried out on the cake originating from the last washing with hexane and containing approximately 200 ml of hexane / kg, by means of a stream of nitrogen sent to the base of the reactor with a flow rate of 3001 / h and distributed through the sintered plate at a temperature of approximately 25 ° C. The temperature of the jacket is around 70 ° C. After 10 minutes, the particles are observed to fluidize.

The drying of the particles is then continued for 4 hours at 70 ° C., with the same nitrogen flow rate. At the end of the treatment, a solid is obtained containing 861 g Ti Cb, 6.9 g of aluminum, 106 g of EDIA and 1.9 g of hexane per kg.

C - Polymerization of propylene using dried particles

Into a 5 liter autoclave made of stainless steel and purged several times with nitrogen, 1 liter of dry and purified hexane is introduced. 240 mg of AlEt2Cl are then successively introduced (in the form of a solution in hexane at 200 g / l) and 58 mg of dried particles, ie approximately 50 mg of TiCb. The AlEt2Cl / TiCb molar ratio is then about 6.2.

The autoclave is heated to 70 ° C. and is returned to atmospheric pressure by slow degassing. Then, an absolute hydrogen pressure of 0.20 kg / cm2 is produced there; then propylene is introduced into the autoclave until a total pressure at the considered temperature of 12.7 kg / cm 2 is reached. This pressure is kept constant during the polymerization by the introduction of propylene gas.

After 3 h, the polymerization is stopped by degassing the propylene.

The contents of the autoclave are poured onto a Büchner filter, rinsed three times with 0.51 of hexane and dried under reduced pressure at 50 ° C. 296 g of polypropylene (PP) insoluble in hexane are collected.

In the polymerization and washing hexane, 12.4 g of soluble polymer are found, which corresponds to 4.2%.

The catalytic activity is therefore 1978 g of polypropylene / hxg TiCb and the productivity of 5103 g of polypropylene / g of particles.

The apparent specific weight (PSA) of the insoluble polypropylene fraction is 0.424 kg / dm3. This polypropylene is in the form of regular and smooth grains of very tight grain size.

Example 2

Dried particles are prepared in the same manner as in Example 1 with the same nitrogen flow rate but for 3 hours at 90 ° C.

The solid obtained contains 841 g of TiCb, 2.7 g of aluminum, 43 g of EDIA and approximately 0.1 g of hexane per kg.

A propylene polymerization test, carried out under the same conditions as in Example 1 but with 105 mg of particles dried at 90 ° C. allows 405 g of polypropylene insoluble in hexane to be obtained.

In the polymerization and washing hexane, 5.3 g of soluble polymer are found, ie 1.3%.

The catalytic activity is therefore 1531 g of polypropylene / hxg TiCb and the productivity of 3850 g of polypropylene / g of particles.

The PSA of the insoluble polypropylene fraction is 0.443 kg / dm3.

Example 3

Test a)

Particles prepared as in Example 1 (A) are dried under a vacuum of 2 Torr for 90 minutes at 25 ° C.

The solid obtained contains 815 g of TiCb, 108 g of EDIA, 6.7 g of aluminum and about 7.9 g of hexane per kg.

A propylene polymerization test is carried out under the general conditions described in Example 1 (C), the specific conditions being as follows:

- quantity of dried particles used: 73 mg (i.e. approximately 59 mg of TiCb)

- AlEy2Q / TiCb molar ratio: 5.2.

368 g of PP insoluble in hexane are collected.

In the polymerization and washing hexane, 28.3 g of soluble polymer are found, ie 7.7%.

The catalytic activity is therefore 2065 g PP / hxg TiCb and the productivity is 5048 g PP / g of particles.

The PSA of the insoluble polypropylene fraction is 0.322 kg / dm3.

There is therefore a decrease in PSA which occurs when the liquid content of the dried particles is relatively higher.

Trial b)

Additional drying of these particles under a higher vacuum (0.1 Torr) for 2 hours at 25 ° C leads to particles whose hexane content is no more than 0.3 g / kg.

A new polymerization test carried out with the latter (AlEt2d / TiCb molar ratio) under the conditions of Example 1 (C) makes it possible to obtain 360 g of PP insoluble in hexane (4.8% of soluble polymer only) .

The catalytic activity is 2131 g PP / hxg TiCb and the productivity is 5210 g PP / g of particles.

The PSA of the fraction of insoluble polypropylene is 0.404 kg / dm3, that is to say much higher than that of the polypropylene obtained in the presence of the particles of Test a).

Example 4R

This example is given for comparison.

Particles are prepared in accordance with Example 1 (A). However, the drying indicated in Example 1 (B) is not carried out, but only the cake from the last washing with hexane is wrung until the flowability of the solid is sufficient and its content is hexane is reduced to 40 g / kg.

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The PSA of the fraction of polypropylene insoluble in the grain morphology of this polymer is very poor,

the hexane collected after a polymerization test carried out with the grains being split up to their core.

as shown in Example 1 (C) is only 0.287 kg / dm3.

B

Claims (11)

619,241 1. Catalytic system for the polymerization of olefins, comprising an organometallic compound of metals from groups la, Da, IIb or ülb of the Periodic Table and particles of titanium trichloride, associated with a liquid, characterized in that these particles of titanium trichloride contain less than 1% liquid based on the weight of titanium trichloride present in the particles. 2. Catalytic system according to claim 1, characterized in that the liquid content of the titanium trichloride particles is less than 0.5%, preferably less than 0.3% by weight. 2 3. Catalytic system according to claim 1, characterized in that the liquid is an aliphatic, cycloali-phatic, aromatic hydrocarbon or a mixture of these liquids. 4. Catalytic system according to the file of claims 1 to 3, characterized in that the particles are spherical in shape and consist of an agglomerate of microparticles which are themselves spherical and porous. 5. Catalytic system according to claim 4, characterized in that the specific surface of the particles is greater than 75 m2 / g and their internal pore volume greater than 0.15 cm3 / g. 6. Catalytic system according to claim 4 or 5, characterized in that the chemical composition of the particles corresponds to the formula TiCb • (AlRCk) x • Qy where R is a C2 to Câ alkyl radical, Q is a complexing agent chosen from organic compounds comprising at least one atom or group having at least one pair of free electrons capable of ensuring coordination with titanium and aluminum, x is a number less than 0.20 and y is a number greater than 0.009. 7. Process for the preparation of a catalytic system according to claim 1, characterized in that particles of titanium trichloride associated with a liquid are dried, for a period of between 15 minutes and 48 hours, at a temperature below 90 ° C, up to a liquid content of less than 0.5% by weight relative to the weight of titanium trichloride present in the particles. 8. Method according to claim 7, characterized in that particles of titanium trichloride obtained by reduction of titanium tetrachloride are dried by means of an organoaluminum compound. 9. Method according to claim 8, characterized in that the particles obtained by reduction of titanium tetrachloride were then treated with a complexing agent. 10. Method according to claim 9, characterized in that the particles treated with the complexing agent were then treated with titanium tetrachloride. 11. Use of the catalytic system according to claim 1 for the stereospecific polymerization of α-olefins.