IE43435B1 - Process for the preparation of a particulate material comprising titanium trichloride suitable for use in the stereopecific polymerisation of alpha-olefins - Google Patents

Abstract

1518058 Titanium trichloride SOLVAY & CIE 11 Oct 1976 [15 Oct 1975] 42129/76 Heading C1A [Also in Division C3] Particles of TiCl 3 associated with a liquid other than water are dried to a liquid content less than 1% by weight, preferably less than 0À3%, the particles being of substantially spherical shape and comprising an agglomerate of smaller particles which are spherical and porous. The liquid associated with the particles may be an aliphatic, cyclo aliphatic or aromatic hydrocarbon, TiCl 4 , Lewis acid or Lewis base used to treat the trichloride. The starting material preferably contains at least 5% of the liquid. Drying is preferably carried out at below 90‹C for 0À2-48 hours at atmospheric or reduced pressure. Drying may be performed under a stream of inert gas in any appropriate apparatus but preferably in a fluidized bed. The spheres suitably have a diameter of 5-100 microns and the diameter of the smaller particles is typically 0À05-1 micron. Such particles suitably have a composition of TiCl 3 .(AlRCl 2 ) x .C y where R is 2-6 C alkyl, C is a complexing agent comprising one or more organic compounds which contain at least one atom or group possessing at least one electron pair capable of forming a coordination bond with Ti and Al; x is less than 0À2 and y is greater than 0À009. Such particles typically have an apparent specific gravity of 0À6-1À2 kg/dm3, a surface area greater than 75 m2/g and an internal pore volume greater than 0À15 cm3/g.

Description

The present invention relates to a process for the preparation of a narticulate material comprising titanium trichloride, suitable for use in the stereospecific polymerisation of alpha-olefins, a material prepared by this process, and a process for the polymerisation of alpha-olefins employing this material.

It is known to polymerise alpha-olefins (e.g. propylene) stereOspecifically by means of a catalyst system comprising a titanium trichloride in the form of solid particles and an activator consisting of an organometallic compound (e.g. di ethyl-aluminium chloride).

In our Belgian Patent Specification No. 780,758, we have described partis of titanium trichloride which it is particularly advantageous to use in the polymerisation of alpha-olefins. These particles are characterised by a narticular structure; they consist in fact of an agglomerate of microparticles, i.e. smaller particles, which are themselves extremely porous. The particles in question therefore have a particularly high specific surface area and a particularly high porosity.

This agglomerated-microparticle structure gives the particles an exceptional performance in polymerisation processes. Because of the porosity of the particles, the catalytic activity is so high that the polymerisation can be carried out under conditions which give a polymerised product whose catalyst residue content is negligible. By this we mean that the catalyst residues are so slight -2<13 4 3 5 that they need not be removed. It is thus possihle to omit the familiar treatment of the polymerised product with alcohol. Furthermore, inasmuch as particles in question have the shape of large regular spheres, the polymer obtained is also in the form of regular spherical particles. Consequently, it has a high apparent specific gravity and possesses very good pourability.

Moreover, when the particles referred to are prepared by the particular method which is also described in our above-mentioned Belgian Patent Specification, the polymers obtained exhibit very good stereo-regularity and comprise only a very small proportion of amorphous polymer. For the great majority of applications, therefore, the polymers can be used as they are, without washing with a hot solvent to remove the amorphous fraction.

However, the particles of titanium trichloride prepared by the method described in our above-mentioned Belgian Patent Specification are liable to suffer from the disadvantage that, if they are used for the polymerisation of propylene (for instance) at a high temperature (of the order of 70°C), the polymer obtained is no longer an enlarged replica of the starting particles, but is in a degraded form, from a morphological point of view; thus there are numerous fine particles, the shape of the particles is irregular, and the apparent snecific gravity is low.

This disadvantage tends to neutralise the advantage of carryinn out the polymerisation at a high temperature to optimise the productivity of the polymerisation equipment.

We have now developed a process for the preparation of a particulate material comprising titanium trichloride which gives a material which retains the advantages of the particles of our above-mentioned Belgian Patent Specification, but which is free from the disadvantage of giving a polymer of mediocre morphology at a high polymerisation temperature.

According to the present invention, we provide a process for the prepara of a particulate material comprising titanium trichloride, suitable for use in the sterospecific polymerisation of alnha-olefins, wherein a starting material comprising particles of titanium trichloride associated with a liquid is dried (as herein defined) to a liquid content less than 1% by weight calculated on the weight of -3titanium trichloride present in the particles, the particles being of substantially spherical shape and comprising an agglomerate of smaller particles which are themselves substantially spherical and which are porous.

The word dried is used in the present description and claims to refer to the reduction of the liquid content of a system in which a liquid other than water is present.

He have in fact found that when the particles employed are dried (as defined above) to a liquid content less than 1% as specified above, a hardening or tempering phenomenon takes place. If the drying is carried out under conditions which do not give such low contents of liquid, the disadvantage mentioned above is observed during polymerisation at a high temperature. On the other hand, if drying is carried out so as to give a liquid content less than 1% as mentioned above, the dried particles exhibit the same catalytic activity as, or even a slightly higher activity than, that of similar particles having a higher liquid content, and give polymers of excellent morphology even if the polymerisation is carried out at a high temperature.

Preferably, the particles are dried to a liquid content less than 0.5$. The best results are obtained when the liquid content of the dried particles is less than 0.3%. However, there is generally no advantage in continuing drying until the liquid content of the particles reaches 0.01%, for example, inasmuch as no further significant improvement in properties is observed.

The present particles of titanium trichloride can, before drying, be associated with any compound, or mixture of compounds which is liquid under ambient temperature and pressure conditions. They may, for example, be associated with titanium tetrachloride which has been used for the preparation of the trichloride, or with a Lewis acid or Lewis base used to treat the trichloride. However, we prefer that the liquid associated with the particles of titanium trichloride subjected to drying should comprise one or more aliphatic, cycloaliphatic or aromatic hydrocarbons which are liquid under ambient temperature and pressure conditions.

The best results are obtained with aliphatic and cycloaliphatic hydrocarbons containing 3 to 12 carbon atoms, technical-grade hexane being used most commonly. -4Other example·, ol preferred hydrocarbons are pentane, heptane, octane, cyclohexane, benzene, toluene and the xylenes.

In the starting material comprising titanium trichloride particles which is subjected to drying, the particles are generally associated with at least IS! of liquid, calculated on the weight of titanium trichloride present in the particles. Preferably, the amount of liquid is at least 22.

The best results are obtained if it is at least 52.

The conditions under which the drying of the particles is preferably carried out are specified below. It has been found that these conditions can enhance the hardening or tempering phenomenon mentioned above, and can thus further improve the morphology of the polymer. (i) Temperature-It is usually advisable that the drying temperature should be below 90°C. In fact, drying at above 90°C tends to give particles having a lower polymerisation activity than that obtained at lower drying temperatures.

On the other hand, drying temperatures below 20°C are hardly practical because they excessively extend the drying time.

Preferably, the particles are dried at a temperature of 50 to 80°C. The best results are obtained if the temperature is 60 to 75°C. (ii) Time-The drying time which is advisable denends not only on the temperature but also on the other prevailing conditions, although in any case drying should of course be 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, e.g. by heating a sample to constant weight. Usually the drying time is 0.25 to 48 hours, and preferably it is 0.5 to 6 hours. If all other conditions remain identical, the drying time is generally the shorter, the higher is the temperature. (iii) Pressure-The pressure under which the particles are maintained during drying is not critical provided it is less than the saturation vapour pressure of the liquid associated with the particles. Usually the drying is carried out at atmospheric pressure or under reduced pressure. It can be advantageous to work under reduced pressure (e.g. a fraction of a millimetre of mercury), if the drying -54 3 4 3 5 temperature is low, for example near ambient temperature, in order tQ accelerate the elimination of the excess liquid, (iv) Atmosphere-The drying can he carried out under a stream of an inert gas. For this purpose, nitrogen is preferred. This, inert gas must ipso facto be free from any substance which could inhibit the catalytic properties of the titanium trichloride, e.g. carbon monoxide or oxygen. The inert gas can he heated so as to provide all or part of the heat required for drying. (v) Apparatus;The drying can be carried out in any appropriate apparatus; thus use may be made of a moving bed drier, e.g. a plate drier, rotating drum drier, pneumatic drier, or tunnel drier. It is also possible to use a fixed-bed drier through which an inert gas is passed. However, it is preferred to carry out the drying in a fluidisation gas being an inert gas as mentioned above.

The present drying operation can he carried out continuously or discontinuosly.

The particles subjected to drying can he employed in the form of a suspension in the liquid with which they are associated. In this case, at the start of the drying operation, the liquid which form the liquid phase of the suspension is first evaporated, before the actual drying commences. Thus it is possible to inject the particles, in suspension in a liquid hydrocarbon, into a fluidised bed.

However, for economic reasons it is preferred that the particles should not be associated with too large a proportion of liquid, the evaporation of which would require too much heat. Preferably, the proportion of liquid associated with the particles should not exceed the amount which the particles are capahle of absorbing without losing their particulate character and without forming a continous liquid phase. If the particles are present in the form of a suspension it is thus advantageous, before drying, to remove the excess liquid phase, for example by filtration, by centrifuging, or by settling and syphoning.

The titanium trichloride particles of the starting material from which are prepared the dried particles in a process according to the present invention are preferably particles obtained by the plain reduction of titanium tetrachloride. This reduction can be carried out by means of hydrogen, or by means of a reducing -64 3 4 3 5 metal, e.g. magnesium or aluminium, aluminium being preferred. The best results, however, are obtained starting from particles formed by reducing titanium tetrachloride with an organometallic compound, e.g. organo-magnesium or organo-aluminium compound, organo-aluminium compounds being preferred.

The organo-aluminium compounds of the type which contain at least one hydrocarbon radical bonded directly to an aluminium atom are particularly preferred. Examples of compounds of this type are mono-, di- and tri-akyl-aluminium compounds wherein the alkyl radicals contain 1 to 12, and preferably 1 to 6, carbon atoms, e.g. triethyl-aluminium, the isoprenyl-aluminiums, diisobutyl-aluminium hydride and ethoxydiethyl-aluminium. With the compounds of this type, the best results are obtained with the dialkyl-aluminium chlorides whose alkyl chains contain 1 to 6 carbon atoms, and in particular with diethyl-aluminium chloride.

The reduction of titanium tetrachloride by means of an organo-aluminium compound can advantageously be carried out under the conditions described in our lb Belgian Patent Specification No. 780,758. The method of preparation concerned commonly requires or at least permits the use, especially for washing operations, of an organic diluent as described above with reference to liquids which are preferred for association with the titanium trichloride particles subjected to drying in accordance with the present invention. The titanium trichloride particles can thus contain one of these liquids as a result of being prepared by this method of reducing titanium tetrachloride.

The particles of titanium trichloride so obtained which are subjected to drying in accordance with the present invention usually have a diameter of 5 to 100 microns and most commonly of 15 to 50 microns. They consist of an agglomerate of microparticles, i.e. smaller particles, also substantially spherical, which usually have a diameter of 0.05 to 1 micron and most commonly 0.1 to 0.3 micron. These particles have a characteristic morphology inasmuch as the micro-particles are extremely porous. Usually the particles have a specific surface area, measured by the BET (Brunauer, Emmett & Teller) method based on nitrogen adsorDtion, 2 which is greater than 75 m /g and most commonly 100 to 250 m /g, and have an internal 3 3 pore volume greater than 0.15 cm /g and most commonly 0.20 to 0.35 cm /g. The -7internal porosity of the particles can be measured by a technique utilising both nitrogen adsorption and mercury penetration observations. The porosity of the micro-particles is witnessed by the high value of the pore volume observed in respect of the particles of which they are the constituents, which implies the presence of pores of less than 200 A.U. in diameter. This pore volume is almost always greater than 0.11 cm /g, e.g. 0.19 to 0.31 cm /g. The apparent soecific 0 gravity (measured by tamping) of these particles is usually 0.6 to 1.2 kg/dm .

In our Belgian Patent Specification No. 780,758, we have also disclosed a particular method of preparation of particles as described in the Dreceding Daragraph. This method comprises the reduction of titanium tetrachloride under mild conditions, by means of a reducing agent constituted preferably by a dialkylaluminium chloride whose alkyl chains comprise 2 to 6 carbon atoms. Thereafter a treatment with a complexing agent is carried out, the complexing agent preferably comprising one or more organic compounds which contain at least one atom or group possessing at least one lone electron pair capable of forming a coordination bond to Ti or Al, i.e. to the titanium or aluminium present in the respective titanium or aluminium halide. The preferred complexing agents are alinhatic ethers whose aliphatic radicals comprise 4 to 6 carbon atoms. The treatment with a complexing agent can be followed by a treatment with titanium tetrachloride and the washing of the particles with diluents as descrihed above.

The particles prepared by this method, under the preferred conditions, t urreK|H>ntl to the formula TiCl3. (AIRCl2)x.Cy, where: R is an alkyl radical comprising 2 to 6 carbon atoms; C is a complexing agent as mentioned above: x is less than 0.20; and y is greater than 0.009, though usually less than 0.20.

In modified versions of the method described above, it is possible to carry out only the post-reduction treatment with the complexing agent, or to carry out only the post-reduction treatment with titanium tetrachloride, or to carry out these two treatments simultaneously. It is also possible to replace the titanium tetrachloride used for the post-reduction treatment by a chemical equivalent, e.g. -843 4 3 5 a tetrachloride oi v.-mndium silicon or carbon. However, the results obtained by these modified versions of the method described above are less advantageous than those obtained by this method in its unmodified form. In fact, these modified versions generally do not give particles having as regular a morphology, or as high an internal porosity, as those obtainable by the preferred method; the catalytic activity of the former is accordingly less high, and the morphology of the polymer obtained is less favourable, than in the case of the latter. Furthermore, these modified versions give titanium trichlorides which contain significant proportions of aluminium chlorides, such that the particles give less stereospecific catalysts.

It is to be understood that the present titanium trichloride particles which are subjected to drying do not consist exclusively of the compound of the chemical formula TiClg. In typical cases this compound is associated, whether in the form of a solid solution, in a co-crystallised form, or in a complexed form, with one or more other compounds, these being compounds which originate from the preparation of the trichloride and which cannot be removed by washing with the hydrocarbons which are Dreferably associated with the particles subjected to drying. In the majority of cases, however, the particles contain at least 50% by weight of TiClg calculated on the total dry weight. Preferably, they contain at least 65% of TiClg. The most favourable results are obtained when they contain at least 80'Z of TiClj.

Certain methods of preparing titanium trichloride particles give particles which are quite dry, but these particles can nevertheless be dried in accordance with the invention after being impregnated with a liquid which preferably comprises one or more of the hydrocarbons described above.

The present particles do not differ significantly in structure from the particles used for their preparation. Thus, since they are prepared from substantially spherical particles consisting of an agglomerate of porous substantially spherical micro-particles, i.e. smaller particles, they have substantially the same structure, dimensions and shapes as the starting particles. Consequently they have a specific surface area and pore volume as high as those of the starting particles. In fact whatever can be said of the physical characteristics of these -9starting particles can also, for practical purposes, be said of the particles according to the invention which are obtained by the drying of these starting particles.

Similarly the dried titanium trichloride particles according to the invention will in the majority of cases contain, like the starting particles, at least 502 by weight of TiClg calculated on the total dry weight Preferably, as before, they contain at least 652 of TiClg, the most favourable results again being obtained when they contain at least 802 of TiClg.

After being dried, but preferably after cooling below 30°C assuming that the drying temperature is above 30°C, the particles according to the invention can immediately be contacted again with a liquid, and more specifically with a liquid comprising one or more hydrocarbons, e.g. hydrocarbons which are preferably associated with the particles before drying, and which can also be used as diluents in a subsequent suspension polymerisation. The particles according to the invention.can also be subjected to a pre-activation treatment and where appropriate, a pre-polymerisation treatment, as described in our Belgian Patent Specification No. 803,873, and they can be stored under hexane for long periods, without losing their properties.

In a alpha-olefin polymerisation or copolymerisation, the particles of titanium trichloride according to the invention are suitable for use with an activator comprising at least one organo-raetallic compound of a metal of group Ia, lib or Illb of the periodic table, preferred activators being the compounds of the formula AlR'n|X2_m where: R1 is an alkyl, aryl, aralkyl, alkylaryl or cycloalkyl hydrocarbon radical, containing from 1 to 18 carbon atoms, and more preferably 1 to 12 carbon atoms, the best results being obtained if R' is an alkyl radical containing 2 to 6 carbon atoms; X is a halogen (flourine, chlori'.ne, bromine or iodine), the best results being obtained if X is chlorine; and m is greater than 0 but not greater than 3, preferably being not less than 1.5 and not greater than 2.5; the best results are obtained if m is equal to 2.

The use of diethyl-aluminium chloride (AIEt^CI.) will in our experience permit the highest possible activity and stereospecificity of the catalyst system to be attained. -104 3 4 3 ίί The above mentioned catalyst systems are applicable to the polymerisation of olefins with terminal unsaturation, the molecule of which contains usually 2 to 18, and preferably 2 to 6 carbon atoms, e.g. ethylene, propylene, 1-butene, 1-pentene, methylbutene, 1-hexene, 3- or 4-methyl-l-pentene, or vinyl5 cyclohexene. They are of particular value for the stereospecific polymerisaticn of propylene, 1-butene and 4-methyl-l-pentene to give crystalline, highly isci.uiic polymers. They are also applicable to the copolymerisation cf two or more alpha-olefins with one another, as well as to the copolymerisation of one or more alpha-olefins with one or more diolefins containing 4 to 18 carbon atoms.

Of these diolefins, the following are preferred: non-conjugated aliphatic diolfins, e.g. 1,4-hexadiene; non-conjugated monocyclic di olefins, e.g. 4-vinylcyclohexene; alicyclic diolfins having an endocyclic bridge, e.g. dicyclcpentadiene, methylenenorbornene and ethylenenorbernene; conjugated aliphatic diolefins, e.g. butadiene or isoprene.

The above-mentioned catalyst systems are also applicable to the production of block copolymers built up from alpha-olefin units of two or more kinds, or from alpha-olefin and diolefin units. In these block copolymers, the macromolecule is made up of a series of segments of various chain lengths, each segment comprising a homopolymer of an alpha-olefin or a randon copolymer comprising an alpha-olefin and at least one comonomer which is an alpha-olefin or a di olefin. The alpha-olefins and diolefins which can be used are as mentioned above.

The particles according to the invention are particularly suitable for use in the production of homopolymers of propylene and the production of propy25 lene copolymers containing at least 505! preferably 755!, by weight of propylene.

Alpha-olefin (co)polymerisation with a catalyst system derived from titanium trichloride particles according to the present invention can be carried out by any applicable method, but is preferably carried out in solution or in suspension in a hydrocarbon solvent or hydrocarbon diluent, preferably comprising one or more aliphatic or cycloaliphatic hydrocarbons e.g. butane, pentane, hexane, heptane, cyclohexane or methyl cyclohexane. If preferrred, however, the (co)polymerisation can instead be carried out in the monomer or monomers (or in -114 3 4 S (5 one or more of the monomers if two or more are used), the respective monomer(s) being kept in the liquid state. (Co)polymerisation in the gas phase may also be restored to.

The polymerisation temperature can generally be 20 to 200°C, and preferably, if the process is carried out in suspension, it is 50 to 80°C, the best results being obtained at 65 to 75°C. The pressure can generally be 1 to 50 atmospheres, and is preferably 10 to 30 atmosoheres. The particular pressure which it is advisable to adopt is of course dependent upon the temperature adopted.

The polymerisation can be carried out continuously or discontinuously.

The preparation of the block copolymers can also be carried out by any applicable method, but we prefer to use a two-stage process comprising polymerisina an alpha-olefin, e.g. propylene, as described above for the homopolymerisation, and subsequently polymerising another alpha-olefin e.g. ethylene, and/or a diolefin, in the presence of the still-reactive first-stage product. This second polymerisation stage can be carried out after complete or partial removal of unreacted first-stage monomer.

The organo-metallic compound(s) and the dried titanium trichloride particles can be added to the polymerisation medium separately, but it is'also possible to bring them together, usually at a temperature of -40 to 80°C, at a stage which can be up to 2 hours before their introduction into the polymerisation reactor.

The total proportion of organo-metallic compound(s) employed is not critical, but it is generally greater than 0.1 millimole per litre of diluent, liquid monomer or reactor capacity and preferably greater than 1 millimole per litre .

The proportion of the dried titanium trichloride particles which it is advisable to employ will depend upon their TiCl^ content. It should generally be sufficient to give a concentration in the polymerisation medium greater than 0.1 millimole of TiClg per litre of diluent, liquid monomer or reactor capacity, -124 3 4 3 5 and preferably greater than 0.2 millimole per litre.

The ratio of the proportions of organo-metallic compound(s) and the said particles is also not critical, but it should generally be such that the molar ratio of the organo-metallic compound(s) to the TiClg present in the said particles is 0.5:1 to 20:1, and preferably 1:1 to 15:1. The best results are obtained when the said molar ratio is 2:1 to 10:1.

The molecular weight of the polymers produced by the process of the invention can be regulated by adding, to the polymerisation medium, one or more molecular weight regulators, e.g. hydrogen, diethyl-zinc, or one or more alcohols, ethers or alkyl halides.

It is also possible to add, to the polymerisation medium, a complexing agent as used in the preparation of titanium trichloride particles by the method described in our Belgian Patent Specification No. 780,758.

The stereospecificity and the activity of the dried titanium trichloride 15 particles according to the invention are generally at least at high as, and are frequently higher than, those of the catalyst complexes described in our Belgian Patent Specification No. 780,758, insofar as the particles are prepared from the latter. Thus, in the homopolymerisation of propylene, the proportion of amorphous polypropylene (evaluated by measuring the weight of polypropylene which is soluble in an inert solvent used for the polymerisation and for washing, and calculated as a percentage of the total polypropylene produced during the polymerisation is almost always less than 3%. As for the activity (expressed in grams of insoluble polypropylene produced per hour per gram of TiCl^ in the dried particles), this easily reaches 2,500 grams of insoluble polypropylene if the homopolymerisation is carried out at approximately 70°C, in hexane suspension.

Finally, the dried titanium trichloride particles according to the invention make it possible, surprisingly, to obtain polymers having an apparent specific gravity which is slightly higher, other conditions being equal, than that of comparable polymers obtained using catalyst systems derived from titanium trichloride particles which have not been dried according to the invention. These unexpectedly high apparent specific gravities are advantageous -13343 5 in that they make it possible to reduce the dimensions of the polymerisation installations and storage areas which they demand. Furthermore, the very narrow particle size distribution of the polymer powders and the very high mean diameter of the particles, combined with this high apparent specific gravity, substantially facilitate the polymer drying operations and the subsequent use of the polymer by the customary moulding methods.

The examples which follow serve to illustrate the invention, without limiting its scope. Examples 1-3 fall within the scope of the invention; Example 4 is comparative. As implied by the foregoing description, particles of substantially spherical shape comprising an agglomerate of porous substantially spherical smaller particles were dried in the cases of Examples 1-3.

Example 1 A. Preparation of the starting particles. 120 ml of dry hexane and 30ml of pure TiCl^ are introduced, under a nitrogen atmosphere, into a 500 ml reactor equipped with a blade stirrer revolving at 140 rpm. This hexane-TiCl^ solution is cooled to 1 (+1)°C. In the course of 4.5 hours, a solution consisting of 90 ml of hexane and 34.2 ml of AlEtgCl is added thereto, whilst maintaining the temperature of 1(+1)°C in the reactor.

After adding the AlEtgCl-hexane solution, the reaction mixture consisting of a suspension of fine particles is stirred at 1(+iPc for 15 minutes and is then heated to 23°C in the course of 1 hour, kept at this temperature for 1 hour, and then heated to 65°C in the course of about 1 hour. The mixture is then stirred for 2 hours at 65°C, The liquid phase is then separated from the solid by filtration and the solid product, referred to as reduced solid, is washed 5 times with 100 ml of dry hexane, the solid being re-suspended for each wash.

The reduced solid is suspended-in 300 ml of diluent (hexane) and 48.5 ml of diisoamyl ether (DIAE) are added thereto. The suspension is stirred for 1 hour at 35°C. Thereafter the solid obtained, referred to as treated solid') is separated from the liquid phase. -144 3 4 3 5 g of the treated solid are suspended in 95 ml of hexane and 25 ml of TiCiyj contained in a 500 ml glass three-neck reactor equipped with a double jacket for water circulation, a sintered disc, a side-tube for filtration and a two-blade stirrer, and the suspension is stirred at 70°C for 2 hours. The liquid phase is then removed hy 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 obtained from the last wash with hexane , and containing about 200 ml of hexane/kg, using a stream of nitrogen fed to the bottom of the reactor at a rate of 300 1/hour and distributed through the sintered disc at a temperature of about 25°C. The temperature of the double jacket is about 70°C. After 10 minutes, fluidisation of the particles is observed.

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 containing 861 g of TiClj, 6.9 g of aluminium, 106 g of DIAE and 1.9 g of hexane per kg is obtained.

C. Polymerisation of proDylene by means of the dried particles litre of dry and purified hexane is introduced into a 5 litre stainless steel autoclave-which has been flushed several times with nitrogen. Thereafter, 240 mg of AlEtgCl (in the from of a solution, containing 200 g/1, in hexane) and 58 mg of dried particles, representing about 50 mg of TiClj, are introduced in succession. The AlEtgCl/TiCl3 molar ratio is thus about 6.2.

The autoclave is heated to 70°C and is brought back to atmospheric pressure by slow letting-down. Thereafter, an absolute hydrogen pressure of o 0.20 kg/cm is set up; propylene is then introduced into the autoclave until a total pressure, at the temperature in question, of 12.7 kg/cm is reached. This pressure is kept constant during the oolymerisation, by introducing gaseous propylene.

After 3 hours, the polymerisation is stopped by venting the propylene.

The contents of the autoclave are poured onto a Buchner filter, rinsed -1543435 three times with 0.5 1 of hexane, and dried under reduced pressure at 50°C. 296 g of hexane-insoluble polypropylene (PP) are obtained. 12.4 g of soluble polymer, corresponding to 4.2%, are found in the hexane from the polymerisation and from the wash.

The catalytic activity is thus, 1,978 g of polypropylene/hourxg TiClg and the productivity is 5,103 g of polypropylene/g of particles.

The apparent specific gravity (ASG) of the insoluble polypropylene fraction is 0.424 kg/dm . This polypropylene is in the form of regular and smooth particles of very narrow particle size distribution.

Example 2 Dried particles are prepared in the same manner as in Example 1, with the same flow rate of nitrogen, but using a treatment of 3 hours at 90°C.

The solid obtained contains 841 g of TiCl3, 2.7 g of aluminium, 43 g of DIAE and about 0.1 g of hexane per kg.

A propylene polymerisation experiment carried out under the same conditions as in Example 1, but v/ith 105 mg of particles dried at 90°C, makes it possible to obtain 405 g of hexane-insoluble polypropylene. .3 g of soluble polymer, representing 1.3%, are found in the hexane from the polymerisation and from the wash.

The catalytic activity is thus 1,531 g of polypropylene/hoursxg TiCl3 and the productivity is 3,850 g of polypropylene/g of particles.

The ASG of the insoluble polypropylene fraction is 0.443 kg/dm .

Example 3 Experiment a) Particles prepared as in Example 1 (A) are dried under a vacuum of 2 mm Hg for 90 minutes at 25°C.

The solid obtained contains 815 g of TiCtg 108 g of DIAE, 6.7 g of aluminium and about 7.9 g of hexane per kg.

A propylene polymerisation experiment is carried out under the general conditions described in Example 1 (C), the particular conditions being as follows amount of dried particles used: 73 mg (that is to say about 59 mg of Tici3) -164 3 4 3 SJ molar ratio AlEt^Cl/tiCl3:6.2. 358 <1 of hexane-insoluble PP are obtained. 28.3 g of soluble polymer, representing I.n, are found in the hexane from the polymerisation and the wash.

The catalytic activity is thus 2,065 g of PP/hourxg TiClg and the productivity is 5,048 g of PP/g of particles.

The ASG of the insoluble polypropylene fraction is 0.322 kg/dm .

The reduction in ASG which occurs when the liquid content of the dried particles is relatively higher can thus be seen.

Experiment b) A supplementary drying of the particles under a higher vacuum (0.1 mm Hg) for 2 hours at 25°C gives particles of which the hexane content is only 0.3 g/kg.

A fresh polymerisation experiment carried out with the latter (molar ratio AlEtgCl/TiCl2:5.5) under the conditions of Example 1 (c) makes it possible to obtain 360 g of hexane-insoluble PP (only 4.82 of soluble polymer).

The catalytic activity is 2,131 g of PP/hourxg TiClg and the productivity is 5,210 g of PP/g of particles.

The ASG of the insoluble polypropylene fraction is 0.404 kg/dm , that is to say markedly higher than that of the polypropylene obtained in the presence of the particles of Experiment a).

Example 4.

This example is given by way of comparison.

Particles according to Example 1 (a) are prepared. However, the drying indicated in Example 1 (b) is not carried out, and instead the cake resulting from the last wash with hexane is merely suction-drained until the pourabiltiy of the solid is adequate and the hexane content of the solid has been brought to 40 g/kg.

The ASG of the hexane-insoluble polypropylene fraction obtained after a polymerisation experiment carried out as indicated in Example 1 (c) is only 0.287 kg/dm . The morphology of the particles of this polymer is very mediocre, the particles being fissured to their core.

Claims (22)

1. Process for the preparation of a particulate material comprising titanium trichloride, suitable for use in the stereospecific polymerisation of alpha-olefins, wherein a starting material comprising particles of titanium trichloride associated with a liquid is dried (as herein defined) to a liquid content less than 1% by weight calculated on the weight of titanium trichloride present in the particles, the particles being of substantially spherical shape and comprising an agglomerate of smaller particles v/hich are themselves substantially spherical and which are porous.

2. Process according to claim 1, wherein the particles are dried (as herein defined) to a liquid content, (calculated as in claim 1) less than 0.5%.

3. Process according to claim 1, wherein the particles are dried (as herein defined) to a liquid content (calculated as in claim 1) less than 0.3%.

4. Process according to any of claims 1 to 3, wherein the particles dried (as s herein defined are particles of titanium trichloride associated with a liquid comprising one or more aliphatic, cycloaliphatic or aromatic hydrocarbons. 5. Process according to claim 4, wherein the said liquid comprises one or more aliphatic or cycloaliphatic hydrocarbons containing 3 to 12 carbon atoms.

5. Process according to claim 5, wherein the said liquid is techical-grade hexane.

6. 7. Process according to any of claims 1 to 6, wherein the particles are dried (as herein defined) at a temperature below 90°C.

7. 8. Process according to any of claims 1 to 7, wherein the particles are dried (as herein defined) for 0.25 to 48 hours.

8. 9. Process according to any of claims 1 to 8, wherein the particles have a diameter of 5 to 100 microns, the diameter of the said smaller particles being 0.05 to 1 micron.

9. 10. Process according to any of claims 1 to 9, wherein the particles are dried q (as herein defined) to an apparent specific gravity of 0.6 to 1.2kg/dm .

10. 11. Process according to any of claims 1 to 10, wherein the particles have a specific surface area (BET) greater than 75 m 2 /g and an internal pore volume -184 3 4 3 5 greater than 0.15 cm /g. 17. Process according to any of claims 1 to 8, wherein the particles have a diameter of 15 to 50 microns, the diameter of the said smaller particles being 0.1 p to 0.3 micron, and have a specific surface area (BET) of 100 to 250 m /g and an 5 internal pore volume greater than 0.15 cm /g.

11. 13. Process according to claim 12, wherein the particles have an internal pore volume of 0.20 to 0.35 cm 3 /g.

12. 14. Process according to any of claims 1 to 13, wherein the particles have a chemical composition which correspond to the formula 10 TiCl 3 . (A1RC1 2 ) x . C y where: R is an alkyl radical containing 2 to 6 carbon atoms; C is a complexing agent comprising one or more organic compounds which contain at least one atom or group possessing at least one lone electron pair capable of forming a coordination bond to titanium and aluminium; x is less than 0.20; and y is greater than 0.009.

13. 15 15. Process according to any of claims 1 to 14, wherein the starting material comprises particles of titanium trichloride obtained by reduction of titanium tetrachloride by means of an orqano-aluminium compound.

14. 16. Process according to claim 15, wherein the orqano-aluminium compound is a dialkyl-aluminium chloride whose alkyl chains contain 1 to 6 carbon atoms. 20

15. 17. Process according to claim 15 or 16, wherein the starting material comprises particles of titanium trichloride obtained by reduction of titanium tetrachloride which have subsequently been treated with a complexing agent comprising one or more organic compounds which contain at least one lone electron pair capable of forming a coordination bond to titanium and aluminium. 25

16. 18. Process according to claim 17, wherein the complexing agent is an aliphatic ether whose aliphatic radicals contain 4 to 6 carbon atoms.

17. 19. Process according to claim 17 or 18, wherein the particles treated with the complexing agent have subsequently been treated with additional titanium tetrachloride. 30

18. 20. Process according to claim 1, substantially as described in Example 1, 2 or 3. -1943435

19. 21. A particulate material comprising titanium trichloride, prepared by a process according to any of claims 1 to 20.

20. 22. Process for the polymerisation or copolymerisation of alpha-olefins in the presence of a catalyst system comprising particles of titanium trichloride and at least one organo-metallic compound of a metal of group Ia, Ila, lib or Illb of the periodic table, wherein the particles of titanium trichloride employed are provided by a material according to claim 21.

21. 23. Process according to claim 22, substantially as described in Example 1, 2 or 3

22. 24. An alpha-olefin polymer or copolymer prepared by a process according to claim