Title of Invention

A PROCESS FOR THE PREPARATION OF A PROCATALYST

Abstract

S Procacalyst for the production of ethylene polymers, which procatalyst comprises an inorganic support, a chlorine compound carried on said support, a magnesium compound carried on said support, a titanium compound carried on said support, whereby the chlorine compound can be different from or the same as the magnesium contpound and/or the titanium compound, characterized in that its activity balance AB in specified polymere or conditions 3.2 Aa > -5 . 1 wherein AS = [(A + A' ) :2 • log (MFR-' : MPR,) (A - A' ) ] , A means polymerization activity expressed aa kq PE / g cat • h, MFR; means the melt flow rate in g/min units at a load of 2.16 kg, according to the standard ISO 1133, the absence of the upper index ' means low melt flow rate polymerisation and the presence of the upper index ' means high melL flow polymerization.

Full Text

Procatalyst for ethylene polymer production, method for its preparation and use DESCRIPTION The invention relates to a procatalyst component of a Ziegler-Natta ca¬talyst composition which is suitable for production of ethylene poly¬mers. The composition comprises a mixture containing a group III (13) metal, chlorine, magnesium and titanium atoms, supported on a particulate inorganic carrier. The invention also relates to a preparation method and use thereof. Ethylene, alone or with other olefinic unsaturated monomers can often be polymerized in the presence of a catalyst composition, which has essentially two components: a compound of a transition metal belonging to groups 4 to 6 of the Periodic Table of Elements (Hubbard, lUPAC 1970) which is often called a procatalyst, and a compound of a metal belonging to groups l to 3 of said Table which is the s.c. cocatalyst. This kind of Ziegler-Natta catalyst composition has been further developed by depositing the procatalyst on a less or more inert and particulate support and by adding to the catalyst composition in the stages of its preparation several additives, among others electron donating compounds. These compounds have improved the polyTnerization activity of the catalyst, the operating life and other properties of the catalyst composition and first of all properties of the polv-mers which are obtained by means of the catalyst composition. When ethylene polymers and all other pol'»Tners, too, are produced the polymer m,ol»cules achieved are not similar by molecular weight, but a mixture having a narrow or broad molecular weight distribution is developed. Different average molecular weights can be defined for the polyTmer mixtures to describe the most common molecular wight by giving he top value of the distribution, and also several, indices has been developed to describe the breadth of the distribution. For controlling the molecular weight we can add to the pol\'mieri2ation reaction a compound called chain transfer agent. In order to obtain polymer products having different molecular weights, a different amou.nt of a compound for controlling the moclecular weight must be fed into the polymerization reaction. The most usual and preferable chain transfer agent is hydrogen, because no foreign atoms or atom groups remain in a growing molecule, which can cause inconveniencies for the polymerization process or disadvantageous properties of the polymer produced. t How well the molecular weight of the produced polymer varies as the function of the hydrogen amount or how much the s.c. hydrogen sensibility changes, greatly depends on the catalyst composition. Generally the problem is, that in polyethylene production the polymerization activity of certain catalyst composition in production of a polymer having high molecular weight is higher, usually many times, even ten times higher, than in the production of a polymer having low molecular weight. This absence of catalyst activity balance is a common drawback for all prior art catalysts today. The imbalance shows up when, using prior art catalysts, a drastic drop in the productivity of the catalysts occurs when going from polymerization conditions giving high molecular weight polymers (low melt flow) to polymerization conditions giving low molecular weight polymers (high melt flow). Even if this kind of a commercial catalyst can have a quite good productivity at a polymer melt flow rate (MFR, defined according to standard ISO 113 3) of 1, there is often only 10 % left of the productivity when producing a MFR of 500. Thus it is desirable to provide a catalyst system having a high activity which is independent from the molar mass of the forming polymer. A novel procatalyst has now been disclosed by which ethylene homopolymers or copolymers having low or high molecular weight can be produced with an even and high activity. Despite of the amount of hydrogen introduced into the polymerization reactor, a balance of the activities in both cases can be achieved by using a procatalyst composition according to claim 1. The unique feature of the catalyst according to the disclosure now lies in its good balance in activity in a very wide range of molar mass regulating hydrogen partial pressures used in the polymerization. It is thus possible to carry out an ethylene polymerization by the use of this novel catalyst at high and low melt flow and still have verv similar b) the first reaction product is contacted with a compound or mixture containing hydrocarbyl, hydrocarbyl oxide and magnesium to give a second reaction product, t) the second reaction product is contacted with a titanium compound which contains chlorine, having the general formula Cl.Ti (OR'^) 4., (2) wherein R"^ is a C2-C20 hydrocarbyl group and x is 3 or 4, to give said procatalyst. The catalyst described in this patent application thus comprises an alkyl metal chloride, which is an internal soluble chlorination agent which also has a cocatalytical impact, a soluble magnesium compound or mixture (named hereafter a magnesium complex) with a sufficiently low viscosity and a titanium compound which contains chlorine. The solubility of the soluble compounds refers to solubility in a non-polar hydrocarbon solution. The catalyst components are deposited on a suitable catalyst support. If a support material is used together with the soluble catalyst components having a sufficiently low viscosity a good morphology can be achieved to the catalyst and thereby to the polymer. The support material must have a suitable particle size distribution, a high porosity and a large specific surface area. A good result is achieved if the support material has a specific surface area between 100 and 500 m2/g support and a pore volume of 1 - 3 ml/g support. The support material can also be chemically pretreated, e.g. by silanation or by treatment with aluminium alkyls etc. Several metal oxides are suitable, but silicon, aluminium, titanium, chromium and zirconium oxide or mixtures thereof are preferred. Silicon dioxide or silica is most preferable. It is good to dry the support before impregnating by other catalyst components. A good result is achieved if the support is heat-treated at 100 °C to 900 °C for a sufficient time, and thereby the surface hydrox\-l groups, in the case of silica, are reduced to below 2 mmol/g Si02 . most preferably 1.2 The compounds (3) to (6) are defined in the following text as the magnesium complexes. A requirement is that in all the compounds (3) to (6) there is a small amount of magnesium alkyl groups. One way to produce these magnesium complexes are to react a soluble magnesium alkyl with an alcohol. To have a good balance of hydrogen response and polymerization activity the MgR2/R0H feed ratio must be larger than 1:2 and smaller than 1:1, preferably between 1:1.75 and 1:1.99, and most preferably between 1:1.80 and 1.98. This ratio does not have to be created immediately when the magnesium complex is prepared but it can also be created later on, for example after impregnation of the magnesium compound into the support by addition of sufficient amount of MgR2 to reach the correct MgR2/R0H feed ratio. The relation between the feed ratio and the complex composition can be obtained from the stoichiometry of the following reaction equation wherein p is the number of R''OH moles per one mol of MgR",. The magnesium complex is preferentially the reaction product of a di-C;-C2o-alk:yl magnesium, more preferentially dibutyl magnesium, butyl ethyl magnesium or butyl octyl magnesium and an alcohol. The magnesium complex is preferentially the reaction product of a dialkyl magnesium and a branched alcohol, more preferentially a 2-alkyl alkanol, most preferentially 2-ethyl hexanol or 2-propyl pentanol. The titanium compound can be a chlorinated alcoholate i.e. TiCl2*0R or a solely chloride containing compound such as TiCl^. The general composition of the compound is (2): In complex (2) R"^ is a C-,-C;o hydrocarbyl group and x is 3 or 4, preferably 4. The Ti compound should be totally soluble in a non-polar hydrocarbon at the temperature applied. If pure TiCl^ is used there is no need of additional hydrocarbon as this chemical is a liquid. The alkyl metal chloride having also a cocatalytical effect, can be deposited on the support material as the first chemical in this catalyst synthesis. It is preferable, if the molar ratio between the alkyl metal chloride and the surface hydroxyls of the inorganic oxide is >1, preferably between 1 and 1.5. An even deposition is achieved if the viscosity of the agent or its solution is below 10 m*Pa*s at the temperature applied. To achieve this low viscosity the alkyl metal chloride agent can be diluted by a non-polar hydrocarbon. The best deposition is however achieved if the total volume of the deposited alkyl metal chloride solution is not exceeding the pore volume of the support, or if the excess of diluting hydrocarbon is evaporated away after the deposition of the alkyl metal chloride. A good choice is to use a 5 - 25 V hydrocarbon solution of ethyl aluinin'om dichloride. The deposition of the agent can be carried out in a wide range of temperatures, preferably between 0 °C and 110 °C. The chemical addition times and the addition techniques have to be adjusted to give an even distribution of the chemical in the support material. A good deposition of the magnesium complex solution is achieved if the volume of the magnesium complex is about two times the pore volume of the support material. This is achieved if the concentration of the complex in a hydrocarbon is between 5 - 60 % in respect of the hydrocarbon used. The ratio between magnesium and chlorine in the alkyl metal chloride agent should be from 1:1.0 to 1:2.5. A good result is achieved if this ratio is from 1:1.5 to 1:2.0. When depositing the magnesium complex on the support material it should have a viscosity that is lower than 10 m*Pa*s at the temperature applied. The viscosity of the magnesium complex solution can be adjusted for example by the choice of the group R' in the formulas (3) zo (6), by the choice of the concentration of the hydrocarbon solution, Dy the choice of the ratio between the magnesium alkyl and the alcohol The titanium compound can be added to the support material with or without a previous drying of the catalyst to remove the volatile hydrocarbons. The mol amount of TiCl^ or corresponding titanium compound should be added to the reaction mixture in a Ti/Mg ratio that is greater than 0.1 and less than one, preferably 1:5-1:1.43. A good result is achieved if the mol ratio Ti/Mg is 0.2 to 0.7. The components should be allowed to react with each other for a sufficient amount of time at a desired temperature. Remaining hydrocarbons can if desired be removed by using slight underpressure, elevated temperature or nitrogen flash. The procatalyst is prepared as follows: If a support is used it first is dried as previously mentioned. Then the support is treated with an alkyl metal chloride (1), preferably ethyl-Al-dichloride (EADC), which is bonded on the surface of the carrier particle by reaction with surface hydroxyl groups. Thus a carrier particle is formed on which a s.c. internal cocatalyst with chlorinating influence has been chemically bonded by forming -0-Al-X; groups. To some extent free alkyl-Al-chloride remains between the support particles. Next Mg atoms are deposited on support particles. The most common way is to precipitate magnesium from its solution onto the particles. The most easily available Mg compounds, such as the Mg halides, particularly MgClj, do not dissolve in liquid non-polar hydrocarbons, but only in polar solvents. For instance lower aliphatic alcohols, such as methanol or ethanol can be used for the preparation of magnesium alcoholates. The thus formed Mg alcoholates do not completely mix with hydrocarbon solvents, but the mixture thereof will fractionate separate layers. Directly onto the carrier, for instance onto silica, precipitated Mg alcoholate has no polymerization activity. On the other hand, a branched alcohol, for example 2-ethyl hexanol or 2-propyl pentanol, which has a steric hindrance in the molecule close to the Mg-0 bond in the Mg-alcoholate and does not coordinate easy and thereby form insoluble compounds. A solution of Mg alcoholate is formed which is completely miscible with liqxiid hydrocarbons. This kind of hydrocarbon solution is to be developed for the impregnation of carrier particles, so that Mg atoms will be located as even as possible on the carrier particles and also cam penetrate into the particle as much as possible when the hydrocarbon is evaporated. Mg alcholate is thus prepared from a branched aliphatic monoalcohol and a Mg dialkyl. The alcohol has a sterically bulky hydrocarbon group which prevents it from coordination tightly. In the Mg dialkyl the alkyl group has from 2 to 10 carbon atoms and can be linear or branched. Suitable examples are dibutyl-Mg (DBM), butyl ethyl-Mg (BEM), butyl octyl-Mg (BOMAG) etc. When the Mg alcoholate is prepared, the solution of monoalcohol and Mg dialkyl has a very high viscosity near the stoichiometric equivalent point, thus there are difficulties to carry-out the reaction. The viscosity of the solution can be decreased by adding Ti tetraalkoxide, preferably Ti tetrabutoxide to the solution. When carrier particles are impregnated by the Mg-alcoholate solution which contains a little Mg dialkyl (from l to 20 mol-%, preferably about 10 mol-%), the groups -O-Al-X, on the surface of the carrier particles are converted to groups -0-Al-(OR)R and on the surfac€ of the particles MgXj molecules are precipitated which both appear from the reaction between Mg compounds and the internal cocatalyst. The alkyl groups R bonded to Al atoms in the surface groups are appeared from Mg dialkyls which very easily react with the internal cocatalyst. Finally to achieve an active procatalyst, the carrier which is treated as described above is titanized by a four valent Ti halide. A preferable Ti halide is TiCli. In the titanized procatalyst a small amount of the alkoxy and alkyl groups in the Al groups bonded to the carrier are converted to halogen groups and a small amount of TiCl4 is reduced to the three valent form. Preparation of complex 1 9.5 ml toluene {0.089 mol) and S8.6 ml (0.060 mol) 20% BOMAG-A was added to a septabottle. 16.65 ml (0.1065 mol) 2-ethyl-1-hexanol was added slowly to the reactor. The temperature was kept below 40 °C. The molar ratio between BOMAG-A and 2 - ethyl-1-hexanol was 1:1.775. Preparation of complex 2 6 kg toluene (65.12 mol) and 27.8 kg (33.21 mol) 19,9% BOMAG-A was added to a multipurpose reactor. The reactor was cooled down to 0°C 7.89 kg (60.45 mmol/g Si) 2-ethyl-1-hexanol was added to the reactor at a speed of 10-30g/min. The temperature was kept below 20°C. The molar ratio between BOMAG-A and 2-ethyl-1-hexanol was 1:1.8 25.6 kg of this complex was transferred to a container and an aliquot was used for the catalyst prepared in example 1. Preparation of complex 3 To the complex left in the multi-purpose reactor in complex preparation example 2, another 0.887 kg (6.79 5 mol) 2 ethyl-1-hexanol was added to complex. Finally 0.34 kg (1 mmol) tetra-isobutoxy-titanium was added. The molar ratio between BOMAG-A and 2-ethyl-hexanol was 1:2.03. The molar ratio between Mg:Ti was 30:1. Preparation of complex 4 1.53 ml 2-ethyl-1-hexanol was added to 76.8 g of complex 3. The molar ratio between BOMAG-A and 2-ethyl-hexanol hecame 1:2.19. Preparation of complex 5 87 kg toluene was added to a reactor. The.n 45.5 kg 20.3% BOMAG-A in haptane was also added in the reactor. 161 kg 99.8% 2-ethyl -1-hexanol was feeded in the reactor at the speed of 24 - 40 kg/h. The molar ratio between BOMAG-A and 2-ethyl-1-hexanol was 1:1.83. Procatalvst preparation Example 2 54.9 ml (2 mmol/g Si) of 20% EADC was added slowly to 30 g of silica (Crosfield ES70X, activated at 600°C) at 25°C. The mixture was stirred for 2.0 h at 20°C. 81.0 g (2 mmol Mg/g Si) of a complex prepared according to complex preparation 2 was added and stirred for 3.5 h at 20-45°C. The catalyst was dried at 45-75°C for two hours. The catalyst was cooled down to 46°C and 3.33 ml (1 mmol/g Si) TiCl^ diluted in 10 ml toluene was added to the precursor. The catalyst was stirred over night at 45°C. The catalyst was dried at 45-70°C for 2.5 h. The composition of the dry catalyst was 2.6% Ti, 3.0% Mg, 14.3% CI and 2.4% Al. The polymerization results are shown in table 1. Example 3 275 kg silica (Grace 955) activated at SO0°C was charged into a reactor. 411 kg 20% EADC (2.0 mmol/g Si) diluted in 555 1 pentane was added to the reactor at ambient temperature during 1 h. The temperature was increased to 35°C. The treated silica was stirred for 1 h. The treated silica was dried at 50°C for 8.5 h. 655 kg of the complex (2 mmol Mg/g Si) prepared in complex preparation example 5 was added at 23°C during 10 min. 86 kg pentane was added into the reactor at 22°C during 10 min. The slurry was stirred for 8 h at 50°C. Finally 52 kg TiCl4 was added during 0.5 h at 45°C. The slurry was stirred at 40°C for 5 h. The catalyst was dried under nitrogen purge. The composition of the dry catalyst was 2.4% Ti, 2.3% Mg, 14.1% CI and 2.9% Al. The polymerization results are shown in table 1. Example 1 54.9 ml (2 mmol/g Si) of 20% EADC was added slowly to 30 g of silica (Crosfield ES70X, activated at 600°C) at 25°C. The mixture was stirred for 2.5 h at 20°C. 72.1 g (2 mmol Mg/g Si) of a complex prepared according to complex preparation 1 was added and stirred for 3.5 h at 20-45°C. The catalyst was dried at 45-75°C for two hours. The catalyst was cooled down to 46°C and 3.33 ml (1 mmol/g Si) TiCl4 diluted in 10 ml toluene was added to the precursor. The catalyst was stirred over night at 45°C. The catalyst was dried at 45-70°C for 2.5 h. The composition of the catalyst was 3.2% Ti. 2.4% Mg, 16.4% CI and 2.8% Al. The polymerization results are shown in table 1. Example 4 54.9 ml (2 mmol/g Si) of 20% EADC was added slowly to 30 g of silica (ES70X, activated at 600°C) at 25"'C. The mixture was stirred for 2.0 h at 20°C. 76.6 g (2 mmol/g Si) of a complex prepared according to complex preparation 3 was added and stirred for 3 h at 20-45°C. The catalyst was dried at 45-70°C for two hours. The catalyst was cooled down to 46°C and 3.33 ml (1 mmol/g Si) TiCl diluted in 10 ml toluene was added to the precursor. The catalyst was stirred over night at 45°C. The catalyst was dried at 45-.70°C for 2.0 h. The composition of the catalyst was 2.8% Ti. 2.0% Mg, 14.6% CI and 2.5% Al. The polymerization results are shown in table 1. Example 5 54.9 ml (2 mmol/g Si) of 20% EADC was added slowly at 25°C to 30 g of silica (Crosfield ES70X, activated at 600°C). The mixture was stirred for 2.0 h at 20°C. 76.7 g (2 mmol Mg/g Si) of a complex prepared according to complex preparation 4 was added and stirred for 3 h at 20- 45°C. The catalyst was dried at 45-70°C for two hours. The catalyst was cooled down to 46°C and 3.33 ml (1 mmol/f Si) TiCl^ diluted in 10 ml toluene was added to the precursor. The catalyst was stirred over night at 45°C. The catalyst was dried at 45-70°C for 2.0 h. The composition of the catalyst was 3.0% Ti, 2.1% Mg, 14.4% CI and 2.7% Al. The polymerization results are shown in table 1. Polymerization Ethylene was polymerized in slurry conditions giving products having different average molecular weights or melt flow ratios as follows. 1.8 litres of purified n-pentane was fed into a 3 litre reactor. The Tiixture was heated up to a temperature 90°C. In the meantime a 500 ml vessel was pressurized with hydrogen to 500 kPa when polymerizing at low melt flow rate conditions (LMFR) and to 1750 K when polymerizing at high melt flow rate conditions (HMFR) . When the temperature 90°C was reached the pressure was about 42 0 kPa in the reactor. Then the procatalyst and the cocatalyst triethylaluminium (TEA) were fed into the reactor. The ethylene stream was then conducted through the bomb containing hydrogen into the reactor. The total pressure was increased to 144 0 kPa and was maintained by means of continuous ethylene supply. The polymerization went on for one hour. The molar ratio Al/Ti was 15. The results of the polymerizations are represented in Table 1. In Figure 1 results are represented by diagrams where the polymerisation activity is as function of average molecular weight described as melt flow ratio (defined according to ISO 1133) . The procatalyst BC-200 was compared to the old catalysts NC-20 (FI 916192), FI 88S05e, FI 906281 + FI 895526, a commercial catalyst, and US 4 354 009. 1.8 1 of purified isobutan was fed into a 3 1 reactor. The content was heated to 95°C. Meanwhile a 500 ml vessel was pressorized with hydrogen, to 6.2 bar when the polymerization was carried out at low melt flow rate conditions (LMFR), and to 18.7 bar when the polymerization was carried out at high melt flow rate conditions. When the temperature 95°C was reached, the procatalyst in question and a triethyl aluminum (TEA) cocatalyst were fed to the reactor. Then, ethylene was fed to the reactor through said hydrogen vessel, whereby the total pressure was raised to 28.5 bar and kept constant by feeding ethylene. The molar ratio Al/Ti was 30. The results are disclosed in table 2 and the figure. The AB index of the claimed catalyst BC-200 was clearly higher than that of the old catalysts. WE CLAIM: 1. A process for the preparation of a procatalyst suitable for the production of ethylene polymers, said procatalyst comprising an inorganic support, a chlorine compound deposited on said support, a magnesium compound deposited on said support and a titanium compound deposited on said support, characterized in that the said process comprises the step of a) contacting the inorganic support with an alkyl metal chloride of the general formula 1 (RnMeCl3.„) n, (1) wherein R is a C1-C20 alkyl group, Me is a metal group (13) of the periodic table, n = 1 or 2 and m = 1 or 2, to produce a first reaction product, b) contacting the first reaction product with a magnesium complex containing hydrocarbyl, hydrocarbyl oxide and magnesium having the general formula 3 Mg3(OR')bR"cXd (3) Wherein R' is a C2-C20 hydrocarbyl group with or without a hetero element, R" is a C2-C20 hydrocarbonyl group , X is halogen , preferably chlorine , a>l, b>0 , c >0, d >_0, a = Vt (b+c+d) and c/b ClxTi(OR%., (2) wherein R'^ is a C2-C20 hydrocarbyl group and x is 3 or 4, to produce said procatalyst. 2. The process according to claim 1, wherein the molar ratio c/b is between approximately 0.06 and 0.1, and that d is 0. 3. The process according to claim 2 wherein the group R' or R' " is a branched aliphatic C2-C20 group, preferably an aliphatic C4-C20 group which is branched in its 2-position with respect to the oxygen, most preferably a 2-lower alkyl-C3-Ci9-alkyl group such as a 2-ethyl hexyl group or a 2-propyl pentyl group. 4. The process according to any of claims 1 to 3, wherein the magnesium complex of step b) is a product of a dialkyl magnesium and an alcohol. 5. The process according.to claim 4, wherein the magnesium complex of step b) is a product of a di-C2-Cio-alkyl magnesium, preferably dibutyl magnesium, butyl ethyl magnesium or butyl octyl magnesium and an alcohol. 6. The process according to claims 4 or 5, wherein the magnesium complex of step b) is a product of a dialkyl magnesium and a branched alcohol, preferably a 2-alkyl aikanol, most preferably 2-ethyl hexanol or 2-propyl pentanol. 7. The process according to any of claims 5 & 6, wherein the magnesium complex of step b) is a product of a dialkyl magnesium and an alcohol, the dialkyl magnesium and the alcohol having been contacted at a molar ratio between 1:1.78 and 1:1.99, preferably between 1:1.80 and 1:1.98. 8. The process according to claims 1 to 7, wherein the magnesium complex is contacted with the first reaction product in step b) so that the compound or mixture containing hydrocarbyl, hydrocarbyl oxide and magnesium is in a hydrocarbon solution, preterably a hydrocarbon solution, the viscosity of which is below 10 mPas. 9. The process according to any of claims 1 to 8, wherein the morganic support in step a) is an inorganic oxide having surface hydrox>'ls. preferably silica. 10. The process according to claim 9, wherein tlie inorganic support is an inorganic support, preferably silica, trom which a part ot" its surface hydroxyl groups has been removed, preterably silica containing at the most 2 0 mmol of surface hydroxy! groups per g of silica. 11. The process according to claims 9 or 10, wherein the inorganic oxide which contains surface hydroxyl gioups in step a), is contacted with an alkyl metal chloride so that the molar ratio between the alkyl metal chloride and the surface hydroxy Is of the inorganic o.xide is al least 1, preferably between 1 and 1.5. 12. The process according to any of claims I to 11, wherein the inorganic support in step a) is contacted with an alkyl metal chloride, which is an alkyl aluminum chloride, preterably a lower alk)'l aluminum dichloride, most preferably ethyl aluminum dichloride. 13. The process according to any of claims 1 to 12, wherein the inorganic support is step a) is contacted with an alkyl metal chloride so that the alkyl metal chloride is in the form of a 5-25 % hydrocarbon solution, the viscosity of which preferably is below 10 mPas. 14. The process according to any of claims 1 to 13, wherein the amount of the magnesium complex of step b) and the alkyl metal chloride of step a) are such that the atomic ratio between the magnesium and the chlorine of the alkyl metal chloride is from l.T.O to 1:1.5, preferably between 1:1.5 to 1:2.0. 15. The process according to any of claims 1 to 14, wherein the titanium compound of step c) is titanium tetrachloride. 16. The process according to any of claims 1 to 15, wherein the ratio between the titanium compound of step c) and the magnesium complex of step b) is such that the atomic ratio between titanium and magnesium is 0.1 17. A process for the preparation of a procatalyst substantially as herein above described and exemphfled.

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