Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F10/00—Homopolymers and copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F110/00—Homopolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond
  • C08F110/04—Monomers containing three or four carbon atoms
  • C08F110/06—Propene

Definitions

• a procatalyst component based on a transition metal compound on a carrier of magnesium chloride and manganese halide is based on magnesium chloride and manganese halide.
• the invention relates to an olefin polymerization catalyst the *- procatalyst component of which comprises a transition-metal compound on a support material of magnesium chloride.
• the in ⁇ vention also relates to a method for preparing a procatalyst component for an olefin polymerization catalyst of the said type, wherein a) a magnesium chloride and a lower alcohol are contacted and the mixture is melted, b) the molten mixture is atomized, and it is solidified by cooling to produce support material particles, and c) the support material particles are caused to react with a transition-metal compound.
• the invention relates to the use of an olefin polymerization catalyst of the said type for the preparation of polypropylene, and preferably a polypropylene with a broad mo ⁇ lecular weight distribution.
• ⁇ -olefins are often polymerized using a Ziegler-Natta catalyst system made up of a so-called procatalyst and a cocatalyst.
• the procatalyst component is based on a compound of a transition metal belonging to any of Groups IVA - VIII in the Periodic Table of the Elements
• the cocatalyst component is based on an organometallic compound of a metal belonging to any of Groups IA - IIIA in the Periodic Table of the Elements (the groups are defined according to Hubbard, i.e. IUPAC) .
• the cata ⁇ lyst system may also include a support material on which the transition-metal compound is deposited and an internal electron donor which enhances and modifies the catalytic properties and is deposited on the support material together with the transition-metal compound.
• a separate so-called external electron donor can also be used together with the procatalyst and the cocatalyst.
• the Ziegler-Natta catalysts used for polypropylene polymeriza ⁇ tion usually produce a polymer having a narrow molecular weight distribution. This material is very suitable for injection molding purposes. However, there are several uses in which a broad molecular weight distribution is required. Especially if a higher melt strength is desired, a wider range of polymer chain lengths would be an advantage.
• active sites of the same type will produce a polymer material of the same type, in which case the uniformity is seen as a narrow molecular weight distribution. Since a broader molecular weight distribution is required for a number of uses of polypropylene, efforts have been made to prepare catalysts with active sites of a variety of types.
• JP application publication 79037911 describes the preparation of a polyolefin having a wide molecular weight distribution by using an active and new procatalyst which is made up of a titanium and/or vanadium compound on a support material.
• the first component is obtained by treating aluminum oxide with sulfur dioxide, and the other component contains a magnesium halide, a manganese halide, and an organic compound of a metal such as aluminum or zinc, e.g. MgC ⁇ MnC ⁇ -AMOR ⁇ ) .
• the object of the present invention is to provide a catalyst comprising a transition-metal compound on a magnesium chloride support material for producing polyolefins having a broad mo ⁇ lecular weight distribution.
• Another aim is a maximal catalyst activity and a suitable catalyst morphology, which will also be reflected in the morphology of the polymer product.
• the inven ⁇ tion also aims at an improved method for the production of an olefin polymerization catalyst of the said type.
• manganese (II) halide is incorporated into its magnesium chlor ⁇ ide support material at a rate of at minimum approx. 0.1 %, and at maximum approx. 50 %, of the total molar amount of magnesium chloride and manganese (II) halide. It is preferable that the minimum concentration of manganese (II) halide is approx. 5 % of the total molar amount of magnesium chloride and manganese (II) halide. The maximum concentration of manganese (II) halide is preferably approx.
• the maximum concentration of manganese (II) halide is less than 30 %, and preferably approx. 10 %, of the said the said total molar amount.
• the active part of the catalyst i.e. the transition-metal compound
• the most preferable transition-metal compound is titanium tetrachloride.
• the manganese (II) halide is selected so that with respect to its ion radii it fits as well as possible into the crystal lattice of magnesium chloride. It has been observed that the most advantageous manganese (II) halide is manganese chloride. The said advantageous concentrations have specifically been measured using manganese (II) chloride, but similar results are probably attainable also using other manganese (II) halides.
• a preferred composition, based on weight, of the procatalyst component for the polymerization catalyst according to the invention is, not including the organometallic cocatalyst used in the polymerization, as follows: magnesium 10-20 %, manganese 1-10 %, titanium 2-4 %, and chlorine 45-60 %, calculated from the total weight of the supported procatalyst component.
• an internal donor which is preferably an aromatic ester of the type of di-isobut ⁇ l phthalate. Benzoic acid esters are also possible.
• the con ⁇ centration of this internal donor may be 10-25 % of the weight of the procatalyst component in the catalyst.
• the catalyst according to the invention preferably also con ⁇ tains an organometallic cocatalyst, which is preferably a tri- alkyl aluminum, preferably triethyl aluminum.
• an organometallic cocatalyst which is preferably a tri- alkyl aluminum, preferably triethyl aluminum.
• a so-called external donor may also be added to the catalyst; the external donor may be silane, cineole or ether, preferably cyclohexyl-methyl- ethoxysilane, cineole, or diphenyl-dimethoxysilane.
• the solid part of the catalyst according to the invention is in the form of substantially spherical particles having a diameter within a range of approx. 100-400 urn.
• the invention also relates to a meth ⁇ od for the preparation of a procatalyst component for an olefin polymerization catalyst.
• magnesium chloride and a lower alcohol are contacted and melted, the molten mixture is atomized and solidified by cooling to produce support material particles, and the support material particles are reacted with a transition-metal compound to produce an active procatalyst.
• a broader molecular weight distribution can be obtained by adding to the magnesium chloride and the lower alcohol a manganese (II) halide at a rate of at minimum approx. 0.1 % and at maximum approx. 50 % of the total molar amount of magnesium chloride and manganese (II) halide. This addition takes place before the solidification and thus yields a homogenous procatalyst doped with manganese.
• step a the magnesium chloride and the lower alcohol are contacted and the mixture is melted
• step b the melt is atomized and it is solidified by cooling it to produce support material par ⁇ ticles.
• steps a) and b) are preferably carried out by suspending a finely-divided magnesium chloride and a finely- divided manganese (II) halide, preferably manganese (II) chlor ⁇ ide, into an inert, heat-resistant medium. Then a lower alcohol is added to the suspension and the suspension is heated until the mixture made up of the said salts and alcohol melts, form ⁇ ing melt drops in the medium. After the said steps, the medium with its melt drops is contacted with a cold liquid, which dissolves the medium and solidifies the melt drops into finished support material particles.
• Manganese (II) halide (preferably chloride) is preferably added to step a) at a rate of at minimum 5 % of the total molar amount of magnesium chloride and manganese (II) halide (prefer ⁇ ably chloride).
• Manganese (II) halide (preferably chloride) is added to step a) at a rate of at maximum approx. 40 % of the total molar amount of magnesium chloride and manganese (II) halide (preferably chloride). It is most preferable to add manganese (II) chloride to step a) at a rate of at maximum approx. 30 % and preferably approx. 10 % of the total molar amount of magnesium chloride and manganese (II) chloride.
• the lower alcohol used in step a) is preferably methanol and/or ethanol, and most preferably ethanol.
• step c) The solid support material obtained from step b) in the form or particles is caused to react with a transition-metal compound in step c) .
• the most preferred transition-metal compound is titanium tetrachloride.
• step c) is carried out by causing the support material particles to react not only with the transition-metal compound but also with an internal electron donor, in which case the electron donor used is preferably an aromatic ester such as di-isobutyl phthalate.
• the catalyst according to the invention is used for producing a polypropylene having a broad molecular weight distribution.
• the said procata ⁇ lyst is combined with an organometallic cocatalyst and prefera ⁇ bly also an external donor, which may be, for example, silane, cineole, ether or other such external donor commonly known in the art.
• Embodiment examples 3, 4 and 5, as well as comparison examples 1 and 6, are presented below in order to elucidate the inven ⁇ tion.
• Examples 1 and 6 are comparison examples, in which the molar concentrations of manganese are respectively 0 and 100 %.
• the man ⁇ ganese concentrations in the support material were respectively 3, 10, 30, and 60 mol-%.
• Figure 4 The mean particle diameter of the support ma ⁇ terial as a function of the Mn concentration (mol-%) in MgCl 2 .
• FIG 7. The X-ray diffraction pattern of a Ziegler- Natta catalyst doped with 10 % Mn in a MgCl 2 support material.
• Figure 8. The activities of Mn-doped Ziegler-Natta cata ⁇ lysts.
• Figure 9 The isotacticities (A) and isotactic indices (B) of polymers produced using Mn-doped catalysts.
• Figure 11 The particle size distribution of a polymer sample produced using a catalyst doped with 30 % manganese.
• the hot silicone oil mixture was siphoned through a teflon tube into a reactor containing 1 liter of cold heptane (-30 °C) .
• the melt drops of the metal salt mixture solidified in this cold solution.
• the solids were washed three times with 600 ml of heptane.
• the support material was vacuum dried.
• the morphology of the support material obtained was such that a higher manganese amount added to the salt mixture hampered the bringing of the mix into a liquid or molten state.
• the molten material was in this case also more viscous. Since the mixing conditions in the silicone bath in the different examples were identical, a higher melt viscosity also yielded larger support material particles. This increase in the particle diameter continued up to a manganese concentration of 30 %. Thereafter the liquid melt drops were no longer capable of forming spheri ⁇ cal particles.
• This change in particle morphology can be seen in Figures 1-3.
• the first figure shows the morphology of a material doped with 3 per cent manganese.
• the morphology of this material resembles that of a conventional magnesium chlor ⁇ ide support material, and the mean particle diameter is approx. 50 ⁇ m.
• the next of these figures shows enlarged particles of a material doped with 10 % manganese, and the last one shows a crystalline material prepared from pure manganese (II) chlor ⁇ ide.
• Table 3 lists the mean particle sizes, and they are also shown graphically in Figure 4. Table 3 also shows the general morphological character and color of the products.
• the catalyst synthesis was carried out without difficulty. The only difference as compared with conventional catalyst syn ⁇ thesis was in the color of the reaction solution. Thereafter, the chemical composition of the procatalyst was measured. The measurement results are presented in Table 4.
• the donor concentration was also observed by determining the di-isobutyl phthalate concentration in the procatalyst. This was done because it was not known whether manganese was capable of binding internal donor to the same degree as magnesium was. In particular, it was desired to see whether a mixture made up of two salts could retain the normal donor to support material ratio during the synthesis. The ratios are shown in Tables 5 and 6. The final proportion is also seen in Figure 6. According to the results, the ability of the support material to bind the donor decreased sharply within the middle range of the salt mixt ⁇ re. Thus, a catalyst doped with 10 % manganese was capable of binding only 50 % of the original donor amount. A 60 % man- ganese (II) chloride material, on the other hand, was capable of binding donor to the same degree as was a pure magnesium chloride material.
• II man- ganese
• DIBP di-isobutyl phthalate
• the dimensions of the doped magnesium chloride crystals were determined by taking X-ray diffraction patterns of all ' the cat ⁇ alyst samples in order to determine the effect of manganese (II) chloride. It proved to be possible to use manganese up to 30 % without the X-ray diffraction pattern of magnesium chlor- ide changing substantially. With these concentrations a normal amorphous magnesium chloride pattern was obtained, in which there was at 15 degrees a small peak indicating the height of the crystal and at 50 degrees a clear peak indicating the width of the crystal (cf. Figure 7) . At higher manganese concentra ⁇ tions, the X-ray pattern of manganese (II) chloride was prevalent and a more crystalline structure was obtained. It was possible to calculate the dimensions of magnesium chloride crystals up to a 30 % concentration of manganese. The results are shown in Table 7, and Figure 7 shows the X-ray diffraction pattern of a catalyst sample doped with 10 % manganese.
• Table 7 Crystal dimensions of Mn-doped catalysts. The heights were measured from a peak at 15° and the widths from a peak at
• Test polymerizations were carried out on all of the procata ⁇ lysts.
• a two-liter bench reactor was used in the test polymer ⁇ ization. 20-30 mg of procatalyst was used for the test polymer ⁇ ization. This amount was mixed with 620 ⁇ l of triethyl aluminum and 200 ⁇ l of a 25 % solution of the external donor cyclohexyl- methyl-dimethoxysilane (CHMDMS) in 30 ml of heptane.
• CHMDMS cyclohexyl- methyl-dimethoxysilane
• the poly ⁇ merizations were carried out at +70 °C and at a propylene mono ⁇ mer pressure of 10 bar. The partial pressure of hydrogen during the polymerization was 0.2 bar.
• the polymerization was con ⁇ tinued for 3 hours. The activity was measured on the basis of the polymerization yield. The soluble part of the polymer was measured by evaporating a measured portion
• Mn-doping seemed to have a crucial effect on the activity of the catalysts.
• Doping with 3 % manganese yielded almost the same result as an undoped procatalyst, if only the activity unit kg PP/g cat. is considered, but caused an increase up to 25 % in the activity when expressed in kg PP/g Ti.
• the activity increase was greatest when a material doped with 10 % manganese was used. In this case activities up to 20 kg PP/g cat. were obtained. Expressed in kg PP/g Ti, the activity increase was in the order of 100 %. With higher doping concentrations there was an almost linear activity decrease with increasing manganese concentrations.
• pure manganese (II) chloride was used instead of magnesium chloride, the activity was only 10 % of the original activity. Characterization of the polymer samples
• the polypropylene material produced using Mn-doped catalysts had a very low fines content when the doping percentage was below 30 %. This is clearly visible also in Figure 10. Compared with an undoped catalyst, the catalyst containing manganese 3 % contained hardly any particles with diameters smaller than 1 mm. A catalyst having a doping percentage of 30 % yields even better results.
• the particle size distribution measurements correlate well with the observations made regarding the morphology of the support material. Good morphology was obtainable with doping values up to 30 %, whereafter the polymer particles showed a collapsing behavior similar to that of procatalyst particles, whereby a large proportion of fines was produced. The best results with respect to the particle size distribution were achieved with a magnesium doping percentage of 30.
• the particle size distribu- tion of this polymer sample is shown in Figure 11.
• the bulk densities of the polymer materials are listed in Table 11. The values seem to decrease as the Mn-doping percentages increase. This seems to be due, first, to the fact that an increasing particle size automatically causes a decrease in the bulk density and, second, to the fact that a strongly doped catalyst produces irregular particles which reduce the bulk density.
• the bulk densities of the polymer samples are shown as a function of the Mn-doping concentration also in Figure 10.
• melt indices of the polymer samples are shown in Table 12. They seem to vary very little within a range of 0-60 % Mn. Thus it can be stated that the melt index measurements yielded rather satisfactory results, although at 10 % the melt index drops somewhat.
• the specific target of interest in the present work is the mo ⁇ lecular weight distribution of the polymer produced, for the idea is to produce in the catalyst differentiated active sites and thereby to form in the polymerization polymer chains of a variety of lengths.
• the analytical results obtained are listed in Table 13, and they are shown graphically in Figure 12.
• the entire molecular weight but especially the viscosity average molecular weight ( y ) and the weight average molecular weight (M ⁇ ,) , increase sharply when the molar percentage of manganese in the procatalyst increases from 0 to 10. At higher doping concentrations, however, there occurs a decrease of the molecular weight.
• the low molecular weights obtained with pure manganese (II) chloride may explain why the polymer products have a low isotacticity and a high melt index.
• the number average molecular weight (M n ) drops sharply when the doping concentration increases from zero to three % Mn, but remains thereafter almost unchanged up to 60 % Mn.
• Polydispersity i.e. the ratio of weight average molecular weight to number average molecular weight, was also calculated from the molecular weight measurement results.
• Figure 13 shows the polydispersity values as a function of the manganese con ⁇ centration in the procatalyst. Polydispersity increased from the conventional value 3 up to 7 when the manganese concentra ⁇ tion in the procatalyst increased from zero to 10 mol-% man ⁇ ganese (calculated from Mn + Mg) . Thereafter, polydispersity dropped to a constant value of 5.
• Figure 14 shows a comparison between a molecular weight distribution obtained with a polymer produced using an undoped procatalyst and the molecular weight distribution of a polymer produced using a procatalyst doped with 10 % manganese.
• a very good polymer product morphology is obtained when the concentration of manganese (II) chloride is below 30 %. Specif ⁇ ically with this manganese concentration the very best par ⁇ ticular size distribution is obtained, in which case the poly ⁇ mer contains hardly any fines.

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