Catalyst Components For The Polymerization Of Olefins And Catalysts Therefrom Obtained

PATENT
Catalyst Components For The Polymerization Of Olefins And Catalysts Therefrom Obtained
Pub. No.: WO/2011/157582
International Application No.: PCT/EP2011/059289
Publication Date:  22.12.2011
Applicants:
BASELL POLYOLEFINE GMBH [DE/DE]; Brühler Straße 60 50389 Wesseling (DE)
Inventors:
GUNDERT, Friedhelm; (DE).
SCHNEIDER, Martin; (DE)
Abstract:
A catalyst component for the polymerization of olefins obtained by: (a) reacting in a inert hydrocarbon suspension medium a Mg(OR₁)(OR₂) compound, in which R₁ and R₂ are identical or different and are each an alkyl radical having 1 to 10 carbon atoms, with a tetravalent transition metal compound having at least a Metal-halogen bond, used in amounts such that the molar ratio metal/Mg is from 0.05 to 10, thereby obtaining a solid reaction product dispersed in a hydrocarbon slurry, (b) washing the solid reaction product dispersed in a hydrocarbon slurry with a liquid hydrocarbon, (c) contacting the washed solid reaction product obtained in (b) with a tetravalent titanium compound and (d) contacting the product obtained in (c) with an organometallic compound of a metal of group 1, 2 or 13 of the Periodic Table.

The present invention relates to catalyst components for the polymerization of olefins CH₂=CHR, wherein R is hydrogen or hydrocarbon radical having 1-12 carbon atoms. In particular, the invention relates to catalyst components suitable for the preparation of homopolymers and copolymers of ethylene and to the catalysts obtained therefrom.
Specifically, the present invention relates to solid catalyst components, comprising titanium magnesium and halogen, and obtainable by a specified sequence of reaction steps. The catalysts of the invention are suitably used in (co)polymerization processes of ethylene to prepare (co)polymers having medium-narrow Molecular Weight Distribution (MWD) and high activity. The MWD is an important characteristic of ethylene polymers in that it affects both the rheological behavior, and therefore the processability, and the final mechanical properties. In particular, polymers with narrow MWD are suitable for cast films and injection moulding in that deformation and shrinkage problems in the manufactured article are minimized. The width of the molecular weight distribution for the ethylene polymers is generally expressed as melt flow rate ratio FRR₂₁.6/5 or melt flow rate ratio FRR₂₁.6/₂.16, respectively. FRR₂₁.6/5 is the ratio between the melt index measured by a load of 21.6 Kg and that measured with a load of 5 Kg, whereas FRR₂₁.6/₂.16 is the ratio between the melt index measured by a load of 21.6 Kg and that measured with a load of 2.16 Kg . The measurements of melt index are carried out according to ISO 1 133 and at 190°C.
Catalyst components having the capability of giving polymers with narrow molecular weight distribution are also useful to prepare polymer compositions with broad molecular weight distribution. In fact, one of the most common methods for preparing broad MWD polymers is the multi-step process based on the production of different molecular weight polymer fractions in each step, sequentially forming macro molecules with different length on the catalyst particles.
The control of the molecular weight obtained in each step can be carried out according to different methods, for example by varying the polymerization conditions or the catalyst system in each step, or by using a molecular weight regulator. Regulation with hydrogen is the preferred method in industrial plants. It has been observed that final compositions of optimal properties are obtainable when a catalyst is used able to provide polymers with narrow MWD and different average Mw in each single step that, when combined together form final compositions with broad molecular weight distribution. In these multistep processes a critical step is that in which the lower average molecular weight polymer fraction is prepared. In fact, one of important features that the catalyst should possess is the so called "hydrogen response", that is the extent of capability to reduce the molecular weight of polymer produced in respect of increasing hydrogen concentration. Higher hydrogen response means that a lower amount of hydrogen is required to produce a polymer with a certain molecular weight. In turn, a catalyst with good hydrogen response would also usually display a higher activity in ethylene polymerization due to the fact that hydrogen has a depressive effect on the catalyst activity. Moreover, it is also important that the polymer chains show a limited amount of long chain branching which in certain applications are responsible for lowering certain properties like impact strength and ESCR.
In view of the above, it would be therefore useful to have a catalyst component able to provide ethylene polymers with narrow molecular weight distribution, combined with a good balance of polymerization activity and morphological stability.
A catalyst component for use in ethylene (co)polymerization is described in the WO03/099882. It concerns polymerizing in the presence of a catalyst consisting of the product of the reaction of a gelatinous dispersion of magnesium alkoxide with a transition-metal compound (component a) and an organometallic compound (component b). The reaction between the gelatinous dispersion of magnesium alkoxide and the transition metal compound for the formation of component (a) is carried out in the liquid hydrocarbon phase. The so obtained reaction mixture is then directly reacted with the organoaluminum compound (b) without any intermediate treatment. Although showing properties of interest, the catalyst did not produce sufficiently high polymerization activity and sufficiently narrow molecular weight distribution. In principle, narrowing of MWD could be obtained by using certain oxygenated electron donor compounds. However, this usually involves a reduced polymerization activity of the catalyst. In the case of the catalysts disclosed in WO03/099882 the activity is already not particularly high, thus the use of an electron donor for narrowing MWD would involve too low activity for operation in an industrial plant.
It has now surprisingly been discovered that by modifying the catalyst preparation recipe disclosed in the prior art, it is possible to greatly improve its polymerization activity making it suitable also for the use in combination with an electron donor. Therefore, it is an object of the present invention a catalyst component for the polymerization of olefins obtained by a process comprising:
(a) reacting in a inert hydrocarbon suspension medium a Mg(ORi)(OR2) compound, in which Ri and R₂ are identical or different and are each an alkyl radical having 1 to 10 carbon atoms, with a tetravalent transition metal compound having at least a Metal-halogen bond, used in amounts such that the molar ratio metal/Mg is from 0.05 to 10, thereby obtaining a solid reaction product dispersed in a hydrocarbon slurry,
(b) washing the solid reaction product dispersed in a hydrocarbon slurry with a liquid hydrocarbon,
(c) contacting the washed solid reaction product obtained in (b) with a tetravalent titanium compound and
(d) contacting the product obtained in (c) with an organometallic compound of a metal of group 1 , 2 or 13 of the Periodic Table.
In step (a) of the preparation of the catalyst component, Ri and R₂ are preferably alkyl groups having from 2 to 10 carbon atoms or a radical -(CH₂)_nOR₃, where R₃ is a C₁-C4-alkyl radical and n is an integer from 2 to 6. Preferably Ri and R₂ are Ci-C₂-alkyl radical. Examples of such magnesium alkoxides are: magnesium dimethoxide, magnesium diethoxide, magnesium di-i-propoxide, magnesium di-n-propoxide, magnesium di-n-butoxide, magnesium methoxide ethoxide, magnesium ethoxide n-propoxide, magnesium di(2-methyl- 1 -pentoxide), magnesium di(2-methyl-l -hexoxide), magnesium di(2-methyl-1-heptoxide), magnesium di(2-ethyl-l -pentoxide), magnesium di(2-ethyl- l-hexoxide), magnesium di(2-ethyl- l-heptoxide), magnesium di(2-propyl-l-heptoxide), magnesium di(2-methoxy-l -ethoxide), magnesium di(3-methoxy-l-propoxide), magnesium di(4-methoxy- l-butoxide), magnesium di(6-methoxy- l-hexoxide), magnesium di(2-ethoxy-l-ethoxide), magnesium di(3-ethoxy-l -propoxide), magnesium di(4-ethoxy- l-butoxide), magnesium di(6-ethoxy- l-hexoxide), magnesium dipentoxide, magnesium dihexoxide. Preference is given to using the simple magnesium alkoxides such as magnesium diethoxide, magnesium di-n-propoxide and magnesium di-i-butoxide. Magnesium diethoxide is the preferred one. It can be used as a suspension or as a gelatineous dispersion. The suspension or the gel can be prepared starting from commercially available Mg(OC₂H₅)₂ usually having average particle diameter ranging from 200 to 1200 μηι preferably from 500 to 800 μηι.
Preferably before the reaction with the transition metal halide the magnesium alcoholate is suspended in an inert, saturated hydrocarbon. In order to lowering the magnesium alcoholate particle size, the suspension can be subject to high shear stress conditions by means of a high-speed disperser (for example Ultra-Turrax or Dispax, IKA-Maschinenbau Janke & Kunkel GmbH) working under inert atmosphere (Ar or N₂). Preferably the shear stress is applied until a gel-like dispersion is obtained. This dispersion differs from a standard suspension in that it is substantially more viscous than the suspension and is gellike. Compared with the suspended magnesium alcoholate, the dispersed magnesium alcoholate settles out much more slowly and to a far lesser extent.
The magnesium alkoxide is firstly reacted with the tetravalent transition metal compound of the formula (II)

where M is titanium, zirconium or hafnium, preferably titanium or zirconium, more preferably titanium, R4 is an alkyl radical having from 1 to 9, preferably from 1 to 4 carbon atoms and X is a halogen atom, preferably chlorine, and m is from 1 to 4, preferably from 2 to 4.
Examples which may be mentioned are: T1CI₄, TiCi₃(OC₂H₅), TiCl₂(OC₂H₅)₂, TiCl(OC₂H₅)₃, TiCl₃(OC₃H₇), TiCl₂(OC₃H₇)₂, TiCl(OC₃H₇)₃, TiCl₃OC₄H₉), TiCl₂(OC₄H₉)₂, TiCl(OC₄H₉)₃, TiCl₃(OC₆H₁₃), TiCl₂(OC₆H₁₃)₂, TiCl(OC₆H₁₃)₃, ZrCk, preference is given to using TiCL or ZrCU- Particular preference is given to TiCL.
The reaction of the magnesium alkoxide with the tetravalent transition metal compounds is carried out at a temperature at from 50 to 140°C, preferably from 60 to 120°C, more preferably from 70 to 90°C over a period of from 0.1 to 20 hours, preferably within 1 to 10 hours, more preferably within 1 to 7 hours. Suitable inert hydrocarbon suspension media for the abovementioned reactions include aliphatic and cycloaliphatic hydrocarbons such as butane, pentane, hexane, heptane, cyclohexane, isooctane and also aromatic hydrocarbons such as benzene and xylene. Petroleum spirit and hydrogenated diesel oil fractions which have carefully been freed of oxygen, sulfur compounds and moisture can also be used.
The magnesium alkoxide and the tetravalent transition metal compound can be reacted in a molar ratio of Metal/Mg ranging from 0.05 to 5, preferably from 0.1 to 1. At the end of the reaction a solid product is obtained by removing of the liquid phase.
In step (b) one or more washing step with inert hydrocarbon are carried out until the supernatant mother liquor has CI and Ti concentrations of less than 10mmol dm³. The washing step can be carried out with the same hydrocarbon medium used in step (a) at a temperature ranging from 10°C to the boiling point of the medium used. Preferably, it is carried out under mild conditions and more preferably at room temperature when working at Ti Mg molar ratios in the range of 0.1 to 1. Washings at higher temperature are suitable for higher Ti Mg molar ratios.
After the washing the solid product coming from (b), preferably still in form of a concentrated slurry, is contacted in step (c) with a tetravalent titanium compound of formula TiX_m(OP₄)4-_m where X and m have the same meaning disclosed above. Preferred titanium compounds are TiC , TiCl₃(OC₂H₅), TiCl₂(OC₂H₅)₂, TiCl(OC₂H₅)₃, TiCl₃(OC₃H₇), TiCl₂(OC₃H₇)₂, TiCl(OC₃H₇)₃, TiCl₃OC₄H₉), TiCl₂(OC₄H₉)₂, TiCl(OC₄H₉)₃, TiCl₃(OC₆H₁₃), TiCl₂(OC₆H₁₃)₂, TiCl(OC₆H₁₃)₃. TiC being the most preferred.
The product coming from (b) and the tetravalent transition metal compound can be contacted in a molar ratio of Ti/Mg ranging from 0.001 to 1 , preferably from 0.01 to 0.1. At the end of the reaction a solid product is obtained by totally or partially removing of the liquid phase.
In the subsequent step (d), an organometallic compound of a metal of group 1 , 2 or 13 of the Periodic Table is reacted with the solid reaction product of step (c). Preferably, the organometallic compound is chosen among organoaluminum compounds. Suitable organoaluminum compounds are chlorine- containing organoaluminum compounds, e.g. dialkylaluminum monochlorides of the formula R³₂A1C1 or alkylaluminum sesquichlorides of the formula R³₃A1₂C1₃, where R³ is an alkyl radical having from 1 to 16 carbon atoms. Examples which may be mentioned are (C₂H₅)₂A1C1, (iC₄H₉)₂AlCl, (C₂H₅)₃A1₂C1₃. It is also possible to use mixtures of these compounds.
The organoaluminum compound can be added in a molar ration of 0.1 to 2, preferably from 0.3 to 1 with respect to magnesium alkoxide. The reaction is carried out in suspension under stirring at a temperature ranging from 0 to 150°C, preferably from 60 to 120°C within 0.5 to 7 hours, preferably from 1 to 5 hours.
At the end of the preparation process the particle size of the catalyst component (component A) preferably ranges from 5 to 30μηι.
As already explained the catalyst component obtained with this process is endowed with such a high activity that makes it possible for it to incorporate also an electron donor for the narrowing of the molecular weight distribution of the polymer while maintaining an activity of industrial interest.
The electron donor is preferably selected from oxygenated compounds belonging to ethers, esters, alcohols, aldehydes, alkoxysilanes, and ketones.
Particularly preferred are the silicon compounds of formula R^I_aRⁿbSi(ORⁱⁿ)4-(a+b) where R¹-_Rm are linear, branched, cyclic or aromatic C₁-C₂₀ hydrocarbon groups a and b are integers from 0 to 2 with the proviso that (a+b) ranges from 1 to 3.
Preferably Rⁿⁱ is a linear Q-C5 alkyl, preferably methyl or ethyl. In this connection, when b is 0, R¹ is preferably a linear, branched or cyclic alkyl radical or an aryl radical having from 3 to 10 carbon atoms and a is 1. In this embodiment, R¹ is preferably selected from propyl, isopropyl, isobutyl, cyclopentyl, and phenyl.
According to another embodiment, a and b are 1 , R¹ is selected from C3-C₁₀ cycloalkyl or aryl groups, Rⁿ is selected from linear Q-C5 alkyl groups and Rⁿⁱ is a linear Q-C5 alkyl, preferably methyl or ethyl.
Non limiting exemplary silicon compounds include diethyldimethoxysilane, dipropyldimethoxysilane, diisopropyldimethoxysilane, dibutyldimethoxysilane, diisobutyldimethoxysilane, isobutylmethyldimethoxysilane, isopropylisobutyldimethoxysilane, dicyclopentyldimethoxysilane, cyclohexylmethyldimethoxysilane, diphenyldimethoxysilane, propyltrimethoxysilane, isopropyltrimethoxysilane, butyltrimethoxysilane isobutyltrimethoxysilane, cyclopentyltrimethoxysilane, phenyltrimethoxysilane, diethyldiethoxysilane, dipropyldiethoxysilane, diisopropyldiethoxysilane, dibutyldiethoxysilane, diisobutyldiethoxysilane, isobutylmethyldiethoxysilane, isopropylisobutyldimethoxysilane, dicyclopentyldiethoxysilane, cyclohexylmethyldiethoxysilane, diphenyldiethoxysilane, propyltriethoxysilane, isopropyltriethoxysilane, butyltriethoxysilane isobutyltriethoxysilane, cyclopentyltriethoxysilane, phenyltriethoxysilane. Preference is given to group of diethoxysilanes. Most preferably compounds selected from group of triethoxysilanes are used.
The electron donor can be used in any of the step (a), (c) or (d). Preferably, it is used after completion of step (d) by combining the solid catalyst component with the silicon compound of formula R^I_aRⁿbSi(ORⁱⁿ)4-(_a+b) reported above. The aforementioned silicon compound can be added in a molar ratio of 0.1 to 3, preferably from 0.3 to 1 with respect to transition metal fixed on the solid component after the reaction with magnesium alkoxide. The reaction is carried out in suspension under stirring at a temperature ranging from 0 to 150°C, preferably from 60 to 120°C within 0.5 to 5 hours, preferably from 1 to 2 hours.
The catalyst component of the invention can be converted into active catalyst system by reacting it with a trialkylaluminum (component B) having from 1 to 6 carbon atoms in the alkyl radical, e.g. triethylaluminum, triisobutylaluminum, triisohexylaluminum, Preference is given to triethylaluminum and triisobutylaluminum.
The mixing of the component (A) and the component (B) can be carried out in a stirred vessel at a temperature of from -30°C to 150°C prior to the polymerization. It is also possible to combine the two components directly in the polymerization vessel at a polymerization temperature of from 20°C to 200°C.
It is also possible firstly to prepolymerize the preactivated catalyst system with alpha-olefins, preferably linear C2-C10-l-alkenes and in particular ethylene or propylene, and then to use the resulting prepolymerized catalyst solid in the actual polymerization. The mass ratio of catalyst solid used in the prepolymerization to monomer polymerized onto it is usually in the range from 1 :0.1 to 1 :2.
It is also possible to isolate the catalyst in the non-prepolymerized form or in the prepolymerized form and store it as a solid and re-suspend it on later use.
The catalysts systems of the invention are particularly suited for liquid phase polymerization process. In fact, the small average particle size of the component (A) , such as less than 30μηι, preferably ranging from 5 to 20 μηι, is particularly suited for slurry polymerization in an inert medium, which can be carried out continuously stirred tank reactor or in loop reactors. In a preferred embodiment the polymerization process is carried out in two or more cascade loop or stirred tank reactors producing polymers with different molecular weight and/or different composition in each reactor. In addition, to the ethylene homo and copolymers mentioned above the catalysts of the present invention are also suitable for preparing very-low-density and ultra-low-density polyethylenes (VLDPE
and ULDPE, having a density lower than 0.920g/cm , to 0.880 g/cm ) consisting of copolymers of ethylene with one or more alpha-olefins having from 3 to 12 carbon atoms, having a mole content of units derived from ethylene of higher than 80%; elastomeric copolymers of ethylene and propylene and elastomeric terpolymers of ethylene and propylene with smaller proportions of a diene having a content by weight of units derived from ethylene of between about 30 and 70%.
The following examples are given in order to further describe the present invention in a no n- limiting manner.
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