WO1999021898A1

WO1999021898A1 - Magnesium halide based metallocene catalyst system

Info

Publication number: WO1999021898A1
Application number: PCT/US1998/022741
Authority: WO
Inventors: Zerong Lin
Original assignee: Exxon Chemical Patents Inc.
Priority date: 1997-10-28
Filing date: 1998-10-27
Publication date: 1999-05-06

Abstract

The invention relates to a process for preparing a particulate catalyst system for heterogeneous polymerization containing magnesium halide, a metallocene preferably of Group IVB of the Periodic Table, and an activating cocatalyst, which process comprises contacting a magnesium hydrocarbon compound, a hydrocarbon halogen compound in a non-polar hydrocarbon solvent medium substantially devoid of electron donor compound, the activating cocatalyst and the metallocene and removing the solvent by drying to obtain the particulate catalyst system. The invention also relates to olefin polymerization using the catalyst prepared in accordance with the invention.

Description

MAGNESIUM HALIDE BASED METALLOCENE CATALYST SYSTEM

Field of the invention This invention relates to a catalyst system comprising a metallocene and alumoxane, a process for preparing the catalyst system and a polyethylene made employing that catalyst system. The invention especially relates to the field of magnesium chloride based heterogeneous catalyst systems, to slurry polymerization processes, particularly continuous polymerization in a slurry loop process and to higher density polyethylene made in such processes. The catalyst system may also be used for polymerization of lower density ethylene copolymers with a C₃ to C₂₀ comonomer and to polymers comprising predominantly propylene derived units optionally with from 0 to 30 wt % of a C₂ to C₂₀ comonomer other than propylene.

Background of the invention

Metallocene based catalyst systems have been supported on solid supports for use in gas phase or slurry polymerization processes. The support is generally a porous mineral oxide such as silica. These supported catalyst systems have been used for the polymerization of LLDPE and other lower density polymers. Magnesium compounds have also been widely used to prepare heterogeneous catalyst for gas phase and slurry polymerization processes with conventional titanium chloride/aluminum alkyl based catalyst systems for making LLDPE and PP. There are some instances for the use of magnesium chloride in the preparation of metallocene based catalyst systems.

US5529965 uses organomagnesium compounds but there is no disclosure of a precipitation with an organic halogen-donating compound. JP63168408-A describes a heterogeneous magnesium halide based catalyst also using electron-donating compounds. EP-283958-B describes on page 4 line 29 onwards the use of a metallocene generally with a alumoxane activating cocatalyst and on page 5 line 35 MgCI₂ as a support but no details of the preparation are given. In one example a metallocene and alumoxane are used in a solution process. In other examples a magnesium diethoxide support is used with conventional titanium chloride catalysts.

EP-318048-B discloses a catalyst system prepared using anhydrous MgCI₂, optionally an electron donor compound and a metallocene. The metallocene appears to be used as the activating cocatalyst. There is no disclosure of an activating cocatalyst used in addition to the metallocene itself as the main catalyst component. Neither is there a disclosure of the magnesium chloride being produced by a reaction of a magnesium alkyl and alkyl chloride precursors.

EP-427697-A describes the use of magnesium chloride as a Lewis acid activating cocatalyst on page 3 line 48. There is no disclosure of the use of magnesium chloride in addition to another activating cocatalyst to help form an inert support for a heterogeneous catalyst system.

EP-509294-A discloses chromocenes supported in a variety of ways. One option is magnesium chloride , see page 5 line 27, but its preparation and combination with the catalyst components is not further illustrated.

EP-576213 uses an electron-donor to solubilize a non-reducing magnesium compound. In the examples 2-ethylhexanol is used for that purpose together with MgCI₂ whose preparation is not otherwise indicated in detail. It does not appear that the process leads to heterogeneous polymerization conditions. EP-609439 uses metallic magnesium in example 1 to make a solid product which we surmise to be magnesium iodide.

EP-737694-A and other documents ( e.g. EP-748823-A ) disclose MgCI₂ as a carrier for supporting a metallocene and alumoxane. These documents do not describe the manner in which the magnesium chloride is produced or the sequence of steps for contacting with the active catalyst components of the catalyst system.

The above references show the many different contexts in which the use of magnesium chloride may be suggested. Of greater pertinence than the above are those references in which the magnesium chloride helps form an inert support.

EP-439964-A describes the use of an anhydrous magnesium chloride support onto which various transition metal components are supported including metallocene compounds.

EP-590486-A in example 18 uses calcined magnesium chloride as a support for a metallocene. Methyl alumoxane is added separately to the polymerization reactor as an activating cocatalyst.

EP-435514-A discloses a catalyst for use in gas phase and suspension polymerization. In example 1 dibutyl magnesium is dissolved in a non-polar hydrocarbon solvent medium formed by n-hexane. It should be noted that next diisoamyl ether is added which is an electron-donor compound. The combination is contacted with t-butyl chloride to give a precipitate. Then a metallocene was placed on the support. Only in the polymerization reactor itself was alumoxane added as activating cocatalyst. In example 3 methyl alumoxane is added to the magnesium chloride support first followed by the addition of a metallocene. In example 4 the metallocene and alumoxane are pre-contacted then added to the magnesium chloride support. In all cases, however, the same magnesium chloride prepared in the presence of an electron-donor was used.

Such catalysts may however have a low activity or an activity which limits application to polymerization of high density polyethylene.

EP-436326-A, EP-447070-A, and EP-447071-A adopt similar catalyst preparation techniques.

WO-9526369 describes olefin polymerisation catalyst components obtainable by contacting a transition metal compound M selected from Ti, V, Zr and Hf containing M-pi bond(s) with a prepolymer obtained by polymerisation of olefin(s): CH₂=CHR (R = H or 1-12C (cyclo) alkyl or aryl), and/or di- or polyene(s) with a coordination catalyst comprising the product obtained by contacting a Ti, V, Zr or Hf compound with a Mg halide in the form of particles with average crystallite size below 300 angstrom, the Mg halide being present in the prepolymer at 50-50000 ppm.

WO-9532995 describes a catalyst for the polymerisation of high density olefins comprising: (a) a compound of a transition metal M, comprising Ti, V, Zr or Hf, and containing at least one M-pi bond; and (b) a halide of Mg. The component has: (i) a surface area (BET) of >50 m2/g; (ii) a porosity (BET) of >0.15 cm3/g; (iii) a porosity (Hg) >0.3 cm3/g; and (iv) a porosity (Hg) of <1.5 cm3/g when the surface area is <150 m2/g.

WO-9601855 describes components of catalysts for the polymerisation of olefins comprising the product (I) obtained by contacting: (a) a compound of a transition metal (M) containing a M-pi bond(s), with a solid component comprising a compound of Ti or V not containing. M-pi bonds, and optionally, an electron-donor compound supported on a Mg halide; or (b) a compound of Ti or V not containing M-pi bonds with a solid component comprising a compound of V, Ti, Zr or Hf containing a M-pi bond(s) supported on a Mg halide; or (c) a compound of Ti or V not containing M-pi bonds and a compound of V, Ti, Zr or Hf having a M-pi bond(s) with a support comprising a Mg halide. It involves the use of an electron donor alcohol and is a bimetallic catalyst system.

Summary of the invention

The invention provides in a first aspect, a process for preparing a particulate olefin polymerization catalyst system containing magnesium halide, a metallocene preferably of Group IVB of the Periodic Table, and an activating cocatalyst, which process comprises (A) contacting a magnesium hydrocarbon compound and an organic halogen-donating compound the activating cocatalyst and the metallocene in a non-polar hydrocarbon solvent medium substantially devoid of electron donor compound and (B) removing the solvent by drying to obtain the particulate catalyst system. The organic halogen- donating compound may be an organohalo-aluminum compound, but is preferably a hydrocarbon halogen compound.

With the phrase substantially devoid of electron-donor compound is meant that no electron-donor compound is added or the mol ratio of electron donor to magnesium chloride B less than 1 :200, especially less than 1 :300 or even less than 1 :400.

Thus, in a second more particular aspect, the invention provides a process for preparing a particulate catalyst system for heterogeneous polymerization containing magnesium halide, a metallocene preferably of Group IVB of the Periodic Table, and an activating cocatalyst, which process comprises contacting a magnesium hydrocarbon compound and an hydrocarbon halogen compound and the activating cocatalyst and/or the metallocene in a non-polar -o- hydrocarbon solvent medium substantially devoid of electron donor compound and removing the solvent by drying to obtain the particulate catalyst system.

The catalyst has as components the metallocene and the cocatalyst. The components may be contacted separately, or together or in stages.

The process can for example be performed so that all of the activating cocatalyst is added, preferably in solution, to the hydrocarbon solvent medium which contains or will be mixed with the magnesium hydrocarbon compound and the hydrocarbon halogen compound. All of the activating cocatalyst may be added to the medium before the magnesium hydrocarbon compound and the hydrocarbon halogen compound are contacted therein. In this way the insoluble magnesium halide is precipitated in the presence of the activating cocatalyst. Alternatively all of the activating cocatalyst may be contacted with the metallocene in the solution to be added to the medium in which the insoluble magnesium halide product has been formed by prior contacting of the magnesium hydrocarbon compound and the hydrocarbon halogen compound. It is also contemplated that the activating cocatalyst may be added in two separate stages, partly with the metallocene and partly to the solvent medium containing one or more of the other components.

The active catalyst system is advantageously produced by further reacting magnesium halide precipitation, preferably magnesium chloride precipitation with a metallocene and an activating cocatalyst such as methylalumoxane or only with metallocene if the cocatalyst is already incorporated into the magnesium halide precipitation. The metallocene and the cocatalyst can be premixed in a non-polar hydrocarbon solvent to substantially form a solution before contacting the magnesium halide precipitation. Similarly, the metallocene should be substantially soluble in a non-polar hydrocarbon solvent before contacting the magnesium halide precipitation containing cocatalyst. The schematic representations in diagram I illustrate some of the possible combination options:

Diagram 1

Combination options for metallocene (CpM); activating cocatalyst (Cocat); magnesium hydrocarbon (MgHc); hydrocarbon halogen (HcHal); solvent medium (S).

Included:

[((Cocat + S) + MgHc) + HcHal] + CpM

[((Cocat + S) + HcHal) + MgHc] + CpM

[((S + MgHc) + HcHal) + CpM + CoCat in sequence or premixed

[((S + HcHal) + MgHc) + CpM + CoCat in sequence or premixed

[((CpM+S)+MgHc)+HcHal]+Cocat

[((CpM+S)+ HcHal)+ MgHc]+Cocat

[(CpM+Cocat+S)+HcHal]+MgHc

[(CpM+Cocat+S)+ MgHc]+ HcHal

The metallocene options

Examples of transition metal compounds capable of insertion polymerization when activated to a cationic state are typically stable, single-sited discrete ionic catalyst systems. Group 4-6 metallocenes are exemplary. The term includes those compounds containing a single cyclopentadienyl ligand or a substituted -o- derivative thereof ("monocyclopentadienyl metallocenes"), and those containing two cyclopentadienyl ligands or substituted and unsubstituted derivatives thereof ("biscyclopentadienyl metallocenes"). Either class may be unbridged or may be bridged, e.g., between the two cyclopentadienyl ligands on, or between the single cyclopentadienyl ligand and a heteroatom ligand on, the same transition metal center. Precursor compounds for and the catalyst systems themselves are well-known in the art. Description of metallocene compounds appear in the patent literature, for example US patents 4,871 ,705, 4,937,299, 5,324,800, EP-A- 0 418 044, EP-A-0 591 756, WO-A-92/00333 and WO-A-94/01471. The metallocene compounds described are those described as mono- or bis-substituted Group 4, 5, and 6 transition metal compounds wherein the cyclopentadienyl substituents may be themselves substituted with one or more groups and may be bridged to each other, or may be bridged through a heteroatom to the transition metal. Preferably for higher molecular weight polymer components the biscyclopentadienyl (or substituted biscyclopentadienyl, such as indenyl or substituted indenyl) rings, will be bridged and will be lower alkyl-substituted (Ci-Cβ) in the 2 position and will additionally comprise alkyl, cycloalkyl, aryl, alkylaryl and or arylalkyl substituents, the latter as either of fused or pendant ring structures including multi-ring structures, for example, those of U.S. patents 5,278,264 and

5,304,614. Such substituents should each have essentially hydrocarbyl characteristics and will typically contain up to 30 carbon atoms but may be hetero-atom containing with not more than 1-3 non-hydrogen/carbon atoms, e.g., N, S, O, P, Si or Ge.

Metallocene compounds suitable for the preparation of linear polyethylene or ethylene-containing copolymers (where copolymer means comprising at least two different monomers) are essentially any of those known in the art, see WO- A-92/00333 and U.S. patents 5,001 ,205, 5,057,475, 5,198,401 , 5,304,614, 5,308,816 and 5,324,800 for specific listings. Selection of metallocene compounds for use to make isotactic or syndiotactic polypropylene polymers, and their syntheses, are well-known in the art, specific reference may be made to both patent literature and academic, see for example Journal of organometallic Chemistry 369, 359-370 (1989). Typically those catalysts are stereorigid asymmetric, chiral or bridged chiral metallocenes. See, for example, U.S. patent 4,892,851 , U.S. patent 5,017,714, U.S. patent 5,296,434, U.S. patent 5,278,264, WO-A-(PCT/US92/10066) WO-A-93/19103, EP-A2-0 577 581 , EP-A1-0 578 838, and academic literature "The Influence of Aromatic Substituents on the Polymerization Behavior of Bridged Zirconocene Catalysts", Spaleck, W., et al, Organometallics 1994, 13, 954-963, and "ansa- Zirconocene Polymerization Catalysts with Annelated Ring Ligands-Effects on

Catalytic Activity and Polymer Chain Lengths", Brinzinger, H., et al, Organometallics 1994, 13, 964-970, and documents referred to therein. Preferably the monocyclopentadienyl metallocene catalyst components are those additionally comprising a Group 15 or 16 heteroatom covalently bound both to the Group 4 transition metal center and, through a bridging group, to a ring carbon of the cyclopentadienyl group-containing ligand. Such catalysts are well-known in the art, see, e.g., background U.S. patents 5,055,438, 5,096,867, 5,264,505, 5,408,017, 5,504,169 and WO 92/00333. See also, U.S. patent 5,374,696, 5,470,993 and 5,494,874; and, see, international publications WO 93/19104 an EP 0 514 828 A. For cyclic olefin-containing copolymers, see WO-94/17113, U.S. 5,635,573, and WO 96/002444. Additionally, the unbridged monocyclo-pentadienyl, heteroatom-containing Group 4 transition metal catalyst components of WO 97/22639, will be suitable in accordance with the invention. Transition metal polymerization catalyst systems from Group 5-10 metals wherein the active transition metal center is in a high oxidation state and stabilized by low coordination number polyanionic ancillary ligand systems are described in US patent 5,504,049. Each of the foregoing references are incorporated by reference for the purposes of U.S. patent practice. Group 4 or 5 compounds containing bulky chelating diamide ancillary ligands, such as those described in U. S. patent 5,318,935 and "Conformationally Rigid Diamide Complexes: Synthesis and Structure of Tantalum(lll) Alkyne Derivatives", D. H. McConville, et al, Organometallics 1995, 14, 3154-3156. Other group 4 and 5 non-metallocene catalyst compounds are bimetallocyclic catalyst compounds comprising two independently selected Group 4 or Group 5 metal atoms directly linked through two covalent bridging groups so as to form cyclic compounds having delocalized π-bonding, see WO96/40805. See also the Group 5 metal compounds of copending U.S. application serial number 08/798,412, filed 2/7/97. Each of the foregoing references are incorporated by reference for the purposes of U.S. patent practice. Suitable Group 10 metal compounds are those wherein the metal is in a +2 oxidation state. Typical Ni ⁺ and Pd ⁺ complexes are diimine complexes that can be prepared by methods equivalent to those used for the compounds described in "New Pd(ll)- and Ni(ll)- Based Catalysts for Polymerization of

Ethylene and α-Olefins", M. Brookhart, et al, J. Am. Chem. Soc, 1995, 117, 6414-6415, WO 96/23010 and WO 97/02298. See also, U.S. application serial number 08/877,390, filed 6/17/97. Each of the foregoing references are incorporated by reference for the purposes of U.S. patent practice.

The metallocene may be a bis-cyclopentadienyl compound. The biscyclopentadienyl compounds, which are preferred, may have monofunctional substituents on the cyclopentadienyl rings which may be 1 , 2, 3, 4, or 5, hydrocarbyl substituent(s), alkyl or aryl or combinations which may have from 1 to 20 carbon atoms. The substituents may also be silylhydrocarbyl or other moieties imparting the desired steric and electronic characteristics. The cyclopentadienyl ligands may be fused rings systems in which a pair of adjacent carbons on the cyclopentadienyl ring are joined to form a fused ring of from 3 to 20 carbon atoms excluding the two carbon atoms in the cyclopentadienyl ring. Examples are indenyl, tetrahydroindenyl, azulenyl, benzoindenyl, fluorene etc. The fused ring itself may be substituted in the same manner as described above for the cyclopentadienyl ring. The term cyclopentadienyl ring includes ring systems which form ancillary ligands in which carbon atoms are joined by non-carbon atoms such as nitrogen, phosphorus, boron. The cyclopentadienyl ligands may be chiral. The two ligands may be quite different through differential substitution. The two cyclopentadienyl rings may be connected covalently through a structural bridge comprising from 1 to 4 atoms, which may have alkyl or aryl substituents such as methyl or phenyl with from 1 to 20 carbon atoms. The atoms in the bridge may be carbon, silicon, germanium, nitrogen or a combination thereof. The solubility of the metallocene can vary with their structure. The process route selected for contacting the catalyst components should be selected advantageously so that the metallocene is present in a dissolved state during its contacting with the other catalyst components.

Preferred bis cyclopentadienyl compounds are Group IV-B metal compounds may be represented by the following general formula:

(A-Cp)MX_n

wherein: M is a metal selected from the Group consisting of titanium (Ti), zirconium (Zr) and hafnium (Hf); (A-Cp) is either (Cp)(Cp) or Cp-A'-Cp^* and Cp and Cp* are the same or different substituted radical R_mCp or unsubstituted cyclopentadienyl radicals Cp, R is a substituent , preferably a hydrocarbyl substituent, having from 1 to 20 carbon atoms covalently bonded to the cyclopentadiene ring with m being 1 , 2, 3 or 4 if bridge A' is present or 1 , 2, 3,

4 or 5 if bridge A' is absent and wherein A' is a covalent bridging group; X may be, independently, selected from the Group consisting of halide, hydride radicals, hydrocarbyl radicals having from 1 to 20 carbon atoms, alkoxy aryloxy, substituted-hydrocarbylradicals, wherein one or more of the hydrogen atoms are replaced with a halogen atom, having from 1 to 20 carbon atoms, organo-metalloid radicals comprising a Group IV-A element wherein each of the hydrocarbyl substituents contained in the organo-portion of said organo- metalloid, independently, contain from 1 to 20 carbon atoms; X may also be an olefin, diolefin or aryne ligand; n is 0, 1 , or 2 depending on the valency of M and the formal valency of X; different X's may be joined and bound to the metal atom to form a metallacycle, in which the metal and the X's form a hydrocarbocyclic ring containing from 3 to 20 carbon atoms.

Each carbon atom in the cyclopentadienyl radical maybe, independently, unsubstituted (H) or substituted with the same or a different radical selected from the Group consisting of hydrocarbyl radicals, substituted-hydrocarbyl radicals wherein one or more hydrogen atoms is replaced by a halogen atom, hydrocarbyl-substituted metalloid radicals wherein the metalloid is selected from Group IV-A of the Periodic Table of the Elements, or halogen radicals.. Suitable hydrocarbyl and substituted-hydrocarbyl radicals which may be substituted for at least one hydrogen atom in the cyclopentadienyl radical will contain from 1 to 20 carbon atoms and include straight and branched alkyl radicals, cyclic hydrocarbon radicals, alkyl-substituted cyclic hydrocarbon radicals, aromatic radicals and alkyl-substituted aromatic radicals. Similarly, and when X is a hydrocarbyl or substituted-hydrocarbyl radical, each may, independently, contain from 1 to 20 carbon atoms and be a straight or branched alkyl radical, a cyclic hydrocarbyl radical, an alkyl-substituted cyclic hydrocarbyl radical, an aromatic radical or an alkyl-substituted aromatic radical. Suitable organo-metalloid radicals include mono-, di- and trisubstituted organo- metalloid radicals of Group IV-A elements wherein each of the hydrocarbyl groups contain from 1 to 20 carbon atoms. Suitable organo-metalloid radicals include trimethylsilyl, tri-ethylsilyl, ethyldimethylsilyl, methyldiethylsilyl, triphenylgermyl.or trimethylgermyl.

Advantageously the activating cocatalyst is methylalumoxane and the metallocene and methylalumoxane are contacted in toluene solution before contacting with the magnesium halide product. The alumoxane may have a degree of oligomerization of the repeat unit [-AIRO-] as determined by vapor pressure osmometry of from 4 to 26. The alumoxane may still contain unreacted aluminum alkyl in which case that fraction is incorporated in the measurement of the degree of oligomerization and the Aluminum to metal ratio in this specification.

The magnesium halide can be prepared by contacting a magnesium hydrocarbon compound MgR.,R₂ and a hydrocarbon halogen R₃X compound in a non-polar hydrocarbon solvent to form a precipitation and optionally in the presence of an activating cocatalyst such as methylalumoxane.

R_1t R₂ are preferably the same or different hydrocarbyls containing from 1 to 20 carbon atoms. Examples of magnesium hydrocarbon compound are dibutylmagnesium, butylethylmagnesium, bis(cyclopentadienyl)magnesium, di- n-hexylmagnesium.

R₃ in the hydrocarbon halogen compound is suitably a hydrocarbyl containing from 1 to 20 carbon atoms, preferably a secondary hydrocarbyl, and more preferably a tertiary hydrocarbyl.

The non-polar hydrocarbon solvent or diluent used for the magnesium halide formation reaction is suitably a hydrocarbon solvent , aromatic or aliphatic, devoid of oxygen containing moieties and is preferably an aliphatic hydrocarbon such as pentane, hexane, heptane, octane, or blends thereof or commercially available mixtures of alkanes (e.g. Isopan™, Exxon Chemical

Co.) an alicyclic hydrocarbon such as cyclohexane, methylcyclohexane and an aromatic hydrocarbon such as benzene, toluene. Preferably the hydrocarbon halogen compound is selected so as to avoid the formation of an aluminum alkyl as by-product. Preferably excess amount of magnesium hydrocarbon compound should be present to ensure substantially complete reaction of hydrocarbon halogen corn-pound. The molar ratio of hydrocarbon halogen or hydrogen halide compound to magnesium hydrocarbon compound is from 0.5 to 3, preferably from 1.5 to 2.

The magnesium halide formation reaction is carried out in the non-polar hydrocarbon solvent with agitation at from 0 to 100°C, preferably at from 5 to 40°C and the reaction time is from 1 to 100 hours, preferably from 2 to 20 hours to ensure formation of suitable precipitation. The precipitation is preferably washed several times with a non-polar hydrocarbon solvent to reduce the amount of solubles in the solvent.

The molar ratio of aluminum in MAO to metal in the metallocene can be in the range from 1 :1 to 10,000:1 , and preferably from 5:1 to 1 ,000:1 so that a suitable catalyst activity can be achieved. The molar ratio of magnesium to metal in the metallocene can be in the range from 1 :1 to 2,000:1 , and preferably from 5:1 to 1 ,000:1 so that a suitable catalyst can be produced for polymerization. For the avoidance of doubt the aluminum in MAO as used herein indicates the total amount of Al in the solution including that in any unhydrolysed trimethyl aluminum that may be present in the solution.

The active catalyst system is preferably washed several times with a non-polar hydrocarbon solvent as appropriate to reduce fouling during polymerization. The catalyst is settled, decanted and dried in vacuum or by evaporation. The catalyst may be used directly in a slurry form.

The invention also provides a heterogeneous particulate catalyst system comprising the contact product obtainable from a process which comprises contacting a magnesium hydrocarbon compound and a hydrocarbon halogen compound in a non-polar hydrocarbon solvent medium substantially in the absence of an electrondonor compound and optionally in the presence of an activating cocatalyst so as to form an insoluble magnesium halide product; contacting the product with a metallocene and optionally an activating cocatalyst and removing the solvent by drying to obtain a particulate catalyst system.

The invention further provides a process which comprises polymerizing ethylene and optionally one or more copolymerizable monomers using the above catalyst system so as to produce a polyethylene .

The polymers prepared by this invention catalyst are homopolymers of ethylene and copolymers of ethylene with higher alpha-olefins having from 3 to 20 carbon atoms, as well as C4-C20 cyclic olefins (e.g., norbomene and methylnorbomene and vinyl aromatics (e.g., etynene, alkyl-substituted styrenes, and generally disubstituted olefins, such as isobutylene. The polymer properties such as density, Ml (HLMI), MIR and PDI can be controlled by selection of metallocene compound, molar ratio of cocatalyst to metallocene, reactor conditions, etc. The polymer density ranges from 0.89 to 0.97 g/cc. The polymer Ml (HLMI) ranges from 0.01 Ml to 200 Ml. The polymer MIR ranges from 10 to 500. The polymer PDI ranges from 2 to 50.

The catalyst may be used to produce high 110/12 polymers at relatively low PDI. Preferably the polymer is a polyethylene polymer having a density higher than 0.93, especially higher than 0.94 which may be produced more efficiently with the catalyst system of this invention. Ml stands for melt index, HLMI is the high load melt index, MIR is the melt index ratio, and PDI is the polydispersity index calculated from the ratio weight average molecular weight and number average molecular weight.

The catalyst system can be used for polymerizing polyethylene which has a high density at much higher activity levels than obtained with prior art silica based supported catalyst systems. The polymers produced had a desirable low Ml. In the case of bridged catalysts a high MIR may be obtained with a superior rheology in the melt processing of the polymer.

As a preferred form of the process, high purity ethylene (99.8%) by weight, low boiling (isobutane) hydrocarbon diluent, and the catalyst (systems described above) are fed continuously to a loop reactor. Polymer is formed as a slurry. The diluent is used to dissolve the ethylene and suspend the catalyst and polymer particles. The hydrocarbon diluent may be selected from the same choice as the solvent or diluent used for the catalyst preparation. It may be isobutane, isopentane, hexane, or n-octane, etc.

Ethylene, hexene-1 comonomer, diluent and catalyst feed rates are adjusted to the production rate, polymer concentration, and polymer density desired. Hydrogen gas is fed at low concentrations as a melt index modifier when needed. Triethylaluminum is added as a scavenger.

The flow velocity in the reactor is maintained sufficiently high to prevent settling due to gravity and in a highly turbulent flow rate.

The pump which produces the circulation of the diluent inside the reactor is located at the base of the reactor loops. The shaft extends through the wall of the reactor in the vicinity of an elbow in the loop and is coupled through suitable elastic means to a pump motor. A portion of the feed is introduced to the reaction zone through a sleeve enclosing a pump impeller shaft so that the fluid feed flows through the inboard bearing and the area adjacent the hub of the impeller and said bearing. In this way, the area adjacent the inboard bearing and impeller hub is maintained free of polymer. The diluent is injected into the passageway between a relief valve and the reactor to provide positive flow through the conduit towards the reactor. The reactors are preferably mounted vertically and the vertical loop portions are much longer than the horizontal portions. The reactor overall is in a double U shape. Two U-shaped half buckles are arranged facing one another and are connected together at the top of the vertical legs of both u's. The walls of the reactor seldom exceed 150°C.

The reactor loop is jacketed and cooling liquid is circulated through the jacket to remove the heat liberated by the polymerization.

Ethylene concentration is maintained by automatic feed controls.

As the polymerization proceeds, polymer particles form. The larger particles enter the settling zone from which a concentrated slurry is discharged intermittently. Settling legs at the bottom of the reactor loop allows maximum slurry concentration before discharge. Thus decreasing the amount of diluent and olefin feed to be recirculated. Suitable flow control valves, such as solenoid-operated valves are provided in the settling legs. These flow control valves can be controlled to periodically open at predetermined frequencies and sequence to permit the discharge of the slurry of concentrated settled particle- form solids which accumulate in the portions of the settling legs upstream of these valves.

Polymer slurry is discharged continuously to a flash chamber, where most of the light hydrocarbon diluent evaporates, yielding a dry bed of polyethylene resin in powder form. The powder is transported pneumatically to the finishing area where various additives and stabilizers are incorporated. Finally, it is extruded into pellets. The hydrocarbon diluent from the flash step and purge dryer is condensed and fractionated for recycle.

The catalyst may be prepolymerized to increase particle integrity, reduce fouling and possibly increase the yield of useful polymer. The catalyst may be used with a low level of scavenger added to the diluent. The particulate catalyst system may be treated with alkyl aluminum or other scavenger like compounds, but preferably is not.

Whereas the prior art referred to above generally produced its magnesium chloride containing catalyst in a medium containing an electron-donating compound, the invention by contrast uses a medium free of a polar, electron- donating compound. The magnesium chloride in the invention is prepared by the reaction of a magnesium alkyl with a suitable halogenating agent such as butyl chloride.

Examples

The preparation of the catalyst is performed substantially in the absence of volatile or non-volatile electron donors which are not an activating cocatalyst. The term electron donor as used herein is not meant to include incidental electron donors which are primarily present as activating cocatalysts. Absence of such non-catalytic electron donors helps in providing the catalyst characteristics useful for the polymerization of higher density polyethylene.

Preparation A of MgCI₂ Supported Metallocene Catalyst in Table 1 and 2: In a

N₂-filled glove box, a 50 ml glass bottle was charged with 8.60 ml dibutylmagnesium (1.0 M solution in heptane) and 15.0 ml hexane. 1.87 ml 'BuCI was added in 2 hrs to maintain temperature at 25-40°C. After standing, the clear liquid was removed. The slurry was washed with 10.0 ml hexane. A mixture of 3.35 ml MAO (10 wt% in toluene) and 20.0 mg (n-BuCp)₂ZrCI₂ dissolved in 4.0 ml toluene which was stirred at 25°C for 1 hr was added. The mixture was stirred for 1 hr at 25°C. After standing, the clear liquid was removed. The yellow slurry was washed with 10.0 ml hexane. 1.14 g light yellow solid was obtained after drying by evaporation. Preparation B of SiO₂ Supported Metallocene Catalyst in Table 1 , 2 and 3: In a N₂-filled glove box, a 50 ml glass bottle was charged with 4.0 ml MAO (10 wt% in toluene) and 24.0 mg (n-BuCp)₂ZrCI₂ dissolved in 2.0 ml toluene. The mixture was stirred for 1 hr at 25°C. 0.98 g SiO₂ (Davison 948 calcined at 600°C) was added. The mixture was stirred for 1 hr at 25°C. After standing, the clear liquid was removed. 1.31 g yellow solid was obtained after drying by evaporation.

Preparation C of MgCI₂ Supported Metallocene Catalyst in Table: In a N₂-filled glove box, a 125 ml glass bottle was charged with 30.0 ml MAO (10 wt% in toluene) and 1.65 ml i-BuAICI₂ (50% in hexane). Then, 4.50 ml dibutylmagnesium (1.0 M solution in heptane) and 83.4 mg (n-BuCp)₂ZrCI₂ dissolved in 6.0 ml toluene were added dropwise to the above mixture. The mixture was stirred at 25°C for 1.5 hr. 30.0 ml hexane was added to the slurry. After standing, the clear liquid was removed. The slurry was further washed with 2x20.0 ml hexane. 2.09 g solid was obtained after drying by evaporation.

Preparation D of MgCI₂ Supported Metallocene Catalyst in Table 3: In a N₂- filled glove box, a 50 ml glass bottle was charged with 10.0 ml MAO (10 wt% in toluene) and 0.157 ml n-BuCI. The solution color turned yellow and gas was given off. The mixture was stirred at 25°C for 0.5 hr. 1.50 ml dibutylmagnesium (1.0 M solution in heptane) and 25.4 mg (n-PrCp)₂ ZrCI₂ dissolved in 2.0 ml toluene were added dropwise to the above mixture. The mixture was stirred at 25°C for 1 hr. 15.0 ml hexane was added to the slurry. After standing, the clear liquid was removed. The slurry was further washed with 10.0 ml hexane. 0.98 g solid was obtained after drying by evaporation.

Polymerization: A 2-liter stainless steel reactor was purged with N₂ for 2 hr.

60.2 mg of metallocene catalyst prepared above and 1.0 ml 10 wt% triethylaluminum in heptane and optional comonomer_, were added to the reactor. 1 liter isobutane was introduced to the reactor and stirring was initiated. Ethylene was fed to the reactor on demand and the reactor temperature and total pressure were maintained at 200°F and 517 psig, respectively. After 30 min, polymerization was ended by venting off ethylene and other volatiles.

Table 1.

Summary of testing results of MgCI₂ and SiO₂ supported (n-BuCp)₂ZrCI₂ catalysts

Zr = 0.4 wt% Al/Zr molar ratio = 100 Ethylene pressure = 269 psig Reactor temperature = 200°F

Table 2.

Summary of testing results of MgCI₂ and SiO₂ supported (n-PrCp)₂ZrCI₂ catalysts

Zr = 0.4 wt% Al/Zr molar ratio = 100 Ethylene pressure = 269 psig Reactor temperature = 200°F TEAL = 1.0 ml 10 wt%

Table 3.

Summary of testing results of MgCI₂ supported metallocene catalysts with high Zr and MAO

I r

TEAL = 1.0 ml 10 wt%

The Ml was measured according to ASTM D-1238-95 Condition E

The HLMI ( high load Ml ) was measured according to ASTM D-1238-95 Condition F

The MIR was measured as the ratio of the Ml condition F over the Ml condition. E.

The density was measured according to. ASTM-D-1505-85(1990)

Prior to particle size measurement, the polymers made with the invention catalysts were ground in a grinder to simulate the forces applied to the polymer produced in a loop reactor. Polymer particles are measured by sieving and weighing polymers on a series of sieves and plotting the results on a probability logarithm paper. APS represents average particle size at 50% cumulative weight.

Claims

1. A process for preparing a particulate olefin polymerization catalyst system containing magnesium halide, a metallocene and an activating cocatalyst, which process comprises (A) contacting a magnesium hydrocarbon compound and an organic halogen-donating compound and the activating catalyst and the metallocene in a non-polar hydrocarbon solvent medium substantially devoid of electron donor compound and (B) removing the solvent by drying to obtain the particulate catalyst system.

2. A process for preparing a particulate olefin polymerization catalyst system containing magnesium halide, a metallocene of Group IVB of the Periodic Table, and an activating cocatalyst, which process comprises contacting a magnesium hydrocarbon compound and an hydrocarbon halogen compound and the activating cocatalyst and the metallocene in a non-polar hydrocarbon solvent medium substantially devoid of electron donor compound and removing the solvent by drying to obtain the particulate catalyst system.

3. The process according to claim 2 in which the contacting includes an initial step of contacting the magnesium hydrocarbon compound and the hydrocarbon halogen compound in the presence of the activating cocatalyst and/or the metallocene; and a further step of contacting the balance of the activating cocatalyst and/or the metallocene.

4. The process according to claim 3 in which, in the initial step, no activating cocatalyst and no metallocene is contacted and both of these components are added in the further step.

5. The process according to claim 3 in which in the initial step a predominant amount of the activating cocatalyst is contacted and in the further step all of the metallocene and any balance of the activating cocatalyst.

6. The process according to claim 1 in which the activating cocatalyst is methylalumoxane.

7. The process according to claim 6 in which the metallocene and at least part of the methylalumoxane are contacted in a toluene solution before contacting with the magnesium halide product.

8. The process according to claim 1 in which the non-polar hydrocarbon solvent medium comprises predominantly an alkaline solvent.

9. A particulate olefin polymerization catalyst system containing magnesium halide, a metallocene preferably of Group IVB of the Periodic Table, and an activating cocatalyst comprising the contact product obtainable from a process which comprises (A) contacting a magnesium hydrocarbon compound and an organic halogen-donating compound and produced with the activating cocatalyst and the metallocene in a non-polar hydrocarbon solvent medium substantially devoid of electron donor compound and (B) removing the solvent by drying to obtain the particulate catalyst system.

10. A polymerization process which comprises polymerizing ethylene and optionally one or more copolymerizable monomers using a catalyst system according to claim 9 under suitable or loop slurry polymerization conditions comprising maintaining ethylene to comonomer ratios, a polyethylene having a density of from 0.90 to 0.96.

11. The process according to claim 9 in which the polyethylene has a density of from 0.93 to 0.95.