WO1997024375A1

WO1997024375A1 - Slurry polymerization process

Info

Publication number: WO1997024375A1
Application number: PCT/US1996/020249
Authority: WO
Inventors: Vispi R. Sagar; Michael J. Veraa; Barry C. Trudell
Original assignee: Exxon Chemical Patents Inc.
Priority date: 1995-12-29
Filing date: 1996-12-23
Publication date: 1997-07-10
Also published as: AU1295397A

Abstract

The present invention relates to a slurry process for the polymerization of olefins utilizing a metallocene catalyst system to produce polymers having a low density and a relatively high molecular weight with essentially no reactor fouling.

Description

SLURRY POLYMERIZATION PROCESS

FIELD OF THE INVENTION

The present invention relates to a slurry polymerization process for producing polymers, particularly polymers having a very low density, such as elastomers and plastomers.

BACKGROUND OF THE INVENTION

It is known in the art that traditional Ziegler-Natta type catalysts cannot make products in a slurry process having a density lower than approximately 0.92 g cc without sacrificing polymer productivity. This is because traditional Ziegler- Natta catalysts produce polymers having a relatively broad molecular weight distribution (MWD) and a relatively broad composition distribution (CD). Such products have a relatively large fraction of very low molecular weight material and a relatively large fraction of material extremely rich in comonomer content. The low molecular weight fraction and the fraction rich in comonomer content (which are often the same fraction) tend to solubilize in the reaction diluent. As the solubilization of such fractions increases, the soluble fraction tends to swell the polymer particle. Also, as the low molecular weight, high comonomer content fraction becomes soluble in the diluent, the viscosity of the diluent increases, thus limiting heat transfer, limiting the polymer content per unit reactor or solvent volume, and thus, the production rate, and leading to fouling ofthe reactor. As the density of the product is lowered (i.e., as more comonomer is added), more and more low molecular weight, comonomer rich product is made, and therefore, the propensity ofthe polymer to swell and the reactor to foul increases. Also, Ziegler- Natta catalyst productivity is temperature-sensitive, so that lowering the reaction temperature to prevent melting the low density product and reduce fouling results in a proportional deactivation ofthe catalyst, and thus, poor productivity.

The use of metallocene compounds as catalysts is a relatively recent development in the polymerization and copolymerization of ethylene. As is known in the art, metallocene catalysts can produce polymers having a relatively narrow MWD and CD, which somewhat reduces the difficulty of producing very low density polymers in a slurry process. However, catalyst migration off the support can still be a problem. Catalyst migration leads to the formation of unsupported polymer that can adhere to the reactor wall or other parts inside the reactor, leading to the formation of fouling material. Such fouling causes the loss of heat transfer capability and can ultimately cause the shut down of the reactor or process. Various metallocenes have been used in slurry processes to produce elastomers and rubbers; however, producing very low density ethylene/alpha-olefin copolymers in a slurry process without reactor fouling has still proven difficult.

WO 94/21691 describes the production of copolymers of ethylene and a comonomer having 3 to 10 carbon atoms having a density of from 0.91 g/cc to 0.94 g/cc in a slurry process using a metallocene catalyst system having a catalyst mixture to support pore volume loading of less than one.

U.S. Patent No. 4,871,705 describes the production of high molecular weight, ethylene/alpha-olefin elastomers using a metallocene/alumoxane catalyst system in a slurry process, but does not appear to require a specific catalyst mixture to support pore volume loading.

Therefore, it would be highly desirable to provide a commercially useful slurry polymerization process for producing a relatively high molecular weight ethylene/alpha-olefin copolymers having a very low density.

SUMMARY OF THE INVENTION

This invention relates to a slurry polymerization process for producing polymers in the presence of a metallocene polymerization catalyst. The process is capable of producing polymers having a density of 0.865 g/cc to 0.96 g/cc using a metallocene catalyst system having a catalyst mixture to support pore volume loading of greater than one. Preferably, the polymer products are plastomeric products having a density less than 0.915 g/cc, more preferably less than 0.91 g/cc. The polymer products may have melt indices according to ASTM D-1238- Condition E from less than 0.01 to greater than 200 dg/min. In one embodiment, the invention provides for a polymerization process for polymerizing two or more olefins, in the presence of a metallocene catalyst system, to produce a polymer having a relatively high molecular weight and a density less than 0.91 g/cc. The polymers of the invention are useful in a variety of end-use applications, particularly in film applications. DETAILED DESCRIPTION OF THE INVENTION Introduction

The invention is directed to a slurry polymerization for producing polymers, and in particular, ethylene/alpha-olefin copolymers having a density below 0.915 g/cc. It has been discovered that these polymers can be produced commercially in a slurry process using a metallocene catalyst with excellent operability. It was particularly surprising that the process could produce such low density polymers with essentially no reactor fouling. It was also surprising that the process could be operated at relatively low temperatures with high catalyst productivity to produce polymers having a relatively high molecular weight.

Catalyst Components and Catalyst Systems of the Invention

Metallocene catalysts are typically those bulky ligand transition metal compounds derivable from the formula: [L]_mM[A]_n where L is a bulky ligand; A is leaving group, M is a transition metal and m and n are such that the total ligand valency corresponds to the transition metal valency. Preferably the catalyst is four co-ordinate and is ionizable to a 1⁺ charge state.

The ligands L and A may be bridged to each other, and if two ligands L or A are present, they may be bridged. The metallocene compound may be full- sandwich compounds having two or more ligands L, which may be cyclopentadienyl ligands or cyclopentadiene derived ligands, or half-sandwich compounds having one ligand L, which is a cyclopentadienyl ligand or derived ligand. In one embodiment, at least one ligand L has a multiplicity of bonded atoms, preferably 4 to 20 carbon atoms, that typically is a cyclic structure or ring system, which may be substituted or unsubstituted. Non-limiting examples of ligands include a cyclopentadienyl ligand, or a cyclopentadienyl derived ligand such as an indenyl ligand, a benzindenyl ligand or a fluorenyl ligand and the like or any other ligand capable of η-5 bonding to a transition metal atom. One or more of these bulky ligands may be π-bonded to the transition metal atom. The transition metal atom may be a Group 4, 5 or 6 transition metal and/or a metal from the lanthanide and actinide series; preferably the transition metal is of Group 4. Other ligands may be bonded to the transition metal, such as a leaving group, such as but not limited to hydrocarbyl, hydrogen, or any other univalent anionic ligand. Non¬ limiting examples of metallocene catalysts and catalyst systems are discussed in for example, U.S. Patent Nos. 4,530,914, 4,871,705, 4,937,299, 5,124,418, 5,017,714, 5,120,867, 5,278,119, and 5,324,800 all of which are herein fully incoφorated by reference for the purposes of U.S. patent practice. Also, the disclosures of EP-A-0 591 756, EP-A-0 520 732, EP-A- 0 420 436, WO 93/08221, and WO 93/08199 are all fully incoφorated herein by reference for the puφoses of U.S. patent practice.

Further, the metallocene catalyst component of the invention can be a monocyclopentadienyl heteroatom containing compound. This compound is activated by either an alumoxane, an ionizing activator, a Lewis acid or a combination thereof to form an active polymerization catalyst system. These types of catalyst systems are described in, for example, PCT International Publications WO 92/00333, WO 94/07927, and WO 91/ 04257, WO 94/03506, U.S. Patent Nos. 5,096,867, 5,055,438, 5,198,401, 5,227,440 and 5,264,405, all of which are fully incoφorated herein by reference for the puφoses of U.S. patent practice. In addition, the metallocene catalysts useful in this invention can include non- cyclopentadienyl catalyst components, or ancillary ligands such as boroles or carbollides in combination with a transition metal or can be a bi-metallic transition metal compound. Additionally it is within the scope of this invention that the metallocene catalysts and catalyst systems may be those described in U.S. Patent Nos. 5,064,802, 5,145,819, 5,149,819, 5,243,001, 5,239,022, 5,276,208, 5,296,434, 5,321,106, 5,329,031 and EP-A- 0 578 838 all of which are herein incoφorated by reference for the puφoses of U.S. patent practice.

The preferred transition metal component of the catalyst of the invention are those of Group 4, particularly, zirconium, titanium and hafnium. The transition metal may be in any oxidation state, preferably +3 or +4 or a mixture thereof. For the puφoses of this patent specification the term "metallocene catalyst" is defined to contain at least one metallocene catalyst component containing one or more cyclopentadienyl moiety in combination with a transition metal. If desired, two or more metallocene components may be used. In one embodiment the metallocene catalyst component is represented by the general formula (Cp)mMRnR'p wherein at least one Cp is an unsubstituted or, preferably, at least one Cp is a substituted cyclopentadienyl ring or cyclopentadienyl moiety, symmetrically or unsymetrically substituted; M is a Group 4, 5 or 6 transition metal; R and R' are independently selected halogen, hydrocarbyl group, or hydrocarboxyl groups having 1-20 carbon atoms or combinations thereof; m=l-3, n=0-3, p=0-3, and the sum of m+n+p equals the oxidation state of M, preferably m = 2, n = 1 and p = 1. The Cp can be substituted with a combination of substituents, which can be the same or different . Non-limiting examples of substituents include hydrogen or a linear, branched or cyclic alkyl, alkenyl or aryl radical having from 1 to 20 carbon atoms. The substituent can also be substituted with hydrogen or a linear, branched or cyclic alkyl, alkenyl or aryl radical having from 1 to 20 carbon atoms. In addition, the Cp can be a substituted or unsubstituted ring system such as an indenyl moiety, a benzindenyl moiety, a fluorenyl moiety or the like.

In another embodiment the metallocene catalyst component is represented by one ofthe formulas:

(CsRWpRYCsRWMQs-p-x and RYCsR'm Q' wherein M is a Group 4, 5, or 6 transition metal, at least one C5R'_m is a substituted cyclopentadienyl, each R', which can be the same or different, is hydrogen, alkyl, alkenyl, aryl, alkylaryl or arylalkyl radical having from 1 to 20 carbon atoms or two or more carbon atoms joined together to form a part of a substituted or unsubstituted ring or ring system having 4 to 20 carbon atoms, R" is one or more of or a combination of a carbon, a germanium, a silicon, a phosphorous or a nitrogen atom containing radical bridging two (C5R'_m) rings, or bridging one (C5R'_m) ring to M, when p = 0 and x = 1 otherwise "x" is always equal to 0, each Q which can be the same or different is an aryl, alkyl, alkenyl, alkylaryl, or arylalkyl radical having from 1 to 20 carbon atoms, halogen, or alkoxides, Q' is an alkylidene radical having from 1-20 carbon atoms, s is 0 or 1 and when s is 0, m is 5 and p is 0, 1 or 2 and when s is 1, m is 4 and p is 1.

For the puφoses of this patent specification and appended claims, the terms "cocatalysts" and "activators" are used interchangeably and are defined to be any compound or component which can activate a metallocene catalyst as defined above, for example, an electron donor or any other compound that can convert a neutral metallocene catalyst component to a metallocene cation. It is within the scope of this invention to use alumoxane as an activator, and/or to also use ionizing activators, neutral or ionic, or compounds such as tri(n-butyl)ammonium tetrakis(pentaflurophenyl) boron or trisperfluorophenylboron metalloid precursor, which ionize the neutral metallocene compound.

There are a variety of methods for preparing alumoxane, non-limiting examples of which are described in U.S. Patent Nos. 4,665,208, 4,952,540, 5,091,352, 5,206,199, 5,204,419, 4,874,734, 4,924,018, 4,908,463, 4,968,827, 5,308,815, 5,329,032, 5,248,801, 5,235,081, 5,157,137, and EP-A-0 561 476, EP- Bl-0 279 586, EP-A-0 594 218 and WO 94/10180, all of which are fully incoφorated herein by reference for the puφoses of U.S. patent practice. Ionizing compounds may contain an active proton, or some other cation associated with but not coordinated or only loosely coordinated to the remaining ion ofthe ionizing compound. Such compounds and the like are described in EP- A-0 277 003 and EP-A-0 277 004, and U.S. Patent Nos. 5,153,157, 5,066,741, 5,206,197 and 5,241,025 and are all herein fully incoφorated by reference for the puφoses of U.S. patent practice. Combinations of activators are also contemplated by the invention, for example, alumoxanes and ionizing activators in combinations, see for example, WO 94/07928.

In an embodiment of the invention two or more metallocene catalyst components as describe above can be combined to form a catalyst system useful in the invention— for example, those mixed catalysts described in U.S. Patent No. 5,281,679, which is incoφorated herein by reference for the puφoses of U.S. patent practice. In another embodiment, metallocene catalyst components can be combined to form the blend compositions as described in PCT publication WO 90/03414, fully incoφorated herein by reference for the puφoses of U.S. patent practice. In another embodiment ofthe invention at least one metallocene catalyst can be combined with a non-metallocene or traditional Ziegler-Natta catalyst or catalyst system, non-limiting examples are described in U.S. Patent Nos. 4,701,432, and 5,183,867 all of which are incoφorated herein by reference for the puφoses of U.S. patent practice.

For puφoses of this patent specification the terms "carrier" or "support" are interchangeable and can be any support material, preferably a porous support material, such as for example, talc, inorganic oxides, inorganic chlorides, for example magnesium chloride, and resinous support materials such as polystyrene or polystyrene divinyl benzene polyolefins or polymeric compounds or any other organic support material and the like, or mixtures thereof.

The preferred support materials are inorganic oxide materials, which include those of Groups 2, 3, 4, 5, 13 or 14 metal oxides. In a preferred embodiment, the catalyst support materials include silica, alumina, silica-alumina, and mixtures thereof. Other inorganic oxides that may be employed either alone or in combination with the silica, alumina or silica-alumina are magnesia, titania, zirconia, and the like.

It is preferred that the carrier ofthe catalyst of this invention has a surface area in the range of from about 10 to about 700 m^/g, pore volume in the range of from about 0.1 to about 4.0 cc/g and average particle size in the range of from about 10 to about 500 μm. More preferably, the surface area is in the range of from about 50 to about 500 ^/g, pore volume of from about 0.5 to about 3.5 cc/g and average particle size of from about 10 to about 200 μm. Most preferably the surface area range is from about 100 to about 400 m²/g, pore volume from about 0.8 to about 3.0 cc/g and average particle size is from about 10 to about 100 μm. The carrier of the invention typically has pore size in the range of from 10 to 1000 A, preferably 50 to about 500 A, and most preferably 75 to about 350 A.

Methods of Producing the Catalyst System of he Invention

The catalyst systems useful in the process ofthe invention can be made in a variety of different ways. In a preferred embodiment, the metallocene catalyst is supported on a carrier, optionally with an activator. In one embodiment, the metallocene catalyst component can be supported on a carrier and the activator added to the reactor, optionally on a support material which can be the same as or difFerent from the carrier.

In the most preferred embodiment, the catalyst system, which includes the metallocene catalyst component and the activator, is prereacted and then supported on a carrier. Non-limiting examples of supporting the catalyst system used in the invention are described in U.S. Patent Nos. 4,937,217, 4,912,075, 4,935,397, 4,937,301, 4,914,253, 5,008,228, 5,086,025, 5,147,949, 4,808,561, 4,701,432, 5,238,892, 5,240,894, 5,332,706, and 5,466,649, all of which are herein incoφorated by reference for the puφoses of U.S. patent practice.

The preferred method for producing the catalyst of the invention is described below.

In one embodiment, the metallocene catalyst component is typically slurried or dissolved in a liquid to form a metallocene solution and a separate solution is formed containing an activator and a liquid. The liquid can be any compatible solvent or other liquid capable of forming a solution or the like with at least one metallocene catalyst component and/or at least one activator. In a preferred embodiment the liquid is a cyclic aliphatic or aromatic hydrocarbon, most preferably toluene. The metallocene and activator solutions are preferably mixed (and the metallocene and activator prereacted) and added to a porous support such that the total volume of the metallocene solution and the activator solution or the metallocene and activator solution is less than five times the pore volume of the porous support, more preferably less than three times the pore volume of the porous support. Preferably, the range for the total volume of the metallocene solution and activator solution or the metallocene/activator solution added to a porous support is between about 1.1 to about 3 times, preferably 1.1 times to about 2.6 times the pore volume ofthe porous support. In an alternative preferred embodiment the range of the total volume of the solutions is in the range of from about 1.2 to about 2.6 times, and preferably being in the range of from about 1.5 to about 2.6 times the pore volume ofthe carrier used to form the catalyst.

In another embodiment, the metallocene and activator solutions are preferably mixed (and the metallocene and activator prereacted) and added to a porous support such that the total volume of the metallocene solution and the activator solution or the metallocene and activator solution is equal to or less than one times the pore volume of the porous support, more preferably less than 0.95 times the pore volume of the porous support. Preferably, the range for the total volume of the metallocene solution and activator solution or the metallocene/activator solution added to a porous support is between about 0.4 to about 0.9 times, preferably about 0.6 times to about 0.9 times the pore volume of the porous support.

A surface modifier, such as Kemamine AS990, (available from Witco Chemical Coφoration, Houston, Texas) may optionally be added at any stage in the preceding methods of making the catalyst system useful in the process of the invention. Preferably, the surface modifier is added after the solution is added to the porous support.

The procedure for measuring the total pore volume of a porous support is well known in the art. Details of one of these procedures are discussed in Volume 1, Experimental Methods in Catalytic Research (Academic Press, 1968) (specifically see pages 67-96). This preferred procedure involves the use of a classical BET apparatus for nitrogen absoφtion. Another method well known in the art is described in Innes, Total Porosity and Particle Density of Fluid Catalysts By Liquid Titration, Vol. 28, No. 3, Analytical Chemistry 332-334 (March, 1956).

In another embodiment, the supported catalyst is produced by contacting an organometallic compound, such as trimethyl aluminum with silica containing water, absorbed or adsorbed, within the carrier to form an activator, alumoxane for example. In this particular embodiment, the metallocene catalyst component is then added to the carrier and formed activator with or separately from a surface modifier, preferably after the metallocene has been added.

In one embodiment the catalyst system of the invention can be added in a dry or slurry state to the reactor.

Although not necessary to achieve the benefits of the invention, in one embodiment of the process of the invention, the catalyst system may be prepolymerized in the presence of monomers, ethylene and/or an alpha-olefin monomer having 3 to 20 carbon atoms prior to the main polymerization. The prepolymerization can be carried out batchwise or continuously in gas, solution or slurry phase including at elevated temperatures and pressures. The prepolymerization can take place with any monomer or combination thereof and/or in the presence of any molecular weight controlling agent such as hydrogen. For details on prepolymerization see U.S. Patent No. 4,923,833 and 4,921,825 and EP- B-0279 863, all of which are fully incoφorated herein by reference for the puφoses of U.S. patent practice.

The mole ratio of the metal of the activator component to the transition metal of the metallocene component is in the range of ratios between 0.3:1 to 1000.1, preferably 20:1 to 800:1, and most preferably 30:1 to 500:1. Where the activator is an ionizing activator as previously described the mole ratio ofthe metal of the activator component to the transition metal component is preferably in the range of ratios between 0.3 : 1 to 3 : 1.

Polymerization Process of the Invention

The catalysts and catalyst systems described above are suited for the polymerization of monomers in a slurry polymerization process.

In a preferred embodiment the invention is directed toward slurry polymerization reactions involving the polymerization of two or more of the monomers including ethylene and at least one alpha-olefin monomer having from 3 to 20 carbon atoms, preferably 4-20 carbon atoms, and most preferably 4-10 carbon atoms. The invention is particularly well suited to the copolymerization reactions involving the polymerization of one or more of the monomers, for example alpha-olefin monomers of ethylene, propylene, butene-1, pentene- 1, 3- methylpentene-1, 4-methylpentene-l, hexene- 1, octene-1, decene-1, and cyclic olefins such as cyclopentene, norbornene, alkyl-substituted norbornenes, and styrene or a combination thereof. Other monomers can include polar vinyl, diolefins such as dienes, polyenes, norbornene, norbornadiene, acetylene and aldehyde monomers. Preferably a copolymer of ethylene or propylene is produced. In another embodiment ethylene or propylene is polymerized with at least two different comonomers to form a teφolymer and the like, the preferred comonomers are a combination of alpha-olefin monomers having 3 to 10 carbon atoms, more preferably 3 to 8 carbon atoms, optionally with at least one diene monomer. The preferred teφolymers include the combinations such as ethylene/butene-1 /hexene- 1, ethylene/propylene/butene-1, propylene/ethylene/ butene- 1 , propylene/ethylene/hexene- 1 , ethylene/propylene/norbornadiene, ethylene/propylene/ethylidene/norbornene, and the like. The polymers of the present invention are preferably produced using a continuous slurry process. Such continuous slurry polymerization processes are well known to those skilled in the art. A slurry polymerization process generally uses pressures in the range of about 1 to about 500 atmospheres and even greater and temperatures in the range of -60°C to about 280°C. In a slurry polymerization, a suspension of solid, particulate polymer is formed in a liquid polymerization medium to which ethylene and comonomers and often hydrogen along with catalyst are added. The liquid employed in the polymerization medium is preferably an alkane or cycloalkane. The most preferred polymerization medium in the present invention is either isobutane, propane, pentane, isopentane or hexane.

In a preferred embodiment of the process of the invention, the process is operated in the absence of or essentially free of a scavenger. In the most preferred embodiment, the process ofthe invention is operated in the absence of a scavenger. For the puφoses of this patent specification and appended claims a

"scavenger" is any organometallic compound which is reactive towards oxygen and/or water and/or polar compounds and which does not include the catalyst components of the invention. Non-limiting examples of scavengers can be generally represented by the formula R_nA, where A is a Group 12 or 13 element, each R, which can be the same or different, is a substituted or unsubstituted, straight or branched alkyl radical, cyclic hydrocarbyl, alkyl-cyclo hydrocarbyl radicals or an alkoxide radical, where n is 2 or 3. Typical scavengers include trialkylaluminum compounds such as trimethylaluminum, triethylaluminum, triisopropyl aluminum, tri-sec-butyl aluminum, tri-t-butyl aluminum triisobutyl aluminum, tri-octyl aluminum, trialkyl boranes and alkoxides and the like.

In one embodiment ofthe process ofthe invention the process is essentially free of a scavenger. For the puφoses of this patent specification and appended claims the term "essentially free" means that during the process ofthe invention no more than 10 ppm of a scavenger based on the total weight ofthe recycle stream is present at any given point in time during the process of the invention. However, the inventive process may be operated with scavenger levels of up to 100 ppm with no fouling and no detrimental effect on catalyst productivity.

The ratio of the hydrogen content (ppm) in the reactor to the ethylene content (mole%) is typically from 0.001 to 0.5, preferably from 0.001 to 0.25, even more preferably from 0.001 to 0.18 and most preferably from 0.001 to 0.12.

The reactivity ratios of the catalysts and catalyst systems of this invention are generally less than 2, preferably less than 1.8 and more preferably less than 1.5 and most preferably less than about 1. Reactivity ratio is defined to be the mole ratio of comonomer to monomer in the reactor (C_x/Cy) divided by the mole ratio of the comonomer to monomer in the polymer product, where C_x is the mole percent of comonomer and Cy is the mole percent ofthe monomer. The reactor pressure may vary from about 100 psig (690 kPag) to about

1200 psig (8280 kPag), preferably in the range of about 300 psig (2070 kPag) to about 800 psig (5520 kPag) and most preferably in the range of about 450 psig (3100 kPag) to about 650 psig (4480 kPag).

Typical reactor temperatures are in the range of about 65°F (18°C) to about 190°F (88°C) , preferably in the range of about 85°F (29°C) to about

180°F (82°C) , more preferably in the range of about 90°F (32°C) to about 175°F (79°C), and even more preferably in the range of about 80°F (27°C) to about 170° F (77°C).

The catalyst productivity (grams of catalyst per gram of polymer (g/g)) is typically greater than 2000, more preferably greater than 4000, even more preferably greater than 5000, still more preferably greater than 6000, and most preferably greater than 7000. The present invention affords high catalyst efficiency without the need for further treatment or additives to the catalyst system, such as alcohols or ketones as required in U.S. Patent No. 5,539,069.

Polymer Produced bv the Process of the Invention

The process of the present invention may be used to produce polymers over a wide density range, including very low density polymers (i.e., less than 0.915 g/cc) with essentially no fouling ofthe reactor. The polymers produced have high molecular weight, narrow molecular weight distribution (as measured by the ratio of weight average molecular weight (Mw) to number average molecular weight (Mn)), and a narrow composition distribution. The high productivity ofthe catalyst used in the invention and the lack of fouling of the reactor are significant and demonstrate the commercial significance ofthe inventive process. More specifically, the lower density polymers made by the process ofthe invention typically have a density less than 0.915 g/cc, preferably in the range of from about 0.865 g/cc to about 0.91 g/cc, more preferably in the range of from about 0.87 g/cc to about 0.91 g/cc, still more preferably in the range of from about 0.87 to about 0.9 g/cc, even more preferably in the range of about 0.88 g/cc to about 0.9 g/cc, and most preferably in the range of from about 0.89 g/cc to about 0.9 g/cc. The polymers of the process of the invention have a weight average molecular weight (Mw) greater than about 40,000 to about 650,000, preferably greater than 45,000 and more preferably greater than 50,000 even more preferably greater than 60,000 and most preferably greater than 70,000. The melt index (MI) ofthe polymers ofthe process ofthe invention is in the range of from less than 0.01 dg/min to above 200 dg/min, preferably in the range of from about 0.01 to about 100 dg/min, more preferably in the range of from about 0.01 dg/min to about 20 dg/min, even more preferably in the range of from at least 0.01 dg/min to about 10 dg/min, and most preferably from about 0.01 dg/min to about 5 dg/min. MI is determined according to ASTM D-1238E.

In one embodiment of the invention, the MI of the polymers of the process ofthe invention is in the range from about 60 to 150 dg/min.

The polymers of the invention have a Mw/Mn generally in the range of from about 1.5 to about 10, preferably from about 1.8 to about 8, more preferably from about 1.8 to about 4.5, and most preferably from about 1.8 to about 3.5.

Another characteristic of the very low density polymers of the invention is their composition distribution (CD). A measure of composition distribution is the "Composition Distribution Breadth Index" ("CDBI"). CDBI is defined as the weight percent of the copolymer molecules having a comonomer content within 50% (that is, 25% on each side) of the median total molar comonomer content. The CDBI of a copolymer is readily determined utilizing well known techniques for isolating individual fractions of a sample ofthe copolymer. One such technique is Temperature Rising Elution Fraction (TREF), as described in Wild, et al., I Polv. Sci.. Polv. Phvs. Ed., vol. 20, p. 441 (1982) and U.S. Patent No. 5,008,204, which are incoφorated herein by reference.

To determine CDBI, a solubility distribution curve is first generated for the copolymer. This may be accomplished using data acquired from the TREF technique described above. This solubility distribution curve is a plot ofthe weight fraction of the copolymer that is solubilized as a function of temperature. This is converted to a weight fraction versus composition distribution curve. For the puφose of simplifying the correlation of composition with elution temperature the weight fractions are assumed to have a Mn > 15,000, where Mn is the number average molecular weight fraction. Low weight fractions generally represent a trivial portion of the polymer of the present invention. The remainder of this description and the appended claims maintain this convention of assuming all weight fractions have a Mn > 15,000 in the CDBI measurement. From the weight fraction versus composition distribution curve the CDBI is determined by establishing what weight percent of the sample has a comonomer content within 25% each side of the median comonomer content. Further details of determining the CDBI of a copolymer are known to those skilled in the art. See, for example, PCT Patent Application WO 93/03093.

The polymers of the invention have CDBI's generally in the range of 10 to 99%, preferably greater than 20%, most preferably greater than 30%. In another embodiment the polymers of the invention have a CDBI in the range of greater than 50% to 99%, preferably in the range of 55% to 98%, and more preferably 60% to 95%, even more preferably greater than 60%, still even more preferably greater than 65%.

In the process of the invention the preferred monomer is ethylene in combination with one or more other alpha-olefin monomers, most preferably C4 to C10 alpha-olefins. The weight percent of ethylene in the polymer is typically in the range of from about 90 weight percent to about 50 weight percent, preferably from about 90 weight percent to about 70 weight percent, and more preferably from about 90 weight percent to about 75 weight percent.

In another embodiment the polymer produced by the process of the invention typically has essentially a single melting point (second melt) characteristic with a peak melting point (Tm) as determined by DSC in the range of from about 20°C to about 115°C, preferably in the range of about 30°C to about 110°C and even more preferably in the range of from about 40°C to about 105°C and most preferably in the range of from about 40°C to about 100°C. The term "essentially a single melting point" as used herein means that at least 70, and preferably, 80 percent by weight of the polymer corresponds to a single Tm peak existing in the range of from about 20°C to about 115°C.

The bulk density ofthe polymer produced by the process ofthe invention is in the range of greater than 0.25 g/cc to about 0.55 g/cc, preferably in the range of 0.30 g/cc to greater than about 0.45 g/cc and most preferably greater than 0.35 g/cc. Bulk density may be measured by pouring the resin via a 7/8" diameter funnel into a fixed volume cylinder of 400 cc; the bulk density is then measured as the weight of resin in the cylinder divided by the 400 cc to give a value in g/cc.

The polymers produced by the process of the invention are useful in such forming operations include film, sheet, and fiber extrusion and co-extrusion as well as blow molding, injection molding, sheet thermoforming and rotational molding. Films include blown or cast films in mono-layer or multilayer constructions formed by coextrusion or by lamination. Such films are useful as shrink film, cling film, stretch film, sealing films, oriented films, snack packaging, heavy duty bags, grocery sacks, baked and frozen food packaging, medical packaging, industrial liners, membranes, etc. in food-contact and non-food contact applications. Fiber forming operations include melt spinning, solution spinning and melt blown fiber operations. Such fibers may be used in woven or non-woven form to make filters, diaper fabrics, medical garments, geotextiles, etc. General extruded articles include medical tubing, wire and cable coatings, geomembranes, and pond liners. Molded articles include single and multi-layered constructions in the form of bottles, tanks, large hollow articles, rigid food containers and toys, etc. Some uses for the polymer of this invention are described in U.S. Patent Nos. 5,358,792, 5,246,783, 5,206,075, 5,241,031 and, 5,322,728, all of which are herein fully incoφorated by reference for the puφoses of U.S. patent practice.

In some instances where it is necessary to improve processability and manipulate final end product characteristics the polymers produced by this present invention can be blended or coextruded into single or multilayer films or the like with various other polymers well known in the art, for instance, LLDPE, LDPE, HDPE, polypropylene, PB, EVA and the like and static controlling agents such as sorbitol. Further, the process of the present invention allows the production of a blend of ethylene inteφolymer components with narrow molecular weight and composition distributions selected to obtain an overall molecular weight and composition distribution in the resulting blend to impart superior properties thereto. Examples of such blends are provided in U.S. Patent No. 5,382,630, which is incoφorated herein by reference for the puφoses of U.S. patent practice.

EXAMPLES

In order to provide a better understanding of the present invention including representative advantages and limitations thereof, the following examples are offered.

The properties of the polymer were determined by the following test methods.

Melt Index (MI) is measured in accordance with ASTM D-1238-Condition E (2.16 kg, 190° C).

High Load Melt Index (HLMI) is measured in accordance with ASTM D- 1238-Condition F (21.6 kg, 190° C). Density is measured in accordance with ASTM D- 1505. Preparation of the Catalyst -- Method 1

The metallocene catalyst was prepared from 850 lbs (385.9 kg) of silica (Davison 948 available from W.R. Grace, Davison Chemical Division, Baltimore, Maryland) dehydrated at 600° C. The catalyst was a commercial scale catalyst prepared in a mixing vessel with an agitator. An initial charge of 1325 lbs (601.6 kgs) toluene was added to the mixer. This was followed by mixing 1050 lbs (476.7 kgs) of 30 percent by weight methyl alumoxane (MAO) in toluene (available from Albermarle Coφoration, Baton Rouge, Louisiana). This was followed with 92 lbs (41.8 kgs) of 20 percent by weight bis(l-methyl, 3-n-butyl cyclopentadienyl) zirconium dichloride in toluene (18.4 lbs (8.35 kgs) of contained metallocene). An additional 500 lbs (227 kgs) of toluene were added to the mixer to rinse the metallocene feed cylinder and allowed to mix for 30 minutes at ambient conditions. The above mixture was added to the silica after which 60 lbs (27.2 kgs) of a Kemamine AS-990 in toluene solution, surface modifier solution, containing 6 lbs (2.7 kgs) of contained Kemamine AS-990 (available from Witco Chemical Coφoration, Houston, Texas) was added. An additional 100 lbs (46 kgs) of toluene rinsed the surface modifier container and was added to the mixer. The total liquid volume was equivalent to 2.58 cc/cc pore volume of the silica. The resulting slurry was vacuum dried at 3.2 psia (22 kPa) at 175°F (79°C) to a free flowing powder. The final catalyst weight was 1190 lbs (540 kgs). The catalyst had a final zirconium loading of approximately 0.40 weight percent and an aluminum loading of approximately 12.0 weight percent.

Preparation of the Catalyst — Method 2 The metallocene catalyst system may also be prepared by adding 7.4 liters of toluene, 5.4 liters of a 30 wt.% solution of methylalumoxane in toluene, and 116 grams of bis( 1-methyl, 3 -n-butyl Cp) ZrCl₂ dissolved in 1.2 liters of toluene to a 37.8 liter stirred tank reactor and mixing at ambient temperature. After these components are mixed, 4 kg of Davison 948 silica, dehydrated at 600°C, is rapidly added to the mixture. The order of addition of the catalyst system components may be varied, if desired. An additional 2 liters of toluene are then added, and the mixture stirred for 20 minutes. The toluene solvent is then stripped off by heating the mixture to 70°C and pulling a mild vacuum for a period of time sufficient to reduce the mixture to a free flowing powder. As one of ordinary skill in the art would understand, the catalyst preparation can be varied such that the total liquid volume of catalyst solution ranges from 1.1 to 5 times the total pore volume ofthe dehydrated silica support. Preparation ofthe Catalyst — Method 3

The metallocene catalyst may also be prepared by first combining 50.22 grams (54 cc) of a 30% by weight methylalumoxane solution (available from Albermarle Coφoration, Baton Rouge, Louisiana) with 4.0 cc of toluene and stirring for about 15 minutes. This is followed with 1.16 grams of 20 percent by weight bis( 1-methyl, 3 -n-butyl cyclopentadienyl)zirconium dichloride in toluene. Then, 40 grams of silica (Davison 948 available from W.R. Grace, Davison Chemical Division, Baltimore, Maryland) dehydrated at 600° C are added at a controlled rate as rapidly as possible without overloading agitation or exceeding 10°F (5.6°C) greater than ambient system temperature. If desired, the liquid components may be added to the silica. The foregoing ingredients are allowed to mix for 15 minutes under ambient conditions. The mixture is dried under vacuum, for example, at 3.2 psia (22 kPa), at 150° F (66°C) to give a light yellow, free flowing catalyst. The total liquid is equivalent to 1.0 cc cc pore volume of the silica. The catalyst has a final zirconium loading of 0.45 weight percent and an aluminum loading of 12.8 weight percent.

As one of ordinary skill in the art would understand, the catalyst preparation procedure may be varied such that the ratio of total liquid volume of catalyst solution to the total pore volume ofthe support can be any value less than one. For example, if a 0.95 loading of liquid catalyst components to pore volume of silica is desired, then the foregoing procedure should be modified to add 1.0 cc of extra toluene to the MAO solution, rather than 4.0 cc of extra toluene. Otherwise, the procedure is the same, and results in a catalyst having the same final zirconium loading and aluminum loading as described above.

Polymerization

Tables I and III set forth the operating parameters and product data for the batch polymerization process used in producing the ethylene/alpha olefin polymers of the present invention. Table II sets forth the operating parameters and product data for the continuous polymerization process used in producing the ethylene/alpha-olefin polymers ofthe present invention.

BATCH POLYMERIZATION EXAMPLES 1-14 The polymerization was conducted in a 1 liter agitated slurry reactor at temperatures ranging from 40° C to 85° C, as indicated in Table I. Isobutane was used as the polymerization diluent. Specifically, 800 cc of polymerization grade (essentially free of any water, oxygen or any other compounds that could poison the catalyst system) isobutane were added to the reactor, along with 0.15 cc of a triethylaluminum (TEAL) solution containing 1.55 mM Al/cc. The TEAL is added because relatively small batch reactors, such as used here, have much higher surface area to volume ratio and can hold more catalyst poisons; therefore, a small amount of a scavenger, such as TEAL, is used initially to "clean up" the reactor system.

Butene or hexene was added as a comonomer in the volumes indicated in Table I. Once the reactor was heated to the desired reaction temperature, ethylene was added at 120 to 130 psi (820 - 897 KPa), such that the reactor pressure ranged from 210 psi to 325 psi (1449 - 2243 KPa), depending upon the reactor temperature chosen, as shown in Table I. This was followed by adding 100 mg (for polymerization examples 1-11) or 50 mg (for polymerization examples 12-14) of the catalyst system prepared according to Method 1 or Method 2 and polymerization was allowed to proceed for 40 minutes. Granular product was obtained with catalyst activity as indicated in Table I. The product was free flowing and easy to remove from the reactor. There were no signs of fouling in the reactor except as indicated otherwise in Table I. Product characteristics, such as melt index I₂, 1₂₁, and melt flow rate (I₂ι/I₂), are also given in Table I.

CONTINUOUS POLYMERIZATION EXAMPLES A-C

Continuous polymerizations were conducted using a loop slurry process using the catalyst system prepared in Method 1 above. The dry catalyst was slurried in isobutane to facilitate feeding the reactor. The reactor was a 16 in. (41 cm) diameter loop reactor. No alkyl scavenger was added for the continuous polymerization examples.

The process conditions product results for the continuous polymerizations are presented in Table II. There were no signs of fouling in the reactor.

BATCH POLYMERIZATION EXAMPLES 15 - 20

The polymerization was conducted in a 1 liter agitated slurry reactor at temperatures ranging from 40° C to 60° C, as indicated in Table HI. Polymerization grade isobutane is ideally used as the polymerization diluent. Specifically, 800 cc of polymerization grade isobutane was added to the reactor, along with 0.15 cc of a triethyl aluminum solution containing 1.55 mM Al/cc to "clean up" the reactor as in Examples 1-14.

Butene was used as a comonomer in the volumes indicated in Table UI. Once the reactor was heated to the desired reaction temperature, ethylene was added at 120 psi (828 KPa), such that the reactor pressure ranges from 210 psi to 250 psi (1449 - 1725 KPa), depending upon the reactor temperature chosen, as shown in Table III. This was followed by adding 50 mg of the catalyst system prepared according to Method 3 above and polymerization was allowed to proceed for 40 minutes. Granular product was obtained with catalyst activity as indicated in Table III. The product was free flowing and easy to remove from the reactor. Only negligible fouling was observed in the reactor. The process and product conditions and results are shown in Table III.

TABLE π

Batch examples 1-9, 11-14, 15-20 and continuous examples A-C illustrate the process of this invention. In Examples 1-9 and 11-14 there was no indication of fouling, except for Example 10. Note that the fouling in Example 10 could be remedied by reducing the reactor temperature and pressure as indicated in Example 11. Only negligible fouling was observed in Examples 15-20. The polymer product produced was dry with good particle moφhology.

While the present invention has been described and illustrated by reference to particular embodiments, it will be appreciated by those of ordinary skill in the art that the invention lends itself to variations not necessarily illustrated herein. The catalyst of the invention can be used in a single reactor or in a series reactor or even in series where one reactor is a slurry reactor and the other being a gas phase reactor. It is contemplated that the catalyst of the invention can be mixed with a traditional Ziegler-Natta catalyst or a catalyst of the invention can be separately introduced with a traditional Ziegler-Natta catalyst or any one or more other metallocene catalyst system. For this reason, then, reference should be made solely to the appended claims for purposes of determining the true scope of the present invention.

Claims

CLAIMS:We Claim:

1. A slurry process for polymerizing monomers in a reactor, the process comprising: a) contacting a mixture comprising a metallocene and alumoxane with a support to form a metallocene catalyst system; b) introducing the metallocene catalyst system into a reactor; c) introducing ethylene monomer and at least one C4-C20 alpha-olefin comonomer into the reactor; d) maintaining the reactor at a temperature below 100°C; e) reacting the ethylene monomer and at least one other alpha-olefin comonomer to form a polymer having a density less than about 0.91 g/cc; wherein the support has a pore volume in the range of from 0.1 to 4.0 cc/g, and wherein the volume of the mixture is greater than the pore volume of the support.

2. The process of claim 1 wherein the volume ofthe mixture is equal to or less than the pore volume ofthe support.

3. The process of claim 1 wherein the volume of the mixture is 1.1 to 2.6, preferably 1.2 to 2.6, and most preferably 1.5 to 2.6 times the pore volume ofthe support.

4. The process of claim 2 wherein the volume ofthe mixture is 0.4 to 0.9 times, preferably 0.6 to 0.9 times the pore volume ofthe support.

5. The process of any of the preceding claims further comprising adding a surface modifier to the metallocene catalyst system.

6. The process of any of the preceding claims wherein the process is continuous and further comprising the step of introducing into the reactor additional monomers and comonomers to replace the monomers and comonomers polymerized.

7. The process of any of the preceding claims wherein the metallocene and alumoxane are prereacted prior to contacting the support.

8. The process of any of the preceding claims wherein the support is selected from the group consisting of silica, alumina, silica-alumina, magnesia, titania, and zirconia.

9. The process of any ofthe preceding claims wherein the polymer has a melt index in the range of from less than 0.01 to 100 dg/min, preferably from

0.01 dg/min to 20 dg/min.

10. The process of any ofthe preceding claims wherein the process is operated essentially free of a scavenger.

11. The process of any ofthe preceding claims wherein the at least one other alpha-olefin comonomer has from 4 to 10 carbon atoms.

12. The process of any ofthe preceding claims wherein the polymer contains in the range of from 90 weight percent to 50 weight percent ethylene.

13. The process of any of the preceding claims wherein the polymer has a density in the range of from about 0.87 g/cc to 0.91 g/cc, preferably from 0.87 g/cc to 0.9 g/cc, more preferably from 0.88 g/cc to 0.9/cc, and most preferably from 0.89 g/cc to 0.9 g/cc.

14. The process of any of the preceding claims wherein the polymer has a composition distribution breadth index greater than 45%, preferably greater than 50%, more preferably greater than 60%, and most preferably greater than 65%.

15. The process of claim 1 wherein the metallocene catalyst system has a productivity of greater than 2000 grams, preferably greater than 3000 grams, and more preferably greater than 4000 grams of catalyst component per gram of polymer product.

16. The process of any of the preceding claims wherein the polymerization takes place at a reactor temperature less than 90°C, preferably less than 75° C.

17. The process of any of the preceding claims wherein the polymer product has a density in the range of from 0.89 g/cc to 0.9 g/cc and a melt index in the range of from 0.01 dg/min to 5 dg/min.