CS257284B2 - Vanadium catalyst precursor for polyethylene production - Google Patents

Abstract

A supported precursor of a vanadium-based catalyst for the production of polyethylene consisting of 1) a vanadium compound which is a reaction product of a vanadium trihalide, where the halogen is chlorine, bromine or iodine, and an electron donor which is a liquid organic Lewis base in which the vanadium trihalide is soluble, 2) modifiers MXa, where M is boron or the radical AlR{3_a), in which R independently represent alkyl groups with the proviso that the total number of aliphatic carbon atoms in any R group is not more than 14, X represents chlorine, bromine or iodine and a represents 0, 1 or 2 with the proviso that when M represents boron, a represents 3 and 3) a solid inert support formed of silica or alumina on which the vanadium compound and the modifier are supported.

Description

A supported precursor of a vanadium-based catalyst for the production of polyethylene consisting of

1) a vanadium compound which is the reaction product of a vanadium halide, where the halogen is chlorine, bromine or iodine, and an electron donor which is a liquid organic Lewis base in which the vanadium halide is soluble,

2) modifiers MX _a , where M represents boron or the radical AlR{3_ _a ), in which R represents independently of each other alkyl groups with the proviso that the total number of aliphatic carbon atoms in any R group is not higher than 14, X represents chlorine, bromine or iodine and a represents 0, 1 or 2 with the proviso that when M represents boron, a represents 3 and

3) a solid inert support, formed of silica or alumina, on which the vanadium compound and the modifier are deposited.

The invention relates to a vanadium-based catalyst support precursor for the production of polyethylene. The term polyethylene ee refers to homopolymers of ethylene or copolymers of ethylene with at least one alpha-olefin having 3 to 10 carbon atoms. The catalyst precursor of the invention is suitable for gas phase polymerization after activation to form polymers having a desirable property profile suitable for certain applications.

Polyethylenes with a relatively broad molecular weight distribution have extensive applications in wire and cable insulation and can be used for blow molding and pipe production. Such polyethylenes with a broad molecular weight distribution, such as those made by the method disclosed in U.S. Patent No. 3,324,095 (Carrick et al.), are unstable due to their relatively high level of unsaturation. Polyethylenes with a relatively narrow molecular weight distribution can be produced in the gas phase, such as those described in U.S. Patent No. 4,302,565 (Gocke et al.) and U.S. Patent No. 4,302,566 (Karol et al.). Such gas phase polymerization processes use high activity catalysts to produce polyethylenes with low unsaturation, which have high utility in a variety of film applications. However, such polyethylenes have limited utility in other areas where higher melt flow and extrusion capabilities are required, and lower melt fracture of polyethylene with a broad molecular weight distribution. It would therefore be desirable to develop a highly active catalyst system and process for the gas phase production of highly saturated polyethylene having a broad molecular weight distribution.

Vanadium catalysts are used to produce polyethylene. U.S. Patent No. 3,956,255 (Ort) describes a catalyst system for the polymerization of ethylene which essentially consists of a vanadium compound reacted with an alkylaluminum alkoxide and a trialkylaluminum. This catalyst system is supported on silica which has been previously reacted with an alkylaluminum or alkylaluminum alkoxide. A halogenated alkane may optionally be used as a promoter.

U.S. Patent No. 4,173,698 (Kanoh et al.) describes a catalyst for the polymerization of ethylene which is a product formed by a complex of vanadium chloride and an ether, combined with an aluminum halide. The product is not supported. An organo-aluminum compound is used as a cocatalyst.

U.S. Patent No. 4,202,958 (Yamaguchi et al.) relates to a process for the polymerization of ethylene using a non-sulfur solid catalyst obtained by the reduction of vanadium halide with an organoaluminum compound in the presence of an ether compound. Here too, an organoaluminum cocatalyst is used.

U.S. Patent No. 4,263,171 (Shida et al.) is a representative publication relating to catalysts for the polymerization of olefins using magnesium-containing compounds. The patent discloses a catalyst supported on silica formed of a magnesium-aluminum complex with a halogenated transition metal compound (including vanadium).

U.S. Patent No. 4,294,947 (Doerk et al., describes the copolymerization of ethylene with 1-butene in liquid 1-butene as a solvent using an unsupported catalyst comprising the reaction product of vanadyl chloride and/or alkoxide with alkylaluminum chloride and organoaluminum ^cocatalysts .

Many of these prior art publications are directed to obtaining a catalyst with high activity or to selectively improve individual polymerization processes or properties of polyethylene. Due to the complexity, it has not been possible to obtain an industrially suitable optimized gas phase process using a vanadium catalyst for the production of polyethylenes with the desired balance of properties prior to the present invention. To achieve such a process, the catalyst must provide an improved hydrogen response in order to achieve a very low level of unsaturation in the polyethylene. Furthermore, it must exhibit a high degree of productivity so that the catalyst residue in the polyethylene is so small, preferably less than 10 ppm vanadium, that it would allow it to remain in it and the catalyst removal step to be omitted. The catalyst must further provide polyethylene that is easily formed by various forming processes, i.e. polyethylene that has a relatively broad molecular weight distribution and a wide range of melt flow indices. The catalyst must also allow for increased copolymerization of ethylene with other alpha-olefins in order to control the density of the polyethylene over a wide range and to expand the range of comonomers that can be used.

The polyethylene obtained using such a catalyst should have a high bulk density so that handling and transportation costs are commercially acceptable. The particles of the polyethylene obtained should be of a size that allows them to be easily suspended in a fluidized bed reactor and should have a low content of dusty fines. The resulting polyethylene should be in the form of free-flowing particles and should not contain agglomerates such as sintered particles or lumps. The catalyst must meet all of these criteria simultaneously and the catalytic system should be as simple as possible. Preference is given to catalytic systems with a minimum number of components.

The subject of the invention is a carrier precursor of a vanadium-based catalyst for the production of polyethylene, which is characterized in that it consists of

1) vanadium compounds, which are reaction products,

a) vanadium halide, where halogen is chlorine, bromine or iodine and

b) an electron donor, which is a liquid organic Lewis base in which vanadium halide is soluble,

2) modifier of general formula I

MX _and (I) where

M represents boron or the radical AlRj ₃ _ _a j, in which R represents independently of each other alkyl groups with the proviso that the total number of aliphatic carbon atoms in any R group is not higher than 14,

X X represents chlorine, bromine or iodine and a represents 0, 1 or 2 with the proviso that when M represents boron, a represents 3 and

3) a solid inert support, formed of silicon dioxide or aluminum oxide, on which the vanadium compound and the modifier are deposited.

After activation with a cocatalyst of general formula II

A1R ₃ (II), where R has the above meaning, and a promoter of the general formula III ^ ^CX (4-b) ^(I1I) ' where R' means hydrogen or an unsubstituted or halogenated alkyl group containing up to 6 carbon atoms,

X' is halogen and b is 0, 1 or 2, the precursor can be used for the homopolymerization of ethylene or the copolymerization of ethylene with at least one alpha-olefin having 3 to 10 carbon atoms carried out in the gas phase. In this polymerization, the monomer or a mixture thereof is brought into contact at a temperature of 10 to 115 ° C with a catalytic system containing the precursor according to the invention and the above-mentioned cocatalyst and promoter. The resulting polyethylenes have a better balance of flow properties, molecular weight distribution, bulk density and saturation. Their density and melt flow index can be selected within a wide range.

The polyethylene thus prepared is a homopolymer of ethylene or a copolymer of a majority, i.e. at least about 50%, of ethylene and a minor molar proportion, i.e. less than about 50%, of one or more alpha-olefins having from 3 to 10 carbon atoms. Preferred alpha-olefins are propylene, 1-butene, 1-hexene, 4-methyl-1-pentene and 1-octene. Other monomers may be used, including conjugated or non-conjugated dienes such as butadiene, 1,4-hexadiene and ethyl diene norbornene.

These polyethylenes have a suitable balance of properties. Their density may lie in the range of approximately 860 to 960 kg.m ³ . They may have a melt flow index from a value at which there is no flow up to about 300 g/10 min, preferably from about 0.1 to 50 g/10 min. They have a broad molecular weight distribution, which is defined by a ratio of weight average molecular weight to number average molecular weight (M _w /M _n ) of greater than about 10, preferably in the range of about 14 to 22. They also have a high bulk density of at least about 320 kg.m ^-3 , preferably in the range of about 384 to about 5,129 kg.m ³ . Their level of unsaturation is very low and tends to be less than 1 carbon-carbon double bond per thousand carbon atoms (C = C/l 000 C), preferably less than about 0.2 C = C/l 000 C and particularly preferably less than about 0.1 C = C/l 000 C. The copolymers have a residual catalyst content of less than about 10 ppm, preferably less than about 6 ppm, expressed in parts of vanadium metal per million parts of copolymers. Preferred polymers produced by the gas phase process of the invention are in the form of loose solid particles that are essentially free of agglomerates in the form of sintered particles or lumps.

These polyethylenes are suitable for a wide range of applications, including use in blow molding, film and tube production, extrusion coatings, as well as for application to wires and cables.

The catalyst support precursor of the invention consists of a vanadium compound and a modifier, which are impregnated on a solid inert support. The vanadium compound in the precursor is a reaction product formed from a vanadium halide and an electron donor. The halogen in the vanadium halide is chlorine, bromine, or iodine or mixtures thereof. A particularly preferred vanadium halide is vanadium chloride of the formula VCl^.

The electron donor is a liquid organic Lewis base in which the vanadium trihalide is soluble. The electron donor is selected from the group consisting of alkyl esters of aliphatic and aromatic carboxylic acids, aliphatic esters, aliphatic ketones, aliphatic amines, aliphatic alcohols, alkyl and cycloalkyl ethers and mixtures thereof. Preferred electron donors are alkyl ethers and cycloalkyl ethers, especially tetrahydrofuran. Each molar part of vanadium is in the form of a complex with about 1 to about 20, preferably about 1 to about 10 and particularly advantageously about 3 molar parts of electron donors.

As a modifier of the general formula I, alkylaluminum mono- and dichlorides with 1 to 6 carbon atoms in the alkyl group or boron trichloride are preferably used in the precursor applied to the carrier. The use of diethylaluminum chloride is particularly preferred. About 0.1 to about 10, preferably about 0.2 to about 2.5 molar parts of the modifier are used per 1 molar part of the electron donor.

The carrier is a solid, porous, particulate material that is inert to polymerization.

The carrier consists essentially of silica or alumina, i.e. silicon dioxide or aluminum oxide, or mixtures thereof. If desired, the carrier may contain other substances, such as zirconium dioxide or thorium dioxide or other compounds which are chemically inert to the polymerization, or mixtures thereof.

The carrier is used in the form of a dry powder with an average particle size of between about 10 and about 250, preferably between about 20 and about 200, and most preferably between about 30 and about 100 microns.

2-1 - 2-1

The porous support has a specific surface area of at least about 3 m 2 g , and preferably at least about 50 m 2 g . A preferred support is silica having a pore size of at least about 8 nm, preferably at least 10 nm.

The support is pre-dried by heating to remove water, preferably to a temperature of at least about 600°C.

The amount of carrier used is selected to achieve a vanadium content of about 0.05 to about 0.5 mmol vanadium per gram (mmol V/g), and preferably between 0.2 to about 0.35 mmol V/g, particularly suitably about 0.25 mmol V/g.

Before forming the precursor supported on the support, the support is usually not pretreated by reaction with an alkyl aluminum compound. Such treatment results in the formation of aluminum alkoxides which are chemically bound to the support molecules. The present inventors have discovered that the use of such a treated support in the catalytic system of the process of the present invention is not only unnecessary, but results in undesirable agglomeration when used in the production of high density polyethylene (greater than 0.94 g.cm ). This results in a lumpy product which is not free flowing.

Furthermore, the present inventors have also discovered that the presence of a magnesium compound in the supported precursor does not significantly increase the activity of the catalyst, and therefore the magnesium compound is an unnecessary component.

The carrier precursor of the invention is preferably prepared by first preparing a vanadium compound by dissolving a vanadium halide in an electron donor at a temperature of from 20°C to the boiling point of the electron donor compound over a period of several hours. The dissolution is preferably carried out at about 65°C for about 3 hours or more. The vanadium compound thus prepared is then impregnated onto a carrier. Impregnated may be by adding the carrier in the form of a dry powder or suspension in the electron donor or other inert solvent. The liquid is removed by drying at a temperature below about 100°C for several hours, preferably at a temperature between about 45 and about 90°C for about 3 to 6 hours. The vanadium-impregnated carrier is then mixed with a modifier dissolved in an inert solvent such as a hydrocarbon. The liquid is removed by drying at temperatures below about 70°C for several hours, preferably at a temperature between about 45 and about 65°C for 3 hours.

Before and/or during the polymerization, a cocatalyst and a promoter are added to the carrier precursor according to the invention. The cocatalyst and the promoter are added either together or separately and either simultaneously or sequentially during the polymerization. The cocatalyst and the promoter are preferably added separately during the polymerization in the form of solutions in an inert solvent, such as isopentane.

Preferred cocatalysts of formula II include trialkylaluminum compounds having 2 to 8 carbon atoms in each alkyl group. A particularly preferred cocatalyst is triisobutylaluminum. The cocatalyst is used in an amount of between about 5 and about 500, preferably between about 10 and about 50 moles per mole of vanadium.

Preferred promoters of formula III include fluorine, chlorine or bromine substituted ethane or methane containing at least 2 halogen atoms attached to a carbon atom. Preferred promoters include CCl^, CHCl^, CH ₂ Cl ₂ , CBr^, CFCl^, CH^CClj and CF ₂ ClCCl _3. Particularly preferred promoters are methylene dichloride (CH ₂ Cl ₂ ), 1,1,1-trichloroethane (CH^CCl^) and chloroform (CHCl^). Between about 0.1 and about 10, preferably between about 0.2 and about 2, molar promoter parts are used per 1 molar part of cocatalyst.

The polymerization of ethylene is carried out in the gas phase using methods well known in the art. Preferably, the polymerization is carried out in a continuous fluidized bed process. In this process, individual charges of the catalyst system and monomers are introduced into the reaction vessel and the polyethylene product is continuously removed from the reaction vessel. The density of the ethylene copolymer produced can vary widely depending on the amount of alpha-olefin comonomer added and its type. The higher the molar fraction of alpha-olefin added, the lower the density of the copolymer is achieved.

The polymerization is carried out at a temperature below the sintering temperature of the polyethylene. The operating temperature is usually in the range of about 10 to about 115°C. The preferred operating temperature varies depending on the desired density of the polyethylene. High density polyethylenes, i.e., with a density greater than about 940 kg.m3 ^, are produced at an operating temperature between about 85 and about 115°C, preferably between about 90 and about 100°C. Low density polyethylenes, i.e., with a density in the range of about 910 to about 940 kg.m3 ^, are preferably produced at an operating temperature between about 75 and about 90°C. Very low density polyethylenes, i.e., with a density less than about 910 kg.m3 ^, are preferably produced at an operating temperature between about 10 and about 80°C. In the case of very low density polyethylenes, it is necessary to dilute the reaction mixture with a large amount of diluent gas to prevent the formation of polymer agglomerates and to maintain continuous polymerization operation, as described in the related Czechoslovak Patent No. 250 660 by Union Carbide Corporation.

The fluidized bed reactor operates at pressures up to 6870 kPa and preferably between about 343 and about 2405 kPa.

A transfer agent such as hydrogen may be used to terminate the polymer chains. A typical ratio of hydrogen to ethylene will vary between about 0.001 and about 2.0 parts by mole hydrogen to 1 part by mole ethylene. The inventors have found that the response to hydrogen is improved using the catalyst system of the present invention, so that less hydrogen is required to produce polyethylene with an extremely low content of unsaturation.

The following examples serve to illustrate the carrier precursor of the invention, the catalyst system prepared therefrom, and the process for polymerizing ethylene using the catalyst system. The examples are not intended to limit the scope of the invention.

The properties of the polymers produced in the examples are determined by py unless otherwise stated.

by the test procedures described below.

Ash content

Bulk density (kg/m ³ )

Density (kg/ ^m3 )

Fine fraction (% by weight)

Test procedure

The polyethylene is converted to ash, which is weighed. The productivity can be calculated, defined as the number of parts by weight of polyethylene produced per 1 part by weight of total catalyst.

It is determined according to the American standard ASTM-D-1895, method B.

It is determined according to the American standard ASTM-1605, based on plaques prepared according to the American standard ASTM-D-1928, procedure C.

The amount of polymer particles that pass through a sieve with a mesh size of 74.10 ⁶ m.

Melt flow index Determined according to American standard ASTM-D-1238, conditions F. at higher load (g/10 min)

Melt flow index ratio

Particle agglomeration

Unsaturation (C=C/1,000 C)

The ratio of the melt flow index at higher load to the melt flow index at lower load. The melt flow index at lower load is measured according to the American standard ASTM-D-1238, condition E.

It is determined based on visual observation of the produced polyethylene leaving the reactor.

It is determined by infrared spectrophotometric measurement of the absorbance (absorbance at 10.35 micrometers corresponding to trans-vinylidene groups, 11.0 micrometers corresponding to terminal vinyl groups and 11.25 micrometers corresponding to pendant vinyl groups) on a 0.63 mm thick polymer extrusion. The concentration of unsaturation is proportional to the absorbance at 0.025 mm divided by the absorptivity (absorbivity values used were published by R. J. doKock et al., J. Polymer Science, Part B., 2, 339, (1964).

Note:

^a The number of carbon-carbon double bonds per 1,000 carbon atoms.

The abbreviations used in the examples have the following meanings:

Marking Explanation of meaning DEAC Diethylaluminum chloride ED A compound that acts as an electron donor TEAL Triethylaluminum THF Tetrahydrofuran TIBA Triisobutylaluminum TnHAL Tri-n-hexylaluminum EADC Ethyl aluminum dichloride

The catalyst systems used in the examples were prepared using the following standard procedures. To a flask containing 4 liters of anhydrous tetrahydrofuran was added 34 g (0.216 mol) of vanadium chloride. The mixture was stirred for 5 hours at 65°C under nitrogen until the vanadium chloride dissolved. To this solution was added 800 g of silica, which had been dehydrated by heating to 600°C, and stirring was continued for 4 hours at 65°C. In Comparative Examples A to D, the silica was pre-treated with 5.5% by weight of triethylaluminum. The flask was vented and the solution was dried to a slurry-like state at 70°C. The temperature is allowed to drop to 45°C and the solution is purged with nitrogen for 6 hours or until the resulting precursor has a tetrahydrofuran level of 4 to 10% by weight. The impregnated silica produced in this manner is a solid powder containing 0.25 mmol of vanadium per gram. The solid is removed from the flask and stored under nitrogen.

Then, except for Comparative Example C, the modifier is introduced using the following procedure. To a flask containing 4 liters of anhydrous isopentane is added 500 g of the impregnated silica described above. To this mixture is added, with stirring, a 25% by weight solution of diethylaluminum chloride, as the modifier, in anhydrous hexane. The modifier is used in such an amount as to achieve the number of moles of modifier per mole of tetrahydrofuran in the vanadium compound as given in the examples. This mixture is heated to 45°C and purged with nitrogen for 3 hours or until the product is in the form of a free-flowing powder.

The vanadium precursor thus produced is then removed from the flask and stored under nitrogen.

Polyethylene is produced in a fluidized bed reactor using the following standard procedure and operating conditions summarized in Table I. Ethylene is copolymerized with the comonomer listed in the examples. The triisobutylaluminum cocatalyst is added during the polymerization as a 5% by weight solution in isopentane. Chloroform CHCl^ is added, except in Comparative Example D, as a 5% by weight solution in isopentane, unless otherwise stated, in the ratio to the cocatalyst listed in the examples.

Each polymerization is carried out continuously for more than one hour after equilibrium is reached at a pressure of about 2061 kPa and at the gas velocity, nitrogen gas concentration and temperature indicated in Table I.

Examples 1 to 8 and Comparative Examples A to D

In these examples, high density ethylene copolymers are prepared using various catalyst systems. The above procedures are used and the parameters are given in Table I. Examples 1 to 6 show an embodiment of the invention in which 1-butene is copolymerized. Examples 7 and 8 relate to another embodiment of the invention in which 1-hexene is copolymerized. Comparative Examples A to D use an inert support which has been chemically treated with an aluminum alkyl prior to impregnation. Comparative Example C uses a catalyst system without a modifier. Comparative Example D uses a catalyst system without a promoter.

The analysis of polyethylene using the test procedures described above is given in Table I.

Table I

A patent relating to the use of catalysts based on precursors of the invention and comparative catalysts in the production of high density ethylene copolymers.

Example number 1 2 3 4 5 6 Catalyst: Modifier DEAC DEAC DEAC DEAC DEAC DEAC Promoter CHCl ₃ and CHCl ₃ and I want ₃ CHC1 ₃ CHCl CHCl Ratio modifier/ tetrahydrofuran 0.9 0.9 0.9 0.9 0.9 0.9 Pre-processing not reported not reported not reported not reported not reported not reported carriers coven coven coven coven coven coven Cocatalyst TIBA TIBA TIBA TIBA TIBA TIBA Promoter/coca ratio talysator 2.0-2.22 2.0-2.22 2 2 2 1.66 Aluminum/vanadium ratio 20-25 20-25 20-25 20t25 20-25 20-25 Polymerization·: Temperature (°C) 100° 100° 100° 100° 90° 100° gas velocity (ms ¹ ) 0.61 0.61 0.61 0.61 0.61 0.61 nitrogen pressure (% molar) 10 10 10 10 10 10 comonomer 1-butene 1-butene 1-butene 1-butene 1-butene 1-butene comonomer/ethylene ratio 0.006 0.006 0.002 0.002 0.006 0.002 hydrogen/ethylene ratio 0.061 0.05 0.051 0.046 0.045 0.028 yield per unit space and time (kg.h~lm ³ ) 106 102 90 102 115 128 Polyethylene: density (kg.m ³ ) 957 958 958 958 956 954 melt flow index at 33-38 23-27 34-38 2 3-.27 35-38 23-25

load capacity (g/10 min)

flow index ratio melts 70-75 70-75 70-75 70-75 90-95 70-75 _3 bulk weight (kg.m ) 424 424 448 448 432 440 fine particles (% by weight) 0.01 0.01 0.01 0.01 0.01 0.01 ash (% wt.) 0.05 0.05 0.052 0.052 0.050 0.048 particle agglomeration small to small to small to small to small to small to none none none none none none Example number 7 8 A B C D Catalyst: modifier DEAC DEAC DEAC DEAC none DEAC promoter I want ₃ I want ₃ I want ₃ I want ₃ CHCl none modifier/tetra- ratio hydrofuran 0.9 0.9 0.25 0.95 - 0.95 pre-processing not reported not reported not reported not reported not reported not reported carriers coven coven coven coven coven coven cocatalyst TIBA TIBA TIBA TIBA TIBA TIBA promoter/cocatalyst ratio laser 1.33 1.33 1 2 2 - aluminum/vanadium ratio 20-25 20-25 20 20 25 12 Polymerization: temperature (°C) 100 90 100 100 100 100 gas velocity (ms ³ ) 0.61 0.61 0.58 0.58 0.34 0.58 nitrogen pressure (% molar) 16.5 20 15 15 15 15 comonomer 1-hexene 1-hexene 1-butene 1-butene 1-butene 1-butene

continuation of table I

Example number 7 8 A B C D comonomer/ethylene ratio 0.010 0.011 0.002 0.002 0.002 0.009 hydrogen/ethylene ratio 0.022 0.038 0.043 0.03 0.07 ^{* x 0.14x} yield per unit of space and time -1 -7 (kg.h .m ) 59 61 88 64 64 64 Polyethylene: density (kg.m ^_J ) melt flow index at higher load 945 943 956-958 956-958 956-958 956 (g/10 min) flow index ratio 5-6 5-6 20-22 20-22 20-22 20-22 melts 70-75 90-95 70-75 70-75 70-75 75 bulk weight (kg.m ^) 424 440 416-432 448-464 320-336 ^X 512 fine particles (% by weight) 0.01 0.01 0.08 0.05 ^8X ₆ xx ash (% by weight) 0.036 0.036 0.036 0.025-0.030 0.040-0.045 0.062 ^XX particle agglomeration little to none little to none strong strong none none

Notes: In all examples 1 to 8, polyethylene was produced with high bulk density, low fines content, low ash content (i.e. catalyst activity is high), good particle flowability (no agglomeration problems) and good hydrogen response (indicating a low hydrogen/monomer ratio).

Examples A and B illustrate severe agglomeration problems.

a) A 1% by weight solution in isopentane is used instead of a 5% solution.

x) Worse response to hydrogen, bulk density and higher fine particle content.

xx) Worse response to hydrogen, higher fine particle content and worse activity.

The results shown in Table I show that the precursor catalyst system of the present invention has high activity as evidenced by low ash content and provides products with the desired balance of properties as evidenced by lower hydrogen to monomer ratio (improved hydrogen response), higher bulk density, improved particle flowability and lower fines content. In contrast, agglomeration in Comparative Examples A and B is very severe. In these examples, catalyst systems similar to the precursor catalyst systems of the present invention were used, except that the supports were pretreated with alkyl aluminum compounds. Furthermore, without the presence of a modifier, as in Comparative Example C, the hydrogen response decreases (as evidenced by the increase in hydrogen to monomer ratio), the bulk density decreases and the fines content is higher, all of which cause less desirable values. Similarly, in the absence of promoter, as in Comparative Example D, the response to hydrogen is less, the fines content increases, and the catalyst activity decreases, all of which leads to less desirable values.

Example 9 and Comparative Examples E and F

These examples demonstrate the improved saturation of polyethylene produced using the precursor catalyst system of the present invention compared to the results of the comparative experiments. The results are summarized in Table II. Example 9 follows the procedures outlined above and produces an ethylene-butene copolymer having the unsaturation levels listed in the table. Comparative Example E follows similar conditions using triethylaluminum as a cocatalyst but without diethylaluminum chloride as a modifier. The resulting polyethylene advantageously has reduced unsaturation even compared to the product obtained using a very similar catalyst system as in Example E.

Comparative Example F shows the unsaturation of polyethylene produced by an alternative process previously known and demonstrates that this polyethylene has a significantly higher level of unsaturation, which leads to instability of the polymer, which degrades over time. In contrast, polyethylene produced using the precursor catalyst system of the present invention exhibits excellent stability due to the very low unsaturation of the polymer.

Table XI

Example 9

Comparative example E

Comparative example F

Catalyst Modified“ vanadium Unmodified“ vanadium Silyl chromate Unsaturation - (C=C/1000 C): * Trans vinyl 0.0108 0.0197 0.038 Terminal vinyl 0.0104 0.0508 0.148 hanging wineglass 0.0619 0.0812 0.106 Total 0.0831 0.1517 0.292 Notes: a) Used catalyst VClj /THF/SiO ₂ /DAEC/TIBA/CHCl ₃ according to the invention.

b) Catalyst VCl ₃ /THF/SiO ₂ /TEAL/CHCl ₃ was used at a polymerization temperature of 90 °C.

c) The polymerization method according to US Patent No. 3,324,095 (Carrick et al.) was used.

Examples 10 to 13

In these examples, low density ethylene copolymers are prepared using the above procedures and conditions listed in Table III. Examples 10 to 12 illustrate the copolymerization of ethylene with 1-butene. Example 13 illustrates the copolymerization of ethylene with propylene. In all of these examples, triethylaluminum is used as the cocatalyst. The results listed in Table III demonstrate that the catalyst system of the present invention has high activity and, as in the preparation of high density ethylene copolymers, provides products with the desired property profile in the preparation of low density ethylene copolymers.

Table III

Production of low density ethylene copolymers.

Example number 10 11 12 13 Catalyst: Modifier DEAC DEAC DEAC DEAC Promoter I WANT, CHC1 ₃ CHCl I want ₃ Ratio·modifier/tetrahydrofuran 1.0 1.0 1.0 1.0 Pre-processing of the media not reported not reported not reported not reported coven coven coven coven Cocatalyst TEAL TEAL TEAL TEAL Promoter/Cocatalyst Ratio 1.54 1.31 1.22 1.0 Aluminum/vanadium ratio 40 40 40 35 Polymerization: temperature (°C) 85 85 85 90 comonomer 1-butene 1-butene 1-butene propylene comonomer/ethylene ratio 0.139 0.086 0.054 0.13 hydrogen/ethylene ratio 0.026 0.016 0.014 0.02 yield per unit area and time (kg.h m ^) 83 82 82 67

continuation of table III

Example number 10 11 12 13 Polyethylene: density (kg.m ^-3 ) 915 922 927 922 melt flow index at higher load (g/10 min) 459 9.5 3.4 19 Melt flow index ratio 49 - - - Bulk density (kg.m ^-J ) 378 374 378 448 Fine particles (% by weight) 0 0 0 0 ash (% by weight) 0.039 0.071 0.082 0.10 particle agglomeration small to small to small to small to none none none .none

Examples 14 to 19

In these examples, very low density ethylene-propylene copolymers are prepared using the above procedures and conditions listed in Table IV. In Example 14, triethylaluminum is used as the cocatalyst instead of triisobutylaluminum. The results listed in Table IV demonstrate that the catalyst system of the present invention can also be used to produce very low density ethylene copolymers having the desired property profile, while the activity of the catalyst system is high.

Table IV

Production of very low density ethylene copolymers

Example number 14 15 16 17 18 19 Catalyst: Modifier DEAC DEAC DEAC DEAC DEAC DEAC Promoter CHC1 ₃ CHC1 ₃ CHC1 ₃ CHC1 ₃ CHC1 ₃ CHCl Modifier/tetrahydrofuran ratio 1.7 1.7 1.7 1.7 1.7 1.7 Pre-processing of the media not reported not reported not reported not reported not reported not reported coven coven coven coven coven coven Cocatalyst TEAL TIBA TIBA TIBA TIBA TIBA Promoter/Cocatalyst Ratio 1.0 1.0 1.0 1.0 1.0 1.0 Aluminum/vanadium ratio 40 40 40 40 43 45 Polymerization: Temperature (°C) 75 70 65 50 40 36 Gas velocity (ms ³ ) 0.46 0.46 0.46 0.46 0.46 0.46 Nitrogen pressure (% molar) 45 50 59 57 60 60 Comonomer propylene propylene propylene propylene propylene propylene Comonomer/ethylene ratio 0.22 0.24 0.26 0.35 0.31 0.34 Hydrogen/ethylene ratio 0.01 0.007 0.006 0.006 0.002 footprints Yield per unit of space and time (kg.h ¹ ,m ³ ) 66 75 61 43 69 67 Polyethylene: -3 Density (kg.m ) 906 895 894 882 871 865 Melt flow index at higher load (g/10 min) 27 9 6 20 3 1 Melt flow index ratio 41 ' 53 64 51 - - *— 3 Bundle weight (kg.m ) 432 384 368 320 368 368

Table IV example number

15 16

18 Earth particles (% by weight) ash (% by weight) 0.10

0.05

0.082 0.11

0

0.14 0.07 1st and 20th graders

In these examples, ethylene is copolymerized with 1-hexene using catalyst systems containing tri-n-hexyl aluminum, ethyl aluminum dichloride, or triethyl aluminum as modifiers. The catalyst is prepared by the above procedures under the conditions shown in Table V. The modifier is treated with vanadium chloride-impregnated silica containing 0.2 mmol of vanadium per gram of vanadium chloride-impregnated silica. In each of the examples, triethyl aluminum is used as the cocatalyst. The results summarized in Table V show that a variety of modifiers can be used in the catalyst systems based on the precursors of the invention.

Pabulka V

Use of catalysts with various modifiers

Example number 20 21 22 Catalyst: Modifier TnHAL EADC TEAL Promoter CHC1 ₃ CHCl CHC1 ₃ Modifier/tetrahydrofuran ratio 0.84 0.84 0.84 Pre-processing of the media unprocessed unprocessed unprocessed Cocatalyst TEAL TEAL TEAL Promoter/Cocatalyst Ratio 1.1 1.1 1.0 Aluminum/vanadium ratio 102 37 38 Polymerization: Temperature (°C) 90 90 90 Gas velocity (m.s ^) 0.55 0.55 0.55 Nitrogen pressure (% molar) 4 10 11.3 Comonomer 1-hexene 1-hexene 1-hexene Comonomer/ethylene ratio 0.0018 0.0018 0.003 Hydrogen/ethylene ratio 0.068 0.057 0.076 Yield per unit area and time (kg.h m 69 128 102 Polyethylene: Density (kg.m 0.957 0.955 0.957 Melt flow index at higher load (g/10 min) 28-30 27-29 23-24 Melt flow index ratio 90-95 95-100 90-100 —3 Bundle weight (kg.m ) 464 451 467 Fine particles (% by weight) 3.4 ^and 3.3 ^and 1.6 ^and Ash (% by weight) 0.041 0.056 0.054 Particle agglomeration little to none little to none little to none

Note: ^a ' passes through a sieve with a mesh size of 130.10 & (instead of 74.10 ®)m.

Claims (4)

(1) the vanadium compound which is the reaction product; (a) vanadium halide, wherein the halogen is chlorine, bromine or iodine; and (b) an electron donor, which is a liquid organic Lewis base in which vanadium halide is soluble; What is claimed is: 1. A supported vanadium-based catalyst precursor for the production of polyethylene, comprising: 2. A carrier precursor according to claim 1, wherein the electron donor is selected from the group consisting of alkyl esters of aliphatic and aromatic carboxylic acids, aliphatic esters, aliphatic ketones, aliphatic amines, aliphatic alcohols, alkyl and cycloalkyl ethers, and mixtures thereof. 2) a modifier of formula I MX _and (I) wherein M represents a boron or an AlR ( _{3 -a} ) radical in which R is independently alkyl, provided that the total number of aliphatic carbon atoms in any R group is not more than 14, X is chlorine, bromine or iodine and a is 0, 1 or 2 with the proviso that when M is boron, a is 3 and 3. A carrier precursor according to claim 1, wherein the vanadium halide comprises chlorine, the electron donor is an alkyl or cycloalkyl ether, the modifier is alkyl C1-6 alkyl or boron trichloride, and the support is silica. 3) a solid inert carrier, consisting of silica or alumina, on which the vanadium compound and modifier are deposited. 4. A carrier precursor according to claim 1, wherein the vanadium halide is vanadium chloride, the electron donor is tetrahydrofuran, the modifier is diethylaluminum chloride, and the carrier is silica.