CS257283B2 - Vanadium based catalytic system for polyethylene production - Google Patents

Abstract

A vanadium-based catalyst system for the production of polyethylene comprising A) a precursor supported on a support consisting of 1) a vanadium compound which is a 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) a modifier MXa, where M is boron or the radical AlRj3_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, B) a cocatalyst AIR3, where R has the meaning given above and C) a promoter RbCxI4-b)< where R' represents hydrogen or an unsubstituted or halogenated alkyl group containing up to 6 carbon atoms, X' represents halogen and b represents 0, 1 or 2.

Description

The invention relates to a vanadium-based catalyst system for the production of polyethylene. The term polyethylene refers to homopolymers of ethylene or copolymers of ethylene with at least one alpha-olefin having 3 to 10 carbon atoms. The catalyst system according to the invention is suitable for gas phase polymerization 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 broad molecular weight distribution polyethylenes, such as those produced by the process 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 disclosed in U.S. Patent No. 4,302,565 (Goeke et al.) and U.S. Patent No. 4,302,566 (Karol et al.). Such gas phase polymerization processes employ high activity catalysts to produce low unsaturation polyethylenes that have high utility in a variety of film applications.

However, such polyethylenes have limited utility in other applications 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 polyethylenes. 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 (Kanoch 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 organoaluminum 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 an unsupported solid catalyst obtained by the reduction of vanadium halide with an organoaluminum compound in the presence of an ether compound. Here too, an organoaluminum catalyst 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 alkyl aluminum chloride and organoaluminum cocatalysts.

Many of these publications, representing the prior art, 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 a better response to hydrogen in order to achieve a very low level of unsaturation of 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 of vanadium, that it would allow it to remain therein and the catalyst removal step to be omitted.

The catalyst must also 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 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 must be of such a size that they can be easily suspended in a fluidized bed reactor and must 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 these criteria simultaneously and at the same time 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 vanadium-based catalytic system for the production of polyethylene, which is characterized in that it contains

A) a precursor supported on a carrier essentially consisting 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 AIR,, ., 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 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 carrier, consisting of silicon dioxide or aluminum oxide, on which the vanadium compound and the modifier are deposited,

B) cocatalyst of general formula II

A1R ₃ (II) where

R has the meaning given above and

C) promoter of general formula III

R' _b CX<4—to) (III) where

R' represents hydrogen or an unsubstituted or halogenated alkyl group containing up to 6 carbon atoms,

X' represents halogen and b represents 0, 1 or 2.

The catalyst system according to the invention can be used for the homopolymerization of ethylene or the copolymerization of ethylene with at least one alpha-olefin of 3 to 10 carbon atoms carried out in the gas phase. In this polymerization, the monomer or their mixture is brought into contact with the catalyst system according to the invention at a temperature of 10 to 115 ° C. 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 predominant molar proportion, 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 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 ethylidene norbornene.

These polyethylenes have a suitable balance of properties. Their density may range from about 860 to 960 kg.m . They may have a melt flow index from no flow to about 300 g/10 min., preferably from about 0.1 to about 50 g/10 min. They have a broad molecular weight distribution, which is defined by the ratio of weight average molecular weight to number average molecular weight (M _w /M _n ), greater than about 10, preferably in the range from about 14 to 22. They also have a high bulk density of at least about 320 kg.m \ _3 , preferably in the range from about 384 to about 512 kg.m

Their level of unsaturation is very low and tends to be less than 1 carbon-carbon double bond per thousand carbon atoms (C=C/1000 C), preferably less than about 0.2 C=C/1000 C, and more preferably less than about 0.1 C=C/1000 C. The copolymers have a residual catalyst content of less than about 10 ppm, preferably less than about 6 ppm, expressed as parts of vanadium metal per million parts of copolymer. Preferred polymers produced by the gas phase process of the present invention are in the form of free-flowing solid particles that are substantially free of agiomerates 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 catalytic system of the present invention consists of a supported precursor, a cocatalyst and a promoter. The supported precursor essentially 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 cations, 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 supported on 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 modifier are used per 1 molar part of 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 materials such as zirconium dioxide or thorium dioxide or other compounds that are chemically inert to 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 40 and about 100 microns.

—I - 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 carrier 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 also results in undesirable agglomeration when used in the production of high density polyethylene (greater than 0.94 g.cm ³ ). 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.

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 CCl2, CHCl2, Cl2Cl3, CBr2, CFCl2, CH2CCl3 and CF2ClCCl3. Particularly preferred promoters are methylene dichloride ( _CH2Cl2 ), 1,1,1-trichloroethane (CH2CCl3) and chloroform (CHCl3). Between about 0.1 and about 10, preferably between about 0.2 and about 2, molar parts of promoter are used per 1 molar part of cocatalyst.

The catalyst system of the present invention is prepared by first preparing a precursor supported on a support. In one embodiment, the vanadium compound is prepared by dissolving the vanadium halide in the electron donor at a temperature between about 20°C and the boiling point of the electron donor for several hours. The dissolution is preferably carried out at about 65°C for about three hours or longer. The vanadium compound thus prepared is then impregnated onto the support. The impregnated may be carried out by adding the support in the form of a dry powder or suspension in the electron donor compound or other inert solvent. The liquid is removed by drying at a temperature below about 100°C for several hours, preferably at a temperature of about 45 to about 90°C for about 3 to 6 hours.

The vanadium-impregnated carrier is then mixed with the modifier dissolved in an inert solvent, such as a hydrocarbon. The liquid is removed by drying at a temperature below about 70°C for several hours, preferably at a temperature in the range of about 45 to about 65°C for 3 hours.

The cocatalyst and promoter are added to the supported precursor before and/or during the polymerization reaction. The cocatalyst and promoter are added either together or separately and are added simultaneously or sequentially during the polymerization. They are preferably added separately during the polymerization as solutions in an inert solvent, such as isopentane.

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 α-olefin comonomer added and its type. .

The higher the molar fraction of alpha-olefin added, the lower the density of the copolymer is obtained. The polymerization is carried out at a temperature lower than 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.m ³ , 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 _3

910 to about 940 kg.m , are preferably produced at an operating temperature in the range of about 75 to about 90°C.

—3

Very low density polyethylenes, i.e., having a density of less than about 910 kg.m , are preferably produced at an operating temperature in the range of about 10 to 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. AO 250,660 of Union Carbide Corporation.

The fluidized bed reactor operates at pressures up to 6870 kPa and preferably at pressures in the range of about 343 to 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 be in the range of about 0.001 to about 2.0 parts by mole hydrogen per 1 part by mole ethylene. The catalyst system of the present invention provides improved hydrogen responsiveness, so that less hydrogen is required to produce polyethylene with an extremely low unsaturation content.

The following examples serve to illustrate the catalyst system of the invention 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 the test procedures described below, unless otherwise stated.

Property Test procedure

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

O

Bulk density (kg/m ) Determined according to American standard ASTM-D-1905, 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.

Density (kg/m3)

Property test procedure

Fine fraction (% by weight)

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

Melt flow index at higher load (g/10 min)

It is determined according to the American standard ASTM-D-1238, conditions F.

Melt flow index ratio

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.

Particle agglomeration

Ethylene is determined based on visual observation of the product leaving the polyreactor.

Unsaturation (C=C/1 000 c) ^and

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 per 0.025 mm divided by the absorptivity (absorbivity values used were published by R. J. deKock et al., J. Polymer Science, Part B, 2, 339, (1964).

Note:

^a Number of carbon-carbon double bonds per 1

000 carbon atoms.

The abbreviations used in the examples have the following meanings:

Designation

Explanation of meaning

DEAC

ED

TEAL THF 'TIBA

TnHAL

EADC

Diethylaluminum chloride

Compound acting as an electron donor

Triethylaluminum

Tetrahydrofuran

Triisobutylaluminum

Tri-n-hexylaluminum

Ethyl aluminum dichloride

The catalyst systems used in the examples are prepared using the following standard procedures. To a flask containing 4 liters of anhydrous tetrahydrofuran is added 34 g (0.216 mol) of vanadium chloride. The mixture is stirred for 5 hours at 65 °C under nitrogen until the vanadium chloride dissolves. To this solution is added 800 g of silica, which has been dehydrated by heating to 600 °C, and stirring is continued for 4 hours at 65 °C.

In Comparative Examples A to D, the silica was pre-treated chemically with 5.5% by weight of triethylaluminum. The flask was vented and the solution dried to a slurry-like state at 70°C. The temperature was allowed to drop to 45°C and the solution was purged with nitrogen for 6 hours or until the resulting product had a tetrahydrofuran level of 4 to 10% by weight. The impregnated silica produced in this manner was a solid bulk material containing 0.25 mmol of vanadium per gram. The solid was removed from the flask and stored under nitrogen.

Then, except for Comparative Example C, the modifier is introduced using the following procedure. 500 g of the impregnated silica described above is added to a flask containing 4 liters of anhydrous isopentane. 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 Example 0. The triisobutylaluminum cocatalyst is added during the polymerization as a 5% by weight solution in isopentane. Chloroform CHCl ₃ is added, except in Comparative Example D, as a 5% by weight solution in isomenthane, 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.

Example 8a 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 X. 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.

In Comparative Example C, a catalyst system without a modifier is used. In Comparative Example D, a catalyst system without a promoter is used.

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

Table I

Data relating to the use of catalysts 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 CHC1 ₃ CHCl CHC1 ₃ CHC1 ₃ Modifier/tetrahydrofuran ratio 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/cocatalyst ratio 2.0 to 2.22 2.0 to 2.22 2 2 2 1.66 Aluminum/vanadium ratio 20 to 25 20 to 25 20 to 25 20 to 25 20 to 25 20 to 25

Continuation table

Example number 1 2 3 4 5 6 Polymerization: Temperature (°C) 100°C 100°C 100°C 100°C 90°C 100°C gas velocity (m.s’·'') 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 area and time /kg.h .m ^J ) 106 102 90 102 115 128 Polyethylene: density (kg.m 957 958 958 958 956 954 melt flow index at higher load (g/10 min) 33 to 38 23 to 21 34 to 38 23 to 27 35 to 38 23 to 25 melt flow index ratio 70 to 75 7 0 to 75 70 to 75 70 to 75 90 to 95 70 to 75 bulk weight (kg.m ^) 424 424 448 448 432 440 fine particles (% wt.) 0.01 0.01 0.01 0.01 0.01 0.01 ash (% by weight) 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 CHC1 ₃ CHCl I WANT 2 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 coven coven coven coven coven coven cocatalyst TIBA TIBA TIBA TIBA TIBA TIBA Promoter/Cocatalyst Ratio 1.33 1.33 1 2 2 - aluminum/vanadium ratio 20 to 25 20 to 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 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 ^0.07X 0.14 ^XX yield per unit area time (kg.hl.m ^- 3) 59 61 88 64 64 64 Polyethylene: density (kg.m ) 945 943 956 to 958 956 to 958 . 956 to ; 958 956 melt flow index at higher load (g/10 min) 5 to 6 5 to 6 20 to 22 20 to 22 20 to 22 20 to 22 melt flow index ratio 70 to 75 90 to 95 70 to 75 70 to 75 70 to 75 ' 75 bulk weight (kg.m-3) 424 440 416 to 432 448 to 464 320 to ^336X512 fine particles (% wt.) 0.01 0.01 0.08 0.05 ' 8 ^X . 6 ^XX ash (% by weight) 0.036 0.036 0.036 0.025 to 0.030 0.040 to 0.045 0.062 particle agglomeration small to small to strong strong none none none none

Comment:

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) 1% by weight instead of 54% solution in isopentane is used.

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 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 those of the present invention were used, except that the supports were pretreated with aluminum alkyl compounds. Furthermore, in the absence of a modifier, as in Comparative Example C, the hydrogen response decreases (as indicated by an increase in the hydrogen to monomer ratio), the bulk density decreases, and the fines content increases, all of which result in less desirable values. Similarly, in the absence of a promoter, as in Comparative Example D, the hydrogen response decreases, the fines content increases, and the catalyst activity decreases, all of which result in less desirable values.

Example 9a comparative examples E and F

These examples demonstrate the improved saturation of polyethylene produced using the catalyst system of the present invention compared to the results of 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 produced 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 catalyst system of the present invention exhibits excellent stability due to the very low unsaturation of the polymer.

Table II

Comparison of polyethylene unsaturation

Example 9

Comparative example E

Comparative example F

Catalyst

Modified ³ vanadium

Unmodified ^b

Silyl chromate ^c vanadium

Example 9

Comparative example E

Comparative example F

Unsaturation (C=C/1 000 C): Trans-vinyl Terminal vinyl pendant vinylidene total

0.010 8 0.010 4 0.0619

0.083 1

0.019 7 0.050 8 0.081 2

0.151 7

0.038

1,148

0.106

1,292

Comment:

a) using the catalyst VCl-j/THF/SiC^/DAEC/TIBA/CHClg according to the invention,

b) using the catalyst VCL^(THF/SiO ₂ /TEAL/CHCl ₃ at a polymerization temperature of 90 °C,

c) using the polymerization method according to US Patent No. 3,324,095 (Carrick et al.).

Example 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 CHC1 ₃ CHC1 ₃ CHC1 ₃ I want ₃ Modifier/tetrahydrofuran ratio 1.0 1.0 1.0 1.0 Media pre-processing not reported not reported not reported not reported ------... coven coven . covan 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 of space and time (kg.h-^.m ^- ^) 83 82 82 67

Polyethylene:

-3 density (kg.m ) 915 922 927 922 melt flow index at higher load (g/10 min) 459 9.5 3.4 19 Melt flow index ratio 49 - - - Bundle weight (kg.m ) 378 374 378 448 Fine particles (% 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

Example 14 to 19

In these examples, very low density copolymers of ethylene and propylene are prepared using the above procedures and the conditions listed in Table IV. In Example 14, triethylaluminum is used as the cocatalyst instead of triisobutylaluminum.

The results shown in Table IV show 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 CHdj 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 ^-1 ) 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 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 ^- lm ^- 3) 66 75 61 43 69 67 Polyethylene: Density (kg.m ^J ) 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 density (kg.m ) 432 384 368 320 368 368 Fine particles (% by weight) - - 0.05 0 0 0 Ash (% by weight) 0.10 0.082 0.11 - 0.14 0.07

Example 20 to 22

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 above procedures are carried out under the conditions given in Table V. The modifier is applied to vanadium trichloride-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 of the invention.

Table V

Use of catalysts with various modifiers.

Example number 20 21 22 Catalyst: Modifier TnHAL EADC TEAL Promoter CHCl CHC1 ₃ 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 (ms ² ) 0.55 0.55 0.55 Nitrogen pressure (% molar) 4 10 11.3 Comonomer 1-hexene 1-hexene 1-hexene Comonomer/ethylene ratio 0.001 8 0.001 8 0.003 Hydrogen/ethylene ratio 0.068 0.057 0.076 Yield per unit of space and time (kg.h ^- ·'·.m“3) 69 128 102 Polyethylene: Density (kg.m ^J ) 0.957 0.955 0.957 Melt flow index at higher load (g/10 min) 28 to 30 27 to 29 23 to 24 Melt flow index ratio 90 to 95 95 to 100 90 to 100 Bulk density (kg.m ² ) 464 451 467 Fine particles (% by weight) 3.4 ^and 3.3® 1.6 ^and Ash (% by weight) 0.041 0.056 0.054 Particle agglomeration small to small to small to none none none Note: ^a ' passes through the sieve with mesh size : 130.10 ^-6 (instead of 74.10 ^-6 ) min.

SUBJECT OF THE INVENTION

Claims (6)

SUBJECT OF THE INVENTION (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; A vanadium-based catalyst system for the production of polyethylene, characterized in that it comprises (A) a precursor deposited on a carrier consisting of: 2. The catalyst system of 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 (I) where M is boron or an AIR (3-a) radical in which R is independently alkyl257283 groups with the proviso that the total number of aliphatic carbon atoms in any R group is not more than 14; X is chlorine, bromine or iodine, and that when M is boron and is 3 and silica or alumina are applied and is 0, 1 or 2 with the condition that 3. A catalyst system as claimed in claim 1, wherein the vanadium halide comprises chlorine, the electron donor is an alkyl or cycloalkyl ether, the modifier is an alkyl (C1 -C6) alkyl or dichloride or boron trichloride, and the carrier is silica. 3) a solid inert carrier consisting of vanadium compounds and a modifier B) a cocatalyst of formula II A1R ₃ where R is as defined above and C) a promoter of formula III ^R b ^CX (4-b) wherein R 'represents hydrogen or unsubstituted up to 6 carbon atoms, X 'is halogen and b is 0, 1 or 2. (XI) (III) or a halogenated alkyl group containing 4. The catalyst system of any one of claims 1 to 3, wherein the vartadium halide is vanadium chloride, the electron donor is tetrahydrofuran, the modifier is diethylaluminum chloride, and the carrier is silica. A catalyst system as claimed in any one of claims 1 to 4 wherein the cocatalyst is a C 2 -C 8 trialkyl group and the promoter is fluoro, chloro or bromo substituted ethane or methane. 6. The catalytic system according to any one of claims 1 to 4, wherein the cocatalyst is triisobutyl aluminum or triethyl aluminum and the promoter is chloroform.