WO2000004057A1

WO2000004057A1 - Method for preparing an activator for the polymerisation of olefins

Info

Publication number: WO2000004057A1
Application number: PCT/GB1999/002227
Authority: WO
Inventors: Ian Raymond Little; Christopher Sharp
Original assignee: Bp Chemicals Limited
Priority date: 1998-07-17
Filing date: 1999-07-12
Publication date: 2000-01-27
Also published as: AU4919499A

Abstract

An activator suitable for use with a catalyst for the polymerisation of olefins is prepared by the treatment of a hydroxylated solid, fore example silica, with a compound containing an oxygen containing ligand, for example acetylacetonate. Alternatively the hydroxylated solid may be treated with a trialkylaluminium compound followed by an oxygen-containing compound, for example acetylacetone. The activators may suitably be used together with metallocene complexes for the polymerisation of olefins.

Description

method for prepari ng an acti vator for the polymeri sati on of ol efi ns

The present invention relates to catalysts suitable for the polymerisation of olefins and to activators for such catalysts, and in particular to activators suitable for use with transition metal complexes supported on inorganic oxides.

The use of certain transition metal compounds to polymerise 1 -olefins, for example, ethylene, is well established in the prior art. The use of Ziegler-Natta catalysts produced by activating titanium halides with organometallic compounds such as triethylaluminium is fundamental to many commercial processes for manufacturing polyolefins. Over the last twenty or thirty years, advances in the technology have lead to the development of Ziegler-Natta catalysts which have such high activities that that olefin polymers and copolymers containing very low concentrations of residual catalyst can be produced directly in commercial polymerisation processes. The quantities of residual catalyst remaining in the produced polymer are so small as to render unnecessary their separation and removal for most commercial applications. Such processes can be operated by polymerising the monomers in the gas phase, or in solution or in suspension in a liquid hydrocarbon diluent. Polymerisation of the monomers can be carried out in the gas phase (the "gas phase process"), for example by fluidising under polymerisation conditions a bed comprising the target polyolefin powder and particles of the desired catalyst using a fluidising gas stream comprising the gaseous monomer. In the so-called "solution process" the (co)polymerisation is conducted by introducing the monomer into a solution or suspension of the catalyst in a liquid hydrocarbon diluent underOonditions of temperature and pressure such that the produced polyolefin forms as a solution in the hydrocarbon diluent. In the "slurry process" the temperature, pressure and choice of diluent are such that the produced polymer forms as a suspension in the liquid hydrocarbon diluent. These processes are generally operated at relatively low pressures (for example 10-50 bar) and low temperature (for example 50 to 150°C).

Commodity polyethylenes are commercially produced in a variety of different types and grades. Homopolymerisation of ethylene with transition metal based catalysts leads to the production of so-called "high density" grades of polyethylene. These polymers have relatively high stiffness and are useful for making articles where inherent rigidity is required. Copolymerisation of ethylene with higher 1 -olefins (eg butene, hexene or octene) is employed commercially to provide a wide variety of copolymers differing in density and in other important physical properties. Particularly important copolymers made by copolymerising ethylene with higher 1 -olefins using transition metal based catalysts are the copolymers having a density in the range of 0.91 to 0.93. These copolymers which are generally referred to in the art as "linear low density polyethylene" are in many respects similar to the so called "low density" polyethylene produced by the high pressure free radical catalysed polymerisation of ethylene. Such polymers and copolymers are used extensively in the manufacture of flexible blown film.

An important feature of the microstructure of the copolymers of ethylene and higher 1 -olefins is the manner in which polymerised comonomer units are distributed along the "backbone" chain of polymerised ethylene units. The conventional Ziegler- Natta catalysts have tended to produce copolymers wherein the polymerised comonomer units are clumped together along the chain. To achieve especially desirable film properties from such copolymers the comonomer units in each copolymer molecule are preferably not clumped together, but are well spaced along the length of each linear polyethylene chain. In recent years the use of discrete metal complexes based on transition metals has provided catalysts with potentially high activity and capable of providing an improved distribution of the comonomer units. Such complexes are known as metallocenes and may be exemplified by biscyclopentadienyl transition metal complexes.

The use of these discrete metal complex based olefin polymerisation catalysts is now well established. Examples of such complexes may be found in EP 129368,

EP 206794, and EP 260130. Typically the metallocene complex comprises a bis(cyclopentadienyl) zirconium complex for example bis(cyclopentadienyl) zirconium dichloride or bis(tetramethylcyclopentadienyl) zirconium dichloride.

In such catalyst systems the discrete metal complex is used in the presence of a suitable activator. The activators most suitably used with such metallocene complexes are aluminoxanes, most suitably methyl aluminoxane or MAO. Other suitable activators are perfluorinated boron compounds.

More recently transition metal complexes having a constrained geometry have been used as components of olefin polymerisation catalyst systems. Such complexes are described in EP 420436 and EP 416815. Such complexes are also used in the presence of the activators described above for example aluminoxanes. It would however be beneficial to improve the performance of discrete metal complex based olefin polymerisation catalysts. It would also be beneficial to use simpler and less costly activators with these discrete metal complexes, or to use lower activator concentrations.

When used for slurry and in particular gas phase processes the discrete metal complex and activator are suitably supported for example on silica. However it is know that when such catalyst systems are supported there may be problems in fixing the complex and the activator to the support leading to a non-homogeneous distribution of the catalyst on the support.

We have now discovered that it is possible to chemically modify the support and to employ the resultant modified support as an activator for polymerisation catalysts based on discrete metal complexes.

Thus according to the present invention there is provided a method for preparing an activator suitable for use in the polymerisation of olefins said method comprising the steps of: (i) treating a hydroxylated solid with a complex of formula:

M_p A, B_r C_s wherein

M = element from Group 4, 13 or 14 (excluding carbon) of the Periodic Table A = hydride or hydrocarbyl B = oxygen-containing ligand

C = halogen p = > 1 and s > 0, and (a) where q > 1 and r > 1

(ii) optionally further treating the product from (i) with

wherein

R = hydrocarbyl

X = halide

H = hydride t > 1, u > 0 and v > 0 provided that t + u + v = 3,

(b) where q > 1 and r > 0

(ii) further treating the product from (i) with an oxygen-containing compound D and

(iii) optionally further treating the product from (ii) with

as defined above,

(c) where q = 0 and r > 1

(ii) further treating the product from (i) with

as defined above,

The hydroxylated solid may be a hydroxylated polymer such as hydroxylated polystyrene or may be an inorganic oxide or other type of hydroxylated material. Preferred materials are inorganic oxides.

The inorganic oxide may be chosen from silica, alumina, zirconia, titania, silica- alumina or similar. The preferred inorganic oxide is silica. It is particularly important that the support is free of adsorbed water. In this respect an inorganic oxide may be pretreated by heating (calcination) at elevated temperatures typically above 200°C in a flowing stream of nitrogen.

Steps (i), (ii) and (iii) may be carried out at elevated temperature eg up to 200°C and if desired without isolation of any intermediate products.

The above procedural steps are preferably carried out in the presence of a suitable solvent.

A preferred solvent for steps (i), (ii) and (iii) is toluene.

Illustrative but non-limiting examples of suitable oxygen-containing ligands B in the metal complex include: acetylacetonate and substituted acetylacetonate carboxylate oxalate oxalate ester nitrate nitrite oxide oxo peroxide. Illustrative but non-limiting examples of suitable oxygen-containing compounds D include: acetylacetone and substituted acetylacetone carboxylic acids oxalic acids oxalic esters hydrogen peroxide carbon dioxide.

By use of the preparative methods described above activators may be prepared in which metal and oxygen containing ligands are irreversibly fixed to the surface of the support. The preferred method of preparation for the supported activators of the present invention is that shown in procedure (b) above when r = 0. Such a procedure comprises the following

(i) treating a hydroxylated solid with a complex of formula M_p A, C, wherein M, A p,q and s are as defined above, and

(ii) further treating the product from (i) with an oxygen-containing compound D and (iii) optionally further treating the product from (ii) with

again as defined above.

Steps (i), (ii) and (iii) are also preferably performed in the presence of a suitable solvent.

In this preferred procedure the preferred complex in stage (i) is a trialkyaluminium compound eg. trimethylaluminium and the oxygen-containing compound D is preferably acetyl acetone. In step (iii) if required the product from step (ii) is further treated with a trialkylaluminium compound eg. trimethylaluminium.

When r is > 0 in step (i), the preferred metal complexes having the above general formula are those wherein M is aluminium and B is acetylacetonate. Such complexes may be suitably prepared from acetyl acetone and a trialkylaluminium compound for example trimethyl aluminium (TMA).

The preferred compound corresponding to the general formulae M_p Aq B_r C_s, M_p A_q C_s or Al Rt V„ H_v is a trialkylaluminium compound. Thus according to another aspect of the present invention there is provided an activator suitable for use in the polymerisation of olefins comprising the reaction product of (a) a hydroxylated solid and (b) a metal complex of formula:

M_p A, B_r C_s wherein M, A, B, C, p, q, r and s are as described above.

The novel activators of the present invention may be used together with well known discrete metal complexes eg metallocenes to provide supported catalysts suitable for the polymerisation of olefins.

Thus according to another aspect of the present invention there is provided a catalyst system suitable for use for the polymerisation of olefins comprising: (A) one or more discrete metal complexes, and

(B) a supported activator prepared as hereinbefore described.

Any discrete metal complexes suitable for use in the polymerisation of olefins may be suitable for use with the activators of the present invention. For example the discrete metal complexes may be metallocenes as described in EP

129368 and EP 206794 the disclosures of which are incorporated herein by reference. Such metallocenes may be suitably represented by the general formula:

(Cp)_x MY₍₄._x) wherein Cp represents a substituted or unsubstituted cyclopentadienyl ligand,

M is zirconium, titanium or hafnium

Y is an anionic ligand for example, hydride, halide or hydrocarbyl and x = 1-3.

The cyclopentadienyl ring may be typically substituted by alkyl eg methyl or alkenyl or two substituents may be joined together to form a ring eg indenyl.

When x is 2 the cyclopentadienyl ligands may be joined by a suitable bridging group eg SiMe₂ or CH₂CH₂.

An alternative type of metallocene complex suitable for use with the activators of the present invention are those disclosed in WO 96/04290. Such complexes mat suitably be represented by the general formula:

wherein Cp and M are as defined above, Z is a bridging group eg. SiMe₂ or CH₂CH₂, and D is a stable conjugated diene.

An alternative type of discrete metal complex suitable for use with the novel activators of the present invention are monocyclopentadienyl complexes having a constrained geometry. Such complexes are disclosed in EP 416815 and EP 418044 again which are incorporated herein by reference. Suitable complexes of this type may be represented by the general formula:

wherein R is typically hydrocarbyl and M, Cp and Y are as defined above.

Alternatively again the complex may comprise a diene moiety as disclosed in WO 95/00526 and may be represented by the general formula:

wherein R is typically hydrocarbyl, M, Cp are as defined above and D is a stable conjugated diene.

Other suitable complexes are those disclosed in EP 672676, WO 98/11144 and WO

98/27124 as well as complexes disclosed in WO 99/12981.

The discrete metal complex may be deposited on the activator by contacting the metal complex with the activator in a suitable solvent eg toluene followed by removal of the solvent to yield a free-flowing powder.

However if desired the activator may not be isolated as a dry powder before contact with the metal complex and the complex may hence be added directly after stages (i), (ii) or

(iii) as necessary. The resultant catalyst compositions comprising the discrete metal complex and activator may be used alone or may also comprise another catalyst component for example a

Ziegler catalyst or another metallocene complex. A suitable Ziegler catalyst may for example comprise atoms of titanium, magnesium and halogen and may be prepared by conventional routes. The present invention also provides a process for the production of pofyolefins, in particular homopolymers of ethylene and copolymers of ethylene with minor amounts of at least one C3 to CIO, preferably C3 to C8 alpha-olefin. The process comprises contacting the monomer or monomers, optionally in the presence of hydrogen, with the catalyst composition according to the invention at a temperature and pressure sufficient to initiate the polymerisation reaction.

Suitably the alpha olefin may be propylene, butene-1, hexene-1, 4-methyl pentene-1 and octene-1.

The olefin polymerisation catalyst compositions according to the present invention may be used to produce polymers using solution polymerisation, slurry polymerisation or gas phase polymerisation techniques. Methods and apparatus for effecting such polymerisation reactions are well known and described in, for example, Encyclopaedia of Polymer Science and Engineering published by John Wiley and Sons, 1987, Volume 7, pages 480 to 488 and 1988, Volume 12, pages 504 to 541. The catalyst according to the present invention can be used in similar amounts and under similar conditions to known olefin polymerisation catalysts.

The supported activators of the present invention may be prepared as described above or alternatively may be prepared in-situ in the polymerisation reactor. In this way the complex may be activated after injection into the reactor thus reducing any catalyst deactivation which may occur during storage.

For example in the above precedures the optional steps (ii) and (iii) involving treatment with a compound Al R X_u H_v may be performed by addition to said compound directly to the reactor.

The polymerisation may optionally be carried out in the presence of hydrogen. Hydrogen or other suitable chain transfer agents may be used to control the molecular weight of the produced polyolefin.

The invention will now be further illustrated with reference to the accompanying examples. Example 1

Trimethylaluminium (lOmmol; 5ml 2.0M solution in toluene) was slowly added to a suspension of silica (5g Crosfield ES 70X; calcined at 250°C forlό h under flowing nitrogen) in dry toluene (40ml). The mixture was allowed to stand for 0.5h after which acetylacetone (20mmol) was added via syringe and, after gas evolution had subsided, the resulting product was left isolated under nitrogen overnight. This resulted in the silica acquiring a yellow appearance with a colourless supernatant above. Trimethylaluminium (60mmol; 30ml 2.0M solution in toluene) was then slowly added via syringe and the mixture heated to 130°C and refluxed for a total of 15h before being allowed to cool to room temperature and left isolated under nitrogen overnight. The supernatant liquid was then removed by syringe and the remaining solvent removed under vacuum at room temperature to yield a free flowing powder that was subsequently employed as an activator for metallocene catalysts. Example 2

A portion (2g) of the solid activator prepared in Example 1 was washed with dry toluene (20ml) and the supernatant removed via syringe. This procedure was repeated and the solid filtered under vacuum in a dry box. The remaining solvent was removed under vacuum at room temperature to yield a free flowing powder that was subsequently employed as an activator for metallocene catalysts. Example 3

A solution of bis(3-propenyl-cyclopentadienyl)zirconium dichloride (lOOμmol in 10ml dry toluene) was slurried with 2g of the solid activator prepared in Example 1 for a period of 2 minutes. Removal of the solvent was then commenced under vacuum at room temperature to yield an orange coloured free flowing powder which was employed immediately as an olefin polymerisation catalyst. Example 4 A solution of bis(3-propenyl-cyclopentadienyl)zirconium dichloride (75μmol in

10ml dry toluene) was slurried with 1.5g of the solid activator prepared in Example 2 for a period of 2 minutes. Removal of the solvent was then commenced under vacuum at room temperature to yield an orange coloured free flowing powder which was employed immediately as an olefin polymerisation catalyst. Example 5

The catalyst (0.280g) (prepared in Example 3) was injected into a stirred gas phase reactor containing dried salt (300g) and to which ethylene was continuously added to maintain a pressure of 8 bar. The polymerisation was carried out at 75°C for 120min and 185g of polyethylene was recovered. Example 6

The catalyst (0.270g) (prepared in Example 4) was injected into a stirred gas phase reactor containing dried salt (300g) and to which ethylene was continuously added to maintain a pressure of 8 bar. The polymerisation was carried out at 75°C for 140min and 189g of polyethylene was recovered. Example 7

Dry toluene (10ml) was placed in a Schlenk tube under nitrogen and acetylactone (20mmol) added via syringe. The solution was cooled to -78°C and trimethylaluminium (20mmol; 10ml 2.0M solution in toluene) added dropwise with stirring. The mixture was allowed to warm to room temperature and stirring continued for lh after which it was isolated under nitrogen and left overnight. The resulting pale yellow solution was then injected into a 3-neck roundbottomed flask equipped with an overhead stirrer and containing silica (lOg Crosfield ES 70X; calcined at 250°C for 16h under flowing nitrogen) suspended in dry toluene (40ml). The suspension was stirred at room temperature for 0.5h after which trimethylaluminium (120mmol; 60ml 2.0M solution in toluene) was added slowly. The mixture was then heated to 80°C and stirring continued for a further 7h before being allowed to cool to room temperature and isolated under nitrogen overnight. The supernatant liquid was then removed by syringe and the remaining solvent removed under vacuum at room temperature to yield a free flowing powder that was subsequently employed as an activator for metallocene catalysts. Example 8

Dry toluene (10ml) was placed in a Schlenk tube under nitrogen and acetylacetone (20mmol) added via syringe. The solution was cooled to -78°C and trimethylaluminium (lOmmol; 5ml 2.0M solution in toluene) added dropwise with stirring. The mixture was allowed to warm to room temperature and stirring continued for lh. The resulting pale yellow solution was then injected into a 3-neck roundbottomed flask equipped with an air condenser and containing silica (5g Crosfield ES 70X; calcined at 250°C for 16h under flowing nitrogen) suspended in dry toluene (40ml). The suspension was allowed to stand at room temperature for 0.5h after which trimethylaluminium (60mmol; 30ml 2.0M solution in toluene) was added slowly. The mixture was then heated to 130°C and refluxed for 5h before being allowed to cool to room temperature and isolated under nitrogen overnight. The supernatant liquid was then removed by syringe and the remaining solvent removed under vacuum at room temperature to yield a free flowing powder that was subsequently employed as an activator for metallocene catalysts. Example 9

A solution of bis(3-propenyl-cyclopentadienyl)zirconium dichloride (lOOμmol in 10ml dry toluene) was added to 2g of the solid activator prepared in Example 7 and the mixture allowed to react for 0.5h under nitrogen. The solvent was then removed under vacuum at room temperature to yield an orange coloured free flowing powder which was employed directly as an olefin polymerisation catalyst. Example 10

A solution of bis(3-propenyl-cyclopentadienyl)zirconium dichloride (lOOμmol in 10ml dry toluene) was added to 2g of the solid activator prepared in Example 8 and the mixture allowed to react for lOmin under nitrogen. The solvent was then removed under vacuum at room temperature to yield an orange coloured free flowing powder which was employed directly as an olefin polymerisation catalyst. Example 11

The catalyst (0.239g) (prepared in Example 9) was injected into a stirred gas phase reactor containing dried salt (300g) and to which ethylene was continuously added to maintain a pressure of 8 bar. The polymerisation was carried out at 75°C for 120min and 26g of polyethylene was recovered. Example 12

The catalyst (0.262g) (prepared in Example 10) was injected into a stirred gas phase reactor containing dried salt (300g) and to which ethylene was continuously added to maintain a pressure of 8 bar. The polymerisation was carried out at 75°C for 120min and 24g of polyethylene was recovered. Example 13 (Comparative)

To a round bottomed flask containing silica (102.5 Crosfield ES 70X, calcined at 800°C for 12 hr. under flowing nitrogen) was added a solution of methylaluminoxane (796 mmol., 512 ml., 1.55M solution in toluene) and bis(3-propenylcyclopentadienyl) zirconium dichloride (5 mmol.). The mixture was heated at 50°C for 1 hr. with frequent agitation. Removal of the solvent was then commenced under vacuum at 50°C to yield an orange free flowing powder. The catalyst was injected into a stirred gas phase reactor containing dried salt (300 gm.) to which ethylene was continuously added to maintain a pressure of 8 bar. Polymerisation was carried out at a temperature of 75°C for 60 min. to give 73 g of polyethylene.

Further details of the polymers prepared in the above examples are given below in the Table.

TABLE

Claims

1. A method for preparing an activator suitable for use in the polymerisation of olefins said method comprising the steps of:

(i) treating a hydroxylated solid with a complex of formula:

M_p A, B_r C_s

wherein

C = halogen p = > 1 and s > 0, and

(a) where q > 1 and r > 1

(ii) optionally further treating the product from (i) with

wherein

R = hydrocarbyl X = halide H = hydride t > l, u > 0 and v > 0 provided that t + u + v = 3,

(b) where q > 1 and r > 0

Al R X_u H_v

as defined above,

(c) where q = 0 and r > 1

(iii) further treating the product from (i) with

Al R X_u H_v

as defined above

2. A method for preparing an activator suitable for use in the polymerisation of olefins said method comprising

(i) treating a hydroxylated solid with a complex of formula

wherein

M = an element from Group 4. 13 or 14 (excluding carbon) of the Periodic Table, A = hydride or hydrocarbyl, C = halogen, and p = > 1, s > 0, and q = > 1,

(iii) optionally further treating the product from (ii) with

wherein

R = hydrocarbyl X = halide

H = hydride t ΓëÑ l, u ΓëÑ O and v ΓëÑ O provided that t + u + v = 3

3. A method according to either of the preceeding claims wherein the hydroxylated solid is silica.

4. A method according to any of the preceeding claims where all steps are performed in a suitable solvent.

5. A method according to claim 4 wherein the solvent is toluene.

6 A method according to any of the preceeding claims wherein the compound D is acetylacetone.

7. A method according to any of the preceeding claims wherein M is aluminium and B is acetylacetonate.

8. A method according to any of the preceeding claims wherein the compound having the formula

M_p A, B_r C_s or M_p A, Cs or Al R X_u H_v is a trialkylaluminium compound

9. A method according to any of the preceeding claims wherein steps (i), (ii) and (iii) are carried out at elevated temperature up to 200┬░C.

10. An activator suitable for use with a catalyst for the polymerisation of olefins comprising the reaction product of (a) a hydroxylated solid and (b) a metal complex of formula:

M_p A, B_r C_s

wherein

M = element from Group 4, 13 or 14 (excluding carbon) of the Periodic Table A = hydride or hydrocarbyl

B = oxygen-containing ligand C = halogen, and p = > 1, s = > 0, r = 0, and q = > 0.

11. A catalyst system suitable for the polymerisation of olefins comprising (a) one or more discrete metal complexes, and

(b) a supported activator prepared according to any of the claims 1-9.

12. A catalyst system according to claim 11 wherein the discrete metal complex is a metallocene complex.

13. A catalyst system according to claim 12 wherein the metallocene complex has the formula:

(Cp)_x MY_(4-x) wherein

Cp represents a substituted or unsubstituted cyclopentadienyl ligand, M is zirconium, titanium or hafnium

Y is an anionic ligand for example, hydride, halide or hydrocarbyl and x = 1-3.

14 A catalyst system according to claim 11 further comprising a second catalytic component.

15. A catalyst system according to claim 14 wherein the second catalytic component is a Ziegler catalyst or a metallocene complex.

16. A process for the polymerisation of olefins comprising polymerising olefins in the presence of a catalyst system according to claim 11.

17. A process according to claim 16 carried out in the gas phase.