GB1559172A - Supported ziegler catalyst component - Google Patents

Description

(54) SUPPORTED ZIEGLER CATALYST COMPONENT (71) We, THE BRITISH PETRO LEUM COMPANY LIMITED, of Britannic House, Moor Lane, London EC2Y 9BU, a British company, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed to be particularly described in and by the following statement: The present invention relates to a process for the production of a supported Ziegler catalyst component to the use of thereof in the polymerisation of olefins.

It has long been known that olefins such as ethylene can be polymerised by contacting them under polymerisation conditions with a catalyst component comprising a transition metal compound, e.g. titanium tetrachloride and a co-catalyst or activator, e.g. an organometallic compound such as triethyl aluminium. Catalyst systems of this type are generally referred to as Ziegler catalysts and will be referred to as such throughout this specification. It is also known to deposit the Ziegler catalyst component comprising the transition metal on support materials such as silicon carbide, calcium phosphate, magnesium carbonate and sodium carbonate and to use the produced supported Ziegler catalyst component in conjunction with a cocatalyst (e.g. triethyl aluminium) to polymerise olefins.

More recently it has been found that the supported transition metal component can be made using magnesium oxide as the support material. Catalysts employing magnesium oxide as support material are disclosed in, for example, UK patent specifications 969,764 (Cabot), 1,226,724 (Solvay), and 1,372,628 (Kanegafuchi).

It is an object of the present invention to provide an improved supported Ziegler catalyst component.

Accordingly the present invention is a process for preparing a supported Ziegler catalyst component comprising forming a support material by heating (A) a magnesium halide, or (B) a mixture of a magnesium halide and an inorganic oxide as herein defined, or (C) the product of heating together a magnesium halide and an inorganic oxide as herein defined, in a vapour stream comprising water vapour or the vapour of an organic hydroxy compound under conditions such that at least 80% by weight of the magnesium halide is converted to magnesium oxide, and incorporating a transition metal compound in the support material.

The magnesium halide used in the present invention can be the fluoride, chloride, bromide or iodide. Magnesium chloride is preferred. The halide can be the anhydrous or hydrated material or can be an organic solvated form, for example, magnesium chloride containing alcohol of crystallisation.

The particle size of the magnesium halide is suitably in the ranee 0.5 to 500 microns, preferably 50 to 200 microns.

The vapour stream comprises water vapour or the vapour of an organic hydroxy compound. Examples of suitable organic hvdroxy compounds are aliphatic or aromatic alcohols, or phenols, for example methanol, ethanol, isopropanol, butanol, benzyl alcohol and phenol. The vapour stream preferablv comprises an aliphatic alcohol containing 1 to 8 carbon atoms, e.g. methanol and isooronanol. or water. The vapour stream can, if desired. consist entirely of water vapour or the vapour of the organic hydroxy compound or mixtures thereof or can contain a diluent gas or vapour, for example nitrogen, argon, helium; or in the case where the vapour stream is water vapour, may contain air or oxygen as diluent gas.

The quantity of water or organic hydroxy compound employed is suitably at least 1 and preferably at least 1.5 moles per gramme atom of magnesium present in the magnesium halide.

The heating is suitably carried out at a temperature in the range 250 to 10000C and preferably in the range 400 to 750"C. The heating can be carried out under reduced pressure, at atmospheric pressure or at an elevated pressure. The conditions of the heating, e.g. time, temperature and pressure must be sufficient to ensure that at least 80% by weight, preferably at least 85%, most preferably at least 90% of the magnesium halide is converted to oxide. Heating times in the range 2 to 10 hours are generally found to be adequate. The degree of conversion to oxide can conveniently be determined by elementary analysis or by X-ray diffraction techniques.

By the term "inorganic oxide" is meant throughout this specification any solid particulate, inorganic oxide having surface hydroxyl groups. Examples of such oxides are silica, alumina, zirconia, thoria and magnesium oxide. Silica is preferred. The quantity of inorganic oxide employed is suitably in the range of 0 to 75 wt % based on the total weight of magnesium halide and inorganic oxide. If desired, the inorganic oxide and the magnesium halide can be heated together and then the product of the heating can be heated in the water or organic hydroxy compound vapour. The conditions under which the magnesium halide and the inorganic oxide are heated together are preferably those disclosed in our UK Patent Specification 1 492 174, in our US Patent No. 3 993 588 or in our corresponding Belgian Patent No. 823,355.

When it is desired to use the product of heating a magnesium halide with an inorganic oxide (as herein defined) in the process of the present invention, the percentage conversion of magnesium halide to magnesium oxide is to be taken as the percentage conversion of the quantity of magnesium halide present prior to the heating with the inorganic oxide.

After the heating step, the formed support material preferably consists of, or is broken down into particles having a maximum particle diameter of 250 microns. If the formed particles already have sizes at or below this maximum size they can be used if desired without being further broken down.

Preferred particle sizes of the support material are in the range 1 to 150 microns, most preferably in the range 40 to 100 microns. The breaking down and screening of oversized particles can be accomplished by conventional techniques, e.g. grinding, milling, crushing and sieving.

The transition metal compound used in making the catalyst component of the present invention may be any of the transition metal compounds known to be useful in forming Ziegler catalysts. Especially useful for this purpose are the halides, haloalkoxides and alkoxides of the metals of groups IVa, Va and VIa of the Periodic Table. Particularly preferred are the compounds of titanium having the empirical formula Ti(OR),(Cl)p, n wherein n is zero, fractional or integral from 0--4 inclusive and R is an alkyl group preferably containing 1-6 carbon atoms, for example, titanium tetrachloride, titanium tetraethylate, titanium tetraisopropylate, Ti(OC2H,),CI, Ti(OiPr)2Cl2 or mixtures thereof.

The quantity of transition metal compound used is suitably such as to give a concentration of transition metal in the range 0.5 to 30% and preferably in the range 4 to 10% based on the total weight of catalyst.

The transition metal compound can be incorporated in the catalyst component of the present invention using any of the known techniques employed in the art. Preferably the support material is heated with the transition metal compound at a temperature in the range 50 ,200 C. This can be carried out, for example, by heating the support material and the transition metal compound either alone or in the presence of an inert diluent or a solvent for the transition metal compound; or the vapour of a volatile transition metal compound may be passed into a heated bed, e.g. a fluidised bed, of the support material. It is preferred to heat the support material and the transition metal compound together at a temperature in the range 70 to 1000 C for + to 5 hours in the presence of an inert diluent or a solvent for the transition metal compound. Suitable inert diluents (which are in some cases also solvents for the transition metal compound) are, for example, saturated aliphatic hvdrocarbons such as petroleum ether, butane, pentaine, hexane, heptane, methvl cyclohexane and cyclohexane and aromatic hvdrocarbons such as benzene, toluene and xvlene.

Any excess transition metal compound remaining in the catalyst component after the incorporation step is preferably removed therefrom, for example, by solvent washing, distillation or other convenient techniques which do not have a deleterious effect on the catalyst. Excess titanium compounds having the formula Ti(OR)nCl~n as hereinbefore described are preferably removed by washing the catalyst component several times with solvents such as, for example, those listed in the previous paragraph.

The treatment of the support material with the titanium compound is preferably carried out in the absence of oxygen or moisture.

The present invention further provides a process for the polymerisation of l-olefins comprising contacting the monomer l-olefin with the supported Ziegler catalyst component of the present invention in the presence of a Ziegler catalyst activator.

The polymerisation process according to the present invention can be applied to the polymerisation of l-olefins e.g. ethylene or propylene or mixtures of olefins, e.g. ethylene with other l-olefins, for example, propylene, l-butene, l-pentene, l-hexene, 4-methyl pentene-l, 1,3-butadiene or isoprene. The process is particularly suitable for the polymerisation of ethylene or copolymerisation of ethylene with up to 40 weight % (based on total monomer) of comonomers, i.e. one or more other 1-olefins.

As in the case with other supported Ziegler catalysts the catalyst component of the present invention must be activated with a Ziegler catalyst activator or co-catalyst. Ziegler catalyst activators and the methods by which they are used to activate Ziegler catalysts are well known. Examples of Ziegler catalyst activators are organic derivatives or hydrides of metals of Groups I, II, III and IV of the Periodic Table. Particularly preferred are the trialkyl aluminiums or an alkyl aluminium halide, e.g. triethyl or tributyl aluminium.

The polymerisation process of the present invention can be used to make high density ethylene polymers and copolymers at high productivity having properties which render them suitable for injection moulding.

The invention is further illustrated by the following examples. Examples 1-3 illustrate the preparation of supported Ziegler catalyst according to the present invention and Example 4 illustrates their use in polymerization.

In the Examples the melt index (my2.16) and high load melt index (my21.6) were determined according to ASTM method 1238 using 2.16 kg and 21.6 kg loads respectively; The polymerization conditions can be in accordance with known techniques used in supported Ziegler polymerisation. The polymerisation can be carried out in the gaseous phase or in the presence of a dispersion medium in which the monomer is soluble. As a liquid dispersion medium use can be made of an inert hydrocarbon which is liquid under the polymerisation conditions, or of the monomer or monomers themselves maintained in the liquid state under their saturation pressure. The polymerisation can, if desired, be carried out in the presence of hydrogen gas or other chain transfer agent to vary the molecular weight of the produced polymer.

The polymerisation is preferably carried out under conditions such that the polymer is formed as solid particles suspended in a liquid diluent. Generally the diluent is selected from paraffins and cycloparaffins having from 3-30 carbon atoms per molecule. Suitable diluents include, for example, isopentane, isobutane and cyclohexane. Isobutane is preferred.

The polymerisation can be carried out under continuous or batch conditions.

Methods of recovering the product polyolefin are well known in the art. the units are grammes per 10 minutes. "MIR" is the ratio MI2l.,/MI2 l,;.

EXAMPLE 1.

10 g. of anhydrous MgCl2 (BDH Technical Grade) was fluidised at 500"C in a stream of dry nitrogen flowing at 1 litre/min. The nitrogen was passed through a flask contain ing 20 ml. of dry isopropanol at room tem perature before being passed into the fluidised MgCl2. After 5 hours at 5000 C, 4.57 g. of support material were recovered. 181 millimoles of HC1 were evolved, equivalent to a conversion of MgCl2 to MgO of 88%. (Ele- mental analysis of the support material gave a Cl level of 7.7% by weight, corresponding to a residual MgCl2 level of 10% by weight).

X-ray diffraction measurements on the material confirmed that it was largely MgO with a relatively minor amount of MgCl2. No Mg(OH) or Mg(OH)CI could be detected by X-ray diffraction.

3.91 g. of the support was slurried with 100 ml. cyclohexane and 8.3 g. of isopropanol and 13.5 g. of TiCl4 were added. This and all subsequent catalyst handling operations were carried out in a dry nitrogen atmosphere.

The mixture was refluxed and stirred for 2 hours, then the produced catalyst component was washed seven times with fresh cyclo hexane, the washings being removed by filtra tion. The catalyst component was finally handled as a slurry in cyclohexane at a solids content of 49 mg/ml.

Example 2.

31.7 g. Davison Grade 951 silica was dried in a fluidising stream of nitrogen at 2000C for 2 hours, then 12.0 g. anhydrous MgCl2 (13DOH Technical Grade) were charged to the fluidising silica. The mixture was fluidised at 5000C for 5 hours. 10 g. of the mixture was refluidised at 5000C in a stream of dry nitrogen flowing at 1 litre/min. The nitrogen was passed through a flask containing 3.0 ml. of dry isopropanol at room temperature before being passed into the fluidised support. After.

5 hours at 5000C, the support was recovered.

X-ray diffraction of the support showed the presence of MgO, but not of Mg(OH)2, MgCI2 or Mg(OH)CI. The magnesium and chlorine levels in the support were 6.2 and 1.6% by weight, corresponding to a conversion of MgCI2 to MgO of 91%.

3.5 g. of this support were impregnated with Ti(OrPri)2Cl2 in the same manner as described in Example 1. The final catalyst component slurry in cyclohexane had a solids content of 50 mg/ml.

Example 3.

The same procedure was followed as described in Example 2 except that 2.65 ml. of water instead of 3.0 rnl. isopropanol was passed over the support in the fluidising nitrogen. In this case the support fluidising time at 500"C was 3 hours. The final support contained 9.1% magnesium and 1.6% chlorine by weight corresponding to a conversion of MgCI2 to MgO of 94% X-ray diffraction of the support showed the presence of MgO, but not of Mg(OH)2, MgCl2 or Mg(OH)Cl.

Example 4.

The polymerisations were carried out in either a 2.3 litre (A) or a 4.5 litre (B) capacity stainless steel stirred autoclave. The catalyst slurry (1.0--2.5 ml) was added with a syringe to the reactor purged with nitrogen and maintained at 30-400 C. Aluminium triethyl was added, followed by 1 litre (A) or 1.4 litre (B) of isobutane diluent. The reactor was heated until the pressure of the isobutane reached 6.9 bar ( 58"C) when hydrogen was added (if required). Further heating brought the reactor to the polymerisation temperature (95"C) when ethylene was added to bring the total pressure of the reactor contents to 41.4 bar. Ethylene was added continuously to maintain this pressure during the reaction. Polymerisation and polymer property data are shown in the Table.

TABLE Polymerisation and Polymer Property Data

Weight (mg) Polymer Catalyst Component Catalyst Hydrogen Partial Productivity Reactor in Example Component AlEt3 Pressure (bar) (hour-1) MI MIR B 1 98 251 0 8240 0 A 1 98 251 6.9 4800 7.3 30 A 2 101 267 5.5 5370 2.3 27 B 2 70 267 6.9 2560 8.0 26 B 3 94 251 0 12940 0 B 3 94 251 6.9 2740 11.2 28

Claims (18)

1. WHAT WE CLAIM IS:1. A process for preparing a supported Ziegler catalyst component comprising forming a support material by heating (A) a magnesium halide, or (B) a mixture of a magnesium halide and an inorganic oxide as herein defines, or (C) the product of heating together a magnesium halide and an inorganic oxide as herein defined, in a vapour stream comprising water vapour or the vapour of an organic hydroxy compound under conditions such that at least 80% by weight of the magnesium halide is converted to magnesium oxide, and incorporating a transition metal compound in the support material.
2. 2. A process as claimed in Claim 1 werein the magnesium halide is magnesium chloride.
3. 3. A process as claimed in Claim 1 or 2 wherein the vapour stream comprises, as the organic hyldroxy compound, an aliphatic alcohol containing 1 to 8 carbon atoms.
4. 4. A process as claimed in Claim 3 wherein the organic hydroxy compound is methanol or isopropanol.
5. 5. A process as claimed in any preceding claim wherein the quantity of water or organic hydroxy compound employed is at least 1.5 moles per gramme atom of magnesium present in the halide.
6. 6. a process as claimed in any preceding claim wherein the heating in the vapour stream is carried out at a temperature in the range 4O0-750C C.
7. 7. A process as claimed in any preceding claim wherein the conditions are such that at least 85% by weight of the magnesium halide is converted to oxide.
8. 8. A process as claimed in any preceding claim wherein the inorganic oxide is silica.
9. 9. A process as claimed in any preceding claim wherein the transition metal compound is a titanium compound having the empirical formula Ti(OR)"(CI)4 " wherein R is an alkyl group containing 1-6 carbon atoms and n is zero or has any integral or fractional value from 0 to 4 inclusive.
10. 10. A process as claimed in any preceding claim wherein the transition metal compound is a titanium compound and this is incorpor a ted in the support material by impregnating the latter with a mixture comprising titanium tetrachloride and isopropanol.
11. 11. A process as claimed in any preceding claim wherein the quantity of transition metal compound employed is sufficient to give a transition metal concentration .in the catalyst in the range 4 to 10 wt% -based on the total catalyst
12. 12. A process for preparing a supported Ziegler catalyst component substantially as described in any one of Examples 1 to 3.
13. 13. A supported Ziegler catalyst component prepared by the process claimed in any preceding claim.
14. 14. A process for polymerising 1-olefins comprising contacting monomeric 1-olefin with the supported Ziegler catalyst component claimed in Claim 13 under polymerisation conditions in the presence of a Ziegler catalyst activator.
15. 15. A process as claimed in Claim 14 wherein the Ziegler catalyst activator is a trialkyl aluminium or an alkyl aluminium halide.
16. 16. A process as claimed in Claim 14 or 15 wherein the polymerisation conditions are such that the polymer is formed as solid particles suspended in a liquid diluent.
17. 17. A process for polymerising ethylene substantially as described with reference to Example 4.
18. 18. Polyethylene prepared by the process claimed in any one of Claims 14 to 17.