GB1569901A - Polymerisation catalyst component - Google Patents

Description

(54) POLYMERISATION CATALYST COMPONENT (71) We, THE BRITISH PETROLEUM COMPtk5YJ IITED, 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 and to the use of the catalyst in the polymerisation of olefins.

It has long been known that olefins such as ethylene can be polymerised by contacting under polymerisation conditions with a catalyst comprising a transition metal compound e.g. titanium tetrachloride, and a co-catalyst, e.g. an organometallic compound such as triethylaluminium. It is also known that the catalyst can be deposited on support materials, for example, silicon carbide, calcium phosphate, magnesium carbonate, magnesium chloride and magnesium hydroxychloride.

Our British patent specification No. 1492174 discloses a process for the production of a supported Ziegler catalyst component comprising heating together at a temperature in the range 150-1000"C an inorganic oxide support material selected from silica or a silica composite containing at least 50% wt. of silica and having chemisorbed surface hydroxyl groups and a magnesium compound selected from magnesium halides or magnesium alkoxides and incorporating a transition metal compound therein.

The present invention provides a process for the production of a supported Ziegler catalyst component comprising heating together (a) an inorganic oxide support material selected from silica, alumina, zirconia, thoria or composites thereof and having surface hydroxyl groups and (b) magnesium hydroxychloride as hereinafter defined, at a temperature in the range 150 to 1000"C, and incorporating a transition metal compound in the product.

The support material is suitably any of the recited inorganic oxides having a porous structure and having surface hydroxyl groups. Silica is preferred. Silica having a mean particle diameter in the range 30 to 300 ,m, a surface area of 50 to 1000 square metres per gram and a pore volume (as determined by water porosimetry) of 0.5 to 3.5 cc/gram is particularly preferred. The support material is preferably substantially dry (i.e. free from physically absorbed water) before heating with the magnesium hydroxychloride. A suitable drying technique is, for example, to heat the support for several hours in a vacuum oven at a temperature in the range 70 to 1500C.

The pore volume is determined by water porosimetry as follows. A sample of the support is dried thoroughly by heating at 500"C for 5 hours. A sample of about 5g. is weighed out accurately from the dry sample and transferred to a 2 ounce wide-necked screw-cap glass jar.

Distilled water is then run in from a burette until approximately 0.3 ml. less than the expected pore volume has been added. The lid is screwed on and the jar shaken vigorously by hand for 20 seconds, then on a laboratory shaker for 3 minutes after which any lumps are broken down with a spatula. A further 0.1 ml of water is added from the burette and the shaking procedure is repeated. The bottom of the jar is then firmly rapped on the bench top 3 times to consolidate the sample and the jar is then quickly inverted. If the sampe does not flow freely but sticks to the bottom of the jar for two seconds or more the end point has been reached (or passed) in which case the determination should be repeated using a smaller quantity of water in the first addition. If the sample flows freely when the jar is inverted then further 0.1 ml aliquots of water are added from the burette and the shaking procedure repeated until the end point is reached. The water pore volume is given by the expression c/w where c = volume (ml) of distilled water used to end point and w = weight (grammes) of dry sample.

The determination is carried out in duplicate and the mean value of the results is taken as the pore volume.

The magnesium hydroxychloride employed is substantially material having the formula Mg(OH)xC12-x, 0 < x < 2, or hydrated forms thereof. Mg(OH)C1 is preferred. Such material can be prepared, for example, by adding an aqueous solution of magnesium chloride to an equimolar quantity of magnesium oxide. Another technique for preparing Mg(OH)C1 by heating MgC12.6 H20 is disclosed in UK patent specification 1,085,679.

The support material and the magnesium hydroxychloride are preferably intimately mixed or ground together prior to the heating. The heating is carried out at a temperature in the range 150 to 1000"C, and preferably at a temperature within this range, which is sufficiently high to result in loss of hydrogen chloride from the mixture, e.g. from 250 to 800"C.

Preferably 15 to 100% of the chlorine present in the hydroxychloride is evolved as hydrogen chloride during the heating. The heating is preferably carried out under fluidised bed conditions using air or an inert gas, e.g. nitrogen, as the fluidising gas, which is preferably dry.

The time of heating can vary widely, for example from a few minutes to several days, but is preferably between 2 and 5 hours.

The quantity of magnesium hydroxychloride employed is suitably 0.5 to 20 wt %, preferably 3 to 10 wt % of the mixture of magnesium hydroxychloride and support material.

The transition metal compound used in making the catalyst of the present invention may be any of the transition metal compounds known to be useful in forming Ziegler catalyst.

Especially useful for this purpose are the halides, halo-alkoxides and alkoxides of the metals of Groups IVa, Va and VIa of the Periodic Table. Particularly preferred are the compounds of titanium having the general formula Ti(OR)n(C1)4.n wherein n has any value 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(OC2H5)3C1, Ti(OiPr)2 C12 or mixtures thereof.

The quantity of transition metal compound is suitably such as to give a concentration of transition metal in the range 0.5 to 20%, preferably 2 to 10% based on the total weight of catalyst component.

The transition metal compound can be incorporated in the catalyst of the present invention using any of the known techniques employed in the art of preparing supported Ziegler catalyst components. Preferably the product of heating together the magnesium hydroxychloride and the support material is treated with the transition metal compound at a temperature in the range -25 to +200"C. This can be carried out, for example, by treating the aforesaid product with 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 said product. It is preferred to heat the said product of heating the magnesium hydroxychloride and the support material and the transition metal compound together at a temperature in the range 70 to 100"C for 2 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 hydrocarbons such as petroleum ether, butane, pentane, hexane, heptane, methylcyclohexane and cyclohexane and aromatic hydrocarbons such as benzene, toluene and xylene.

Any excess transition metal compound remaining in the catalyst after the incorporation is preferably removed from the catalyst, 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)nC14-n as hereinbefore described are preferably removed by washing the catalyst several times with solvents such as, for example, those listed in the previous paragraph.

All stages of catalyst preparation are preferably carried out in the absence of oxygen or moisture.

As in the case with other supported Ziegler catalysts the catalyst component of the present invention must be activated with a Ziegler catalyst activator. Ziegler catalyst activators and the methods by which they are used to activate Ziegler catalyst components are well known.

Examples of Ziegler catalyst activators are organometallic derivatives or hydrides of metals of Groups I, II, III and IV of the Periodic Table. Particularly preferred are the trialkylaluminiums or an alkyl-aluminium halide, e.g. triethyl-or tributylaluminium.

The polymerisation catalyst according to the present invention can be used in 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-1, 1,3butadiene or isoprene. The catalyst is particularly suitable for the polymerisation of ethylene or the copolymerisation of ethylene with up to 40 weight % (based on total monomer) of comonomers, i.e. one or more other 1-olefins.

The polymerisation 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 polymerisation catalyst 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: In the Examples the melt index (M12. 16) and high load melt index (MI21.6) were determined according to ASTM method 1238 using 2.16 kg and 21.6 kg loads respectively; the units are grammes per 10 minutes.

Examples 1 and 2 SUPPORT PREPARATION 32.8 g Davison grade 951 Silica (predried at 1500C under vacuum) was charged to a fluidised bed and heated at 200"C for 3 hours under dry nitrogen. 7.2 g Mg(OH)C1 (prepared from MgC12.6H20 according to GB 1,085,679) was added to the fluidised bed and the temperature raised to 500"C and held there for 3 hours. The support contained 5.5 w/w% Mg and 3.0 w/w!Zo C1, corresponding to a conversion to magnesia of ~73% CATALYST COMPONENT PREPARATION Example 1 10 g of the above support was slurried in 100 ml dry deoxygenated cyclohexane, and 27 ml (0.353 moles) isopropanol plus 20 ml (0.182 moles) TiC14 added. The mixture was stirred under reflux for 2 hours (under dry N2), cooled, and the solvent decanted off. The solid residue was washed six times with fresh cyclohexane to remove unreacted titanium. The resulting slurry in cyclohexane had a concentration of 92.6 mg catalyst component ml and analysis of a dried sample gave 4.1 w/w% Mg, 13.5 w/w% C1 and 7.5 w/w% Ti.

Example 2 10 g of the above support was slurried in 100 ml dry deoxygenated cyclohexane and 40 ml (0.364 moles) TiC14 added. The mixture was stirred under reflux for 2 hours in a dry nitrogen atmosphere, then the supernatent liquid was decanted off. The solid residue was washed six times with fresh cyclohexane to remove unreacted titanium. A dried sample of the final catalyst component contained 4.3 w/w% Mg, 10.4 w/w% and 6.3 w/w% Ti. The catalyst component was handled as a slurry in cyclohexane at a concentration of 94.4 mg catalyst/ml.

POLYMERISATION Polymerisation details are given in the accompanying Table and results are compared to those obtained with an unsupported Mg(OH)C1 catalyst. In each case, 1.0 ml of catalyst component slurry was charged to a reactor (t gallon or 1 gallon) which had previously been preheated at 1200C for 3 hours and purged with dry No. 251 mg triethylaluminium was then charged to the reactor, followed by approximately 1000 ml isobutane. The reactor was heated to 60"C and hydrogen added as required (see Table). The temperature of the reactor was then raised to 95 0C and ethylene admitted to raise and maintain a pressure of 600 psig.

The polymerisations were controlled at 950C for 40-60 minutes.

SUPPORT TITANIUM REACTOR H2/C2H2 YIELD PRODUCTIVITY POLYMER PROPS COMPOUND SIZE RATIO (BAR) g g/g hr MI MIR Example 1 951/Mg(OH)Cl/500 C Ti(OPri)2Cl2 1 gal. 7/19 630 8160 0.89 33 gal. 10/16 445 7210 39 27 Example 2 951/Mg(OH)Cl/500 C TiCl4 gal. 0/26 177 2250 -* gal. 6/20 140 1780 0.46 37 Comparison Mg(OH)Cl TiCl4 1 gal. 0/26 110 1460 -* 1 gal. 7/19 NIL - - * Ml 100 low to measure

Claims (14)

WHAT WE CLAIM IS:

1. A process for the production of a supported Ziegler catalyst component comprising heating together (a) an inorganic oxide support material selected from silica, alumina, zirconia thoria or composites thereof and having surface hydroxyl groups and (b) magnesium hydroxy chloride having the formula Mg(OH)xC12.xwherein 0 < x < 2, at a temperature in the range 150 to 1000"C and incorporating a transition metal compound in the product.

2. A process as claimed in Claim 1 wherein x = 1.

3. A process as claimed in Claim 1 or 2 wherein the inorganic oxide support material is silica having a surface area in the range 50 to 1000 square metres per gram and a pore volume (as determined by water porosimetry) of 0.5 to 3.5 cc per gram.

4. A process as claimed in any preceding claim wherein the heating is carried out at a temperautre in the range 250-800"C.

5. A process as claimed in any preceding claim wherein 15 to 100% of the chlorine present in the hydroxy chloride is evolved as hydrogen chloride during the heating.

6. A process as claimed in any preceding claim wherein the quantity of magnesium hydroxy chloride employed is from 3 to 10 wt % of the mixture of magnesium hydroxy chloride and support material.

7. A process as claimed in any preceding claim wherein the transition metal compound has the formula Ti(OR)n(Cl)4-n wherein n is 0-4, R is an alkyl group.

8. A process as claimed in Claim 7 wherein the transition metal compound is titanium tetraisopropylate.

9. A process as claimed in any preceding claim wherein the quantity of transition metal compound is sufficient to give a concentration of transition metal in the range 2 to 10% wt based on the total weight of catalyst component.

10. A process for the preparation of a supported Ziegler catalyst component substantially as described in either of the Examples.

11. A supported Ziegler catalyst component produced by the process claimed in any preceding claim.

12. A process for polymerising l-olefins comprising contacting the monomeric l-olefin with the supported Ziegler catalyst component claimed in Claim 10 in the presence of a Ziegler catalyst activator.

13. A process as claimed in Claim 12 wherein the monomeric l-olefin is ethylene or a mixture of ethylene with up to 40 wt % (based on total monomer) of one or more other l-olefins.

14. Polyolefins prepared by the process claimed in Claim 12 or 13.