GB2072201A - Agglomeration Process for Polymerisation Catalyst Components - Google Patents

Abstract

A suspension of a component of an olefin polymerisation catalyst in an inert liquid medium is evaporated to remove essentially all of the liquid medium and the solid mass obtained is then subjected, in the dry state, to a crushing process for a limited period of time. This process can be applied to finely-divided titanium trichloride based catalyst systems in order to improve their particle form for use in the gas-phase polymerisation process. The procedure is particularly useful when using transition metal compounds which have been ground with Lewis Base compounds and subsequently subjected to an extraction process with a liquid medium. The transition metal compound may be one which has been ground with a sulphur- containing organic compound in the presence of added aluminum chloride and titanium tetrachloride, and subsequently washed several times with a hot solvent. Catalyst components which have been treated by the described process can be used together with an organic compound of a non-transition metal to give an olefin polymerisation catalyst system. The catalyst can be used to effect polymerisation of olefin monomers and is particularly suitable for use in the gas-phase polymerisation process.

Description

SPECIFICATION Agglomeration Process and Product The present invention relates to a process for the production of agglomerated particles of transition metal compounds and to the use of such agglomerated particles as a component of an olefin polymerisation catalyst.

Olefin monomers such as ethylene, propylene and the higher c-olefins can be polymerised using the so-called "Ziegler-Natta" catalysts. The term "Ziegler-Natta" catalyst is generally used to mean a catalyst system obtained by mixing a compound of a transition metal of Groups IVA to VIA of the Periodic Table together with an organic compound of a non-transition metal of Groups IA to IIIA of the Periodic Table. Using such catalysts, ethylene, propylene and the higher a-olefin monomers can be polymerised to solid crystalline polymers. Copolymerisation may also be effected by using two or more of the olefin monomers.For the polymerisation of propylene and the higher a-olefln monomers, it is desirable that the catalyst is capable of providing a high yield of polymer relative to the amount of catalyst used and also that the polymer obtained should be primarily in the isotactic form, which form is the commercially desirable product. The catalyst systems originally described by Natta were of comparatively low activity and stereospecificity and hence it was necessary, at the end of the polymerisation, to treat the polymer to remove catalyst residues and also to remove a comparatively large proportion of the undesirable atactic polymer. To improve the economics of the polymerisation process catalysts have been developed which give higher yields of polymer and a larger proportion of the desired isotactic polymer.To simplify the system even further, processes have been developed in which the polymerisation is effected using a gaseous monomer which contacts a solid polymerisation catalyst to give a solid polymer. To carry out such a process it is desirable that the catalyst system should have, in addition to high activity and good stereo-specificity, a suitable particle form. Some catalyst systems which combine high activity and high stereo-specificity have a particle form which is such as to give problems when effecting polymerisation in the gas phase, or which gives a polymer product having an undesirable particle form or particle size.

According to the present invention there is provided a process for modifying the particle form of solid particulate materials which contain transition metal compounds, which process comprises suspending a solid particulate material which contains a transition metal compound in an inert liquid medium, treating the suspension to evaporate off essentially all of the inert liquid medium and form a solid residue, and crushing the solid residue in the essential absence of a liquid medium.

Optionally, either subsequent to the crushing, or simultaneously therewith, the solid may be classified to give particles having a desired maximum or minimum particle size.

The particles of the solid particulate material preferably have a particle size of not more than 10 microns and particularly of not more than 5 microns. The solid particulate material may be a transition metal compound or may be a complex material which includes a transition metal compound. Complex materials which include a transition metal compound may be prepared by the reduction of a transition metal compound in which the transition metal is in a valency state greater than its minimum valency state, and particularly in its maximum valency state, with a reducing agent such as aluminium metal, an organic aluminium compound or an organic magnesium compound. Alternative systems which may be used include systems in which the transition metal compound is supported on a suitable support material such as, for example, silica, alumina or magnesium chloride.

The solid particulate material may be obtained directly in a finely-divided form as a consequence of the preparative conditions used or the finely-divided form may be generated during post-treatment of the transition metal composition. Post-treatments of the transition metal composition may be effected in order to increase either the activity or stereospecificity of the catalyst system. Such posttreatments of the reduced transition metal composition may include treatments with Lewis Base compounds such as ethers or organic phosphorus compounds and the treatment with these Lewis Base compounds may be effected in the presence or absence of a liquid medium.In one type of posttreatment process, the finely-divided form may be gen'erated by grinding a transition metal composition in the presence of at least one Lewis Base compound and thereafter subjecting the ground transition metal composition to an extraction process using a suitable liquid medium which is a solvent for one or more of the materials present in the ground transition metal composition.

The inert liquid medium in which the transition metal composition is suspended may be any liquid medium which is inert to the transition metal composition and does not affect its characteristics as an olefin polymerisation catalyst component. Thus, the inert liquid medium may be an aliphatic, aromatic or cycloaliphatic hydrocarbon and, although aliphatic hydrocarbons such as pentane, hexane or heptane can be used, we particularly prefer that the inert liquid medium is an aromatic hydrocarbon medium such as benzene, toluene orxylene.

In addition to the solid and the inert liquid medium, the suspension may also contain a small amount of a material which assists in the agglomeration of the solid particulate material. This material, which will hereafter be referred to as an "agglomeration aid", is conveniently present as a solution in the inert liquid medium.

The suspension of the solid particulate material in the inert liquid medium is then treated to evaporate off essentially all of the inert liquid medium. This treatment can be effected by using an elevated temperature, a reduced pressure or a combination of both. It is preferred to effect this treatment using conditions which will not significantly affect the characteristics of the transition metal as a component of an olefin polymerisation catalyst. Accordingly, it is preferred to avoid the use of excessively high temperatures and in particular it is prefered to avoid the use of temperatures in excess of about 1 500C. It is preferred to evaporate off the inert liquid medium at a temperature of between 80"C and 1 300C, particularly from 900C up to 1 200C.

The dry solid which remains after the evaporation of the inert liquid medium is typically in the form of a cake of solid or large lumps of solid. This dry solid is broken up by crushing the solid in the essential absence of a liquid medium. The crushing may be effected by grinding the solid for a limited period of time. The crushing can be combined with the optional classification step by crushing the dry solid in contact with a suitable coarse sieve, for example a 105 micron sieve (150 mesh B. S. sieve), whereby the crushed solid passes through the sieve when suitably reduced in size. If a control of the particle size desired, the particles may be sieved to give a maximum and minimum particle size.

The crushing of the dry solid may be effected by grinding. The grinding is preferably effected for a limited period of time. The grinding may be effected using any suitable type of grinding apparatus, for example a rotating ball mill or a vibrating ball mill. Since the intensity of grinding will be dependent on the grinding conditions including the type of grinding apparatus used, the time of grinding will also be dependent on the grinding conditions.

The grinding conditions are preferably such that the solid obtained, when used as a component of a catalyst to polymerise an olefin monomer in an amount of more than 1000 g of monomer polymerised for each millimole of the transition metal present in the catalyst system, gives a polymer product which is essentially free from lumps and fine polymer. By "essentially free" we mean that the polymer contains not more than 10% by weight of lumps and not more than 10% by weight of fine polymer. It is preferred that the solid is such that the polymer contains less than 5% by weight, and especially less than 2% by weight, of each of lumps and fine polymer. By "lumps" we means polymer particles one dimension of which is one cm or greater. By "fine polymer" we mean polymer particles having a maximum dimension of less than 75 microns.

We have found that a satisfactory product may be obtained by using a vibrating ball mill containing steel balls with grinding times of from 10 minutes up to 2 hours, for example 30 minutes.

We prefer to effect the crushing of the solid by grinding and it is then particularly convenient to evaporate off the inert liquid medium in the grinding apparatus.

The inert liquid medium can be evaporated by passing a stream of a hot inert gas either through the suspension or over the surface of the suspension. The hot inert gas is preferably at a temperature of from 500C up to 1 500C, especially from 800C up to 1 300C. The inert gas may be any gas which does not deleteriously affect the catalytic properties of the solid and is conveniently nitrogen, although hydrogen or other inert gases such as helium or argon may be used.

If evaporation of the inert liquid medium is effected using a stream of a hot inert gas, the completion of evaporation may be checked by directing the flow of the hot inert gas, which contains vapours of the inert liquid medium, past a surface maintained at a temperature which is considerably below the boiling temperature of the inert liquid medium. The disappearance of condensation on this cooled surface signifies that essentially all of the inert liquid medium has been evaporated.

If the solid particulate material which contains a transition metal compound has been obtained by a process which includes grinding stages, it is particularly convenient to effect all stages in the preparation of the agglomerated solid using the same grinding apparatus. Thus, the process involved may include a grinding step followed by several washing stages followed by the evaporative step and finally the crushing step and all of these stages may be effected using the same grinding apparatus.

Thus, as a preferred embodiment of the present invention, there is provided a process in which a solid material containing a transition metal compound is ground with a Lewis Base compound, the ground material is subjected to extraction with a suitable liquid medium, the extracted solid is suspended in an inert liquid medium, the suspension is treated to evaporate off essentially all of the inert liquid medium and form a solid residue and the solid residue is crushed in the essential absence of a liquid medium.

It is particularly preferred that the final stages of this process are effected in a grinding apparatus.

Thus, the stages of evaporating the suspension to dryness and crushing the dried solid are conveniently effected in a grinding apparatus and it is especially convenient to effect all the stages described in the same grinding apparatus.

If the solid particulate material which is suspended in the inert liquid medium has been obtained by a process which includes a treatment with a Lewis Base compound, it is preferred that the Lewis Base compound is an organic Lewis Base compound which can be any organic Lewis Base compound which has been proposed for use in a Ziegler polymerisation catalyst and which affects either the activity or stereospecificity of such a system.Thus, the Lewis Base compound may be an ether, an ester, a ketone, an alcohol, an ortho-ester, a thioether, a thioester, a thioketone, a thiol, a sulphone, a sulphonamide, a fused ring compound containing a heterocyclic sulphur atom, an organo-silicon compound such as a silane or siloxane, an amide such as formamide, urea and the substituted derivatives thereof such as tetramethylurea, thiourea, an alkanolamine, an amine, a cyclic amine such as pyridine or quinoline, a diamine such as tetramethyiethylenediamine or an organic phosphorus compound such as an organic phosphine, an organic phosphine oxide, an organic phosphite or an organic phosphate.The use of organic Lewis Base compounds is disclosed, inter alia, in British Patent Specifications 803 198, 809 717, 880 998, 896 509, 920 118,921 954,933236,940 125,966 025,969 074,971 248,1 013 363,1 017 977,1 049 723,1 122 010,1 150 845, 1 Z08 815, 1 234 657,1 1 324 173, 1 359 328, 1 383 207, 1 423 658, 1 423 659, 1 423 660, 1 495 031, 1 550810,1 553291 and 1 554574.

We particularly prefer to use the sulphur-containing organic compounds which are disclosed in British Patent Specification 1 495 031.

The process of the present invention has been found to be suitable for use with the catalyst systems described in British Patent Specification 1 554 574. More specifically, the solid particulate material which contains a transition metal compound is obtained by grinding together titanium trichloride and aluminium chloride, adding to the ground material titanium tetrachloride and diphenyl sulphone or another specified sulphur-containing organic compound, grinding the mixture, and washing the ground material. The product obtained is typically a finely-divided solid. When this solid is used as a component of an olefin polymerisation catalyst, the catalyst has a high activity and stereospecificity but because of the fine particle size of the solid component, the catalyst is not particularly suitable for use in effecting polymerisation in the gas phase.The particle form of the finelydivided solid may be modified by the process of the present invention.

Thus, as a further aspect of the present invention there is provided a process for the preparation of a transition metal composition which comprises grinding titanium trichloride, aluminium chloride and titanium tetrachloride in the presence of a sulphur-containing organic compound which is selected from compounds having one of the formulae A), B) or C) in the accompanying formula drawings, washing the ground solid with a liquid medium capable of either dissolving the sulphur-containing organic compound and one or both of aluminium chloride and titanium tetrachloride, or of dissolving a complex of the sulphur-containing organic compound and at least one of aluminium chloride or titanium tetrachloride, suspending the ground and washed solid in an inert liquid medium, treating the suspension to evaporate off essentially all of the inert liquid medium and form a solid residue and crushing the solid residue in the essential absence of a liquid medium.

In the formulae A). B) and C) as set out in the attached formulae drawings, the significance of the symbols is as follows:- X, or each X, is, independently, a halogen atom, an alkyl, aryl, alkoxy, aryloxy, alkylthio, or arylthio group, or a group -NR1R2, or two groups X can, together with at least two ofthe carbon atoms of the phenyl group to which they are attached, form an unsaturated hydrocarbon ring; Y, or each Y, is, independently, a halogen atom, an alkyl, aryl, alkoxy, aryloxy, alkylthio, or arylthio group, or a group -NR1R2, or two groups Y can, together with at least two of the carbon atoms of the phenyl group to which they are attached, form an unsaturated hydrocarbon ring; or a group X and a group Y may be replaced by a iink between the two phenyl groups attached to the SO2 group, the linkage being either direct or through a group -0-, -CH2-, -N R1-, -S-or -CO-; Z, or each Z, is, independently, a halogen atom, an alkyl, aryl, alkoxy, aryloxy, alkylthio, or arylthio group, or a group -NR1R2, or two groups Z can, together with at least two of the carbon atoms of the phenyl group to which they are attached, form an unsaturated hydrocarbon ring; D, or each D, is, independently, a halogen atom, an alkyl, aryl, alkoxy, aryloxy, alkylthio, or arylthio group, or a group -NR1R2; T is --SS-, --OO-, -NR2- or -CO-; R1 is a hydrogen atom or a hydrocarbon radical; R2 is a hydrocarbon radical;; R3 is a hydrocarbon radical or can be a group of the formula D; n, m, p and q are each, independently, zero or an integer from 1 up to 5; and x is a positive integer.

The transition metal which is present in the solid particulate material is preferably a transition metal of Groups IVA to VIA of the Periodic Table and is especially a compound of titanium. A particularly useful titanium compound is titanium trichloride which term is used to include titanium trichloride-containing materials which contain aluminium trichloride associated with the titanium trichloride, for example a material which has been prepared by the reduction of titanium tetrachloride with aluminium metal and which has the approximate formula TiCI3.1/3AICI3. A titanium trichloridecontaining material which also contains aluminium trichloride is conveniently used in the process of the present invention and this material may be ground with a further quantity of aluminium chloride, which further quantity is preferably between 10% and 100% molar relative to the titanium trichloride content of the material.

A titanium trichloride-containing material which has been ground with aluminium chloride is then preferably mixed with a mixture, or complex, of titanium tetrachloride and a sulphur-containing organic compound, which is particularly diphenyl sulphone, and this mixture is then milled. The amount of titanium tetrachloride added to the mixture is typically from 5% up to 50% molar relative to the titanium trichloride and is especially from 10% up to 20% molar. The quantity of the sulphur-containing organic compound which is added to the mixture is typically from 50% up to 100% molar relative to the titanium trichloride.

The ground material is then washed several times with a suitable liquid medium which is typically a hot aromatic solvent such as toluene at a temperature of between 80 and 1 200C. The washing with the liquid medium is preferably repeated several times.

The washed solid is finally suspended in a suitable inert liquid medium which is conveniently a further quantity of the liquid medium used to effect the washing.

To the suspension of the solid particulate material in the inert liquid medium optionally there may be added an agglomeration aid, which is very desirably soluble in the inert liquid medium in which the solid particulate material is suspended. The agglomeration aid should be such that, or should be used in an amount such that, it does not have an appreciable adverse effect on the activity and stereospecificity of an olefin polymerisation catalyst system which includes the crushed solid product of the present process. If the crushed solid product is subsequently to be suspended in a liquid medium, the agglomeration aid should not be such as to cause dispersion of the crushed solid into smaller particles in the presence of the liquid medium in which the solid is to be suspended.

The agglomeration aid may be polystyrene, polyvinylacetate, atactic polypropylene, or an AB block copolymer for example of t-butylstyrene-styrene. Alternatively, the agglomeration aid may be a sulphur-containing organic compound such as diphenyl sulphone, or may be aluminium chloride or may be a mixture or complex of a sulphur-containing organic compound and either aluminium chloride or titanium tetrachloride. It will be appreciated that not all agglomeration aids will'be equally effective with all types of solid particulate materials containing a transition metal compound. Some of the agglomeration aids, when added to the suspension of the solid particulate material, may cause swelling of the solid.It has been found that when using an agglomeration aid during the evaporation of the inert liquid medium, the crushed material may be in the form of firmer agglomerates than a similar crushed material obtained without using an agglomeration aid. The amount of the agglomeration aid is preferably from 1% up to 10% molar relative to the transition metal present in the solid particulate material. The suspension containing the agglomeration aid is evaporated to dryness, and the solid residue is crushed as hereinbefore described.

During the evaporation of the inert liquid medium, the suspension may be agitated but effective removal of the inert liquid medium can be achieved without agitation.

The crushed solid which is obtained by the process of the present invention may be used, together with organic compounds of the non-transition metals of Groups IA to IIIA of the Periodic Table, to give an olefin polymerisation catalyst.

More specifically, as a further aspect of the present invention, there is provided an olefin polymerisation catalyst which comprises: 1) the crushed solid obtained by the process of the present invention: and 2) an organic compound of a metal of Group IIA of the Periodic Table or of aluminium or a complex of an organic compound of a metal of Group IA or Group IIA of the Periodic Table with an organic compound of aluminium.

Component 2) of the catalyst can be a magnesium-containing compound of formula E or a magnesium-containing complex compound of formula F in the attached formulae drawings, wherein: each R4, which may be the same or different, is a hydrocarbon radical; each Q, which may be the same or different, is a group OR5 or a halogen atom other than fluorine; R5 is a hydrocarbon radical or a substituted hydrocarbon radical; a has a value of greater than 0 up to 2; b has a value of greater than 0 up to 2; and c has a value of from 0 up to 3.

The groups R4 are all typically alkyl groups and conveniently are alkyl groups containing from 1 up to 20 carbon atoms and especially 1 up to 6 carbon atoms. The value of a is preferably at least 0.5 and it is particularly preferred that a has a value of 2. The value of b is typically in the range 0.05 up to 1.0.

The value of c is typically at least 1 and is preferably 3.

If the component 2) is a complex of a metal of Group IA with an organic aluminium compound, this compound may be of the type lithium aluminium tetraalkyl. It is preferred that the component 2) is an organic aluminium compound which may be, for example, an aluminium hydrocarbyl halide such as a dihydrocarbyl aluminium halide, an aluminium hydrocarbyl sulphate, or an aluminium hydrocarbyl hydrocarbyloxy but is preferably an aluminium trihydrocarbyl or a dihydrocarbyl aluminium hydride. The aluminium trihydrocarbyl is preferably an aluminium trialkyl in which the alkyl group contains from 1 up to 8 carbon atoms and is particularly an ethyl group.

Using an aluminium trihydrocarbyl compound as component 2), it is preferred that the catalyst system also includes a Lewis Base compound if the catalyst system is to be used to polymerise a higher olefin monomer such as propylene. The Lewis Base compound can be any Lewis Base compound of the type disclosed for the treatment of the solid particulate material containing a transition metal compound and is preferably an organic Lewis Base compound.

Suitable Lewis Base compounds include esters of the formula G given in the attached formulae drawings.

In the formula G, R6 is a hydrocarbon radical which may be substituted with one or more halogen atoms and/or hydrocarbonoxy groups; and R7 is a hydrocarbon radical which may be substituted by one or more halogen atoms.

The groups R6 and R7 may be the same or different and it is preferred that one, but not both, of the groups R6 and R7 includes an aryl group. The group R6 is conveniently an optionally substituted alkyl or aryl group, for example a methyl, ethyl, or especially a phenyl, tolyl, methoxyphenyl or fluorophenyl group. The group R7 is preferably an alkyl group containing up to 6 carbon atoms, for example an ethyl or a butyl group. It is particularly preferred that Ro is an aryl or haloaryl group and R7 is an alkyl group.

Esters of formula G include ethyl benzoate and esters of anisic acid (4-methoxybenzoic acid) such as ethyl anisate.

In addition to, or instead of, the Lewis Base compounds, the catalyst system may also include a substituted or unsubstituted polyene, which may be an acyclic polyene such as 3-methylheptatriene (1,4,6), or a cyclic polyene such as cyclooctatriene, cyclooctatetraene, or cycloheptatriene or the alkylor alkoxy-substituted derivatives of such cyclic polyenes, tropylium salts or complexes, tropolone or tropone.

The proportions of components 1) and 2) of the catalyst system can be varied within a wide range as is well known to the skilled worker. The particular preferred proportions will be dependent on the type of materials used and the absolute concentrations of the components but in general we prefer that for each gramme atom of the transition metal which is present in component 1) of the catalyst system there is present at least one mole of component 2). The number of moles of component 2) for each gramme atom of the transition metal in component 1) may be as high as 1000 but conveniently does not exceed 500 and with some transition metal compositions may be not more than 25, for example from 5 up to 10.

When the catalyst system includes a Lewis Base component in addition to component 2), it is preferred that the Lewis Base compound is present in an amount of not more than one mole for each mole of component 2) and particularly from 0.1 up to 0.5 mole of the Lewis Base compound for each mole of the component 2). However, depending on the particular organic metal compound and Lewis Base compound, the proportion of the Lewis Base compound may need to be varied to achieve the optimum catalyst system.

If the catalyst system includes a polyene, it is preferred that the polyene is present in an amount of not more than one mole for each mole of component 2), and especially from 0.01 up to 0.20 mole for each mole of component 2). If the catalyst system includes both a Lewis Base component and a polyene, it is preferred that both of these materials are together present in an amount of not more than one mole for each mole of component 2).

Catalysts in accordance with the present invention can be used to polymerise or copolymerise olefin monomers.

Thus, as a further aspect of the present invention there is provided an olefin polymerisation process which comprises contacting, under polymerisation conditions, at least one olefin monomer with a catalyst in accordance with the present invention.

The olefin monomer which may be contacted with the catalyst system is one having the formula H as set out in the accompanying formula drawings.

In the formula H, R8 is a hydrogen atom or an alkyl radical.

Thus, the olefin may be ethylene, propylene, butene-1, pentene-1, hexene-1, 4-methylpentene-1 or any other olefin which satisfies formula H. The olefin monomer is preferably one containing not more than 10 carbon atoms. The olefin monomers may be homopolymerised or may be copolymerised together. If propylene is copolymerised it is preferred to effect the copolymerisation with ethylene, conveniently using a sequential copolymerisation process as is described in British Patents 970 478; 970 479 and 1 014 944. If ethylene is being copolymerised using the process of the present invention, it is preferred to carry out the copolymerisation using a mixture of ethylene and the desired comonomer, for example butene-1 or hexene1,wherein the mixture of monomers has essentially the same composition throughout the polymerisation process.

Component 1) of the catalyst may be mixed with the other component, or components, of the catalyst in the presence of the olefin monomer. If the catalyst includes a Lewis Base compound, it is preferred to premix the organic metal compound which is component 2) with the Lewis Base compound and then to mix this pre-mixture with the reaction product which is component 1).

As is well known, Ziegler-Natta type catalysts are susceptible to the presence of impurities in the polymerisation system. Accordingly, it is desirable to effect the polymerisation using a monomer, and a diluent if this is being used, which has a high degree of purity, for example a monomer which contains less than 5 ppm by weight of water and less than 1 ppm by weight of oxygen. Materials having a high degree of purity can be obtained by processes such as those described in British Patent Specifications 1111 493; 1 226659 and 1 383611.

Polymerisation can be carried out in the known manner, for example in the presence or absence of an inert diluent such as a suitably purified paraffinic hydrocarbon, in the liquid phase using an excess of the liquid monomer as the polymerisation medium or in gas phase, this latter term being used herein to mean the essential absence of a liquid medium.

If polymerisation is effected in gas phase, it may be effected by introducing the monomer, for example propylene, into the polymerisation vessel as a liquid and operating with conditions of temperature and pressure within the polymerisation vessel which are such that the liquid monomer vaporises, thereby giving an evaporative cooling effect, and essentially all of the polymerisation occurs with a gaseous monomer. Polymerisation in gas phase may be effected using conditions which are such that the monomer is at a temperature and partial pressure which are close to the dew point temperature and pressure for that monomer, for example as described in more detail in British Patent Specification 1 532 445.Polymerisation in gas phase can be effected using any technique suitable for effecting a gas-solid reaction such as a fluidised-bed reactor system, a stirred-bed reactor system or a ribbon blender type of reactor.

Using the catalyst systems of the present invention, ethylene may be polymerised or copolymerised, for example with butene-1 as the comonomer, in a fluidised-bed reactor system to give a high yield of polymer. The fluidising gas is the gas mixture to be polymerised together with any hydrogen which is present as a chain transfer agent to control molecular weight. Thus, for the copolymerisation of ethylene and butene-1 to produce an ethylene copolymer having a density of less than about 940 kg/m3, the gas composition is typically from 50 to 60 mole % ethylene, 15 to 25 mole % butene-1 with the remainder, apart ftm inert materials and impurities, being hydrogen.

Polymerisation may be effected either in a batch manner or on a continuous basis, and the catalyst components may be introduced into the polymerisation vessel separately or all the catalyst components may be mixed together before being introduced into the polymerisation reactor. If all of the catalyst components are pre-mixed, this pre-mixing is preferably effected in the presence of a monomer and such pre-mixing will result in at least some polymerisation of this monomer before the catalyst system is introduced into the polymerisation vessel. If the polymerisation is being carried out in the gas phase, the catalyst components may be added to the polymerisation reactor suspended in a stream of the gaseous monomer or monomer mixture.

The polymerisation can be effected in the presence of a chain transfer agent such as hydrogen or a zinc dialkyl, in order to control the molecular weight of the product formed. If hydrogen is used as the chain transfer agent in the polymerisation of propylene, it is conveniently used in an amount of from 0.01 up to 5.0%, particularly from 0.05 up to 2.0% molar relative to the monomer. When the monomer being polymerised is ethylene, or a mixture in which ethylene is a major polymerisable component (by moles), the amount of hydrogen used may be greater, for example, in the homopolymerisation of ethylene the reaction mixture may contain in excess of 50% molar of hydrogen, whereas if ethylene is being copolymerised, a proportion of hydrogen which is typically up to 35% molar is used.The amount of chain transfer agent will be dependent on the polymerisation conditions, especially the temperature, which, at polymerisation pressures not exceeding 50 kg/cm2, is typically in the range from 200C up to 1000C, preferably from 500C up to 850C.

Polymerisation can be effected at any pressure which has been previously proposed for effecting the polymerisation of olefin monomers. However, although the polymerisation may be effected at pressures up to 3000 kg/cm2, at which pressures the polymerisation temperature may be as high as 3000 C, it is preferred to carry out the polymerisation at relatively low pressures and temperatures.

Whilst the polymerisation may be effected at atmospheric pressure, it is preferred to use a slightly elevated pressure and thus it is preferred that the polymerisation is effected at a pressure of from 1 kg/cm2 up to 50 kg/cm2, preferably from 5 up to 30 kg/cm2. The polymerisation temperature is preferably above ambient temperature and typically will not exceed 100 C.

It will be appreciated that the particle form of the polymer obtained is dependent upon, and hence is affected by, the particle form of the crushed solid which is component 1) of the catalyst system.

Hence, by controlling the crushing conditions, a polymer of a desired form may be obtained.

Various aspects of the present invention will now be described with reference to the following Examples which are illustrative of the invention. In the Examples, all operations are effected under an atmosphere of nitrogen unless otherwise indicated. All the glass apparatus was dried in an air oven at 1 200C for at least one hour and purged with nitrogen before use.

Example 1 A) Milling Stage A Siebtechnik SM 50 Vibromill having a total volume of about 1 65 litres and containing 570 kg of steel balls of 25.4 mm diameter was sealed, evacuated to a pressure of 0.2 mm of mercury, and purged with nitrogen, to give a nitrogen atmosphere in the mill. A mixture of water and ethylene glycol at OOC was passed through the jacket of the mill. 12.01 kg of titanium trichloride (Stauffer-TiCI3-AA of the approximate formula TiCl30.33AlCl3) were introduced as a free-flowing powder into the mill, and then 2.95 kg of aluminium chloride (0.50 mole for each mole of TiC13 present in the Stauffer-TiCI3-AA) were added.The mill was vibrated for 24 hours using a frequency of 1 500 oscillations per minute and an amplitude of 2 mm, whilst continuing to pass the mixture of water and ethylene glycol at OOC through the jacket of the mill. The vibration of the mill was stopped. 9.02 kg of diphenyl sulphone (0.70 mole for each mole of TiCI3 present in the Stauffer-TiCI3-AA) were added, the mixture was milled for 5 minutes and milling was then stopped. 650 cm3 of titanium tetrachloride (0.10 mole for each mole of TiC13 present in the Stauffer-TiCI3-AA) were added to the contents of the mill and milling was continued for a further 24 hours whilst passing the mixture of water and ethylene glycol at OOC through the jacket of the mill.

At the end of the milling, the titanium trichloride product was removed from the mill by inverting the mill, vibrating the inverted mill and collecting the solid product under nitrogen.

B) Washing Stage A sample (1.1 kg) of the milled product from stage A) was transferred to a 6 litre, jacketted glass vessel which was provided with a stirrer. Five litres of degassed toluene were added to the glass vessel, the mixture was stirred and the resulting suspension was heated to 1 000C. The suspension was maintained at 1000C for one hour and then heating and stirring were terminated and the solid was allowed to settle. The supernatant liquid was syphoned off from the settled solid.

The whole process was repeated four more times, each time using a sufficient quantity of degassed toluene to fill the vessel to the six litre mark on the vessel. After the final wash and removal of the wash liquid, a concentrated suspension remained.

C) Drying Stage The procedure described in stage B) was repeated several times and the concentrated suspensions thus obtained were combined.

A Siebtechnik SM 10 Vibromill having a total volume of about 40 litres and containing 130 kg of steel balls of 25.4 mm diameter was sealed, evacuated to a pressure of 0.2 mm of mercury, and purged with nitrogen to give a nitrogen atmosphere in the mill. 10 litres of the combined concentrated suspensions from stage B) were poured into the mill.

Steam at 1 000C was passed through the jacket of the mill and nitrogen gas was bubbled through the suspension. The nitrogen gas removed from the mill was flowed past a cold finger and the process was continued until no condensation was visible on the cold finger. The steam was then turned off and the mili and its contents were allowed to cool to ambient temperature.

D) Crushing Stage The mill was vibrated for 30 minutes using a frequency of 1 500 oscillations per minute and an amplitude of 2 mm. The mill was inverted and vibrated to remove the solid, which was collected under nitrogen.

Example 2 A) Milling Stage The procedure of stage A) of Example 1 was repeated using a Siebtechnik SM 10 Vibromill.

2.415 kg of Stauffer-TiCI 3-AA, 870 g of aluminium chloride (0.536 mole for each mole of TiCI3 present in the Stauffer-TiCl3-AA), 1.864 kg of diphenyl sulphone (0.7 mole for each mole of TiCI3 present in the Stauffer-TiCI3-AA) and 133 cm3 of titanium tetrachloride (0.1 mole for each mole of TiCI3 present in the Stauffer-TiCl3-AA).

B) Washing Stage A sample (362 g) of the milled product from stage 2A), was transferred to a 1.5 litre jacketted glass vessel which was provided with a stirrer and a sinter base.

One litre of degassed toluene was added to the glass vessel, the mixture was stirred and the suspension was heated to 11 0 C. The temperature of 1 00C was maintained for 30 minutes and then heating was stopped and the liquid was filtered off to leave a wet cake of solid particles.

The whole process was repeated four more times.

C) Drying Stage The wet cake obtained in stage 2B) was dried for two hours at 1 000C and a pressure of 0.2 mm of mercury. This resulted in a hard cake on the sinter base. This hard cake was broken up sufficiently for it to be removed from the glass vessel.

D) Crushing Stage The solid obtained in stage 2C) was transferred, under nitrogen, to a vessel which was divided into two regions by a sieve (105 microns-1 50 B. S. mesh size) the region above the sieve having a polytetrafluoroethylene stirrer blade mounted in ciose proximity to the sieve. The solid was added to the region abode the sieve. The stirrer blade was rotated at 60 rpm and this rotation of the blade crushed the lumps of solid through the sieve into the region below in which the crushed solid was collected.

Example 3 The procedure of Example 2 was repeated with the exception that in state D), the sieve was a 53 micron sieve (300 B. S. mesh size).

Example 4 The procedure of stages A) and B) of Example 2 were repeated.

C) Drying Stage The wet cake from stage B) was suspended in four times its weight of degassed toluene. The suspension was transferred, under nitrogen, to a vessel having no sinter base but otherwise being as described for stage B) of Example 2. To the stirred suspension was added a 5% by weight solution of diphenyl sulphone in toluene, this solution being added in an amount to provide 0.1 mole of diphenyl sulphone relative to the titanium trichloride present in the solid. As stirring was continued, the mixture became gelatinous, at which stage the stirring was stopped. The mixture was heated to 700C at a pressure of 0.2 mm of mercury and these conditions were maintained for three hours. The dried solid was broken up sufficiently for it to be removed from the glass vessel.

D) Crushing Stage The procedure of stage D) of Example 2 was repeated. The solid was found to be more difficult to break up than in stage D) of Example 2.

Comparative Example A The procedures of stages A) and B) of Example 2 were repeated. The wet cake was suspended in an aliphatic hydrocarbon fraction to give a 25% by weight suspension which was then used with no further treatment. The aliphatic hydrocarbon fraction consisted mainly of pentamethylheptane isomers and had a boiling point in the range 1 700C up to 1 800C.

Examples 5 to 7 Into a 91-litre stainless steel autoclave fitted with a stirrer were placed 9 kg of polypropylene powder having a flexural modulus of 1.49 GN/m2 and 4.0% by weight of which was soluble in hot heptane using the procedure as described hereafter in Note (d) to the Table. The stirrer was rotated at 60 rpm and stirring was continued throughout the following procedure. The autoclave was purged at 700C with nitrogen, then evacuated to a pressure of 0.1 mm of mercury. Propylene containing 1.5% weight of hydrogen was added to raise the pressure to 28 kg/cm2 gauge.

A solution of diethyl aluminium chloride in the pentamethylheptane fraction and a 25% by weight suspension in the pentamethylheptane fraction of the product of Example 1, Example 2 or Comparative Example A were introduced into the autoclave in the molar proportions of 8:1 until polymerisation was observed to start.

Once polymerisation had started, liquid propylene at 200C was introduced into the autoclave at a rate of about 3 kg/hr and polypropylene was intermittently withdrawn from the autoclave at the same rate. The temperature and pressure were maintained at 700C and 28 kg/cm2 gauge respectively. The diethyl aluminium chloride solution and the suspension were continuously introduced into the autoclave in the molar proportions of diethyl aluminium chloride to titanium trichloride of 8 to 1 and at a rate to maintain the rate of polymer production at about 3kg/hr of polymer.

Some properties of the polymer products removed at various times during the polymerisations are set out in the following Table.

Table

Flex ~ Flex Catalyst Heptane Hot Heptane Wt % Sample Mod Residues Soluble Fine TMC removed MFl {GN/m2) tppm by wt) {% wt) Polymer Eg (a) (hers) (b) (c) Ti Al C/ (d) (e) 5 5 1 24 30 1.49 30 153 160 2.9 ND 6 1 25 20.2 1.40 32 168 171 3.2 7.5 7 2 15 18.3 1.47 30 122 ND ND 6.5 B A 12 28 1.59 32 418 ND ND ND C A 13 ND ND ND ND ND ND 26 C A ND ND ND ND 26 D A 17 23.2 1.46 38 472 ND ND ND Notes to Table (a) TMC means transition metal component and the number, or letter, identifies the Example, or Comparative Example, in which the preparation of the transition metal component is set out.

(b) MFI is melt flow index measured by ASTM Test Method D 1238/70, Condition N (1 900C and 10keg).

(c) Flex Mod is the flexural modulus as measured using a cantilever beam apparatus as described in Polymer Age March 1970, pages 57 and 58. The deformation of a test strip at 1% skin strain after 60 seconds at 230C and 50% relative humidity was measured. The test strip, which had dimensions of approximately 1 50x 1 9x 1.6 mm, was prepared in the following manner.

23 g of the polymer were mixed with 0.1% by weight of an antioxidant ('Topanol' CA), and the mixture was added to a Brabender Plasticiser, at 190 C,30 rpm and under a load of 10 kg of convert it to a crepe. The crepe was placed within a template, between aluminium foil and pressed by means of an electric Tangye press at a temperature of 2500C. The pressing was pre-heated for a period of 6 minutes, under just enough pressure to make the polymer flow across the template, that is an applied force of about 1 ton. After the pre-heat period, the applied force was raised to 1 5 tons in 5 ton increments, degassing (that is releasing pressure) every 5 tons. After 2 minutes at 1 5 tons, the press was cooled by means of air and water for 10 minutes or until room temperature was reached.The plaque obtained was then cut into strips of dimensions 1 50x 1 9x 1.6 mm. Duplicate strips of each polymer were placed into an annealing oven at 1 300C and after 2 hours at this temperature the heat was switched off and the oven cooled to ambient temperature at 1 50C per hour.

(d) Heptane soluble is the percentage by weight of the polymer which is soluble in hot heptane using the following procedure. A weighed amount of polymer (about 5 g) were placed in the thimble of a Soxhlet extractor, n-heptane was refluxed through the sample in the thimble for 24 hours, the polymer was dried and reweighed. The % weight loss corresponds to the heptane soluble polymer.

(e) Wt % fine polymer is the proportion of the polymer product which has a particle size of less than 75 microns. By inspection it was observed that the polymer product contained less than 10% by weight of material having a particle size of one cm or greater ND means not determined.

Example 8 A 20 cm internal diameter fluidised bed reactor vessel, operated in a continuous manner, was used to produce an ethylene/butene-1 copolymer. A reaction mixture comprising ethylene, butene-1 and hydrogen was circulated continuously through the bed at a superficial velocity estimated to be about four times the minimum necessary for fluidisation. In the fluidised bed, the reaction temperature was controlled at 800C by adjusting the temperature of the gas fed to the fluidised bed reactor vessel using a heat exchanger in the circulating gas loop. A 0.25 molar solution in n-hexane of aluminium trioctyl was pumped continuously into the reactor at a rate of 50 cm3 per hour.The product of Example 3 was blown into the reactor as a dry powder in a stream of process gas at frequent intervals so as to maintain a rate of polymer production of about 1.5 kg/hr, which corresponds to a mean residence time of four hours. The reaction pressure was maintained automatically at 14 kg/cm3 gauge by admitting an ethylene/hydrogen mixture through a control valve. Liquid butene-1 was pumped into the circulating gas stream so as to maintain a constant composition as determined by Gas Liquid Chromotography.

The polymer formed was removed periodically so as to maintain an essentially constant level in the reactor vessel. The polymer collected was degassed in a stream of nitrogen which had been passed over a bath of water at ambient temperature, and then through a steam jacket. The use of this warm, moist nitrogen removed monomers and also de-activated the catalyst and alkyl residues.

Further details, together with some characteristics of the polymer obtained, are set out hereafter.

Circulating gas composition (% moles) Hydrogen 51 Ethylene 31 Butene-1 13 Nitrogen 5 Catalyst residues in polymer (ppm by weight) Titanium 30 Chlorine 80 Polymer density (f) 930 kg/m3 Polymer MFI (g) 11 Polymer Stress Exponent (h) 1.30 Notes (f) Polymer density was measured as described in ASTM 1928/70, Method A, using a density gradient column at 230C.

(g) MFI (melt flow index) was measured by ASTM D 1238-70 at 1900C using a 2.16 kg weight.

(h) stress exponent is given by the relationship: Log OMFI 5-Log ,O MFI 2.16 Log,0 5-Log10 2.16 where MFI 5 is the melt flow index measured by ASTM Method D 1238-70 at 1 900C using a 5kg weight and MFI 2.16 is the melt flow index measured in the same manner but using a 2.16 kg weight.

Example 9 The product of Example 4 was used to polymerise propylene.

The propylene used for the polymerisation had been purified by passing gaseous propylene in turn through a column (7.6 cm in diameter, 0.9 m in length) containing 1.6 mm granules of Alcoa (Alcoa is a Registered Trade Mark) F1 alumina at 50-600C, and then through a similar column containing BTS catalyst (cupric oxide reduced to finely-divided metallic copper on a magnesium oxide support) at 40-500C, condensing the issue gas and passing the liquid propylene through four columns (all 7.6 cm in diameter; two of 0.9 m in length, two of 1.8 m in length) at 250C, each containing 1.6 mm pellets of Union Carbide 3A molecular sieves.

This treatment reduced the water content of the monomer from 5-10 ppm by volume to < 1 ppm by volume and the oxygen content from 1-2 ppm by volume to < 0.5 ppm by volume. The level of inert compounds (nitrogen, ethane, etc) was unchanged at 0.3% and the level of unsaturated hydrocarbons (allene, methyl-acetylene etc) was uncnanged at < 1 ppm.

A polymerisation flask equipped with efficient stirrer and a water jacket was dried carefully and one litre of the pentamethyiheptane fraction used in Comparative Example A was introduced. The flask was evacuated at 700C, the liquid purged with nitrogen and evacuated, which treatment effectively reduced the water and oxygen contents of the liquid to below 10 ppm by weight.

The pentamethylheptane fraction was then saturated with the purified propylene, which contained 0.12% molar of hydrogen, to one atmosphere pressure. 10 millimoles of diethyl aluminium chloride were introduced into the polymerisation flask. After half an hour, a 25% by weight suspension of the product of Example 4 in the pentamethylheptane fraction was introduced into the polyrmerisation flask in an amount sufficient to provide 2 millimoles of Tics3. The pressure in the polymerisation flask was maintained at one atmosphere by supply of propylene containing 0.12% molar of hydrogen. After a period of 3 hours from the introduction of the Tics3, the run was terminated with 5 ml of isopropanol and 5 ml of propylene oxide, and a sample of supernatant liquid extracted for determining the concentration of soluble polymer dissolved in the polymerisation diluent. The solid was filtered and washed three times with petrol ether and dried in a vacuum oven at 1 200C for an hour.

The result obtained is set out hereafter.

Polymer Yield (i) 34 g/millimole % Diluent Soluble Polymer (j) 0.5% by weight Notes (i) Yield is expressed in grammes of total polymer (solid+soluble) obtained for each milligramme atom of titanium present in the catalyst system.

(j) Given by the relationship Wt of diluent soluble polymerx 100 Wt of total polymer

Claims (12)

Claims

1. A process for modifying the particle form of a solid particulate material which contains a transition metal compound by suspending the solid particulate material in an inert liquid medium, treating the suspension to evaporate off essentially all of the inert liquid medium and form a solid residue, and crushing the solid residue in the essential absence of a liquid medium.

2. A process as claimed in claim 1 wherein the inert liquid medium is an aromatic hydrocarbon medium.

3. A process as claimed in claim 1 or claim 2 wherein the suspension also contains a small amount of a material which assists in the agglomeration of the solid particulate material.

4. A process as claimed in claim 3 wherein the suspension contains polystyrene in an amount of from 1% up to 10% molar relative to the transition metal present in the solid particulate material.

5. A process as claimed in any one of claims 1 to 4 wherein the inert liquid medium is evaporated at a temperature not exceeding 1 500 C.

6. A process as claimed in claim 5 wherein evaporation is effected at a temperature of between 800C and 1 300 C.

7. A process as claimed in any one of claims 1 to 6 wherein the stages of evaporating the suspension to dryness and crushing the solid residue are effected in a grinding apparatus.

8. A process as claimed in any one of claims 1 to 7 wherein the solid residue is crushed in contact with a suitable sieve.

9. A process as claimed in any one of claims 1 to 8 wherein the solid particulate material containing a transition metal compound has been ground with a Lewis Base compound.

10. A process as claimed in claim 9 wherein the solid material which has been ground with a Lewis Base compound has also been subjected to extraction with a liquid medium.

11. A process as claimed in claim 9 or claim 10 in which the Lewis Base compound is a sulphone, a sulphonamide or a fused ring compound containing a heterocyclic sulphur atom.

12. A process as claimed in any one of claims 9 to 11 wherein the solid particulate material has been ground with the Lewis Base compound and also with aluminium chloride and titanium tetrachloride.

1 3. A process as claimed in any one of claims 9 to 1 2 wherein the solid particulate material is, or contains, titanium trichloride.

1 4. An olefin polymerisation catalyst which comprises 1) a transition metal compound which has been obtained by a process as claimed in any one of claims 1 to 13; and 2) an organic compound of a metal of Group IIA of the Periodic Table or of aluminium or a complex of an organic compound of a metal of Group IA or Group IIA of the Periodic Table with an organic compound of aluminium.

1 5. An olefin polymerisation process wherein at least one olefin monomer is contacted, under polymerisation conditions, with an olefin polymerisation catalyst as claimed in claim 14.

1 6. A process claimed in claim 1 5 wherein ethylene or propylene is polymerised in the gas phase.