GB2132214A - L-olefin polymers - Google Patents

Abstract

A process for (co)-polymerising one or more l-olefins under a pressure of at least 500 bars and at a temperature in the range 150 to 320 DEG C in the presence of a co-ordination catalyst and wherein the (co)polymerisation is terminated by addition of a deactivating agent to the polymerisate is characterised in that the deactivating agent comprises a polyalkylene glycol, a polyvinyl alcohol or an aliphatic alcohol containing at least 10 carbon atoms.

Description

SPECIFICATION Polymerisation process The present invention realtes to a process for polymerising ethylene optionallytogetherwith one or more 1-olefins.

More particularly the invention relates to the homoorcopolymerisation of ethylene at relatively high temperature and pressure to provide substantially linear homo-polyethylene or copolyethylenes.

The polymerisation and copolymerisation of ethylene has been carried out on a large commercial scale for many years. Thefirstcommercial process to be used involved the polymerisation of ethylene at high temperature (eg 200-300"C) and at high pressure (eg 1000 to 3000 bars) in the presence of a catalyst capable of generating free radicals eg a peroxide. The polyethylene produced by this free radical catalysed process has a highly branched structure.Subsequently it was discovered that ethylene could be polymerised using transition metal-based coordination catalysts (eg Zieg ler or Ph illips catalysts) to form essentially linear polyethylene having little or no chain branching. Homopolyethylenes manufactured using coordination catalysts generally have a relatively high density, high rigidity and high softening temperature dueto their substantially linear, unbranched structure.

Linear copolyethylenes, for example, copolymers of ethylene and C3 to C8 1 -olefins, manufactured using coordination catalysts have lower density and higher flexibility than the corresponding homopolyethylene due to the presence of chain branches arising from the copolymerised 1-olefin units. These linearcopolyethylenes are generally referred to as "linear low density polyethylenes". Commercial processes for the homo- and co-polymerisation of ethylene are carried out under gas phase, solution phase and slurry phase conditions using relatively low polymerisation temperatures (eg 75 to 1 500C) and relatively low pressures (eg 10 to 50 bar).

GB-A-1321061 discloses a polymerisation process wherein a mixture of ethylene and at least one other alpha-olefin is polymerised using an organometallic catalyst at a temperature in the range 75-300"C and a pressure in excess of 600 atmospheres, wherein the organometallic catalyst is a mixture of a transition metal compound and an organometallic compound of a non-transition metal, or a benzyl derivative of a transition metal.

G B-A-2093047A discloses a process for copolymerising ethylene and a minor proportion of an alphaolefin having 4to 10 carbon atoms under pressure of more than 200 kg/cm2, preferably from 500 to 4000 kg/cm2, and at a temperature of at least 125"C, p refera bly i n th e range of fro m 150 to 350 C i n th e absence of liquid dispersion medium using as catalyst (A) an organometallic compound and (B) the product of contacting a magnesium compound with a titanium compound. The magnesium compounds can be, for example, (i) magnesium halides such as magnesium dichloride, magnesium dibromide and magnesium diiodide; (ii) halohydrocarbyloxymagnesiums such as magnesiumethoxychloride and magnesiumhydroxychloride; (iii) magnesium dialcoholates such as mag nesium diethoxideand magnesium dimethoxide; (iv) magnesium oxide and magnesium carbonate, and (v) organomagnesium compounds such as diethylmag nesium and ethylmagnesium chloride. Magnesium chloride is preferred.Thetitanium compound is selected from halides, oxyhalides, alcoholates and alkoxyhalides oftitanium.

In the conventional high pressure, free-radical catalysed polymerisation of ethylene, the polymerisation reaction substantiallyterminates when the polymerisation mixture, which essentially comprises a solution ofpolyethylene and residual catalyst in supercritical ethylene, is discharged to a zone (eg a separator) at lower pressure and/or lowertempera- ture. However, catalysts of the co-ordination type generally retain their activity over a broad range of temperature and pressure, and in the high temperature/high pressure co-ordination catalysed process it is found that undesirable polymerisation can continue in the polymerisation mixture after it has been discharged from the polymerisation zone into zones of lower pressure and/or lower temperature.

In conventional low pressure co-ordination catalysed polymerisation of alpha-olefins, it is known to deactivate residual catalyst present in the produced polyolefin using various deactivating agents, for example, water, alcohol, epoxides and alkali metal hydroxides. However, itis undesirableto use these deactivating agents in high pressure co-ordination catalysed polymerisation systems as they can, for example, contaminate the recycle monomer or cause corrosion ofthe polymerisation apparatus.

GB-A-1535568 discloses a continuous process for the polymerisation and copolymerisation of ethylene which process comprises polymerising or copolymerising under a pressure above 500 bars and at temperatures above 1 60"C in the presence of a catalyst comprising a transition metal compound and an organometallic compound of aluminium, said polymerisation being stopped by injecting into the reaction mixture at leastonezinc, alkali metal or alkaline earth metal salt of a carboxylic acid which is either in the pure molten state or in suspension or in solution in a hydrocarbon in an amount sufficient to bring about the deactivation ofthe catalyst the said salt being so chosen that its reaction products with the constituents of the catalyst remain in the recovered polymer.

It is an object of the present invention to provide a process for polymerising 1 -olefins under conditions of high temperature and high pressure using an improved method ofterminating the polymerisation.

Accordingly, the present invention provides a pro cuss for (co)-polymerising one or more 1 -olefins under a pressure of at least 500 bars and at a temperature in the range 150 to 320"C in the presence ofaco- ordination catalyst and wherein the (co)polymerisation is terminated by addition of a deactivating agent to the polymerisate, characterised in that the deactivating agentcomprises a polyalkylene glycol, a polyvinyl alcohol or an aliphatic alcohol containing at least 10 carbon atoms.

In the process of the present invention, when the (co)polymerisation has reached the desired state of completion the (co)polymerisation reaction is termin ated by adding the polyalkylene glycol, polyvinyl alcohol or aliphatic alcohol deactivating agent.

Examples of suitable aliphatic alcohols are stearyl alcohol and palmityl alcohol. Preferred deactivating agents are polyethylene glycol having a weight average molecular weight Mw in the range 50 to 1200, most preferably in the range 200 to 400, and polyvinyl alcohol having a weight average molecularweight in the range 50 to 100000, most preferably in the range 500 to 10000. The deactivating agent is preferably free from volatile constituents, for example air, water and lower alcohols, which themselves act as Ziegler catalyst deactivators. The deactivating agent can contain inert diluent if desired, for example, cyclohex ane, heptane, toluene, xylene.

The quantity ofthe defined deactivating agent employed in the present invention is suitably at least sufficientto inactivate the catalyst.

If desired, the defined deactivating agent can be used togetherwith a conventional involatile deactivating agent, for example a metal salt of a carboxylic acid.

Examples of metal salts of carboxylic are sodium stearate, potassium stearate, calcium stearate, magnesium stearate, sodium benzoate, potassium benzoate, sodium naphthenate and potassium naphthenate.

The deactivating agent can be added to the (co)polymerisate by any convenient technique, for example, by injection into a 'batch' autoclave reactor containing the (co)polymerisation mixture or into a separator downstream of a tubular reactor in a 'continuous' process.

The treatment with the deactivating agent is suitably carried out by adding said agentto the (co)polymerisate when the latter is at a temperature in the range 50 to 300 C, preferably 100 to 250 C. Preferably the addition is carried out in such a mannerthatthe deactivating agent is dispersed uniformlythrough the (co)polymerisate. The (co)polymerisate can then be recovered from the reactor by conventional techniques.

The one or more 1 -olefins employed in the polymerisation process ofthe present invention are suitably selected from C2toC20, preferably C2 to C12 1-olefins. Examples of suitable 1 -olefins are ethylene, propylene, 1 -butene, 1 -hexene, 4-methyl-1 -pentene, 3-methyl-1-pentene, 1-octeneand and 1 -decene. The process is preferably applied to the homopolymerisation of ethylene orto the copolymerisation of ethylene with up to 70 moles % (based on total monomer) of one or more other 1 -olefins.Particularly useful copolymers can be made by the process ofthe present invention by copolymerising a mixture of 100 to 50 weight % of ethylene with 0 to 50 moles % of 1-butene, 1 -hexene, 4-methyl-i -pentene or 1 -octene.

The pressure employed in the (co)polymerisation process of the present invention is suitably at least 500 bars and preferably at least 1000 bars. The (co)poly merisation temperature is suitably in the range 150 to 320"C, preferably in the range 175 to 275"C.

Catalysts ofthe co-ordination type are well known in the art and include for example Phillips and Zielger catalysts. Ziegler catalysts generally comprise the product of reacting together one or more transition metal compounds with one or more so-called 'activators'. Preferred transition metal compounds are com pounds ofthe metals of lVA, VA and VIA ofthe Periodic Table, for example, titanium, vanadium, zirconium, chromium and molybdenum compounds. Titanium and vanadium compounds are particularly preferred. The activators are generally selected from organometal, organoboron, metal hydride or boron hydride compounds.

Phillips catalysts comprise the product of heating chromium oxide or a compound calcinable thereto supported on a refractory oxide material to a temper ature at leastsufficientto produce an active catalyst.

It is also known to use as co-ordination catalysts certain organotransition metal compounds, for exam- ple, zirconium tetrabenzyl and titanium tetrabenzyl.

Any ofthe aforesaid catalysts ofthe co-ordination type can be employed as the co-ordination catalyst in the present invention.

It is also known thatthe activity of co-ordination catalysts ofthe Ziegler type can frequently be improved by incorporating certain inorganic compounds in the catalyst composition for example bysupporting the transition metal compound on an inorganic support material. Examples of suitable support materials are silica, alumina, magnesia, titania, magnesium chloride, calcium chloride, magnesium carbonate and magnesium hydroxychloride.Catalysts ofthis type are described, for example, in GB-A-1 024336, GB-A-1269068, GB-A-1257040, GB-A-1 287396, GB-A 1264416, GB-A-1351488, GB-A-1211287, GB-A 1189038, GB-A-1286867, GB-A-1553673 and EP-A- 22658, and reference may be made to these patent specifications for details of preparation of supported Ziegler catalysts which can be used as the coordination catalyst in the present invention.

In a preferred embodiment ofthe present inven tion,the co-ordination catalyst comprises the product of contacting (a) a solid particulatetitanium-contain- ing component prepared by a process comprising impregnating a solid particulate support material comprising a hydroxyl-groupscontaining magnesium compound with one or more halogen-containing titanium compounds and removing unadsorbed titanium compound (if any) therefrom, with (b) a Ziegler catalyst activator.

In this preferred embodimentthe hydroxyl groups containing magnesium compound can be, for example, magnesium hydroxide, magnesium oxide or magnesium hydroxychloride. Magnesium oxide is preferred. The hydroxyl groups containing magnesium compound preferably has a particle size less than 500 micron, for example 0.01 to 500 microns, most preferably 0.1 to 100 microns. Magnesium oxide having a surface area in the range 1 to 100 square metres per gram and a hydroxyl content less than 0.2 OH groups per magnesium atom is particularly preferred. It is preferred to employ magnesium oxide that has been obtained by the thermal decomposition of magnesium hydroxide aithough magnesium ox ides obtained byforexamplethermallydecomposing magnesium carbonate, magnesium nitrate or basic magnesium carbonate or by combustion of magne sium metal are also suitable.

In the aforesaid preferred embodimentthe one or more halogen-containing titanium compounds can be, for example, halides, haloalkoxides or oxyhalides oftitanium. The halogen is preferably chlorine or bromine, chlorine being particularly preferred. Prefer red halogen-containing titanium compounds are those compounds having the empirical formula Ti(OR)nCl4.n wherein n is zero, or an integer or fraction less than 4, and R is a hydrocarbon group, for example an alkyl, cycloalkyl, aryl or arylalkyl group. Preferably R is an alkyl group containing 1-6 carbon atoms.Examples of compounds having this formula are titanium tetrach loridèrtrTchlorotitanium ethylate (Ti(OEt)CI3) and dich lorotitanium-diisopropylate (Ti(OiPr)2Cl2). Compounds ofthis type can be prepared, for example, by the reaction oftitanium tetrachloride with an alcohol or by the reaction oftitanium tetrachloride with a titanium alkylateora chloro-titanium alkylate.

In this preferred embodiment, the quantity of halogen-containing titanium compound employed is suitably at leastsufficientto provide a concentration of 0.1 to 30 weight %, preferably 0.5 to 15weight %, most preferably 1 to 7weight % oftitanium based on the total weight of component (a). If desired, an excess, for example up to 100 times the concentration in thefinal catalyst component (a), of halogencontaining titanium compound may be employed, provided thatthe final catalyst component (a) contains 0.1 to30weight% oftitanium.The impregnation of the support material with the halogen-containing titanium compound can be carried out, for example, by mixing the materials together at any desired temperature. It is preferred to carry out the impregnation in the presence of a liquid hydrocarbon diluent.

Examples of suitable hydrocarbon diluents are hex ane, cyclohexane, isobutane, isopentane, toluene, gasoline or naphtha. Preferably a hydrocarbon diluent is employed which is a solventforthe halogencontaining transition metal compound. It is preferred to carry out the impregnation by refluxing together a mixture ofthe halogen-containing titanium compound, the support material and the hydrocarbon diluent at a temperature in the range 50 to 150 C.

In the preferred embodiment ofthe present invention the halogen-containing titanium compound is preferably reacted with an aicohol prior to orduring the impregnation ofthe support material. The reaction of the alcohol with the halogen-containing titanium compound liberates hydrogen halide and this is believed to be beneficial in the impregnation step. The alcohol is preferably a straight or branched chain aliphatic alcohol containing 1 to 12 carbon atoms.

Alcohols having 1 to 6 carbon atoms are particularly preferred, for example methanol, ethanol, isopropanol and secondary butanol. The quantity of alcohol employed in this preferred embodiment is suitably 0.1 to 4.0 moles, preferably 1.0 to 3.5 moles, most preferably 1 .5 to 3.0 moles per mole of halogencontaining titanium compound. The impregnation of the support material can be carried out for example by reacting the halogen-containing titanium compound withthealiphaticalcohol in the presence ofthe supportmaterial. Alternatively, the halogen-containing titanium compound and the alcohol can be reacted together and then added to the support material.The reaction between the halogen-containing titanium compound and the alcohol is preferably carried out in the presence of a liquid diluent, examples of suitable diluents being hexane, cyclohexane, isobutane, isopentane,toluene and mixed aliphatic and aromatic hydrocarbon solvents. The reaction can be carried out at any desired temperature. Normally temperatures in the range 0 to 150"C are found to be satisfactory.

OurGB-A-1553673 discloses a processforthe production of a supported Ziegler catalyst component comprising reacting together underanhydrouscondi tons a halogen-containing transition metal compound, for example a halogen-containing liquid compound, and an aliphatic alcohol, and simultaneously or subsequently impregnating an anhydrous hydroxyl groups-containing support material comprising magnesium oxide, magnesium hydroxide or magnesium hydroxychloride with the reaction mixture to produce the solid catalyst component. Reference may be made to GB-A-i553673forfurtherdetails regarding the preparation ofthe solid titanium-containing component (a) employed in the preferred embodiment of the present invention.

The Ziegler catalyst activator (b) employed in the preferred embodiment ofthe present invention is suitably an organometallic compound, an organoboron compound, a boron hydride, or a metal hydride wherein the metal is present in Groups 1,11,111 and IV of the PeriodicTable. Preferred activators are organoaluminium compounds, for example, triethyl aluminium, tri-n-butyl aluminium, trioctyl aluminium and diethyl aluminium chloride. The quantity of Ziegler catalyst activator employed is suitably 1 to 50 moles, preferably3to 20 moles per gram atom oftitanium present in the component (a).The activation of the component (a) can be carried out "in situ" in the polymerisation reactor or can be carried outpriorto feeding the catalystcomponentsto the polymerisation, or a combination of thesetechniques can be employed as desired. It is preferred to activate the catalyst in a separate stage priorto feeding the produced activated catalyst to the polymerisation. The activated supported Ziegler catalyst preferably has a mean particle size less than 200 microns, most preferably less than 50 microns. The particles can be reduced in size by conventional mechanicaltechni- ques if desired.

It is preferred to carry out all steps of the Ziegler catalyst preparation and activation under anhydrous conditions and in the absence of air and other substances which are known deleteriously to affect the performance of Ziegler catalysts.

To facilitate addition ofthe Ziegler catalyst to the polymerisation reaction zone in the process of the present invention it is preferred to feed the catalyst as a concentrated suspension in an inert liquid suspension medium,forexample in a saturated hydrocarbon diluent. Examples of saturated hydrocarbons suitable for this purpose are n-hexane, n-heptane, n-octane, cyclohexane and dodecane. It is desirableto employ a uniform dispersion of Ziegler catalyst suspension and this may be facilitated, for example, by using a catalyst having fine particle size, by agitation ofthe catalyst suspension, or by employing a suspension medium having sufficiently high viscosity to maintain the catalyst particles in suspension priorto feeding to the reaction zone.

In the process of the present invention it is preferred to feed the Ziegler catalystto the polymerisation in the form of a fluid catalyst/polymer composition having sufficiently high viscosity to maintain the catalyst particles in suspension. The fluid catalyst-polymer composition can be, for example, a liquid polymer, a polymer solution or a polymer melt, containing a suspension of the Ziegler catalyst particles. A preferred method for obtaining the fluid catalyst/polymer composition comprises pre-polymerising a C6to C12 alpha-olefin in hydrocarbon solution in the presence ofthe Ziegler catalyst to give a product containing a weight ratio of polymer: catalyst in the range 1:1 00to 100: 1, preferably in the range 1 :10to 20:1. The alpha-olefin employed is preferably 1-hexene or 1-decene.The hydrocarbon employed in the prepolymerisation can be any saturated hydrocarbon in which the produced polymer is soluble. The quantity of hydrocarbon employed is preferably sufficient to provide 10 to 200 litres per kilogram of prepolymer/ catalyst.

Theformation ofthe catalyst as a fine dispersion makes it particularly suitable for continuous operation and continuous injection into the reactorsincethefine particles can be pumped using a high pressure pump which would be damaged by the use of coarse particles.

The ethylene (co)polymerisation process ofthe present invention can be carried out under batch or continuous operation conditions. When operating on a continuous basis, the process may be carried out in a continuous stirred reactor or a continuous tubular reactor.The useoftubulargenerallyleadstothe production of polyethylene or ethylene copolymers having broader molecularweight distribution than is obtained using stirred reactors. The process can carried out as a single zone process using a single reactor, butforthe production of many products it is preferred to use either a number of reactors in series optionally linked by coolers or a single reactor which is effectively divided internally into several zones to give a multi-zone process.It will be appreciated that in a multi-zone process the reaction conditions in each zone will normally be different and it may be necessary to add monomers, and/or catalystto the different reactors orzonesto control the characteristics ofthe polymer obtained in the different reactors or zones.

Chain transfer agents may, if desired, be used in the polymerisation to lowerthe molecular weight and hence raise the meltflow index of the product.

However, the molecularweightofthe polymer product is dependent not only on the presence or absence of a chain transferagent, butalso on the reaction conditions including the temperature and the nature ofthe monomeric material, and in general the use of a chain transferagent is not necessary in the present polymerisation process. If it is desired to use a chain transfer agent a suitable agentfor use in conjunction with the catalyst is hydrogen.

The deactivating agent employed in the present invention has a number of advantages compàred with conventional deactivating agents. For example, the deactivating agent is relatively involatile and can be readily separated from the unreacted 1-olefin monomer er, thus allowing recycling ofthe monomer usinga simple recompression cycle. Furthermore, the deactivating agent employed in the present invention does not deletiously affectthe properties of the produced (co)polymers.

The present invention is illustrated inthefollowing Tests and Control Experiments.

Tests and Control Experiments A sample of a solid supported Ziegler catalyst componentwas prepared from a magnesium oxide support material (Maglite K), titanium tetrachloride and isopropanol using a method similartothat disclosed in our GB-A-1553673, at page 3, Example 2.

The catalyst component was activated using 2.249 triethylaluminium per g of catalyst component and simple low pressure/low temperature ethylene polymerisation tests were carried outto test the efficacy of polyethylene glycol in terminating the polymerisation. The polymerisation tests were carried out in 1 litre of isobutane at 90"C using samples (0.1 g) ofthe activated catalyst. The reactor was maintained at40 bars (by continuous addition of ethylene) after initial introduction of hydrogen (7 bars). In Tests 3-6, after an initial polymerisation period of 10 minutes, polyethylene glycol was added and an attempt was made to restartthe polymerisation.Control 2 was similar exceptthat cyclohexane was added instead of polyethylene glycol. In Control 1, the polymerisation was discontinued afterthe initial polymerisation period (10 minutes) to measure the polymer yield. In Tests 3-5, the TABLE

Deactivating 2nd Polymerisation Test 1st Polym Agent Period Total No Period . Yield (minutes) Type quantity Time Reaction g (ml) (minutes) Regained I (control) 10 None - 0 - 98 2 (control) 10 cyclohexane 3.0 30 Yes 212 3 10 PEG 200 3.0 33 No 103 4 10 PEG 200 1.0 40 No 114 5 10 PEG 200 0.25 20 No 93 6 10 PEG 400 1 0.25 27 1 No 101 polyethylene glycol was "PEG 200" which has an average molecularweight (Mw) of 200 and in Test 6 it was "PEG 400" having a Mw of 400.

It can be seen from theTablethat polyethylene glycol has effectivelyterminated the polymerisation in Tests 3-6. In Control Test 2, polymerisation continued for a further 30 minutes afterthe initial period showing that the catalyst had not been inactivated by addition of cyclohexane in piace of the PEG.

Claims (11)

1. A process for (co)-polymerising one or more 1-olefins under a pressure of at least 500 bars and at a temperature in the range 150 to 3200C in the presence of a co-ordination catalyst and wherein the (co)poly rnerisatfon isterminated by addition of a deactivating agent tathe polymerisate, chamcterised in that the deactivating agent comprises a polyalkyleneglycol, a polyvinyl alcohol oran aliphatic alcohol containing at least 10 carbon atoms.

2. Aprocessasclaimedinclaim 1 wherein the deactivating agent is polyethylene glycol having a weight average molecularweight Mw in the range 50 to 1200.

3. A process asclaimed inclaim 1 wherein the deactivating agent is polyvinyl alcohol having a weightaverage molecularweight in the range 50 to 100,000.

4. A process as claimed in claim 1 wherein the deactivating agent isstearyl alcohol or palmityl alcohol.

5. A process as claimed in any one of the preceding claims wherein the deactivating agent is used togetherwith a metal salt a carboxylic acid.

6. A process as claimed in any one of the preceding claims wherein the deactivating agent is added to the (co)polymerisate when the latter is ata temperature in the range 50to 300at.

7. A process as claimed in any one of the preceding claims wherein the co-ordination catalyst is a Phillips catalyst or a Ziegler catalyst.

8. A process as claimed in any one of the preceding claims wherein the co-ordination catalyst comprises the product of contacting (a) a solid particulate titanium-containing component prepared by a process comprising impregnating a solid par ticulatesupportmaterial comprising hydroxylgroups containing magnesium compound with one or more halogen-containing titanium compounds and removing unadsorbedtitanium compound (if any) therefrom, with (b) a Zieglercatalystactivator.

9. A process as claimed in claim 8 wherein the halogen-containing titanium compound is reacted with an alcohol during the impregnating.

10. A process as claimed in any one of the preceding claims wherein the (co)polymerisation is carried out under continuous polymerisation conditions.

11. (Co)polyolefins prepared by the process claimed inanyoneoftheprecedingclaims.