GB2073761A - Olefin polymerisation catalyst - Google Patents

Abstract

An olefin polymerisation catalyst is prepared by heating at 300-1200 DEG C an oxide support having surface -OH groups (e.g. silica) and a titanium compound, (e.g. Ti(OPr)4), impregnating the product with an anhydrous chromium compound and heating at 250-1200 DEG C to give an active catalyst and finally adding organometallic or organoboron compound(s), (e.g. triethylaluminium). The catalyst can be further modified by the addition of a polyene and is preferably used to polymerise ethylene, optionally with other 1- olefins, to give solid, mouldable polyolefins.

Description

SPECIFICATION Polymerisation of 1-olefins and catalyst therefor The present invention relates to a process for polymerising 1-olefins and to a catalyst for use therein.

UK patent no. 1429174 filed in the name of BP Chemicals International Limited relates to a polymerisation catalyst prepared by (I) heating together a support material comprising silica, alumina, zirconia or thoria or composites thereof and a defined titanium compound at a temperature in the range 1 50 to 1 2000C and (II) incorporating in the product from step (I) under substantially anhydrous conditions a chromium compound and heating at a temperature in the range 100 to 1 2000C to produce an active polymerisation catalyst. UK patent No. 1495547 filed in the name of the British Petroleum Company Limited relates to a similar type of catalyst and a precursor thereof.Catalysts of this type are used to polymerise 1 -olefins, for example ethylene, under solution, suspension or gas-phase polymerisation conditions to form solid polyolefins.

It is an object of the present invention to provide an improved polymerisation process and a modified catalyst therefor.

Accordingly the present invention provides a modified polymerisation catalyst prepared under substantially anhydrous conditions by a process comprising: (A) heating together at a temperature in the range 300-1 2000C a refractory oxide support material having surface hydroxyl groups and a titanium compound which reacts the said hydroxyl groups of the support material under the heating conditions.

(B) impregnating the product from (A) with an anhydrous chromium compound which is chromium oxide or a compound calcinable thereto, and heating the impregnated material at a temperature in the range 250 to 1 2000C to produce an active polymerisation catalyst, (C) forming the modified polymerisation catalyst by adding to the active polymerisation catalyst obtained from step (B) one or more organometallic or organoboron compounds having the general formula MR2pYqp wherein M is an atom of Groups 1 A, 2A, 2B or 3A of the Periodic Table (Mendeieef) R2 is a hydrocarbon group containing 1 to 10 carbon atoms, Y is hydrogen, halogen or alkoxide, q is the valency of M, p is an integer from 1 to q inclusive and when the organometallic or organoboron compound contains more than one R2 or Y group they may be the same or different.

In a preferred embodiment according to the present invention the catalyst is further modified by the addition of a polyene compound during, or subsequent to, the performance of step (C).

The refractory oxide support material can be, for example silica, silica-alumina, silica-titania, alumina, zirconia or thoria. Silica is preferred, particularly silica having a mean particle diameter in the range 20 to 1 50 microns, and a surface area in the range 1 50 to 600 square metres per gramme. The support material must be substantially dry, i.e. free from unbound water. Adequate dryness of the support material can be achieved, for example, by heating the support material "in vacuo" at temperatures in the range 30-1 200C until further heating under these conditions produces no substantial loss in weight.

If desired, the refractory oxide support material employed in the present invention can itself be the product obtained by pretreating a "primary" refractory oxide support material, e.g. as listed in the previous sentence, with a titanium compound capable of reacting therewith, heating to a temperature in the range 300-1 2000C and treating the product with a volatile hydroxyl groups containing compound, e.g. water or alcohol, to reform hydroxyl groups on the surface of the support material. The heating and rehydroxylation steps can be carried out more than once if desired. Finally the produced titanium-treated support material is dried before being employed as the refactory oxide support material in the present invention.The process of heating the "primary" support material with titanium and the rehydroxylation can be carried out, for example, as disclosed in UK patent specification No: 1495547.

The titanium compound (S) employed in the present invention can be any titanium compound capable of reacting with the surface hydroxyl groups of the support material at a temperature in the range 300-1 2000 C. Examples of suitable titanium compounds are titanium oxychloride (TiOCL2), titanium acetylacetonate compounds, alkanolamine titanates, titanium err - bonded complexes (e.g. dicyclopentadienyl titanium) and compounds having the general formulae Ti (OR) mXn, wherein m + n is 4, m is zero or an integer from 1 to 4, R is an organic hydrocarbon group having 1 to 12 carbon atoms, X is halogen or a hydrocarbon group and when the titanium compound contains more than R or X group the groups may be the same or different.Tetravalent titanium compounds are preferred. When the titanium compound employed in the present invention is Ti(OR)mXn, R is preferably selected from alkyl, aryl, cycloalkyl and combinations thereof, for example aralkyl and alkaryl, each group having from 1 to 12 carbon atoms and X is preferably selected from R, cyclopentadienyl, alkenyl and halogen.

Titanium compounds represented by the formula (RO)4Ti are preferred, particularly the alkyl compounds having from 1 to 6 carbon atoms in each alkyl group, for example, titanium tetraethylate and titanium tetraisopropylate. The titanium acetyl acetonate compound can be, for example, titanium diacetylacetonate di-isopropylate, titanium dichloro diacetyl acetonate or the so called "titanium acetyl acetonate" or titanyi acetyl actonate". The alkanolamine titanate can be for example triethanolamine titanate.

The quantity of titanium compound employed is suitably sufficient to give a titanium concentration (derived from said titanium compound) in the support material in the range 0.05 to 20 wt %, preferably 0.5 to 5 wt %, based on the weight of the solid product from step (A).

The titanium compound is preferably added to support material in a form in which it becomes well dispersed. For example if the titanium compound is liquid it can be mixed with the support material as such, if desired. If it is a liquid or a solid it can be dissolved in a suitable non-aqueous solvent or comminuted in a non-aqueous diluent and then mixed with the support material.

Alternatively, the titanium compound can be added as a vapour if it is volatile, or carried into the support material as an aerosol in a suitable carrier gas, for example nitrogen. The titanium compound can, if desired, be formed "in situ" on the support material. For example if it is desired to employ titanium tetramethylate as the titanium compound, the support material may be impregnated with titanium tetrachloride and subsequently heated with methanol until the reaction between the methanol and the titanium tetrachloride has gone substantially to completion. The progress of this reaction can be monitored, for example by distilling the evolved hydrogen chloride from the reaction vessel and titrating with standard alkali.

The refractory oxide support material and the titanium compound are preferably heated together at a temperature in the range 400--10000C, most preferably 500-9000C for a period of time which can range from a few minutes to several hours. The heating may be carried out, for example, by heating in a fixed bed or in a fluidised bed. Preferably the heating is carried out in a bed fluidised by dry air.

The an hydros chromium compound employed in step B can be chromium oxide (i.e. CrO3) or a compound calcinable thereto, for example chromium nitrate, chromium carbonate, chromium acetate, ammonium chromate, chromyl chloride, tertiary butyl chromate, chromium acetylacetonate or bis (cyclopentadienyl) chromium. di-tertiary butyl chromate is preferred.

The quantity of chromium compound supported on the solid product from step (A) is suitably 'such as to provide a chromium concentration of at least 0.1%, preferably in the range 0.2-30 wt%, most preferably 0.5 to 5 wt % based on chromium compound and solid product from step (A) together.

The supporting of the chromium compound on the product from step (A) can be achieved, for example, be dissolving a soluble chromium compound in an anhydrous volatile liquid, impregnating the product from step (A) with the solution and evaporating the solvent: by impregnating the product from step (A) with a liquid chromium compound, e.g. chromyl chloride; by passing the vapour of a volatile chromium compound, e.g. chromyl chloride, into a bed of the product from step (A); or by mixing together a finely divided chromium compound and said product in the presence of a small quantity of non-aqueous solvent, continuing the mixing until a substantially homogenous mix is obtained and then evaporating the solvent. Examples of solutions that can be used to impregnate the support material are tertiary butyl chromate/hexane, and chromyl chloride/chloroform.

The chromium-impregnated material is heated in step (B) to a temperature in the range 250 to 12000 C, preferably 400--9000C, most preferably 500-8000C to produce an "active polymerisation catalyst". By this is meant that the product from step (B) must have been heated to a temperature within one of the defined ranges under conditions such that it is capable of catalysing the polymerisation of ethylene under convention polymerisation conditions, e.g. under the polymerisation conditions disclosed in Example 1 of UK patent specification No. 14291 74 at page 3 lines 51-53. The chromium -- impregnated material is suitably heated to a temperature within one of the defined ranges for a period of time within the range 5 minutes to 24 hours, preferably 30 minutes to 1 5 hours although times outside the broader range can be used if desired. It is preferred to employ heating conditions in step (B) which favour the formation of, or retention of, chromium in its hexavalent state. The heating is preferably acrried out in a non-reducing atmosphere and most preferably in an oxidising atmosphere or in vacuo. Dry air is an example of a suitable oxidising atmosphere. The heating must be performed under anhydrous or dehydrating conditions and the activated catalyst must be protected from ingress of moisture.

Preferably, the heating temperature employed in step (A) is higher than that employed in step (B).

In step (C) the activated catalyst is converted to the modified catalyst of the present invention by adding the defined organometallic or organoboron compound. The term "organometallic compound" as employed hereinafter includes a reference to organoboron compounds, and similarly unless indicated to the contrary the term "metal" includes boron although it is appreciated that boron is, strictly speaking, a metalloid.

In the organometaliic compound employed in the present invention the R2 group is preferably an alkyl, cycloalky or aryl group. Metal alkyls are particularly preferred.

The metal present in the organometallic compound in the present invention is preferably lithium, sodium, beryllium, magnesium, calcium, zinc, cadmium, boron, aluminium or gallium.

Metals alkyls particularly preferred are dibutyl magnesium, triethyl boron, triethyl aluminium, triisobutyl aluminium. The quantity of organometallic compound employed is suitably 0.1 to 100%, preferably 1 to 10 wt % based on the total weight of catalyst.

The organometallic compound can be added to the active catalyst per se, or to the active catalyst in the presence of the substance or substances forming or intended to form the ingredients of an olefin polymerisation reaction. For ease of handling, it is preferred to add the organometallic substance to the active catalyst, or to a polymerisation system employing the active catalyst, in solution in a hydrocarbon solvent, e.g. n-hexane.

In the preferred embodiment of the present invention wherein the modified catalyst is further modified by the addition of a polyene compound, the polyene is suitably a C, to C20 conjugated or non-conjugated polyene. The polyene may be substituted by alkyl, cycloalkyl, or aryl or may be unsubstituted. Preferably the polyene contains 2 double bonds. Examples of suitable polyenes are butadiene, isoprene, 1,5-hexadiene, 1,4-hexadiene, myrcene, cyclo-pentadiene, dicyclopentadiene and ethylidene norbornene.

The quantity of polyene employed is suitably from 0 to 50 parts by weight, preferably 0 to 10 parts by weight per unit weight of catalyst.

The addition of the polyene can be carried out at any stage subsequent to the completion of step (B) of the present invention. However, it is preferred to add the polyene to the polymerisation system in which the modified catalyst of the present invention is to be employed.

The present invention further provides a process for polymerising monomeric 1-olefin comprising contacting the monomeric 1 -olefin under polymerisation conditions with the modified catalyst of the present invention.

The monomeric 1-olefin employed in the polymerisation process of the present invention is preferably ethylene or a mixture of ethylene with one or more other comonomer 1 -olefins. When comonomer 1 -olefins are employed they preferably comprise up to 40 wt %, most preferably up to 25 wt % of the total monomer. Examples of comonomer 1 -olefins and 1 -butene, 1 -pentene, 1 - hexene and 4-methyl-1-pentene.

The polymerisation conditions employed in the process of the present invention can be, for example, any of the conditions used in the well-known Phillips polymerisation processes described, for example, in UK patent specifications 790195; 804641; 853414; 886784; and 899156.

Preferably the polymerisation conditions are the so called "particle form" process conditions.

In the "particle form" process the monomeric 1 -olefin is contacted with a suspension or a fluidised bed of the catalyst particles in a fluid medium under conditions such that the polymeric 1-olefin forms as solid particles suspended in orfluidised in the fluid medium.

The fluid medium employed in particle form processs conditions can be a liquid or a gas.

Preferably it is a liquid. Examples of suitable liquid media are hydrocarbons which are chemically inert and non-deleterious to the modified catalyst under the reaction conditions. Preferred liquid media are paraffins or cycloparaffins having from 3-30 carbon atoms per molecule, for example isopentane, isobutane, cyclohexane, most preferably the liquid medium is isobutane.

When a liquid medium is employed in the process of the present invention preferably the concentration of monomer therein is in the range 2-20 wt % although concentrations outside this range can be employed if desired.

When the process of the present invention is under particle form process conditions the polymerisation temperature is preferably in the range 50 to 1 120C, most preferably 80 to 1 080C.

The polymerisation pressure is preferably in the range 2 to 100 bar when the fluid medium is a liquid and 1 to 60 bar when the fluid medium is a gas. The residence or reaction time can vary from a few minutes to several hours and is generally in the range 1 5 minutes to 3 hours. The particle form process can be conducted under batch or continuous polymerisation conditions.

Preferably the conditions are continuous. Preferred apparatus for conducting the reaction under continuous conditions in a liquid medium is described in UK patent specification 899156.

For further details of examples of solution form and particle form process conditions and apparatus which can suitably be employed in the process of the present invention, reference may be made to UK patent specification Nos: 790195, 804641, 899156, 886784 and 853414.

If desired, the polymerisation process can be conducted in the presence of hydrogen gas to increase the melt index of the produced polymer. In general, the higher the partial pressure of hydrogen in the reaction zone, the lower becomes the molecular weight of the produced polymer.

The invention is illustrated by the following Examples wherein Test X is by way of comparison and Examples 1-4 are according to the present invention.

COMPARATIVE TEST X AND EXAMPLES 1-4 (a) Catalyst Preparation Davison 951 silica (33 g), dried overnight at 1500C and 18" Hg vacuum, was slurried in 40-60 petroleum ether (150 ml). Titanium tetraisopropylate (8.2 g, 8.6 ml) was added and the petroleum ether distilled off in a rotary evaporator. The solid product was further dried at 1 500C and 18" Hg vacuum for 2 hours, before being calcined at 7500C for 5 hours in a bed fluidised with 900 ml/min of dry air. This calcined solid was then slurried in petroleum ether (1 50 ml) and impregnated with approximately 1% by weight chromium as t-butyl chromate.The petroleum ether was removed in a rotary evaporator followed by oven drying for 2 hours at 1 500C and 18" Hg vacuum. The resulting chromium impregnated solid was then activated by heating at 4750C for 5 hours in a bed fluidised with 900 ml/min of dry air. The activated catalyst was kept stored under nitrogen. Analysis showed that it contained 1.11% by weight Cr, 1.08% by weight CrV' and 3.52% by weight Ti.

(b) Polymerisation Polymerisations were carried out in a 2.3 litre stainless steel stirred autoclave. The reactor was purged with nitrogen, baked out for 2 hours at 1 1 OOC, then cooled to the required polymerisation temperature. The catalyst prepared as described above was charged to the reactor followed by 1 litre of dry isobutane containing between 0--0.2 ml of a 10% solution of an alkylaluminium modifier in n-hexane. In test X, no alkylaluminium modifier was added.

The reactor was maintained at the required polymerisation temperature and ethylene was added to bring the total pressure inside the reactor to 41.4 bar. Ethylene was then added continuously throughout the reaction to maintain this pressure. Polymerisation and polymer property data are given in Table 1.

The Kd value is determined by a method similar to that given in Sabia, R J Appl Polymer Sci 1963, 7,347. Kd is a measure of shear response of the polymer and, generally, Kd increases with breadth of polymer molecular weight distribution. Ml216 is the melt index measured by the method of ASTM 1238 using a 21.6 kg load. The units are grammes/10 minutes.

It can be seen that in all the Examples according to the present invention, the modified catalyst has higher activity than in Test X wherein no aluminium alkyl modifier was employed. TABLE 1

Polymerisation Polymer Properties Catalyst Example Weight Temp Time Yield Acitivity Density No. (g) Alkyl C (mins) (g) (kg/kgh) Ml2.16 Ml21.6 MlR Kd (kg/m ) Test X 0.352 None 98 60 300 852 0.260 22.9 88.1 7.6 955 1 0.930 TEA 98 35 426 1873 0.097 11.00 113.4 10.0 957 2 0.383 TEA 104 40 430 1684 0.303 27.5 90.8 6.9 960 3 0.354 IA 98 43 502 1979 0.116 12.8 110.4 8.8 958 4 0.361 IA 102 38 446 1951 0.310 20.5 66.1 8.0 958 Alkyls: TEA Triethylaluminium (40 mg TEA/g Catalyst) IA Isoprenylaluminium (40 mg lA/g Catalyst)

Claims (23)

1. A modified polymerisation catalyst prepared under substantially anhydrous conditions by a process comprising: (A) heating together at a temperature in the range 300-1 2000C a refractory oxide support material having surface hydroxyl groups and a titanium compound which reacts with the said hydroxyl groups of the support material under the heating conditions, (B) impregnating the product from (A) with an anhydrous chromium compound which is chromium oxide or a compound calcinable thereto, and heating the impregnated material at a temperature in the range 250 to 1 2000C to produce an active polymerisation catalyst, (C) forming the modified polymerisation catalyst by adding to the active polymerisation catalyst obtained from step (B) one or more organometallic or organoboron compounds having the general formula MR2pYqp wherein M is an atom of groups 1 A, 2A, 2B or 3A of the Periodic Table (Mendeleef), R2 is a hydrocarbon group containing 1 to 10 carbon atoms, Y is hydrogen, halogen or alkoxide, q is the valency of M, p is an integer from 1 to q inclusive and when the organometallic or organoboron compound contains more than one R2 or Y group they may be the same or different.

2. A modified polymerisation catalyst as claimed in claim 1 wherein the support material employed is silica.

3. A modified polymerisation catalyst as claimed in any preceding claim wherein the support material employed is itself the product of heating at a temperature in the range 300-1 2000C a refractory oxide support material having surface hydroxyl groups with titanium compound capable of reacting therewith, treating the product with a volatile hydroxyl groups -- containing compound and removing and residual volatile hydroxyl groups containing compound.

4. A modified polymerisation catalyst as claimed in any preceding claim wherein the titanium compound or compounds employed and selected from one or more of the following; titanium oxychioride (TiOCL2); titanium acetyl acetonate compounds; alkanolamine titanates; titanium 7 X bonded complexes; and compounds having the general formula Ti(OR)mXn, wherein m + n is 4, m is zero or an integer from 1 to 4, R is an organic hydrocarbon group.

5. A modified polymerisation catalyst as claimed in any preceding claim wherein the titanium compound is titanium tetraisopropylate or titanium tetraethylate.

6. A modified polymerisation catalyst as claimed in any preceding claim wherein the quantity of titanium compound employed is sufficient to give a titanium concentration (derived from said titanium compound) in the support material in the range 0.5 to 5.0 wt % based on the weight of solid product from step (A).

7. A modified polymerisation catalyst as claimed in any preceding claim wherein the heating in step (A) is carried out at a temperature in the range 400-1 0000C.

8. A modified polymerisation catalyst as claimed in any preceding claim wherein the heating step (A) is carried out at a temperature in the range 500--9000C.

9. A modified polymerisation catalyst as claimed in any preceding claim wherein the anhydrous chromium compound is ditertiarybutyl chromate.

10. A modified polymerisation catalyst as claimed in any preceding claim where the heating in step (B) is carried out at a temperature in the range 400--9000C.

11. A modified polymerisation catalyst as claimed in any preceding claim wherein the heating temperature employed in step (A) is higher than that employed in step (B).

12. A modified polymerisation catalyst as claimed in any preceding claim wherein the organometallic compound is selected from one or more of dibutyl magnesium, triethyl boron, triethyl aluminium, triisobutyl aluminium.

1 3. A modified polymerisation catalyst as claimed in any preceding claim wherein the quantity of organometallic compound employed is 1 to 10% based on the total weight of catalyst.

14. A modified polymerisation catalyst as claimed in any of the preceding claims wherein the catalyst is further modified by adding a polyene compound during, or subsequent to the performance of step (C).

1 5. A modified polymerisation catalyst as claimed in claim 14 wherein the polyene is a Ca to C20 conjugated or non-conjugated polyene.

1 6. A modified polymerisation catalyst as claimed in claim 14 or 1 5 wherein the polyene contains 2 double bonds.

17. A modified polymerisation catalyst substantially as hereinbefore described in the Examples.

1 8. A process for polymerising monomeric 1-olefin by contacting said 1-olefin with the modified polymerisation catalyst claimed in any of claims 1-1 7 under polymerisation conditions.

1 9. A process as claimed in claim 1 8 wherein the monomeric 1 -olefin is ethylene or a mixture of ethylene with one or more other comonomer 1-olefins.

20. A process as claimed in claim 1 8 or 1 9 wherein the polymerisation conditions comprise the use of a fluid medium to suspend or fluidise particles of the modified catalyst under conditions such that the produced polymeric 1 -olefin forms as solid particles suspended in or fluidised by said fluid medium.

21. A process as claimed in claim 20 wherein the fluid medium is liquid isobutane.

22. A process as claimed in claim 20 wherein the fluid medium is a gas.

23. Polyolefins prepared by the process claimed in any of claims 1 8-22.