NO169776B - PROCEDURE FOR PREPARING A MODIFIED SPAERIC POLYMERIZATION CATALYST AND USING THE CATALYST - Google Patents

Abstract

Process for the treatment of a spherical catalyst for the polymerisation of olefins, containing at least one transition metal, a magnesium compound and a halogen, characterised in that ethylene is prepolymerised in the presence of the spherical catalyst, in the presence of a cocatalyst chosen from alkylaluminiums, at least partially in suspension, to a degree of prepolymerisation adapted to the polymerisation process in which the prepolymer will be subsequently used, a spheroprotector being used in combination with the various components not later than after the prepolymerisation, the accepted formula of the said spheroprotector being: AlR'mR''nClpHq in which 0.05 < p </= 1 0 < m < 2.95 0 < n < 2.95 0 </= q </= 1 it being known that m + n + p + q = 3 and R' and R'', which are identical or different, are linear, branched or cyclic hydrocarbon radicals containing from 1 to 14 carbon atoms. The catalyst thus treated conserves its spherical morphology in the subsequent polymerisation of ethylene. It is particularly suited for the manufacture of linear polyethylene powder with spherical morphology.

Description

The present invention relates to a method for the production of modified spherical olefin polymerization catalysts which enable the morphology to be maintained during the polymerization. The method consists in pre-polymerizing ethylene with the assumption that the term ethylene also means mixtures of ethylene and olefins, up to a certain reduced degree of production, with a product called ferroprotectant, with the intention of preserving the spherical character and essentially consisting of a specific halogenated alkyl aluminium, is combined with components at the latest after the pre-polymerisation. Such a modified catalyst is particularly suitable for the production of linear polyethylene in powder form with a spherical morphology.

The invention also relates to the use of a catalyst, prepared as above, in the production in suspension or gas phase of a linear, powdery polyethylene with a spherical morphology.

In order to produce linear spherical polymers: ethylene homopolymers and ethylene-α-olefin copolymers, it is known to use spherical catalysts based on transition metals and more particularly titanium. Under the industrial polymerization conditions, however, the spherical morphology of the catalyst is rapidly destroyed. The spherical particles are quickly destroyed into particles with ill-defined morphology of, for example, granular state, which leads to more or less granular polymers with poor flowability characteristics which are associated with the more or less spherical morphology of the obtained polymer. These polymers are also enriched in finely divided particulate material with a particle size below 100 µm, which leads to safety problems and entails difficulties in manufacturing.

The method according to the invention and according to which the catalyst's spherical morphology is retained during the polymerization of used olefins confirms the principle according to which the formed polymers are the catalyst's morphological replicator, leads to a prepolymer catalyst which, by polymerization in suspension or gas phase of ethylene or mixtures of ethylene and a- olefin allows to obtain a linear polyethylene in powder form in spherical morphology. This spherical morphology is then determined subjectively. Without wishing to be bound by any particular theory, it can be determined that a polyethylene powder has a spherical morphology when the powder particles in the medium and by optical microscopic examination are essentially spherical, symmetrical, without elongation and with a surface of the order of magnitude 20. This approximation method seems confirmed by the experimental analyzes reported by J.K.Beddow, Fine Particle Research Group., Chemical and Materials Engineering, University of Iowa in "Proceedings and the ACS Division of Polymeric Materials: Science and Engineering" vol. 53 Fall Meeting 1985 - Chicago pp. 261-262.

Accordingly, the present invention relates to a method for producing a modified spherical

polymerization catalyst for olefins containing at least one transition metal, a magnesium compound and a halogen, wherein, in the presence of the unmodified spherical catalyst and a cocatalyst selected from alkylaluminum compounds, at least partially in suspension, ethylene is prepolymerized to a degree of prepolymerization that is below 100 when the prepolymer is to is used as a catalyst in a suspension polymerization process and over 50 for a gas phase polymerization process without, in the latter case, the prepolymer representing more than 10% of the final polymer, and this method is characterized by the addition of a spheroprotector in the form of a halogenated alkyl aluminum with the formula:

there

where m+n+p+q=3

wherein R' and R'', the same or different, are linear, grafted or cyclic hydrocarbons containing 1 to 14 carbon atoms.

The sphere protector, as it is defined, can be a monohalogenated alkylaluminum but is preferably the result of a mixture of the two alkylaluminums, one non-halogenated aluminum and the other a monohalogenated alkylaluminum, as it may however be a mixture of one or more non-halogenated -halogenated alkyl aluminums and one or more monohalogenated alkyl aluminums. The alkyl residues in the two compounds of aluminum are chosen arbitrarily from those previously defined. It is prepared by mixing the two compounds under known conditions, adapted to the precise manipulation of the products in proportions that comply with the definition of the given formula. A liquid mixture is obtained.

These alkyl aluminums, which are used in the production of the sphere protector, are known per se and are selected from among those which are usually used as cocatalysts. They correspond to the general formula A1RX Hx and Al RxClyHz where x+zogx+y+z = 3 and where R means a linear, branched or cyclic

Cl_i4hydrocarbon residue. As an example, the following should be mentioned:

The prepolymer obtained according to the method of the invention is used as a catalyst in polymerization processes in suspension and in the gas phase, either in a fluidized bed or in a stirred bed. According to the intended polymerization process, the prepolymerization in the presence of the catalyst can be more or less encouraged. In the case where prepolymer is used as a catalyst in a suspension process, the degree of prepolymerization is preferably below 100, while the degree of prepolymerization for a gas phase process is preferably above 50 and so that the formed prepolymer represents at least 10% by weight of the final polymer.

The original spherical polymerization catalyst for the olefins is a product known per se. It is usually the result of the combination of at least one transition metal compound, a magnesium compound, a halogen and at least one electron donor or acceptor and any other compound that can be used in this type of catalyst.

The transition metal compound is usually selected from compounds of the formula Me(OR)nXm_n where: Me is vanadium, chromium and especially titanium; - X is bromine, iodine and especially chlorine;

R is an aliphatic or aromatic C 1-14 hydrocarbon residue or COR' where R' is an aliphatic or aromatic C 1-14 hydrocarbon residue;

"m" is the value of the transition metal and "n" is a value

below or equal to "m".

The transition metal compound that is particularly recommended is chosen from compounds of titanium with the formula Ti(OR)xCl4_x, R being as stated above, x being between 0 and 4.

The magnesium compound is usually chosen from compounds with the formula Mg(0R)nX2_n where X is bromine, iodine and especially chlorine; R is hydrogen or an alkyl or cycloalkyl radical and "n" is equal to or less than 2.

The electron donor or acceptor is a liquid or solid organic compound known to enter into mixtures in these catalysts. The electron donor can be a mono- or polyfunctional compound which is preferably chosen from among aliphatic or aromatic carboxylic acids or their alkyl esters, aliphatic or cyclic ethers, ketones, vinyl esters, acrylic derivatives and especially alkyl acrylates or methacrylates as well as silanes. In particular, as electron donors, compounds such as methyl paratoluate, ethyl benzoate, ethyl or butyl acetate, ethyl ether, ethyl paraanisate, dibutyl phthalate, dioctyl phthalate, diisobutyl phthalate, tetrahydrofuran, dioxane, acetone, methyl isobutyl ketone, vinyl acetate, methyl methacrylate and silanes such as phenyltriethoxysilane should be noted. aromatic or aliphatic alkoxysilanes.

The electron acceptors are a Lewis acid preferably chosen from aluminum chloride, boron trifluoride, chloranil or optionally alkyl aluminum and alkyl magnesium.

In a preferred method for prepolymerization in suspension under vigorous stirring, ethylene is prepolymerized, optionally in the presence of a chain interrupter and/or a cocatalyst selected from alkylaluminium, known for this application, at a temperature between 0 and 110°C and preferably between 20 and 60 ° C, for an absolute total pressure below 20 bar, essentially consisting of an inert gas such as nitrogen. In order to maximally preserve the original spherical morphology of the catalyst, it is recommended to control the supply of monomer to the reactor. An average feed rate that has proven favorable is below or equal to 500 NI x t"<1> x g"<1> catalyst in suspension is followed up until a degree of prepolymerization adapted to the later polymerization process, the degree of prepolymerization being defined by the ratio between the sum of the weight of the prepolymer plus the weight of catalyst used. At a suitable stage during the prepolymerization, the sphere protecting compounds are added. These can be introduced into the pre-polymerization reaction medium. It can also be advantageously added to the prepolymer after the prepolymerization, either directly to the reaction medium or to the prepolymer stored in suspension or in a dry state under inert gas.

In another preferred embodiment, the prepolymerization is carried out in suspension under vigorous stirring under the conditions described above until a reduced degree of progress for the prepolymerization, preferably below 20 g of polymer per grams of catalyst.

At this point, the prepolymer is isolated and then taken up in a gas phase prepolymerization system to bring the reduced rate of progress of the polymerization to the prepolymerization rates appropriate for the later polymerization.

This part of the gas-phase prepolymerization is carried out under normal conditions for ethylene polymerization in the gas phase. One can, for example, in a reactor combine the prepolymer with a reduced degree of progress with a polyolefin charge with an average granulometry below or equal to 3000 and preferably or equal to 100 µm, in the presence of preferably a cocatalyst as indicated above. After homogenization, the prepolymerization is followed by the introduction of monomer and preferably ethylene or a mixture of ethylene and butene. Preferably, the prepolymerization is carried out in the gas phase at a temperature between 30 and 110°C under a total pressure below or equal to 20 bar.

This prepolymerization in gas phase is continued until a prepolymerization gas is obtained which is adapted to the later polymerization process. After preserving the original spherical morphology as much as possible, it is recommended to control the supply of monomer to the reactor. A moderately favorable feed rate is below or at most 500 NI x l-<1> x g-<1> of the catalyst.

As before, the sphere protector can be introduced at any stage of the prepolymerization process or even added to stored prepolymer under inert gas after the prepolymerization. When the sphere protector is added to the prepolymer after prepolymerization, this takes place under an inert atmosphere, either by mixing the prepolymer in suspension in a liquid liquid or by impregnating the prepolymer powder.

This sphere protector is connected in a preferably proportion of 500 to 4000 ppm, calculated for aluminium, per 1,000 to 25,000 ppm catalyst in the prepolymer with a degree of prepolymerization adapted to the subsequent polymerization process. The indicated weight ratio between aluminum and catalyst is between 30 x 10~3 and 4.

Where a chain limiter is used during the pre-polymerisation, hydrogen is preferably chosen.

The prepolymer obtained according to the invention is usually stored in dry form in anticipation of later use as a polymerization catalyst in suspension or in gas phase for the production of linear polyethylene in powder form with spherical morphology. This catalyst, in the form of prepolymer with spherical morphology, preserves its morphology during the polymerization and, thanks to this property, allows linear polyethylenes which also have a spherical morphology to be obtained.

The catalyst treated according to the invention is used as a classic catalyst in suspension or gas phase polymerization processes of olefins. Although it can be used as such, it is not excluded, in order to control the productivity, in addition to allowing a cocatalyst in the reaction medium. In this case, the co-catalyst can be a spheroprotector and preferably the spheroprotector is used in the production of the prepolymer.

In a method for polymerization of ethylene in suspension, one usually works in a liquid hydrocarbon environment at temperatures that can range from 120°C and vacuum that can go up to 250 bar.

Polymerization of ethylene in gas phase and in the presence of hydrogen and inert gas can be carried out in any reactor that allows polymerization in gas phase and especially in a fluidized bed reactor or a reactor with a stirred bed. The conditions used are known in the art. One generally works at a temperature below the melting point Tf for the polymer or copolymer to be synthesized and more particularly between 20 and Tf - 5°C and under a pressure such that ethylene and possibly other hydrocarbon monomers present themselves in the reactor essentially in vapor phase.

The following examples illustrate the invention.

Preferably, the spherical catalyst which is treated according to the invention is produced under the conditions given below.

In a glass reactor with a volume of 1.5 1, equipped with a stirrer, introduce under nitrogen and after drying and rinsing, 200 mM n-butyl-butyl sec. magnesium and 33 mM triethylaluminum, both in molar solution in heptane. The substances are kept in contact for 1 hour at 80°C. 200 mM diisoamyl ether is then added with stirring at 50°C and then after 2 hours, still at 50°C, 550 mM tert-butyl chloride. The whole is filtered and the resulting solid, which constitutes a carrier, is washed twice with 400 m<3> of heptane at 50°C.

The solid is suspended in 400 cm<3> of heptane at 80°C and 600 mM TiCl4 is added over the course of 1 hour. The whole is filtered and the catalyst obtained is washed twice with 400 cm<3> of heptane. The catalyst is dried at 70°C under nitrogen and stored under an inert atmosphere. The solid catalyst is available in particle form with spherical granulometry and an average dimension of approx. 30 etc.

EXAMPLE

Preparation of the prepolymer

To a dry and degassed reactor of 8.2 1 is introduced under nitrogen and stirring at 400 rpm. successively and at 40°C

3 1 dry hexane

6 mM pure trihexylaluminum (THA)

3 g of spherical catalyst, taken in suspension in 75 cm<3>

hexane

0.8 has absolute hydrogen, as well

4 bar absolute nitrogen,

and then:

ethylene in an amount of 30 Nl/h for 1 hour followed by an amount of 60 Nl/h for 1 hour, an amount of 130 Nl/h for 2 hours and finally 200 Nl/h for 50 minutes.

The introduction of ethylene is stopped, the total pressure drops from 6 bar absolute to 5 bar absolute within 5 minutes. The stirring is stopped to settle and to evacuate the supernatant. After removing the remaining solvent at 50° C under nitrogen, the prepolymer powder is extracted and stored under an inert atmosphere. One recovers 650 g of dry prepolymer powder with spherical morphology, without agglomerates, with a prepolymerization degree of 218 g of prepolymer per grams of catalyst with a mean diameter for the particles, dp 50, equal to 280 ym.

Production of spherobesk<y>tters and catalyst in the form of active prepolymer

In a Schlenk tube, pure alkyl aluminum and a monochlorinated alkyl aluminum with a molar ratio are introduced and mixed in the absence of light, with stirring and nitrogen purging. for each sample as given in Table I below. The thus produced complexes are applied drop by drop to the previously mentioned powdery prepolymer which is stirred and which is kept under an inert atmosphere. The amount deposited is such that the concentration of aluminum on the prepolymer is 2000 ppm.

Copolymerization of butene-1 and ethylene

One works in a reactor of 8.2 1, dried in advance, in the presence of 100 polyethylene powder, equipped with a stirrer rotating at a speed of 400 rpm. and which is kept at 85° C during the polymerization. To the reactor, which is kept under a negative pressure of approx. 1.33 Pa, butene 1 is injected until a pressure of 1 bar is reached and then as a co-catalyst a certain volume, given for each analysis as indicated in table I below, of the sphere protector identical to that used in the production of the prepolymer according to the invention . The injection of butene-1 is completed in order to achieve a pressure of 2.5 bar. 1.5 bar of hydrogen and 13 bar of ethylene are then successively injected into the reactor until the partial pressure for hydrogen and ethylene of 1.5 and 13 bar respectively is reached.

One then introduces into the reactor x g (given in Table I) of the pre-produced active prepolymer by carrying out the supply under nitrogen pressure with subsequent blowing of nitrogen until the total pressure in the interior of the reactor reaches 21 bar. The pressure in the reactor is maintained at this value by injecting ethylene and butene-1 in a molar ratio of butene-1:ethylene equal to 0.0466.

After 4 hours of reaction, the polymerization is stopped by decompressing the reactor. The whole thing is flushed with nitrogen and allowed to cool.

The missing operating conditions and results from the checks that have been carried out on the obtained linear polyethylene are given in Table I, with examples 1, 2, 7, 8, 9 and 10 being comparative examples.

EXAMPLE 2

Into a dry and degassed reactor of 8.2 1, under nitrogen and stirring 330 rpm. successively at 40°C

3 1 dry hexane

. 10 mM THA

. 30 mM DEAC

. 10 cm<3> of a suspension of 88 g/l spherical prepolymer or 0.88 g of catalyst

. 0.5 has hydrogen

A mixture of ethylene and butene containing 1.6 mol-56 butene in a quantity of 30 Nl/h is then introduced over the course of 15 minutes and then over the course of 3 hours and 15 minutes. the same mixture in a quantity of 40 Nl/h.

Introduction of the monomers is stopped. Stirring is stopped to enable decantation and evacuation of the supernatant. After removing the remaining solvent at 50° C under nitrogen, the prepolymer powder is extracted and stored under an inert atmosphere.

235 g of dry prepolymer powder with spherical morphology and without agglomerates is recovered with a degree of prepolymerization of 267 g of prepolymer per grams of catalyst with a mean diameter for the particles, dp 50, of 283 pm. The prepolymer has an amount of aluminum in the order of 1000 ppm.

Under the conditions according to example 1, butene-1 and ethylene are polymerized in the presence of the obtained active prepolymer.

The missing operating conditions and the results of the checks carried out on the linear polyethylene obtained are given in Table II.

EXAMPLE 3

Production of active prepolymer

To an 8.2 1 reactor equipped with an agitator system, introduce at 50°C under nitrogen:

. 3 1 dry and degassed hexane under nitrogen

. 29 mM tri-n-hexyl aluminum

. 40 mM diethylaluminum chloride

. 3 has nitrogen

46 g of catalyst are injected into the reactor in the form of a suspension in 0.5 l of hexane. Then add:

. 0.5 bar hydrogen

. 100 Nl/h ethylene within 1 hour

. 200 Nl/h ethylene within 1 hour

The product formed is dried by stripping under nitrogen and 387 g of consolidated catalyst with a reaction degree of 8.4 g PE/g catalyst is recovered under nitrogen.

20 g of consolidated catalyst, 100 g of a polyethylene powder and a mixture of 3 mmol DEAC and 9 mmol THA are mixed in a suitable container under a nitrogen atmosphere.

This mixture is fed under nitrogen to a polymerization reactor of 8.2 1 which has previously been dried and degassed and equipped with an agitator.

Add successively at 50°C:

. 4 bar nitrogen

. 0.8 bar hydrogen

. 50 Nl/h ethylene within 30 minutes

. 100 Nl/h ethylene within 3 hours

483 g of powder is recovered in this way, of which 383 g is prepolymer with a degree of polymerization of 158 g PE/g catalyst.

Copolymerization of butene-1 and ethylene

The prepolymer obtained under the polymerization conditions specified in example 1 is used.

The operating conditions and the results obtained for the performed checks on the obtained linear polyethylene are given in the following table III.

Claims (8)

1. Process for the preparation of a modified spherical polymerization catalyst for olefins containing at least one transition metal, a magnesium compound and a halogen, wherein, in the presence of the unmodified spherical catalyst and a cocatalyst selected from the alkyl aluminum compound, at least partially in suspension, ethylene is prepolymerized to a degree of prepolymerization which is below 100 when the prepolymer is to be used as a catalyst in a suspension polymerization process and above 50 for a gas phase polymerization process without, in the latter case, the prepolymer representing more than 10% of the final polymer, characterized in that during or after the prepolymerization a sphere protector in the form of a halogenated alkyl aluminum with the formula: there where m+n+p+q=3 wherein R' and R'', the same or different, are linear, grafted or cyclic hydrocarbons containing 1 to 14 carbon atoms. 2. Method according to claim 1, characterized in that the sphere protector is obtained by a mixture of at least one non-halogenated alkyl aluminum with at least one monohalogenated alkyl aluminum. 3. Method according to claim 1, characterized in that the degree of development of the polymerization is below 10 g of polymer per grams of catalyst. 4. Process according to any one of claims 1 to 3, characterized in that the monomer is introduced to the reactor during the prepolymerization in the gas phase in an amount equal to or less than 500 NI/t/g of spherical catalyst. 5. Method according to any one of claims 1 to 4, characterized in that the monomers during prepolymerization in suspension are introduced into the reactor in an amount equal to or less than 500 Nl/t/g of spherical catalyst. 6. Method according to any one of claims 1 to 5, characterized in that the sphere protector is added in a proportion of 500 to 4000 ppm, calculated for aluminium, per 1000 to 25000 ppm catalyst in the prepolymer. 7. A method according to any one of claims 1 to 6, characterized in that the weight ratio between aluminum and catalyst is between 30.IO"<3> and 4. 8. Use of a catalyst, prepared as indicated above, optionally with an added co-catalyst, for the production in suspension or gas phase of linear, powdery polyethylene with spherical morphology.