FI93367B - Process for treating a spherical catalyst used in the polymerization of olefins, use of the obtained catalyst in olefinic polymerization - 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

93367

Process for treating a spherical catalyst used in the polymerization of olefins, use of the obtained catalyst in the polymerization of olefins

The invention relates to a process for the treatment of spherical catalysts used in the polymerization of olefins, by means of which the catalyst can retain its spherical structure during the polymerization. The process prepolymerizes ethylene (as ethylene also refers to mixtures of ethylene and olefins) to a stage of underdevelopment, the so-called spheroprotectant, which has a sphericity-maintaining effect consisting mainly of a specific halogenated alkylaluminum and is added to the other components at the latest. Such a modified catalyst is particularly well suited for the production of spherical linear polyethylene.

In the preparation of spherical linear polyethylenes: ethylene homopolymers and ethylene-alpha-olefin copolymers, spherical catalysts based on transition metals, in particular titanium, have been commonly used. However, under the conditions under which industrial polymerization takes place, the sphericity of the catalyst is soon destroyed. The spherical particles soon break into vaguely shaped bodies, for example granular ones, resulting in more or less granular polymers with poor flow properties (which is related to the more or less spherical shape of the resulting polymer.) Such polymers also have many very fine particles below. 100 microns, which pose safety risks and complicates the manufacturing process.

The process according to the invention, in which the spherical structure of the catalyst is preserved during the polymerization of the olefin or olefins, confirming the principle that the polymers formed are copies of the catalyst structure, provides a prepolymerization catalyst. polyethylene. So far, the spherical shape has been defined only subjectively.

Using a non-exhaustive definition, polyethylene powder is spherically structured when the particles of the powder are, on average, clearly spherical, symmetrical, non-flattened and smooth at magnification under microscopy at magnification 20. This assessment seems to be confirmed by experimental analysis experiments performed by J.K. BEDDOW, Fine Particle Research Group, Chemical and Materials Engineering, University of Iowa, Proceedings of the ACS Division of Polymeric Materials: Science and Engineering, Volume 53, Fall Meeting 1985 - Chicago, pp. 261-262. Process for the treatment of a spherical catalyst for the polymerization of olefins 3 93367 is characterized in that in the presence of said catalyst a prepolymerization is carried out in the presence of a cocatalyst selected from alkylalumines, at least partially in suspension, halogenated in the form is incorporated into the components at the latest after prepolymerization.

The essential features of the invention are set out in the appended claims.

When all the components required for a spheroprotector are added, it can be written in the form: AI R'm R "n Clp Hq where 0.05 <psl 0 <m <2.95 0 <n <2.95 0 sgs 1 assuming that m + n + p + q = 3 and R 'and R ", identical or different, are linear, branched or cyclic hydrocarbon radicals having 1 to 14 carbon atoms.

Thus, a spheroprotectant as defined above may be monohalogenated alkylaluminum, but preferably it should be a mixture of two alkylaluminum, one being non-halogenated alkylaluminum and the other monohalogenated alkylaluminum; it may, of course, be a mixture of one or more non-halogenated alkylaluminum or a mixture of one or more monohalogenated alkylaluminum. The alkyl radicals of both 4,9367 small aluminum compounds can be freely selected from the above-mentioned radicals. It is prepared by mixing two compounds under known conditions suitable for the complex handling of these products under conditions such that the given equation is followed. A liquid mixture is obtained.

The alkylalumines used in the preparation of the sphere portector are known per se and are selected from the group whose members are commonly used as cocatalysts. They correspond to the general formulas AI R, Hj, x + z = 3 and AI Rx Cly Hz, x + y + z = 3 and in which R represents a linear, branched or cyclic hydrocarbon having 1 to 14 carbon atoms. Examples which may be mentioned are: A1 (C4H9) 3, A1 (C4H9) 2H, A1 (C2H5) 3, AKCft), AKQHpij, A1 (C2H5) 2H and A1 (C2H5) 2Cl, Al (C6H13) 2Cl, A1C1 (QHgisoJj.

The prepolymer obtained according to the process is used as a catalyst in polymerization processes carried out in suspension and in the gas phase, either on a mobile support or on a liquefied support. According to the polymerization process, the prepolymerization carried out in the presence of a catalyst should be more or less enhanced. When the prepolymer is used in the suspension process, the degree of prepolymerization should preferably be less than 100, while in the gas phase process the degree of prepolymerization should preferably be more than 50 and such that the resulting prepolymer constitutes no more than 10% by weight of the final polymer.

A spherical initial catalyst for the polymerization of olefins is a product known per se. It is usually the result of combining at least one transition metal, a magnesium compound, a halogen and possibly an electron donor or acceptor, or any compound used in this type of catalyst.

The transition metal compound is generally selected from the group consisting of compounds of formula Me (OR) Xm-n, wherein - Me is vanadium, chromium and especially titanium; - X is bromine, iodine and in particular chlorine; - R is an aliphatic or aromatic C1-C3 * hydrocarbon radical or COR 'and R * is an aliphatic or aromatic C1-Cx * hydrocarbon radical - "m" corresponds to the valence of the transition metal and "n" is less than or equal to "m ".

A particularly preferred transition metal may be selected from the group consisting of titanium compounds of formula Ti (0R), * Cl * -, *, R being the same as defined above and x being 0-4.

The magnesium compound is usually selected from the group consisting of compounds of formula Mg (OR) «X & -n, wherein X is bromine, iodine and especially chlorine, R is hydrogen or an alkyl or cycloalkyl radical and" n "is less than or equal to than 2.

6 93367

The electron donor or acceptor is an organic liquid or solid compound known to be suitable for the composition of these catalysts. The electron donor may be mono- or polyfunctional, preferably selected from the group consisting of aliphatic or aromatic carboxylic acids or their alkyl esters, aliphatic or cyclic ethers, ketones, vinyl esters, acrylic derivatives, especially alkyl acrylates or methacrylates. Suitable electron donors are, in particular, compounds such as methyl paratoluate, ethyl benzoate, ethyl or butyl acetate, ethyl ether, ethyl paranisate, dibutyl phthalate, dioctyl phthalate, diisobutyl phthalate, tetrahydrofuran, dioxobutane, isethone, acetone, methyl methacrylate and silanes such as phenyltriethoxysilane and aromatic or aliphatic alkoxysilanes.

The electron acceptor is a Lewis acid, preferably selected from the group consisting of aluminum chlorides, boron trifluoride, chloranil or also alkylaluminum or alkylmagnesium.

In the prepolymerization carried out in the preferred suspension, with stirring in a turbulence reactor, the ethylene is prepolymerized, optionally with a chain limiter and / or a cocatalyst selected for this purpose from the alkylalumines used in the presence of alkylalumines used. At 0-110 ° C, preferably 20-60 ° C, the total pressure is less than 20 absolute bars, derived mainly from an inert gas such as nitrogen. In order to preserve the original spherical structure of the catalyst as well as possible, it is recommended to control the feed of the monomer in the reactor. A suitable average feed rate is less than or equal to 500 N 1 x h-1 x g-1 catalyst. The prepolymerization as a suspension is continued until the degree of prepolymerization is suitable for subsequent polymerization, the degree of prepolymerization being defined as the ratio of the sum of the weight of prepolymer formed plus the weight of catalyst used to the weight of catalyst used.

At any stage of the prepolymerization, a spheroprotectant is added to the components. A spheroprotectant can be added to the prepolymerization reaction medium. It can also be added to the prepolymer after prepolymerization, either directly to the reaction medium or as a suspension or to a prepolymer stored dry in an inert gas.

In another preferred prepolymerization as a suspension with stirring in a turbulence reactor, the prepolymerization is carried out under the conditions described above to a low degree of prepolymerization, preferably less than 20 g of polymer per gram of catalyst.

At this point, the prepolymer is isolated and introduced into the prepolymerization system in the gas phase so that the low degree of polymerization becomes a suitable degree of prepolymerization for subsequent polymerization.

Said prepolymerization in the gas phase is carried out under the conditions of the polymerization of ethylene in the usual gas phase. For example, in the reactor, a deficient prepolymer may be combined with a polyolefin charge having a grain size of less than or equal to 3,000, preferably less than or equal to 1,000 microns, preferably in the presence of a cocatalyst as defined above. After homogenization, the prepolymerization is continued by adding a monomer, preferably ethylene or a mixture of ethylene and butene. Preferably, the prepolymerization in the gas phase is carried out at a temperature of 30-110 eC with a total pressure of less than or equal to 20 bar.

The prepolymerization in the gas phase is continued until a suitable prepolymerization degree is reached for subsequent polymerization. In order to preserve the original spherical structure of the catalyst as well as possible, it is recommended to control the supply of monomer to the reactor. The most suitable average feed rate is less than or equal to 500 N 1 x h-1 x g-x catalyst.

As above, the spheroprotectant can be added at any stage of the prepolymerization or also added to the prepolymer stored in an inert gas after the prepolymerization> 93 μM. When the spheroprotectant is added to the prepolymer after prepolymerization, it is carried out in an inert atmosphere, either with a mixture in which the prepolymer is suspended in an inert liquid or by impregnating the prepolymer powder.

The spheroprotectant is combined in a calculated ratio, preferably 500-4000 ppm aluminum per 1000-2500 ppm catalyst for subsequent polymerization in a prepolymer in a suitable prepolymerization step. The weight ratio of aluminum to catalyst is between 30.10 ~ ® - 4.

If a chain limiter is used in the prepolymerization, hydrogen is preferably selected.

The prepolymer prepared according to the invention is generally kept dry for later use as a catalyst for polymerization in suspension or in the gas phase in the preparation of a linear polyethylene powder having a spherical structure. This catalyst, a spherical prepolymer, retains its shape during polymerization and this property gives linear polyethylenes which are also spherical in shape.

The catalyst treated according to the invention is used as conventional catalysts in olefin suspension or gas phase polymerization processes. Although it can be used as is if desired, some cocatalyst can be added to the reaction medium to increase its productivity. In that case, the cocatalyst may be a spheroprotectant and preferably a spheroprotectant used in the preparation of the prepolymer.

The polymerization of ethylene in suspension is generally carried out in a hydrocarbonated liquid environment, with a maximum temperature of 120 ° C and a pressure of 250 bar.

The polymerization of ethylene in the gas phase, in the presence of hydrogen and an inert gas, can be carried out in any reactor in which the polymerization can be carried out in the gas phase and in particular in a reactor with a mobile support or a liquefied support. The starting conditions are familiar to a person skilled in the art. The temperature is generally kept below the boiling point (Tf) of the polymer or copolymer to be synthesized, and in particular between 20 ° C and (Tf -5 ° C), such that ethylene and possibly other hydrocarbon monomers in the reactor are mainly in the gas phase.

The following examples illustrate the invention without, however, limiting it.

The spherical catalyst treated according to the invention has been prepared in advance under the following conditions.

After drying and purification under nitrogen, 200 ml of dry 11,9367 magnesium n-butylbutyl and 33 mM triethylaluminum, each as a molar solution in heptane, are placed in a glass 1.5 L reactor equipped with a stirrer. Allow to react for 1 hour at 80 ° C. Then, with stirring, 200 mM diisoamyl ether at 50 [deg.] C. and, after 2 hours, still at 50 [deg.] C., 550 mM tert-butyl chloride are added. Filter and wash the solid which forms the medium twice with 400 cm3 of heptane at 50 ° C.

The solid is suspended in 400 cm3 of heptane at 80 ° C and 600 mM TiCl 3 is added over 1 hour. The catalyst obtained is filtered off and washed twice with 400 cm3 of heptane. The catalyst is dried at 70 ° C under nitrogen and stored in an inert atmosphere. This solid catalyst is particulate, the particles are perfectly round and have an average diameter of about 30 microns.

Example 1 An 8.2 L degassed and dried reactor is charged with nitrogen and stirring at 400 rpm successively at 40 ° C: 3 l of dry hexane 6 mM pure trihexylaluminum (THA) 3 g of the above spherical catalyst suspended in 75 cm3 of hexane 0.8 absolute bar of hydrogen 4 absolute bar of nitrogen and then: 12 93367 ethylene 30 N 1 / h for 1 hour, then 60 N 1 / h for 1 hour, 130 N 1 / h 2 for one hour and finally 200 N 1 / h for 50 minutes.

Stop the addition of ethylene, the total pressure drops from 6 absolute bar to 5 absolute bar in 5 minutes. Stirring is stopped to allow decantation and removal of the supernatant. After removal of the remaining solvent at 50 ° C under nitrogen, the prepolymer powder in an inert atmosphere is extracted.

650 g of a dry, spherical, non-agglomerated prepolymer powder with a prepolymerization degree of 218 g of prepolymer per gram of catalyst with a mean particle diameter of 280 microns are obtained.

Preparation of spheroprotectors and catalyst in the form of an active prepolymer

A Schlenk tube is placed and mixed, protected from light, under a nitrogen purge, with pure alkylaluminum and monochlorinated alkylaluminum in the molar ratios given for each experiment in Table I below.

The complexes thus prepared are added dropwise to said prepolymer powder with stirring and in an inert atmosphere. The amount added is such that the concentration of aluminum in the prepolymer is 2000 ppm.

13 93367

Copolymerization of butene-1 and ethylene Using a 8.2 l reactor pre-dried in the presence of 100 g of polyethylene, a reactor rotating at 400 rpm and maintaining the temperature at 85 ° C throughout the polymerization is used.

In a reactor maintained under vacuum, about 1.33 Pa, butene-1 is first injected until a pressure of about 1 bar is reached, then a certain amount of a spheroprotector similar to that used in the preparation of the prepolymer according to the invention is used as a cocatalyst. . The injection of butene-1 is continued until a pressure of 2.5 bar is reached. 1.5 reactants of hydrogen and 13 bar of ethylene are then injected successively into the reactor until hydrogen and ethylene partial pressures of 1.5 and 13 bar are obtained.

Next, x g (amounts given in Table I) of the active prepolymer prepared above are added to the reactor; the addition is carried out under nitrogen boosting and then nitrogen is injected until the total pressure inside the reactor is 21 bar. The pressure is maintained at this reading by injecting ethylene and butene-1 in a molar ratio of butene-1 / ethylene = 0.0466.

After 4 hours, the polymerization reaction is stopped by reducing the pressure in the reactor. Purify with nitrogen and allow to cool.

93367 14

The missing operating conditions and the results of the control experiments performed on linear ethylene are shown in Table I below. Experiments 1,2,7,8,9 and 10 are included for comparison.

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Example 2 16 93367 An 8 L degassed and dried reactor is charged with 3 liters of dry hexane 10 mM trihexylaluminum (THA) 30 mM monochlorinated diethylaluminum (330 L / min) at 40 ° C with stirring at 330 rpm. DEAC) 10 cm3 of a suspension containing 88 g / l of the spherical catalyst described above, i.e. 0.88 g of catalyst 0.5 bar of hydrogen

A mixture of ethylene and butene with 1.6 mol% butene, 30 N 1 / h is added for 15 minutes, and then the same mixture of 40 N 1 / h is added for 3 hours 15 minutes.

The addition of monomers is stopped. Stirring is stopped to allow decantation and removal of the supernatant. After removal of the remaining solvent at 50 ° C under nitrogen, the prepolymer powder stored under an inert atmosphere is extracted.

235 g of a dry prepolymer powder having a spherical structure, without agglomeration, with a degree of polymerization of 267 g of prepolymer per gram of catalyst, with a mean particle diameter of 283 microns, are obtained. The aluminum content of the prepolymer is of the order of 1000 ppm.

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

17 93367

The missing operating conditions and the results of the control experiments performed on linear ethylene are shown in Table II below.

TABLE II

18 93367

Weight of active prepolymer in g 10

Catalyst weight in g 0.037

Nature of the spheroprotector THA / DEAC

The molar ratio of monochlorinated alkyl Al / reactor added to the reactor is 8.5

alkyl Al

Amount of THA / DEAC added to the reactor 0.15 molar ratio of THA / DEAC in the prepolymer cm3 of pure

The density of the obtained polyethylene was 0.919% of the particles <200 microns 0.2

Appearance spherical

Flow capacity in seconds 28

Yield g / 4 hours 740

Yield g polyethylene / g catalyst 20,000

Example 3 19 91167

Preparation of active prepolymer In an 8.2 l reactor equipped with a stirrer, nitrogen is placed at 50 ° C: 3 l of dried and nitrogen-purified hexane 29 mM tri-n-hexylaluminum 40 mM diethylaluminum chloride 3 bar nitrogen

46 g of catalyst are injected into the reactor as a suspension in 0.5 l of hexane. Then successively add: 0.5 bar of hydrogen 100 N 1 / h ethylene for 1 hour 200 N 1 / h ethylene for 1 hour.

The product formed is dried under nitrogen to give 387 g of a fortified catalyst with a development of 8.4 g of PE / g of catalyst.

In a nitrogen atmosphere, 20 g of fortified catalyst, 100 g of polyethylene powder and a mixture of 3 millimoles of DEAC and 9 millimoles of THA are mixed very well under a nitrogen atmosphere.

The mixture is placed under nitrogen in a polymerization reactor having a volume of 8.2 l, previously dried and degassed and equipped with a stirrer.

Add successively at 50 ° C: 4 bar nitrogen 20 93367 0.8 bar hydrogen 50 N 1 / h ethylene for 30 minutes 100 N 1 / h ethylene for 3 hours

483 g of powder are obtained, of which 383 g is a prepolymer with a prepolymerization degree of 158 g PE / g catalyst.

Copolymerization of Butene-1 and Ethylene The prepolymer prepared under the polymerization conditions of Example 1 is used.

The operating conditions and the results of the control experiments performed on linear polyethylene are given in Table III below.

TABLE III

21 93367

Weight of active prepolymer in g 5

Catalyst weight in g 0.031

Nature of the spheroprotector THA / DEAC

The molar ratio of monochlorinated alkyl Al / reactor added to the reactor is 8.5

alkyl Al

Amount of THA / DEAC added to the reactor 0.3 molar ratio of THA / DEAC in the prepolymer cma pure

The resulting polyethylene had a density of 0.920% of the particles <200 microns 0.6

Appearance spherical

Flow capacity in seconds 30

Yield g / 4 hours 1162

Yield g polyethylene / g catalyst 37480

Claims (11)

22 93367 A process for treating a spherical catalyst used in the polymerization of olefins, which catalyst contains at least one transition metal, one magnesium compound and one halogen, characterized in that in the presence of a spherical catalyst the prepolymerization is prepolymerized, at least suitable for polymerization in which the prepolymer is subsequently used; at the latest after prepolymerization, a spherical protector consisting of monohalogenated alkylaluminum and / or non-halogenated alkylaluminum is added to the various components, said spheroprotectant having the form: AI R'm R "n Clp Hq where 0.05 <ps 1 0 <m < 2.95 0 <n <2.95 0. qs 1 provided that m + n + p + q = 3 and R 'and R ", identical or different, are linear, branched or cyclic hydrocarbon radicals having 1-14 carbon atoms. Process according to Claim 1, characterized in that the spheroprotectant is the result of a mixture of at least one non-halogenated alkylaluminum and at least one monohalogenated alkylaluminum. Process according to Claim 1 or 2, characterized in that the prepolymerization is carried out in suspension until a low degree of polymerization is reached and that the prepolymer formed in the gas-phase prepolymerization system is treated and brought to a degree of prepolymerization suitable for subsequent polymerization. Process according to Claim 3, characterized in that the degree of failure is less than 10 g of polymer per gram of catalyst. Process according to one of Claims 1 to 4, characterized in that the degree of prepolymerization is less than 100 when the prepolymer is used as a catalyst for polymerization in suspension and more than 50 when polymerizing in the gas phase, in the latter case the prepolymer constitutes more than 10% of the final polymer. Process according to one of Claims 1 to 5, characterized in that the monomer is reacted in the gas phase prepolymerization. in an amount less than or equal to 500 N 1 / h x h1 x g'1 spherical catalyst. Process according to one of Claims 1 to 6, characterized in that, in the prepolymerization in suspension, the monomer is introduced into the reactor in an amount less than or equal to 500 N 1 / h x h-1 x g'1 of a spherical catalyst. Process according to one of Claims 1 to 7, characterized in that the spheroprotectant is combined in a calculated ratio of 500 to 4000 ppm aluminum per 1000 to 25,000 ppm catalyst in a prepolymer having a suitable degree of prepolymerization for subsequent polymerization, in which the prepolymer is subsequently used. Process according to one of Claims 1 to 8, characterized in that the weight ratio of aluminum to catalyst is between 30.10.2 and 4. 2 24 93367 Process for the preparation of a spherical linear polyethylene powder in suspension or in the gas phase, characterized in that a catalyst prepared according to one of Claims 1 to 9 is used. Process according to Claim 10, characterized in that a cocatalyst selected from the group consisting of spheroprotectors is added to the reaction medium.