CS232750B2 - Method of treated precursor preparation suitable as a catalytic system's component for homopolymer and copolymer production of ethylene with high density - Google Patents

Abstract

Modified catalyst component precursor for ethylene polymerization and copolymerization obtained by modifying the halide-based precursor magnesium, titanium compounds and electron donors compound mixed with inert carrier with a halide compound boron chloride, e.g. ethyl borohydride. Own catalyst with from the modified precursor by activation organoaluminum compound.

Description

The invention relates to a process for preparing a modified precursor suitable as a component of a catalytic system for the production of high density homopolymers and copolymers. Using the catalyst component precursor prepared according to the invention, it is possible to obtain polymers having a high melt flow index and a low melt flow rate ratio (defined below). The polymers have a density of about 940 kg / m ³ to about 970 kg / m ³ , a melt index greater than 1.0 g / 10 min. and up to about 100 g / 10 min. and a melt flow rate ratio in the range of about 22 to about 32 and are prepared by the low pressure gas phase process.

High density, high melt index ethylene homopolymers and copolymers can be prepared as described in European Patent Application Publication Nos. 0 012 147 and 0 012 148. High polymerization temperatures need to be used to produce these polymers and maintain a high hydrogen / hydrogen ratio in the reactor. ethylene to obtain polymers with a melt index greater than 1.0 g / 10 min. Unfortunately, however, it has been found that both raising the polymerization temperature above 90 ° C and using high hydrogen / ethylene ratios results in a decrease in the activity of the catalysts used in these processes. Thus, the desired polymers can only be obtained at the cost of reduced catalyst activity.

Another feature of the process described in European Patent Applications Nos. 0.0121-47 and 0.022 148 is that it undergoes to some extent undesirable hydrogenation of ethylene during polymerization. Hydrogenation of ethylene is particularly pronounced when temperatures above 90 ° C and high hydrogen / ethylene ratios are used to obtain polymers with an index of melt flow rates greater than 1.0 g / 10 minutes. Although the amount of ethane produced by this hydrogenation is initially relatively small, this gaseous product gradually builds up in the reactor and replaces the reactive monomers present therein. A decrease in the amount of monomer in the reactor results in a corresponding decrease in catalyst productivity.

It has now been found in the context of the invention that a catalyst composition with improved thermal stability suitable for use in the production of high density ethylene polymers, high melt index and low melt flow rate ratio by a low pressure gas phase process can be produced by: the catalyst precursor is prepared from a magnesium compound, a titanium compound, and an electron donor compound, the precursor is diluted with an inert carrier and the diluted precursor thus obtained is treated with a boron halide compound, followed by activation of the organoaluminum compound. This catalyst can be used to produce the above-described ethylene polymers at higher temperatures than hitherto possible, while maintaining high polymer productivity and a low range of ethylene accompanying hydrogenation.

SUMMARY OF THE INVENTION The present invention provides a process for preparing a precursor suitable as a catalyst system component for the production of high density ethylene homopolymers and copolymers at pressures below 6.87 MPa, accompanied by a small range of ethylene hydrogenation in which

A. prepare a precursor of the formula Mg _m Ti (QR) _n Xp [ED] _q wherein m is 0.5 to 56, n is 0, 1 or 2, p is 2 to 116, q is 2 to 85 ,

R represents an aliphatic or aromatic hydrocarbon radical having 1 to 14 carbon atoms or a radical of formula

COR 'where

R ‘represents an aliphatic or atomatic hydrocarbon radical containing from 1 to 14 carbon atoms,

X is chlorine, bromine, iodine, or a mixture thereof, and

ED is an organic electron donor compound selected from the group consisting of alkyl esters of aliphatic and aromatic carboxylic acids aliphatic ethers, cyclic ethers and aliphatic ketones by dissolving at least one magnesium compound and at least one titanium compound in at least one liquid organic electron donor compound to form a precursor solution in the electron donor compound; the magnesium compound used is a compound of the formula

MgXs where

X is chlorine, thunder, iodine, or a mixture thereof, and the titanium compound used is a compound of the formula

Ti (ORj _and X _b where

R and X are as defined above, and is 0, 1 or 2, and b is 1 to 4, inclusive, wherein the sum of a + b is 3 or 4, and the magnesium, titanium, and electron donor compounds are is used in such quantities to suit the meaning of the symbols m, n, p and q in the resulting precursor and then

B. The resulting precursor is diluted with an inert carrier, characterized in that the dilute precursor is treated with a boron halide compound of the formula br _c x ₃ '

R represents an aliphatic or aromatic hydrocarbon radical having 1 to 14 carbon atoms or a radical of formula

OR * where

R ‘also represents an aliphatic or aromatic hydrocarbon radical having 1 to 14 carbon atoms,

X * is chlorine, bromine or a mixture thereof, and c is 0 or 1 when R is an aliphatic or aromatic hydrocarbon radical and 0, 1 or 2 when R is a radical of formula OR *.

The attached drawing shows a fluidized bed reaction system for gas-phase polymerization which can be used in the polymerization catalyzed by the catalyst system of the invention.

If the above-described catalytically active composition is subjected to treatment with a boron halide compound according to the invention, a catalyst is obtained which is more stable when exposed to temperatures above 90 ° C, whose activity decreases more slowly when used at such high temperatures compared to the untreated catalyst. Surprisingly, it has been found that whether such treated catalyst is used in polymerization at temperatures above or below 90 ° C, it is always possible to obtain polymers with higher productivity and polymerization is accompanied by a lesser extent of ethylene hydrogenation than when using an analogous untreated catalyst.

The ethylene polymers produced using the treated catalysts have a density of about 940 to about 970 kg / m ³ . The density of the polymer at a given melt index can be controlled primarily by the amount of comonomer that is copolymerized with ethylene. In the absence of comonomer, ethylene would homopolymerize with the catalyst of the present invention to form homopolymers having a density of at least 960 kg / m ³ . The addition of increasing amounts of comonomers results in a gradual decrease in copolymer density. Under the same reaction conditions, the amount of comonomers required to achieve the same result varies from monomer to monomer. To achieve the same results for copolymers, i.e. the same density at a certain melt index, increasing molar amounts of the different comonomers in the series C 2 C 5 Cs 5 C 7 Cs are needed.

By using modified catalysts, copolymers can be prepared containing as the major molar proportion ethylene (at least 97%) and as the minor molar proportion (not more than 3%) one or more C 3 -C 8 α-olefins. These ia-olefins, which should contain no branching on any of their carbon atoms closer to the copolymer backbone than the fourth carbon atom, include propylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1. pentene, 1-heptene and 1-octene. Preferred α-olefins are propylene, 1-butene-1-hexene, 4-methyl-1-pentene and 1-octene.

The melt index of the polymers is a reflection of its molecular weight. The relatively high molecular weight polymers have a relatively low melt index. Ultra-high molecular weight ethylene polymers have a high load melt index (HLMI) of about 0.0 g / 10 minutes and very high molecular weight polymers have a high load melt index of about 0.0 to about 1.0 g / 10 min. Polymers produced using treated catalysts, on the other hand, have a melt flow index under normal load of greater than 1.0 g / 10 min. and up to about 10 g / 10 min, preferably in the range of about 2 to about 50 g / 10 min, and a high load melt index (HLMI) of about 22 to about 2200 g / 10 min. The melt index of the polymers produced by the process of the invention is dependent on the combination of the polymerization reaction temperature, polymer density, and hydrogen / monomer ratio in the reaction system. The melt flow index increases with increasing polymerization temperature and / or decreasing polymer density and / or increasing hydrogen / monomer ratio. In addition to hydrogen, other chain transfer agents can also be used to further increase the melt index of the copolymers.

The ethylene polymers prepared using the supported catalysts have a melt flow rate ratio of from about 22 to about 32, preferably from about 25 to about 30%. The melt flow rate ratio is another way of characterizing the molecular weight distribution of the polymer. A melt flow rate (MFR) of about 22 to 32 corresponds to a Mw / Mn of about 2.8 to about 3.6.

Polymers produced using treated catalysts have a catalyst residue content, expressed in ppm of titanium metal, below 10 ppm at a productivity level of at least 100,000 kg of polymer per kg of titanium.

The polymers obtained are granular substances having a mean particle size of the order of about 0.51 to about 1.27 mm and preferably about 0.51 to about 1.02 mm. The particle size is important for the easy fluidization of the polymer particles in the fluidized bed reactor as described below. These granular substances also contain low dust fractions (to more than 4% of the total polymer product) and the particles of these dust fractions have no diameter greater than 125 µm.

Polymers produced using treated catalysts have a bulk density of about

340.4 to about 518.72 kg / m ³ .

As the titanium compounds of formula Ti · (OR) _a X _b wherein R, X, and b are as defined above, may be modified in the process of preparing the precursor according to the invention to use for example the compounds of formulas

TÍC13,

TiCld,

Ti (OCHs) Cl3,

Ti (OC 5 H 3) Cl 3,

Ti (OCOCH 3) Cl 3,

T 1 OOCOC 5 H 5 O 2 Cl, individually or in mixtures.

Magnesium chloride, magnesium bromide and magnesium iodide may be used, for example, as magnesium compounds of the general formula MgX,, where X is as defined above, both individually and in combination. Magnesium chloride is particularly preferred among the magnesium compounds.

The titanium and magnesium compounds should be in a form to facilitate their dissolution in the electron donor compound ED.

Suitable electron donor compounds are organic compounds liquid at 25 ° C in which the titanium compound and the magnesium compound are soluble. Electron donor compounds are also sometimes referred to as Lewis base stirrups.

Electron donor compounds include such compounds as alkyl esters of aliphatic and aromatic carboxylic acids, aliphatic ethers, cyclic ethers and aliphatic ketones. Of these electron donor compounds, alkyl esters of C 1 to C 6 saturated aliphatic carboxylic acids, alkyl esters of C 7 to C 6 aromatic carboxylic acids, C 2 to C 5, and preferably C 3 to C 1 aliphatic ethers, C 3 to C 4, cyclic ethers and C3 to Cs and preferably C3 to C1 aliphatic ketones. Most preferred of these electron donor compounds are methyl formate, ethyl acetate, butyl acetate, ethyl ether, hexyl ether, tetrahydrofuran, diosane, acetone and methyl isobutyl ketone.

The electron donor compounds can be used singly or in mixtures.

Boron halide compound of formula R _c X ₃ _ _c where R, X and c are as defined above, can be used individually or in combinations thereof and include for example the following compounds · formulas:

BCI3,

ΒΒΓ3,

B (C ₂ H ₅ ) Cl 2,

B (OC2H5) Cl2,

B (OC2, H5) 2C1,

BfCsHsjClz,

B (OC6H5) <Cl2,

B (CsHi3jCl ₂

B (OC 3 H 13) Cl 2,

BJOC5H5J2Cl.

A preferred boron compound is boron trichloride.

Carriers are solid porous substances in particulate form which are inert to the other components of the catalyst composition and to other reactive components of the reaction system. Carriers include, for example, inorganic materials such as silicon and / or aluminum oxides. The carriers are used in the form of dry powders having a mean particle size of from about 10 to about 250 µm, preferably from about 50 to about 150 µπι. These substances are also porous and have a specific surface area of at least 3 m ² / g, preferably at least 50 m ² / g. The activity of the catalyst or its productivity is increased by using silica having pores with an average diameter of at least 8 nm, preferably at least 10 nm. The carrier should be dry and not contain absorbed water. The carrier is dried by heating to a temperature of at least 600 ° C. Alternatively, the carrier may be dried at a temperature of at least 200 ° C and then treated with about 1 to 8% by weight of one or more of the above-described aluminum compounds. This modification of the support with aluminum compounds is advantageous in that, with the use of the modified support, catalysts with increased activity are obtained which provide ethylene polymers with improved particle morphology. Other organometallic compounds, such as diethylzinc, may also be used to modify the support.

The catalyst precursor is prepared by dissolving the titanium compound and the magnesium compound in the electron donor compound at a temperature from about 20 ° C to about the boiling point of the electron donor compound. The titanium compound may be added to the electron donor compound before or after or simultaneously with the addition of the magnesium compound. The dissolution of the titanium compound and the magnesium compound may be aided by stirring and, in some cases, heating the two compounds in the electron donor to reflux. After dissolution of the titanium compound and the magnesium compound, the precursor may be isolated by crystallization or precipitation by an aliphatic or aromatic hydrocarbon containing 5 to 8 carbon atoms, such as hexane, isopentane or benzene. The crystalline or precipitated precursor can then be isolated. After drying at temperatures of not more than 60 ° C, the precursor is in the form of a fine particulate having a mean size of from about 10 to about 100 ₍ µm).

About 0.5 to about 56 moles, preferably 1 to 10 moles, of the magnesium compound are used per mole of the titanium compound to prepare the precursor.

The precursor thus obtained is then treated with an inert carrier either by 1) mechanical mixing or 2) by impregnating the precursor into the carrier material.

Mechanical mixing of the inert carrier and precursor is accomplished by mixing these materials using conventional techniques. Suitably, the resulting mixture contains about 10 to about 50% by weight of the precursor.

Impregnation of the inert carrier with the precursor can be carried out by dissolving the precursor in the electron donor compound and then mixing the carrier with the precursor solution to impregnate the precursor. The solvent is removed by drying at temperatures up to 70 C. ³

The NO2 carrier can also be impregnated with a precursor by adding to it a solution of the raw materials needed to form the precursor in the electron donor compound. In this case, the precursor is not isolated from the solution. The excess electron donor compound is then removed by drying at a maximum of 70 ° C.

When proceeding as described above, the catalyst composition mixed with the carrier or the impregnated carrier has compositions corresponding to an empirical formula

_Mg: Ti _n | [OR) _n Xp _[q EDJ which the general symbols are as defined above.

The impregnated carrier expediently contains about 3 to 50% by weight, preferably about 10 to about 30% by weight of the precursor. .

After mixing the precursor with the carrier or impregnating it in the carrier, the diluted precursor is treated with a boron halide compound. Treatment with the boron halide compound can be carried out by dissolving the boron halide compound in an inert liquid solvent and applying the resulting solution to the diluted precursor in any conventional manner. Preferably, the diluted precursor is simply immersed in this solution. The solvent used must be non-polar, inert to the boron halide compound and all catalyst components, and must dissolve the boron halide compound, but not the precursor. Polar solvents are undesirable because, in addition to the halide compound. boron also dissolves the precursor and forms complexes with it. In order to prevent the formation of these complexes, it is important to treat the precursor with a solution of the boron halide compound in a non-polar solvent in an independent step up to the formation of the precursor in a polar electon donor solvent.

if desired, the dilute precursor can also be added to the linseed liquid solvent to form a suspension before the boron halide compound is dissolved in the solvent. This technology is particularly useful when a gaseous substance such as boron trichloride (BCbj) is used. The gaseous substance can dissolve in the solvent after the suspension is bubbled through, or the gaseous substance can first be liquefied and then added Alternatively, the boron halide compound may be dissolved in an inert liquid solvent before it is added to the suspension or even before it is added to the dry, dilute precursor.

As solvents that can be used to dissolve the boron halide compound, hydrocarbon solvents can be used, including substituted hydrocarbon solvents such as isoheptane, hexane, heptane, toluene, xylene, naphtha, and methylene chloride. Preferably, these solvents are used together with the boron halide compound in amounts such that the resulting solution contains about 1 to about 15% by weight of the boron halide compound.

Usually, the treatment of the diluted precursor with the boron halide compound is carried out at room temperature, but if desired, this treatment can be carried out at temperatures as low as about -30 ° C. When used in solution, the working temperature should not exceed the boiling point of the solution. In any case, the process should be such that the precursor can absorb a sufficient amount of a sufficiently concentrated solution of boron halide or gaseous boron halide compound. This amount should correspond to about 0.1 to about 3.0 mol, preferably about 0.3 to about 1.0 mol, of the boron halide compound, based on the mole of the electron donor compound contained in the precursor. Usually, a treatment time of from about 1 hour to about 24 hours, usually from about 4 to about 10 hours, is sufficient for this purpose.

. In order to be used for the production of ethylene polymers, the treated precursor must first be activated, i.e., treated with a sufficient amount of the activating compound to bring the titanium atoms contained in the precursor to active state.

The activating compound has a structure corresponding to the general formula

Al (R ") _d X _e " H _f where

X "represents chlorine or a group of the formula OR" ‘and each symbol

R 'and R' ', which are the same or different, represent a saturated hydrocarbon radical having 1 to 14 carbon atoms, e representing a number from 0 to 1.5, f representing a number from 1 or 0, the sum of d + e + f is 3.

The activating compounds may be used singly or in combination and exemplified by compounds of the formula

A1 (C2H5) 3

AlfCžHsjžCl,

Alfi-CáHob

Ah (C2H5) SCL ₃

Al (i-C 6 H 9) 2H,

Al (CeH13) 3,

Al (C ₈ H 17) 3,

A1 (C2H5) 2H and A1 (C2H5) z (OC2H5).

About 10 to 400, and preferably about 15 to 30 moles of activating compound per mole of titanium compound are used to activate the treated precursor.

The precursor may be partially activated before being introduced into the polymerization reactor. When the precursor is partially activated in this manner, a sufficient amount of activator must be used to obtain a precursor in which the molar ratio of activator compound to titanium is at most 10: 1, preferably about 1: 4 to about 8: 1. slurry in a hydrocarbon solvent, then the resulting mixture is dried to remove the solvent. The drying is carried out at a temperature of about 20 to 80 ° C, preferably at a temperature ranging from ais 50 to about 70 ° C. The resulting product is in the form of a particulate solid which can be readily fed to a polymerization reactor where activation is completed with an additional activating compound. The same substances as for the pre-activation or other substances can be used as additional activating compounds.

If desired, the partial activation can be carried out in the same suspension in which the precursor is treated with a boron halide compound.

If a precursor impregnated into the carrier is used, the activation can be carried out in its entirety in the polymerization reactor, except that some pre-activation outside the reactor would be performed.

The partially activated or totally inactive precursor and the required amount of activating compound required to fully activate the precursor are preferably introduced into the reactor. They are led through separate dosing pipes. The activator compound may be injected into the reactor as a solution thereof in a hydrocarbon solvent such as isopentane, hexane or mineral oil. This solution typically contains about 2 to about 30% by weight of the activating compound. The activator compound is introduced into the reactor in an amount such that a total Al / Ti molar ratio in the range of 10: 1 to 400: 1, preferably from about 15: 1 to 30: 1, is achieved in the reactor.

In a continuous gas phase process such as the fluidized bed process described below, separate batches of a partially activated or not activated precursor are continuously fed into the reactor during polymerization, while simultaneously reporting the separate batches of activating compound needed to activate the unactivated precursor or complete. activation of a partially activated precursor. This replaces the active sites of the catalyst that have been consumed during the reaction during the polymerization.

The polymerization is carried out by contacting the monomer stream (s) in the gas phase, for example in the fluidized bed process described below, substantially in the absence of catalytic poisons such as moisture, oxygen, carbon dioxide and acetylene, with a catalytically effective amount of fully activated precursor. (hereinafter referred to as the catalyst) at a pressure and temperature sufficient to initiate the polymerization.

In order to achieve the desired density range of the copolymers, it is necessary to copolymerize with no more than 3 mole% of any other oro-olefins, therefore no more than 50 mole% of these other and olefins.

A fluidized bed reaction system that can be used in the process of the invention is illustrated in the figure. Reactor 1 consists of reaction zone 2 and speed reduction zone 3.

Reaction zone 2 comprises a bed of growing polymer particles, formed polymer particles, and a minor amount of catalyst particles fluidized by the continuous flow of polymerizable and modifying gaseous components consisting of make-up gas and gas recycled to the reaction zone. To maintain the fluidized bed in a fluidized state, the gas mass flow rate through the bed must be greater than the minimum flow rate required for fluldization. Preferably, a suitable gas mass flow rate through the bed is about 1.5 to about 10X higher, preferably about 3 to 6X higher than the minimum gas mass flow rate required for fluidization (Gmf). The Gmf designation for the minimum gas mass flow rate required to achieve fluidization was suggested by C. Y Wan and Y. H, Yu, "Mechanics of Fluidizaton", Chemical Engineering Progression Syttposium Series, Vol. 62, pp. 100-111 (1966).

It is important that the bed always contain particles that prevent "hot spots" and that trap and distribute the pulverulent catalyst in the reaction zone. Upon commencement of operation, a polymeric particle is usually introduced as a base into the reaction zone before the gas stream is introduced. These particles may be identical to the nascent polymer or may be different. When they are different, they are drawn off with the undersized polymer particles as the front product. Finally, the fluidized bed of the desired polymer particles displaces the starter bed.

The fully unactivated precursor or the portion of the tangent activated precursor used in the fluidized bed is preferably stored in a standby container 4 under an atmosphere of an inert gas such as argon nitrogen.

Fluidization is achieved by a high rate of gaseous recycle introduced into and through the bed, which is typically of the order of about 50 times higher than that of the make-up gas. The fluidized bed usually looks like a dense mass of moving particles flowing in the free vortex created by the passage of gas through the bed. The pressure drop across the bed is equal to or somewhat higher than the weight of the bed divided by the cross-section of the bed, so it is dependent on the reactor geometry.

The make-up gas is introduced into the bed at the same rate as the withdrawal rate of the polymer product particles. The make-up gas composition is determined by an analyzer 5 located above the bed. The gas analyzer determines the composition of the gas to be recycled and accordingly adjusts the composition of the make-up gas to maintain the composition of the gaseous mixture at substantially steady-state in the reaction zone accordingly.

In order to guarantee complete fluidization, the recycle gas and possibly part of the make-up gas is fed through the recycle line 6 through the feed 7 below the bed. Above the inlet 7 there is a gas distribution plate 8 which assists fluidization of the bed.

The portion of the gaseous stream that does not react in the bed forms recycled gas, which is discharged from the polymerization zone preferably by passing through a zone 3 located above the bed in which the velocity is reduced and the entrained particles fall back into the bed.

The recycle gas is then compressed, in a compressor 9, and passed through a heat exchanger 10 where it is stripped of the reaction heat before returning to the bed. The bed temperature is kept constant at steady state conditions by dissipating the heat of reaction. There is no apparent temperature gradient at the top of the bed. A temperature gradient exists in the lower 152 to 304 mm bed, between the temperature of the exiting gas and the temperature of the rest of the bed. The recycle gas is fed to the bottom of the reactor through an inlet 7 and into a fluidized bed through a distribution plate 8. The compressor 9 can also be placed downstream of the heat exchanger 10.

The distribution plate 8 plays an important role in the operation of the reactor. The fluidized bed contains both growing and formed polymer particles and catalyst particles. Since the polymer particles are hot and may be active, they must be prevented from settling, since if any calm mass is formed, the active catalyst contained in these particles could cause the reaction to continue and the particles would melt due to the heat generated. It is therefore important that diffuse recycle gas is passed through the bed at a rate sufficient to fluidize the bed particles. For this purpose, the distribution plate A can be used, and this plate can be a screen, slotted plate, perforated plate, plate with caps (analogous to distillation column trays) and the like. All plate parts can be stationary or of a movable type such as plate as described in U.S. Patent No. 3,298,792. Whatever the design of the plate, the plate must disperse recycle gas between the particles at the bottom of the bed and keep the particles of the bed in fluidized state. The board also aims to support a quiet bed of resin particles when the reactor is not in operation. The movable portions of the plate may be used to extrude polymer particles retained on or within the plate.

Hydrogen can be used as the chain transfer agent in the polymerization of the invention. The hydrogen / ethylene molar ratio that can be used is in the range of about 0.1 to about 2.0 moles of hydrogen per mole of monomer in the gas stream.

Any gas inert to the catalysts and reactants may also be present in the gas stream. The activator compound is preferably added to the reaction system downstream of the heat exchanger 10 (in terms of flow). The activator can therefore be introduced into the pipeline and recycled, for example, from the container 11 through the pipeline 12.

In addition to hydrogen, the compounds of the formula I may be used as molecular weight control agents, i.e., as chain transfer agents, together with the treated catalysts of the invention.

Zn (R _a ) (R _b ) where

R _a and R _b are the same or different aliphatic or aromatic hydrocarbon radicals having 1 to 14 carbon atoms.

This further increases the melt index values of the produced copolymers. About 0 to 100, and preferably about 20 moles of zinc compound (calculated as Zn) per mole of titanium compound (calculated as Ti) can be added to the gaseous stream introduced into the reactor. Preferably, the zinc compound may be introduced into the reactor in the form of a dilute solution (2 to 30% by weight) in a hydrocarbon solvent or in absorbed form in a solid diluent such as silica in an amount of about 10 to 50% by weight. These substances are often pyrophoric. The zinc compound can be fed alone or together with an additional activating compound, which is also fed to the reactor, from a dispenser (not shown) which can be placed next to the container 11.

The fluidized bed reactor must be operated at a temperature below the sintering temperature of the polymer particles to avoid sintering of the particles. The production of high density ethylene polymers having a high melt index and a low melt flow rate ratio is preferably carried out at a temperature of from about 90 to about 115 ° C. As explained above, the catalysts used in the polymerization process of the present invention, after treatment with a boron halide compound, are more stable when exposed to temperatures above 90 ° C and are capable of producing polymers with higher productivity and less ethylene concomitant hydrogenation than similar catalysts. which have not been modified.

The fluidized bed reactor is operated at a pressure of up to about 6.87 MPa, preferably at about 0.687-2.061 MPa, and when operating at higher pressures in this range, heat transfer is facilitated, since an increase in pressure results in an increase in unit volumetric thermal gas capacity.

The partially activated precursor or unactivated precursor is injected into the bed at a rate equal to the rate at which it is consumed by an inlet 13 located above the manifold plate 8. The precursor is preferably injected at a point in the bed where good mixing occurs. An important feature of the invention is that the precursor is injected at a location above the manifold plate. Since the catalysts formed from these precursors are highly active, injecting into the space below the manifold could result in polymerization being initiated at this point, which could eventually lead to blockage of the manifold. On the contrary, injecting the catalyst into the fluidized bed helps to distribute the catalyst in the bed and prevents the formation of sites with a high catalyst concentration which could lead to hot spots. Injecting the catalyst into the reactor above the bed may result in excessive entrainment of the catalyst into the recycle line where polymerization may start, which could eventually lead to clogging of the line and heat exchanger.

A gas inert to the catalyst, such as nitrogen or argon, is used to introduce the partially or fully activated precursor into the bed.

Bed productivity is controlled by catalyst injection rate. Bed productivity can simply be increased by increasing the catalyst injection rates and reduced by reducing the catalyst injection rate.

Since any change in catalyst injection rate results in a change in the rate of reaction heat evolution, the temperature of the recycle gas entering the reactor is adjusted up or down to accommodate the rate of heat evolution. This ensures a substantially constant temperature in the bed. Both the fluidized bed and the recycle gas cooling system must, of course, be equipped with appropriate devices for detecting temperature changes in the bed and the cooling system so that the operator can appropriately adjust the recycle gas temperature.

Because of a combination of operating conditions, the fluidized bed is maintained substantially in the fluidized bed

1β at the same height by withdrawing a portion of the bed as a product at the same rate as the particle formation rate of the polymer product. Since the rate of heat evolution is directly proportional to product formation, the rate of gas formation along the reactor (i.e., the temperature difference between the inlet gas temperature and the outgoing gas temperature) determines the rate of increase of the polymer particles at a constant gas velocity.

The polymer product particles are preferably collected continuously through a conduit 14 in the vicinity of the distributor plate 8. The particles are collected in the form of a suspension with a portion of the gaseous stream that is ventilated prior to particulate deposition to prevent further polymerization and speckling before the particles reach the zone. where they gather. Suspension gas can also be used to transfer product from one reactor to another.

The polymer product particles are expediently and preferably removed by means of two sequentially operated time-adjusted valves 15, 16 between which a separation zone 17 is provided. When the valve 18 is closed, the valve 15 is opened so that the gas / product mixture passes through zone 17. valve 16 opens to transfer the product to the outer insulation zone. The valve 18 is then closed and closed until the product is removed. The vented gas containing unreacted monomers can be removed from zone 17 via line 18. It can then be compressed in the compressor 19 and fed directly or via a scrubber 20 and via line 21 to the gas recycle line 6 upstream (downstream J of the recycle compressor 9).

Finally, the fluidized bed reactor is equipped with a suitable venting system that allows venting of the bed during start-up and shutdown. The reactor does not require the use of any mixing devices or / or wall scraping devices. The recycle gas line 8 and the devices located therein (compressor 9, heat exchanger 10) should have a smooth surface and should not contain unnecessary elements that could impede the continuous flow of gas.

The highly active catalyst system described provides a fluidized bed product with an average particle size of about 0.508 to 1.27 mm, preferably between about 0.508 to 1.016 mm. The product usually contains a low amount of catalyst residues. The polymer particles in the bed are relatively easy to fluidize.

The feed monomer feed stream, optionally with inert gaseous diluents, is fed into the reactor at a rate to provide a space and time yield of about 32.42 to about 102.1 kg / h / m ³ bed volume,

The term "crude resin or polymer" as used herein refers to a polymer in granular form as obtained from a polymerization reactor.

The following examples serve to illustrate the invention in more detail, but do not limit the scope of the invention in any way.

The properties of the polymers produced in the examples are determined by the following test methods:

Density

A test plate is made and tempered at 120 ° C for 1 hour to approach equilibrium crystallinity. The plate was then rapidly cooled to room temperature. The density measurement is then carried out in a column s

Flow Rate Ratio (MFR)

Productivity

The resin product sample is ashed and is determined by weight of ash as the ash is essentially a catalyst. The productivity is therefore expressed in kg of polymer produced per kg of total catalyst consumed. The amount of titanium, magnesium, boron and halogen in the ash is determined by elemental analysis.

Bulk weight

ASTM D-1895 Method B. Pour the resin through a funnel with a stem diameter

9.5 mm into a 400 ml graduated cylinder up to the 400 ml mark. Do not shake the cylinder during filling. The weight difference is determined by weighing.

Mean particle size

This property is calculated from the sieve analysis data according to ASTM-D-1921, Method A, using a 500 g sample. The calculations are based on the weight fractions retained on the sieves.

Example 1

Carrier loading with precursor

A 121 liter flask equipped with a mechanical stirrer was charged with 41.8 g (0.439 mol) of anhydrous magnesium chloride and 2.5 liters of tetrahydrofuran. To this mixture was added dropwise 27.7 g (0.146 mol) of titanium tetrachloride over 0.5 hour. The mixture was heated at 60 ° C for about 0.5 hours to completely dissolve all substances.

500 g of silica are dehydrated by heating to 800 DEG C. and then suspended in 3 l of isopentane. 142 ml of a 20% by weight solution of triethyl aluminum in hexane are added to the suspension with stirring over 0.25 hours. The mixture is dried for about 4 hours at 60 ° C with a stream of nitrogen to a dry, free-flowing powder containing 4% by weight triethyltin.

density gradient. The density is given in feg / m ³ .

Melt Flow Index (MI)

ASTM D-1238-Condition E measurements are performed at 190 ° C, g data per 10 minutes.

Melt flow rate (HLMI)

ASTM D-1238-Conditio® F. The measurement is performed using 10 times the load than the melt index.

flow rate melt flow index

Alternatively, the silica is similarly dried and treated with a solution of tri-n-hexyl aluminum or diethylzinc to give a product containing 4% by weight of the alkylated compound.

The treated silica was then added to the solution prepared above and stirred for 0.25 hours. The resulting mixture was dried at 60 ^° C with a stream of nitrogen for about 4 hours to a dry impregnated bulk powder having a particle size equal to the original silica.

Example 2

Treatment of the precursor with boron trichloride

500 g of precursor silica, prepared as described in Example 1, are suspended in 3 L of isopentane and a 1 molar solution of boron trichloride in methylene chloride is added to the suspension with stirring over 0.25 hours. The precursor impregnated with silica and boron trichloride solution is used in amounts sufficient to correspond to a boron to electron molar ratio of the onorous compound (in the precursor) of 0.75: 1. The mixture is then dried for about 4 hours at 60 ° C with a stream of nitrogen. . A dry, free-flowing powder is obtained with a particle size equal to that of the original silica particles. Example 3

Treatment of the precursor with ethyl borohydride

500 g of precursor silica, prepared as described in Example 1, are suspended in 3 l of isopentane and a 10% by weight solution of ethyl borohydride in heptane is added under stirring over 0.25 hours. The precursor impregnated with silica and ethyl borohydride solution is used in amounts sufficient to correspond to a molar ratio of boron to elec232750 of the trondonium compound (in the precursor) of 0.75: 1. A dry, free-flowing powder is obtained with a particle size equal to that of the original silica particles.

,. ‘- '. i- * ·

Example 4

Preparation of a partially activated precursor

After treatment with the boron halide compound described in Examples 2 and 3, the desired weight of the silicon-impregnated precursor described in each of these examples is suspended in anhydrous isopentane along with a sufficient amount of activating compound to obtain a partially activated precursor containing aluminum and titanium in molar. 4: 1 ratio of Al-Ti.

In both cases, the resulting suspension is thoroughly mixed at room temperature for 0.25 to 0.5 hours. The isopentane diluent is then removed from the suspension by drying at 65 + 10 ° C in a stream of dry nitrogen for about 4 hours. A loose substance is obtained consisting of a partially activated precursor impregnated in the pores of silica. The substance has the same particle size and shape as the original silica. The substance is stored under dry nitrogen until used.

Examples 5 to 8

Ethylene was homopolymerized in a series of 4 experiments employing the reaction system of a fluidized bed as described ¹ above. The lower part of the polymerization reactor is 3.05 m high and has a diameter of 0.343 m, the upper part is 4.88 m high and has a diameter of 0.597 m.

Each of the polymerization reactions was carried out at 105 ° C for 24 hours at a pressure of 20 psi, at a gas velocity of about three to six times Gmf and a space and time yield of 45.388 to 79.429 kg / h / m ³ and molar. H2 / C2 ratio 0.35 to 0.42.

In the first polymerization (Example 5), a precursor impregnated in silica prepared according to Example 1 was fed into the polymerization reactor together with a 5% (by weight) solution of triethyl aluminum in isopentane to obtain a fully activated catalyst having an Al / mole ratio. They range from 15: 1 to 30: 1.

In the other three polymerizations (Examples 6 to 7), the other precursor impregnated in silica prepared according to Example 1 is first treated with the boron halide compound as described in Examples 2 or 3 prior to introduction into the polymerization reactor. ¹ in the first polymerization.

The reaction conditions used in all examples, the properties of the polymers obtained, the extent of ethylene hydrogenation that occurs during polymerization and the productivity of the catalyst system are summarized in Table I below.

TABLE I

Example number 5 6 7 8 Pre-processing silicon dioxide EŤ3A1 Et3Al EtaZn EtsAl Boron halide compound none BC13 BCI3 EtBCl2 Polymerization conditions Activator EŤ3A1 EtsAl EtsAl EtsAl Temperature f ° C] 105 105 105 105 Pressure [MPa] 2,061 2,061 2,061 2,061 Space-related yield and time [kg / h / m ³ ] 45.39 79.43 66.46 68.08 H2 / C2 molar ratio 0 0.42 0.36 0.35 0.39 Polymer properties Melt flow index [g / 10 min. ] 7 8 8 9 Ratio of melt flow rates 30 27 Mar: 27 Mar: 26 Density [kg / m ³ ] 968 967 966 967 Hydrogenation % ethylene conversion 0.96 0.39 0.21 0.32 Productivity kg polymer / kg Ti 65 000 245 000 350 000 . 280 000 ppm Ti in the polymer 15.5 4 2 3.5

Examples 9 and 12 Ethylene is homopolymerized in a series of 4 experiments using the fluidized bed reaction system also used in Examples 5 to 8.

In a series of these polymerizations, a silica precursor soaked in Example 1 and partially activated prior to reactor feed as described in Example 4 is used. In the first two experiments (Examples 9 and 10), a precursor that has not been treated with a halide compound boron. In the other two examples (Examples 11 and 12), the precursor was treated with boron trichloride as described in Example 2 before undergoing partial activation.

In any case, activation of the precursor in the reactor is completed by introducing a 5% (by weight) solution of alkyl aluminum in isopentane into the reactor in such an amount as to obtain a fully activated catalyst with an Al / Ti molar ratio of 15: 1 to 30: 1.

Each polymerization is carried out for 24 hours at 105 ° C, 20 psi gas pressure corresponding to three to six times Gmf at a space and time yield ranging from 53.49 to 81.05 and a H2 / C2 molar ratio in ranging from 0.40 to 0.51.

The reaction conditions used in all examples, the properties of the polymers obtained, the extent of ethylene hydrogenation occurring in the polymerization and the productivity of the catalyst system are summarized in Table II below.

TABLE II

Example number 6 10 11 12 Silicon dioxide pretreatment Et3Al Et3Al (C6H13) 3Al Et3Al Boron Balogenide Compound none none BC13 BC13 Partial activation (outside the reactor) (C 6 H 13) sAl (C ₆ H 13) 3Al (C6H13) 3Al (CsH17) 3A1 Total activation (inside reactor) Et3Al Et3Al EI3A1 _(CH3) 3A1 Polymerization conditions Temperature f ° C] 105 105 105 105 Pressure [MPal 2,061 2,061 2,061 2,061 Space and time yield [kg / h / m ³ ] 53.49 81.05 56.73 81.05 H2 / C2 molar ratio 0.45 0.51 0.41 0.40 Polymer properties Melt flow index. [g / 10 min. ] 9 13 9 9 Ratio of melt flow rates 27 Mar: 27 Mar: 25 25 Density [kg / m ³ ] 969 - 967 967 Hydrogenation % Conversion of ethylene 2.66 1.79 1.49 1.03 Productivity kg polymer / kg Ti 90 000 118 000 135 000 210 000 ppm Ti in the polymer 12 8.5 7.5 5

SUBJECT

Claims (8)

Process for preparing a precursor suitable as a component of a catalyst system for the production of high density ethylene homopolymers and copolymers under a pressure of less than 6.87 MPa, accompanied by a small range of ethylene hydrogenation, in which: A. prepare a precursor of the formula Mg _m Ti, (OR) _n X _p [ED] _q wherein m is 0.5 to 56, n is 0, 1 or 2, p is 2 to 116, q is 2 to 85, I will invent R represents an aliphatic or aromatic hydrocarbon radical having 1 to 14 carbon atoms or a radical of formula COR 'where R * represents an aliphatic or aromatic hydrocarbon radical having 1 to 14 carbon atoms, X is chlorine, bromine, iodine or a mixture thereof; ED is an organic electron donor compound selected from the group consisting of alkyl esters of aliphatic and aromatic carboxylic acids, aliphatic ethers, cyclic ethers and aliphatic ketones, by dissolving at least one magnesium compound and at least one titanium compound in at least one liquid organic electron donor compound to form a precursor solution in the electron donor compound; wherein the magnesium compound is a compound of the formula MgXz where X is chlorine, bromine, iodine, or a mixture thereof, and the titanium compound used is a compound of formula Ti (ORj _and X _b where R and X are as defined above, and is 0, 1 or 2, and b is 1 to 4 inclusive, wherein the sum of a + b is 3 or 4, and the magnesium, titanium, and electron donor compounds are used in such amounts to suit the meaning of the symbols m, n, p and q in the resulting precursor and then B. The resulting precursor is diluted with an inert carrier, characterized in that the diluted precursor is treated with a boron halide compound of the formula BR _C X ₃ '_ _C where R represents an aliphatic or aromatic hydrocarbon radical having 1 to 14 carbon atoms or a radical of formula OR ‘where R ‘also represents an aliphatic or aromatic hydrocarbon radical having 1 to 14 carbon atoms, X ‘represents chlorine, bromine or a mixture thereof and c represents the number 0 or 1 when R represents an aliphatic or aromatic hydrocarbon radical and 0, 1 or 2 when R represents a radical of the general formula OR‘. 2. A process according to claim 1, wherein the precursor is mechanically mixed with an inert carrier, wherein the mixture comprises 10 to 50% by weight of the precursor. 3. The method of claim 1, wherein the precursor is impregnated in a carrier, wherein the impregnated carrier comprises 3 to 50% by weight of the precursor. 4. The process according to claim 1, wherein the inert carrier is silica. 5. The process of claim 4, wherein the silica is modified with diethyl zinc. 6. A method according to claim 1, 2, 3, 4 or 5, wherein in formulas X and X 'are chlorine atoms, [ED] is tetrahydrofuran, n is a number · 0, m is a number of 1.5 to 5, p is a number of 6 to 14 and q is a number of 3 to 10. 7. The process of claim 1, 2, 3, 4, 5 or 6 wherein the boron halide compound is boron trichloride. 8. A process according to claim 1, 2, 3, 4, 5 or 6 wherein the boron halide compound is ethyl borohydride. sheet of drawings