CS216209B2 - Method of catalytic production of ethylene homopolymere - Google Patents

Abstract

The present invention relates to a process for the catalytic production using an ethylene homopolymer a titanium-containing catalyst at productivity of at least 50,000 kg of polymer per 1 kg of titanium in the reactor at a pressure below 6.87 MPa in the gas phase, wherein the polymer is formed in granular form and has a density of 958 up to 972 kg / m3, including limit values, and ratio melt flow rates 22 to 32, inclusive limit values. The method is characterized by ethylene homopolymerization at temperature 30 to 115 ° C such that the monomer feed is is contacted in the presence of about 0 to 2.0 moles of hydrogen per mole of ethylene in the reaction gas phase reaction with particles a catalyst system containing a precursor, which is the reaction product of the halide magnesium, certain titanium compounds and electron donor compounds, and which is mixed with an inert carrier. The precursor is activated by an organoaluminum compound. Polymerization is preferably carried out in a fluidized bed loži

Description

The invention relates to catalytic homopolymerization of ethylene using catalysts containing a highly active magnesium-titanium complex in a low pressure gas phase process to produce polymers having a density of 958 to 972 kg / m ³ , including limit values, and a melt flow rate ratio (defined further) in the range of 22 to 32 (including limit values).

Ethylene homopolymers with a density of 960 kg / m ³ and higher and a melt flow index of about 5 to 50 are suitable for the production of injection molded articles with excellent impact resistance if they have a relatively narrow molecular weight distribution. Polymers of ethylene with a density of 960 kg / m ³ and above and a melt index of 20 g / 10 min or less can be prepared using the catalysts and low pressure gas phase processes described in U.S. Patent Nos. 3,023,203, 4,003,712 and 3, respectively. However, the polymers produced using the chromium oxide, silylchromate and chromocene supported catalysts of these patents have a relatively broad molecular weight distribution, as shown by the melt flow rate ratio of 35 or higher. The polymers produced according to these patents therefore have a relatively limited use for injection molding where excellent impact resistance is desired. It is therefore desirable to find catalysts which make it possible to readily prepare, by a gas-phase process, ethylene polymers with a relatively narrow molecular weight distribution.

In order to be useful in an industrial gas phase process, such as in the fluidized bed process of U.S. Patent Nos. 3,709,853, 4,003,712 and 4,011382, Canadian Patent 991,798, and Belgian Patent 839,380, the catalysts must have a high activity, i. have a productivity of at least 50,000 and preferably at least 100,000 kg of polymer per kg of catalyst metal or higher. This is because such processes in the gas phase generally do not employ any processes to remove catalyst residues. The catalyst residues in the polymer must therefore be so small that they can be left in the polymer without causing undesirable difficulties in the processing of the resins and / or their application to the end customer. Where highly active catalysts are successfully used in such fluidized bed processes, the heavy metal content of the resin is of the order of 20 ppm or less at a productivity of at least 50,000 or greater, 10 ppm or less at a productivity of at least 100,000 or greater; ppm or less at a productivity of 300 000 or more. The low content of catalyst residues is also important when the catalyst contains chlorine-containing substances, such as titanium, magnesium and / or aluminum chlorides, used in so-called Ziegler or Ziagler-Natta catalysts. The high chlorine content of the forming resin can cause pitting and other corrosion of the metal surfaces of the forming apparatus. A chlorine content of 200 ppm or higher is unacceptable for industrial production.

U.S. Patent No. 3,989,881 discloses the use of a highly active catalyst for a slurry process for producing ethylene polymers having a relatively low molecular weight distribution Mw / Mn ranging from about 2.7 to 3.1. Attempts have been made to use catalysts similar to those described in U.S. Pat. No. 3,989,881 in the production of narrow molecular weight polyethylene by polymerization of ethylene alone or in conjunction with propylene in a gas-phase fluidized bed process using apparatus and conditions similar to those described in U.S. Patent No. 4,011,382 and Belgian Patent No. 3,929,881. However, these attempts were unsuccessful. To avoid the use of solvents used in the slurry type catalyst systems described in U.S. Patent No. 3,989,881, titanium and magnesium containing components were dried. However, the dried substance was in the nature of a viscous, resin-like pyrophoric substance which could not be fed well into the reactor because it was not freely movable. Even when the agitator was mixed with silica and fed to the reactor in this form, industrially acceptable results were not achieved. The catalyst productivity was low or the catalyst was pyrophoric and difficult to handle, or the polymer product was obtained in the form of needles that are difficult to float and that have very poor mobility or flowability.

U.S. Patent No. 4,124,532 discloses the polymerization of ethylene and propylene using highly active catalysts. These catalysts include complexes which may contain magnesium and titanium. Said complexes are prepared by reacting a halide of formula MX2 (where M may be magnesium) with a compound of formula ΜΎ (where M ´ may be titanium and Y a halogen or an organic moiety) in an electron donor compound. These complexes are then isolated either by crystallization, solvent evaporation or precipitation.

The polymerization is carried out using these catalyst complexes and an alkyl-aluminum compound.

However, U.S. Patent No. 4,124,532 does not disclose any special technique or methods of preparing the catalyst to achieve the desired results in the process of the invention described in these positions. The use of the catalysts disclosed in U.S. Patent No. 4,124,532 without these special methods would not result in an industrial fluidized bed process suitable for the production of polyethylene on an industrial scale.

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U.S. Pat. Nos. 3,922,322 and 4,035,560 disclose the use of several titanium and magnesium containing catalysts for the production of granular ethylene polymers by a fluidized bed gas phase process under a pressure of below

6.87 MPa. However, the use of these catalysts in these processes has considerable disadvantages. Using the catalyst of U.S. Pat. No. 3,922,322, polymers having a very high content of catalyst residues, i.e., about 100 ppm Ti and more than about 300 ppm Cl, are obtained, as exemplified in this patent. In addition, as exemplified in U.S. Patent No. 3,922,322, the catalyst is used in the form of a prepolymer and very high volumes of catalyst composition need to be charged to the reactor. The preparation and use of this catalyst therefore requires the use of relatively large equipment for the production, storage and transport of the catalyst.

Also, using the catalysts of U.S. Patent No. 4,035,560, polymers containing high amounts of catalyst residues are obtained, and the catalyst compositions used appear to be pyrophoric, as is apparent from the types and amounts of reducing agents used in these catalysts.

It has now unexpectedly been found that ethylene homopolymers with a wide density range of 960 to 970 kg / m ⁵ and a melt flow rate of 22 to 32, including limit values having a relatively low catalyst residue content, can be produced at relatively high productivity, for industrial production, by a low pressure vapor phase process such that ethylene is homopolymerized in the presence of a highly active magnesium-titanium complex catalyst prepared as described below, under specific conditions of activation with an organoaluminum compound and in the presence of an inert carrier.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a process for producing ethylene homopolymers having a density of about 960 to 970 kg / m ³ , a melt flow rate ratio of 22 to 32 with a relatively low catalytic residue content by a low pressure gas phase process.

It is a further object of the present invention to provide a simple process for the production of ethylene homopolymers suitable for numerous end applications.

Yet another object of the invention is to produce various novel ethylene homopolymers suitable for the production of shaped articles.

The attached figure shows a fluidized bed reaction system for the gas phase process in which the catalyst system of the invention can be used.

Homopolymers produced by the process of the invention have a melt flow rate ratio (melt flow index ratio at lower and higher load), denoted MFR, in the range of 22 MFR 32, preferably 25 MFR 30. The melt flow rate is another way of characterizing molecular weight distribution of the polymer. The melt flow rate (MFR) value of 22 to 32 (including limit values) corresponds to a Mw / Mn of about

2.7 to 4.1 and an MFR of from 25 to 30 (including limit values) corresponds to an Mw / / Mn ratio of about 2.8 to 3.6.

The homopolymers have a density ranging from about 958 to about 972, preferably from about 961 to about 968 kg / m ³ , including limit values.

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, and very high molecular weight polymers have a high load melt index of about 0.0 to about 1.0 g / 10 min. Such high molecular weight polymers are difficult to mold in conventional injection molding machines and sometimes even impossible. The polymers produced by the process according to the invention, on the other hand, are easily formed in such a device. They have a melt index under normal load (MI) ranging from g 0.0 to about 50, preferably ranging from about 0.5 to 35, and a melt flow index under high load (HLMI) of about 11 to about 950 kg / 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, the copolymer density, and the 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.

Homopolymers of this invention typically comprise went> 0.1 0.3 CC double bonds per 1,000 carbon atoms and having cyclohexane extractables content of less than about 3 ^iO / o and preferably less than about 2% by weight.

These homopolymers contain as catalyst residues of the order of from 0 to 20 ppm inclusive at a productivity of 50,000 or more, from 0 to 10 ppm inclusive at a productivity of 100,000 or more, and from 0 to 3 ppm inclusive at a productivity of 300,000 or more. With respect to residues C1, Br or I., the content of these elements in the homopolymer depends on their content in the precursor. From the ratio of titanium to chlorine, bromine or iodine in the original precursor, the chlorine, bromine or iodine residue content can be calculated based on the known productivity value relative to the titanium residue itself. Many of these homopolymers produced using only chlorine-containing catalyst components (Cl / Ti = '7) can calculate chlorine residues in the range of 0 to 140 ppm inclusive at a productivity of 50,000 or

216260 higher, from 0 to 70 ppm inclusive at a productivity of 100,000 or greater and from 0 to 21 ppm at a productivity of 300,000 or greater. In the process of the invention, homopolymers are readily produced at productivity rates of up to about 300,000.

The homopolymers produced according to the invention are granules of a substance having an average particle size of the order of about 0.127 to about 1.52 mm, and preferably of about 0.5 to about 1 mm. The particle size is important for easy fluidization of the polymer particles in the reactor and the fluidized bed as described below. The bulk density of these homopolymers is from about 292 to about 519 kg / m ³ , preferably from about 405 to about 519 kg / m ³ .

The compounds used to prepare the highly active catalyst to be used according to the invention include at least one titanium compound, at least one magnesium compound, at least one electron donor compound, at least one activating compound, and at least one inert substance as a carrier.

The titanium compound has a structure corresponding to the general formula

Ti (OR) _and X _b wherein represents

R a C 1 to C 14 aliphatic or aromatic hydrocarbon radical or a radical of formula COR ', where R' is a C 1 to C 11 aliphatic or aromatic hydrocarbon radical,

X is chlorine, bromine, iodine, or a mixture thereof, and the number 0 or 1, b is 2 to 4 inclusive, wherein the sum of a-j-b is 3 or 4.

The titanium compounds can be used singly or in mixtures and include compounds of the formulas

TiCls,

TiCh,

Ti (OC 6 H 5) Cl 3,

Ti (OCOCH 3) Cl 3 and Ti (OCOC 6 H 5) Cl 3.

The magnesium compound has a structure corresponding to the general formula

MgX ₂ where

X represents chlorine, bromine, iodine or a mixture thereof.

These magnesium compounds can be used singly or in combination and include compounds of the formulas MgCl 2, MgBr 2 and Mg 12. Of the magnesium compounds, anhydrous magnesium chloride is particularly preferred.

In the preparation of the catalysts used in the process of the invention, about 0.5 to 56, preferably about 1 to 10 mol, of the magnesium compound are used per mole of titanium compound.

The titanium compound and the magnesium compound are conveniently used in a form which facilitates their dissolution in the electron donor compound as described below.

The electron donor compound is an organic compound that is liquid at 25 ° C and in which the titanium compound and the magnesium compound are partially or fully soluble. The electron donor compounds are known either under this name or under the name of the Lewis base.

By electron donor compounds are meant 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 4 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 4 aliphatic ethers, C 3 to C 4 cyclic ethers and preferably C 4 cyclic mono- or diethers to C3 and preferably C3 to C4 aliphatic ketones. Most preferred of these electron donor compounds are methyl formate, ethyl acetate, butyl acetate, ethyl ether, hexyl ether, tetrahydrofuran, dioxane, acetone and methyl isobutyl ketone.

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

About 2 to 85 and preferably about 3 to 10 moles of the electron donor compound are used per mole of titanium.

The activating compound has a structure corresponding to the general formula

Al (R 'j _c X _d H _e wherein

X 'represents chlorine or a group of formula' OR 'and each symbol

R 1 and R 1 ', which are the same or different, represent a C 1 -C 14 saturated hydrocarbon radical, d represents a number from 0 to 1.5, e represents a number from 1 or 0, the sum of c - | - d - | - θ is 3.

The activating compounds can be used singly or in combination and exemplified by compounds of the formulas

A1 (C ₂ H ₅₎ 3,

A1 (C ₂ H 5) 2c1,

A1 (C1-C4H9) 3,

Al ₂ (C2H5) 3Cl3,

Al (i-C4H9) ₂ H,

Al (C6H13) 3,

Al (CeH17) 3,

A1 (C2H5] 2 H and A1 (C ₂ H 5] 2 (OC 2 H _5).

About 10 to 400, and preferably about 10 to 100 moles of activating compound per mole of titanium compound are used to activate the catalysts used in the present invention.

Substances used as carriers are particulate solids which are inert to the other components of the catalyst composition and to the other active components of the reaction system. Such carriers include inorganic materials such as silica and alumina, and molecular sieves and organic materials such as polyolefins such as polyethylene. The carriers are used in the form of dry powders having a mean particle size of about 10 to 250, preferably about 50 to 150 μΐη. These substances are preferably also porous and have a specific surface area of at least 3 and preferably at least 50 m ² / g. The carrier should be dry, ie 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 1-8% by weight of one or more of the alkyl aluminum compounds described above. This modification of the support with alkyl-aluminum compounds provides a catalyst system with increased activity, and using such a catalyst system, the resulting polyethylene particles also have improved morphology.

The catalyst used in the process of the invention is prepared by first preparing a precursor from a titanium compound, a magnesium compound, and an electron donor compound in the following manner, then contacting the precursor with the carrier and activating compound in one or more stages as described below.

The precursor is prepared by dissolving the titanium compound and the magnesium compound in the electron donor compound at a temperature of 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 the addition of the magnesium compound or simultaneously with the addition thereof. Dissolution of the titanium compound and the magnesium compound can 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 can be isolated by crystallization or precipitation of a C 5 -C 6 aliphatic or aromatic hydrocarbon such as hexane, isopentane or benzene.

The crystallized or precipitated precursor may be isolated in the form of fine, free-moving particles of medium size about

10: up to 100 φΐη and bulk density about 292 to about 535 kg / m ³ .

In the fluidized bed process, a particle size of 100 μτη is preferably used. or smaller. The particle size of the isolated precursor can be controlled by the rate of crystallization or precipitation.

The precursor thus prepared has a composition corresponding to the general formula

MgmTUORlnXptED], where it represents

ED electron donor compound, in number from 0.5 to 56, preferably from 1.5 to 5 including limit values, n number from 0 or 1, p number from 6 to 116, preferably from 6 to 14, including limit values, q number from 2 to 85, preferably 4 to 11, including limit values,

R a C 1 to C 14 aliphatic or aromatic hydrocarbon radical or a radical of formula COR ', where R' is a C 1 to C 14 aliphatic or aromatic hydrocarbon radical, and

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

The elemental titanium index Y (Ti) means the Arabic number one.

The polymerization activity of the fully activated catalyst in the process of the invention is so high that it is necessary to dilute the precursor with a carrier to effectively control the reaction rate. Dilution of the precursor may be performed before or simultaneously with the activation of the precursor as described below. The dilution of the precursor is carried out by mechanical stirring or mixing of about 0.033 to 1, and preferably about 0.1 to 0.33 parts of the precursor with 1 part by weight of carrier.

In order to be used in the process according to the invention, the precursor must be fully or partially activated, i.e. it must be treated with a sufficient amount of the activating compound to bring the titanium atoms contained in the precursor into active state. However, it has been found that the method of activating the catalyst is very important for obtaining the active ingredient even in the presence of an inert carrier. For example, when attempts have been made to activate the catalyst in a manner similar to that described in U.S. Patent No. 3,989,881, the entire amount of the reducing agent theoretically required to fully activate the catalyst has been added to the precursor in suspension in the hydrocarbon, and then the suspension is dried at at 20 to 80 ° C (including limits) to remove the solvent and allow the catalyst to be used in the gas phase operation, a product was obtained that was not sufficiently active in the industrial scale gas phase fluidized bed operation described below .

In the preparation of the useful catalyst, it is necessary to carry out the activation such that at least the last activation stage is carried out in the absence of a solvent, so that the fully active catalyst does not need to be dried to remove the solvent. Two approaches have been developed to achieve this.

According to a first procedure, the precursor is completely activated outside the reactor in the absence of solvent by dry mixing the precursor with the activating compound. In this dry mixing, the activating compound is preferably used in the soaked state in the carrier. However, this process has the disadvantage that the resulting fully activated catalyst is pyrophoric when it contains over 10% by weight of the activating compound.

According to a second preferred method, the precursor is partially activated outside the polymerization reactor. This partial activation is carried out in a hydrocarbon solvent suspension. The resulting product is then dried to remove the solvent. The partially activated impregnated precursor is fed into a polymerization reactor in which activation with an additional activator, which may be the same or another compound, is completed.

In the preparation of the catalyst by dry blending, the solid particulate precursor is uniformly mixed with the solid particles of the porous carrier in which the activating compound is absorbed. The activator compound is absorbed into the carrier from its solution in a hydrocarbon solvent such that 10 to 50% by weight of the activator is stored in 90 to 50% by weight of the carrier. The amount of precursor, activator and carrier is selected so as to achieve the desired Al / Ti molar ratio and to give the resulting catalyst with a weight ratio of precursor to carrier of less than about 0.50, preferably less than about 0.33. This amount of support provides the necessary dilution of the activated catalyst to allow desired control of the polymerization activity of the catalyst in the reactor. When the final catalyst contains more than 10% by weight of the activator, it is pyrophoric. During dry mixing, which can be carried out at ambient temperature (25 ° C) or below, the dry mixture is well mixed to prevent heat buildup on subsequent activation, which is initially effcothermic. A catalyst is thus obtained which is fully activated and can be used in the polymerization solution. It is a free-flowing (loose) substance.

According to a second preferred method, the catalyst is activated in at least two stages. In the first step, the solid particulate precursor, diluted with the carrier, is partially activated by reacting with an amount of activating compound to give a partially activated precursor in which the molar ratio of activator to titanium is about 1 to 10: 1 and preferably about 3 to 6: 1. This partial activation is carried out in a hydrocarbon solvent suspension. The resulting product is then dried to remove the solvent, at a temperature of 20 to 80, preferably 50 to 70 ° C. The resulting product has the character of a free-flowing particulate material and can be readily introduced into the polymerization reactor. In this partial activation, the activator may be used in absorbed form in the carrier used to dilute the activator. The partially activated precursor is preferably poorly effective as a polymerization catalyst in the process of the invention. In order to activate the partially activated precursor for ethylene polymerization, an additional activator must be introduced into the polymerization reactor. This completes the activation of the precursor in the reactor. The additional activator compound and the partially activated precursor are preferably fed to the reactor via separate lines. The additional activating compound can be injected into the reactor as a solution in a hydrocarbon solvent such as isopentane, hexane or mineral oil. This solution usually contains about 2 to 30 why. by weight of activating compound. The activator can also be added to the reactor in solid form, absorbed in the carrier. The carrier usually contains 10 to 50% by weight of activator. The additional activating compound is added to the reactor in an amount such that, together with the amount of activating compound and titanium compound, given in the form of the partially activated precursor, an overall Al / Ti molar ratio of about 10 to 400 and preferably about 15 to 60 is achieved. the amount of activating compound introduced into the reactor reacts with the partially activated precursor and completes the activation of the titanium compound directly in the reactor.

In a continuous gas phase process such as the fluidized bed process described below, separate batches of partially or fully activated precursor are continuously introduced into the reactor during polymerization, optionally with separate batches of additional activating compound needed to complete activation of the partially activated precursor, thus replacing the active sites of the catalyst that were consumed during the reaction.

The polymerization is carried out by contacting the ethylene stream 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 monoxide, carbon dioxide and acetylene, with a catalytically effective amount of fully activated of a precursor (catalyst) at a pressure and temperature sufficient to initiate the polymerization.

The fluidized bed reaction system that can be used in the process of the invention is illustrated in Figure 1.

The reactor 10 comprises a reaction zone 12 and a speed reducing zone 14.

Reaction zone 12 comprises a bed of growing polymer particles, formed polymer particles, and a minor amount of catalyst fluidized by a continuous flow of polymerizable and modifying gaseous components consisting of make-up gas and gas recycled to the reaction zone. In order 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 fluidization. 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. Wen and Y.H. Yu, Mechanics of Fluidization, Chemical Engineering Progress Symposium Series, Vol. 62, pp. 100-111 (1966).

It is important that the bed always contain particles that prevent the formation of "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 polymer formed or may be different. When different, they are drawn off with the resulting polymer particles as a leading product. Finally, the fluidized bed of the desired polymer particles displaces the starter bed.

The partially or fully activated precursor (catalyst) used in the fluidized bed is preferably stored in a standby container 32 under an atmosphere of an inert gas such as nitrogen or argon.

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 the rate of 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 16 located above the bed. The gas analyzer determines the loss of components in the gas to be recycled and the composition of the make-up gas is adjusted accordingly to keep the composition of the gaseous mixture substantially steady state in the reaction zone.

In order to ensure complete fluidization, the recycle gas and possibly part of the make-up gas is fed into the reactor via an inlet 18 under the bed. Above the inlet 18 is placed 14 on a gas distribution plate 20 to assist 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 14 located above the bed in which the velocity is reduced and the entrained particles fall back into the bed. Particle separation may be aided by the inclusion of a cyclone 22, which may either be part of or outside the speed reducing zone 14. If necessary, the recycle gas can then be passed through a filter 24, which is adapted to separate small particles therein at high flow rates to prevent dust from depositing on the heat transfer surface and on the compressor sheets.

The recycle gas is then compressed in a compressor 25 and passed through a heat exchanger 26 where it is stripped of the reaction heat before returning to the bed. By constantly removing the heat of reaction, there is no apparent temperature gradient in the upper part of the bed. A temperature gradient exists in the lower 152 to 304 nm bed, between the inlet gas temperature and the bed rest temperature. It has been observed that the bed almost instantly adapts the temperature of the recycle gas above this 152 to 304 nm bed zone to the bed temperature value so that the bed temperature is substantially constant under steady state conditions. The recycle gas is fed to the bottom of the reactor through the inlet 18 and into the fluidized bed through the distributor plate 20. The compressor 25 may also be placed upstream of the heat exchanger 26 in the direction of flow.

The distributor plate 20 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 possibly 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 the recycle gas is passed through the bed at a rate sufficient to fluidize the particles at the bottom of the bed. The bottom of the bed is formed by a separating plate 20, and may be a screen, slotted plate, perforated plate, plate plate (analogous to the distillation column trays) and the like. All plate portions may be stationary or of a movable type such as The plate described in U.S. Pat. No. 3,298,792. Whatever the structure of the plate, the plate must disperse the recycle gas between the particles at the bottom of the bed and maintain it in a 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 according to the invention. The hydrogen / ethylene molar ratio that can be used is in the range of about 0 to about 2.0 moles of hydrogen per mole of ethylene in the gas stream.

In addition to hydrogen, the compounds of the formula I can be used in addition to hydrogen as molecular weight control agents, i.e. as chain transfer agents.

Zn (R _a ) (R _b ) where

R _a and R l are the same or different C 1 to C 14 aliphatic or aromatic hydrocarbon radicals.

This further increases the melt index values of the produced copolymers. About 0 to 50, and preferably about 20 to 30 moles of the zinc compound (calculated as Zn) per mole of the titanium compound (calculated as Ti) can be added to the gaseous stream introduced into the reactor. The zinc compound may preferably 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 of the type described above in an amount of about 10 to 50. % by weight. These substances are often pyrophoric. The zinc compounds may be added alone or optionally together with the addition of the activator to be introduced into the reactor. These compounds are fed to the hottest part of the recycle gas system from the dispenser, which is not plotted and which may be adjacent to the dispensing device 27.

Any gas inert to the catalysts and reactants may also be present in the gas stream. The activator compound is preferably added to the gas recycle system in its hottest part. Preferably, therefore, the activator is introduced into the recycle line downstream of the heat exchanger, such as from the reservoir 27 through line 27A.

The fluidized bed reactor must operate at a temperature below the sintering temperature of the polymer particles. In order to prevent sintering of the particles, the working temperature must be below the sintering temperature. The production of ethylene homopolymers according to the invention is preferably carried out at a temperature of about 30 ° C to about 115 ° C. Temperatures of about 90 to 105 ° C are used to produce products with a density of about 961 to 968 kg / m ³ .

The fluidized bed reactor operates at a pressure of up to about 6.87 MPa, preferably at a pressure of from about 1.03 to 2.40 MPa, and when operating at higher pressures in this range, heat transfer is facilitated since the pressure increase causes as a result of the increase in unit heat capacity of the gas.

A partially or fully activated precursor is injected into the bed at a rate equal to the rate at which it is consumed by an inlet 30 located above the manifold plate 20. An important feature of the invention is that the catalyst is injected at a point above the manifold plate. Since the catalysts used according to the invention are highly active, injection into the space below the distributor plate could result in polymerization being initiated at this point, which could eventually lead to blockage of the distributor plate. On the contrary, injecting the catalyst into the fluidized bed helps to distribute the catalyst in the bed and avoids the formation of sites with high catalyst concentrations which could lead to hot spots.

A gas inert to the catalyst, such as nitrogen or argon, is used to introduce the partially or fully reduced precursor and any activating compound into the bed.

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

Since any change in catalyst injection rate results in a change in reaction heat evolution rate, the recycle gas temperature is adjusted up or down to accommodate the heat evolution rate. 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 to detect temperature changes in the bed and cooling system so that the operator can appropriately adjust the recycle gas temperature.

Under a certain combination of operating conditions, the fluidized bed is maintained at substantially the same height by withdrawing a portion of the bed as product at the same rate as the rate of particle formation of the polymer product. Since the rate of heat evolution is directly proportional to product formation, the measurement of the increase in gas temperature along the reactor (i.e., the temperature difference between the inlet gas temperature and the outgoing gas temperature) determines the rate of polymer particle formation at a constant gas velocity.

Preferably, the polymer product particles are collected continuously through a conduit 34 or near the distributor plate 20. The particles are collected in the form of a suspension with a portion of the gaseous stream vented prior to settling to prevent further polymerization and caking before the particles reach the zone where are gathering. Suspension gas can also be used to transfer the product from one reactor to another.

The polymer product particles are expediently and preferably removed by means of two stage 16 operating time-controlled valves 36 and 38 between which a separation zone 40 is provided. When valve 38 is closed, valve 36 is opened so that it permits a gas-product mixture into zone 40. Then valve 38 is opened to transfer the product to the outer insulation zone. The valve 38 is then closed and closed until the product is removed.

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 and / or wall scraping devices.

The supported catalyst system of the present invention provides in a fluidized bed a product having an average particle size of about 0.13 to 1.52 mm, preferably between about 0.51 to 1.0 mm, the residues of the supported catalyst in the polymer being unusually small.

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 32.4 to about 162.2 kg / hr / 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 density measurement is then performed in a density gradient column.

Melt Flow Index (MI)

ASTM D-1238-Condition E measurements are performed at 190 ° C, g data per 10 minutes. Flow rate (melt flow index at higher load) (HLMI)

ASTM D-1238-Condltion F, measurement is performed using tenfold load than melt index measurement

Flow Rate Ratio Flow Rate Melt Flow Index

Productivity

A sample of the resin product is ashed and the weight% ash is determined, since 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 and chlorine in the ash is determined by elemental analysis.

Cyclohexane extractable substances

The resin sample is extracted with boiling cyclohexane at atmospheric pressure for at least 18 hours.

Bulk density

The resin is poured into a 100 ml graduated cylinder through a funnel with a 9.5 mm stem diameter up to the 100 ml mark. The cylinder does not shake during filling. The weight difference is determined by weighing.

Molecular weight distribution (Mw / / Mn)

It is determined by gel chromatography on Styrogel with a pore size sequence ΙΟ ⁶ , 10 ⁵ , ΙΟ ⁴ , 10 ³ , 6 nm. The solvent used is o-dichlorobenzene at 135 ° C. Detection was performed by infrared radiation at 3.45 µm. Unsaturation

Measurements are performed using an infrared spectrophotometer (Perkin Elmer Model 21). Resins of 0.635 mm thickness are made from the resin and serve as test specimens. Absorbance is measured at 10.35 µm for transvinylidene unsaturation, at 11.0 µm for terminal vinyl unsaturation and at 11.25 µιη for vinylidene unsaturation in the side chains. Absorbance per 1 mm of thickness of the compact is directly proportional to the multiple of the concentration of unsaturation and absorbency. Absorbency values are taken from literature [R. J. de Kock, et al., J. Polymer Science. Part B, 2, 339 (1964)].

Example I

Preparation of precursor

In a five-liter flask equipped with a mechanical stirrer, 16.0 g (0.168 mol) of anhydrous magnesium chloride under nitrogen are mixed with 850 ml of pure tetrahydrofuran. The mixture was stirred at room temperature (about 25 ° C) and 13.05 g (0.069 mol) of titanium tetrachloride was added dropwise. At the end of the addition, the contents of the flask were refluxed for 1/2 hour to 1 hour to dissolve the solids. The system was cooled to room temperature and then 3 liters of n-hexane was slowly added over 1/4 hour. A yellow solid precipitated. The supernatant was decanted and the solid was washed three times with one liter of n-hexane. The solids are then filtered off and dried on a rotary evaporator at. 40-60 ° C. 55 g of a solid precursor are obtained.

At this point, the precursor can be lysed to magnesium and titanium, since certain amounts of the magnesium and / or titanium compound may have been lost in the isolation of the precursor. The empirical formulas used herein to characterize the precursor composition are derived provided that magnesium and titanium still exist in the form of compounds that were originally added to the electron donor compound and that the remaining weight of the precursor is the electron donor compound.

Analysis of solids revealed Mg composition:

6.1%, Ti: 4.9%, which corresponds to the formula

TiMg ₂ , ₁₅ Cl _{8> 9} (THF) _7;

THF is tetrahydrofuran. Example II

Activation procedures

Procedure

This activation procedure involves a multi-step activation of the precursor. Activation is carried out in such a way that the precursor is only partially activated before being introduced into the polymerization reactor and the activation is completed in the reactor.

The required weight of dry inert carrier is placed in a mixing vessel or drum. In the examples described herein, about 500 g of silica and about 1000 g of polyethylene carrier are used as carriers. The inert carrier is then mixed with a sufficient amount of an anhydrous aliphatic hydrocarbon diluent, such as isopentane, to form a suspension. Usually about 4 to 7 ml of diluent per g of inert carrier is required. The desired weight of the precursor is then placed in a mixing vessel and thoroughly mixed with the suspension. In the examples given herein, about 80 to 135 g of precursor containing 1 ± 0.1 mmol of titanium per gram of precursor are used to produce the catalysts.

The required amount of activator required to partially activate the precursor is added to the contents of the mixing vessel. An amount of activator is used such that the Al / Ti ratio in the partially reduced precursor is up to 10: 1 and preferably 3 to 6: 1. The activator is added to the mixing drum in the form of a solution containing about 20% by weight of the activator (in these examples triethyl aluminum) in an inert aliphatic hydrocarbon solvent (in these examples hexane). Activation is performed by thorough mixing and bringing the activator into contact with the precursor. All operations described above are carried out at room temperature and at atmospheric pressure under an inert atmosphere.

The resulting suspension is dried under a stream of dry inert gas such as nitrogen or argon at atmospheric pressure and at a temperature of up to 60 ° C to remove the hydrocarbon diluent. This usually takes about 3 to 5 hours. The substance is in the form of a free-flowing pulverulent material consisting of a uniform mixture of activated precursor with an inert carrier. The dried product is stored under an inert gas.

When the additional activator of Process A is introduced into the polymerization reactor to complete activation of the precursor, the activator may first be absorbed in an inert carrier such as silica gel or polyethylene, but most preferably the activator is introduced into the reactor as a dilute solution in a hydrocarbon solvent such as isopentane. .

When the activator is to be absorbed in a silica gel carrier, the two substances are mixed together in a container containing about 4 ml of isopentane per gram of carrier. The resulting suspension is then dried for about 3-5 hours with a stream of nitrogen at atmospheric pressure at 65 ± 10 ° C to remove the hydrocarbon diluent.

When the activator is injected into the polymerization system in the form of a dilute solution, a concentration of about 5 to 10% by weight is preferably used.

Regardless of the method of introducing the activator into the polymerization reactor to complete activation of the precursor, the activator is used in an amount such that the Al / Tl ratio in the polymerization reactor is maintained at from 10 to 400: 1 and preferably from 10 to 100: 1, including values.

The silica is dried at a temperature of at least 200 ° C for at least 4 hours before use. Procedure B

In this procedure, complete activation of the precursor is accomplished by contacting the precursor with the activator absorbed in the inert carrier during mixing.

The activator is absorbed in the inert carrier by suspending it together with the carrier in an inert hydrocarbon solvent and then drying the suspension to remove the solvent. The mixture obtained contains about 10 to 50% by weight of activator. The procedure is therefore as follows: 500 g of silica (previously dried at 800 ^{DEG C. for} 4 hours) are introduced into a mixing vessel. Then the required amount of activator in the form of a 20% (w / w) solution in a hydrocarbon solvent such as hexane is added to the mixing vessel and the mixture is mixed, suspended with an inert carrier at room temperature and atmospheric pressure. Then the solvent is evaporated by drying the resulting suspension at 65 ± 10 ° C for about 3-5 hours at atmospheric pressure with a stream of dry inert gas such as nitrogen. The dried composition is in the form of bulk particles having the same size as the particles of the carrier used.

About 500 g of dried silica are charged to a mixing vessel with an activator (50:50 by weight) applied to the reme, and the desired weight of precursor (80-135 g) is added. The material is thoroughly mixed for 1 to 3 hours at room temperature and atmospheric pressure under a dry inert gas such as nitrogen or argon. The resulting mixture is similar to a physical mixture of bulk particles having a size of the order of 10 to 150 μιη. During mixing, the activator on the carrier comes into contact with the precursor and activates it completely. During the exothermic reaction that occurs, the catalyst temperature should not exceed 50 ° C to prevent any catalyst deactivation. The resulting activated catalyst has an Al / Ti ratio of about 10 to 50 and, if it contains more than 10% by weight of the activator, may be pyrophoric. It is stored under a dry inert gas such as nitrogen or argon before being introduced into the reactor. Examples 1 to 3

In each of these three examples, ethylene is homopolymerized using the catalyst described above and activated by activation procedure A. The precursor diluted with silica contains 18.4 ± 1% by weight of the precursor. In each case, the partially activated precursor has an Al / Ti molar ratio of 4.52 ± 0.03. Completion of the precursor activation in the polymerization reactor is accomplished with triethyl aluminum absorbed in silica (50/50 weight ratio of the two compounds) so as to obtain a fully activated catalyst with an Al / Ti 30 molar ratio in the reactor.

Each of the polymerization reactions is carried out continuously for at least 1 hour after equilibration at a pressure of 2.06 MPa at a gas velocity of about three to four times the Gmf value and a space velocity of yield of 48.7 to 97.3 kg / m ² / h.

The reaction system described above is shown. Its lower part is 3.05 m high and its inner diameter is 0.343 m. The upper part is high

4.88 m and its inner diameter is 0.597 m.

Table I shows the molar ratio of H 2 / / ethylene, the ethylene content in the reactor in volume 0 / o and the polymerization temperature in Examples 1 and 3 and the various properties of the granulated crude resins produced in these Examples.

TABLE I

The reaction conditions and properties of the resins in Examples 1 to 3

3

Example

Operating conditions Molar ratio Hz / Cz temperature [° Cj ethylene content in reactor [° / o vol catalyst productivity [kg resin / kg Ti]

Properties, resin Density [kg / m ³ ]

Melt flow index [g / 10 min]

Melt flow rate ratio,

Cyclohexane extractable content [%]

Ash content [% by weight]

Ti content [ppm]

Cl content [ppml (estimated)]

Cl content [ppm] (by analysis)

Bulk density [kg / m ³ ]

Mean particle size [mm]

Dust content (> 10 mesh) [% by weight]

Examples 4 to 16

In each of these 13 examples, ethylene is homopolymerized using a catalyst prepared by the above process and activated by activation process A. The partially activated precursor in each case has an Al / Ti molar ratio of 4.71 ± 0.01. Completion of the precursor activation is carried out in a polymerization reactor with triethyl carbonate as a solution in isopentane at a concentration of 2.6 to 5% by weight. Using

0.201 0.411 0.418 90 110 104 74.8 53.8 58.6 210 000 74 000 142 000 962.6 970.8 970.1 0.63 14.6 7.38 29.2 27.0 27.9 0.16 0.74 0.43 0,054 0.196 0,068 4.8 13.5 7.0 32 89 46 - 53—62 39—45 293.6 425.0 405.5 0.93 0.49 0.65 7.9 20.0 5.0

The amount of Al-Ti molar ratio is 13 to 62.

Each of the reactions was carried out in the same manner as in Examples 1 to 3. Table II below sets forth, for Examples 4 to 16, the operating conditions also shown in Table I, the Al / Ti molar ratio maintained in the reactor and the precursor content in the precursor / silicon dioxide, diluted with silicon dioxide. Table III lists the various properties of the polymers produced in Examples 4 to 16.

In Examples 5, 6 and 9, diethylzinc was introduced into the reactor as a 2.6% by weight solution of isopentane, in an amount such that the Zn / Ti ratio in the reactor was maintained at 30. In these examples, the reactor activator was also is added as a solution in 2,6% by weight of isopentane.

TABLE II

The reaction conditions in Examples 4 to 16

Example Content precursor [% weight] Molar ratio Al / Ti in the reactor Temperature [° C] The ethylene content of the reactor was 1% by volume.] Molar ratio H2 / C2 Catalyst productivity [kg resin / kg titanium] 4 17.7 30 100 ALIGN! 62.9 0.421 333 000 5 17.7 30 110 71.9 0.263 333 000 6 18.2 24.1 100 ALIGN! 69.3 0.198 200 000 7 18.0 12.7 110 63.0 0.226 143 000 8 18.8 22.1 99.9 57.2 0.405 125 000 9 17.0 51.0 104 55.5 0.400 105 000 10 17.0 48.0 104 54.9 0.390 91000 11 17.4 62.3 104 52.5 0.393 80 000 12 17.2 43.7 104 55.9 0.400 100 000 13 17.2 23.4 104 54.7 0.403 83 000 14 17.6 38.1 104 58.6 0.399 77 000 15 Dec 17.5 46.9 104 55.2 0.390 125 000 16 17.5 49.9 104 57.2 0.406 105 000

TABLE III

Properties of the polymers produced in Examples 4 to 16

Example Density Melt flow index [g / 10 min] Ratio speed flow Ash content [% by weight] Content Ti [ppm] Bulk density [kg / m ³ ] Medium size of particles [mm] 4 969.3 9.0 28.4 0,073 3.0 384.4 0.79 5 969.1 7.57 28.0 0,054 3.0 374.7 0.78 6 965.6 1.74 26.2 0.019 5.0 343.9 1,02 7 963.5 3.08 25.1 0,074 7.0 381.2 0.83 8 970.1 9.93 27.4 0.106 8.0 343.9 0.79 9 970.6 6.47 27.8 0.100 9.5 384.4 0.54 10 970.1 7.33 25.6 0,090 11.0 394.1 0.53 11 970.6 8.12 27.7 0,110 12.5 353.6 0.57 12 969.9 8.37 26.9 0,080 10.0 353.6 0.61 13 970.8 7.28 27.7 0.125 12.0 363.3 0.66 14 970.9 9.33 27.7 0.100 13.0 384.4 0.62 15 Dec 970.7 7.33 27.4 0.117 8 272.5 0.46 16 971.6 10,03 28.4 0.105 9.5 374.7 0.58

Claims (3)

A process for the catalytic production of an ethylene homopolymer using a titanium-containing catalyst at a productivity of at least 50,000 kg of polymer per kg of titanium in a reactor under a gas pressure of below 6.87 MPa, the polymer being formed in granular form and having a density of 958 to 972 kg / m ³ , including limit values, and a melt flow rate ratio of 22 to 32, including limit values, characterized in that ethylene is homopolymerized at a temperature of 30 to 115 ° C by contacting the monomer feed in the presence of about 0 to 2 0 moles of hydrogen per mole of ethylene in the reaction zone for gas phase reactions with particles of a catalyst system consisting of a precursor of the general formula Mg _m Ti ₁ (OR) _n X _p [ED] _q where represents ED electron donor compound, m number from 0.5 to 56 including limit values, n number 0 or 1, p number from 6 to 116 including limit values, q number from 2 to 85 including limit values, R a C 1 to C 14 aliphatic or aromatic hydrocarbon radical or a radical of formula COR ‘, wherein R‘ represents a C 1 to C 14 aliphatic or aromatic hydrocarbon radical, and X chlorine, bromine or iodine or a mixture thereof, which is mixed with 1 to 20 parts by weight per 1 part by weight of the precursor of at least one inert carrier and is first partially activated outside the reactor by not more than 10 moles of activating compound per mole of titanium contained in the precursor; OF THE INVENTION either outside the reactor of> 10 to 400 moles of activating compound per mole of titanium in the precursor, wherein complete activation is effected to form a solid dry catalyst system prior to feeding the system to the polymerization reactor without heating it above 50 ° C during These activation steps, which are carried out with an amount of activating compound above 10 moles, or fully activated in the reactor of> 10 to> 400 moles of activating compound per mole of titanium contained in the precursor, the activating compound being a compound of the general formula Al (R ') _c X _d ' H _c 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 C 1 -C 14 saturated hydrocarbon radical, d is a number from 0 to 1.5, e is a number of 1 or 0, the sum of c + d + e being 3 , and the electron donor compound is a liquid organic compound in which the precursor is soluble, selected from the group consisting of alkyl esters of aliphatic and aromatic carboxylic acids, aliphatic ethers, cyclic ethers and aliphatic ketones. 2. A process according to claim 1, wherein the process is carried out in a fluidized bed process. 3. The process of claim 1 wherein the partially activated catalyst is metered into the reaction zone where complete activation takes place.