WO1999002573A1

WO1999002573A1 - Method for reducing sheeting during olefin polymerization

Info

Publication number: WO1999002573A1
Application number: PCT/US1998/013884
Authority: WO
Inventors: Gary Hafernick; Thomas James Mcneil; Todd Alan Prey; Jesus Sergio Tijerina
Original assignee: Union Carbide Chemicals & Plastics Technology Cor Poration
Priority date: 1997-07-08
Filing date: 1998-07-07
Publication date: 1999-01-21
Also published as: AU8382698A

Abstract

There is provided a method for reducing sheeting during polymerization of one or more olefins, including diolefins, in a fluidized bed reactor in the presence of a polymerization catalyst, optionally in the presence of an inert particulate material, which method comprises lowering the reactor bed temperature, optionally with the addition of a prostatic agent, by an amount sufficient to maintain the electrostatic levels at the site of potential sheet formation at levels which avoid sheeting without substantially altering the activity of said catalyst.

Description

METHOD FOR REDUCING SHEETING DURING OLEFIN POLYMERIZATION

Field of the Invention

This invention relates to a method for reducing electrostatically-induced sheeting during polymerization of olefins.

Background of the Invention

It has been found that a static mechanism is a contributor to a sheeting phenomena in which catalyst and resin particles adhere to the reactor walls due to static forces. If electrical static is allowed to reside long enough under a reactive environment, excess temperatures can result in particle fusion which in turn can lead to sheeting. The sheets vary widely in size, but are similar in most respects. They are usually about 1/4 to 1/2 inch thick and about 1 to 5 feet long, with a few specimens even longer. They have a width of about 3 to 18 inches or more. The sheets are composed of a core of fused polymer oriented in the length dimension of the sheets and their surfaces are covered with granular resin fused to the core. The edges of the sheets can have a hairy appearance from strands of fused polymer.

Numerous causes for static charge exist. Among them are generation due to frictional electrification of dissimilar materials, limited static dissipation, introduction to the polymerization process of minute quantities of prostatic agents, and so forth.

A correlation exists between sheeting and the presence of excess static charges of either negative or positive polarity. This is evidenced by sudden changes in static levels followed closely by deviation in temperatures at the reactor wall. These temperature deviations can be either higher or lower. A lowering of the temperature indicates particle adhesion causing an insulating effect from the bed temperature. A raising of the temperature is indicative of a reaction taking place in zones of limited heat transfer. Following this, disruption in fluidization patterns is generally evident, catalyst feed interruption can occur, product discharge system pluggage results, and undesirable thin fused agglomerates (sheets) appear in the granular product.

The art teaches various processes for reducing or eliminating static voltage. They include (1) reducing the rate of charge generation, (2) increasing the rate of discharge of electrical charge, and (3) neutralization of electrical charge. One or more of these is accomplished in a fluidized bed by (1) using an antistatic agent or prostatic agent to increase the conductivity of the particles, thus, providing a path for discharging; (2) installation of grounding devices in a fluidized bed to provide additional area for discharging electrostatic charges to ground; (3) ionization of gas or particles by electrical discharge to generate ions to neutralize electrostatic charges on the particles; (4) the use of radioactive sources to produce radiation that will create ions to neutralize electrostatic charges on the particles; (5) use of sonic devices or sound waves to keep particles from adhering to the reactor wall; and/or (6) treating the surface of the inside wall of the reactor to reduce static generation. A species that when injected into a fluidized bed gives rise to static levels is termed a prostatic agent. There are species of prostatic agents that can generate static voltage of negative polarity and those that generate voltage of positive polarity.

A relatively simple method of controlling static in a fluidized bed reactor is to feed a prostatic agent in ppm quantities to the reactor in order to neutralize the existing static voltage as taught in U.S. Patent No. 4,855,370 and U.S. Patent No. 4,803,251. However, we .have found on certain resin grades produced with trimethylaluminum as cocatalyst that even when this technique is performed in accordance with the teachings of the above patents, the static is insufficiently neutralized. High static levels, in turn, may lead to sheeting in the reactor.

The art does not teach using temperature as a means of sheeting or static control. This is so, because commercial polymerizations of alpha-olefins are conducted at a constant temperature in order for the catalyst activity to remain constant and to provide for continuous, even product discharge. Even slight changes in temperature have been known to seriously affect the overall operation of a polymerization and product properties.

Conventional low density polyethylene has been historically polymerized in heavy walled autoclaves or tubular reactors at pressures as high as 50,000 psi and temperatures up to 300°C or higher. The molecular structure of high pressure, low density polyethylene (HP-LDPE) is highly complex. The permutations in the arrangement of their simple building blocks are essentially infinite. HP-LDPE' s are characterized by an intricate long chain branched molecular architecture. These long chain branches have a dramatic effect on the melt rheology of these resins. HP-LDPE's also possess a spectrum of short chain branches, generally 1 to 6 carbon atoms in length. These short chain branches disrupt crystal formation and depress resin density.

More recently, technology has been provided whereby low density polyethylene can be produced by fluidized bed techniques at low pressures and temperatures by copolymerizing ethylene with various alpha-olefins. These low pressure, low density polyethylene (LP-LDPE) resins generally possess little, if any, long chain branching and are sometimes referred to as linear LDPE resins. They are short chain branched with branch length and frequency controlled by the type and amount of comonomer used during polymerization.

As is well known to those skilled in the art, low pressure, high or low density polyethylene s, as well as other polymers, can now be conventionally provided by a fluidized bed process utilizing several families of catalysts to produce a full range of low density and high density products. The appropriate selection of catalysts to be utilized depends in part upon the type of end product desired, i.e., high density, low density, extrusion grade, film grade resins and other criteria. These polymerizations, products, and the catalysts used to produced them are plagued with static electricity in varying degrees of severity and the ensuing sheeting phenomena.

There is an on- going need to provide additional methods of static control, particularly ones which are not disruptive of the overall operation during polymerization, adversely affect the activity of the catalyst, and/or add additional reactants to the polymerization process.

SUMMARY OF THE INVENTION

Accordingly, there is provided a process for reducing sheeting in fluidized bed reactors during steady- state and transitioning.olefin and diolefin polymerizations in which static electricity is present.

The present invention provides a method for reducing sheeting during polymerization of olefins or diolefins in a fluidized bed reactor in the presence of a polymerization catalyst, optionally in the presence of an inert particulate material, which method comprises lowering the reactor bed temperature, optionally with the addition of a prostatic agent, by an amount sufficient to maintain the electrostatic levels at the site of potential sheet formation at levels which avoid sheeting without substantially altering the activity of said catalyst.

In a preferred embodiment of the invention the above- described method for reducing sheeting is employed in the polymerization of an ethylene-hexene copolymer in a gas phase fluidized bed reactor in the presence of a titanium-based catalyst such as a TiCl3 or TiCl4 catalyst. Preferably, the ethylene-hexene

copolymer has a density of about 0.915 to 0.932 g/cm , e.g., 0.925

g/cm , and a melt index of about 0.1 to 2.0 dg/10 minutes, e.g., 0.5 dg/10 minutes. The ethylene-hexene copolymer is produced such that the feeds are 35-41% C2; 2-6% CQ; 5-8.1% H2 with the balance being made up of inerts (e.g., N2, isopentane and/or hexane). The normal temperature for this product is 90-92°C, but can be and is preferably polymerized at temperatures ranging from 75-92°C, most preferably 75-85°C to prevent or reduce sheeting.

Conventional static countermeasures (RSC, condensing mode, higher condensing levels) have met with little or limited success. Only lowering the bed temperature improved static, especially when polymerizing the preferred ethylene-hexene copolymer. Because of the nature of static, the differences in reactors (and products when there is more than one of interest), and induced condensing agents (isopentane or hexane), it was discovered that there is no way to suggest a priori a temperature that will work for a given product.

Accordingly, it was found that the bed temperature is lowered until one of three things happens: 1) static is ameliorated or abated, 2) skin thermocouple temperatures return to normal and stay there, or 3) the lowest bed temperature maintained with the various system constraints (cooling limit, purging limit, etc.) is reached. Typically, the reactor temperature is lowered by 1 to 2 degrees every 20-30 minutes depending on the observed stability of the system. While not wishing to be bound by theory, it is believed that the lower temperature works because the condensables are kept condensed longer and that they are thus penetrating into more of the static areas of the bed. This is not the same as higher condensing levels or even condensing mode per se, since condensing mode per se does not appreciably help with the production or polymerization of this product. Therefore, simultaneously, the inlet temperature is lowered as much as possible so that the gas/liquid entering the reactor is as cold as possible for the same reason. This is accomplished by a number of ways including reducing superficial velocity, use of a chiller or refrigeration unit, or by eliminating the induced condensing agent.

BRIEF DESCRIPTION OF THE DRAWING

Figure 1 is a schematic depiction of a gas phase polymerization reactor and system. Figure 2 shows reactor transition from a first product (0.917 density; 1.0 MI) to a second product (0.925 density; 0.5 MI) of Example 1. Figure 3 demonstrates effectiveness of decreasing temperature to control/reduce static when employing a triethylaluminum cocatalyst.

Detailed Description of the Invention

Polymers. Illustrative of the polymers which can be produced in accordance with the process of the invention are the following: homopolymers and copolymers of C2-C18 alpha olefins, preferably homo- and co-polymers of ethylene and a C3-C8 alpha olefin; ethylene propylene rubbers (EPRs); ethylene-propylene diene rubbers (EPDMs); polyisoprene; polystyrene; polybutadiene; polymers of butadiene copolymerized with styrene; polymers of butadiene copolymerized with isoprene; polymers of butadiene copolymerized with acrylonitrile; polymers of isobutylene copolymerized with isoprene; ethylene butene rubbers and ethylene butene diene rubbers; polychloroprene; norbornene homopolymers and copolymers with one or more C2-C18 alpha olefin; terpolymers of one or more C2-C18 alpha olefins with a diene (conjugated nonconju ated); and the like. The preferred polymers to which the present invention is primarily directed, and which cause the sheeting problems referred to above, are those produced using a titanium catalyst. Such preferred polymers can include, for example, linear homopolymers of ethylene or linear copolymers of a major mol percent (greater than or equal to 80%) of ethylene, and a minor mol percent (less than or equal to 20%) of one or more C3 to Cg alpha olefins. The C3 to Cs alpha olefins should not contain any branching on any of their carbon atoms which is closer than the fourth carbon atom. Preferably, the C3 to Cg alpha olefins are present in amounts ranging from 1% to 20%, most preferably from 1% to 12%. The preferred C3 to CQ alpha olefins are propylene, butene- 1, pentene-1, hexene-1, 4-methylpentene-l, heptene- 1, and octene-1. The most preferred C3 to Cg alpha olefin for use in an ethylene copolymer is hexene-1.

These homopolymers and copolymers have a density ranging from about 0.84 to 0.97, preferably from about 0.88 to 0.94. The density of the copolymer, at a given melt index level, is primarily regulated by the amount of the C3 to Cg comonomer which is copolymerized with the ethylene. Thus, the addition of progressively larger amounts of the comonomers to the copolymers results in a progressive lowering of the density of the copolymer. The amount of each of the various C3 to Cg comonomers needed to achieve the same result will vary from monomer to monomer, under the same reaction conditions. In the absence of the comonomer, the ethylene would homopolymerize. This description is not intended to exclude the use of this invention with alpha olefin homopolymer and copolymer resins in which ethylene is not a monomer.

The melt index of a homopolymer or copolymer is a reflection of its molecular weight. Polymers having a relatively high molecular weight, have relatively high viscosities and low melt index.

Catalysts. Any type of polymerization catalyst may be used in the polymerization process. A single catalyst may be used, or a mixture of catalysts may be employed, if desired. The catalyst can be soluble, or insoluble, supported or unsupported. It may be a prepolymer, spray dried with or without a filler, a liquid, or a solution, slurry or dispersion. These catalysts are used with cocatalysts and promoters well known in the art. Typically these are aluminum- alkyls, halides, as hydrides and well as aluminoxanes. For illustrative purposes only, examples of suitable catalysts include:

A. Ziegler-Natta catalysts, including titanium based catalysts such as those described in U.S. Patent Nos. 4,302,566; 4,376,062; and 4,379,758. Ziegler-Natta catalysts are well known in the art, and typically are magnesium/titanium/electron donor complexes used in conjunction with an organoaluminum cocatalyst.

B. Chromium based catalysts such as those described in U.S. Patent Nos. 3,709,853; 3,709,954; and 4,077,904.

C. Vanadium based catalysts such as vanadium oxychloride and vanadium acetylacetonate, such as described in U.S. Patent No. 5,317,036.

D. Metallocene catalysts and other single-site or single-site-like catalysts such as those taught in U.S. Patent Nos. 4,530,914; 4,665,047; 4,752,597; 5,218,071; 5,272,236; 5,278,272; 5,317,036; and 5,527,752.

E. Cationic forms of metal halides, such as aluminum trihalides.

F. Anionic initiators such as butyl lithiums.

G. Cobalt catalysts and mixtures thereof such as those described in U.S. Patent Nos. 4,472,559 and 4,182,814; PCT Application Nos. 95/09826 and 95/09827.

H. Nickel catalysts and mixtures thereof such as those described in U.S. Patent Nos. 4,155,880 and 4,102,817; PCT Application Nos. 95/109826 and 95/09827.

I. Rare earth metal catalysts, i.e., those containing a metal having an atomic number in the Periodic Table of 57 to 103, such as compounds of cerium, lanthanum, praseodymium, gadolinium and neodymium. Especially useful are carboxylates, alcoholates, acetylacetonates, halides (including ether and alcohol complexes of neodymium trichloride), and allyl derivatives of such metals, e.g., of neodymium. Neodymium compounds, particularly neodymium neodecanoate, octanoate, and versatate, and n-alkyl neodymium are the most preferred rare earth metal catalysts. Rare earth catalysts are especially preferred and used to produce polymers polymerized using butadiene, styrene, or isoprene and the like. Such rare earth catalysts are disclosed for example in PCT 95/09826; PCT 95/09827; and EPO 647,657.

Since polymerizations employing them are associated with static electricity, the preferred catalysts for the process of the present invention include rare earth metal catalysts, titanium catalysts, vanadium catalysts, and the metallocene/single-site/single- site-like catalysts. Of these, titanium catalysts and metallocenes or other single-site or single-site like catalysts or catalyst complexes containing titanium and their polymerizations can especially benefit from the present invention.

The titanium catalysts which are particularly preferred in the process of the invention are as described in U.S. Patent No. 4,302,566 to F.J. Karol et al. entitled, "Preparation of Ethylene Copolymers in Fluid Bed Reactor" and assigned to the same assignee as the present application. These catalysts comprise at least one titanium-based compound, at least one magnesium compound, at least one electron donor compound, at least one activator compound and at least one inert carrier material.

The titanium compound has the structure: Ti(OR)_aX_D)wherein R is a C to C14 aliphatic or aromatic hydrocarbon radical, or COR' where R' is a C to C14 aliphatic or aromatic hydrocarbon radical; X is Cl, Br, or I; a is 0 or 1; b is 2 to 4 inclusive; and a+b equals 3 or 4.

The titanium compounds can be used individually or in combinations of two or more, and include TiCl3, TiCl4, Ti(OCH)Cl3, Ti(OC₆H₅)Cl3, Ti(OCOCH₃)Cl₃, and Ti(OCOC₆H₅)Cl. Of these, TiCl3 and TiCl4 are most preferred.

The magnesium compound has the structure: MgX2, wherein X is Cl, Br, or I. Such magnesium compounds can be used individually or in combinations and would include MgCl2, MgBr2 and Mgl2- Anhydrous MgCl2 is the preferred magnesium compound.

The titanium compound and the magnesium compound are generally used in a form which will facilitate their dissolution in the electron donor compound. The electron donor compound is an organic compound which is liquid at 25°C and in which the titanium compound and the magnesium compound are partially or completely soluble. The electron donor compounds are known as such or as Lewis bases.

Illustrative electron donor compounds include such compounds as alkyl esters of aliphatic and aromatic carboxylic acids, aliphatic ethers, cyclic ethers and aliphatic ketones.

The catalyst may be modified with a boron halide compound having the structure: BR_CX'3__C) wherein R is an aliphatic or aromatic hydrocarbon radical containing from 1 to 14 carbon atoms or OR', wherein R' is also an aliphatic or aromatic hydrocarbon radical containing from 1 to 14 carbon atoms; X' is selected from the group consisting of Cl and Br, or mixtures thereof; and c is 0 or 1 when R is an aliphatic or aromatic hydrocarbon and c is 0, 1 or 2 when R is OR'.

Illustrative boron halide compounds can be used individually or in combination of two or more include BCI3, BBr3, B(C₂H₅)Cl2, B(OC₂H₅)Cl₂, B(C₂H5)₂C1, B(C₆H₅)C1₂, B(OC₆H₅)Cl₂, B(C6H₁₃)C1₂, B(C6Hι₃)Cl₂, B(OC₆H₅)Cl₂. Boron trichloride is the particularly preferred boron compound.

The activator compound has the structure: A1(R")_CX ₍jH_e, wherein X' is Cl or OR'"; R" and R'" are the same or different and are Ci to C14 saturated hydrocarbon radicals; c is as set forth above; d is 0 to 1.5; e is 1 or 0, and c+d+e equals 3. A single activator compound can be employed or a mixture of them can be used.

The carrier materials of this particular titanium catalyst system are solid, particulate materials and include inorganic materials such as oxides of silicon and aluminum and molecular sieves, and organic materials such as olefin polymers, e.g., polyethylene. The process of the present invention is most effective when used in alpha olefin polymerizations utilizing these titanium catalysts, especially supported titanium catalysts. Titanium catalysts on a silica support are most preferred. It is therefore an object of the present invention to provide a method for substantially reducing or eliminating the amount of sheeting which occurs during the low pressure fluidized bed polymerization of alpha-olefins (e.g., an ethylene-hexene copolymer) utilizing titanium-based compounds as catalyst with alkyl aluminum as cocatalysts.

Fluidization Aids. Also referred to herein as inert particulate materials or flow aids, fluidization aids employed in the invention can be inert particulate materials which are chemically inert to the reaction. Examples of such fluidization aids include carbon black, silica, clays, other like materials such'as talc, and mixtures thereof. Organic polymeric materials can also be employed as a fluidization aid. Carbon blacks, silica, and mixtures of them are the preferred fluidization aids with carbon black being the most preferred. The carbon black materials employed have a primary particle size of about 10 to 100 nanometers and an average size of aggregate (primary structure) of about 0.1 to about 10 microns. The specific surface area of the carbon black is about 30 to 1,500 m2/gm and the carbon black displays a dibutylphthalate (DBP) absorption of about 80 to about 350 cc/100 grams.

Silicas which can be employed are amorphous and have a primary particle size of about 5 to 50 nanometers and an average size of aggregate of about 0.1 to 10 microns. The average size of agglomerates of silica is about 2 to about 120 microns. The silicas employed have a specific surface area of about 50 to 500 m2/gm and a dibutylphthalate (DBP) absorption of about 100 to 400 cc/100 grams.

Clays which can be employed according to the invention have an average particle size of about 0.01 to about 10 microns and a specific surface area of about 3 to 30 m2/gm. They exhibit oil absorption of about 20 to about 100 gms per 100 gms.

Organic polymeric substances which can be used include polymers and copolymers of ethylene, propylene, butene, and other alpha olefins and polystyrene, in granular or powder form. These organic polymeric materials have an average particle size ranging from about 0.01 to 100 microns, preferably 0.01 to 10 microns.

In general, the amount of fluidization aid utilized generally depends on the type of material utilized and polymer produced. When utilizing carbon black or silica, or preferably a mixture of the two, as the fluidization aid, they can be employed in amounts of about 0.3% to about 80% by weight, preferably about 5% to about 60%, and most preferably about 10% to about 45%, based on the weight of the final product (polybutadiene or polyisoprene) produced. When clays or talcs are employed as the fluidization aid, the amount can range from about 0.3% to about 80% based on the weight of the final product, preferably about 12% to 75% by weight. Organic polymeric materials are used in amounts of about 0.1% to about 50% by weight, preferably about 0.1% to about 10% based on the weight of the final polymer product produced.

Inert particulate materials or flow aids are generally employed in polymerizations which produce sticky polymers (EPRs and other rubbery materials such as polybutadiene, polystyrene and other vinyl-substituted aromatic compounds).

The fluidization aid can be introduced into the reactor at or near the top of the reactor, at the bottom of the reactor, directly into the polymerization zone of the reactor, and/or to the recycle line directed into the bottom of the reactor. Preferably, the fluidization aid is introduced at or near the top of the reactor or above the fluidized bed. It is preferred to treat the fluidization aid prior to entry into the reactor with an aluminum alkyl or other scavenger compound to remove traces of moisture and oxygen. This can be accomplished by purging the material with nitrogen gas and heating by conventional procedures. The fluidization aids can be added separately or combined with one or more monomers, or with one or more of the catalysts or with one or more individual components of the catalyst (precursor or co-catalyst, for example). Preferably, the fluidization aid is added separately.

In the absence of a fluidization aid, the polymerization is conducted at or preferably below the sintering temperature of the polymer product being produced. Use of a fluidization aid, among other benefits, enables polymer products to be produced at, preferably above their sintering or softening temperature.

Prostatic Agents. Optionally a prostatic agent can be employed in the present invention. Illustrative prostatic agents can include, for example, water and alcohols such as methanol, ethanol, and isopropanol. When employed, prostatic agents are introduced into the reactor by bubbling a gaseous stream such as ethylene or nitrogen through an appropriate vessel filled with the agent to saturate the gas. The resulting vapor is then fed to the reactor and metered in controlled amounts in response to excursions in static. Typically, such agents are employed in amounts ranging from about 0.1 to 100 ppm, preferably about 0.1 to 10 ppm.

Polymerization Conditions. The present invention is not limited to any specific type of stirred or fluidized gas phase polymerization reaction and can be carried out in a single reactor or multiple reactors (two or more reactors preferably connected in series). In addition to well known conventional gas phase polymerizations processes, "condensed mode", including the so-called "induced condensed mode", and "liquid monomer" operation of a gas phase polymerization reactor can be employed.

A conventional fluidized bed process for producing resins is practiced by passing a gaseous stream containing one or more monomers continuously through a fluidized bed reactor under reactive conditions in the presence of a polymerization catalyst. Product is withdrawn from the reactor. A gaseous stream of unreacted monomer is withdrawn from the reactor continuously and recycled into the reactor along with make-up monomer added to the recycle stream. Conventional gas phase polymerizations are disclosed, for example, in U.S. Patent Nos. 3,922,322; 4,035,560; and 4,994,534. Optionally, and preferably, a conventional polymerization of the present invention is conducted in the presence of one or more inert particulate materials as described in U.S. Patent No. 4,994,534.

Condensed mode polymerizations are disclosed in U.S. Patent Nos. 4,543,399; 4,588,790; 4,994,534; 5,352,749; and 5,462,999. Condensing mode processes are employed to achieve higher cooling capacities and, hence, higher reactor productivity. In these polymerizations a recycle stream, or a portion thereof, can be cooled to a temperature below the dew point in a fluidized bed polymerization process, resulting in condensing all or a portion of the recycle stream. The recycle stream is returned to the reactor. The dew point of the recycle stream can be increased by increasing the operating pressure of the reaction/recycle system and/or increasing the percentage of condensable fluids and decreasing the percentage of non-condensable gases in the recycle stream. The condensable fluid may be inert to the catalyst, reactants and the polymer product produced; it may also include monomers and comonomers. The condensing fluid can be introduced into the reaction/recycle system at any point in the system. Condensable fluids include saturated or unsaturated hydrocarbons. In addition to condensable fluids of the polymerization process itself, other condensable fluids, inert to the polymerization can be introduced to "induce" condensing mode operation. Examples of suitable condensable fluids may be selected from liquid saturated hydrocarbons containing 2 to 8 carbon atoms (e.g., ethane, propane, n-butane, isobutane, n-pentane, isopentane, neopentane, n-hexane, isohexane, and other saturated CQ hydrocarbons, n-heptane, n-octane and other saturated C7 and Cg hydrocarbons, and mixtures thereof). Condensable fluids may also include polymerizable condensable comonomers such as olefins, alpha -olefins, diolefins, diolefins containing at least one alpha olefin, and mixtures thereof. In condensing mode, it is desirable that the liquid entering the fluidized bed is dispersed and vaporized quickly. Optionally, and preferably, inert particulate materials as described in U.S. Patent No. 4,994,534 can be employed in condensing and/or induced mode polymerizations. Liquid monomer polymerization mode is disclosed in U.S. Patent No. 5,453,471; U.S. Serial No. 510,375; PCT 95/09826 (US) and PCT 95/09827 (US). When operating in the liquid monomer mode, liquid can be present throughout the entire polymer bed provided that the liquid monomer present in the bed is adsorbed on or absorbed in solid particulate matter present in the bed, such as polymer being produced or fluidization aids, also known as inert particulate materials (e.g., carbon black) present in the bed, so long as there is no substantial amount of free liquid monomer present more than a short distance above the point of entry into the polymerization zone. Liquid mode makes it possible to produce polymers in a gas phase reactor using monomers having condensation temperatures much higher than the temperatures at which conventional polyolefins are produced. In general, a liquid monomer process is conducted in a stirred bed or gas fluidized bed reaction vessel having a polymerization zone containing a bed of growing polymer particles. The process comprises continuously introducing a stream of one or more and optionally one or more inert gases or liquids into the polymerization zone optionally in the presence of one or more inert particulate materials; continuously or intermittently introducing a polymerization catalyst into the polymerization zone; continuously or intermittently withdrawing polymer product from the polymerization zone; and continuously withdrawing unreacted gases from the zone; compressing and cooling the gases while maintaining the temperature within the zone below the dew point of at least one monomer present in the zone. If there is only one monomer present in the gas-liquid stream, there is also present at least one inert gas. Typically, the temperature within the zone and the velocity of gases passing through the zone are such that essentially no liquid is present in the polymerization zone that is not adsorbed on or absorbed in solid particulate matter. The use of fluidization aids is preferred in the liquid monomer process of the present invention. In view of the dew points or condensation temperatures of the dienes and vinyl- substituted aromatic compounds employed in the gas phase polymerization process of the present invention, liquid monomer mode is the preferred polymerization mode.

Generally, all of the above modes of polymerizing are carried out in a gas phase fluidized bed made up of or containing a "seed bed" of polymer which is the same or different from the polymer product being produced. The bed is preferably made up of the same granular resin that is to be produced in the reactor. Thus, during the course of the polymerization, the bed comprises formed polymer particles, growing polymer particles, and initiator particles fluidized by polymerizing and modifying gaseous components introduced at a flow rate or velocity sufficient to cause the particles to separate and act as a fluid.

The fluidizing gas is made up of the initial feed, make-up feed, and cycle (recycle) gas, i.e., monomers, and, if desired, modifiers and/or an inert carrier gas (e.g., nitrogen, argon, or inert hydrocarbon such as ethane, with nitrogen being preferred). A typical cycle gas is comprised of one or more monomers, nitrogen, and optionally hydrogen, either alone or in combination. The process can be carried out in a batch or continuous mode, the latter being preferred. The essential parts of the reactor are the vessel, the bed, the gas distribution plate, inlet and outlet piping, at least one compressor, at least one cycle gas cooler, and a product discharge system. In the vessel, above the bed, there is a velocity reduction zone, and in the bed, a reaction zone. Both are above the gas distribution plate.

Variations in the reactor can be introduced if desired. One involves the relocation of one or more cycle gas compressors from upstream to downstream of the cooler and another involves the addition of a vent line from the top of the product discharge vessel (stirred tank product) back to the top of the reactor to improve the fill level of the product discharge vessel.

Polymerization can also be conducted by charging one monomer initially, allowing it to polymerize, and then adding a second monomer, and allowing it to polymerize in a single polymerization vessel. Alternatively, two or more polymerization vessels, preferably connected in series, can be used to polymerize with one or even two or more monomers. Using multiple reactors, one monomer can be polymerized in the first reactor, and one or more additional monomers can be polymerized in second or subsequent reactors.

In general, the polymerization conditions in the gas phase reactor are such that the temperature ranges from about 0° to 120°C, preferably about 40° to 110°C, and most preferably about 70° to 90°C. Partial pressure will vary depending upon the particular monomer employed and the temperature of the polymerization, and it can range from about 1 to 150 psi. Condensation temperatures of the monomers are well known. Typically for polymers produced using ethylene, the ethylene partial pressure ranges from about 80 to 120 psia. In general, it is preferred to operate at a partial pressure slightly above to slightly below the dew point of the monomer (that is, for example, + 10°C for low boiling monomers). For example, for butadiene and styrene-butadiene, the partial pressure ranges from about 10 to about 100 psi; isoprene partial pressure ranges from about 10 to about 50 psi. For styrenic polymers, styrene is fed as a ratio to achieve the desired polymer composition. For styrene polymerization in liquid monomer mode the liquid monomer (styrene) is maintained at a concentration of about 1 to about 30 wt/% of styrene monomer to polymer in the reactor. Total reactor pressure ranges from about 300 to about 500 psi.

Use of Temperature to Control Static. During a polymerization reaction, static voltage levels can rise approaching the levels which induce sheeting. In the present invention, the bed temperature is lowered to sufficiently alter the phase equilibria of the recycle and/or make-up gas to achieve enhanced gas distribution plate washing and fluidized bed penetration leading to a reduction of the static voltage in the critical region wherein electrostatically-induced sheets form.

In the present invention, static voltage in the reactor is monitored near the reactor wall by one or more static voltage indicators such as static probe (50) inserted into the reactor bed, preferably approximately 5 feet above the gas distribution plate. During a sheeting episode, the static rises as indicated by the static probe followed by one or more skin thermocouples indicating a local temperature above the bed temperature. This means that there is a sheet growing on the thermocouple. The voltage range of the indicators is in the range of about +15,000 volts. With polymerization reaction in progress, changes in static voltage levels from neutral to either positive or negative polarity can lead to agglomerate formation which may incur a process upset or even shutdown. This can be counteracted by lowering the bed temperature in order to sufficiently change the thermodynamics of the polymerization in the reactor in the critical region of the reactor which extends from the gas distribution plate to a height above the reactor null zone.

When this is successfully accomplished, there is an increased fraction of condensables, for example, an inert "induced- condensing agent" or ICA such as hexane, isopentane, hexene, or other readily condensable monomer (butadiene, isoprene, styrene, etc.). This increased fraction and the aforementioned change in the thermodynamics in the critical region allows the condensables to "wash" the gas distribution plate and penetrate farther into the fluidized bed, since the bed temperature has been moved closer to the entering gas stream's dew point. It is believed that this is so, because a liquid droplet of a component is able to carry a charge much more readily than the same component in its gaseous state. The result is a reduction of the electrostatic voltage in the critical region and concomitantly a reduction in the tendency of the reactor to sheet. This lowering of the bed temperature should be done in 2°C increments until the desired improvement is seen. The normal range of this decrease in temperature is from 5° to 20°C below the temperature one skilled in the art would choose based upon resin density/melt index considerations alone. It is understood that the extremely complex nature of the static generation/dissipation mechanisms and their interrelationship with existent reaction conditions and resin properties precludes an exact formula by which the operator could "dial in" the proper temperature for the minimization of static a priori.

In the present invention, catalyst activity is not altered significantly by lowering the temperature and/or the washing effect (which occurs in less than 4% of the total bed volume) because the catalyst kinetics are such that the loss of activity is less than 10%.

Using Figure 1 depicting a conventional gas fluidized reactor (10) and reaction system, the invention will be more particularly described for the polymerization of a low pressure, low density polyethylene homopolymer or copolymer utilizing a titanium- based catalyst with an alkyl aluminum cocatalyst. In Figure 1, a conventional fluidized bed reaction system for polymerizing alpha- olefins includes a reactor (10) which consists of a reaction zone (12) and a velocity reduction zone (14). The reaction zone (12) includes 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 in the form of makeup feed and recycle gas through the reaction zone.

Thermocouples (50) were installed just inside the reactor walls at elevations of 1/4 to 1/2 reactor diameter above the gas distribution plate (22). Under conventional operations, skin thermocouples indicate temperatures equal to or slightly lower than the temperature of the fluidized bed. When sheeting occurs, these thermocouples can indicate temperature excursions of up to 30° C above the temperature of the fluidized bed, thus providing reliable indication of the occurrence of sheeting. Typically three sets of four skin thermocouples (TC's) at elevations of 3 feet, 5-5^ feet, and 7-8 feet above the plate. Sheeting generally does not take place at higher elevations in the bed. The 7-8 foot TC's that indicate sheeting are typically about 1/2 the plate diameter of the reactors.

In addition, an electrostatic voltmeter was used to measure voltage on a 1/2-inch spherical electrode located in the fluid bed, 1 inch radially from the reactor wall and usually 5 to 6 feet above the gas distributor plate (22). The location was selected because sheet formation was observed to initiate in a band ranging from 1/4 to 3/4 reactor diameter in elevation above the base (i.e., the distributor plate) of the fluid bed. For deep fluidized beds, this corresponds to the region of least mixing intensity near the wall, i.e., a null zone, where particle motion near the wall changes from generally upward to generally downward. It is recommended and preferred to use one static probe per reactor located about 1/2 to 3/4 the plate diameter up from the plate (i.e., the location of static-induced sheeting). Static at this location is generally believed to be a good indicator of the state of the reactor. Use of a plurality of static probes can give false readings. That is, static changes magnitude and even polarity in different, non- fixed, regions of the reactor.

The reactor is partially filled with granular polyethylene resin which is purged with a non-reactive gas such as nitrogen and is fluidized by circulating the non-reacting gas through the reactor at a velocity above the minimum fluidizing velocity (Gmf) of the granular polyethylene, and preferably at 3 to 5 Gmf.

It is highly desirable that the bed always contains particles to prevent the formation of localized "hot spots" and to entrap and distribute the particulate catalyst throughout the reaction zone. On start up, the reactor is usually charged with a seed bed of particulate polymer particles before gas flow is initiated. Such particles may be identical in nature to the polymer to be formed or different therefrom. When different, they are withdrawn with the desired formed polymer particles as the first product. Eventually, a fluidized bed of the desired polymer particles supplants the start-up bed. The reactor is brought up to operational temperatures by the gas, and the reaction is started by introducing the catalyst and cocatalyst to the reactor.

To maintain a viable fluidized bed, the mass gas flow rate through the bed is normally maintained above the minimum flow required for fluidization, and preferably from about 1.5 to about 10 times Gmf, and more preferably from about 3 to about 6 times Gmf. Gmf is used in the accepted form as the abbreviation for the minimum gas flow required to achieve fluidization, C, Y. Wen and Y. H. Yu, "Mechanics of Fluidization", Chemical Engineering Progress Symposium Series, Vol. 62, pg. 100-111 (1966).

Hydrogen may be used as a chain transfer agent for conventional polymerization reactions of the types contemplated herein. In the case where ethylene is used as a monomer the ratio of hydro gen/e thy lene employed will vary between 0 to about 2.0 moles of hydrogen per mole of the monomer in the gas stream.

Any gas inert to the catalyst and reactants can also be present in the gas stream. The cocatalyst is added to the gas recycle stream upstream of its connection with the reactor as from dispenser (28) through line (30). The appropriate catalyst used in the fluidized bed is preferably stored for service in a reservoir (16) under a blanket of a gas which is inert to the stored material, such as nitrogen or argon.

The catalyst is injected into the bed at a rate equal to its consumption at a point (32) which is above the distribution plate (22). A gas which is inert to the catalyst such as nitrogen or argon is used to carry the catalyst into the bed. It is generally preferred to inject the catalyst above the distribution plate, since the catalysts normally used are highly active, injection into the area below the distribution plate may cause polymerization to begin there and eventually cause plugging of the distribution plate. Injection into the viable bed, instead, aids in distributing the catalyst throughout the bed and tends to preclude the formation of localized spots of high catalyst concentration which may result in the formation of "hot spots".

For the production of ethylene polymers an operating temperature of from about 90°C to about 107°C is preferably used to prepare products having a density of about 0.94 to 0.97 while a temperature of about 65° to 95°C is preferred for products having a density of about 0.88 to 0.94.

Under a given set of operating conditions, the fluidized bed is maintained at essentially a constant height by withdrawing a portion of the bed as product at a rate equal to the rate of formation of the particulate polymer product. Since the rate of heat generation is directly related to product formation, a measurement of the temperature rise of the gas across the reactor (the difference between inlet gas temperature and exit gas temperature) is determinative of the rate of particulate polymer formation at a constant gas velocity.

The particulate polymer product is preferably withdrawn at a point (34) at or close to distribution plate (22). The particulate polymer product is conveniently and preferably withdrawn through the sequential operation of a pair of timed valves (36) and (38) defining a segregation zone (40). While valve (38) is closed, valve (36) is opened to emit a plug of gas and product to the zone (40) between it and valve (36) which is then closed. Valve (38) is then opened to deliver the product to an external recovery zone and after delivery, valve (38) is again closed to await the next product recovery operation.

Finally, the fluidized bed reactor is equipped with an adequate venting system to allow venting the bed during the start up and shut down. The reactor does not require the use of stirring means and/or wall scraping means. The system is operated with various flow and check valves which are common in the art and hence, not illustrated. The reactor vessel is normally constructed of carbon steel and is designed for the operating conditions stated above.

Under conventional operation, after a period of time, sheets begin to form in reactor (10), at a site in the reactor proximate the wall of the reactor and located about a distance of one-half the reactor diameter up from the base of the fluid bed. The sheets of fused resin begin to appear in segregation zone (40), rapidly plugging the system, causing the reactor to be shut down. Characteristically, the sheeting begins after production equivalent to 6 to 10 times the weight of the bed of resin in reactor.

Sheeting is substantially reduced, and in most cases entirely eliminated, by controlling static voltage in the fluidized bed at a site proximate the reactor walls below the critical level for sheet formation. This critical level for sheet formation is not a fixed value, but is a complex function dependent on variables including resin sintering temperature, operating temperature, drag forces in the fluid bed, resin particle size distribution, other physical properties, and recycle gas composition. In the polymerization sheeting is controlled by manually or by automation (i.e., by computer) adjusting the temperature downward in about 1 to 4 degree increments over a time interval of 30 to 60 minutes until the reading from the voltmeter and/or thermocouples register normal levels or a return to previous non-sheeting readings.

The sintering temperature of the resin under reactor operating conditions is the temperature at which a settled bed of resin in contact with a gas having the same composition as the reactor recycle gas used in producing the resin will sinter and form agglomerates when refluidization is attempted after allowing the bed to remain settled for fifteen minutes. The sintering temperature is decreased by decreasing the resin density, by increasing the melt index, and by increasing the amount of dissolved monomers and monomer type.

The voltage indicated on the voltage probe described earlier varies with time due to the random nature of a fluidized bed. Thus, the critical voltage is expressed as a time averaged voltage. Voltage measurements are difficult to interpret because additional static electric charge is generated when a sheet is formed and then separates from the reactor wall. In addition, the sheeting phenomena can start as a very local phenomenon and subsequently spread, further making interpretation of voltage readings difficult.

Fluidization is achieved by a high rate of gas recycle to and through the bed, typically in the order of about 50 times the rate of feed of make-up gas. The fluidized bed has the general appearance of a dense mass of viable particles in possible free-vortex flow as created by the percolation of gas through the bed. The pressure drop through the bed is equal to or slightly greater than the mass of the bed divided by the cross -sectional area. It is thus dependent on the geometry of the reactor.

Make-up gas is fed to the bed at a rate equal to the rate at which particulate polymer product is withdrawn. The composition of the make-up gas is determined by a gas analyzer (18) positioned above the bed. The gas analyzer determines the composition of the gas being recycled and the composition of the make-up gas is adjusted accordingly to maintain an essentially steady state gaseous composition within the reaction zone.

To ensure complete fluidization, the recycle gas and, where desired, part or all of the make-up gas are returned to the reactor at base (20) below the bed. Gas distribution plate (22) positioned above the point of return ensures proper gas distribution and also supports the resin bed when gas flow is stopped.

The portion of the gas stream which does not react in the bed constitutes the recycle gas which is removed from the polymerization zone, preferably by passing it into velocity reduction zone (14) above the bed where entrained particles are given an opportunity to drop back into the bed.

The recycle gas is then compressed in a compressor (24) and thereafter passed through a heat exchanger (26) wherein it is stripped of heat of reaction before it is returned to the bed. By constantly removing heat of reaction, no noticeable temperature gradient appears to exist within the upper portion of the bed. A temperature gradient will exist in the bottom of the bed in a layer of about 6 to 12 inches, between the temperature of the inlet gas and the temperature of the remainder of the bed. Thus, it has been observed that the bed acts to almost immediately adjust the temperature of the recycle gas above this bottom layer of the bed zone to make it conform to the temper^" ature of the remainder of the bed thereby maintaining itself at an essentially constant temperature under steady conditions. The recycle is then returned to the reactor at its base (20) and to the fluidized bed through distribution plate (22). The compressor (24) can also be placed downstream of heat exchanger (26).

In transitioning, the procedure is the same except for changes in recycle gas composition, and starting or desired bed temperature based on the properties of the resin to be produced. When static has increased such that sheeting would occur (or it had already started), then the temperature is lowered until 1) static decreased, 2) the skin thermocouple temperature returned to normal and stayed there, or 3) the lowest bed temperature at which the various system constraints (cooling limit, purging limit, etc.) could still be maintained was reached.

All references cited in this application are hereby incorporated by reference.

Whereas the scope of the invention is set forth in the appended claims, the following specific examples illustrate certain aspects of the present invention. The examples are set forth for illustration only and are not to be construed as limitations on the invention, except as set forth in the claims. All parts and percentages are by weight unless otherwise specified.

EXAMPLES

Examples 1 through 4 were conducted in a conventional fluidized bed reactor. The catalyst used was a Ziegler type, titanium- based catalyst supported on porous silica. The cocatalyst used was trimethylaluminum. The products made in the examples were copolymers of ethylene and 1 -hexene. Hydrogen was used as a chain transfer agent to control the melt index of the polymer. Hexane was the induced condensing agent (ICA) in Example 1 while isopentane was the ICA in Examples 2 through 4.

EXAMPLE 1

A fluidized bed reactor was transitioned from a 0.917 density, 1.0 melt index (MI) ethylene/hexene copolymer to a 0.925 density, 0.5 melt index ethylene/hexene copolymer. The catalyst (Ziegler titanium-based) was the same for both products. Specifically, the catalyst was a mixture of 6.8 parts titanium trichloride, 9.8 parts magnesium dichloride, and 10 parts tetrahydrofuran deposited on 100 parts Davison grade 955 silica which had been dehydrated at 600°C and treated with 5.8 parts triethylaluminum prior to deposition. The final catalyst was of a 0.45 mole diethyl aluminum chloride per mole of tetrahydrofuran, 0.20 mole tri-n-hexylaluminum per mole of tetrahydrofuran reduction ratio. The bed temperature was increased from 86°C to 91°C during the transition to the higher density product. Ethylene, hexene, and hydrogen were established at 35, 3.5, and 5% respectively. The cocatalyst was trimethylaluminum and was fed at a 22:1 aluminum to titanium ratio.

The transition was smooth but as the 0.917 density, 1.0 MI material was replaced by the 0.925 density, 0.5 MI resin, static became more pronounced as shown in Figure 2. Static ultimately grew to as much as +10,000 volts. A prostatic agent (water) was fed to the reactor in accordance with the teachings of U.S. Patent No. 4,855,370 and U.S. Patent No. 4,803,251 but could not neutralize the static. The bed temperature was lowered to 86°C and static quickly returned to neutral. Static remained at neutral for the rest of the run. At the end of the run, the bed temperature was raised in a test and static increased as can be see in Figure 2.

EXAMPLE 2

A fluidized bed reactor was running smoothly on a 0.920 density, 0.5 MI ethylene/hexene copolymer with trimethylaluminum as cocatalyst. The catalyst was similar to that described in Example 1. The bed temperature was originally maintained at 86°C. During production, an upset occurred which caused the static voltage to increase markedly. The bed temperature was lowered to 83°C and the static returned to a nearly zero baseline as shown in Figure 3. The rest of the run was without incident and the required quantity of resin was produced. EXAMPLE 3 (COMPARATIVE)

A fluidized bed reactor was transitioned smoothly from a 0.918 density, 1.0 MI ethylene/hexene copolymer with triethylaluminum as cocatalyst to a 0.920 density, 0.5 MI ethylene/hexene copolymer with trimethylaluminum as cocatalyst. The catalyst was the same for both products being similar to that described in Example 1. During production of the 0.920 density, 0.5 MI ethylene/hexene copolymer, the bed temperature was maintained at 87°C. Ethylene, hexene, and hydrogen were established at 31, 4.7, and 4.7% respectively. The cocatalyst was trimethylaluminum and was fed at a 31:1 aluminum to titanium ratio. Static voltage increased during the run to +1500 volts. A prostatic agent (water) was fed to the reactor in accordance with the teachings of U.S. Patent No. 4,855,370 and U.S. Patent No. 4,803,251 but could not neutralize the static. Sheets were formed which hampered operation. The run was aborted and the reactor transitioned to another product and static returned to neutral.

EXAMPLE 4 (COMPARATIVE

A fluidized bed reactor was transitioned smoothly from a 0.929 density, 0.5 MI ethylene/hexene copolymer with triethylaluminum as cocatalyst to a 0.920 density, 0.5 MI ethylene/hexene copolymer with trimethylaluminum as cocatalyst. The catalyst was the same for both products being similar to that described in Example 1. During production of the 0.920 density, 0.5 MI ethylene/hexene copolymer, the bed temperature was maintained at 87°C. Ethylene, hexene, and hydrogen were established at 38, 5.6, and 5.7% respectively. The cocatalyst was trimethylaluminum and was fed at a 24:1 aluminum to titanium ratio. Following the transition to the 0.920 density, 0.5 MI product, static voltage increased with spikes to +3500 volts. A prostatic agent (water) was fed to the reactor in accordance with the teachings of U.S. Patent No. 4,855,370 and U.S. Patent No. 4,803,251 but could not neutralize the static. Sheets were formed which hampered operation. The run was aborted and the reactor transitioned to another product and static returned to neutral.

EXAMPLE 5

A fluidized bed reactor was transitioned smoothly from a 0.925 density, 0.8 MI ethylene/hexene copolymer running at 90°C with triethylaluminum as cocatalyst to a 0.925 density, 0.5 MI ethylene/hexene copolymer with trimethylaluminum as cocatalyst. The catalyst was the same for both products being similar to that described in Example 1. During the transition the reactor bed temperature was lowered to 78°C. This was in response to the findings delineated in Example 1 regarding the effect on static of lower-than- customary bed temperature. Ethylene, hexene, and hydrogen were established for the production of the 0.925 density, 0.5 MI product at 41, 4, and 8.7% respectively. The cocatalyst was trimethylaluminum and was fed at a 28:1 aluminum to titanium ratio. The average static voltage was lower during the run at +500 volts than in the aborted runs and no sheets were formed throughout the run.

Claims

WHAT IS CLAIMED IS:

1. A method for reducing sheeting during polymerization of (1) at least one olefin with optionally a diene or (2) a diolefin in a gas phase reactor in the presence of a polymerization catalyst, which method comprises lowering the reactor bed temperature by an amount sufficient to maintain the electrostatic levels at the site of potential sheet formation at levels which avoid sheeting without substantially altering the activity of said catalyst.

2. The method of Claim 1 wherein the reactor is equipped with one or more voltage indicators for monitoring electrostatic levels; and wherein in response to a rise in electrostatic levels as indicated on said one or more voltage indicators, the temperature of the fluidized bed is lowered in 2 degree increments until said rise in electrostatic levels ceases or returns to its previous level.

3. The method of Claim 2 wherein said voltage indicators have a voltage range of about + 15,000 volts; and said voltage indicators are positioned in the reactor at locations of 4 to 8 feet above the distribution plate; and optionally the reactor is equipped with an electrostatic voltmeter having a spherical electrode located in the fluid bed, 1 inch radially from the reactor wall and 5 to 6 feet above a gas distributor plate.

4. The method of Claim 1 wherein the catalyst is selected from the group consisting of a titanium catalyst, chromium catalyst, a vanadium catalyst, a metallocene catalyst or other single- site or single-site like catalyst, cationic forms of metal halides, anionic initiators, cobalt catalysts, nickel catalysts, rare earth catalysts, and mixtures thereof.

5. The method according to Claim 1 wherein a prostatic agent, selected from the group consisting of water, methanol, ethanol, isopropanol, and mixtures thereof, is introduced intermittently or continuously into the reactor, into the recycle lines, or both.

6. The method according to Claim 1 wherein a fluidization aid, selected from the group consisting of carbon black, silica, clay, talc, and mixtures thereof, is introduced into the reactor.

7. The method according to Claim 1 wherein the olefin is one or more C2 -Cg alpha olefins, the catalyst is titanium catalyst, the cocatalyst is an alkyl aluminum.

8. The method according to Claim 7 wherein the olefins are ethylene and a C3-Cg alpha olefin selected from the group consisting of propylene, butene-1, pentene-1, hexene-1, 4- methylpentene-1, heptene-1, and octene-1.

9. The method according to Claim 8 wherein the titanium catalyst has the formula: Ti(OR)_aXb wherein R is a C╬╣-C 4 ahphatic or aromatic hydrocarbon radical, or COR' wherein R' is a C^- C14 ahphatic or aromatic hydrocarbon radical; X is Cl, Br, or I; a is 0 or 1; b is 2 to 4 inclusive; and a+b equals 3 or 4.

10. The method according to Claim 9 wherein the polymer produced by the polymerization has a melt index ranging from about 0.1 and 2.0 dg/10 minutes and a density ranging from about 0.915 and 0.935 g/cm³.

11. The method according to Claim 10 wherein the olefins being polymerized are ethylene and hexene- 1; the hexene is present in the copolymer being produced in an amount ranging from about 1% to 20% by weight based upon the total weight of the copolymer; the catalyst employs TiCl3, TiCLj, or a mixture of them; and the cocatalyst is trimethylaluminum, triethylaluminum or a mixture of them.