Olefin polymerization

Abstract: A process is disclosed for the particle form polymerization of olefins. The process employs a titanium-containing having hydrocarbon soluble titanium components. The resulting catalyst is pretreated with an organometallic reducing agent prior to the introduction of the catalyst into the polymerization zone to give a catalyst which can be used satisfactorily in a loop reactor with lower levels of cocatalyst.

Description: Field of the Invention The present invention relates to the polymerization of olefins. In one aspect the present invention relates to slurry or particle form polymerization. In another aspect the present invention relates to olefin polymerization using a continuous loop-type reactor. In still another aspect the present invention relates to novel catalyst systems for use in the polymerization of olefins. Background of the Invention One of the more common techniques employed for the polymerization of olefins involves carrying the polymerization out in a liquid diluent under conditions such that the polymer is formed in the forms of solid particles such that the reaction product is a slurry of particulate polymer solids suspended in a liquid medium. Such reaction techniques have been referred to as slurry or particle form polymerizations. A particularly desirable method for carrying out such particle form polymerization involves the use of continuous loop-type reactors. Examples of such reactor systems are disclosed in U.S. Patent No. 3,152,872 and U.S. Patent No. 4,424,341, the disclosures of which are incorporated herein by reference. In the past, many of the commercial particle form polymerization processes have used chromium based catalysts. Such processes have, however, also been carried out using titanium based catalyst and organometallic cocatalysts. When using low levels of cocatalyst in the particle form polymerization the applicants have noted some problems in using a titanium based catalyst. Even though the levels of cocatalysts are high enough to ensure sufficient productivity, it has been observed that with a titanium-containing catalyst system when the level of cocatalyst drops below a certain level there is a tendency for a skin of some type to form within the reactor walls inhibiting heat transfer. On bench scale units where the polymerization is only an hour or so long and where heat transfer is usually not critical the phenomena is usually not observed. However, in commercial scale polymerizations, particularly in loop reactors the phenomena has been observed. The exact nature of this skin formation is not understood at this time. It has been theorized by the applicants that it may be due to the formation of soluble polymer or soluble catalyst. One theory of the applicants is that it may actually be due to the bleeding off of hydrocarbon soluble species from the catalyst. EP-A-0 324 587 relates to a catalyst which is prepared by contacting a slurry of a solid porous support in a non-polar solvent with at least one organomagnesium composition. Thereafter, the resulting slurry is contacted with an alcohol, and the thus obtained slurry is contacted with a transition metal compound and the resulting product finally with trimethylaluminium. FR-A-2 474 039 is directed to a process for producing α-olefin polymers in the presence of a preactivated catalyst. This catalyst is prepared by first reacting TiCl 4 with an organoaluminium compound, with an electron-donor and electron-acceptor to obtain a solid product. This solid product is combined with an organoaluminium compound, an α-olefin and the reaction product of an organoaluminium compound with an electron-donor. EP-A-0 178 982 discloses a catalyst system for the polymerization of propylene, which catalyst system comprises a solid catalyst composed of TiCl 4 and magnesium chloride, and isoprenyl aluminium as cocatalyst. An object of the present invention is to provide a method for the particle form polymerization of olefins using a titanium containing catalyst system with a reduced tendency to cause the formation of a skin during the polymerization. Another object of the present invention is to provide a process for the particle form polymerization of olefins using a titanium based catalyst which can be employed satisfactorily with low cocatalyst levels. Another object of the present invention is to provide a titanium catalyst which can be used in a commercial scale particle form polymerization without the employment of high levels of cocatalyst. Other aspects, objects, and advantages of the present invention will be apparent to those skilled in the art having the benefit of the following disclosure. Summary of the Invention In accordance with the present invention there is provided a method for the polymerization of olefins as defined in claim 13, which comprises contacting an olefin with a titanium-containing catalyst under particle form polymerization conditions in a polymerization zone. In accordance with another aspect of the present invention there is provided a process for preparing a catalyst as defined in claim 1 and a catalyst for the polymerization of olefins as defined in claim 11. In accordance with a particularly preferred embodiment the titanium-containing catalyst is prepared by contacting a titanium alkoxide and a magnesium dihalide in a suitable liquid to produce a solution, the solution is contacted with a suitable precipitating agent to obtain a solid, the solid after possibly being contacting with olefin to form prepolymer is contacted with titanium tetrachloride, then the resulting solid is contacted with a hydrocarbyl aluminum compound and washed several times with a hydrocarbon solvent prior to the introduction of the solid into a polymerization vessel. Detailed Description of the Invention It is considered that this invention would have application for any particle form polymerization when the catalyst is a titanium-containing catalyst which contains hydrocarbon soluble titanium components and is prepared according to claim 1. For the purpose of this disclosure a catalyst is deemed to be a catalyst containing hydrocarbon soluble titanium components if the titanium components are soluble when the catalyst is placed in a C 4 to C 8 hydrocarbon at a temperature in the range of 0°C to 110°C and the catalyst is prepared according to claim 1. The organometallic reducing agent that is contacted with the titanium-containing solid catalyst can be selected from generally any of those type of organometallic reducing agents that have in the past been used as cocatalysts with such titanium-containing catalysts. Examples include organometallic compounds such as hydrocarbyl aluminum compounds, hydrocarbyl boron compounds, and hydrocarbyl alkali or alkaline earth metal compounds. Some specific examples of such reducing agents include triethylboron, diethylmagnesium, diethylzinc, and n-butyl lithium. The currently preferred organometallic reducing agent is selected from compounds of the formula R m AlZ 3-m wherein R is a hydrocarbyl group having 1 to 8 carbons, Z is a halogen, hydrogen, or hydrocarbyl group having 1 to 8 carbons, and m is a number in the range of 1 to 3. The currently most preferred organometallic reducing agents are selected from trialkylaluminum compounds, especially triethylaluminum. The amount of reducing agent employed in pretreating the titanium-containing catalyst can vary over a wide range. The optimum amount needed for the best overall improvement in the particle form polymerization can be determined by routine experimentation. Generally, excess organometallic reducing agent can be used; however, in such cases it is desirable to subject the resulting product to a number of washes with a hydrocarbon solvent to assure that soluble organometallic reducing agent is removed from the catalyst prior to the introduction of the catalyst into the polymerization process. The invention is particularly useful when applied to a titanium-containing catalyst containing olefin prepolymer of the type disclosed in U.S. Patent No. 4,325,837. Soch catalysts are prepared by reacting a titanium alkoxide with a magnesium dihalide in a suitable liquid to form a solution. The resulting solution is then contacted with a suitable precipitating agent and the resulting solid is contacted with titanium tetrachloride either before or after prepolymer of an olefin is added to the solid. Examples of the titanium alkoxides include the titanium tetraalkoxides in which the alkyl groups contain 1 to 10 carbon atoms each. Some specific examples include titanium tetramethoxide, titanium dimethoxide diethoxide, titanium tetraethoxide, titanium tetra-n-butoxide, titanium tetrahexyloxide, titanium tetradecyloxide, titanium tetraisopropoxide, and titanium cyclohexyloxide. The magnesium halide is preferably selected from magnesium chlorides. The titanium alkoxide and the magnesium dihalide can be combined in any suitable liquid. Examples include substantially anhydrous organic liquids such as n-pentane, n-hexane, n-heptane, methylcyclohexane, toluene, and xylenes. The molar ratio of the transition metal compound to the metal halide can be selected over a relatively broad range. Generally, the molar ratio is within the range of 10 to 1 to 1 to 10, preferably between 3 to 1 to 0.5 to 2; however, more often the molar ratios are within the range of 2 to 1 to 1 to 2. Generally, it is necessary to heat the liquid mixture to obtain a solution. Generally, the components are mixed at a temperature in the range of 15°C to 150°C. The mixing could be carried out at atmospheric pressure or at higher pressures. The time required for heating the two components is any suitable time which will result in a solution. Generally, this would be a time within the range of 5 minutes to 10 hours. Following the heating operation, the resulting solution can be filtered to remove any undissolved material or extraneous solid, if desired. The precipitating agent is selected from the group consisting of organometallic compounds in which the metal is selected from the metals of Groups I to III of the Mendelyeev Periodic Table, metal halides and oxygen-containing halides of elements selected from Groups IIIA, IVA, IVB, VA, and VB of the Mendelyeev Periodic Table, hydrogen halides, and organic acid halides, the latter preferably of the formula R'-C-X wherein R' is an alkyl, aryl, cycloalkyl group or combinations thereof containing from 1 to 12 carbon atoms and X is a halogen atom. Some specific examples of such precipitating agents include lithium alkyls, Grignard reagents, dialkyl mngnesium compounds, dialkyl zinc compounds, dihydrocarbyl aluminum monohalides, monohydrocarbyl aluminum dihalides, hydrocarbyl aluminum sesquihalides, aluminum trichloride, tin tetrachloride, silicone tetrachloride, vanadium oxytrichloride, hydrogen chloride, hydrogen bromide, acetyl chloride, benzoyl chloride, and propionyl fluoride. The amount of precipitating agent employed can be selected over a relatively broad range depending upon the particular activities desired. Generally, the molar ratio of the transition metal of the titanium-containing solid component to the precipitating agent is within the range of from 10 to 1 to 1 to 10 and more generally within the range of 2 to 1 to 1 to 3. In especially preferred embodiments the catalyst contains an amount of prepolymer sufficient to improve the particle size of the catalyst and ultimately the size of the polymer particles produced in a polymerization reaction. One way of forming prepolymer involves conducting the precipitation in the presence of an aliphatic mono-1-olefin. Another technique involves contacting the precipitated solid with an aliphatic mono-1-olefin under suitable conditions to form prepolymer. This can be done either before or after the solid is treated with titanium tetrachloride. Examples of olefins which can be used for forming prepolymer include ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 4-methyl-1-pentene, 1-heptene, and 1-octene, and mixtures of one or more thereof. The weight of prepolymer based on the total weight of the prepolymerized catalyst is generally in the range of from 1 to 90 wt. %, more preferably 1 to 20 wt. %, and still more preferably 1 to 15 wt. %. The relative ratios of the titanium tetrachloride to the solid can vary over wide range; however, as a general rule, the weight ratio of the titanium tetrachloride to the prepolymerized or unprepolymerized solid would generally be within the range of 10 to 1 to 1 to 10, more generally 7 to 1 to 1 to 4. The pretreatment of the titanium-containing catalyst with an organometallic reducing agent prior to the introduction of the catalyst into the polymerization zone is preferably carried out in a substantially inert liquid, generally a hydrocarbon. The term organometallic reducing agent as used herein refers to generally those same type of organometallic reducing agents that have been used in the past as cocatalysts for transition metal based olefin polymerization catalysts systems. As noted above a preferred type of reducing agent includes organoaluminum compounds such as triethylaluminum, trimethylaluminum, diethylaluminum chloride, ethylaluminum dichloride, ethylaluminum sesquichloride, methylaluminum sesquichloride, triisopropylaluminum, dimethylaluminum chloride, tridecylaluminum, trieicosylaluminum, tricyclohexylaluminum, triphenylaluminum, 2-methylpentyldiethylaluminum, triisoprenylaluminum, methylaluminum dibromide, ethylaluminum diiodide, isobutylaluminum dichloride, dodecylaluminum dibromide, dimethylaluminum bromide, diisopropylaluminum chloride, methyl-n-propylaluminum bromide, di-n-octylaluminum bromide, diphenylaluminum chloride, dicyclohexylaluminum bromide, methylaluminum sesquibromide, ethylaluminum sesquiiodide, and mixtures thereof. Preferably conditions are employed in all the catalyst preparation steps to minimize the presence of oxygen and water. The contacting can be carried out over a broad range of temperature conditions. Typically, the contacting would be conducted at a temperature in the range of 15°C to 150°C, more typically, 20°C to 100°C. After the contacting the mother liquor is generally decanted and the resulting solids washed several times with a suitable liquid solvent such as a hydrocarbon. The amount of organometallic reducing agent employed can vary over a broad range. Excess organometallic reducing agent can be employed. Generally the organometallic reducing agent would be used in an amount such that the molar ratio of the reducing agent to the titanium in the catalyst to be treated is in the range of 0.01:1 to 10:1, more preferably 0.02:1 to 3:1. The resulting pretreated catalyst may if desired be mixed with a particulate diluent such as, for example, silica, silica-alumina, silica-titania, magnesium dichloride, magnesium oxide, polyethylene, polypropylene, and poly(phenylene sulfide), prior to the use of the catalyst in a polymerization process. The weight ratio of the particulate diluent to the catalyst can be varied over a wide range. Typically, the weight ratio of the particulate diluent to the catalyst is generally within the range of 100 to 1 to 1 to 100, or more often in the range of 20 to 1 to 2 to 1. The use of a particulate diluent has been found to be particularly effective in facilitating the controlled charging of the catalyst to the reactor. The pretreated catalyst can be used in the polymerization of a variety of polymerizable compounds. It is particularly useful for the homopolymerization or copolymerization of mono-1-olefins. Olefins having 2 to 18 carbon atoms would most often be used. The pretreated catalyst is particularly useful in slurry or particle form polymerization processes. In particle form polymerization processes the temperature and pressure conditions are generally selected to assure that polymer can be recovered as discreet particles. Typically, this would involve temperatures in the range of 60 to 110°C. More generally, 80 to 110°C. The inventive pretreated catalyst is particularly useful in situations where the cocatalyst is triethylaluminum and the level of triethylaluminum used in the polymerization is less than 25 ppm, based upon the weight of the liquid diluent used in the polymerization, more preferably the triethylaluminum is used at a level in the range of 5 to 10 ppm based on the weight of the liquid diluent used in the polymerization. In a continuous process, for example, a suitable reactor such as a loop reactor is continuously charged with suitable quantities of liquid diluent, catalyst, cocatalyst, polymerizable compounds and hydrogen, if any, in any desirable order. The reactor product is continuously withdrawn and the polymer recovered as appropriate, generally by flashing the liquid diluent and unreacted monomers and drying and recovering the resulting polymer. The olefin polymer produced with this invention can be used in preparing articles by conventional polyolefin processing techniques such as injection molding, rotational molding, and extrusion of film. A further understanding of the present invention and its objects and advantages will be provided by the following examples: Example I Catalyst Preparations Under a nitrogen atmosphere n-hexane, dry MgCl 2 and titanium tetraethoxide, Ti(OEt) 4 were combined. The stirred mixture was heated to 100°C and held at this temperature for one hour. The mixture was cooled to 26°C. Ethylaluminum dichloride (EADC) as a 25 wt. % solution in n-hexane was added to the stirred reaction mixture over a period of sixty minutes. After an additional 30 minutes, stirring was discontinued and the solids allowed to settle. The solids were washed and decanted with dry n-hexane followed by successive washing and decantation with two additional portions of dry n-hexane. The reactor contents were then treated at ambient temperature with ethylaluminum dichloride (EADC) as a 25 wt. % solution in n-hexane. The addition of the EADC solution to the stirred reaction mixture required about 30 minutes. Then ethylene was added to the reactor at ambient temperature by pressuring and repressuring an ethylene metering tank, to form polyethylene (prepolymer) on the catalyst in the reactor. The reactor was purged of ethylene with nitrogen and the "prepolymerized" catalyst was washed and decanted successively with two portions of dry n-hexane. Finally, dry n-hexane was added to the reactor. Then titanium tetrachloride was gradually added to the reaction mixture and the system was stirred for one hour at about 25°C. After the solids were allowed to settle, the mother liquor was decanted and the solids were washed and decanted with dry n-hexane. The solids were then washed and decanted successively with four additional portions of dry n-hexane. The catalyst slurry in dry n-hexane was transferred under nitrogen to a storage tank. Two identical catalyst preparations gave about 182.7 kg (402.5 lb) of catalyst slurry in dry n-hexane for use in the inventive pretreatment of the catalyst with triethylaluminum (TEA). A 9.1 kg (20 lb) sample of the catalyst slurry (15.57% solids containing 7.4 wt. % Ti) under nitrogen was transferred from the storage tank to the reactor and stirred for 10 minutes at ambient temperature. A 0.34 kg (0.75 lb) quantity (3.0 moles) of triethylaluminum was added to the reactor as a 2.3 kg (five pound) portion of a 15 wt. % n-hexane solution and the stirred reaction mixture was heated to 50°C. After two hours at 50°C, the system was cooled to 30°C and the mother liquor decanted. The solids were washed and decanted successively with four 18.9 dm 3 (5 gal.) portions of dry n-hexane before transferring the treated catalyst as a hexane slurry into a storage tank. The estimated molar ratio of aluminum (from added triethylaluminium) to titanium present in the catalyst was about 3:2.2. This TEA pre-treated catalyst will be referred to herein as Catalyst A. Another catalyst was prepared by reacting dry magnesium chloride with titanium tetraethoxide in a hydrocarbon diluent and then reacting the mixture with ethylaluminum sesquichloride to produce a solid. Ethylene prepolymer was then formed on the solid. A hydrocarbon slurry of the resulting prepolymerized catalyst was then contacted with triethyl aluminum (TEA) to give a pre-activated, pre-polymerized catalyst. This catalyst will be referred to as Catalyst B. Example II Pilot plant runs with the inventive TEA-pretreated Catalyst B were carried out at reduced triethylaluminum levels in a loop reactor. This is one of the catalysts prepared using ethylaluminum sesquichloride rather than ethylaluminum dichloride. A summary of four inventive runs directed toward the production of polyethylene is presented in Table I. The levels of TEA in the loop reactor for runs 1, 2, 3 and 4 were, respectively, 22, 10, 5 and 5 ppm. The normal level of TEA required in a loop reactor with untreated catalyst is much higher, viz., in the range of 25-150 ppm TEA. With an untreated catalyst, the use of TEA at levels below 25 ppm causes fouling of the loop reactor. Pilot plant runs were conducted in a liquid full 87 dm 3 (23 gal.) loop reactor containing isobutane as a diluent. Effluent was periodically discharged from the reactor and passed to a flash chamber where the polymer was recovered, dried and sieved. Diluent was intermittently charged to the reactor along with catalyst and with a dilute solution of triethylaluminum in n-hexane to maintain desired levels of TEA and productivity. Hydrogen was used as a molecular weight modifier for the polymer. Circulation in the reactor was accomplished by means of an agitator operating at 1850 RPM in each run. The reactor temperature in runs 1, 2, 3 and 4 was 82°C (180°F). In order to facilitate feeding of the pretreated catalyst through the standard ball-check feeders, the TEA-pretreated catalyst was diluted with 5 parts calcined (200-300°C) silica per part of catalyst. 2-Day Continuous Pilot Plant Polyethylene Runs With TEA-Pretreated Catalyst Run 1 Run 2 Run 3 Run 4 Hydrogen Concentration (Mole Percent) 1.35 1.50 2.23 2.14 H 2 /C 2 = Mole Ratio 0.18 0.20 0.29 0.28 Triethylaluminum (ppm) 22 10 5 5 Polymer Melt Index 4.2 5.9 7.4 11.5 HLMI/MI 35 36 38 37 Polymer Density (g/cm 3 ) 0.967 0.968 0.968 0.970 Flexural Modulus, MPa 1720 1800 1790 1830 Productivity (g Polymer/g Catalyst/Hr) (excluding silica) 26,320 18,870 22,730 17,860 Polymer Bulk Density (kg/m 3 (lb/ft 3 )) 398.4 (24.9) 409.6 (25.6) 414.4 (25.9) 420.8 (26.3) Referring to runs 1, 2, 3 and 4 in Table I it can be seen that at start-up the TEA level in the loop reactor was 22 ppm (Run 1) and no reactor fouling was observed. After the reactor had lined out, the TEA level was reduced to 10 ppm and there was still no fouling problem (Run 2). In runs 3 and 4 the TEA level was further reduced to 5 ppm TEA and no fouling was detectable. The total operating time represented by Runs 1-4 in Table I was two days, i.e., these runs represent two days of continuous operation in the pilot plant over the inventive TEA-pretreated catalyst at reduced levels of TEA in the reactor loop during which time no reactor fouling was detectable. Other parameters in Table I do not appear to be significantly altered by the lower TEA levels. The activity of the catalyst was relatively constant. Since the hydrogen concentration was increased during the series, a slight decrease in activity would be expected. The increasing levels of hydrogen would likewise cause increases in melt index. The breadth of molecular weight distribution reflected by the HLMI/MI values was essentially constant. The relatively higher HLMI/MI values were most likely caused by the relatively low reactor temperature (82°C (180°F)) rather than the lower TEA levels. Flexural modulus and bulk density values did not change with TEA level. In general, the system did not respond in a negative manner to the reduced levels of TEA. Example III The results of pilot plant runs covering three days of continuous operation using Catalyst A are summarized in Table II. In order to facilitate feeding of the inventive pretreated catalyst, the TEA-pretreated catalyst was diluted with 600°C calcined silica. The exact dilution rate was not known but was considered to be in the range of 3 to 5 parts by weight silica to 1 part by weight of Catalyst A. The reactor temperature in runs 5, 6, 7, 8, 9 and 10 was 88°C (190°F). The TEA levels in these runs were, respectively, 11, 10, 10, 12, 9 and 8 ppm. 3-Day Continuous Pilot Plant Copolymer Resin Runs With TEA-Pretreated Catalyst Run 5 Run 6 Run 7 Run 8 Run 9 Run 10 Hydrogen Concentration (Mole Percent) 1.56 1.53 1.57 1.37 1.64 2.18 H 2 /C 2 = Mole Ratio 0.18 0.21 0.21 0.17 0.21 0.29 Triethylaluminum (ppm) 11 10 10 12 9 8 1-Hexene, Wt% of Ethylene 0 3.3 3.4 15.0 14.9 14.9 Polymer Melt Index 4.2 15.2 18.2 14.5 19.7 27.2 HLMI/MI 37 29 18 21 42 30 Polymer Density (g/cm 3 ) 0.968 0.967 0.966 0.960 0.960 0.961 Flexural Modulus, MPa 1689 1770 1671 1515 1472 1563 Productivity (g Polymer/g Catalyst/Hr) (including silica) 2040 2040 2040 2080 1520 1890 Polymer Bulk Density (kg/m 3 (lb/ft 3 )) 369.6 (23.1) 376 (23.5) 380.8 (23.8) 353.6 (22.1) 364.8 (22.8) 392 (24.5) Referring to runs 5, 6,7, 8, 9 and 10 in Table II it can be seen that the TEA level in the reactor at start-up was 11 ppm and varied between 8 ppm and 12 ppm over a 3 day period of continuous operation. During this period there was no detectable fouling problem and activity was essentially unchanged. Referring to runs 6, 7, 8, 9 and 10 the effect of adding 1-hexene to the reactor can be seen. In general, the melt index increased as the 1-hexene was increased. Density decreased with increasing 1-hexene and flexural modulus decreased as expected. The somewhat lower values of HLMI/MI were most likely due to the higher reactor temperatures used in runs 6-10. Bulk density remained relatively constant at the lower TEA levels. The results in Table II show that the inventive TEA-pretreated catalyst permits the use of lower levels of TEA in the loop reactor during the copolymerization of ethylene and 1-hexene. No reactor fouling was detectable during 3 days of continuous operation. Example IV The results of pilot plant runs based on five days of continuous operation using Catalyst A are summarized in Table III. In order to facilitate feeding of the inventive pretreated catalyst, the TEA-pretreated catalyst was diluted with 600°C calcined silica. Here again the dilution was at the rate of 3 to 5 parts by weight of silica per part by weight of Catalyst A. The reactor temperatures in runs 11, 12, 13, 14, 15 and 16 were, respectively, 82°C, 83°C, 87°C, 88°C, 88°C, and 88°C (180°F, 182°F, 189°F, 191°F, 191°F and 191°F). The TEA levels in these runs were, respectively, 9, 5, 5, 4, 2 and 2 ppm. 5-Day Continuous Pilot Plant Copolymer Resin Runs With TEA-Pretreated Catalyst Run 11 Run 12 Run 13 Run 14 Run 15 Run 16 Hydrogen Concentration (Mole Percent) 1.95 1.99 2.05 2.06 1.97 2.09 H 2 /C 2 = Mole Ratio 0.24 0.26 0.27 0.31 0.25 0.27 Triethylaluminum (ppm) 9 5 5 4 2 2 1-Hexene, Wt% of Ethylene 14.4 14.8 14.9 15.3 15.8 6.6 Polymer Melt Index 38 42.2 64 118.7 59.9 34 HLMI/MI 24 NA 15 NA NA NA Polymer Density (g/cm 3 ) 0.960 0.959 0.960 0.959 0.958 0.962 Flexural Modulus, MPa 1544 NA 1498 NA NA NA Productivity (g Polymer/g Catalyst/Hr) (including silica) 3640 3610 4650 3030 3130 3450 Polymer Bulk Density (kg/m 3 (lb/ft 3 )) 396.8 (24.8) 403.2 (25.2) 422.4 (26.4) 422.4 (26.4) 420.8 (26.3) 417.6 (26.1) Referring to runs 11, 12, 13, 14, 15 and 16 in Table III it can be seen that the TEA level in the reactor at start-up was 9 ppm and was gradually reduced down to 2 ppm over a 5 day period of continuous operation. During this period there was no detectable fouling problem and activity was essentially unchanged. The general comments made in the previous example relating to the results summarized in Table II also apply to the results shown in Table III. It should be noted that on decreasing the TEA level in the reactor loop to 0.5 ppm the activity dropped sharply and the operation was terminated. Since the overall drop in density was slight considering the relatively large amount of 1-hexene present, it can be concluded that the TEA treatment did not significantly affect the comonomer incorporation, even at lower reactor temperatures. It is noteworthy that, e.g., in run 14 with very high hydrogen and very high 1-hexene, the melt index was a very high 118.7. Example V The results of pilot plant runs based on ten days of continuous operation using silica diluted Catalyst B are summarized in Table IV. Runs 17, 18, 19 and 20 are related to a first type of copolymer resin whereas runs 21, 22 and 23 are related to a different type of copolymer resin. Higher reactor temperatures were used to duplicate conditions routinely used with an untreated catalyst. The reactor temperature used in runs 17, 18, 19 and 20 was 102°C (215°F) whereas the reactor temperatures in runs 21, 22 and 23 were, respectively, 96°C (205°F), 96°C (205°F) and 93°C (199°F). 10-Day Continuous Pilot Plant Copolymer Resin Runs With TEA-Pretreated Catalyst Run 17 Run 18 Run 19 Run 20 Run 21 Run 22 Run 23 Hydrogen Concentration (Mole Percent) 1.0 0.86 0.86 0.92 0.48 0.55 0.05 H 2 /C 2 = Mole Ratio 0.14 0.14 0.14 0.15 0.08 0.09 0.09 Triethylaluminum (ppm) 10 10 10 5 5 5 5 1-Hexene, Wt% of Ethylene 0.21 0.25 0.27 0.29 1.07 1.15 1.27 Polymer Melt Index 24 19 19 17 6 8 9 HLMI/MI 14 26 15 25 16 27 28 Polymer Density (g/cm 3 ) 0.958 0.954 0.957 0.957 0.945 0.944 0.944 Productivity (g Polymer/g Catalyst/Hr) (including silica) 5000 3510 3570 3080 4170 4000 4000 Polymer Bulk Density (kg/m 3 (lb/ft 3 )) 468.8 (29.3) 465.6 (29.1) 468.8 (29.3) 472 (29.5) 414.4 (25.9) 420.8 (26.3) 401.6 (25.1) Referring to runs 17, 18, 19 and 20 in Table IV it can be seen that the TEA levels in the reactor for production of one of the Phillips commercial scale copolymers were, respectively, 10, 10, 10 and 5 ppm. In runs 21, 22 and 23 for the production of the other Phillips commercial scale copolymer, the TEA level in the reactor was 5 ppm. Since higher temperatures were used in these runs relative to the copolymer runs of Table II and Table III of the previous examples, bulk densities were higher. Other reaction parameters and polymer properties were similar to the conventional technology used for producing these copolymers with untreated catalyst and higher TEA levels in the loop reactor. The results shown in Table IV demonstrate the efficacy of the inventive TEA-treated catalyst to provide systems which produce quality copolymer at reduced TEA levels in the loop reactor. These systems also were free of fouling problems during a continuous operation period of 10 days. Example VI A commercial scale titanium-containing catalyst was evaluated. The catalyst was prepared by contacting titanium tetraethoxide and magnesium dichloride to obtain a solution, then contacting the solution with aluminum sesquihalide to obtain a precipitate, contacting the precipitate with ethylene to form a prepolymer, then contacting the prepolymerized solid with TiCl 4 , followed by a number of hydrocarbon washes to remove soluble titanium components. It has been observed by applicants that even though a plurality of hydrocarbon washes are used in such catalyst preparations, as the catalyst ages the level of soluble titanium components increases. Five separate portions of the commercial scale catalyst were subjected to treatment with triethylaluminum under different conditions to evaluate the effect. In each case 1.6 kg (3.5 lb.) of the solid catalyst in a hexane slurry was charged into a reactor. After mixing for 10 minutes, a 15 wt. % triethylaluminum heptane solution was charged to the reactor. The slurry was then taken to the chosen reaction temperature and mixed for 2 hours. Thereafter the resulting solid was washed 5 times with hexane. The variables in the catalyst pretreatment are set forth in Table V. Catalyst Pretreatment Conditions Catalyst TEA Solution (kg (lbs)) Reaction Temperature (°C) C 2.27 (5.0) 60 D 0.23 (0.5) 60 E 0.23 (0.5) 20 F 2.27 (5.0) 20 G 1.25 (2.75) 40 Hexane slurries of each of the catalysts and of the original untreated commercial scale Control catalyst were subjected to analytical tests to determine the relative amounts of soluble titanium components. The results are set forth in Table VI. Analytical Results Supernatant Liquid (ppm) Dried Catalyst (wt. %) Catalyst Color Al Ti Mg Al Ti Mg C black 95.0 1.8 0.5 5.8 12.8 7.2 D lt. brown 0.2 4.5 0.1 2.3 14.1 7.4 E lt. brown <0.1 0.3 <0.1 2.4 14.0 7.6 F black 92.6 0.2 <0.1 5.2 12.8 6.9 G dk. brown 24.0 <0.1 <0.1 4.2 13.0 6.7 Control lt. brown 0.2 >1699.1 0.2 1.6 14.0 7.4 Treatment of the Control catalyst slurry with TEA at different concentrations and temperatures resulted in soluble titanium levels under 5 ppm in all cases. Example VII The effectiveness of the TEA treated catalysts of Example VI in polymerization was then compared to that of the untreated Control catalyst. A 3.8 dm 3 (one gallon) capacity reactor was used for the polymerization. The reactor was prepared for each polymerization run by adding about one liter of isobutane, heating to 110°C for one hour, draining the reactor, and then flushing it with nitrogen free isobutane. Catalyst slurry and TEA cocatalyst were added to the reactor. The reactor was sealed and hydrogen added. About 2 liters of isobutane was pressured into the reactor. Ethylene was then fed to the reactor continually over a one hour period so that constant pressure was obtained. At the end of the hour, the ethylene flow was stopped, and the reactor was vented. The polymer was collected, vacuum dried at 60°C, and weighed. The polymerizations were run in 1.1 Kg of isobutane, 90 g 1-hexene, and 0.5 cm 3 of 15% by weight triethylaluminum in n-heptane at 90°C and 2.34 MPa (324 psig) total pressure for one hour. The hydrogen was measured into the reactor in the amount of 0.27 MPa (25 psi) from a 2.25 l vessel. Reactant molar ratios were 0.7 hexene/ethylene and 0.05 hydrogen/ethylene at an ethylene concentration of about 7 mole percent. The results are summarized in Table VII. Productivity (kg/g/hr) Run Catalyst From Catalyst Weight From Ti Analyses MI (g/10 min) HLMI/MI Ratio Density (g/cm 3 ) 24 C 24 18 1.26 27.3 .9429 25 D 23 20 1.68 27.4 .9443 26 E 25 23 1.65 27.4 .9435 27 F 21 18 1.62 27.0 .9433 28 G 24 25 1.39 27.6 .9440 29 Control 26 23 (25) 1.16 30.7 .9439 The data shows that the productivity and polymer molecular weights were slightly reduced by the TEA treatment. The shear ratios, fluff bulk densities, and densities of the polymers were not materially affected by the treatment. The TEA treatment thus reduced the soluble Ti levels of the catalyst without any significant adverse effect on the polymer formed or the performance of the catalyst. By reducing the hydrogen levels it should be possible to increase the molecular weights and productivities to values very close to those obtained with the untreated Control catalyst. Example VIII Another series of polymerizations were carried out using the various TEA pretreated catalysts and the Control catalyst to determine whether the TEA pretreatment would affect the type of polymer fines produced. The polymerizations were run in 1.1 Kg of isobutane at 100°C and 3.55 MPa (500 psig) total pressure for 1 hour. Triethylaluminum, 0.5 cm 3 of 15% by weight solution in n-heptane, cocatalyst was used; hydrogen, 1.01 MPa (132 psi) from a 2.25 1 vessel, was in the reactor. The hydrogen/ethylene molar ratio was 0.36 at 6.05 mole percent ethylene. The results are summarized in Table VIII. Productivity (Kg/g/hr) Run Catalyst From Catalyst Weight From Ti Analyses MI (g/10 min.) Fines (% - 150 µm (100 Mesh)) 30 C 12 9 109 2.98 31 D 11 12 161 2.50 32 E 15 13 121 2.38 33 F 11 9 147 3.75 34 G 11 8 207 2.50 35 Control 11 8 192 2.29 The data show that the TEA pretreatment does not have any significant adverse effect upon the polymer fines. Example IX Another series of polymerizations were carried out to evaluate the TEA pretreated Catalyst G at different cocatalyst levels in the co-polymerization of ethylene and 1-hexene. The polymerizations were run in 1.1 Kg isobutane, 90 g 1-hexene, and variable levels of 15% by weight triethylaluminum in n-heptane at 90°C and 2.34 MPa (324 psig) total pressure for one hour. Hydrogen, 0.27 MPa (25 psi) from a 2.25 l vessel, was also in the reactor. Reactant molar ratios were 0.7 hexene/ethylene and 0.05 hydrogen/ethylene at an ethylene concentration of about 7 mole percent. The results are summarized in Table IX. Run Triethyl Aluminum Productivity (kg/g/hr) MI (g/10 min.) HLMI/MI Ratio (cm 3 ) (ppm) 36 3.0 286 10.0 3.78 27.4 37 1.5 143 10.8 2.52 26.2 38 0.5 48 25.0 1.39 27.6 39 0.5 48 21.3 1.74 28.3 40 0.25 24 14.4 0.99 30.7 41 0.15 15 3.9 1.19 26.8 42 0.10 10 ND ND ND The data shows that in the bench scale pot-type reactor the productivity in the copolymerization was decreased as the TEA cocatalyst level was decreased. The effect upon productivity is apparently more notable in the bench scale reactor than in a loop reactor. Example X Another series of catalysts were prepared to evaluate the effects of other organometallic reducing agents. The Control catalyst was prepared by forming a solution of titanium tetraethoxide and magnesium chloride. The solution was contacted with ethylaluminum dichloride to obtain a precipitate. Ethylene was polymerized on the precipitate to form prepolymer. The resulting solid was then washed with TiCl 4 and then with several hydrocarbon washes. Separate portions of the resulting control catalyst slurried in hydrocarbon were contacted with different reducing agents, namely triethylaluminum, diethylaluminum, triethylboron, diethylzinc, n-butyllithium, and Magala (a mixture of dibutylmagnesium and triethyaluminum). The effects of the various catalysts in the polymerization of ethylene were then compared. The polymerizations were carried out in substantially the same manner as those described in Example VII. The variables and results are summarized in Table X. Run TEA (cm 3 ) Hydrogen (MPa (psi)) Productivity (kg/g/hr) MI (g/10 min.) HLMI/MI Control Catalyst 43 0.1 0.41 (45) 6.0 0.48 36.4 44 0.25 0.45 (50) 20.7 1.02 29.5 45 0.5 0.41 (45) 33.6 1.35 29.7 46 1.0 0.41 (45) 41.2 1.24 29.7 47 2.0 0.34 (35) 41.2 1.28 31.8 48 4.0 0.34 (35) 43.1 1.32 31.5 49 6.0 0.31 (30) 39.5 1.20 30.0 TEA Treated Catalyst 50 0.1 0.38 (40) 14.3 0.65 34.5 51 0.25 0.38 (40) 21.4 0.65 30.9 52 0.5 0.38 (40) 27.8 1.47 24.6 53 1.0 0.38 (40) 36.0 1.26 29.8 DEAC Treated Catalyst 54 0.05 0.38 (40) 2.0 --- --- 55 0.1 0.38 (40) 34.4 0.89 32.6 56 0.25 0.38 (40) 66.6 1.57 29.6 57 0.5 0.38 (40) 53.8 2.06 27.6 58 1.0 0.38 (40) 57.5 1.93 28.2 TEB Treated Catalyst 59 0.5 0.41 (45) 51.4 1.98 28.2 DEZ Treated Catalyst 60 0.5 0.41 (45) 33.8 1.58 28.8 MAGALA Treated Catalyst 61 0.5 0.41 (45) 22.1 2.0 27.8 Butyllithium Treated Catalyst 62 0.5 0.41 (45) 37.6 0.89 37.8 In Table X a dash indicates that no determination was made. The results of Table X demonstrate that a particulate titanium catalyst containing soluble titanium components can be effectively treated with a wide range of organometallic reducing agents. It will be noted in many cases the productivity of the organometallic reducing agent treated catalyst was higher than that of the control at a given cocatalyst level. Particularly notable are the triethylboron and diethylaluminum chloride treated catalysts.

Claims: A process for preparing a solid particulate olefin polymerization catalyst comprising (1) reacting a titanium alkoxide and a magnesium dihalide to form a solution; (2) then reacting that solution with a precipitating agent selected from organometallic compounds in which the metal is selected from Groups I to III of the Periodic Table, metal halides and oxygen-containing halides of elements selected from Groups IIIA, IVA, IVB, VA and VB of the Periodic Table, hydrogen halides, and organic acid halides to obtain a precipitated solid, (3) contacting the resulting solid with titanium tetrachloride, and, optionally contacting the resulting solid with an olefin to form a prepolymerized solid before contacting or after having contacted the resulting solid with titanium tetrachloride, and (4) then contacting the titanium-treated, optionally prepolymerized, solid with an organometallic reducing agent, wherein the resulting solids obtained in the steps (2), (3) and (4) are washed several times with a hydrocarbon solvent. The process according to claim 1, wherein excess organometallic reducing agent is used, and the resulting product is subjected to a number of washes with said hydrocarbon solvent. The process according to claim 1 or 2, wherein said organometallic reducing agent is selected from hydrocarbyl aluminum compounds, hydrocarbyl boron compounds, hydrocarbyl alkali or alkaline earth metal compounds, and hydrocarbyl zinc compounds. The process according to claim 3, wherein said organometallic reducing agent is selected from trialkylaluminum compounds, in particular triethylaluminum. The process according to any of claims 1 to 4, wherein said catalyst is prepared by reacting a titanium tetraalkoxide in which the alkyl groups contain 1 to 10 carbon atoms each. The process according to any of the preceding claims, wherein said titanium alkoxide is titanium tetraethoxide, said magnesium dihalide is magnesium dichloride, the reaction thereof is carried out in a liquid and the organometallic compound is an organoaluminum compound. The process according to any of the preceding claims, wherein said precipitating agent is selected from hydrocarbyl aluminum sesquihalides and monohydrocarbyl aluminum dihalides, preferably selected from ethylaluminum sesquichloride and ethylaluminum dichloride. The process according to any of the preceding claims, wherein said catalyst contains 1 to 10 wt% of an olefin prepolymer. The process of claim 8 wherein said solid is contacted with ethylene under polymerization conditions to form polyethylene prepolymer prior to the solid being contacted with the titanium tetrachloride. The process according to any of claims 1 to 3 and 5 to 9, wherein said organometallic reducing agent is triethylboron. An olefin polymerization catalyst obtainable by a process according to any of the preceding claims. The catalyst of claim 11 having been obtained by contacting titanium tetraethoxide and magnesium dichloride in a liquid to produce a solution, contacting said solution with a precipitating agent selected from ethylaluminum sesquichloride and ethylaluminum dichloride to produce a solid, contacting the solid with an olefin to produce a prepolymerized solid, contacting said prepolymerized solid with titanium tetrachloride, contacting a hydrocarbon slurry of the resulting solid with a trialkylaluminum compound, recovering the resulting solid from the reaction mixture and combining it with an organometallic cocatalyst. A process for the polymerization of olefins under particle form polymerization conditions comprising contacting said olefin with a catalyst, and optionally a cocatalyst, in a diluent, wherein said catalyst has been prepared by a process according to any of claims 1 to 10, wherein in step (4) the titanium-treated, optionally prepolymerized, solid is contacted with the organometallic reducing agent and washed several times with said hydrocarbon solvent prior to its introduction into the polymerization zone. The process according to claim 13, wherein excess organometallic reducing agent is used, and the resulting product is subjected to a number of washes with said hydrocarbon solvent prior to the introduction of the solid catalyst into the polymerization zone. The process according to claim 12 or 13, wherein said polymerization is conducted in a continuous loop reactor. The process according to any of claims 13 to 15, wherein said catalyst contains 1 to 10 weight percent of an olefin prepolymer. The process according to any of claims 13 to 16, wherein, after said catalyst has been contacted with said organometallic reducing agent, it is slurried with dehydrated silica in a liquid diluent to produce a titanium based silica diluted catalyst before said catalyst is introduced into the polymerization zone. The process according to any of claims 13 to 17, wherein the cocatalyst triethylaluminum is used in an amount of less than 25 parts per million by weight based on the weight of the liquid polymerization diluent. The process claim 18, wherein said cocatalyst triethylaluminum is used in an amount of 5 to 10 ppm based on the weight of the liquid polymerization diluent. The process according to any of claims 13 to 19, wherein ethylene is polymerized to produce ethylene homopolymers. The process according to any of claims 13 to 20, wherein ethylene and 1-hexene are polymerized to produce an ethylene/1-hexene copolymer. The process according to any of claims 13 to 21, wherein ethylene and at least one other 1-olefin having 3 to 8 carbon atoms are polymerized to produce an ethylene copolymer.

Inventors: BENHAM ELIZABETH ANN, CONE GROVER WINDLE, MCDANIEL MAX PAUL, MITCHELL KENT EDWARD, WELCH MELVIN BRUCE, BENHAM, ELIZABETH ANN, CONE, GROVER WINDLE, MCDANIEL, MAX PAUL, MITCHELL, KENT EDWARD, WELCH, MELVIN BRUCE
Applicants: PHILLIPS PETROLEUM CO, PHILLIPS PETROLEUM COMPANY
Application year: 1991
Main classification: C08F10
IPC codes: C08F4, C08F10, C08F2