MXPA00001432A

MXPA00001432A - A process for the preparation of polyethylene

Info

Publication number: MXPA00001432A
Application number: MXPA/A/2000/001432A
Authority: MX
Inventors: Dale Andrew Wright; Theodore Randolph Engelmann; Antonis Nicholas; Francois Alexandre
Original assignee: Peiromont And Company Limited; Union Carbide Chemicals & Plastics Technology Corporation
Priority date: 1997-08-14
Filing date: 2000-02-10
Publication date: 2001-03-05

Abstract

A process for preparing high density polyethylene in the gas phase comprising contacting a mixture comprising ethylene and one or more alpha-olefins with the supported reaction product of a bis-hydrocarbylsilyl chromate and a hydrocarbylaluminum compound or a hydrocarbyl boron compound in afluidized bed reactor having a recycle gas line, under polymerization conditions, with the following provisos:(i) the atomic ratio of aluminum to chromium is in the range of about 0.1:1 to about 2.9:1;(ii) the amount of catalyst is in the range of about 0.005 to about 0.25 part by weight based on 100 parts by weight of the high density polyethylene;(iii) the partial pressure of ethylene is in the range of about 200 to about 400 psia;(iv) oxygen and/or another catalyst poison is introduced into the reactor in the range of about 0.005 to about 0.5 part by volume of catalyst poison per million parts by volume of ethylene;(v) the molar ratio of alpha-olefin to ethylene is about 0.0001:1 to about 0.1:1;(vi) hydrogen is introduced into the reactor in the range of about 0.005 to about 0.5 mole of hydrogen per mole of ethylene;(vii) the polymerization is carried out at a temperature in the range of about 80 to about 110 degrees C;and (viii) a relatively low boiling inert hydrocarbon is introduced into the recycle gas line in an amount sufficient to raise the dew point of the recycle gas, which is comprised of alpha-olefins and other reactor gases, and the recycle gas is partially condensed and recycled to the reactor where it promotes cooling by evaporation.

Description

"A PROCESS FOR THE PREPARATION OF POLYETHYLENE" TECHNICAL FIELD This invention relates to a process for preparing a high density polyethylene, which is particularly useful in pipe, molded part, and geomembrane applications.

BACKGROUND INFORMATION High density polyethylene (HDPE), which covers a density scale of 0.940 to 0.958 gram per cubic centimeter, finds applications in injection molding, rotational molding, sheets, tube, hose, and, of specific interest here, pipe, blow molding and geomembranes. In order to be competitive, HDPE products for pipe, blow molding and geomembranes must exhibit high resistance to slow crack growth in order to prevent or significantly delay occurrence of fragility failures under stress. Currently, one of the emerging test methodologies, most widely used to evaluate the slow resistance to crack growth, particularly for pipes, is the Pensilavania Notch Stress Test (PENT). The PENT test was developed in an effort to simulate the resistance to slow crack growth in a resin or pipe manufactured in an accelerated manner. The PÉNT test has been approved as the F 1473 method of the American Society for the Testing of Materials and is widely used in the pipe industry as a quality control / quality safety tool for the production of pressure-rated pipe. In addition, HDPE must have consistently good extrusion processability. The industry is continually looking to find HDPEs that are easily processed, and, in product form, have extended the PENT duration.

COMPENDIUM OF THE INVENTION An object of this invention, therefore, is to provide HDPE resins that exhibit good crack growth resistance when converted into pipe, molded articles, geomembranes, or other products, and have a high level of processability. Other objects and advantages will become evident below. In accordance with the present invention, a process has been discovered. The process is one to prepare - high density polyethylene in the gas phase comprising contacting a mixture consisting of ethylene and one or more alpha-olefins with the sustained reaction product of a bis-hydrocarbylsilyl chromate and a hydrocarbylaluminum compound or a boron compound of hydrocarbyl and a fluidized bed reactor having a recycle gas line, under polymerization conditions, with the following stipulations: (i) the atomic ratio of aluminum to chromium is within the range of about 0.1: 1 to about 2.9 :1; (ii) the amount of catalyst is within the range of about 0.005 to about 0.25 part by weight based on 100 parts by weight of high density polyethylene; (iii) the ethylene partial pressure is within the range of approximately 14.06 to approximately 28.12 kilograms per absolute square centimeter; (iv) oxygen and / or other catalyst contaminant is introduced into the reactor within the range of about 0.005 to about 0.5 part by volume of the catalyst contaminant per million parts by volume of ethylene; - - (v) the molar ratio of alpha-olefin to ethylene is from about 0.0001: 1 to about 0.1: 1; (vi) hydrogen is introduced into the reactor within the range of about 0.005 to about 0.5 mole of hydrogen per mole of ethylene; (vii) the polymerization is carried out at a temperature within the range of about 80 ° C to about 110 ° C; and (viii) an inert hydrocarbon of relatively low boiling temperature is introduced into the recycle gas line where it raises the condensation temperature of the recycle gas, which consists of alpha-olefins and other reactor gases and the recycle gas it is partially condensed and recycled to the reactor where it promotes cooling by evaporation.

DESCRIPTION OF THE PREFERRED MODALITY (S) HDPE is a copolymer of ethylene and one or more alpha-olefins. The alpha-olefin can have from 3 to 12 carbon atoms, and preferably has from 3 to 8 carbon atoms. Examples of alpha-olefins are propylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, and 1-octene. One or two alpha-olefins are preferred. The alpha- - - Especially preferred olefin is 1-hexene. The total amount of alpha-olefin in the copolymer can be from about 0.1 to about 3 parts by weight based on 100 parts by weight of the copolymer, and is preferably from about 0.5 to about 2.5 parts by weight. The resin may have a melt index (I2) within the range of about 0.01 to about 0.5 gram per 10 minutes, and preferably has a melt index (I2) within the range of about 0.04 to about 0.2 gram per gram. minutes It may also have a melt index (I5) of about 0.06 to about 2.5 grams per 10 minutes, and preferably has a melt index (I5) of from about 0.2 to about 1.0 gram per 10 minutes. The resin may have a flow index (I21) within the range of about 2 to about 40 grams per 10 minutes, and preferably has a flow index within the range of about 6 to about 20 grams per 10 minutes. The melt index (I2) is determined under method D-1238 of the American Society for the Testing of Materials, Condition E. It is measured at 190 ° C and 2.16 kilograms and is reported as grams per 10 minutes. The melt index (I5) can be determined under the method D-1238 of the American Society for the Testing of Materials, Condition P. It is measured at 190 ° C and 5 kilograms and is reported as grams per 10 minutes. the flow index (I21) is determined under method D-1238 of the American Society for the Testing of Materials, Condition F. It is measured at 190 ° C and 21.6 kilograms, and is reported as grams per 10 minutes. The melt flow ratio is the ratio of the flow index to the melt index. The melt flow ratio (I21 / I5) of the HDPE can be within the range of about 16 to about 33, and preferably falls within the range of about 20 to about 29. The density of the HDPE falls within the scale from 0.940 to 0.958 gram per cubic centimeter, and preferably falls within the range of 0.943 to 0.953 gram per cubic centimeter. The copolymerization of ethylene and alpha-olefin (s) in the presence of a catalyst system consisting of a sustained reaction product of a bis-hydrocarbylsilyl chromate and a hydrocarbylaluminum compound has been previously disclosed in US Pat. No. 5,137,994. The last compound is sometimes identified as a co-catalyst and, sometimes, as a promoter or reducing agent when reacted with the chromate before carrying out the copolymerization. See, for example, U.S. Patent Nos. 3,324,095; 3,324,101 and 3,704,287. The bis-triarylsilyl chromates and a method for their preparation are described in these patents. Examples of these compounds are bis-triphenylsilyl chromate; bis-tritolylsilyl chromate; bis-trixylsilyl chromate; bis-trinaphthylsilyl chromate; bis-triethylphenylsilyl chromate, bis-tri-ethylnaphthylsilyl chromate and bis-adamantyl chromate. The hydrocarbylaluminum compounds which can be used as co-additives are the trihydrocarbylaluminum compounds, hydrocarbylaluminum halides, hydrocarbylaluminum hydrocarbyloxides and hydrocarbylaluminium hydrides. In these compounds, the hydrocarbyl group may contain from 1 to about 14 carbon atoms, and the halogen may be chlorine, bromine, fluorine or iodine. The hydrocarbyl group may be an alkyl, aralkyl, aryl, alkaryl, alicyclic or bicyclic group. Examples of the hydrocarbylaluminium compounds are trimethylaluminum, triethylaluminum, tributylaluminum, tridecylaluminum, tridodecylaluminum, diethylaluminum chloride, dibutylaluminum chloride, dibutylaluminum bromide, dibutylaluminum iodide, dibutylaluminium fluoride, dihexylaluminum chloride, methylaluminium dichloride, ethylaluminum dibromide, butylaluminum dichloride, pentylaluminum dichloride , diethylaluminum hydride, dibutylaluminum hydride, dihexylaluminum hydride, methylaluminum dihydride, ethylaluminum dihydride, butylaluminum dihydride and pentylaluminum dihydride. They can be classified generically as compounds having the formula Rn lX3_n wherein R is a hydrocarbyl group as defined above, X is a halogen, a hydrocarbyloxide, or a hydrogen and n is an integer of 1 to 3. The compounds of hydrocarbylboro that can be used in the practice of this invention are the compounds of the general formula BR3 wherein R is a hydrocarbyl group having from 1 to 14 carbon atoms. Examples are trimethylborane, triethylborane, triisobutylborane and tributylborane. The triethylborane is the preferred modifying agent of this class The hydrocarbylaluminum hydrocarbyloxides, which are commonly referred to as "alkylaluminum alkoxides", are compounds of the general formula RnAl (OR) 3_n wherein n is an integer from 1 to 2, and R is a hydrocarbyl group having from 1 to 14 carbon atoms, preferably from 1 to 8 carbon atoms. The hydrocarbyl group may be alkyl, aralkyl, aryl, alkaryl, alicyclic or bicyclic. Examples are methyl, ethyl, propyl, iso-propyl, n-butyl, iso-butyl, n-pentyl, iso-pentyl, t-pentyl, hexyl, cyclohexyl, 2-methyl-pentyl, heptyl, octyl, 2-ethylhexyl cyclohexylmethyl, nonyl, undecyldecyl, dodecyl, tridecyl, tetradecyl, benzyl, pinyl, phenylmethyl, phenethyl, p-methylbenzyl, phenyl, tolyl, xylyl, naphthyl, ethylphenyl, ethylnaphthyl, dimethylnaphthyl, norbornyl and norbornylmethyl. The most preferred hydrocarbylaluminum hydrocarbyloxide compound is diethylaluminum oxide. In all the aforementioned cases, the hydrocarbyl groups, the halide groups and the hydride groups are independently selected, that is, these groups may be the same or different. As mentioned above, the reaction product of the chromate and the hydrocarbylaluminum compound or the hydrocarbyl boron compound is supported. Even though silica is the preferred support, other inorganic oxides may be used. Examples of useful support materials are aluminum phosphate, alumina, silica / alumina mixtures, silica modified with a hydrocarbylaluminum compound such as triethylaluminum, silica modified with diethylzinc, silica modified with a titanium tetrahydrocarbyloxide compound such as titanium tetraisopropoxide , silica / titania co-gels, titanias and a mixture of silica and calcium carbonate. A typical support is a dehydrated particulate porous solid material essentially inert with respect to polymerization. It is used as a dry powder having an average particle size of from about 2 to about 250 microns and preferably from about 30 to about 180 microns; a surface area of from about 100 to about 750 square meters per gram and preferably from about 240 to about 550 square meters per gram; and a pore size of about 80 Angstrom units to about 300 Angstrom units and preferably from about 120 to about 250 Angstrom units. The catalyst can be prepared by reacting the bis-triarylsilyl chromate, the hydrocarbylaluminum compound or the hydrocarbylboro compound, and a dehydrated support material together. The bis-triarylsilyl chromate reacts with the hydroxyl groups that are present on the surface of the support. In this way, the chromate is chemically adsorbed for the most part on the surface of the support. Any part of the chromate, which is not chemically adsorbed, is physically adsorbed on the surface of the support. Usually, about 50 to about 100 percent of the chromate is chemically adsorbed. It should be noted, however, that the chromate retains one or more reactive groups, which react with the hydrocarbylaluminum compound or boron. The amount of the support used is generally that which will provide about 0.01 to about 0.3 millimole of chromium per gram of support and preferably about 0.03 to about 0. 1 millimole of chromium per gram of the support. The polymerization is carried out in the gas phase using a fluidized process. It is preferably carried out in a continuous mode. A typical fluidized bed reactor is described in the US Patent Number 4,482, 687. The parameters of the most important process are the following: (i) the atomic ratio of aluminum to chromium can be within the range of approximately 0.1: 1 to approximately 2.9: 1, and is preferably within the scale of about 1: 1 to about 2: 1. A ratio of approximately 1.5: 1 is especially preferred. (ii) the amount of catalyst may be within the range of about 0.005 to about 0.25 part by weight based on 100 parts by weight of high density polyethylene, and preferably is within the range of about 0.01 to about 0.1 part by weight. (iii) the partial pressure of ethylene can be within the range of approximately 14.06 to 28.12 kilograms per absolute square centimeter, and preferably falls within the range of approximately 14.75 to 21.09 kilograms per absolute square centimeter. A partial pressure within the range of about 15.82 to about 19.33 kilograms per absolute square centimeter is especially preferred. (iv) Oxygen can be introduced into the reactor within the range of about 0.005 to about 0.5 part by volume per million parts by volume of the ethylene feed, and preferably is added within the range of about 0.005 to about 0.25 part by volume per million parts by volume of the ethylene feed. The especially preferred amount is within the range of about 0.01 to about 0.1 pp v (parts by volume per million parts by volume) of ethylene feed. This can be referred to as "Newly Added Oxygen," which is an oxygen system diluted in nitrogen added to the reactor in a controlled flow relative to the ethylene feed rate to the reactor to achieve the desired newly added oxygen level. in ppmv. As an alternative to or in combination with this, other catalyst contaminants must be used to produce the same effect. These catalyst contaminants may be introduced from external sources just like oxygen or may be present as impurities in the feed of ethylene or other gases or liquids added to the reactor. Examples of useful and preferred catalyst contaminants in addition to oxygen are acetone and other compounds that carry oxygen, methanol and other hydroxyl bearing compounds, and water. Various compounds carrying nitrogen, phosphorus, sulfur, arsenic and halogen may be useful in this respect, but are less commonly encountered as impurities in the feed of ethylene or other gases or liquids added to the reactor. One of the effects of the catalyst contaminant is to decrease the molecular weight of the polymer. This is reflected in increased melting and flow rates. In any case, oxygen is the preferred catalyst pollutant. (v) the molar ratio of alpha-olefin to ethylene can be from about 0.0001: 1 to about 0.1: 1, and is preferably from about 0.005: 1 to about 0.03: 1. More preferably, it is a molar ratio of from about 0.0075: 1 to about 0.01: 1. (vi) hydrogen can be introduced into the reactor in a molar ratio of about 0.005 to about 0.5 mole of hydrogen per mole of ethylene, and is preferably introduced in a molar ratio of about 0.01: 1 to about 0.1: 1. More preferably, it is a molar ratio of approximately 0.05: 1. (vii) the polymerization can be carried out at a temperature within the range of about 80 ° C to about 110 ° C, and preferably it is carried out at a temperature within the range of about 85 ° C to about 100 ° C. More preferably, it is a temperature within the range of about 90 ° C to about 95 ° C. (viii) An inert hydrocarbon of relatively low boiling temperature can be introduced into the reactor and passed through the recycling line where it evaporates when it is introduced upstream of the condenser. The hydrocarbon is introduced in an amount sufficient to raise the condensing temperature of the cycle gas. The cycle gas is partially condensed in the cycle gas cooler, and recycled to the reactor to promote cooling by evaporation. The hydrocarbon may also be introduced downstream of the recycle gas line from the condenser. This condensation mode technique is discussed in more detail below. The pressure, that is, the total pressure in the reactor, can be within the range of approximately 17.58 to 36.20 kilograms per absolute square centimeter and preferably falls within the range of approximately 21.09 and 29.17 kilograms per absolute square centimeter. The partial pressure of ethylene is graded as mentioned in the foregoing. The remainder of the total pressure is provided by the alpha-olefin (s) and / or an inert gas such as nitrogen. Volumetric production regimes are reported in kilograms per hour per cubic foot. This is also referred to as Space / Time / Performance (STY). The STY for the process of the invention can be about 20 pounds per hour per cubic foot, and is preferably about 7.5 to about 15 pounds per hour per cubic foot. A typical fluidized bed reactor can be described as follows and is also described in U.S. Patent Number 4,482,687.

- The bed is usually made up of the same granulated resin that can be produced in the reactor. Therefore, during the course of the polymerization, the bed comprises formed polymer particles, growing polymer particles, and catalyst particles fluidized by polymerization and modifying the gaseous components introduced at a rate of flow or sufficient velocity to cause the particles separate and act like a fluid. The fluidizing gas is constituted by the initial feed, the replacement feed and the cycle gas (recycled), ie the alpha-olefins and / or an inert carrier gas, and other reactor gases. As mentioned, an inert hydrocarbon of low boiling temperature is also added to the reactor. When added upstream of the cycle gas cooler, it evaporates and becomes part of the cycle gas. This hydrocarbon usually boils (normal boiling temperature at atmospheric pressure) at a temperature within the range of about 10 minutes to about plus 100 ° C. Examples of these hydrocarbons are isobutane, isopentane, hexane and heptane. Isopentane and hexane are preferred. The isopentane is introduced into the recycle line in an amount of about 2.5 to about 25 parts by volume per 100 parts by volume of cycle gas. He - Hexane is introduced in an amount of about 1 to about 10 parts by volume per 100 parts by volume of the cycle gas. The essential parts of the reaction system are the vessel, the bed, the gas distribution plate, the inlet and outlet piping, a cycle or recycle gas line, a compressor, a cycle gas cooler, and a product download system. In the container, above the bed, there is a zone of speed reduction, and, in the bed, a reaction zone. Both are above the gas distribution plate. The inert hydrocarbon enters the recycling line, raises the condensing temperature of the cycle gas (or recycled), partially condenses in the cycle gas cooler (condenser) when added upstream of the cooler, and then passes to the reactor where, together with the other condensed cycle gas, the exothermic polymerization reaction evaporates and cools. This is a particularity of the condensation mode technique described for example in the North American Patents Number 4,543,399 and 4,588,790. The condensed level of the cycle gas at the outlet of the cycle gas cooler can be from about 2.5 percent to about 25 percent by weight based on the weight of the cycle gas, and preferably is from about 5 percent to about 20 percent by weight. More preferably, it is from about 7.5 percent to about 15 percent by weight. It is found that the cyclohexane extractables are from about 3 percent to about 7 percent by weight based on the weight of the HDPE, and preferably from about 4 percent to about 6 percent by weight. In addition, PENT test failure times are found to be at least 50 hours, and preferably greater than 50 hours. The gaseous feed streams of ethylene, other alpha-olefins, hydrogen and oxygen, are preferably fed to the reactor recycle line as well as the liquid alpha-olefins and the catalyst. The catalyst can be fed as a slurry of mineral oil or a solid. Optionally, the catalyst it can be fed directly to the fluidized bed. The composition of the product can be varied by changing the molar ratios of the alpha-olefins introduced into the fluidized bed. The product is continuously discharged in granular or particulate form from the reactor as the level of the bed accumulates with the polymerization. The production rate is controlled by adjusting the catalyst feed rate. The temperature of the reactor and / or the oxygen added can be adjusted to control the average molecular weights. The residence time of the reagent mixture including gaseous and liquid reagents, the catalyst and resin in the fluidized bed reactor can be within the range of about 1 to about 4 hours and preferably falls within the range of about 1.25 to about 3 hours. The HDPE resin can be extruded into a pipe, or other products in a conventional extrusion apparatus adapted for the specific product desired. Extrusion apparatuses and processes for extrusion are described in US Pat. Nos. 4,814,135; 4,857,600; 5,076,988; and 5,153,382. A typical single screw type extrusion apparatus can be described as one having a hopper at its end upstream and a die at its downstream end. The hopper is fed to a cylindrical body, which contains a screw. At the downstream end, between the end of the screw and the die, there is a sieve pack and a rupture plate. The screw portion of the extrusion apparatus is considered as being, divided into three sections, the feeding section, the compression section and the regulated supply section, and multiple heating zones from the rear heating zone to the heating zone front, multiple sections and areas that run from upstream to downstream. If it has more than one cylindrical body, the cylindrical bodies are connected in series. The length-to-diameter ratio of each cylindrical body is within the range of about 16: 1 to about 30: 1. The extrusion can be carried out at temperatures within the range of about 160 ° C to about 270 ° C, and preferably carried out at temperatures within the range of about 180 ° C to about 240 ° C. The advantage of the invention lies in the pipe, molded part, geometry and other products that are produced from the HDPE made from the process of this invention. The products exhibit high resistance to slow crack growth as measured by the Pennsylvania State Tension Test (PENT), that is, the products survive more than 50 hours in the PENT test. The HDPE also consistently shows good extrusion capability. Conventional additives, which can be introduced into the HDPE are exemplified by antioxidants, ultraviolet absorption agents, anti-static agents, pigments, dyes, nucleating agents, fillers or fillers, slipping or slip agents, flame retardants, plasticizers , processing aids, lubricants, stabilizers, smoke inhibitors, viscosity control agents and crosslinking agents, catalysts and reinforcers, tackifiers and antiblocking agents. In addition to the filler or filler materials, the additives may be present in the mixture in amounts of about 0.05 to about 5 parts by weight of the additive per 100 parts by weight of the polymer blend. The filler or filler materials may be added in amounts of up to 20 parts by weight and more per 100 parts by weight of the mixture. In general, these products contain a primary antioxidant, a secondary antioxidant, and, in many cases, a processing aid. An example of a primary antioxidant is IRGANOX ™ 1010, and an example of the secondary antioxidant is IRGAFOS ™ 168. Examples of the processing aids are calcium stearate, zinc stearate, and fluoroelastomers. A preferred additive system includes IRGANOX ™ 1010 and IRGAFOS ™ 168 as antioxidants. In parts per million by weight, the preferred amounts are from about 500 to about 2,000 ppmw for each of the primary and secondary antioxidants, and about 200 to about 800 ppmw for the processing aid. The ppmw are based on parts per million by weight of ethylene. The Patents mentioned in this specification are incorporated by reference herein. The invention is illustrated by the following examples. Examples 1 to 5 Polymerization is carried out in a typical fluidized bed reactor as described above using as a catalyst the silica-supported reaction product of the triphenylsilyl chromium and diethylaluminium ethoxide having an atomic ratio of aluminum / chromium of 1.5: 1. The preparation of the catalyst is described above. The catalyst is introduced into the reactor in an amount of 0.02 to 0.04 part by weight per 100 parts by weight of the high density polyethylene product. The feed to the recycling line consists of ethylene, 1-hexene, hexane, hydrogen and oxygen (in Examples 3 to 5). This is the cycle gas. The total pressure in the reactor is approximately 22.85 kilograms per absolute square centimeter. The rest of the pressure is constituted with nitrogen. The variables and the results are indicated in the Table. Hexane is introduced in an amount of 4 to 6 parts by volume based on 100 parts by volume of cycle gas.

Picture Example 1 2 3 4 5 T grades C 93.4 92 92.2 93.3 94.6 C2PP Kg / cm ^ abs 11.99 16.52 17.35 16.52 17.12 H2 / C2 molar 0.05 0.05 0.05 0.05 0.05 Cg / C2 molar 0.007 0.0085 0.0086 0.008 0.008 o2 / c2 ppmv 0 0 0.04 0.021 0.037 Res Time 2.5 2.5 2.5 2.5 3 MI (I5) g / 10 min 0.42 0.4 0.38 0.39 0.4 FI (I21) g / 10 min 10.8 10.1 10.1 10.2 9.95 MFR 25.5 25 26.4 25.9 25 d2l l5) CHE% by weight 5 4.8 5.4 5.53 4.75 Density g / cc 0.945 0.945 0.945 0.945 0.945 PENT hours 30 to 80 to 75 to 70 > 80 40 90 90 80 Extrumargi- good capacity good good good nal Notes for the Table: T = temperature in degrees Celsius C2PP = partial pressure of ethylene in kilograms per absolute square centimeter.

H2 / C2 = molar ratio of ethylene hydrogen. C6 / C2 = molar ratio of 1-hexene to ethylene. O2 / C2 = part by volume of oxygen per million parts by volume of the ethylene feed to the reactor. In Example 2, the process takes advantage of another catalyst contamination present in the ethylene feed in an amount of at least 0.005 ppmv. Res Time = time of permanence in hours. MI (l5) = melt index at 5 kilograms in grams per 10 minutes. FI (l2i) - Flow rate at 21.6 kilograms in grams per 10 minutes. MFR (± 2i / l5) = FI (I2?) = Melting flow ratio. CHE = cyclohexane extractables in percent by weight based on the weight of the HDPE product. Density in grams per cubic centimeter. PENT = is determined as described above. Extrusion capacity in a subjective determination based on the experience of the operator in the extrusion line.

Claims

CLAIMS:

1. A process for preparing a high density polyethylene in the gas phase comprising contacting a mixture consisting of ethylene and one or more alpha-olefins with the sustained reaction product of a bis-hydrocarbylsilyl chromate and a hydrocarbylaluminum compound or a hydrocarbyl boron compound in a fluidized bed reactor having a recycle gas line, under polymerization conditions, with the following stipulations: (i) the atomic ratio of aluminum to chromium is within the scale of about 0.1 : 1 to about 2.9: 1; (ii) the amount of catalyst is within the range of about 0.005 to about 0.25 part by weight based on 100 parts by weight of high density polyethylene; (iii) the ethylene partial pressure is within the range of approximately 14.06 to approximately 28.12 kilograms per absolute square centimeter; (iv) oxygen and / or other catalyst contaminant is introduced into the reactor within the range of from about 0.005 to about 0.5 part by volume of the catalyst contaminant per parts per million by volume of ethylene; (v) the molar ratio of alpha-olefin to ethylene is from about 0.0001: 1 to about 0.1: 1; (vi) hydrogen is introduced into the reactor within the range of about 0.005 to about 0.5 mole of hydrogen per mole of ethylene; (vii) the polymerization is carried out at a temperature within the range of about 80 ° C to about 110 ° C; and (viii) an inert hydrocarbon of relatively low boiling temperature is introduced into the recycle gas line in an amount sufficient to raise the condensation temperature of the recycle gas, which consists of alpha-olefins and other reactor gases, and The recycle gas is partially condensed and recycled to the reactor where it promotes cooling by evaporation.

2. The process according to claim 1 wherein (i) the atomic ratio of aluminum to chromium is within the range of about 1: 1 to about 2: 1. (ii) the amount of the catalyst is within the range of about 0.01 to about 0.1 part by weight based on 100 parts by weight of high density polyethylene. (iii) the partial pressure of ethylene is within the range of approximately 14.75 to approximately 21.09 kilograms per absolute square centimeter. (iv) oxygen is introduced into the reactor within the range of about 0.005 to about 0.5 part by volume per million parts by volume of ethylene; (v) the molar ratio of alpha-olefin to ethylene is within the range of about 0.005: 1 to about 0.03: 1. (vi) the hydrogen is introduced into the reactor in a ratio of about 0.01 to about 0.1 mole of hydrogen per mole of ethylene; and (vii) the polymerization is carried out at a temperature within the range of about 85 ° C to about 100 ° C.

3. The process according to claim 2, wherein (i) the atomic ratio of aluminum to chromium is about 1.5; (ii) the amount of catalyst is within the range of about 0.01 to about 0.1 part by weight based on 100 parts by weight of high density polyethylene. (iii) the partial pressure of ethylene is within the range of about 15.82 to about 19.33 kilograms per absolute square centimeter; (iv) the oxygen is introduced into the reactor within the range of about 0.01 to about 0.1 part in volume per million parts of ethylene; (v) the alpha-olefin is 1-hexene, and the molar ratio of 1-hexene to ethylene is from about 0.0075: 1 to about 0.01: 1; (vi) the hydrogen is introduced into the reactor in a molar ratio of about 0.05 mol of hydrogen per mole of ethylene; and (vii) the polymerization is carried out at a temperature within the range of about 90 degrees to about 95 degrees centigrade.

4. The process according to claim 1, wherein, in stipulation 8, the condensed level of the inert hydrocarbon is from 2.5 to about 25 weight percent based on the weight of the gas passing through the recycle gas line. The process according to claim 1, wherein the extractables of cyclohexane are from about 3 percent to about 7 percent by weight based on the weight of the high density polyethylene; STY is from about 5 to about 20 pounds of high density polyethylene per hour per cubic foot of the reactor; and the failure time of the PENT test is at least 50 hours. The process according to claim 1, wherein the high density polyethylene is prepared by the process having the following properties: (a) density = 0.940 to 0.958 gram per cubic centimeter; (b) flow index (I21) = from about 2 to about 40 grams per 10 minutes; (c) melt index (I5) = from about 0.06 to about 2.5 grams per 10 minutes; and (d) melt flow ratio (I21 / I5) = about 16 to about 33. 7. A process for preparing high density polyethylene in the gas phase consisting of contacting a mixture comprising ethylene and hydrogen. -hexene with the reaction product supported by silica of a triphenylsilyl chromate and diethylaluminomethoxide in a fluidized bed reactor having a recycle gas line, under the polymerization conditions, with the following stipulations: (i) the atomic ratio of aluminum to chrome is about 1.5; (ii) the amount of catalyst is within the range of about 0.01 to about 0.1 part by weight based on 100 parts by weight of high density polyethylene; (iii) the partial pressure of ethylene is within the range of about 15.82 to about 19.33 kilograms per absolute square centimeter; (iv) the oxygen is introduced into the reactor within the range of about 0.01 to about 0.1 part in volume per million parts of ethylene; (v) the molar ratio of 1-hexene to ethylene is from about 0.0075: 1 to about 0.01; 1; (vi) the hydrogen is introduced into the reactor in a molar ratio of about 0.05 mol of hydrogen per mole of ethylene; (vii) the polymerization is carried out at a temperature within the range of about 90 to about 95 degrees centigrade; and (vii) an inert hydrocarbon of relatively low boiling temperature is introduced into the recycle gas line in an amount sufficient to raise the condensation temperature of the recycle gas, which consists of alpha-olefins and other reactor gases, and the recycle gas is partially condensed and recycled to the reactor where it promotes cooling by evaporation, the condensed level of the inert hydrocarbon being from about 2.5 to about 25 weight percent based on the weight of the gas passing through the recycle gas line. SUMMARY OF THE INVENTION A process for preparing high density polyethylene in the gas phase comprising contacting a mixture consisting of ethylene and one or more alpha-olefins with the sustained reaction product of a bis-hydrocarbylsilyl chromate and a hydrocarbylaluminum compound or a hydrocarbyl boron compound in a fluidized bed reactor having a recycle gas line, under polymerization conditions, with the following stipulations: (i) the atomic ratio of aluminum to chromium is within the scale of about 0.1: 1 approximately 2.9: 1. (ii) the amount of catalyst is within the range of about 0.005 to about 0.25 part by weight based on 100 parts by weight of high density polyethylene. (iii) the ethylene partial pressure is within the range of about 14.06 to about 28.12 kilograms per absolute square centimeter. (iv) Oxygen and / or other catalyst contaminant are introduced into the reactor within the range of from about 0.005 to about 0.5 part by volume of the catalyst contaminant per million parts by volume of ethylene; (v) the molar ratio of alpha-olefin to ethylene is from about 0.0001: 1 to about 0.1: 1; (vi) hydrogen is introduced into the reactor within the range of about 0.005 to about 0.5 mole of hydrogen per mole of ethylene; vii) the polymerization is carried out at a temperature within the range of about 80 ° C to about 110 ° C; and (viii) an inert hydrocarbon of relatively low boiling temperature is introduced into the recycle gas line in an amount sufficient to raise the condensation temperature of recycle gas, which consists of alpha-olefins and other reactor gases, and The recycle gas is partially condensed and recycled to the reactor where it promotes cooling by evaporation.