JP2010031296A - Method for producing polyethylene - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve a method for producing a polyethylene suitable for producing a film having an extract level, high impact resistance and a well-balanced tear-strength value in longitudinal and lateral directions. <P>SOLUTION: The new method for producing a homopolymer and a copolymer of ethylene, includes a process of bringing ethylene and/or ethylene with at least one olefine copolymer into contact with a Ziegler-Natta catalyst, trimethylaluminum and tetrahydrofuran under conditions of polymerization. The Ziegler-Natta catalyst contains titanium, magnesium and chlorine. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a polymerization process for the production of polyethylene. Preferably, the polyethylene has only a reduced level of extract. Films made from the polyethylene are characterized by having improved high strength properties.

  Polyethylene polymers are well known and are useful in many applications. In particular, linear polyethylene polymers have characteristics that distinguish them from other polyethylene polymers such as branched ethylene homopolymers commonly referred to as LDPE (low density polyethylene). Some of these properties are described in Anderson et al.

  A particularly useful polymerization medium for producing polyethylene polymers is the gas phase process. Such examples are described in Patent Documents 2-11.

  Ziegler-Natta based catalyst systems for olefin polymerization are well known in the art and have been known at least since the publication of US Pat. Many patents have since been issued for new or improved Ziegler-Natta based catalysts. Specific examples of such patents include Patent Documents 13-24.

  These patents disclose Ziegler-Natta based catalysts that are well known as being typically comprised of a transition metal component and a cocatalyst, typically an organoaluminum compound. If necessary, an activation agent such as a halogenated hydrocarbon and an activation modifier such as an electron donor are used together with the catalyst.

  The use of a halogenated hydrocarbon together with a Ziegler-Natta polymerization catalyst in the production of polyethylene is disclosed in Patent Document 25 and Patent Documents 26-27. As disclosed therein, halogenated hydrocarbons reduce ethane production rates, improve catalyst efficiency, or provide other benefits. Representative of such halogenated hydrocarbons are saturated or unsaturated aliphatic, alicyclic or aromatic hydrocarbons having 1 to 12 carbon atoms, substituted with one halogen or multiple halogens. is there. Specific examples of aliphatic compounds include methyl chloride, methyl bromide, methyl iodide, methylene chloride, methylene bromide, methylene iodide, chloroform, bromoform, iodoform, carbon tetrachloride, carbon tetrabromide, carbon tetraiodide. , Ethyl chloride, ethyl bromide, 1,2-dichloroethane, 1,2-dipromoethane, methyl chloroform, perchloroethylene and the like. Specific examples of the alicyclic compound include chlorocyclopropane, tetrachlorocyclopentane and the like. Specific examples of the aromatic compound include chlorobenzene, hexabromobenzene, benzotrichloride and the like. These compounds can be used alone or as a mixture thereof.

  It is also well known to use electron donors as needed, especially in the polymerization of olefins where Ziegler-Natta based catalysts are used. Such electron donors often help increase catalyst efficiency and / or control the stereospecificity of the polymer when olefins other than ethylene are polymerized. Electron donors are typically known as Lewis bases, but are called internal electron donors when used during the catalyst manufacturing process. An electron donor when used outside of the catalyst production process is called an external electron donor. For example, the external electron donor can be added to the preformed catalyst, to the prepolymer and / or the polymerization medium.

  The use of electron donors in the propylene polymerization field is well known and is primarily used to reduce atactic type polymers and increase the production of isotactic polymers. The use of an electron donor usually improves the catalyst productivity in isotactic polypropylene production. This is shown schematically in US Pat.

  In the field of ethylene polymerization where ethylene constitutes at least about 70% by weight of the total monomer present in the polymer, electron donors are used to control the molecular weight distribution (MWD) of the polymer and the catalytic activity in the polymerization medium. . Specific examples of patents describing the use of internal electron donors in the production of linear polyethylene include: Patent Document 16; Patent Document 29; Patent Document 19; Patent Document 30; Patent Document 31; Patent Document 24; 32; Patent Document 5; and Patent Document 33. The use of an external monoether electron donor, such as tetrahydrofuran (THF), to adjust the molecular weight distribution is shown in US Pat. No. 6,057,036; and uses an external electron donor to adjust the reactivity of the catalyst particles. This is described in Patent Document 35.

  Examples of electron donors include carboxylic acids, carboxylic esters, alcohols, ethers, ketones, amines, amides, nitriles, aldehydes, thioethers, thioesters, carbonates, oxygen atom-containing organosilicon compounds, and carbon or oxygen atoms. And phosphorus, arsenic or antimony compounds bonded to organic groups.

U.S. Pat. No. 4,076,698 US Pat. No. 3,709,853 U.S. Pat. No. 4,003,712 US Pat. No. 4,011,382 U.S. Pat. No. 4,302,566 US Pat. No. 4,543,399 U.S. Pat. No. 4,882,400 US Pat. No. 5,352,749 US Pat. No. 5,541,270 Canadian Patent No. 991,798 Belgian Patent No. 839,380 US Pat. No. 3,113,115 U.S. Pat. No. 3,594,330 US Pat. No. 3,676,415 U.S. Pat. No. 3,644,318 U.S. Pat. No. 3,917,575 U.S. Pat. No. 4,105,847 U.S. Pat. No. 4,148,754 U.S. Pat. No. 4,256,866 U.S. Pat. No. 4,298,713 U.S. Pat. No. 4,311,752 U.S. Pat. No. 4,363,904 US Pat. No. 4,481,301 US Reissue Patent No. 33,683 US Pat. No. 3,354,139 European Patent No. 0 529 977 B1 European Patent Publication No. 0 703 246 A1 US Pat. No. 4,981,930 U.S. Pat. No. 4,187,385 US Pat. No. 4,293,673 U.S. Pat. No. 4,296,223 U.S. Pat. No. 4,302,565 US Pat. No. 5,470,812 US Pat. No. 5,055,535 US Pat. No. 5,410,002 U.S. Pat. No. 4,012,573

  In the polymerization method of the present invention, in a polymerization medium containing ethylene and optionally at least one other olefin, a Ziegler-Natta polymerization catalyst, an external electron donor, tetrahydrofuran (THF), and a cocatalyst, Introducing trimethylaluminum (TMA), the Ziegler-Natta catalyst comprising titanium, magnesium and chlorine. Halogenated hydrocarbon compounds can be used in the polymerization medium as required. THF and / or TMA may be added to the catalyst immediately prior to addition to the polymerization medium, or may be added to the polymerization medium separately from the catalyst in any manner known in the art. For example, THF may be premixed with the TMA cocatalyst, if desired, prior to addition to the polymerization medium.

  We do not expect to enable the production of polyethylene in a particularly improved manner of Ziegler-Natta based catalyst, trimethylaluminum (TMA) cocatalyst and tetrahydrofuran (THF) external electron donor. I found it. Preferably, the resulting polyethylene has a reduced level of extractables. Furthermore, films produced from these polyethylenes have surprisingly high impact resistance represented by drop impact values and good tear values in the machine direction (MD) and transverse direction (TD). Have a balance.

  When utilizing a gas phase fluidized bed process for the polymerization of ethylene, it is advantageous to add THF before the heat removal means, eg, the heat exchanger, to reduce the contamination rate of the heat removal means.

  All references herein to elements of the Periodic Table Group refer to the Periodic Table of Elements published in “Chemical and Engineering News”, 63 (5), 27 (1985). In this table, groups are numbered 1-18.

  The polymerization method of the present invention can be carried out using any suitable method. For example, polymerization in suspension, solution, super-critical or gas phase media can be utilized. These polymerization methods are all well known.

  A particularly desirable method for producing the polyethylene polymer according to the present invention is a gas phase polymerization process, preferably utilizing a fluidized bed reactor. This type of reactor and the means for operating the reactor are well known and are fully described in US Pat. These patents disclose gas phase polymerization processes in which the polymerization medium is either mechanically agitated or fluidized by a continuous flow of gaseous monomers and diluent. The entire contents of these patents are incorporated herein by reference.

  Usually, the polymerization method of the present invention can be carried out as a continuous gas phase method such as a fluidized bed method. The fluidized bed reactor used in the process of the present invention typically comprises a reaction zone and a so-called deceleration zone. The reaction zone includes a bed of growing polymer particles, shaped polymer particles and a small amount of catalyst particles fluidized by a continuous flow of gaseous monomer and diluent that removes the heat of polymerization in the reaction zone. If desired, a portion of the recycle gas may be cooled and compressed to produce a liquid that increases the heat removal capacity of the recycle gas stream when reintroduced into the reaction zone. An appropriate gas flow rate can be easily determined by simple experimentation. The incorporation of gaseous monomer into the circulating gas stream is at a rate equal to the rate at which the particular polymer and its entrained monomer are removed from the reactor, and the composition of the gas passing through the reactor is essentially within the reaction zone. Adjust to maintain steady state gas composition. The gas leaving the reaction zone passes through the deceleration zone where it removes entrained particles. Finer entrained particles and dust can be removed with a cyclone and / or a fine filter. The gas passes through a heat exchanger where it removes the heat of polymerization, pressurizes in the compressor and then returns to the reaction zone.

  Specifically, the reactor temperature for the fluidized bed process herein is in the range of about 30 ° C to about 110 ° C. Usually, the reactor temperature is operated at the highest temperature that can be carried out taking into account the sintering temperature of the polymer product in the reactor.

  The process of the present invention is suitable for the production of ethylene homopolymers and / or copolymers of ethylene with at least one or more other olefins, terpolymers, and the like. Preferably, the olefin is an α-olefin. The olefin can contain, for example, 3 to 16 carbon atoms. Particularly suitable for the production here according to the invention is linear polyethylene. Preferably, such linear polyethylene is a linear homopolymer of ethylene and a linear copolymer of ethylene and at least one α-olefin that is at least about 70% by weight of the total monomer including ethylene content. It is. Specific examples of typical α-olefins that can be used here are propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 4-methylpent-1-ene, 1-decene, 1-dodecene, 1-hexadecene and the like. Also usable herein are polyenes such as 1,3-hexadiene, 1,4-hexadiene, cyclopentadiene, dicyclopentadiene, 4-vinylcyclohex-1-ene, 1,5-cyclooctadiene, There are 5-vinylidene-2-norbornene and 5-vinyl-2-norbornene, as well as olefins that are generated in situ in the polymerization medium. If the olefin is produced in situ in the polymerization medium, a linear polyethylene with long chain branches will be produced.

  The polymerization reaction of the present invention is carried out in the presence of a Ziegler-Natta catalyst. In the process of the present invention, the catalyst can be introduced by any method known in the art. For example, the catalyst can be introduced directly into the polymerization medium in the form of a solution, slurry or free-flowing dry powder. The catalyst can also be used in the form of a deactivated catalyst or in the form of a prepolymer obtained by contacting the catalyst with one or more olefins in the presence of a cocatalyst.

  Ziegler-Natta catalysts are well known in the industry. The simplest form of a Ziegler-Natta catalyst is composed of a transition metal compound and an organometallic cocatalyst compound. The metals of the transition metal compounds are Group 4, Group 5, Group 6, Group 7, Group 8, Group 10 and Group 10 of the periodic table published in “Chemical and Engineering News”, 63 (5), 27 (1985). A group metal. In this table, groups are numbered 1-18. Specific examples of such transition metals are titanium, zirconium, vanadium, chromium, manganese, iron, cobalt, nickel and the like and mixtures thereof. In a preferred embodiment, the transition metal is selected from the group consisting of titanium, zirconium, vanadium and chromium, and in a more preferred embodiment, the transition metal is titanium. The Ziegler-Natta catalyst can contain magnesium and chlorine as required. Such magnesium and chlorine containing catalysts can be produced by any method known in the art.

  The cocatalyst added to the polymerization medium of the present invention is trimethylaluminum (TMA).

  When a prepolymerized form of the catalyst is employed, the organometallic cocatalyst compound used to form the prepolymer is selected from the groups 1, 2, 11, 12, 13 of the periodic table of elements. And any organometallic compound comprising a Group 14 metal. Specific examples of such metals include lithium, magnesium, copper, zinc, boron, silicon and the like. However, TMA is still used as a cocatalyst in the polymerization medium when employing prepolymers.

  The catalyst system may contain conventional components in addition to the transition metal component, THF as the external electron donor, and TMA as the cocatalyst component. For example, any internal electron donor, any halogenated hydrocarbon, etc. known in the art may be added.

  The Ziegler-Natta catalyst can be produced by any method known in the art. The catalyst can be in the form of a solution, slurry or free-flowing dry powder. The amount of Ziegler-Natta catalyst used is sufficient to allow the production of the desired amount of polyethylene.

  In carrying out the polymerization process of the present invention, TMA is added to the polymerization medium in any amount sufficient to result in the production of the desired polyethylene. It is preferred to incorporate TMA in a molar ratio of TMA: transition metal component of the Ziegler-Natta catalyst ranging from about 1: 1 to about 100: 1. In a more preferred embodiment, the molar ratio of TMA: transition metal component ranges from about 1: 1 to about 50: 1.

  In carrying out the polymerization method of the present invention, THF as an external electron donor is added by any method. For example, THF can be added to the preformed catalyst, to the prepolymer during the prepolymerization stage, to the preformed prepolymer and / or to the polymerization medium. The THF may be premixed with the TMA cocatalyst as required. THF is added in any amount sufficient to produce the desired polyethylene. Preferably, the THF is incorporated in a THF: Ziegler-Natta catalyst transition metal component molar ratio ranging from about 0.01: 1 to about 100: 1. In a more preferred embodiment, the molar ratio of THF: transition metal component ranges from about 0.1: 1 to about 50: 1.

  In carrying out the polymerization process of the present invention, any other conventional additive commonly used in olefin polymerization processes can be added. In particular, halogenated hydrocarbons including those mentioned above, preferably chloroform, can be added. The molar ratio of the halogenated hydrocarbon to the transition metal component of the Ziegler-Natta catalyst is preferably in the range of about 0.001: 1 to about 1: 1.

The molecular weight of the polyethylene produced according to the present invention can be adjusted by any known method, for example using hydrogen. As the hydrogen: ethylene molar ratio in the polymerization medium increases, the adjustment of the molecular weight can be evidenced by an increase in the melt index (I ₂ ) of the polymer.

  The molecular weight distribution of the polyethylene produced according to the present invention is represented by the melt flow ratio (MFR). Preferably, the polyethylene has an MFR value that varies from about 24 to about 34 and a density in the range of about 0.880 g / cc to about 0.964 g / cc.

  The polyethylene of the present invention can be made into a film by any technique known in the art. For example, the film can be made by well-known cast film techniques, infiltration film techniques, and extrusion coating techniques.

  Furthermore, polyethylene can be made into other products, such as moldings, by any well-known technique.

  The invention will be more readily understood by reference to the following examples. There are, of course, many other variations that will be apparent to those skilled in the art once the present invention has been fully disclosed, and therefore, these examples are illustrative. It will be appreciated that this is for illustrative purposes only and should not be construed as limiting the scope of the invention in any way.

EXAMPLES In the following examples, the test procedures listed below were used to evaluate the analytical properties of the polyethylene here and to evaluate the physical properties of the films of the examples.
a) Drop impact value is measured according to ASTM D-1709 Method A (using a 38.1 mm heel with a smooth phenolic head, drop height 0.66 m, film thickness approximately 1 mil) Do;
b) Longitudinal (machine) direction tear, MD _TEAR (g / mil): ASTM D-1922
c) Lateral tear, TD _TEAR (g / mil): ASTM D-1922
d) Density is determined by ASTM from plaques prepared according to ASTM D1928.
Measured according to D-4883;
e) Melt index (MI), I ₂ is measured according to ASTM D-1238, Condition E (measured at 190 ° C.) and reported in dg / min;
f) High load melt index (HLMI), I ₂₁ is measured according to ASTM D-1238, condition F (measured at a load 10 times the load used in the melt index test I ₂ above);
g) Melt flow ratio (MFR) = I ₂₁ / I ₂ , ie high load melt index / melt index;
h) Ether extract: Obtain about 100 g of powdered polymer sample from the reactor before any compounding step. The sample is placed in an extraction cylindrical filter paper whose tare has been measured, and weighed to the nearest 0.1 mg (to the nearest 0.1 mg). The extraction cylindrical filter paper containing the sample is then placed in a Soxhlet extractor and continuously extracted with ether for 6 hours. The extraction cylindrical filter paper containing the extracted sample is then dried to constant weight for 2 hours under reduced pressure. The ether extract is then reported as a weight fraction normalized to the original sample weight of the sample dissolved in ether. For example, an ether extract of 2% indicates that 2% by weight of the polymer has been extracted with ether; and i) n-hexane extract is measured according to 21 CFR 177.1520 (option 2). More specifically, an approximately 1 in ² film test piece having a thickness of 4 mils or less and a weight of 2.5 ± 0.05 g is placed in a sample container in which a tare is measured, and precisely weighed to the nearest 0.1 mg. The sample bowl containing the test piece is then placed in a 2 liter extraction vessel containing about 1 liter of n-hexane. The soot is put so that the whole is below the liquid level of the n-hexane solvent. The sample resin film is extracted at 49.5 ± 0.5 ° C. for 2 hours, then the soot is pulled over the solvent level and drained for a while. Remove the sputum and rinse the contents by submerging several times in fresh n-hexane. The basket is allowed to dry between rinses. Excess solvent is removed by briefly blowing a stream of nitrogen or dry air into the tub. Place firewood in vacuum oven at 80 ± 5 ° C for 2 hours. After 2 hours, the basket is taken out and placed in a desiccator and cooled to room temperature (about 1 hour). After cooling, reweigh the soot to the nearest 0.1 mg. The n-hexane extract% is then calculated from the weight loss of the original sample.

  The Ziegler-Natta catalyst used here was prepared according to Example 1-a of European Patent Publication No. 0 703 246 A1 (Patent Document 27).

  The prepolymers used in Examples 1-7 herein are those prepared according to Example 1-b of European Patent Application No. 0 703 246 A1 (Patent Document 27). A prepolymer containing about 34 g of polyethylene per millimole of titanium was thus obtained.

  The polymerization process used in Examples 1-7 was carried out in a fluidized bed reactor for gas phase polymerization consisting of a vertical cylinder with a diameter of 0.9 m and a height of 6 m, with a deceleration chamber on top. The reactor is equipped at its lower part with an external line for recirculating gas that connects the fluidization grid and the top of the deceleration chamber to a point below the fluidization grid at the bottom of the reactor. A heat transfer means such as a compressor and a heat exchanger for circulating gas is attached to the recirculation line. In particular, a line for supplying ethylene, olefins, such as 1-butene, 1-pentene and 1-hexene, hydrogen and nitrogen, which represents the main constituents of the gaseous reaction mixture passing through the fluidized bed, Send it in. The reactor includes a fluidized bed of polyethylene powder formed on particles having a weight average diameter of about 0.5 mm to about 1.4 mm on a fluidized grid. The gaseous reaction mixture contains ethylene, olefin comonomer, hydrogen, nitrogen and minor amounts of other components, but at a pressure in the range of about 290 psig to about 300 psig, about 1.8 ft / sec to about 2.0 ft / sec. It passes through the fluidized bed at an ascending fluidization rate (herein referred to as fluidization rate).

Furthermore, in each of Examples 1-7, the catalyst is intermittently introduced into the reactor in the form of a prepolymer. This catalyst contains magnesium, chlorine and titanium. The prepolymer form contains about 34 grams of polyethylene per millimole of titanium and tri-n-octylaluminum (TnOA) so that its Al / Ti molar ratio is equal to about 1.1: 1. In Example 8, the Ziegler-Natta catalyst is introduced directly into the reactor without forming into a prepolymer. The rate of introduction of the prepolymer or catalyst into the reactor is adjusted according to predetermined set conditions to achieve the desired production rate. During the polymerization, a solution of trimethylaluminum (TMA) in n-hexane is continuously introduced at a concentration of about 2% by weight to a set point downstream of the heat transfer means in a line for recirculating the gaseous reaction mixture. To do. The feed rate of TMA is expressed as the molar ratio of TMA to titanium (TMA / Ti), and the feed rate of TMA (in moles of titanium per hour) relative to the feed rate of catalyst or prepolymer (in moles of TMA per hour). Defined as the ratio of At the same time, a solution of chloroform (CHCl ₃ ) in n-hexane is continuously introduced into the line for recirculating the gaseous reaction mixture at a concentration of about 0.5% by weight. The molar ratio of CHCl ₃ feed rate of CHCl ₃ is to titanium (CHCl ₃ / Ti) expressed as a catalyst or feed rate of the prepolymer (in moles of titanium per hour) for per feed rate (time CHCl ₃ Defined as the ratio (in moles of CHCl ₃ ).

  When using an external donor in any of the following examples, it was THF. Tetrahydrofuran (THF) in n-hexane can be introduced continuously at a concentration of about 1% by weight into a line for recycling the gaseous reaction mixture. The feed rate of THF is expressed as the molar ratio of THF to titanium (THF / Ti), and the feed rate of THF (in moles of titanium per hour) to the feed rate of catalyst or prepolymer (in moles of THF per hour). Defined as the ratio of

  Catalyst or prepolymer productivity (productivity) is the ratio of the number of pounds of polyethylene produced to the number of pounds of catalyst or prepolymer added to the reactor. The activity of the catalyst or prepolymer is expressed as grams of polyethylene per millimole of titanium, per hour and per bar of ethylene pressure.

Example 1 The operating conditions of LLDPE using TMA as a cocatalyst and THF as an external electron donor are shown in Table 1, and the resin properties are shown in Table 2. The molar ratio of TMA to titanium was 7. The molar ratio of CHCl ₃ to titanium was 0.06. This method was carried out by adding tetrahydrofuran (THF) as an external electron donor at a molar ratio of THF to titanium of 3. 1-hexene was used as a comonomer. Under these conditions, linear polyethylene without agglomerates was withdrawn from the reactor at a rate of 206 lb / hr (pounds per hour). The catalyst productivity is 179 pounds of polyethylene per pound of prepolymer, which corresponds to an activity of 261 g of polyethylene per millimole of titanium, per hour, and bar of ethylene partial pressure.

The linear polyethylene had a density of 0.918 g / cc and a melt index MI _2.16 , I ₂ of 0.9 dg / min. The melt flow ratio I ₂₁ / I ₂ was 30, and the ether extract was 2.8% by weight. The drop impact value was 530 g / mil and MD _TEAR and TD _TEAR were 410 g / mil and 540 g / mil, respectively.

Example 2 (Comparative Example): Table 1 shows the production operation conditions of linear low density polyethylene (LLDPE) using TMA as a cocatalyst, and Table 2 shows the resin characteristics. The molar ratio of trimethylaluminum (TMA) to titanium was 3. The molar ratio of CHCl ₃ to titanium was 0.03. This method was carried out without adding THF. 1-hexene was used as a comonomer. Under these conditions, linear polyethylene without agglomerates was removed from the reactor at a rate of 150 lb / hr. The catalyst productivity is 375 pounds of polyethylene per pound of prepolymer, which corresponds to an activity of 1154 g of polyethylene per millimole of titanium, per hour, and bar of ethylene partial pressure.

The linear polyethylene had a density of 0.918 g / cc and a melt index MI _2.16 , I ₂ of 0.9 dg / min. The melt flow ratio I ₂₁ / I ₂ was 33 and the ether extract was 4.8% by weight. The drop impact value was 200 g / mil, and MD _TEAR and TD _TEAR were 450 g / mil and 500 g / mil, respectively.

Example 3 (Comparative Example): Table 1 shows the production operation conditions of LLDPE using TEAL as a cocatalyst and THF as an external electron donor , and Table 2 shows resin characteristics. The molar ratio of triethylaluminum (TEAL) to titanium was 7. The molar ratio of CHCl ₃ to titanium was 0.06. The molar ratio of THF to titanium was 3. 1-hexene was used as a comonomer. Under these conditions, linear polyethylene without agglomerates was removed from the reactor at a rate of 197 lb / hr. The catalyst productivity is 122 pounds of polyethylene per pound of prepolymer, which corresponds to an activity of 168 grams of polyethylene per millimole of titanium, per hour, and bar of ethylene partial pressure.

The linear polyethylene had a density of 0.918 g / cc and a melt index MI _2.16 , I ₂ of 0.9 dg / min. The melt flow ratio I ₂₁ / I ₂ was 31, and the ether extract was 3.6% by weight. The drop impact value was 260 g / mil and MD _TEAR and TD _TEAR were 430 g / mil and 560 g / mil, respectively.

Example 4 (comparative example): Table 1 shows the operating conditions for the production of LLDPE using TEAL as the cocatalyst and THF as the external electron donor , and Table 2 shows the resin properties. The molar ratio of TEAL to titanium was 13. The molar ratio of CHCl ₃ to titanium was 0.06. The molar ratio of THF to titanium was 3. 1-hexene was used as a comonomer. Under these conditions, linear polyethylene without agglomerates was withdrawn from the reactor at a rate of 207 lb / hr. The catalyst productivity is 150 pounds of polyethylene per pound of prepolymer, which corresponds to an activity of 216 grams of polyethylene per millimole of titanium, per hour, and bar of ethylene partial pressure.

The linear polyethylene had a density of 0.918 g / cc and a melt index MI _2.16 , I ₂ of 0.9 dg / min. The melt flow ratio I ₂₁ / I ₂ was 32, and the ether extract was 4.0% by weight. The drop impact value was 190 g / mil and MD _TEAR and TD _TEAR were 416 g / mil and 571 g / mil, respectively.

Table 1: Reactor conditions for Examples 1-4
Example
1 2 3 4
Reactor pressure (psig) 295 290 297 296
Reactor temperature (℃) 86 84 86 86
Fluidization speed (ft / sec) 1.94 1.79 1.94 1.93
Fluidized bulk density (Ib / ft ³ ) 15.8 17.0 15.6 15.9
Reactor bed height (ft) 11 9.4 11 11
Ethylene (C ₂ ) (mol%) 28 38 28 28
H ₂ / C ₂ (molar ratio) 0.152 0.178 0.160 0.134
1-hexene / C ₂ (molar ratio) 0.165 0.191 0.168 0.165
Cocatalyst TMA TMA TEAL TEAL
Al / Ti (molar ratio) 7 3 7 13
External electron donor THF --- THF THF
THF / Ti (molar ratio) 3 --- 3 3
CHCl ₃ / Ti 0.06 0.03 0.06 0.06
Production rate (lb / h) 206 150 197 207
Space-time yield (Ib / hr.ft ³ ) 4.05 3.59 3.80 4.08
Productivity (mass ratio) 179 375 122 150
Activity 261 1154 168 216
(G PE / mmol Ti-time-bar _{of ethylene)}
Residual titanium (ppm) 8.6 1.1 12.3 9.5

Table 2: Resin properties of LLDPE produced in Examples 1-4
Example
1 2 3 4
Density (g / cc) 0.918 0.918 0.918 0.918
Melt index, I ₂ (dg / min) 0.9 0.9 0.9 0.9
Melt flow ratio (I ₂₁ / I ₂ ) 30 33 31 32
Ether extract (wt%) 2.8 4.8 3.6 4.0
n-Hexane extract (wt%) 1.6 3.0 2.4 2.5
Drop impact value (g / mil) 530 200 260 190
MD _TEAR (g / mil) 410 450 430 416
TD _TEAR (g / mil) 540 500 560 571

  A review of the data shown in Tables 1 and 2 reveals the unexpectedly excellent results obtained for polyethylene produced using the method of the present invention, as shown in Example 1. More specifically, as shown in Example 1 where both TMA and THF are used in the polymerization process, the drop impact is greater than twice that of the polyethylene produced in Example 2 where TMA is used but no THF is present. A polyethylene having a level of strength is produced. Further, as shown in Examples 3 and 4 where TEAL is used with THF instead of TMA, the resulting polyethylene is a drop of polyethylene produced according to the process of the present invention, as shown in Example 1. It has a drop impact value that is less than half of the impact value. In addition to the above, the polyethylene produced according to the present invention in which a specific combination of TMA and THF is used is narrow compared to the polyethylene of Examples 2, 3 and 4 as evidenced by melt flow rate values. It will also be noted from the data in Table 2 that it is characterized by having a molecular weight distribution. Furthermore, it should be noted that the extract of polyethylene of the present invention (Example 1) is significantly lower than the extract of polyethylene of Comparative Examples 2, 3 and 4. Note also that the other physical properties of the polyethylene of Examples 1, 2, 3, and 4 are substantially similar.

Examples 5-7
Examples 5, 6 and 7 below attempt to demonstrate similar results when using olefins such as 1-butene, 1-pentene and 1-hexene as comonomer with ethylene.

Example 5: Table 3 shows the operating conditions for producing LLDPE with a density of 0.908 using TMA as a cocatalyst, THF as an external electron donor and 1-hexene as a comonomer, and Table 4 shows resin characteristics. The molar ratio of TMA to titanium was 6. The molar ratio of CHCl ₃ to titanium was 0.06. The molar ratio of THF to titanium was 3. 1-hexene was used as a comonomer. Under these conditions, linear polyethylene without agglomerates was removed from the reactor at a rate of 196 lb / hr. The catalyst productivity is 168 pounds of polyethylene per pound of prepolymer, which corresponds to an activity of 259 grams of polyethylene per millimole of titanium, per hour, and bar of ethylene partial pressure.

The linear polyethylene had a density of 0.908 g / cc and a melt index MI _2.16 , I ₂ of 0.6 dg / min. The melt flow ratio I ₂₁ / I ₂ was 34 and the ether extract was 5.2% by weight. The drop impact value was greater than 1500 g / mil, and MD _TEAR and TD _TEAR were 700 g / mil and 750 g / mil, respectively.

Example 6: Table 3 shows operating conditions for producing LLDPE having a density of 0.908 using TMA as a cocatalyst, THF as an external electron donor and 1-pentene as a comonomer, and Table 4 shows resin characteristics. The molar ratio of TMA to titanium was 7. The molar ratio of CHCl ₃ to titanium was 0.06. The molar ratio of THF to titanium was 3. Under these conditions, linear polyethylene without agglomerates was removed from the reactor at a rate of 200 lb / hr. The catalyst productivity is 129 pounds of polyethylene per pound of prepolymer, which corresponds to an activity of 239 grams of polyethylene per millimole of titanium, per hour, and bar of ethylene partial pressure.

The linear polyethylene had a density of 0.908 g / cc and a melt index MI _2.16 , I ₂ of 0.5 dg / min. The melt flow ratio I ₂₁ / I ₂ was 31, and the ether extract was 3.1% by weight.

Example 7: Table 3 shows operating conditions for producing LLDPE having a density of 0.908 using TMA as a cocatalyst, THF as an external electron donor and 1-butene as a comonomer, and Table 4 shows resin characteristics. The molar ratio of TMA to titanium was 7.5. The molar ratio of CHCl ₃ to titanium was 0.06. The molar ratio of THF to titanium was 3. Under these conditions, linear polyethylene without agglomerates was removed from the reactor at a rate of 200 lb / hr. The catalyst productivity is 98 pounds of polyethylene per pound of prepolymer, which corresponds to an activity of 210 grams of polyethylene per millimole of titanium, per hour, and bar of ethylene partial pressure.

The linear polyethylene had a density of 0.908 g / cc and a melt index MI _2.16 , I ₂ of 0.4 dg / min. The melt flow ratio I ₂₁ / I ₂ was 28, and the ether extract was 1.9% by weight.

Table 3: Reactor conditions for Examples 5-7
Example
5 6 7
Reactor pressure (psig) 294 297 297
Reactor temperature (° C) 81 80 78
Fluidization speed (ft / sec) 1.96 1.97 1.93
Fluidized bulk density (lb / ft ³ ) 14.6 14.8 14.9
Reactor floor height (ft) 12 12 12
Ethylene (C ₂ ) (mol%) 25 22 19
H ₂ / C ₂ (molar ratio) 0.119 0.100 0.102
1-butene / C ₂ (molar ratio) --- --- 0.672
1-Pentene / C ₂ (molar ratio) --- 0.447 ---
1-hexene / C ₂ (molar ratio) 0.211 --- ---
Cocatalyst TMA TMA TMA
Al / Ti (molar ratio) 6 7 7.5
External electron donor THF THF THF
THF / Ti (molar ratio) 3 3 3
CHCl ₃ / Ti 0.06 0.06 0.06
Production rate (lb / h) 196 200 200
Space-time yield (lb / hr · ft ³ ) 3.56 3.70 3.73
Productivity (mass ratio) 168 129 98
Activity 259 239 210
(G PE / mmol Ti-time-bar _{of ethylene)}
Residual titanium (ppm) 8.5 10.6 14

Table 4: Resin properties of LLDPE produced in Examples 5-7
Example
5 6 7
Density (g / cc) 0.908 0.908 0.908
Melt index I ₂ (dg / min) 0.6 0.5 0.4
Melt flow ratio (I ₂₁ / I ₂ ) 34 31 28
Ether extract (wt%) 5.2 3.1 1.9
n-Hexane extract (wt%) 3.5 1.8 1.3
Drop impact value (g / mil)>1500> 2000 950
MD _TEAR (g / mil) 700 550 313
TD _TEAR (g / mil) 750 470 323

  Reviewing the data shown in Tables 3 and 4 allows the following observations to be made. As the olefin comonomer shortens the chain length, for example from 1-hexene to 1-pentene, to 1-butene, the data has a smaller molecular weight distribution as measured by melt flow rate (MFR) and less polyethylene extract. Become.

Example 8: Production of LLDPE using TMA as cocatalyst and THF as external electron donor and direct reactor addition of Ziegler-Natta catalyst Direct reactor without conversion of Ziegler-Natta catalyst into prepolymer form The method of Example 1 was reworked except that it was injected into. A linear polyethylene was obtained.

The embodiments of the invention described in this specification are listed below.
Aspect 1. Contacting ethylene and / or ethylene with at least one or more other olefins under polymerization conditions with Ziegler-Natta based catalyst, trimethylaluminum and tetrahydrofuran as an external electron donor, and / Or a method of polymerizing ethylene and at least one or more other olefins.
Aspect 2. The method of embodiment 1, further comprising the presence of a halogenated hydrocarbon.
Aspect 3. The process according to embodiment 2, wherein the halogenated hydrocarbon is chloroform.
Aspect 4. An embodiment in which the Ziegler-Natta catalyst comprises a transition metal compound selected from metals of Group 4, Group 5, Group 6, Group 7, Group 8, Group 9 and Group 10 of the Periodic Table of Elements as defined herein The method according to 1.
Aspect 5 The method according to embodiment 4, wherein the metal of the transition metal compound is selected from the group consisting of titanium, zirconium, vanadium and chromium.
Aspect 6 The method according to embodiment 5, wherein the metal of the transition metal compound is titanium.
Aspect 7. The method of embodiment 1, further comprising the presence of at least one internal electron donor.
Aspect 8 The method of embodiment 1, further comprising magnesium and chlorine being present in a Ziegler-Natta catalyst.
Aspect 9. The method of embodiment 4, further comprising the presence of magnesium and chlorine incorporated in the Ziegler-Natta catalyst.
Aspect 10 The method of embodiment 7, further comprising magnesium and chlorine being present in the Ziegler-Natta catalyst.
Aspect 11 The process according to embodiment 2, wherein the halogenated hydrocarbon is added in a molar ratio of the halogenated hydrocarbon to the transition metal component of the Ziegler-Natta catalyst in the range of 0.001: 1 to 1: 1.
Aspect 12 The method according to embodiment 1, wherein the trimethylaluminum is added in a molar ratio of trimethylaluminum to Ziegler-Natta catalyst transition metal component in the range of 1: 1 to 100: 1.
Aspect 13 The method according to embodiment 12, wherein the molar ratio of the transition metal component of the trimethylaluminum: Ziegler-Natta catalyst is in the range of 1: 1 to 50: 1.
Aspect 14. The method according to embodiment 1, wherein the tetrahydrofuran is added in a molar ratio of the transition metal component of the tetrahydrofuran: Ziegler-Natta catalyst in the range of 0.01: 1 to 100: 1.
Aspect 15 The method according to embodiment 14, wherein the molar ratio of the transition metal component of the tetrahydrofuran: Ziegler-Natta catalyst is in the range of 0.1: 1 to 50: 1.
Aspect 16. The method according to embodiment 1, wherein the polymerization conditions are a gas phase.
Aspect 17 The method of embodiment 1, wherein the polymerization conditions are solution phase.
Aspect 18. The method according to embodiment 1, wherein the polymerization condition is a slurry phase.
Aspect 19 The process of embodiment 1, wherein the at least one or more other olefins are olefins having 3 to 16 carbon atoms.
Aspect 20 The process according to embodiment 19, wherein the at least one or more other olefins are selected from the group consisting of 1-octene, 1-hexene, 4-methylpent-1-ene, 1-pentene, 1-butene and propylene.
Aspect 21. The process of embodiment 1, wherein the copolymer obtained by polymerization of ethylene and at least one or more olefins comprises ethylene in an amount of at least 70% by weight of the copolymer.
Aspect 22 The method according to embodiment 1, wherein the Ziegler-Natta catalyst comprises titanium, magnesium and chlorine.
Aspect 23. Embodiment 23. The method of embodiment 22, further comprising the presence of a halogenated hydrocarbon.
Aspect 24. The method according to embodiment 22, wherein the polymerization conditions are gas phase.

  Films made from the polyethylene of the present invention are typically characterized by having improved strength properties, particularly as indicated by the drop impact values in Tables 2 and 4. Products such as molded articles can also be produced from the polyethylene of the present invention.

  It should be clearly understood that the forms of the invention described herein are for illustrative purposes only and are not intended to limit the scope of the invention. The present invention includes all modifications that fall within the scope of the claims.

Claims (13)

  Contacting ethylene and / or ethylene with at least one or more other olefins under polymerization conditions with Ziegler-Natta based catalyst, trimethylaluminum and tetrahydrofuran as an external electron donor, and A method of polymerizing ethylene and at least one or more other olefins, wherein the Ziegler-Natta catalyst comprises titanium, magnesium and chlorine.   The method of claim 1 further comprising the presence of a halogenated hydrocarbon.   The process according to claim 2, wherein the halogenated hydrocarbon is chloroform.   The method of claim 1, further comprising the presence of at least one internal electron donor.   The process according to claim 2, wherein the halogenated hydrocarbon is added in a range of a molar ratio of the halogenated hydrocarbon to the transition metal component of the Ziegler-Natta catalyst of 0.001: 1 to 1: 1.   The process of claim 1 wherein the molar ratio of the transition metal component of the trimethylaluminum: Ziegler-Natta catalyst is in the range of 1: 1 to 50: 1.   The process according to claim 1, wherein the molar ratio of the transition metal component of the tetrahydrofuran: Ziegler-Natta catalyst is in the range of 0.1: 1 to 50: 1.   The process according to claim 1, wherein the polymerization conditions are a gas phase.   The process according to claim 1, wherein the polymerization conditions are solution phase.   The process according to claim 1, wherein the polymerization condition is a slurry phase.   The process of claim 1, wherein the at least one or more other olefins are olefins having from 3 to 16 carbon atoms.   12. The method of claim 11, wherein the at least one or more other olefins are selected from the group consisting of 1-octene, 1-hexene, 4-methylpent-1-ene, 1-pentene, 1-butene and propylene. .   The process according to claim 1, wherein the copolymer obtained by polymerization of ethylene and at least one or more olefins comprises ethylene in an amount of at least 70% by weight of the copolymer.