CS250660B2 - A process for the continuous preparation of copolymers of ethylene and higher alphaolefins - Google Patents

Abstract

Process for the continuous preparation of copolymers of ethylene and higher alpha-olefins. Ethylene copolymers with higher alpha-olefins with 3 to 8 carbon atoms with a density of less than 0.91 g. cm'5 and a value of the secant modulus of elasticity in tension at 1% deformation of less than 140,000 kPa are prepared in a continuous manner without agglomeration of particles by introducing a gaseous mixture formed by ethylene and at least one Cs to Cs alpha-olefin in a molar ratio of Cs to Cs alpha-olefin to ethylene in the range from 0.35:1 to 8.0:1 and at least 25 percent. molar dilution gas, in a fluidized bed reaction zone at a temperature in the range of 10 to 80 °C into contact with a catalytic system, which is prepared by diluting a precursor made from a magnesium compound, a titanium compound and an electron donor compound with an inert carrier and activating the resulting diluted precursor with an organoaluminum compound.

Description

(54) Process for the continuous preparation of copolymers of ethylene and higher alpha-olefins

Process for continuous preparation of copolymers of ethylene and higher alpha-olefins.

Copolymers of ethylene with higher alpha-olefins with 3 to 8 carbon atoms with a density of less than 0.91 g. cm' ⁵ and a tensile modulus of elasticity at 1% strain of less than 140,000 kPa are prepared in a continuous manner without agglomeration of particles by introducing a gaseous mixture formed by ethylene and at least one Cs to Cs alpha-olefin in a molar ratio of Cs to Cs alpha-olefin to ethylene in the range of 0.35:1 to 8.0:1 and at least 25 percent by molar diluent gas, in a fluidized bed reaction zone at a temperature in the range of 10 to 80 °C into contact with a catalytic system, which is prepared by diluting a precursor made from a magnesium compound, a titanium compound and an electron donor compound with an inert support and activating the resulting diluted precursor with an organoaluminum compound. ........M'.á22£

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The invention relates to a process for preparing low density ethylene copolymers with a low modulus in a fluidized bed. In particular, it can be stated that the invention relates to a process for preparing ethylene copolymers with a density of less than 0.91 g/cm ³ and a secant modulus of elasticity in tension, at 1% deformation, of less than 140,000 kPa in a fluidized bed.

In the prior art, ethylene copolymers having densities in the range of 0.91 g/cm ³ to 0.96 g/cm ³ can be prepared in a fluidized bed by the processes described in U.S. Patents Nos. 4,302,565 and 4,302,566, wherein ethylene is continuously copolymerized with one or more higher alpha-olefin monomers using a catalyst mixture prepared by forming a precursor mixture in a first step of the process from a magnesium compound, a titanium compound, and a compound that is an electron donor, in a second step of the process by diluting said precursor mixture with an inert carrier material, and in a third step of the process by activating said precursor mixture with an organoaluminum compound. The copolymers prepared by the processes of the above-mentioned U.S. Patents are rigid materials with relatively high modulus that can generally be used for the preparation of films and melt-molded articles. However, these patents do not teach how to prepare low modulus copolymers having a density of less than 0.91 g/cm ³ . These low modulus copolymers could be useful for preparing tubes and hoses and other applications where flexibility and toughness of the product are required.

If modifications are made to the above processes of the aforementioned United States patents to obtain ethylene copolymers with low modulus and a density of less than 0.91 g/cm ³ , such as increasing the concentration of higher alpha-olefin comonomers in the reactor, it has been found that sticky, resinous polymer products are obtained in this manner.

Due to the aforementioned sticky nature of these products, these materials tend to stick together and form large agglomerates. After a short time, these agglomerates reach such a size that they prevent further fluidization, or rather, this fluidization can no longer be maintained. The result of this procedure is that the polymerization process stops after only a small amount of the desired copolymer is obtained, because the reactor is clogged with these large agglomerates.

In the United Kingdom Patents Nos. 2,033,910 A, 2,034,336 A, 2,034,723 A and 2,066,274 A, a process for preparing ethylene copolymers and terpolymers by vapor phase polymerization of a monomeric olefin mixture in the presence of a catalytic mixture which comprises as a first component an organoaluminum compound and as a second component a solid comprising a magnesium-containing compound and a titanium compound and/or a vanadium compound is disclosed. However, these patents do not disclose any conditions which are necessary to prevent reactor fouling due to particle agglomeration when polymers having a density lower than 0.91 g. cm/' ³ are to be continuously prepared by a fluidized bed process at high polymer productivity. Furthermore, these patents do not provide any guidance on how to carry out the polymerization without the use of lengthy grinding of the catalyst in a ball mill.

United Kingdom Patents Nos. 2,006,232 A, 2,053,246 A and 2,053,935 A disclose processes for preparing copolymers and terpolymers of ethylene by polymerizing mixtures of monomeric olefins in a fluidized bed in the presence of a catalyst system comprising 1) an organometallic compound and 2) a titanium compound.

However, these patents also do not disclose the conditions necessary to prevent agglomeration of particles and to maintain the polymerization process in a continuous manner with high productivity of the polymer obtained, if polymers with a density lower than 0.91 g. cm ^-3 are to be obtained. Furthermore, these patents do not provide any information on how to carry out the polymerization without initial preparation of a prepolymer.

The subject of the invention is a method for the continuous preparation of copolymers of ethylene and higher alpha-olefins with 3 to 8 carbon atoms, the density of which is lower than 0.91 g. cm ^-3 and the value of the secant modulus of elasticity in tension at 1% deformation lower than 140,000 kPa, wherein these copolymers contain by molar not more than 94 percent of polymerized ethylene and at least % of polymerized alpha-olefins, by a fluidized bed process in which no agglomeration of particles occurs, such that a gaseous mixture containing ethylene and at least one higher alpha-olefin is continuously brought into contact in the reaction zone with the fluidized bed at a temperature in the range from 10 to 80 °C and at a pressure of not more than

000 kPa with particles of a catalytic system which includes a precursor of the general formula

Mg _m Ti(OR) _n X _p /ED/ _q where

R represents an aliphatic or aromatic hydrocarbon radical containing 1 to 14 carbon atoms or a radical of the general formula —COR’, where R’ represents an aliphatic or aromatic hydrocarbon radical containing 1 to 14 carbon atoms,

X represents a substituent selected from the group consisting of chlorine, bromine, iodine and mixtures thereof,

ED represents an organic electron donor compound selected from the group consisting of alkyl esters of aliphatic and aromatic250660

In the case of acids, aliphatic ethers, cyclic ethers and aliphatic ketones, n1 represents a number with a value of 0.5 to 56, n represents a number with a value of 0, 1 or

2, p represents a number with a value of 2 to 116 and η represents a number with a value of 2 to 85, wherein this precursor is diluted with an inert carrier and pplue is activated with an organoaluminum compound of the general formula

Al(R“) _d XýH _f where

X' represents chlorine or a group of the general formula —OR'',

R" and R"' represent saturated hydrocarbon radicals containing 1 to 14 carbon atoms, e represents a number with a value of 0 to 1.5 and f represents a number with a value of 0 or 1, it being true that the sum of d+e+f has a value of 3, the activating compound being used in such an amount that the total molar ratio of aluminum to titanium in the reaction zone is in the range of 10:1 to 400:1. The process according to the invention is characterized in that the molar ratio of ethylene to alpha-olefin with 3 to 8 carbon atoms in the gaseous monomer mixture introduced into the polymerization is in the range of 0.35:

: 1 to 8.0 : 1 and the gaseous monomer mixture contains at least 25 molar % of at least one diluent gas selected from the group consisting of inert gases and hydrogen.

Fluidized bed reactors suitable for the process for the continuous production of ethylene copolymers according to the invention are well known and are published in the prior art. Reactors which can be advantageously used are described, for example, in U.S. Patent Nos. 4,302,565 and 4,302,566. These patents also disclose catalytic systems suitable for the preparation of such copolymers.

In the process for preparing ethylene copolymers having a density of less than 0.91 g/cm ³ and using a fluidized bed method, it is necessary to use a gaseous reaction mixture which contains a greater amount of the alpha olefin comonomers relative to the amount of ethylene used, compared to the processes for preparing copolymers having a density greater than 0.91 g/cm ³ . By adding ever increasing amounts of these higher olefins to the reaction mixture, gradually decreasing densities are obtained at any given melt flow index. The amount of higher olefin required to obtain copolymers of a given density varies from olefin to olefin, with greater amounts of these higher olefins being used under the same conditions as the number of carbon atoms in the molecule of these olefins decreases. In general, it can be stated that in order to obtain copolymers with a density of less than 0.91 g/cm ³ it is necessary to use reaction mixtures which contain these higher olefins and ethylene in a molar ratio of higher olefin to ethylene of at least 0.35:1. Usually, reaction mixtures which contain higher olefin and ethylene in a molar ratio ranging from 0.35:1 to 8.0:1 are used for these purposes, with mixtures with a molar ratio ranging from 0.6:1 to 7.0:1 being preferred.

These higher alpha olefins which are polymerized with ethylene to prepare the low density, low modulus ethylene copolymers of the present invention contain from 3 to 8 carbon atoms. These alpha olefins should not be branched at any of their carbon atoms which are closer than two carbon atoms to a double bond. These alpha olefins may be, for example, propylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-heptene and 1-octene. In a preferred embodiment of the present invention, propylene, 1-butene, 1-hexene, 4-methyl-1-pentene and 1-octene are used.

If necessary, it is possible for one or more dienes to be present in the reaction mixture, whether conjugated or non-conjugated. These dienes can be used in an amount ranging from 0.1 mole percent to 10 mole percent, based on the total gas mixture that is fed to the fluidized bed, in a preferred embodiment of the invention this amount ranges from 0.1 mole percent to 8 mole percent. These dienes can be, for example, butadiene, 1,4-hex,a,diene, 1,5-hexadiene, vinylnorbornene, ethylidenenorbornene and dicyclopentadiene.

According to the present invention, it has been found that in order to prevent the formation of polymerized agglomerates and to maintain a continuous polymerization process, in those cases where a reaction mixture with a high ratio of higher alpha olefin comonomers to ethylene is used, which is necessary to prepare the desired copolymers having a density below 0.91 g/cm ³ , it is essential to dilute the reaction mixture with a large amount of diluent gas. Diluting the reaction mixture with a diluent gas in this way serves to achieve reduced stickiness in the polymers thus prepared, which is the main cause of their agglomeration. Typically, the diluent gas constitutes at least 25 mole percent of the total gas mixture, which is introduced into the fluidized bed of the reactor in order to prevent said agglomeration of the particles. In a preferred embodiment of the present invention, the gas mixture contains this gas in an amount ranging from 33 mole percent to 95 mole percent, with the most preferred use of this gas in an amount ranging from 40 mole percent to 70 mole percent. According to the present invention, this "diluent gas" means a gas that is not reactive under the conditions used in the polymerization reactor, i.e., it does not decompose and/or react with the monomers introduced into the polymerization reaction and with the components of the catalyst mixture under the polymerization conditions used in the polymerization reactor. However, the diluent gas can terminate the growth of the polymer chain.

In addition, this gas must not be soluble in the polymer product thus obtained, so as not to contribute to the stickiness of the polymer product thus obtained. The group of these gases can include nitrogen, argon, helium, methane, ethane and similar other gases.

Hydrogen can also be used as a diluent gas. In this case, the hydrogen dilution not only serves to dilute the reaction mixture and prevent agglomeration of the polymer particles, but also serves as a chain transfer agent to control the melt flow index of the copolymers obtained by the process according to the invention. Typically, the reaction mixture contains hydrogen in an amount sufficient to achieve a molar ratio of hydrogen to ethylene in the range of 0.01:1 to 0.5:1. In addition to said hydrogen, other chain transfer agents can be used to control the melt flow index of said copolymers.

This said reaction mixture should of course be substantially free of catalytic poisons, such as moisture, oxygen, carbon monoxide, carbon dioxide, acetylene and the like.

In addition to diluting the reaction mixture with a diluent gas, it has also been found necessary in the present invention to maintain a relatively low temperature in the reactor in order to prevent agglomeration of the polymer particles and to maintain a continuous polymerization. This temperature used varies directly with the concentration of diluent gas present in the mixture, with higher concentrations of diluent gas allowing somewhat higher temperatures to be used without adverse effects. Similarly, the lower the concentration of higher alpha-olefin comonomers used in the reaction mixture relative to the concentration of ethylene, i.e. the higher the density and modulus of the copolymers thus prepared, the higher the temperature values that can be used. In general, if copolymers with a density of less than 0.91 g. cm ^-3 and a tensile modulus at 1% strain of less than 140,000 kPa are to be continuously prepared and coagulation of particles is to be avoided, then the temperature must not rise above 80 °C. On the other hand, the temperature must be high enough to prevent a large extent of condensation of the reaction mixture, including the diluent gas, which could result in the formation of liquid condensate.

Condensation would result in the resulting polymer particles sticking together, thus exacerbating the agglomeration problem. This problem can occur particularly when alpha-olefins containing 5 or more carbon atoms are used, which have a relatively high dew point. While a small amount of condensation can be tolerated, excessive condensation would cause the polymerization process to fail. Temperatures in the range of 10 to 60 °C are typically used to produce copolymers with densities in the range of 0.86 to 0.90 g . cm ^-3 and a secant tensile modulus at 1% strain in the range of 600 to 100,000 kPa. Higher temperatures, in the range of 60 to 80°C, are typically used in the production of copolymers having densities ranging from 0.90 g/ ^cm3 to 0.91 g/ ^cm3 and a tensile modulus at 1% strain of 100,000 kPa to 140,000 kPa. The maximum polymerization temperatures that can be used to prepare ethylene copolymers of a given tensile modulus without agglomeration of a portion of the polymer when the reaction mixture is diluted with 50 mole percent diluent gas are illustrated in the accompanying Figure 1. The area defined above the depicted curve represents the area in which the reaction can be carried out, while the area below the curve represents the conditions under which the reaction cannot be carried out.

For the process according to the invention, pressures up to about 7,000 kPa can be used, with a preferred embodiment of the process according to the invention using pressures in the range of about 70 kPa to 2,500 kPa.

In order to maintain a functioning fluidized bed during the process of the invention, the superficial gas velocity of the gaseous reaction mixture passing through the bed must be higher than the minimum flow rate required for fluidization of the bed, and in a preferred embodiment of the invention, this velocity is at least 0.2 m/s higher than the minimum flow rate. In a typical embodiment, the superficial gas velocity does not exceed 1.52 m/s, and even more typical embodiments are those in which a maximum of 0.76 m/s is sufficient.

The catalytic mixtures used in the process according to the invention are prepared by first producing a precursor from a magnesium compound, a titanium compound and an electron donor compound, then diluting said precursor with an inert carrier substance and activating this diluted precursor mixture with an organoaluminum compound.

The precursor is prepared by dissolving at least one titanium compound and at least one magnesium compound in at least one electron donor compound at a temperature ranging from about 20°C to the va250660 ru temperature of said electron donor compound. Said titanium compound or compounds may be added to said electron donor compound or compounds before or after the addition of said magnesium compound or compounds, or may be added simultaneously with said compound or compounds. Dissolution of said titanium compound or compounds and magnesium compound or compounds may be facilitated by stirring, and in some cases by refluxing, the two compounds in the electron donor compound. After the titanium compound or compounds and the magnesium compound or compounds have dissolved, the precursor is separated from the mixture by crystallization or precipitation with an aliphatic or aromatic hydrocarbon containing 5 to 8 carbon atoms, such as hexane, isopentane or benzene. The precipitated or crystallized precursor can be separated in the form of fine, free-flowing particles, the size of which ranges from about 10 to about 100 µm after drying at a temperature of not more than 60 degrees Celsius.

In preparing the precursor, the magnesium compound or compounds are used in an amount ranging from about 0.5 mole to about 56 moles, and in a preferred embodiment of the invention in an amount from 1 to about 10 moles, per mole of said titanium compound or compounds.

In the preparation of the precursor, a titanium compound or compounds having the following general formula are used:

Ti(OR) _and X _b in which means

R is an aliphatic or aromatic hydrocarbon radical containing 1 to 14 carbon atoms, or a COR' group in which the substituent R' is an aliphatic or aromatic hydrocarbon radical containing 1 to 14 carbon atoms,

X is a substituent selected from the group consisting of chlorine, bromine, iodine and mixtures thereof, a is a value of 0, 1 or 2, b is a value from 1 to 4 inclusive, where a + b = 3 or 4.

Suitable compounds that can be used in the process of the invention include TiCl,, TiCl<, Ti(OCH ₃ )Cl ₃ , Ti(OC _e H ₅ )Cl ₃ , Ti(OCOCH ₃ )Cl ₃ , and Ti(OCOC ₆ Hj jCl;!·

In a preferred embodiment of the process according to the invention, titanium trichloride TiCl ₃ is used, since catalysts containing this substance exhibit higher efficiency at lower temperatures and monomer concentrations used in carrying out the process according to the invention.

For the preparation of precursors according to the invention, a magnesium compound or compounds having the following general formula are used:

MgX ₂ in which X is a substituent selected from the group consisting of chlorine, bromine, iodine and mixtures thereof.

Suitable magnesium compounds which can be used in the process of the invention include MgCl ₂ , MgBr ₂ and MgCl ₂ . In a particularly preferred embodiment of the process of the invention, anhydrous MgCl ₂ is used.

The electron donor compound or compounds used for the preparation of the precursor according to the invention are organic compounds which are liquid at 25°C and in which the titanium and magnesium compounds are soluble. The electron donor compounds are known as such or are known under the name Lewis base.

Suitable electron donor compounds which can be used in the process of the invention include alkyl esters of aliphatic and aromatic carboxylic acids, aliphatic ethers, cyclic ethers and aliphatic ketones. In a preferred embodiment of the invention, these electron donor compounds include alkyl esters of saturated aliphatic carboxylic acids containing 1 to 4 carbon atoms, alkyl esters of aromatic carboxylic acids containing 7 to 8 carbon atoms, aliphatic ethers containing 2 to 8 carbon atoms, preferably up to 5 carbon atoms, cyclic ethers containing 4 to 5 carbon atoms, preferably monoethers or diethers containing 4 carbon atoms, and aliphatic ketones containing 3 to 6 carbon atoms, preferably aliphatic ketones containing 3 to 4 carbon atoms. According to the most preferred embodiment of the process according to the invention, methyl formic acid, ethyl acetate, butyl acetate, ethyl ether, tetrahydrofuran, dioxane, acetone and methyl ethyl ketone are used.

After preparation, the precursor is diluted with an inert carrier, which is done either by mechanically mixing the two substances or by impregnating the precursor onto the carrier.

Mechanical mixing of the inert carrier with the precursor is carried out by conventional methods and using conventional equipment. The resulting mixture typically contains the precursor in an amount ranging from about 3 to about 50% by weight.

Impregnation (impregnation) of an inert support with a precursor can be carried out by dissolving the precursor in an electron donor compound and then mixing the support to be impregnated with the dissolved precursor. The solvent used is then removed by drying at a temperature of not more than about 85°C.

The carrier can also be impregnated with the precursor by adding it to the solution for preparing the precursor in the electron donor compound without separating the precursor from this solution. The excess electron donor compound is then removed by drying at a temperature of not more than about 85°C.

Following this above procedure, a mixed or impregnated precursor of the general formula is obtained:

Mg _ni Ti(OR)„X _p [ED] _q in which R represents an aliphatic or aromatic hydrocarbon radical containing 1 to 14 carbon atoms or the radical COR' in which R' represents a substituent which also represents an aliphatic or aromatic hydrocarbon radical containing 1 to 14 carbon atoms,

X is a substituent selected from the group consisting of chlorine, bromine, iodine and mixtures thereof,

ED is a compound that is an electron donor, m is a value from 0.5 to 56, in a preferred embodiment, a value from 1.5 to 5, n is 0, 1 or 2, p is a value from 2 to 116, in a preferred embodiment a value from 6 to 14, and q is a value from 2 to 85, in a preferred embodiment a value from 3 to 10.

In a preferred embodiment, the impregnated carrier material contains the precursor in an amount ranging from about 3 weight percent to about 50 weight percent, and in a preferred embodiment of the invention in an amount ranging from about 10 weight percent to about 30 weight percent.

The carrier materials used to dilute the precursor are solid, particulate, porous materials that are inert to the other components of the catalyst mixture and to the other components of the reaction system. These carrier materials include inorganic materials such as silicon and/or aluminum oxides. These carrier materials are used in the process of the invention in the form of dry powders, the average particle size of which ranges from about 10 to about 250 μm, and in a preferred embodiment of the invention the particle size of these substances ranges from about 20 to about 150 μm. These materials are also porous, with a specific surface area of at least 3 square meters per gram of material, and in a preferred embodiment of the invention substances are used whose surface area is at least 50 square meters per gram. The catalytic activity or productivity can be greatly improved if silica having an average pore size of at least 8 nm is used as the support material, and in a preferred embodiment of the present invention, this pore size is at least 10 nm. The support material used should be dry, that is, it should not contain absorbed water. Drying of the support material can be carried out by heating, such as heating to a temperature of at least 600 ° C, in the case where silica is used as the support material.

Alternatively, if silica is used, the material is dried at a temperature of at least 200°C and then treated with one or more aluminum activating compounds, as described below, in an amount ranging from about 1 weight percent to about 8 weight percent. Modification of the support material with an aluminum compound by the above procedure provides a catalyst system with increased activity, while also providing improved polymer particle morphology in the resulting ethylene copolymers. Other organometallic compounds, such as diethylzinc, can also be used to modify the support material.

In order for the precursor to be useful for the preparation of ethylene copolymers, it must be activated with a compound capable of converting the titanium atoms in the precursor into a state in which they would be able to efficiently copolymerize ethylene with higher alpha olefins. This activation is carried out with the help of organoaluminum compounds having the following general formula:

Al[R“) _fl X/H ₍ in which means

X' a chlorine atom or an OR"' group,

R ^;< and R“' represent saturated hydrocarbon radicals containing 1 to 14 carbon atoms, which radicals may be the same or different, e is a value from 0 to 1.5, f is 0 or 1, and d + e + f = 3.

These activating compounds can be used individually or in combination with each other, and these compounds include:

Al(C ₂ H ₅ j ₃ ,

A1 _{( C2H5} ) _2iC1 ,

A1 ₂ (C _{2 i} H ₅ ) ₃ C1 ₃ ,

A1( _C2H5 ) _{2H ,}

A1(C ₂ H ₅ ) ₂ [OC ₂ H ₅ ],

Al(iC ₄ H ₉ j ₃ ,

Al(iC ₄ H ₉ ) ₂ H,

Al(C ₆ H ₁₃ ) ₃ a

A1(C ₈ H _I7 ) ₃ ,

If necessary, it can be partially activated before being introduced into the polymerization reactor. However, the activation carried out outside the polymerization reactor must be limited in such a way that the amount of activating compound added does not cause the molar ratio of the activating compound to the compound that is the electron donor in the precursor to increase above 1.4::1. In a preferred embodiment of the present invention, if the activation is carried out outside the reactor, the activation compound used is used in an amount such that in the obtained precursor the molar ratio of the activating compound to the compound that is the electron donor is in the range of about 0.1:1 to about 1.0::1. This partial activation is carried out in a suspension of a hydrocarbon solvent, followed by drying the resulting mixture to remove this solvent at a temperature ranging from about 20 degrees Celsius to about 80 ^C C, and in a preferred embodiment of the process according to the invention at a temperature ranging from about 50 ^C C to about 70 ^C C. The resulting product thus obtained is a loose solid, particulate material that can be easily introduced into a polymerization reactor where activation is completed by further addition of an activating compound, which compound may be the same substance or a different one.

In an alternative embodiment of the process according to the invention using an impregnated precursor process, the complete activation can optionally be carried out exclusively in the polymerization reactor without any pre-activation outside the reactor. This can be done by the process described in European Patent No. 12,148.

The partially activated or non-activated precursor and the required amount of activating compound necessary for complete activation of the precursor are preferably introduced into the reactor through separate lines. The activating compound can be sprayed into the reactor in the form of a solution in a hydrocarbon solvent, such as isopentane, hexane or mineral oil. This solution usually contains the activating compound in an amount ranging from about 2 to about 30% by weight. The activating compound is added to the reactor in an amount such that a molar ratio of total aluminum to titanium in the range from about 10:1 to about 400:1, preferably from about 25:1 to about 60:1 is achieved.

In the continuous gas phase process in a fluidized bed reactor according to the invention, individual portions of the partially activated precursor mixture or the completely unactivated precursor mixture are continuously introduced into the reactor together with individual portions of the activating compound which are necessary to carry out the complete activation of the partially activated or completely unactivated precursor mixture during the polymerization process, in order to replace the active catalytic sites which are consumed during the reaction being carried out.

In the case where the process is carried out under the abovementioned polymerization conditions, it is possible to continuously polymerize ethylene in a fluidized bed with one or more higher alpha olefins containing 3 to 8 carbon atoms and optionally also with one or more dienes, in order to prepare ethylene polymers having a density below 0.91 g/ ^cm3 and whose secant modulus of elasticity in tension at 1% deformation is lower than 140,000 kPa. The term "continuous polymerization" as used in the above text means carrying out the polymerization uninterruptedly for a period expressed in weeks, that is to say for a period of at least exceeding 18 hours, and usually for a period of at least exceeding 1,000 hours, without stopping the reactor due to the formation of large agglomerates of polymer.

The copolymers prepared by the process of the present invention typically have a density in the range of 0.86 g/cm ³ to 0.90 g/cm ³ and a tensile modulus at 1% strain in the range of 600 kPa to 100,000 kPa. These copolymers contain at most 94 mole percent polymerized ethylene and at least 6 mole percent polymerized alpha olefin having 3 to 8 carbon atoms and optionally a polymerized diene. If a polymerized diene is present, the polymer contains at least one such diene in an amount ranging from 0.01 mole percent to 10 mole percent, further 6 mole percent to 55 mole percent of at least one polymerized alpha olefin having 3 to 8 carbon atoms, and further 35 mole percent to 94 mole percent polymerized ethylene.

The molar ratios of propylene to ethylene that must be used in the reaction mixture to obtain copolymers having a given propylene content are given in Table 1 below. In the case where higher olefins than propylene are used, similar results can be obtained with a lower ratio of these higher alpha olefins to ethylene in the reaction mixture.

Table 1

Ratio of C ₃ H ₆ /C ₂ H ₄ in the reaction mixture

Mol. % C ₃ H _G in copolymer

Moth. θ/ο C ₂ H ₄ in the copolymer

0.7 6 1.5 12 3.0 25 6.0 50 8.0 62

The ethylene polymers prepared by the process of the present invention have a melt flow index at standard or normal load of greater than 0 g/10 minutes to about 25.0 g/10 minutes, preferably in the range of about 0.2 g/10 minutes to about 4.0 g/10 minutes. These polymers have a high load melt flow index (HLMI) of greater than 0 g/10 minutes to about 1,000 g/10 minutes. The melt flow index of the polymer of the present invention varies inversely with its molecular weight, and is a function of the polymerization temperature used in the reaction, the density of the polymer, and the hydrogen to monomer ratio in the reaction system. That is, the melt flow index value increases with increasing polymerization temperature, with increasing ratio of higher alpha olefins to ethylene in the reaction system, and/or with increasing hydrogen to monomer ratio.

The ethylene polymers obtained by the process of the present invention have a melt flow ratio (MFR) value ranging from about 22 to about 40, and in a preferred embodiment of the present invention, this value ranges from about 26 to about 35. The melt flow ratio is another way of expressing the molecular weight distribution of the polymer, i.e. the ratio M _w /M _n . A melt flow ratio ranging from about 22 to about 40 corresponds to a ratio M _w /M _n ranging from about 2.7 to about 6.5, and a melt flow ratio ranging from about 26 to about 35 corresponds to a ratio M _w /M _n ranging from about 2.9 to about 4.8.

The ethylene polymers prepared by the process of the present invention have a residual catalyst content, expressed as parts per million of titanium metal, of less than 10 parts per million (ppm), with a productivity of at least 100,000 kilograms of polymer per kilogram of titanium. The copolymers of the present invention are readily prepared using catalyst systems having a productivity of about 500,000 kilograms of polymer per kilogram of titanium.

The ethylene polymers prepared by the process of the present invention are granular materials having an average particle size in the range of about 0.25 millimeters to about 1.78 millimeters, with the particle size typically being in the range of about 0.508 millimeters to about 1.27 millimeters in diameter. The particle size is important in terms of the ability to form a suitable fluidized bed of polymer particles in a given reactor. The granular material also contains no more than 4.0 percent fines having a diameter of less than 0.127 millimeters.

The ethylene polymers obtained by the process of the present invention have a bulk density in the range of from about 256.3 kg/m ³ to about 496.57 kg/m ³ .

The accompanying figure shows a graph of the value of the secant modulus of elasticity in tension at 1°/0 deformation, of ethylene copolymers with a low modulus value, as a function of the reaction temperature used for the copolymerization of ethylene with higher alpha olefins, such as propylene or butene, in a fluidized bed reactor, using the catalytic system according to the invention. This graph illustrates the range of temperatures that can be used for the smooth progress of the polymerization reaction, while ethylene copolymers with a given value of the secant modulus of elasticity in tension are obtained, without agglomeration of the polymer particles, using a gas mixture containing 50 mole percent diluent gas and a reactor pressure of 2,000 kPa. The area above the depicted curve is the area in which the process according to the invention can be operated, while the area below the curve is not.

The following examples illustrate the process according to the invention in more detail, and these examples do not limit the scope of the invention in any way.

The properties of these polymers, prepared according to the procedures of the above-mentioned embodiments, were determined based on the following test methods.

Density was determined by ASTM D-1505. This method used a plate that had been conditioned for one hour at 1.00 C to achieve equilibrium crystallinity. Density measurements were then made in a density gradient column, with the density value reported in grams/ ^cm3 .

Melt flow index (MI).

The melt flow index value was determined using ASTM D-1238, condition E. The measurement was carried out at a temperature of 190 ^° C, and the results are given in grams per 10 minutes.

High Load Melt Flow Index (HLMI).

The melt flow index value at high load was determined using ASTM D-1238, Condition F. The values were determined at ten times the weight used for the melt flow index determination, see the test above. Melt Flow Ratio (MFR).

This value is the ratio of the melt flow index at high load to the melt flow index.

Productivity

In this determination, a sample of the resin product is converted to ash and the percentage by weight of ash is determined. Since this ash essentially constitutes the catalyst, the productivity value is calculated as kilograms of polymer produced per kilogram of total catalyst consumed. The amounts of titanium, magnesium and halides in the ash are determined by elemental analysis.

Bulk density

The bulk density value is determined using ASTM D-1895, Method B. The resin is poured into a 400-milliliter graduated cylinder using a 0.95-cm diameter funnel, filled to the 400-milliliter mark without shaking, and then weighed and the contents determined.

Average particle size

The average particle size is determined from the results of a sieve analysis carried out by ASTM D-1 921, Method A, using a sample weighing 500 grams. Calculations are made using the weights of the individual fractions retained on the sieves. Extractable fraction in n-hexane

In this case, the FDA test for polyethylene film intended for applications in which the film comes into contact with food is used. A sample of 1,290.32 ^cm2 and 0.0381 millimeter thick film is cut into strips measuring 2.54 centimeters by 15.24 centimeters and weighed to the nearest 0.1 milligram. These strips are then placed in a container and extracted with 300 ml of n-hexane at a temperature of 50 ± 1 °C for 2 hours. The extract is then decanted into a weighed Petri dish. After drying the extract in a vacuum desiccator, the dish is weighed to the nearest 0.1 mg. The extractable fraction, normalized to the original sample weight, is then reported as the mass fraction of n-hexane extractables.

Molecular weight distribution M _w /M„

This determination uses gel permeation chromatography, with styrogel as the column packing. The successive pore sizes of the packing are 10°, JO ⁴ , 10 ³ , 10 ¹ and 6 nm. The solvent is perchloroethylene, the temperature is 117 °C. Detection is carried out by infrared radiation at 3.45 gm.

Melting point ( ^° C)

The melting point is determined on a 0.127 to 0.152 mm thick film sample using a DuPont Differential Thermal Analyzer, Model 990. The sample is heated rapidly under nitrogen to 150°C, then held isothermally at this temperature for 5 minutes, cooled at a rate of 10 ^° C/ ^min to 50°C, and then reheated at a rate of 10°C/ ^min until the softening point is reached.

Percentage crystallin i la

Crystallinity is determined by X-ray diffraction using a Norelco XRG-500 X-ray diffractometer with K _u . copper radiation. Crystallinity is calculated from the integrated intensity of the (020) reflection.

Secant modulus of elasticity in tabu at 1% strain

This value is determined by the method according to ASTM D—633. Strips of foil measuring 254 x 12.7 mm are clamped between the jaws at a distance of 127 mm and deformed by moving the jaws apart at a speed of 5 mm. min“ ¹ . A curve of the dependence of deformation on stress is drawn. The secant modulus of elasticity in tension at 1% deformation is the slope of the straight line drawn from the origin to the point corresponding to 1% deformation. The deformation is determined according to the position of the crosshead. Normalization is performed to the cross section of the undeformed sample and the secant modulus of elasticity in tension is expressed in kPa.

Tensile strength and ductility

The determinations are made according to the ASTM D-633 method. Strips of foil measuring 25.4 x 127 mm are clamped between jaws at a distance of 50.3 mm and deformed by moving the jaws apart at a speed of 50S mm, min“ ¹ . The tensile strength is the operating stress developed at rupture. The elongation is determined by monitoring the deformation of a foil sample on which marks are placed at a distance of 25.4 mm. It is given in °/o.

Example 1

Impregnation of the carrier material with a precursor.

In this embodiment, 41.8 grams of anhydrous magnesium chloride M _o Cl ₂ (corresponding to 0.439 moles) and 2.5 liters of tetrahydrofuran (THF) are placed in a 12-liter vessel equipped with a mechanical stirrer. To this mixture, 27.7 grams of titanium tetrachloride TiCl 2 (corresponding to 0.146 moles) are then added dropwise over a 0.5 hour period. The mixture is then heated at 60° C. for a further 0.5 hour to completely dissolve the material.

In particular, 500 grams of silica are dehydrated by heating at 600°C, and this material is then mixed with 3 liters of Isopontane. This suspension is then stirred, while 186 milliliters of a 20 percent by weight solution of triethylaluminum in hexane are added thereto over a period of 15 minutes. The resulting mixture is then dried under a nitrogen atmosphere at 60°C for about 4 hours, yielding a dry, free-flowing powder containing 5.5 percent by weight of alkylaluminum.

The treated silica is then added to the solution prepared as described above. The resulting suspension is then stirred for 0.25 hours and then dried under a nitrogen atmosphere at 60 degrees Celsius for about 4 hours to obtain a dry, impregnated, free-flowing powder.

b) In this embodiment, the procedure as described above is repeated, using 29.0 grams of TiCl 3 _:1 .0.33 AlCl ₃ (corresponding to 0.146 moles) instead of TiCl 3 .

Example 2

Preparation of partially activated precursor

a) In this embodiment, the silica-impregnated precursor prepared according to the procedure of Example 1(a) above is diluted with 3 liters of anhydrous isopentane and the mixture is then stirred while a 20 weight percent solution of diethylaluminum chloride in anhydrous hexane is added over a period of 0.25 hours. This diethylaluminum chloride solution is added in an amount sufficient to obtain a ratio of 0.4 moles of this compound per mole of tetrahydrofuran in the precursor. After the addition of diethylaluminum chloride is complete, the mixture is continued to stir for a further 0.25 hours to 0.5 hours while a 20 weight percent solution of tri-n-hexylaluminum in anhydrous hexane is added in an amount sufficient to obtain a ratio of 0.6 moles of this compound per mole of tetrahydrofuran in the precursor. This mixture is then dried under a nitrogen atmosphere at a temperature in the range of 65 ± 10°C for a period of about 4 hours to give a dry, free-flowing powder. This material is then stored under a dry nitrogen atmosphere until use.

b) The silica-impregnated precursor according to this embodiment is prepared in the same manner as in Example 1(b), partially activated with diethylaluminum chloride and tri-n-hexylaluminum, using the same procedure as in Embodiment 2(a), except that tri-n-hexylaluminum is used in an amount sufficient to provide a ratio of 0.4 moles of this compound per mole of tetrahydrofuran in said precursor.

c) According to this embodiment, the precursor impregnated on silica, prepared in the same manner as in Example 1(b), is partially activated with diethylaluminum chloride and tri-n-hexylaluminum, using the same procedure as in Example 2(a), except that the individual compounds are used in the amount necessary to produce a ratio of 0.3 moles of that compound per mole of tetrahydrofuran in said precursor. Examples 3 — 4

According to these examples, ethylene is copolymerized with 1-butene under various reaction conditions in a fluidized bed reactor similar to the apparatus described in U.S. Patent Nos. 4,302,565 and 4,302,566. This polymerization reactor had a lower section 3.05 meters high, with a diameter of 34.29 centimeters, and an upper section 4.88 meters high and a diameter of 59.69 centimeters.

In each polymerization reaction, the precursor impregnated in silica, prepared according to the procedure of Example (la), and partially activated according to the procedure of Example 2(a), was introduced into the polymerization reactor together with a solution of triethylaluminum in isopentane at a concentration of 5 percent, the aim of this measure being to obtain a fully activated catalyst in said reactor, the molar ratio in said catalyst corresponding to an aluminum:titanium ratio ranging from 15:1 to 55:1.

The following Table 2 summarizes the reaction conditions used in each polymerization process, the properties of the polymers obtained in these polymerization processes, and the productivity of the catalytic system used in the single-layer process, expressed in terms of residual titanium in the obtained polymer cases.

Table 2

Example

4

Polymerization conditions:

Temperature (°C)

Pressure (kPa)

Gas velocity (m/s) Space-time yield (kg/h/ni ³ )

Molar ratio of butylene/ethylene Molar ratio of hydrogen/ethybylene Mol. % nitrogen in the reaction mixture Mol. % hydrogen in the reaction mixture Molar ratio of aluminum : titanium in the fully activated catalyst

Polymer properties:

Density (g/ ^cm3 )

Melt flow index (g/10 minutes)

Melt flow index at high load (g/10 minutes) Melt flow index ratio Bulk density (kg/m ³ ) Average particle size (cm) Extractable fraction in n-hexane (%)

Molecular weight distribution, M _w /M _n Melting point (°C)

Crystallinity (%)

Polymer properties:

Tensile modulus at 1% strain (kPa) Tensile strength (kPa)

Elongation (°/o)

068 0.67

84.9

0.75

0.25

6.4

0.900

1.2

33.3 27.5

328.38

0.076

9.8

4.8 120.8

32.4

738 19 906 1009

068 0.67

72.1

0.91

0.21

4.7

0.898

1.2

36.7

30.8 301.15

0-.076

14.3

4.4

117.4

19.0

047 16 720

918

Productivity:

Titanium content in copolymers (ppm)

4.6

6.1

When the reaction temperature in Example 4 is increased to 65°C, the reactor becomes clogged with agglomerated particles, so that the polymerization must be stopped.

Examples 5 to 6

Ethylene is copolymerized with propylene under different reaction conditions, using the same fluidized bed reactor and the same catalyst system as in Examples 3 to 4.

Table 3 summarizes the reaction conditions used in each polymerization and the properties of the polymers obtained in these polymerizations,

Example

6

Table 3

Polymerization conditions:

Temperature (°C)

Pressure (kPa)

Gas velocity (m/s) Space-time yield (kg/h/m ³ )

Molar ratio propylene//ethylene

Molar ratio hydrogen//ethylene

Mol. % of nitrogen in the reaction mixture Mol. θ/o of hydrogen in the reaction mixture Molar ratio of aluminum : titanium in the fully activated catalyst

Polymer properties:

Density (g/ ^cm3 )

Melt flow index (g/10 minutes)

Melt flow index at high load (g/10 minutes) Melt flow index ratio Bulk density (kg/m ³ ) Average particle size (cm) Extractable fraction in > h-hexane (%)

Molecular weight distribution M _w /M„

Melting point (°C)

Crystallinity (°/o)

Polymer properties:

Tensile modulus at 1% strain (kPa) Tensile strength (kPa)

Ductility (%)

58 57 2,068 2,068 0.58 0.58 70.48 44.85 1.0 1.5 0.18 0.24 39 46 5.1 4.8 17

0.899 0.898 1.1 1.1 39.0 _ 31.4 — 349.20 291.54 0.05 0.076 9.3 15.1 4.3 4.2 114.8 104.4 16.0 18.3

99,591 57,217 13,225 9,653 927 973

If one operates under essentially the same conditions as in Example 6, but uses a reaction mixture containing 36% molar nitrogen and the reaction temperature is 65°C, then the reactor will become clogged with agglomerated particles and the polymerization must be stopped.

Examples 7 to 8

Ethylene is copolymerized with propylene under various reaction conditions, using the same fluidized bed reactor as in Examples 3 to 4.

In both polymerizations, the silica-impregnated precursor prepared according to the procedure of Example 1(b) and partially activated according to the procedure of Example 2(b) is introduced into the polymerization reactor together with a 5 percent solution of triethylaluminum in isopentane to achieve complete activation of the catalyst in said reactor, the aluminum:titanium molar ratio ranging from 40:1 to 55:1.

The following table No. 4 summarizes the reaction conditions used in carrying out each polymerization reaction, as well as the properties of the polymers thus obtained and the productivity of the catalytic system, expressed in the content of residual titanium in the copolymers obtained.

Example

8

Table 4

Polymerization conditions:

Temperature ( ³ Cj 55

Pressure (kPa) 2,068

Gas speed (m/s) 0.70

Space-time yield (kg/h/m ³ ) 72.08

Molar ratio propylene//ethylene 1.1

Molar ratio hydrogen//ethylene 0.14

Mol. % nitrogen in the reaction mixture 52.5

Mol. % hydrogen in the reaction mixture 3.0

Molar ratio of aluminum:titanium in fully activated catalyst 50

Polymer properties:

Density (g/ ^cm3 ) 0.895

Melt flow index (g/10 minutes) 1.6

Melt flow index at high load (g/10 minutes) 52.6

Melt flow index ratio 32.9

Bulk density (kg/m ³ ) 285.13

Average particle size (cm) 0.152

Extractable fraction in n-hexane (%) 23.2

Melting point (°C) 77.7

Crystallinity (%) 17.2

Polymer properties:

Tensile modulus at 1% strain (kPa) 29,662

Tensile strength (kPa) 3,095

Elongation (%) 456

Productivity:

Titanium content in copolymers (ppm) 4.6

068 0.70

76.89

1.0

0.21

3.5

0.885

0.9

32.9 36.6

387.65

0.102

28.9

346

900 870

5.9

Ethylene could not be copolymerized with butene under the conditions given in Example 8. The reason is that the dew point of the reaction mixture would exceed the bed temperature.

If the propylene to ethylene ratio in Example 8 is increased to 1.9, the reactor will become clogged with agglomerated particles, so the polymerization must be stopped.

Example 9

Ethylene is copolymerized with propylene and ethylene norbornene in the same fluidized bed reactor as used in Examples 3 to 4,

The precursor impregnated in silica, prepared according to the procedure of Example Ib and partially activated according to the procedure of Example 2c, is introduced into the polymerization reactor together with a solution of triethylaluminum in isopentane at a concentration of 5%, in order to obtain a fully activated catalyst in the reactor with a molar ratio of aluminum to titanium of 24::1.

The reaction conditions used in carrying out this polymerization as well as the properties of the polymer obtained by this polymerization process are given in the following table.

5.

Example 9

Table 5

Polymerization conditions:

Temperature (°C)

Pressure (kPa)

Gas velocity (m/s)

Space-time yield (kg/h/m ³ )

Molar ratio propylene/ethylene

Hydrogen/ethylene molar ratio

Mol. % of nitrogen in the reaction mixture

Mol. % hydrogen in the reaction mixture

Mol. % ethylidene norbornene in the reaction mixture

Polymer properties:

Density (g/ ^cm3 )

Ethylidennorbornene content (mol. %]

Melt flow index (g/10 minutes)

Melt flow index at high load (g/10 minutes)

Melt flow index ratio

Bulk density (kg/m ³ )

Average particle size (cm)

Secant modulus of elasticity in thallium, at 1% strain. (kPa)

Tensile strength (kPa)

Ductility (%)

2,075

0.457

24.03

0.91

0.23

55.7

4.7

4.3

0.902

2.3

2.0

3(0.76

0.05

773

020 948

Claims (3)

Subject A process for the continuous preparation of copolymers of ethylene and higher alpha-olefins having 3 to 8 carbon atoms having a density of less than 0.91 g. cm ³ and a tensile modulus at 1% deflection of less than 140 000 kPa, the copolymers containing not more than 94% of polymerized ethylene and at least 6% of polymerized alpha-olefins by a fluidized bed process that does not agglomerate the particles by contacting the gaseous mixture containing ethylene and at least one higher alpha-olefin continuously in a fluidized bed reaction zone at a temperature in the range of from 10 to 80 ^° C and at a pressure of not more than 7000 kPa with particles of the catalyst system comprising a precursor of the formula Mg, _n Ti (OR) _n X _p [ED] _q where R represents an aliphatic or aromatic hydrocarbon radical having 1 to 14 carbon atoms or a radical of the formula —COR ‘, where R‘ represents an aliphatic or aromatic hydrocarbon radical having 1 to 14 carbon atoms, X represents a substituent selected from the group consisting of chlorine, bromine, iodine and mixtures thereof, VYNALEZU ED is an organic electron donor compound selected from the group consisting of alkyl esters of aliphatic and aromatic acids, aliphatic ethers, cyclic ethers and aliphatic ketones, m is a number between 0.5 and 56, n is a number with 0, 1, or 2, p is a number ranging from 2 to 116 and q is a number from 2 to 85, the precursor being diluted with an inert carrier and fully activated with the organo-lithium compound of formula Al (R '), X.'H _f where X ‘represents chlorine or a group of the general formula" OR " R 'and R' 'represent saturated hydrocarbon radicals having 1 to 14 carbon atoms, e is a number from 0 to 1.5, f is a number with a value of 0 or 1, with the sum d + e + f having an hour250660 note, wherein the activating compound is used in an amount such that the total molar ratio of aluminum to titanium in the reaction zone is in the range of 10: 1 to 400: 1, characterized in that the molar ratio of ethylene to alpha-olefin is 3 to 8 the carbon atoms in the gaseous monomer mixture to be polymerized range from 0.35: 1 to 8.0: 1 and the gaseous monomer mixture contains at least 25% by weight of at least one diluent gas selected from inert gases and hydrogen. 2. The process of claim 1 wherein the monomer gas mixture comprises 33-95% molar dilution gas and the higher alpha-olefin and ethylene are present in the mixture in a molar ratio of higher alpha-olefin to ethylene in the range cd 0.6 : 1 to 7.0:: 1. 3. The process according to claim 1 or 2, wherein the monomer gas mixture contains nitrogen as inert gas. 1 sheet of drawings 1% SECONDARY MODULE (kP ·)