KR100245204B1 - Activation of catalyst in ethylene polymerization at high temperature - Google Patents

Abstract

Polymers of ethylene and / or mixtures of ethylene and C ₃ -C ₁₂ higher alpha-olefins in the presence of a catalytic amount of titanium-containing coordination catalyst in an inert solvent at temperatures above 105 ° C., homopolymers of ethylene and ethylene and C ₃ -C A solution process for the preparation of high molecular weight polymers of alpha-olefins selected from the group consisting of copolymers of higher ₁₂ alpha-olefins is described. Improvements

(a) activating the catalyst with a solution of alkoxyalkyl aluminum in an inert solvent; And

(b) carrying out the method at least partially at a temperature of at least 180 ° C.

In one embodiment, the coordination catalyst is formed from a first component and a second component, wherein the first component contains titanium and the second component is from the group consisting of alkoxy alkyl aluminum alkyl and a mixture of alkyl aluminum and alkoxy alkyl aluminum. Is selected. Aluminum alkyl is of the general formula AIR _n X _3-n and said alkoxy alkyl aluminum is of the general formula AIR ' _n OR " _3-n , _wherein each R, R' and R" may be the same or different and independently 1-20 Aryl or alkyl of the two carbon atoms, X is halogen, n is 1-3 and m is 0-2.

Description

[Name of invention]

Activation of the Catalyst in High Temperature Ethylene Polymerization

Detailed description of the invention

The present invention is directed to methods and catalysts for the production of polymers of ethylene, in particular homopolymers of ethylene and copolymers of ethylene and higher alpha-olefins. In particular, the present invention relates to a solution polymerization process for the preparation of the polymer, wherein the process is carried out at a temperature of at least 180 ° C. and the catalyst is activated with an alkoxy alkyl aluminum compound.

Polymers of olefins, such as homopolymers of ethylene and copolymers of ethylene and higher alpha-olefins, are used in large amounts for various end uses, for example in the form of film fibers, molded or thermoformed articles, pipe coatings, and the like. .

There are two types of methods for preparing polyethylene involving polymerization of monomers in an inert liquid medium in the presence of an actor catalyst: a method which operates at a temperature below the melting or solubilization temperature of the polymer and a method which operates at a temperature above the melting or solubilization temperature of the polymer. There is this. The latter is referred to as the "solution" method, an example of which is patented on April 9, 1963. W., Anderson, A.W. L. E.L. Fallwell and Jay. M. Described in Canadian Patent 660,869 to J. M. Bruce. In the solution process, the process is performed such that both monomer and polymer are dissolved in the reaction medium. Accurate control of the degree of polymerization, and thus the molecular weight of the polymer obtained, can be achieved by controlling the reaction temperature. In the solution polymerization process, it is advantageous to carry out the process at very high temperatures such as> 250 ° C. and to use the heat of polymerization to evaporate the solvent from the polymer solution obtained.

In the process, steps of removing the catalyst from the polymer after the polymerization step may be taken, but the solution polymerization method is preferably performed without the catalyst removal step. As a result, the catalyst will remain in the polymer. Such catalysts, which may be referred to as "catalyst residues", can contribute to the color of the polymer obtained and to polymer degradation during or after polymer processing. The higher the total activity of the catalyst, the less the catalyst required to carry out the polymerization at generally acceptable rates, so that the amount of catalyst residue is correlated, at least in part, with the total activity of the catalyst used in the polymerization step of the process. Therefore, in the solution polymerization method, a relatively high total activity catalyst is preferable.

Two important factors in determining the total activity of the catalyst are the stability of the catalyst and the instantaneous activity of the catalyst under operating conditions, in particular at operating temperatures. Many catalysts that are said to be very active in low temperature polymerization processes also exhibit high instantaneous activity at the higher temperatures used in solution processes, but tend to decompose in a very short time in solution processes, resulting in total activity than expected. better. The catalyst does not attract commercial heavyweight by the solution method. Other catalysts may exhibit acceptable total activity at the higher temperatures of the solution process, but tend to yield polymers of broad molecular weight distribution or polymers that are too low in molecular weight to be commercially available for the production of a wide variety of useful products. . As a result, the performance of the catalyst in the solution polymerization process and the requirements for the catalyst are entirely different from the catalyst in the low temperature polymerization process, which will be apparent to those skilled in the art.

The preparation of ethylene polymers by the solution polymerization process was published on November 14, 1991. second. D.J. Giilis, M. Shii. M.C. Hughson and V. JI. Z. Zboril, published in PCT Patent Application No. WO 91/17193. The catalyst activated by siloxane may polymerize ethylene at very high temperatures. However, siloxane residues from these catalysts are used to purify the solvent in the associated solvent recovery and recycle the sections of the polymerization process, which tends to adversely affect the performance of the adsorbent.

In order to increase the activity and / or stereospecificity of the catalyst, there is a wide range of prior art for the use of various electron donors as appendages to Ziegler-Natta catalysts in low temperature (less than 90 ° C.) polymerization of ethylene and other alpha-olefins. Esters, ethers and alcohols of aromatic acids such as tolurylic acid or benzoic acid are often used for this purpose. However, most electron donors useful at low temperatures destroy the catalytic activity as the polymerization temperature increases. As an example of the use of an electronic donor, the patent of H.M.J.C. dated June 27, 1978 U.S. Patent No. 4 097 659 to Krimers et al. Describes a low temperature polymerization process performed in an inert solvent at a temperature range of 20-100 ° C., with examples of activators listed in this patent for dimethylmonobutoxy aluminum, monodecylpro Foxy aluminum chloride and monobutyl monobutoxy aluminum hydride.

As exemplified hereinafter, the substitution of a portion of the trialkylaluminum with an alkoxyalkylaluminum of the type used in US Pat. No. 4 097 659, even though the temperature is only 130 ° C., ie the lowest temperature range of the performance of the solution polymerization process, Results in a substantial reduction. Surprisingly, it was found that this tendency to decrease catalyst activity at higher temperatures was reversed and the alkoxyalkyl aluminum active catalysts showed good activity at temperatures above about 180 ° C.

Accordingly, the present invention provides a homopolymer of ethylene and / or a polymer of ethylene and / or a mixture of ethylene and C ₃ -C ₁₂ higher alpha-olipine in the presence of a catalytic amount of titanium-containing coordination catalyst in an inert solvent at a temperature of 105 ° C. or higher. A solution process for the preparation of high molecular weight polymers of alpha-olefins selected from the group consisting of copolymers of ethylene and C ₃ -C ₁₂ higher alpha-olefins, comprising: (a) a catalyst with a solution of alkoxyalkyl aluminum in an inert solvent And (b) at least partially carried out at a temperature of at least 180 ° C.

The present invention provides a reactor with a monomer, a coordination catalyst and an inert hydrocarbon solvent selected from the group consisting of ethylene and a mixture of ethylene and at least one C ₃ -C ₁₂ higher alpha-olefin, polymerizing the monomer and recovering the polymer thus obtained. A solution process for the preparation of polymeric polymers of alpha-olefins selected from the group consisting of homopolymers of ethylene and copolymers of ethylene and C ₃ -C ₁₂ higher alpha-olefins, the monomers being 180-320 ° C. Wherein the coordination catalyst is formed from a first component and a second component, contains the first component titanium and the second component is selected from the group consisting of alkoxy aluminum alkyl and mixtures of alkyl aluminum and alkoxyalkyl aluminum Wherein said aluminum alkyl is of the general formula AIR _n X _3-n and said alkoxy alkyl aluminum Is the general formula AIR ' _n OR " _3-n , _wherein each R, R' and R" may be the same or different and independently selected from aryl or alkyl of 1-20 carbon atoms, X is halogen, n is 1-3 and m is 0-2.

In a preferred embodiment of the process of the invention, R is alkyl of 2-8 carbon atoms and n is 3, each of R 'and R "is alkyl of 2-8 carbon atoms and m is 2.

In an embodiment of the method of the present invention, the second component is in the form of a mixture of trialkyl aluminum and alcohol, wherein the amount of alcohol is less than stoichiometrically forming dialkyl alkoxy aluminum, in particular trialkyl aluminum as AIR ³ ₃ Each R 3 is an alkyl group having 1-10 carbon atoms and the alcohol is of the general formula R ⁴ OH wherein R ⁴ is alkyl or aryl of 1-20 carbon atoms, in particular alkyl of 1-16 carbon atoms.

In another embodiment of the method, the first component is formed from (i)-(iii) below.

(i) a mixture of MgR ¹ ₂ and AIR ² ₃ , wherein each R ¹ and R ² are the same or different and each is independently selected from alkyl groups having 1-10 carbon atoms:

(ii) a reactive chloride component: and

(iii) titanium tetrachloride.

Alternatively, the first component is a mixture of a titanium tetrahalide, optionally containing vanadium oxytrihalide, at a temperature below 30 ° C. with an organoaluminum compound, such as trialkyl aluminum or dialkyl aluminum halad, and the resulting mixture It is formed by heating to a temperature of 150-300 ° C. for a period of 5 seconds to 60 minutes.

In an additional embodiment, the formation of the first and second catalyst components and mixtures thereof are carried out in-line at temperatures below 30 ° C.

The present invention relates to a process for producing high molecular weight polymers of alpha-olefins, which polymers are used for molding into articles by extrusion, injection molding, thermoforming, rotational molding and the like. In particular, the polymers of alpha-olefins are homopolymers of ethylene and ethylene and higher alpha-olefins, ie the higher alpha-olefins having ethylene-based alpha-olefins, in particular C ₃ -C ₁₂ , ie C ₃ -C ₁₂ higher alpha-ores. Copolymers of fins, examples of the higher alpha-olefins are 1-butene, 1-hexene and 1-octene. Preferred higher alpha-olefins have 4-10 carbon atoms. In addition, cyclic endomethylene dienes can be fed into the process together with ethylene or a mixture of ethylene and C ₃ -C ₁₂ higher alpha-olefins. Such polymers are known.

In the process of the invention, monomers, coordination catalysts and fluorinated hydrocarbon solvents, and optionally hydrogen, are fed to the reactor. The monomer may be ethylene or a mixture of ethylene and at least one C ₁₃ -C ₁₂ higher alpha-olefin, preferably a mixture of ethylene or ethylene and at least one C ₄ -C ₁₀ higher alpha-olefin, wherein the alpha-olefin is a hydrocarbon Im going to be of course.

The coordination catalyst is formed of two components, a first component and a second component. The first component is an organometallic component of the type containing titanium or other transition metals lower than the maximum valence and mixtures thereof and typically used in solution polymerization processes. The first component will be in solid form. Examples of first components are provided above.

The second component is a solution of alkoxyalkyl aluminum or a mixture of aluminum alkyl and alkoxy alkyl aluminum in an inert solvent, and the ratio of aluminum alkyl to alkoxy aluminum alkyl in the mixture can be used to control the process. Aluminum alkyl is of the general formula AIR _n- X _3-n and alkoxy aluminum alkyl is of the general formula AIR ' _n OR " _3-n , _wherein each R, R' and R" is alkyl or aryl of 1-20 carbon atoms, X is halogen or in particular fluorine, chlorine or bromine, n is 1-3 and m is 2. Preferred halogen is chlorine.

Alkoxy aluminum alkyls can be prepared by mixing with the corresponding alkyl aluminum corresponding alcohol to form alkoxy aluminum alkyl. Preferably, the alkyl aluminum is the same as the aluminum alkyl in the second component. In fact, a preferred second component formation method is to add alcohol to the alkyl aluminum in less than the stoichiometric amount needed to convert all of the alkyl aluminum to alkoxy aluminum alkyl. Mixing is conveniently carried out in-line at temperatures below 30 ° C. to allow the reaction to take place for a few minimum hours. This time depends on the type and reactivity of the components used to prepare the particular catalyst. As illustrated later, the direct supply of alcohol to the reactor in the polymerization process is detrimental to the polymerization process.

The ratio of alcohol to alkyl aluminum used to carry out the control of the polymerization process is in the range of 0.1-1 (alcohol: aluminum).

The concentration of components in the solution used to prepare the catalyst is not critical and depends mainly on practical matters. Concentrations as low as 25 ppm by weight may be required, but higher dynamics, such as at least 100 ppm, are preferred.

As exemplified later, the order of catalyst preparation steps is important for obtaining a catalyst with high activity.

The coordination catalysts described herein are used in the process of the present invention without separation of any component of the catalyst. In particular, neither liquid or solid fractions are separated from the catalyst before it is fed to the reactor. In addition, the catalyst and its components are not slurries. All ingredients are storage stable liquids that are easy to handle.

The solvent used in the preparation of the coordination catalyst is an inert hydrocarbon, in particular a hydrocarbon which is inert to the coordination catalyst. Such solvents are known and include, for example, hexane, heptane, octane, cyclohexane, methylcyclohexane and hydrogenated naphtha. The solvent used for the preparation of the catalyst is preferably the same as that fed to the reactor for the polymerization process.

The first component of the catalyst described herein can be used over a wide range of temperatures that can be used in the alpha-olefin polymerization process carried out under solution conditions in accordance with the process of the invention. For example, the polymerization temperature may be in the range of 105-320 ° C., in particular in the range of 105-310 ° C. However, as exemplified later, the activator is particularly effective at a temperature of 180 ° C. and therefore the invention is carried out at said high temperature at least separately.

The pressures used in the process of the invention are those known in the solution polymerization process, such as in the range of about 4-20 MPa.

In the process of the invention, the alpha-olefin monomer is polymerized in the reactor in the presence of a catalyst. The pressure and temperature are adjusted so that the polymer formed remains in solution.

To improve the control of the melt index and / or molecular weight distribution, small amounts of hydrogen, such as 1-100 parts by weight based on the total solution supplied to the reactor, can be added and thus more uniform as described in Canadian Patent No. 703,704. Help to produce a product.

Usually the solution passing through the polymerization reactor is treated to inactivate any catalyst remaining in the solution. Various catalyst deactivators are known and examples thereof include fatty acid, alkaline earth metal salts of aliphatic carboxylic acids, alcohols and trialkanolamines such as triisopropanolamine.

The hydrocarbon solvent used for the deactivator is preferably the same solvent used in the polymerization process. If different solvents are used, they must be compatible with the flux used in the polymerization mixture and should not adversely affect the solvent recovery system associated with the polymerization process.

After inactivation of the catalyst, the polymer containing solution is passed through a layer of activated alumina or bauxite to remove some or all of the residues and / or other impurities. However, it is preferred to carry out the process without removing the deactivated catalyst residues. The solvent may then be evaporated off from the polymer and then extruded into water and cut into pellets or other suitable milled forms. The recovered polymer can then be treated with saturated steam at atmospheric pressure, for example, to reduce the amount of volatiles and improve the color of the polymer. The treatment is carried out for about 1 to 16 hours, followed by drying the polymer and Cool for 4 hours using an air stream. Pigments, antioxidants, UV selectors, hindered amine light stabilizers and other additives may be added to the polymer before or after the polymer is initially formed in pellet or other milled form.

In an embodiment, the antioxidant incorporated into the polymer obtained from the process of the present invention may be one antioxidant such as a hindered phenol antioxidant, or a mixture of antioxidants such as a hindered phenol antioxidant in combination with a second antioxidant such as phosphite. have. Both types of antioxidants are known in the art. For example, the ratio of phenolic antioxidant to second antioxidant may range from 0.1: 1 to 5: 1 and the total amount of antioxidant ranges from 200 to 3000 ppm.

The process of the present invention can be used to prepare homopolymers of ethylene having a density in the range of, for example, about 0.900-0.970 g / cm 3 and in particular 0.915-0.965 g / cm 3, and copolymers of ethylene and higher alpha-olefins, more Polymers of high density, such as at least about 0.960, are homopolymers. The polymers have a melt index as measured by the method of ASTM D-1238, Condition E, such as in the range of about 0.1-200, and in particular in the range of about 0.1-120 dg / min. Polymers can be prepared with narrow or wide molecular weight distributions. For example, the polymer has a stress index in the range of about 1.1-2.5 and in particular in the range of about 1.3-2.0, which is a measure of the molecular weight distribution.

The stress index is measured by measuring the melt index throughput at two stresses (2160 g and 6480 g load) using the procedure of the ASTM melt index test method and the following equation.

Stress index values below about 1.40 represent a narrow molecular weight distribution, while values above about 1.70 represent a broad molecular weight distribution.

The polymers produced by the process of the present invention can be secondary processed into a variety of different articles, as is known for homopolymers of ethylene and copolymers of ethylene and higher alpha-olefins.

Unless otherwise indicated, the following procedures were used in the following embodiments.

The reactor was a 81 mL free-volume (normal form, dimension of approximately 15 × 90 mm) pressure reactor equipped with six regularly spaced internal baffles. The vessel was equipped with a six blade turbine type impeller, a heating jacket, a pressure and temperature regulator, three feed lines and one outlet. The feed lines were wikied on top of the vessel, each at a radial distance of 40 mm from the axis while the outlet line was laterally with the stirrer drive shaft. Catalyst precursors and other reagents were prepared as a solution in cyclohexane purified through layers of activated alumina, molecular sieves and silica gel before stripping with nitrogen.

Ethylene was metered into the reactor as a cyclohexane solution prepared by dissolving the purified gas ethylene in the purification solvent. The desired residence time in the sideline line was achieved by adjusting the length of the tubes through which the components passed. The residence time in the reactor was kept constant by adjusting the solvent flow rate to the reactor so that the overall flow rate was still constant.

Reactor pressure was maintained at 7.5 MPa and temperature and flow rate were kept constant during each experiment.

The initial (no conversion) monomer concentration in the reactor was 3-4% by weight. A solution of the deactivator, ie triisopropanolamine or nonanoic acid in toluene or cyclohexane, was injected into the reactor effluent at the reactor outlet line. The pressure of the stream was then reduced to about 110 kPa (absolute pressure) and unreacted monomers were monitored by gas chromatography. Catalytic activity is as defined below.

Kp = (Q / (1-Q) (1 / HUT) (1 / catalyst concentration)

Where Q is the fraction of ethylene (monomer) converted to polymer, HUT is the reactor residence time expressed in minutes and catalyst concentration is expressed in mmol and corrected for impurities in the reaction vessel. The catalyst concentration is based on the sum of the transition metals. The polymerization activity (Kp) was calculated.

The invention is illustrated by the following examples. Unless stated otherwise, the solvent used in each example was cyclohexane, the monomer was ethylene and the reactor residence time was kept constant at 3.0 minutes.

Example I

A solution of each of dibutyl magnesium, triethyl aluminum, t-butylchloride and titanium tetrachloride in cyclohexane at ambient temperature (approximately 30 ° C.) was in-line mixed, followed by addition of a solution of triethyl aluminum in cyclohexane to Prepared. The concentration and flow rate of each species were adjusted to obtain the following molar ratios:

Chlorine (from t-butylchloride) /magnesium=2.4:

Magnesium / Titanium = 5.0:

Aluminum (first triethyl aluminum) / titanium = 0.9:

Aluminum (second triethyl aluminum) /titanium=3.0.

Reactor polymerization was carried out at a temperature of 230 ° C. as measured in the reactor. As described above, the solution passing from the reactor was inactivated and the polymer was recovered. Catalytic activity (Kp) was calculated and the results obtained are shown in Table 1. The reported ratios for Cl / Mg and Al ² / Ti are the optimum ratios necessary to obtain maximum catalytic activity at the specified ratios of Mg / Ti and Al ¹ / Ti.

In runs 2 and 3, the catalyst preparation was as above except adding 1 molar equivalent of t-butylalcohol (per mole of Al ² ) to the second aliquot of triethyl aluminum (thus forming alkoxy).

TABLE I

Note:

1. The ratio of triethyl aluminum to titanium in the first addition.

2. The ratio of triethyl aluminum or alkoxydiethyl aluminum to titanium in the second addition.

Kp Calculated polymerization rate constant. 1 / mmol / min.

3. t-butanol added to the reactor rather than a catalyst.

Runs 1, 2 and 3 illustrate that the proportion of catalyst components in the alkoxide system has a significant effect on increasing activity, which is predicted to vary with the type and composition of the remaining catalyst components and the manner in which the method is performed. Nevertheless it illustrates that a greater increase in catalytic activity than either one can be obtained. See Run 3 Run 2 illustrates that the catalytic activity is sensitive to the proportion of the components and thus can be used to adjust the method.

Runs 4, 5, 6 and 7 illustrate the use of alcohols other than t-butanol.

Run 8 illustrates the deleterious effects of adding alcohol directly to the reactor rather than on the second triethyl aluminum stream. This means that the alkoxy cidialkyl aluminum species is required prior to formation.

Example II

As a comparison with other known activators for the high temperature polymerization process, the procedure of Example I was repeated using the activators and reaction temperatures indicated in Table II. The obtained result was as follows.

TABLE II

BUODEAL t-butoxydiethyl aluminum

DESI dimethylaluminum ethyldimethylsiloxane

DIBALO diisobutylaluminooxane

TEAL triethylaluminum

1 molar ratio of triethyl aluminum to titanium

2 Molar ratio of activator to titanium

Kp 1 / mmol / min

This example shows a relative improvement in catalytic activity at high temperatures, which is shown by comparing t-butoxy diethyl aluminum with the rest of the activator.

Example III

The catalyst was prepared from a solution of titanium tetrachloride, vanadium oxytrichloride and diethylaluminum chloride in cyclohexane. The mixed solution was mixed with a hot cyclohexane solvent and heat treated at 205-210 ° C. for 110-120 seconds. An activator was then added to activate the catalyst. The polymerization reactor was run at the temperatures indicated in Table 3. The polymer was recovered as described above. The catalytic activity was calculated. The results obtained were as follows: (Ti moles) / (V moles) = 1 in each run.

TABLE III

BUODEAL t-butoxydiethyl aluminum

DESI diethylaluminum ethyldimethylsiloxane

DIBALO diisobutylalumino-oxane

TEAL triethylaluminum

1.The molar ratio of sum of diethylaluminum chloride to titanium and vanadium

2. The sum of molar ratios of activator to titanium and vanadium

This example illustrates the improvements that can be obtained using t-butoxydiethyl aluminum as activator.

Example IV

In order to compare the use of alkoxydialkyl aluminum with other activators, the procedure of Example III was repeated using a reactor temperature of 130 ° C. The results were as follows.

Table IV

BUODEAL t-butoxydiethyl aluminum

DESI diethylaluminum ethyldimethylsiloxane

DIBALO diisobutylaluminooxane

TEAL triethylaluminum

1.The molar ratio of sum of diethylaluminum chloride to titanium and vanadium

2. The sum of molar ratios of activator to titanium and vanadium

This example shows poor low temperature activity of the catalyst when using alkoxydialkyl aluminum as the activator, so good high temperature activity is surprising.

Claims (2)

A solution polymerization process for the preparation of polymers of alphaolefins selected from the group consisting of homopolymers of ethylene and copolymers of ethylene and one or more C ₃ -C ₁₂ alpha olefins, wherein the polymer is prepared by ASTM D 1238 (190 ° C./2.16 kg). It has a melt index of less than 200 dg / min as measured and the method Monomers, coordination catalysts and inert hydrocarbon solvents selected from the group consisting of ethylene and ethylene and one or more C ₃ -C ₁₂ alpha olefins are fed to the reactor, the monomers being brought to a temperature of 180-32 ° C. and 4-20 Mpa pressure And recovering the polymer thus obtained, wherein the coordination catalyst is (a) MgR ¹ , wherein R ¹ and R ² are the same or different and are independently selected from alkyl radicals having 1 to 10 carbon atoms A component comprising a mixture of ₂ and AlR ² ₃ , (b) t-butyl chloride, and (c) a titanium tetra halide compound, wherein the ratio of Mg: Ti is from 4: 1 to 8: 1 and the halide: Mg The ratio of is 1.9: 1 to 2.6: 1, the atomic ratio of Mg: Al is 1.0: 0.1 to 1.0: 0.4, titanium tetrahalide optionally containing vanadium oxytrihalide at a temperature of less than 30 ℃, and oil A catalyst precursor, and (d) of triethylaluminum obtained by hameu doing rapidly mixing the solution of aluminum heating temperature results obtained mixture for 5 seconds to 60 minutes in the period of 150-300 ℃ R "is _2-8 C A chamber formed by mixing an alcohol of the formula R ″ OH which is an alkyl radical with a catalyst activator prepared by mixing at a molar ratio of 1: 0.1 to 1: 1. The method of claim 1, wherein the alcohol is t-butyl alcohol.