EP0640012A1

EP0640012A1 - Olefin polymerization catalyst system

Info

Publication number: EP0640012A1
Application number: EP93911186A
Authority: EP
Inventors: Charles K. Buehler
Original assignee: Quantum Chemical Corp
Current assignee: Millennium Petrochemicals Inc
Priority date: 1992-05-11
Filing date: 1993-05-11
Publication date: 1995-03-01
Also published as: NO944286D0; BR9306341A; FI945294A0; JPH07508062A; WO1993023162A1; NO944286L; RU94046060A; CN1082058A; ZA933286B; KR950701550A; FI945294A; EP0640012A4; AU4241193A; CA2135401A1

Abstract

The present invention is directed to a cocatalyst comprising an aluminum trialkyl and an alkoxysilane for use in preparing a catalyst system for the polymerization of olefins containing a titanium III component and an electron donor having an ultraviolet absorption wavelength of less than 250 nanometers.

Description

OLEFIN POLYMERIZATION CATALYST SYSTEM

The present invention is directed to an olefin polymerization catalyst system based upon a member of the class of conventional titanium trichloride catalysts, in association with a novel cocatalyst based upon an aluminum trialkyl and a silane component as further described herein. The cocatalyst provides isotactic olefin polymers with higher catalytic activity than catalyst systems of the prior art.

One of the earliest classes of Ziegler-Natta catalyst systems developed for use in the polymerization of olefins, especially alpha-olefins such as ethylene and propylene, were catalyst systems that include titanium and aluminum in the form of titanium trihalide catalysts and organoaluminum compounds as cocatalysts. The relatively simple nature of these systems provided a compelling case for their use compared to more complex so-called 'high activity' Ziegler-Natta solid catalyst components which include titanium (IV) and magnesium.

The polymerization of propylene among other stereochemical monomers concerns itself with the structural ordering of the resulting polymer. The most desirable polymers for industrial use are isotactic, those where in recurring triads, the depending methyl groups are on the same side of the molecule, affording long term order and hence properties related to developed crystallinity.

Naturally, it was and is important commercially to secure such highly isotactic polymers in high yield, and therefore one sought catalysts of high activity as measured by weight of polymer per unit weight of catalyst, and to control other polymerization parameters to direct morphology of the resulting polymer to afford other desirable properties such as high crystalline melting point, and high bulk density.

Unfortunately, the use of aluminum trialkyl cocatalysts with titanium trichloride catalysts never provided commercially useful polymers. It was discovered, however, that dialkyl aluminum halides were effective and these cocatalysts have been used nearly exclusively in industry. No satisfactory substitute had heretofore been found despite considerable interest and economic motivation. It became generally recognized in the art that while aluminum alkyls such as triethyl aluminum could usefully be employed as cocatalysts for titanium (IV) catalysts they were unuseable on a commercial scale for titanium (III) polymerizations.

It was, therefore, highly surprising to discover that an aluminum alkyl used coordinately with a silane modifier as described was not only effective in a titanium (III) polymerization to provide polymer in high yield, but would produce stereoregular polypropylene of high isotacticity and other desirable properties such as high crystalline melting point and high bulk density. This convenient, homogeneous catalyst system, commercially effective in slurry polymerizations, also finds similar advantage in the gas phase polymerization of propylene. Thus, in optimized systems, polypropylene of greater than 95 to 97% heptane insolubles can be sustainably produced at an activity in excess of 6000- 8000 lb/lb catalyst with a crystalline melting point of at least 160 to 165°C and bulk densities in excess of 24.

As noted above, such cocatalyst systems have been used heretofore in connection with titanium (IV) catalysts. And where polymers for film-making were to be prepared other researchers have utilized such systems as, for example, coground TiCl₃.AA and phosphine oxide with added alkoxysilane in conjunction with an aluminum alkyl, with some success, although the resulting polymer is of lower crystallinity so to reduce haze in the film. The phosphine oxide is contraindicated in any event insofar as its donative potential is somewhat too great for successful mediation of the catalytic process, and it is less acceptable in the sense of ecological concerns.

The more typical disclosures involving the use of silanes as cocatalyst components for titanium (III) polymerization, with or without an internal election donor, uniformly utilize as cocatalyst the conventional diethyl aluminum chloride.

In experimenting with systems employing a titanium (III) catalyst component including an (internal) electron donor, it has also been found by the present inventor that the characteristics, particularly the donative potential of shareable electrons provided by the electron donor can play a key role in providing polymers of desirable characteristics for commercial applications.

In general, the selected electron donor will exhibit an ultraviolet absorption wavelength of less than about 250 nanometers, reflective of the strength of electron bonding and hence the relative ease of donative coordination. The lower wavelengths are associated with more strongly bound electron pairs and thus evidence more moderate donative potential. While not wishing to be bound by an essentially hypothetical elucidation of the invention, it is believed that the coordinate use of a selected internal donor, and the trialkyl aluminum/alkoxysilane cocatalysts, moderates and modulates the oxidation reduction reaction in polymerization so as to maintain and stabilize in a relative steady state the active form of the Ti^""3 catalyst, preventing overreduction of the active species while directing and ordering the production of the desired isotactic product in the case of propylene. In the case of use of the donor at the preparative stage for the titanium component, the internal donor is believed as well to assist in the forming of the desired ff or Δ crystalline form of the TiCl₃ component.

In accordance with the present invention a catalyst system is provided which comprises, as a catalyst, a titanium (III) containing component, such as TiX₃.rMX _m, where X and X are the same or different and are halogen; M is a metal of Group III of the Periodic Table of the Elements; π is an integer of 3; and r is 0 to 0.7.

The titanium (III) component is associated with a selected electron donor of moderate donative potential, preferably an ether or an ester. Preferably, in the titanium (III) catalyst component X and X are chlorine; and is aluminum. More preferably, r is 0 to 0.33.

The cocatalyst component comprises a trialkyl aluminum compound modified with a silane compound having the structural formula (OR )-_a__E,-.₃SiR^a _ssR³ _<-_t, where R^x is hydrocarbyl; and R² and R³ are the same or different and are hydrocarbyl; p is 0 or an integer of 1 or 2; and g is an integer of 1 to 3, with the proviso that the sum of p and g does not exceed 3.

Preferably, the trialkylaluminum compound which functions as a cocatalyst has the structural formula

A1R₃ where R is to C_e alkyl. More preferably, in this component R is C_α to C₄ alkyl. Most preferably, this component is triethylaluminum.

The TiCl₃ or TiCl₃.AA component is associated with an electron donor, preferably an organic ether or ester. This titanium (III) component may comprise as prepared the electron donor, as described, for example in U.S. Patent Nos. 4,060,593 or 4,115,533 incorporated herein by reference. Thus, titanium tetrachloride may be reduced in situ, for example, with an aluminum alkyl, reacted with an electron donor and activated with titanium tetrachloride to form the active TiCl₃ component, preferably in the 8^" or Δ form.

In this embodiment, the preferred electron donor is an organic ether such as a di-alkyl ether, preferably C₆ - C₁₂ alkyl, and most preferably di- isoamyl ether, di-n-octyl ether or di-n-dodecyl ether. Obviously, other readily associable electron donors may be utilized to equivalent effect. The electron donor is employed in an amount of 0.1 to 0.4 mm/mol TiCl₃, preferably 0.2 to 0.3 mm/mol TiCl₃.

Alternatively, the source of titanium (III) may be free of an electron donor, for example, it may be a coground TiCl₃/AlCl₃ as is known and available in the art. In such case, the titanium (III) containing component is associated with an electron donor prior to use. In this embodiment, the preferred electron donor is an organic ester such as a compound having the structural formula

where R⁴ is hydrogen, C_x to C₄ alkyl or C_α to C₄ alkoxy; R⁵ is C_a. to C₄ alkyl; and n is 0 or an integer of 1 to 3. This electron donor component, more preferably, is a compound where R⁴ is hydrogen; R⁵ is C_z to C₄ alkyl; and n is 1. Most preferably, this component is butyl benzoate.

In this embodiment the molar ratio of the titanium component to ester is in the range of between about 1:1 and about 20rl. More preferably, this molar ratio is in the range of between about 3:1 and about 6:1.

In this embodiment, the electron donor component is preferably introduced into the catalyst system by being intimately blended together with the titanium (III) component. Preferably, this intimate blending is provided by milling or simple mixing. More preferably, this blending is accomplished by milling, especially by ballmilling.

The silane compound, useful as a cocatalyst modifier has the structural formula

(OR^x)₄__1?__<ISiR² _s,R³ _<; where R^x is hydrocarbyl; ² and R³ are the same or different and are hydrocarbyl; p is 0 or an integer of 1 or 2; and q is an integer of 1 to 3, with the proviso that the sum of p and q does not exceed 3. Preferably, in this cocatalyst component R^x is alkyl; and R² and R³ are the same or different and are alkyl or cycloalkyl. More preferably, this component is a silane compound where R is C_α to C_β alkyl; and R² and R³ are the same or different and are C to C_s alkyl or cycloalkyl.

Still more preferably R^x is C-**. to C₄ alkyl; and R² and R³ are the same or different and are alkyl or cycloalkyl. Even still more preferably, p is 0 or 1; and q is 1.

Typically, the silane cocatalyst modifier is one or more of isobutyltrimethoxysilane, isobutylisopropyldimethoxysilane, diisopropyldimethoxysilane, cyclohexylmethyldimethoxysilane or dicyclopentyldimethoxysilane.

Most preferably, the second catalyst component is isobutylisopropyldimethoxysilane or diisopropyldimethoxy- silane.

The components of the catalyst system are present in concentrations such that the molar ratio of the titanium-(III)-containing compound to the silane compound is in the range of between about 1:0.2 and about 1:1.2. Preferably, this molar ratio is in the range of between about 1:0.4 and about 1:1.1. Still more preferably, this molar ratio is in the range of between about 1:0.5 and about 1:0.9.

The molar ratio of the trialkylaluminum compound, to the silane compound, is in the range of between about 5:1 and about 20:1. Preferably, this molar ratio is in the range of between about 7:1 and about 15:1. Still more preferably, the molar ratio of the trialkylaluminum component to the silane compound is in the range of between about 8:1 and about 12:1.

The present invention is also directed to a process for polymerizing an olefin, generally in slurry or gas phase. In this process an olefin is polymerized under olefinic polymerization conditions in the presence of the catalyst system of the subject invention. Olefinic polymerization conditions are preferably those that involve conducting the polymerization reaction at a temperature in the range of between about 20°C and about 150°C and at a pressure in the range of between about atmospheric and about 2,000 pounds per square inch gauge (psig) .

Preferably, the process of polymerizing an olefin is directed to alpha-olefins which are polymerized in the presence of a catalyst system within the scope of the present invention under alpha-olefin polymerization conditions which include a temperature in the range of between about 40°C and about 110°C and a pressure in the range of between about 100 psig and about 1000 psig.

More preferably, the process of this invention is directed to the polymerization of an alpha-olefin having 2 to 8 carbon atoms under alpha-olefin polymerization conditions which include a polymerization reaction temperature in the range of between about 50°C and about 100°C and a polymerization reaction pressure of between about 200 psig and about 800 psig.

Still more preferably, the process of this invention involves the polymerization of an alpha-olefin having 2 to_.6 carbon atoms under alpha-olefin polymerization conditions comprising a temperature of -9-

between about 60°C and about 92°C and a pressure in the range of between about 300 psig and about 600 psig.

Even still more preferably, the process of the subject invention concerns the polymerization of an alpha-olefin selected from the group consisting of ethylene and propylene under alpha-olefin polymerization conditions comprising a temperature in the range between about 62°C and about 80°C and a pressure in the range of between about 350 psig and about 550 psig.

Most preferably, the process of the present invention is directed to the polymerization of propylene under propylene polymerization conditions which involve a reaction at a temperature in the range of between about 65°C and about 90°C and at a pressure in the range between about 400 psig and about 500 psig.

In a preferred embodiment of the process of the present invention, the polymerization of an olefin utilizing the catalyst system of this invention, hydrogen may optionally be provided thereto.

In the preferred embodiment where the polymerization occurs in the liquid phase the reaction occurs in a so-called liquid pool wherein the only diluent is the olefin polymerized, preferably propylene. In the preferred embodiment where the polymerization reaction occurs in the gas phase, the reaction occurs in a stationary fluidized bed or a stirred bed. The polymerization may also be conducted in cascaded reactors, i.e., reactors whether for suspension, gas phase or high pressure polymerization, are linked functionally or in practice such that the polymerization product of the first reactor is further reacted, usually under different conditions, in a second reactor to -10-

secure a compatibilited product of diverse characteristics.

In the first embodiment aforementioned in which an electron donor, preferably an ether is reacted with the catalyst in a preparative stage an aluminum alkyl or alkyl halide component is employed as a reductant; in consequence this component may have some catalyst reactivity before it is associated with the TEAL/silane cocatalyst component of this invention. This can be inconvenient for catalyst feed systems utilizing polymerizable monomer carrier such as is commonly the case in gas phase operations. Accordingly, in such instances it is typical to deactivate for example any residual aluminum chloride, which can conveniently be accomplished by reaction with butyl benzoate. The resulting coordination cocatalyst then relies solely upon the TEAL/silane system for cocatalyst function.

A particular advantage of the present cocatalyst resides in its capacity to function effectively both with the titanium (III) catalysts and titanium (IV) catalysts, such that the respective catalysts used conjointly in a single reactor may be commonly cocatalyzed so to prepare polymer product of diverse characteristics, e.g., different molecular weight. These characteristics may then be controllably altered by suitable selection of catalyst ratio having regard for the individual characteristics such as activity levels, or stereoregulating capacity, etc. In consequence, the invention is understood to relate as well to catalyst systems which include, in the broadest sense, transition metal (III) and (IV) combinations which are then commonly cocatalyzed with the disclosed TEAL/silane components.

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EXAMPLE 1

A catalyst system was prepared by combining titanium trichloride (0.04 g.),(itself prepared according to the protocol of Example 4 of U.S. Patent No. 4,115,533) isobutylisopropyldimethoxy-silane (IBIP) and triethylaluminum (TEAL) in a concentration such that the molar ratio of these components was 1.0:0.5:4.6, respectively. This catalyst system was introduced into a reactor free of air and water.

The reactor into which the catalyst system was introduced was next charged with hydrogen gas (500 ml.) and liquid propylene (325 g., 650 ml.). The polymerization reaction was thereupon initiated by heating and pressurizing the reactor to a temperature of 70°C and a pressure of 460 psig. Concurrently with this heating and pressurizing step the stirrer, with which the reactor was equipped, was activated. The stirrer rotated at 400 revolutions per minute. The polymerization reaction, operated under these conditions, was continued for 1 hour. The reaction was terminated after 1 hour by venting the excess propylene.

After the one hour propylene polymerization, the polypropylene product of the polymerization reaction was weighed and analyzed. The polymer analysis constituted the determination of the concentration therein of titanium, a measure of undesirable catalyst incorporation therein, by quantitative analysis well known in the art. In addition, a determination of percent heptane insolubility of the polymer, a measurement- of polypropylene isotacticity, was also conducted. 385

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The polypropylene percent heptane insolubility was determined in a procedure wherein a finely ground sample (20 mesh) of the polypropylene obtained in the above-discussed polymerization reaction was heated at 100°C for 30 minutes in a vacuum oven. The heated sample, disposed in a tare container, i.e., a thimble, was then carefully weighed. The ground polymer, disposed in the thimble was thereupon disposed in an extraction flask already filled with approximately 150 ml. of n-heptane. The n-heptane was heated to boiling and refluxed, with the polypropylene sample disposed therein, for 90 minutes. After 90 minutes, reflexing ceased and the thimble containing the polypropylene sample was removed.

The thimble containing the polypropylene sample was rinsed in acetone after which it was again heated in the same vacuum oven, at 100°C for 30 minutes. The polypropylene sample, still in its tare container, was cooled to ambient temperature and again weighted.

Percent heptane insolubility was determined as the ratio of the difference in net weight of the polypropylene before and after contact with boiling n- heptane for 90 minutes to the net polypropylene weight prior to such contact.

Another polymer property analyzed was melt flow rate, determined in accordance with ASTM Test Procedure

D-1238. Finally, the polypropylene was tested to determine its bulk density, in pounds per cubic foot, which was obtained by taring a vessel of known volume and weighing the vessel of known volume filled with the polypropylene produced in the above-discussed polymerization.

The activity of the catalyst, in terms of polypropylene weight per unit weight of catalyst, was determined by weighing the polypropylene generated during the 1 hour polymerization run and dividing that number by the weight of catalyst charged into the reactor.

The results of this example are summarized in the Table which follows the last example.

EXAMPLE 2

Example 1 was identically reproduced but for the composition of the catalyst. In Example 2 the molar ratio of titanium trichloride, to isobutylisopropyldimethoxysilane, to triethylaluminum, was 1:0.7:6.0. Again titanium trichloride, was present in an amount of 0.04 g.

The results of this example are summarized in the Table.

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EXAMPLE 3

Example 1 was identically reproduced again but for the composition but for the relative amounts of the catalyst components of the catalyst system. In Example 3 the molar ratio of titanium trichloride to isobutylisopropyldimethoxy-silane to triethylaluminum was 1:0.9:7.5. Again, the weight of the titanium trichloride component of the catalyst system was 0.04 g.

The results of this example are tabulated in the Table.

4385

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COMPARATIVE EXAMPLE 1

Example 1 was identically reproduced but for the composition of the catalyst system. The catalyst system of this comparative example omitted the silane component, isobutylisopropyldimethoxysilane. However, the molar ratio of titanium trichloride to triethylaluminum was identical to the molar ratio of these components in Example 1. That is, the molar ratio of titanium trichloride to triethylaluminum was 1:4.6. Otherwise, the polymerization reaction was conducted in exact accordance with the polymerization conditions that existed during the polymerization of Example 1.

Unfortunately, this example was run for only 20 minutes. The reason for this abbreviated testing period was that the product produced was so sticky that stirring could not be maintained even at maximum power.

The polypropylene generated during the 20 minute run was weighed to provide catalyst activity, albeit over this abbreviated 20 minute period. Unfortunately, the stickiness of the polypropylene product was such that the only physical property that could be measured was an analysis of percent heptane insolubility of the polypropylene product, which analysis was determined in accordance with the procedure set forth in Example 1. That result, in view of low crystallinity of the polypropylene product, could only be certain to the extent that the percent heptane insolubility of the polypropylene product was less than 85%. A brief summary of this example is included in the Table.

93/04385

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EXAMPLE 4

In this example propylene was polymerized in accordance with the procedure set forth in Example 1. However, the catalyst system utilized in this example substituted the complex TiCl₃.0.33AlCl₃. The other components were identical with those of Example 1, viz- isobutylisopropyl-dimethoxysilane (IBIP) and triethylaluminum (TEAL) , respectively. This catalyst system also differed from the catalyst system of Example 1 in that it included butyl benzoate (BBE) (0.25 mole). The molar ratio of titanium compound to silane to aluminum compound to BBE, moreover, was 1:0.9:7.0:0.25, respectively. The TiCl₃.033AlCl₃ complex, furthermore, was introduced into the polymerization reactor after being ballmilled with the BBE component. As in all the previous examples the first catalyst component, in this example TiCl₃.0.33AlCl₃, was present in an amount of 40 mg.

The results of this example are tabulated in the Table.

EXAMPLE 5

The polymerization reaction of Example 4 was reproduced but the silane utilized was isobutyltrimethoxysilane.

The results of this example are included in the Table.

04385

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EXAMPLE 6

A polymerization in accordance with Example 4 was identically reproduced but the silane was diisopropyldimethoxysilane.

The results of Example 6 are incorporated in the Table.

EXAMPLE 7

A polymerization in accordance with Example 4 was reproduced. However, although the catalyst system of this example included TiCl₃. 1C1₃, as well as IBIP and TEAL as components, this catalyst system did not include butyl benzoate (BBE) . This catalyst system also differed from the catalyst system of Example 4 in that the molar ratio of titanium compound to silane to aluminum compound was 1.0:0.9:10.0, respectively. Moreover, in this example the titanium (III) catalyst component was introduced into the polymerization reactor in an amount such that its total weight was 75 mg. Finally, the reaction time was 2 hours instead of the 1 hour duration employed in Example 4.

The results of this example are tabulated in the Table.

COMPARATIVE EXAMPLE 2

Example 4 was identically reproduced except for the omission of the silane component. That is, the catalyst system comprised the complex TiCl₃.0.33AlCl₃ (40 g.), ballmilled with BBE, and triethylaluminum present in a molar ratio of the Ti complex to TEAL to BBE of 1:7.0:0.25.

An analysis of the polypropylene product of this reaction is summarized in the Table. It is noted that no values are provided for melt flow rate and bulk density. These physical properties could not be obtained because of the extremely low heptane insolubility of the polypropylene product. That is, the product obtained was too sticky to provide accurate measurement of these properties in accordance with the standard ASTM tests under which these properties were measured.

COMPARATIVE EXAMPLE 3

Example 4 was reproduced except that it was conducted in accordance with prior art teachings. That is, although polymerization reaction conditions were identical with Example 4 and the catalyst system again comprised 40 milligrams of TiCl₃.0.33A1C1₃, the aluminum-containing compound was not triethylaluminum but rather, in accordance with prior art teachings, diethylaluminum chloride. As in Comparative Example 2, the molar ratio of the titanium compound to the organoaluminum compound, diethylaluminum chloride, was again 1:7.0 with no silane present.

The results of this example are also included in the Table.

TABLE

A. The Catalyst System

Molar Ratio of Components

Polymerization Conditions: Footnotes:

Time: 1 hour ^Isobutylisopropyldimethoxysilane Temp.: 70°C ³Isobutyltrimethoxysilane Pressure: 460 psig ³Diisopropyldimethoxysilane Hydrogen: 400 ml "Butylbenzoate Stirring: 400 rpm "Triethylaluminum Total Ti-Containing Component ^Diethylaluminum chloride Wt: 40 mg. ⁷Total Ti-Containing Component Wt: 75 mg. and 2-hour polymerization

B. Polypropylene Reaction and Product

*Could not be processed.

A ALYSIS OF RESULTS

An analysis of the Table establishes that the examples within the contemplation of the catalyst system of the present invention produce acceptable catalyst activities. Moreover, the isotacticity, as measured by percent heptane insolubility, is superior to that of the examples utilizing prior art catalyst systems. Indeed, Comparative Examples 1 and 2, because of the low level of isotacticity in the polypropylene product, could not be processed.

The only exception to the above remarks is the comparison between Example 7 and Comparative Example 3. These two examples differed by the presence in the catalyst system of Example 7 of the silane IBIP which silane was not present in the catalyst system of Comparative Example 3. In addition, the aluminum compound of Example 7, in accordance with the present invention, was a trialkylaluminum compound, TEAL, whereas the aluminum compound of the catalyst system of Comparative Example 3 was diethylaluminum chloride.

The catalyst system of Comparative Example 3 had marginally improved catalyst activity compared to the catalyst system of Example 7. However, the degree of polymerization of the polypropylene produced using the catalyst system of Comparative Example 3 was significantly lower than the polypropylene produced using the catalyst system of Example 7. This is manifested by the melt flow rate which, as those skilled in the art are aware, is a measure of polymer viscosity, which is proportional to the degree of polymerization. The lower the melt flow rate the greater the polypropylene viscosity.

Claims

WHAT IS CLAIMED IS:

1. A cocatalyst comprising an aluminium trialkyl and an alkoxysilane for use in preparing a catalyst system for the polymerization of olefins containing a titanium III component and an election donor having an ultraviolet absorption wave length of less than 250 nanometers.

2. The cocatalyst of Claim 1, wherein the alkoxy silane has the structural formula of (OR¹)₄__p-. .-.SiR^ ³^, where R¹ is hydrocarbyl; R² and R³ are the same or different and are hydrocarbyl; p is 0 or an integer of 1 or 2; and g is an integer of 1 to 3, with the proviso that the sum of p and g does not exceed 3.