BRPI0611461A2 - catalytic components for olefin polymerization - Google Patents

Abstract

Catalytic components for the olefin polymerization. The present invention describes catalytic components for ethylene polymerization comprising Ti, Mg, halogen, OR 'groups, where R' is a C1-C12 hydrocarbon group optionally containing heteroatoms, having an OR '/ Ti molar ratio in the range of 0 -1 to 1,5, a molar ratio of Mg / Ti less than 8, an amount of titanium in relation to the total weight of said solid catalytic component greater than 4% by weight, characterized by a specific SS-NMR standard, and which are particularly useful for preparing narrow MWD crystalline ethylene polymers.

Description

Catalytic components for polymerization of olefins.

The present invention relates to catalytic components for the ethylene polymerization and mixtures thereof with CH2 = CHR1 olefins wherein R is a radical alkyl, cycloalkyl or aryl having from 2 to 12 carbon atoms in the presence of a catalyst comprising Ti1 Mg1 halogen, OR1 in a specific ratio, which may be obtained by reacting, under specific conditions, a titanium compound having at least one Ti-Cl bond with a particular precursor. The catalytic components according to the present invention are suitably used in ethylene (co) polymerization processes to prepare, in high yields, especially ethylene polymers having a medium-narrow molecular weight distribution (MWD). MWD is an important feature of polymers ethylene because it affects both rheological behavior, and therefore processability, as the final mechanical properties. In particular, in the case of LLDPE1 narrow MWD polymers are suitable for films and injection molding because deformation and shrinkage problems are minimized in the manufactured article. The molecular weight distribution width for ethylene polymers is generally expressed as the melt flux ratio F / E, which is the ratio of the melt flux index measured by a load of 21.6 kg (melt flux index F ) and that measured with a load of 2,16 kg (melt flow rate E). Melt flow index measurements are performed according to ASTM D-1238 and at 190 ° C. A catalytic component for preparing ethylene (co) polymers having a narrow MWD is described in EP-A-553805. The catalyst comprising Ti, Mg, halogen, OR1 groups is characterized by an OR / Ti ratio of at least 0.5, a porosity (determined with mercury porosimeter) of 0.35 to 0.7 which additionally has a specific pore distribution. . Said catalyst is obtained by a particularly long process comprising the preparation of an MgCl2 alcohol adduct having about 3 moles of alcohol which is first thermally de-alcoholized to an intermediate content and then chemically almost completely de-alcoholized. The porous precursor created is then reacted with an alkoxy titanium compound in the presence of a halogenating agent and optionally a reducing agent. The catalyst thus obtained is capable of producing (MW) ethylene polymers with a narrow MWD but the polymerization activities are low. Catalysts which are the product of a somewhat simpler process are described in US 4 220 554. They are obtained by reacting a large excess of TiCl4 with catalytic precursors of the general formula MgCln (OR) 2-n in the presence of a compound donor of internal electrons at high temperatures (120 ° C). The hydrogen response of the final catalytic component, however, is not satisfactory.

In EP 301 894, a catalyst comprising Ti, Mg, halogen, OR groups (R is an aliphatic, aromatic or cycloaliphatic hydrocarbon radical) wherein the Mg / Ti molar ratio is 0.5 to 50 and the OR / Ti ratio is 1.5 to 5, is used for the preparation of amorphous ethylene copolymers. All examples are directed to the production of amorphous copolymers and terpolymers without any indication as to the suitability for the production of crystalline ethylene polymers with a narrow average molecular weight distribution.

Therefore, there is still a need for a suitable catalytic component to form a catalytic system exhibiting a good balance of polymerization reactivity, ability to form ethylene polymers with a restricted MW and good hydrogen response.

The applicant has found that the above-mentioned needs are met by catalytic components characterized by certain chemical characteristics and a specific standard when analyzed by solid state NMR (SS-NMR). In particular, said solid catalyst component comprises Ti1 Mg, halogen, OR1 groups wherein R1 is a C1-C12 hydrocarbon group optionally containing heteroatoms having a molar ratio of OR '/ Ti in the range 0.1 to 1.5, a molar ratio of Mg / Ti less than 8, an amount of titanium, with respect to the total weight of said solid catalytic component greater than 4% by weight, and exhibiting an SS-NMR standard recorded under the conditions set forth below one or more signals (A) having a 60 to 75 (ppm) and one or more signals (B) having a maximum in the region of 78 to 108 (ppm) such that the 1A / 1B ratio, where Ia is the integral of the maximum signal in the region between 60 and 75 ppm and Ib is the integral of signals having the maximum region between 78 and 108 ppm, is greater than 0.8.

Preferably, the 1A / 1B ratio is greater than 1 and most preferably is in the range of 1 to 10. In particular cases, the 1A / 1B ratio may preferably be greater than 10.

In a preferred aspect the amount of titanium, relative to the total weight of said solid catalyst component, is greater than 5% and preferably greater than 6% by weight.

Furthermore, said ORVTi molar ratio is preferably greater than 0.3, most preferably greater than 0.5. In an even more preferred embodiment said ratio is greater than 0.7 and is in the range of 0.8 to 1.4.

The depositor has also found that the above-mentioned catalytic components comprising Ti, Mg, halogen, OR1 groups, where R1 is a C1 -C12 hydrocarbon group optionally containing heteroatoms, an OR '/ Ti molar ratio in the range 0.1 to 1.5, a Mg / Ti molar ratio of less than 8 and a quantity of titanium in relation to the total weight of said solid catalyst component, greater than 4% by weight, can be characterized by the fact that a titanium compound having at least a Ti-Cl bond with a precursorcatalytic of formula MgCIn (OR1) 2-R1 where η is 0.5 to 1.5 and R1 has the above meaning.

In a preferred embodiment of the present invention R 1 is a C 1 -C 8 hydrocarbon group chosen from alkyl groups. Among them, methyl, ethyl, n-propyl, n-butyl, i-butyl and t-butyl are particularly preferred.

In addition, said OR '/ Ti molar ratio is preferably greater than 0.3, more preferably greater than 0.5. In an even more preferred embodiment, said ratio is greater than 0.7 and is in the range of 0.8 to 1.4.

Among the titanium compounds containing at least one Ti-halogen bond, those having the formula Ti (ORl) p ^ CIy, where Rl has the meaning given above, ρ is the valence of titanium and y is a number between 1 and p are preferred. Particularly preferred are titanium compounds wherein y is 3 or 4, TiCl 4 being especially preferred.

Among the catalytic precursors are particularly preferred those wherein R1 is chosen from a C1-C8 hydrocarbon group, preferably ethyl, and η ranges from 0.6 to 1.4, in particular from 0.7 to 1.3, especially from 0.8. at 1.2. Said catalytic precursors may be generated by exchange reaction between organometallic compounds of formula ClmMgR2.m wherein m is 0.5 to 1.5, R is a hydrocarbon group, with an appropriate source of OR1 group. The sources of OR1 are, for example, alcohols R1 OH or preferably a silicon compound of formula (R1) rSiR4-r, where r is from 1 to 4 and R1 has the meaning given above. In turn, as is generally known in the art, the organometallic compounds of formula ClmMgR2.m may be obtained by reaction between the metal Mg and an organic chloride RCI, where R is as defined above, optionally in the presence of suitable promoters. Preferably, the formation of ClmMgR2.m and subsequent exchange with the OR1 source occurs in a single step. The reaction may be performed in an inert liquid medium such as a hydrocarbon that is liquid at room temperature. Usually, when a substantial amount of exchange with the OR source occurs, the catalytic precursors are precipitated and can be easily isolated.

As mentioned above, the reaction between the detitanium compound having at least one Ti-Cl bond and the catalytic precursor should be performed under conditions such that the reaction product has a final OR '/ Ti molar ratio comprised between 0.1 and 1.5. This is within the ordinary skill of the artisan and there are several ways to achieve the same results.

According to a preferred embodiment, the catalytic component is obtained by reacting the catalytic precursor with a detitanium compound, preferably TiCl4 used in an amount such that the molar ratio between the titanium compound and the catalytic precursor OR1 groups is greater than 4. This ratio may be greater than 6 or even greater than 10. In this embodiment, the temperature is not particularly critical and is preferably maintained at values ranging from 40 to 150 ° C and preferably in the range of 70 to 140 ° C. When using an excess of liquid titanium compound, preferably TiCl4, an inert liquid medium may be omitted since the titanium compound acts simultaneously as halogenating agent and reaction medium. However, if desired, an inert liquid medium may also be used in this embodiment. Preferred inert media are optionally chlorinated aliphatic or aromatic hydrocarbons, including from 3 to 20 carbon atoms. Especially preferred are propane, n-butane, n-pentane, n-hexane, n-heptane, benzene, toluene and isomers thereof. Mixtures of two or more of said hydrocarbons may be used. Due to the halogenating capacity of the titanium compound, by reaction with the catalytic precursor, a certain amount of magnesium chloride may be formed.

According to another preferred embodiment, the titanium compound is used in such amounts that the molar ratio between the detitanium compound and the catalytic precursor OR1 groups may be less than 4. Under these conditions, the temperature becomes critical and is preferably It is maintained at values greater than 100 ° C even more preferably in the presence of a liquid medium such as that described above.

The catalytic components according to the present invention are converted into catalysts for olefin polymerization by reaction with organoaluminum compounds according to known methods.

In particular, it is an object of the present invention a catalyst for the polymerization of CH2 = CHR olefins, wherein R is hydrogen or a hydrocarbyl radical having from 1 to 12 carbon atoms, the product comprising:

(a) a solid catalytic component as described above,

(b) an alkylaluminum compound and optionally

(c) an external electron donor compound.

The alkyl aluminum compound may preferably be chosen from trialkyl aluminum compounds such as for example trimethyl aluminum (TMA), triethyl aluminum (TEA), triisobutyl aluminum (TIBA), tri-n-hexyl aluminum, tri-n-octyl aluminum. Alkyl aluminum halides, and in particular alkyl aluminum chlorides, such as diethyl aluminum chloride (DEAC), diisobutyl aluminum chloride, aluminum sesquichloride and dimethyl aluminum chloride (DMAC) may also be used. It is also possible to use, and in certain cases it is preferred to use, detrialkylaluminum mixtures with alkylaluminum halides. Among them, mixtures between TEA and DEAC are particularly preferred. The components of (a) to (c) mentioned above may be separately fed to the reactor where, under the polymerization conditions, its activity may be exploited.

The catalytic system thus formed may be used directly in the main polymerization process or alternatively may be prepolymerized beforehand. A prepolymerization step is usually preferred when the main polymerization process is carried out in the gas phase. The polymerization may be performed with any of the olefins CH2 = CHR1 wherein R is H or a C1 -C10 hydrocarbon group. In particular, it is especially preferred to recolymerize ethylene or mixtures thereof with one or more α-olefins, said mixtures containing up to 20 mol% α-olefin, forming polymer amounts of about 0.1 g per gram of solid catalyst component to up to 1000 g per gram of solid catalytic component. The prepolymerization step may be performed at temperatures from 0 to 80 ° C, preferably from 5 to 70 ° C, in the liquid or gas phase. The de-polymerization step may be performed in-line as part of a continuous polymerization process or separately in a batch process. The batch catalyst prepolymerization of the present invention with ethylene to produce a polymer amount ranging from 0.5 to 20 g per gram of catalyst component is particularly preferred. Examples of gas phase processes in which catalysts may be used in accordance with the present invention are described in patent application WO92 / 21706 and W0 / 03078 and US 5 733 987. These processes comprise a pre-contact step of catalytic components. , a prepolymerization step and a gas phase polymerization step in one or more reactors in a series of fluidized or mechanically stirred bed reactors. In a particular embodiment, the gas phase polymerization process may be suitably performed according to the following steps:

(i) prepolymerize with one or more olefins of the formula wherein R is H or a C1-C10 hydrocarbon group to polymer amounts of about 0.1 to about 1000 g per gram of solid catalyst component (a) ; and

(ii) polymerize gas ethylene, or mixtures thereof with olefins of formula CH2 = CHR1 wherein R is H or a hydrocarbon group having from 1 to 10 carbon atoms in one or more fluidized or mechanically stirred bed reactors, in the presence of the product from (i).

However, the catalysts of the present invention are particularly suitable for slurry polymerization in an inert medium such as propane, butane, pentane, hexane, heptane and mixtures thereof.

As already mentioned, the catalysts of the present invention are suitable for preparing crystalline ethylene polymers having the desired balance of catalytic activity, hydrogen response and adequate MWD. In particular, it is possible to obtain a very narrow molecular weight distribution which is characterized by an F / E ratio of less than 40 and in some cases less than 35 and in some cases less than 30. When ethylene is polymerized together with a minor amount α-olefin as comonomer, chosen from propylene, butene-1, hexene-1 and octeno-1, is obtained a low density linear polyethylene having a lower density than 0.940 g / cm3 with a very good quality which is indicated by the low ratio between weight of the xylene soluble fraction and the weight of the comonomer in the chain. In addition, the catalyst of the present invention also exhibits a very good response to hydrogen, i.e. the ability to produce low molecular weight polymers depending on a given molecular weight regulator content (usually hydrogen) in the polymerization system. This feature is particularly useful when bimodal molecular weight distribution polymers should be prepared in sequential polymerization steps. In this case, it is appropriate to have a catalyst with a good hydrogen response because low molecular weight polymers are produced with a lower amount of molecular weight regulator and, as a consequence, with higher activity.

Non-limiting examples of other polymers that can be prepared with the catalyst according to the present invention are very low and ultra low density polyethylenes (VLDPE and ULDPE having a lower density than 0.920 g / cm3, up to 0.880 g / cm3) consisting of copolymers. ethylene having one or more α-olefins having from 3 to 12 carbon atoms, having an ethylene derivative unit molar content of more than 80%; high density ethylene polymers (HDPE having a density greater than 0.940 g / cm3) comprising ethylene homopolymers and α-olefin ethylene copolymers having from 3 to 12 carbon atoms; ethylene and propylene elastomeric copolymers and ethylene and propylene elastomeric terpolymers with smaller proportions of a diene having a weight content of ethylene-derived units of between about 30 and 70%. The following examples are given in order to further describe the present invention without limitation.

DESCRIPTION

The properties were determined according to the following methods:

Melt flow rate: Measured at 190 ° C according to ASTM D-1238, condition Έ "(2.16 kg load), condition" P "(5.0 kg load) and condition" F " (load 21.6 kg);

Xylene-soluble fraction: The xylene solubility at 25 ° C was determined according to the following method: about 2.5 g of polymer and 250 cm3 of o-xylene were placed in a round bottom flask with cooler and reflux condenser. kept under nitrogen. The obtained mixture was heated to 135 ° C and kept under stirring for 60 minutes. The final solution was allowed to cool to 25 ° C under continuous stirring, and then filtered. The filtrate was then evaporated in a nitrogen stream at 140 ° C to constant weight. The content of said xylene-soluble fraction is expressed as a percentage of the original 2.5 g.

Comonomer content: Butene-1 or α-olefins were determined via infrared spectroscopy.

Effective Density: ASTM-D 1505

Thermal Analysis: Calorimetric measurements were performed using a Perkin-Elmer DSP differential analysis calorimeter. The instrument was calibrated to indium and tin standards. The heavy sample (5 to 10 mg) obtained from the Melt Flow Index determination was sealed in aluminum pots, thermostated at 5 ° C for 3 minutes, heated to 200 ° C to 20 ° C / min. and maintained at that temperature for a long enough time (5 minutes) to allow complete melting of all crystallites.

Successively, after cooling to 20 ° C / min. to -20 ° C, the peak temperature was assumed as crystallization temperature (Tc). After 5 minutes at 0 ° C, the sample was cooled to 200 ° C at a rate of 20 ° C / min. In this second heating step, the peak temperature was assumed as the melting temperature (Tm) and the area as the melting global head (ΔΗ).

Determination of Mg. Ti: was performed via inductively coupled plasma emission spectroscopy (ICP).

Cl determination: was performed via potentiometric titration.

Determination of alkoxides (as ROH): via gas chromatography analysis after catalyst hydrolysis.

Solid state NMR analysis: Solid state 13 C-NMR spectra were recorded on a Bruker DPX-200 spectrometer operating at 50.32 MHz in Fourier Transform mode. Samples were measured at room temperature on a 7 mm ZrO2 rotor using a 4 kHz spin rate. The transients were accumulated using the magic gyrus cross-polarization (CP-MAS) technique with a 5 s cycle interval and a 1 ms contact time. All NMR experiments employed a sufficiently large proton decoupling field to ensure full decoupling across the spectral window.

The rotors were prepared under nitrogen atmosphere.

The orthorhombic phase crystalline polyethylene was taken as an external reference at 32.85 ppm from tetramethylsilane (TMS).

U is defined as the signal integral having the maximum in the region between 60 and 75 ppm.Ib is defined as the signal integral having the maximum in the region between 78 and 108 ppm.

Polymerization of ethylene: general procedure. A 4.5 L stainless steel autoclave equipped with comagitator, temperature and pressure indicator, feed line for hexane, ethylene and hydrogen was used and purified by pure nitrogen flow at 70 ° C for 60 minutes

Then, 1550 cm3 of hexane containing 4.9 cm3 of 10% w / v TEA / hexane solution was introduced at a temperature of 30 ° C under nitrogen flow. In a 200 cm3 round-bottom separate glass bottle were successively introduced 50 cm3 of anhydrous hexane, 1 cm3 of 10% w / v TEA / hexane solution and about 0.010 to 0.025 g of the catalytic component of Table 1. They were mixed, waited 10 min. at room temperature and were introduced under nitrogen flow to the reactor. The autoclave was closed, then the temperature was raised to 85 ° C, and hydrogen (partial pressure as indicated in table 2) and ethylene (7.0 bar partial pressure) were added.

Under continuous agitation, the total pressure was maintained at 85 ° C for 120 min. by the ethylene feed. In the end, the reactor was depressurized and the temperature dropped to 30 ° C. The recovered polymer was dried at 70 ° C under denitrogen flux.

EXAMPLES

All solvents were deoxygenated, dried over LiAIH4, and distilled under a nitrogen atmosphere before use.

TEA is triethylaluminium.

TiBA is triisobutylaluminum.

Precursor General Preparation

The synthesis of the precursor was performed as described in US Patent Example 4 220 2204. The support thus obtained had the following composition:

Mg, 20.2% ρCl1 29.8% ρGroups EtO 41.5% ρ

Example 1

In a 500-neck nitrogen-purged four-neck round-bottom flask, 280 cm3 of heptane and 17.7 g (147 mg.at Mg) of the previously prepared support were introduced at 25 ° C. Then, at the same temperature, 103mmol TiCl4 was added under stirring. Then the temperature was raised to 120 ° C 1 h and held for 2 hours. Then stirring was stopped, the solid product was decanted for 30 minutes and the supernatant liquid was siphoned off.

The solid was washed twice with anhydrous heptane (2 x 100cm 3) at 50 ° C and three times at 25 ° C. Finally, the solid was dried under vacuum and analyzed. Results are reported in Table 1. The catalyst was used in the polymerization of ethylene according to the general polymerization procedure under the specific conditions reported in Table 2.

Example 2

In a 500-neck four-neck round-bottom flask equipped with a mechanical stirrer and purged with nitrogen, 220 cm3 of TiCl4 was charged. The temperature was set at 0 ° C and 15.3 g (127 mg.at Mg) of the solid supports were slowly added. The temperature was raised to 120 ° C and the mixture stirred for 1 hour. Then stirring was stopped, the solid product was allowed to decant and the supernatant liquid was siphoned off. This titanation procedure was repeated twice under the same conditions for 0.5 hour.

The solid was washed twice with anhydrous heptane (2 x 100cm 3) at 40 ° C and twice at 25 ° C, recovered, dried under vacuum and analyzed. The characteristics are collected in table 1.

The catalyst was used in the ethylene polymerization according to the general polymerization procedure under the specific conditions reported in table 2.

Example 3

In a 800 cm3 four neck round bottom flask equipped with a mechanical stirrer and purged with nitrogen, 600 cm3 TiCl4 was charged. The temperature was set at 0 ° C and 30 g (249 mg.at Mg) of the solid supports were slowly added. The temperature was raised to 135 ° C in about 90 minutes and the mixture was stirred for 2 hours. Then stirring was stopped, the solid product was allowed to decant and the supernatant liquid was siphoned off. The solid was washed twice with anhydrous heptane (2 x 100 cm 3) at 60 ° C and twice at 25 ° C, recovered, dried under vacuum and analyzed. The characteristics are collected in table1. The catalyst was used for ethylene polymerization according to the general polymerization procedure under the specific conditions reported in table 2.

Comparative Example 1

A catalytic component was prepared according to the description of Example 2 (a) of US 4 220 554. The catalyst was used in ethylene polymerization according to the general polymerization procedure under the specific conditions reported in table 2.

TABLE 1

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TABLE 2

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Claims (10)

1. "Catalytic components for the polymerization of olefins", characterized in that they comprise Ti, Mg1 halogen, OR1 groups where R1 is a CrCi2 hydrocarbon group optionally containing heteroatoms, having an OR '/ Ti molar ratio in the range 0.1 to 1. 1.5 a molar ratio of Mg / Ti less than 8, an amount of titanium, relative to the total weight of said solid catalytic component greater than 4% by weight, and showing in the SS-NMR standard recorded under the conditions set forth below, one or more signals (A) having a maximum in the region of 60 to 75 (ppm) and one or more signals (B) having a maximum in the region of 78 to 108 such that the ratio A / 1B, where Ia is the integral of Signals having the maximum in the region between 60 and 75 ppm and I8 is full of signals having the maximum in the region between 78 and 108 ppm, is greater than 0.8. "Components" according to claim 1, characterized in that the ratio U / Ib β greater than 1. "Components" according to claim 1, characterized in that R 1 is a C 1 -C 8 hydrocarbon group chosen from alkyl groups. "Components" according to claim 1, characterized in that the amount of titanium relative to the total weight of the solid catalytic component is greater than 5%. "Components" according to claim 1, characterized in that the OR '/ Ti molar ratio is greater than 0.3. 6. "Catalytic components for the polymerization of olefins", characterized in that they comprise Ti, Mg1 halogen, OR1 groups where R1 is a CrCi2 hydrocarbon group optionally containing heteroatoms, an OR '/ Ti molar moiety in the range 0.1 to 1.5. a molar Mg / Ti ratio of less than 8 and a quantity of titanium in relation to the total weight of said solid catalytic component, greater than 4% by weight, obtainable by the reaction of a titanium compound having at least one Ti-Cl bond with a catalytic precursor of the formula MgCln (OR ') 2.n, where η is from 0.5 to 1.5 and R1 has the meaning given above. "Components" according to claim 6, characterized in that the titanium compounds are those compounds having the formula Ti (ORl) ^ yCly, where R1 has the meaning given above, ρ is the valence of titanium and yé a number from 1 to p. "Components" according to Claim 6, characterized in that the catalytic precursor is reacted with a titanium compound used in such an amount that the molar ratio of the titanium compound to the catalytic precursor OR1 groups is less than 4 9. "catalyst for polymerization of olefins" means olefinsCH2 = CHR1 wherein R is hydrogen or a hydrocarbyl radical having from 1 to 12 carbon atoms, characterized in that it comprises the reaction product of: (a) a solid catalytic component of (b) an alkyl aluminum compound and optionally (c) an external electron donating compound. "Olefin polymerization process", characterized in that it is carried out in the presence of the catalyst according to claim 9.