CATALYST COMPONENTS FOR THE POLYMERIZATION OF OLEFINS

FIELD OF THE INVENTION

[0001] The present disclosure relates to a process for the preparation of catalyst components for the homo or copolymerization of olefins, in particular ethylene, comprising Mg, Ti and halogen elements and an electron donor compound selected from cycloalkyl ethers.

BACKGROUND OF THE INVENTION

[0002] Linear low-density polyethylene (LLDPE) is one of the most important families of products in the polyolefin field. The family comprises ethylene/cc- olefin copolymers containing an amount of cc-olefin deriving units such that products with a density in the range 0.88-0.925 are produced. Due to their characteristics, these copolymers find application in many sectors and in particular in the field of wrapping and packaging of goods where, for example, the use of stretchable film based on LLDPE constitutes an application of significant commercial importance. LLDPE is commercially produced with liquid phase processes (solution or slurry) or via more economical gas-phase processes. Both types of processes involve the widespread use of Ziegler-Natta MgCL.- supported catalysts that are generally formed by the reaction of a solid catalyst component, in which a titanium compound is supported on a magnesium halide, with a suitable activator such as an alkylaluminium compound.

[0003] For the preparation of LLDPE catalysts need to show good comonomer distribution suitably coupled with high polymerization yields.

[0004] The homogeneous distribution of the comonomer (cc-olefin) in and among the polymer chains is very important. In fact, having a comonomer randomly or alternatively distributed along the polymer chain and, at the same time, having the polymer fractions with a similar average content of comonomer (narrow distribution of composition) allows the achievement of high quality ethylene copolymers. These latter usually combine, at the same time, a density sufficiently low with respect to HDPE and a low content of polymer fractions soluble in hydrocarbon solvents like hexane or xylene that may worsen certain properties of the resulting copolymers.

[0005] A type of Ziegler-Natta heterogeneous catalyst effective in producing good quality LLDPE is based on Ti compounds supported on magnesium chloride further containing a substantial amount of cycloalkyl ether as internal electron donor, such as tetrahydrofuran (THF).

[0006] According to WO2012/025379 solid catalyst components of this type can be obtained in a two-step process which comprises reacting a MgCl ₂ -ROH complex with an excess of TiCl ₄ thereby obtaining an intermediate solid catalyst component; as a second step, following the isolation of the solid obtained in the first step, a contact step with the cyclic ether is followed. By this route, it is necessary to isolate the solid at the end of first step and, in addition, using a solid Ti compound in the first step instead of liquid TiCl ₄ would greatly increase the complexity of the process. In fact, since a solid titanium compound would not be very effective in dealcoholating the MgCl ₂ -ROH complex, an excessive amount of it should be used which would then impact on the Ti/Mg relative ratios.

[0007] Use of solid T1CI ₃ is described in EP661301. This document discloses a first step in which T1CI ₃ (reduced from TiCl ₄ ) and MgCl ₂ are dissolved in an excess of THF. The so obtained solution in a further step is then made solid by either impregnation on a support or added with a filler and then spray-dried. It is clear that this route makes necessary the use of a further solid component (filler or support) that must be heavily chemically and physically dehydrated before use. Moreover, it will be the further solid component that will influence or control the particle size of the solid catalyst and its distribution.

The applicant has instead now surprisingly found a simple and versatile process for the preparation of the above described catalyst component that can make use of solid T1CI ₃ , can be carried out in one-pot mode and does not require the use of a further solid component.

SUMMARY OF THE INVENTION

[0008] An object of the present disclosure is a process for the preparation of a solid catalyst component for the homo or copolymerization of olefins CH ₂ =CHR, in which R is hydrogen or a hydrocarbyl radical with 1-12 carbon atoms, which comprises Mg, Ti , halogen and an electron donor selected from cycloalkyl ethers , said process comprising: [0009] (a) dissolving a Mg based compound of formula (MgCl _m X ₂ - _m ) in which m ranges from 0 to 2, X is, independently R ¹ , OR ¹ , -OCOR ¹ or 0-C(0)-OR ¹ group, in which R ¹ is a Q-C ₂₀ hydrocarbon group, and a T1CI ₃ based compound in a liquid medium further comprising a cycloalkyl ether and a compound of formula R 2 OH where R 2 is a C C ₂ o hydrocarbon group, in which the Ti/Mg molar ratio ranges from 0.1 to 0.5, the cycloalkyl ether/Mg ratio ranges from 1 to 4 and the R OH/Mg molar ratio ranges from 1 to 4; and

(b) adding, to the solution coming from step (a), S1CI ₄ in an amount such that the R OH/S1CI ₄ molar ratio ranges from 0.5 to 1.5 and maintaining the temperature in the range 50-150°C thereby allowing precipitation of the solid catalyst component particles.

DETAILED DESCRIPTION OF THE INVENTION

[0010] In a particular embodiment of the first step, the magnesium based compound used as a starting compound in the first of the one or more steps (a) is preferably MgCl _2. The compound can be used as such or it can be milled to reduce the particle size thereby favoring its dissolution.

[0011] The T1CI ₃ based compounds are known since long time as species capable to catalyze the polymerization reaction. They are commercially available and can be prepared by different methods. For instance, the T1CI ₃ used may be the product obtained by one of the following methods:

(a) reduction of T1CI ₄ with hydrogen, at temperatures higher than 600°C;

(b) reduction of T1CI ₄ with Al;

(c) reduction of T1CI ₄ with organometallic compounds of Al,

(d) reduction of T1CI ₄ with other metal such as Mg or Zn.

Particularly preferred is the use complexes having composition T1CI ₃ 1/3AICI ₃ obtained by reducing T1CI ₄ with aluminum metal.

[0012] The magnesium and titanium compounds are dispersed in liquid medium, preferably a hydrocarbon medium which is inert to the above mentioned compounds. Such a medium is preferably selected among aliphatic or aromatic hydrocarbons that are liquid at room temperature and atmospheric pressure. Among them preferred are hexane, heptane, decane benzene and toluene; possible isomers of these hydrocarbons are also included. Toluene is the preferred liquid medium. [0013] As mentioned, the liquid medium also contains a cycloalkyl ether and an alcohol of formula R OH. The cycloalkyl ether is preferably selected among cyclic ethers having 3-5 carbon atoms such as tetrahydrofurane, dioxane, methyltetrahydrofurane. Tetrahydrofurane is the most preferred. In the alcohol R 2 OH, R 2 is preferably selected among C ₃ -Q5 alkyl groups preferably C4-Q0 alkyl groups. Among them preferred alcohols are butanol, pentanol, hexanol, heptanol, octanol and isomers thereof. Particularly preferred is n-butanol, 1-octanol and 2-Me-l- pentanol.

[0014] Preferably, the cycloalkyl ether/Mg molar ratio ranges from 1.5 to 3.0. Preferably, the Ti/Mg molar ratio ranges from 0.15 to 0.35 and more preferably from 0.15 to 0.3.

[0015] In a particular embodiment, in addition to the Mg based compound and T1CI ₃ based compound it is also added an additional compound selected from compounds of elements of the Lantanides series or transition metal belonging to groups 3-12 of the periodic table, excluding Ti. Particularly preferred are the halides, in particular chlorides, alcoholates and carboxylates of such compounds.

If employed the said compound is added to the mixture in amount such that its molar ratio ratio with Mg ranges from 0.01 to 0.40, preferably from 0.05 to 0.20.

Preferably, said compound is selected among chlorides of Cu, Zn, Pr, and Nb. Among them Q1Q ₂ and ZnCl ₂ are the most preferred.

The dissolution step takes place under stirring, preferably at a temperature ranging from 25 to 150°C. As it usual in chemical reaction, the temperature has also an effect on the dissolution time which however may also depend on other factors. Taking into account the temperature only, it was observed that increasing the temperature may reduce the time necessary for the dissolution. Preferably the temperature is maintained in the range 50-120°C and, in this range, the dissolution time may range from 2 to 7 hours. It is preferred that step (b) is started once a clear solution is obtained. However, it may be possible that step (b) is also started when the dissolution is not totally completed. In these cases, it may be advisable to remove the solids from the mixture before starting step (b).

[0016] Step (b) is carried out by controlled addition of S1CI ₄ to the solution obtained in step (a).

Preferably, it is added in an amount such that the R OH/S1CI ₄ molar ratio ranges from 0.6 to 1.3, more preferably from 0.8 to 1.2 and especially from 0.9 to 1.1. [0017] The SiCl ₄ is preferably added dropwise, pure or better if diluted in the hydrocarbon used as liquid medium of step (a) while maintaining the mixture under stirring. The temperature is preferably maintained in the range 60-130 °C and more preferably in the range 70-100°C. When the amount of S1CI ₄ reaches a critical amount, solid particles start to precipitate even if the addition of S1CI ₄ is not complete. The time needed to complete precipitation is varying, however, it was observed that by carrying out the reaction at R OH/S1CI ₄ molar ratio of about 1 under a temperature in the range 80-90°C, the time to complete the reaction is from 2 to 5 hours.

[0018] Particularly, but not exclusively, when step (b) is carried out at a relatively low temperature, i.e., in the range 60-75°C, it is preferred that a post reaction step is followed in which the temperature is raised to 80-100°C for a time ranging from 2 to 4 hours.

[0019] The precipitated particles constituting the solid catalyst component can be collected by the usual techniques such as, siphoning, filtration, centrifugation, thermal removal of the solvent. Preferably, they are collected by filtration, then washed with hydrocarbon solvents and dried. The solid catalyst component average particle size can vary from 10 to 100 μιη and can be regulated by varying the intensity of mixing.

[0020] The solid catalyst component prepared according to the process of the present disclosure is converted into catalyst for the polymerization of olefins by reacting it with alkyl-Al compounds according to known methods.

[0021] The alkyl-Al compound is preferably chosen among the trialkyl aluminum compounds such as for example triethylaluminum, triisobutylaluminum, tri-n-butylaluminum, tri-n- hexylaluminum, tri-n-octylaluminum. It is also possible to use alkylaluminum halides, alkylaluminum hydrides or alkylaluminum sesquichlorides, such as AlEt ₂ Cl (diethyl aluminum chloride) and Al ₂ Et ₃ Cl ₃ , possibly in mixture with the above cited trialkylaluminums. A mixture of aluminum triethyl and diethylaluminum chloride is particularly preferred.

[0022] The Al/Ti ratio is higher than 1 and is generally between 50 and 2000.

[0023] Optionally, an external electron-donor (ED) compound(s) can be used. It is preferably selected from silicon compounds, ethers, esters, amines, heterocyclic compounds and particularly 2,2,6,6-tetramethylpiperidine and ketones. [0024] The catalyst prepared according to the present disclosure can be used in a process for the (co)polymerization of olefins CH ₂ =CHR, in which R is hydrogen or a hydrocarbyl radical with 1-12 carbon atoms.

[0025] As already mentioned, the catalysts of the present disclosure are suitable for preparing ethylene polymers in very high yields.

[0026] Non-limiting examples of other polymers that can be prepared with the catalyst of the disclosure are very-low-density and ultra-low-density polyethylene (VLDPE and ULDPE, having densities lower than 0.920 g/cm 3 , including values down to 0.880 g/cm 3 ) consisting of copolymers of ethylene with one or more alpha-olefins having from 3 to 12 carbon atoms, having a mole content of units derived from ethylene of higher than 80%; and high density ethylene polymers (HDPE, having a density higher than 0.940 g/cm ), comprising ethylene homopolymers and copolymers of ethylene with alpha-olefins having 3-12 carbon atoms and UHMWPE characterized by an intrinsic viscosity [η] in tetraline at 135 °C of higher than 10.

[0027] The polymerization process can be carried out according to known techniques, for example, slurry polymerization using as a diluent an inert hydrocarbon solvent, or bulk polymerization using a liquid monomer (for example, propylene) as a reaction medium. Moreover, it is possible to carry out the polymerization process in gas-phase operating in one or more fluidized or mechanically agitated bed reactors. However, the slurry polymerization in an inert medium such as propane, butane, pentane, hexane, heptane and mixtures thereof is a preferred technique.

[0028] The following examples are given in order to better illustrate the disclosure without limiting it.

EXAMPLES

CHARACTERIZATIONS

[0029] Determination of Mg. Ti rrrvn. Zn and Cu

The determination of Mg, Ti ₍ τοτ Zn and Cu content in the solid catalyst component has been carried out via inductively coupled plasma emission spectroscopy on "LC.P Spectrometer ARL Accuris".

The sample was prepared by analytically weighting, in a "Fluxy" platinum crucible", 0.1÷0.3 grams of catalyst and 2 grams of lithium metaborate/tetraborate 1/1 mixture. After addition of some drops of KI solution, the crucible is inserted in a special apparatus "Claisse Fluxy" for the complete burning. The residue is collected with a 5% v/v HNO ₃ solution and then analyzed via ICP at the following wavelengths: magnesium, 279.08 nm; titanium, 368.52 nm; Zinc, 213.86 nm; copper, 327.40 nm.

[0030] Determination of CI

The determination of CI content in the solid catalyst component was carried out by potentiometric titration with silver nitrate. In a 250 mL beaker were subsequently charged 5 mL of a sodium hydroxide solution 10% wt./vol. in water and 0.1÷0.3 grams of catalyst. After 20 min stirring at room temperature, 40 mL of a 3.6 M nitric acid solution in water were added and stirring continued for additional 10 min. After dilution with 100 mL of demineralized water, the titration started with a 0.1 N AgN0 ₃ solution in water. As soon as the point of equivalence was found, the amount of titrant used was calculated and the chlorine amount present in the catalyst was quantified.

[0031] Determination of internal donor content

The determination of the content of internal donor in the solid catalyst component was done through 1H NMR analysis, dissolving the catalyst (about 40 mg) in acetone d ⁶ (about 0.6 ml) in the presence of an internal standard and transferred into a 5 mm (O.D.) NMR tube. The amount of donor present was referred to the weight of the catalyst compound.

[0032] Determination of Melt Index (MIE, MIF)

The melt indices are measured at 190°C according to ASTM D-1238, condition "E" (load of 2.16 kg).

[0033] Determination of comonomer content

l-Butene was determined via 13 C NMR analysis.

13 C NMR spectra were acquired on a Bruker AV-600 spectrometer equipped with cryo-probe, operating at 150.91 MHz in the Fourier transform mode at 120°C.

The peak of the S55 carbon (nomenclature according to C. J. Carman, R. A. Harrington and C. E. Wilkes, Macromolecules, 10, 3, 536 (1977)) was used as internal reference at 29.90 ppm. The samples were dissolved in l,l,2,2-tetrachloroethane-d2 at 120°C with a 8 % wt/v concentration. Each spectrum was acquired with a 90° pulse, 15 seconds of delay between pulses and CPD to remove 1 H- 13 C coupling. About 512 transients were stored in 32K data points using a spectral window of 9000 Hz. Assignments of the spectra were made according to J.C. Randal, Macromol. Chem Phys., C29, 201 (1989).

Triad distribution and composition were made starting from relations between peaks and triads described by Kakugo et al. modified to consider overlaps of signals in the spectra.

Triads

BBB = 100 Τββ/S

BBE = 100 Τβδ/S

EBE = 100 2B2 (EBE) /S

BEB = 100 S /S

BEE= 100 Scc5/S

EEE = 100 (0.25 Sy5+0.5 S55)/S

Molar composition

B= BBB + BBE+ EBE

E = EEE + BEE + BEB

[0034] Determination of fraction soluble in xylene

2.5 g of polymer and 250 ml of o-xylene were placed in a round-bottomed flask equipped with a cooler and a reflux condenser and kept under nitrogen. The resulting mixture was heated to 135 °C and was kept under stirring for about 60 minutes. The final solution was allowed to cool to 25 °C under continuous stirring, and the insoluble polymer was then filtered. The filtrate was then evaporated in a nitrogen flow at 140 °C to reach a constant weight. The content of the xylene- soluble fraction is expressed as a percentage of the original 2.5 grams.

[0035] Determination of effective density

Effective density: ASTM-D 1505-10 but referred to ΜΓΈ" 1 g/10' as corrected by the following equation: density (MIE=1) =density(measured) -0.0024 ln(MI E)

[0036] Procedure for the preparation of the solid catalyst component

[0037] Example 1

Into a 1.0 liter round-bottom flask with breakwaters, purged with nitrogen and equipped with mechanical stirrer, cooler and thermometer, were introduced at room temperature under stirring 300 mL of toluene, 8.0 grams of magnesium dichloride, 4.1 grams of titanium(III)chloride- aluminum chloride TiCi ₃ *l/3AlCi ₃ complex, 23.9 mL of n-butanol and 12.3 mL of THF. The temperature was raised to 80°C and kept at this value for 4 hours. On the resulting solution, was subsequently added at 80°C in 1 h a mixture of 26.4 mL of SiCl ₄ and 25 mL of toluene. At the end of addition, the temperature was increased at 85°C and kept at this value for 3.5 h. Then the stirring was discontinued, the solid product was allowed to settle and the supernatant liquid was siphoned off. The solid was washed twice at 85°C with anhydrous heptane, thus once at 40°C with anhydrous hexane and dried under vacuum. A free-flowing powder was obtained and analyzed. The composition of solid catalyst component is reported in Table 1, while Tables 2 and 3 show related performance in copolymerization of ethylene and 1-butene, tests in slurry and in gas phase, respectively.

[0038] Example 2

The procedure reported in Example 1 was repeated with the difference that, in addition to the MgCl ₂ and T1CI ₃ based compound, solid zinc chloride ZnCl ₂ was added in step (a) in the amount reported in Table 1.

[0039] Examples 3-7

The procedure reported in Example 1 was repeated with the difference that, in addition to the MgCl ₂ and T1CI ₃ based compound, solid copper (II) chloride CuCl ₂ was added in step (a) in the amount reported in Table 1. Furthermore, in example 4, SiCl ₄ was added in a n-butanol/SiCl ₄ molar ratio of 0.67. In example 5, the addition of SiCl ₄ was carried out at 60°C, while in examples 6-7 the addition of SiCl ₄ was carried out at 70°C.

[0040] Example 8

The procedure reported in Example 1 was repeated with the difference that, in addition to the MgCl ₂ and T1CI ₃ based compound, solid praseodymium (III) chloride PrCl ₃ was added in step (a) in the amount reported in Table 1.

[0041] Example 9

The procedure reported in Example 1 was repeated with the difference that toluene was replaced with heptane and n-butanol with 1-octanol.

[0042] General procedure for the LLDPE polymerization test in slurry

A 4.5 liter stainless-steel autoclave equipped with a magnetic stirrer, temperature, pressure indicator, and feeding line for ethylene, propane, 1-butene, and hydrogen, and a steel vial for the injection of the catalyst, was purified by fluxing pure nitrogen at 70°C for 60 minutes. The autoclave was then washed with propane, heated to 75°C and finally loaded with 800 grams of propane, 1-butene in the amount reported in Table 2, ethylene (7.0 bar, partial pressure) and hydrogen (1.5 bar, partial pressure). In a separate 100 cm round bottom glass flask were subsequently introduced 50 cm of anhydrous hexane, the cocatalyst mixture solution composed by triethyl aluminum/diethyl aluminum chloride, TEA/DEAC 2/1 weight ratio (8.5 mmol of aluminum), 0.12 g of tetrahydrofuran as external donor, and 0.010÷0.020 grams of the solid catalyst component. They were mixed together and stirred at room temperature for 10 minutes and then introduced in the reactor through the steel vial by using a nitrogen overpressure. Under continuous stirring, the total pressure was maintained constant at 75°C in order to absorb 150 g of ethylene or for a maximum time of 2 h by continuous ethylene feeding into the system. At the end of the polymerization, the reactor was depressurized and the temperature was reduced to 30°C. The recovered polymer was dried at 70°C under a nitrogen flow and weighted. Polymer characteristics are reported in Table 2.

[0043] General procedure for the LLDPE polymerization test in gas-phase

The polymerization test was carried out in a 15.0 liter stainless- steel fluidized reactor, equipped with a gas-circulation system, a cyclone separator, a thermal exchanger, a temperature and pressure indicator, a feeding line for ethylene, propane, 1-butene, and hydrogen. The gas-phase of the reactor is recycled with such a velocity that the polymeric bed in the reactor is kept in fluidized conditions. The gas phase reactor is controlled at a temperature of 86°C, and a pressure of 21 barg. The gas phase is composed of 25% mol ethylene, 5% mol hydrogen, 1-butene ranging from 10 and 15% mol and propane to reach the final pressure. The solid catalyst component, 0.070-0.150 grams, is precontacted at room temperature for 15 min in hexane slurry, 45 cm , with trihexyl aluminum (THA), at THA/THF = 0.23 molar. Subsequently, diethyl aluminum chloride (DEAC) solution in hexane is added to the catalyst/THA slurry, such to have DEAC/THF = 0.44 molar. The mixture is contacted for another 15 min at room temperature, then, triethyl aluminum (TEA) solution in hexane is added to the slurry, in order to meet a final molar ratio Al total/THF = 4.1÷4.2. Directly after the addition of TEA, the precontact- slurry is discharged into the gas phase reactor that was prepared at the desired conditions before described. After the introduction of the precontacted catalyst into the reactor, an ethylene/ 1-butene mixture (6÷10% wt. of 1- butene) is continuously fed to the reactor in order to maintain constant pressure and composition during the polymerization test. After 90 minutes, the monomer feed is stopped and the polymer bed formed during the polymerization run is discharged into a degassing vessel. The polymer is recovered and additionally degassed under vacuum. Polymer characteristics are reported in Table

Table 1: solid catalyst components composition

n.d. = not determined

Table 2: LLDPE slurry polymerizations

Table 3: LLDPE gas phase polymerizations