Patent Description:
Ziegler-Natta catalyst components may be used for the stereospecific polymerization of olefins, such as propylene. The catalyst preparation may involve the use of a precursor to be reacted with a titanium compound and optionally with an internal electron donor compound.

The precursor, may comprise adducts of formula MgCl<NUM>(R<NUM>OH)n where R<NUM> is a C<NUM>-C<NUM> alkyl group, in particular ethyl, and n is from <NUM> to <NUM>. Their specific particle size from about <NUM> to about <NUM>. Due to their intrinsic nature, the adduct particles may be subject to cohesiveness problems that worsen flowability and decrease the homogeneous distribution of the precursor particles during catalyst preparation.

In order to address these issues, use of slip agents such as stearates or erucamide is suggested in the art. However, these additives have not improved the flowability features of the precursor particles. <CIT> suggests coating the catalyst or carrier particles with a layer of nanoparticles made of conductive material, such as carbon black. However, this process is burdensome because an additional, separate step for the preparation of a gel comprising the nanoparticles must be performed. Moreover, the presence of an additional layer may prevent the necessary interaction between the catalytically active metal(s) and the carriers. Additionally, the procedure, which comprises the use of a water-based nanoparticles gel, can subsequently inactivate the Ti based catalyst.

<CIT> describes a catalyst preparation route in which the final catalyst component is precipitated from a reaction mixture including several ingredients. When silica is one of the ingredients the catalyst obtained shows the capability to produce polymers with a narrow particle size distribution. Nothing is described or suggested about flowability of precursors.

A simple way of improving precursor flowability without compromising its performance is therefore needed.

Surprisingly, it has been found that precursors with enhanced flowability may be obtained by mechanically mixing the MgCl<NUM>-ROH adduct particles with low amounts of separated inorganic particles having specific composition.

An object of the present disclosure relates to ZN catalyst component precursor comprising a dry mechanical mixture of: (a) distinct particles of adducts of formula MgCl<NUM>(R<NUM>OH)n where R<NUM> is a C<NUM>-C<NUM> alkyl group, preferably ethyl, and n is from <NUM> to <NUM> having average particle size (P50a) ranging from <NUM> to <NUM>; and (b) from <NUM> to <NUM>% by weight of distinct particles of a solid compound containing more than <NUM>% by weight of SiO<NUM> units and having average particle size (P50b) such that the ratio P50b/P50a ranges from <NUM> to <NUM>.

The term mechanical mixture indicates that the particles of adduct (a) are distinct and separated from those of solid compound (b). Said particles of adduct (a) and particles of compound (b) being brought in contact to each other by means of mechanical mixing.

Preferably, in the precursor of the present disclosure the solid compound (b) has average particle size (P50b) ranging from <NUM> to <NUM>, more preferably from <NUM> to <NUM> and especially ranging from <NUM> to <NUM>.

The values of P50a and P50b are in both cases referred to the powder samples excluding aggregates. Powder samples substantially free from aggregates can be obtained by subjecting the powder to mechanical rolling or ultrasound treatment according to the procedure set forth in the experimental section.

Preferably, the ratio P50b/P50a ranges from <NUM> to <NUM>, more preferably from <NUM> to <NUM> and especially from <NUM> to <NUM>.

Preferably, the amount of particles of solid compound (b) ranges from <NUM> to <NUM>% more preferably from <NUM>% to <NUM>% and especially from <NUM> to <NUM>%wt based on the total weight of mixture (a)+(b).

The adduct (a) can be suitably prepared by mixing alcohol and magnesium chloride in the presence of an inert hydrocarbon immiscible with the adduct, operating under stirring conditions at the melting temperature of the adduct (<NUM>-<NUM>). Then, the emulsion is quickly quenched, thereby causing the solidification of the adduct in form of spherical particles. Representative methods for the preparation of these spherical adducts are reported for example in <CIT>, <CIT>, <CIT> and <CIT>. Another useable method for the spherulization is the spray cooling described for example in <CIT> and <CIT>.

Particularly interesting are the MgCl<NUM>·(EtOH)m, adducts in which m is from <NUM> to <NUM> and particle size ranging from <NUM> to <NUM> obtained by subjecting the adducts with a higher alcohol content to a thermal dealcoholation process carried out in nitrogen flow at temperatures comprised between <NUM> and <NUM> until the alcohol content is reduced to the above value. A process of this type is described in <CIT>.

The dealcoholation can also be carried out chemically by contacting the adduct with compounds capable to react with the alcohol groups.

The dealcoholated adducts may also be characterized by a porosity (measured by mercury method) due to pores with radius up to <NUM> ranging from <NUM> to <NUM><NUM>/g preferably from <NUM> to <NUM><NUM>/g.

Preferably, according to the present disclosure, adducts particles (a) have a prevailing spherical shape. In particular, they can be characterized by a sphericity factor higher than <NUM> and preferably higher than <NUM>. The sphericity factor being calculated using the image analysis technique described in the characterization section of the present application.

The precursor comprising the dry mixture of distinct particles of adduct (a) and the distinct particles of solid compound (b) can be prepared with several blending methods the preferred of which comprises dry blending the two solids in a suitable apparatus. Preferably, the dry blending is carried out at room temperature for a time ranging from <NUM> to <NUM> hours, preferably from <NUM> to <NUM> hours and more preferably from <NUM> to <NUM> hours in a nitrogen environment.

It is also possible preparing the dry precursor by stirring a liquid hydrocarbon slurry of the particles (a) and (b) and afterwards removing the liquid phase followed by drying the particles.

As it can be seen from the examples, the so obtained precursors show a reduced break and avalanche energy with respect to the adduct particles (a) as such. The improvement is particularly pronounced in combination with the use of the ratio P50b/P50a is <NUM> or higher. The break and avalanche energy are properties inversely related to the powder flowability. Lower values for these properties indicate higher flowability. Precursors with improved flowability allow an easier transfer and dosing of powder in the stage of solid catalyst component preparation. In general, the precursors show percentage of improvement in term of break energy of <NUM>% or higher, preferably <NUM>% or higher and especially higher than <NUM>% with respect to the particles of adducts (a) as such. Moreover, the precursors show percentage of improvement in term of avalanche energy of <NUM>% or higher, preferably <NUM>% or higher and especially higher than <NUM>% with respect to the particles of adducts (a) as such. The sum of percentage of improvement in terms of break and avalanche energy is higher than <NUM>%, preferably higher than <NUM>% and especially higher than <NUM>%.

The so obtained precursors can then be used to prepare solid catalyst components. According to a preferred method, the solid catalyst component can be prepared by reacting a titanium compound of formula Ti(OR<NUM>)m-yXy, where m is the valence of titanium and y is a number between <NUM> and m and R<NUM> is a C1-C10 alkyl group, with the solid mixtures of the present disclosure. The Ti compound is preferably TiCl<NUM>. The reaction with the Ti compound can be carried out by suspending the solid mixtures in cold TiCl<NUM> (about <NUM>); the mixture is heated up to <NUM>-<NUM> and kept at this temperature for <NUM>-<NUM> hours. The treatment with TiCl<NUM> can be carried out one or more times. The electron donor compound is preferably added during the treatment with TiCl<NUM>. The preparation of catalyst components in spherical form are described for example in European Patent Applications <CIT>, <CIT>, <CIT>, <CIT> and WIPO Pat.

When prepared according to this method, the solid catalyst component may comprise from <NUM> to <NUM>% more preferably from <NUM> to <NUM>%wt of Mg based on the total weight of solid catalyst component. Preferably, the amount of Ti ranges from <NUM> to <NUM>%, more preferably from <NUM> to <NUM>% and even more preferably from <NUM> to <NUM>%wt based on the total weight of the solid catalyst component.

In a preferred aspect of the present disclosure the so obtained catalyst components further comprise an electron donor compound (internal donor). Preferably, it is selected from esters, ethers, amines, silanes, carbamates and ketones or mixtures thereof.

The internal donor is preferably selected from the group consisting of alkyl and aryl esters of optionally substituted aromatic mono or polycarboxylic acids such as for example esters of benzoic and phthalic acids, and esters of aliphatic acids selected from malonic, glutaric, maleic and succinic acids. Specific examples of such esters are n-butylphthalate, di-isobutylphthalate, di-n-octylphthalate, ethyl-benzoate and p-ethoxy ethyl-benzoate. Also, the diesters disclosed in <CIT> and <CIT> can be used. Among this class, particularly preferred are the <NUM>,<NUM>-pentanediol dibenzoate derivatives and <NUM>-methyl-<NUM>-t-butyl catechol dibenzoates. In addition, the internal donor can be selected among diol derivatives chosen among dicarbamates, monoesters monocarbamates and monoesters monocarbonates. Moreover, can be advantageously used also the <NUM>,<NUM> diethers of the formula:
<CHM>
wherein R, RI, RII, RIII, RIV and RV equal or different to each other, are hydrogen or hydrocarbon radicals having from <NUM> to <NUM> carbon atoms, and RVI and RVII, equal or different from each other, have the same meaning of R-RV except that they cannot be hydrogen; one or more of the R-RVII groups can be linked to form a cycle. The <NUM>,<NUM>-diethers in which RVI and RVII are selected from C<NUM>-C<NUM> alkyl radicals are particularly preferred. It is also possible to use mixtures of the above mentioned donors. Specific mixtures are those constituted by esters of succinic acids and <NUM>,<NUM> diethers as disclosed in <CIT>.

When it is desired to increase the capability of the catalyst to distribute an olefin comonomer within a polymer chain, such as in case of production of ethylene/α-olefin copolymers, it is preferred to choose the electron donor among monofunctional donors, in particular ethers and esters. Preferred ethers are the C<NUM>-C<NUM> aliphatic ethers and in particulars cyclic ethers preferably having <NUM>-<NUM> carbon atoms cyclic ethers such as tetrahydrofurane, dioxane. Preferred esters are C<NUM>-C<NUM> alkyl esters of aliphatic mono carboxylic acids such as ethylacetate and methyl formiate. Tetrahydrofurane and ethylacetate are the most preferred.

In general, the final amount of electron donor compound in the solid catalyst component may range from <NUM> to <NUM>% by weight preferably in the range from <NUM> to <NUM>% by weight.

The solid catalyst components can then be converted into catalysts for the polymerization of olefins by reacting them with organoaluminum compounds. The organo aluminum compounds are preferably selected among alkyl-Al compound and in particular 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<NUM>Cl and Al<NUM>Et<NUM>Cl<NUM>, possibly in mixture with the above cited trialkylaluminums. The Al/Ti ratio is higher than <NUM> and is preferably comprised between <NUM> and <NUM>.

The catalyst may in addition comprise an external donor which can be chosen among silicon compounds, ethers, esters, amines, heterocyclic compounds and particularly <NUM>,<NUM>,<NUM>,<NUM>-tetramethylpiperidine and ketones. Preferably it is selected among silicon compounds of formula (R<NUM>)a(R<NUM>)bSi(OR<NUM>)c, where a and b are integers from <NUM> to <NUM>, c is an integer from <NUM> to <NUM> and the sum (a+b+c) is <NUM>; R<NUM>, R<NUM>, and R<NUM>, are alkyl, cycloalkyl or aryl radicals with <NUM>-<NUM> carbon atoms optionally containing heteroatoms. Particularly preferred are the silicon compounds in which a is <NUM>, b is <NUM>, c is <NUM>, at least one of R<NUM> and R<NUM> is selected from branched alkyl, cycloalkyl or aryl groups with <NUM>-<NUM> carbon atoms optionally containing heteroatoms and R<NUM> is a C<NUM>-C<NUM> alkyl group, in particular methyl. Examples of such preferred silicon compounds are methylcyclohexyldimethoxysilane (C donor), diphenyldimethoxysilane, methyl-t-butyldimethoxysilane, dicyclopentyldimethoxysilane (D donor), diisopropyldimethoxysilane, (<NUM>-ethylpiperidinyl)t-butyldimethoxysilane, (<NUM>-ethylpiperidinyl)thexyldimethoxysilane, (<NUM>,<NUM>,<NUM>-trifluoro-n-propyl)(<NUM>-ethylpiperidinyl)dimethoxysilane, methyl(<NUM>,<NUM>,<NUM>-trifluoro-n-propyl)dimethoxysilane. Moreover, the silicon compounds in which a is <NUM>, c is <NUM>, R<NUM> is a branched alkyl or cycloalkyl group, optionally containing heteroatoms, and R<NUM> is methyl are also preferred. Examples of such preferred silicon compounds are cyclohexyltrimethoxysilane, t-butyltrimethoxysilane and thexyltrimethoxysilane.

The electron donor compound (iii) may be used in such an amount to give a molar ratio between the organoaluminum compound and said electron donor compound (iii) of from <NUM> to <NUM>, preferably from <NUM> to <NUM> and more preferably from <NUM> to <NUM>. Therefore, it constitutes a further object of the present disclosure a process for the (co)polymerization of olefins CH<NUM>=CHR, in which R is hydrogen or a hydrocarbyl radical with <NUM>-<NUM> carbon atoms, carried out in the presence of a catalyst comprising the product of the reaction between:.

The polymerization process can be carried out according to various techniques, for example slurry polymerization using as diluent an inert hydrocarbon solvent, or bulk polymerization using the 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.

The polymerization may be carried out at temperature of from <NUM> to <NUM>, preferably of from <NUM> to <NUM>. When the polymerization is carried out in gas-phase the operating pressure is ranges from <NUM> and <NUM> MPa, preferably from <NUM> to <NUM> MPa. In the bulk polymerization the operating pressure is may range from <NUM> to <NUM> MPa, preferably from <NUM> to <NUM> MPa.

The following examples are given in order to better illustrate the subject-matter without limiting it.

Determined by a method based on the principle of the optical diffraction of monochromatic laser light with the "Malvern Instruments <NUM>" apparatus. The average size is given as P50. P10 and P90 are also determined with this method.

The Malvern Mastersizer <NUM> particle size analyzer is divided into three units:.

For the measurements described herein n-heptane (plus <NUM>/l antistatic Span <NUM>) is used as dispersing agent.

The Measuring cell is loaded with dispersing agent, while pump/agitator speed is set up to <NUM> RPM. Background measurement is then taken. Then sample is loaded, by using a dedicated loading mean for solids or slurries. A that point, before being subject to PS Determination, the sample undergoes <NUM> seconds of ultrasound treatment. After that, the measurement is taken.

Measurements were carried out with a Revolution Powder Analyzer (Mercury Scientific Inc. , Newtown, CT, USA). Specific measurement conditions are provided in the user manual revised on August <NUM>, <NUM>.

The determination was carried out with the image analyzer commercial software Analysis Pro <NUM> which describes the sphericity of a particle using an algorithm applied to a source of image constituted by a SEM picture the dimension of which are selected based on the average size of the catalyst particle so as to include a statistically representative number of particles. For the catalyst sample having average particle size of <NUM> the size of the picture was <NUM>. For instance, for the catalyst sample having particle size of about <NUM> the size of the picture was <NUM> x150 µm.

Three different lots of microspheroidal MgCl<NUM>·<NUM>. 8C<NUM>H<NUM>OH were prepared according to the method described <CIT> having the following P50:.

A series of three mixtures was prepared by dry mixing the lot A of the solid adduct with the specific amount reported in Table <NUM> of Celite®. The blending was carried out as follows. <NUM> grams of the solid catalyst component were introduced in a <NUM> glass bottle and then, the amount of Celite® reported in table 1was also added. The solids were mixed by tumbling the bottle for <NUM> at 60rpm. The resulting mixtures were subject to energy break and avalanche energy determination and the results are reported in Table <NUM>.

The mixtures were prepared as described in Examples <NUM>-<NUM> with the difference that the compounds (b) reported in table <NUM> were used. The resulting mixtures were subject to energy break and avalanche energy determination and the results are reported in Table <NUM>.

The mixtures were prepared as described in Examples <NUM>-<NUM> with the difference that Examples Lot B of adduct (a) was used instead of Lot A and the SiO<NUM> based unit compounds reported in Table <NUM> were used instead of Celite® The resulting mixtures were subject to energy break and avalanche energy determination and the results are reported in Table <NUM>.

The mixtures were prepared as described in Examples <NUM>-<NUM> with the difference that Lot C of adduct (a) was used instead of Lot A and the SiO<NUM> based unit compounds reported in Table <NUM> were used instead of Celite® The resulting mixtures were subject to energy break and avalanche energy determination and the results are reported in Table <NUM>.

Claim 1:
A Ziegler-Natta catalyst component precursor comprising a dry mechanical mixture of (a) distinct particles of adducts of formula MgCl<NUM>(R<NUM>OH)n where R<NUM> is a C<NUM>-C<NUM> alkyl group, and n is from <NUM> to <NUM> having average particle size (P50a) ranging from <NUM> to <NUM> as determined according to the description and (b) from <NUM> to <NUM>% by weight, based on the total amount of (a)+(b), of distinct particles of a solid compound containing more than <NUM>% by weight of SiO<NUM> units and having average particle size (P50b) such that the ratio P50b/P50a ranges from <NUM> to <NUM>.