WO2006063973A1

WO2006063973A1 - PROCESS FOR THE PREPARATION OF A SPHERICAL SUPPORT COMPRISING MgC12 AND ALCOHOL

Info

Publication number: WO2006063973A1
Application number: PCT/EP2005/056664
Authority: WO
Inventors: Enrico Aldrovandi; Daniele Evangelisti; Gino Alessandrini; Gianni Collina
Original assignee: Basell Poliolefine Italia S.R.L.
Priority date: 2004-12-14
Filing date: 2005-12-12
Publication date: 2006-06-22

Abstract

The present invention relates to a process for preparing spherical support particles used in the preparation of catalytic components for the polymerization of olefins. The process comprises, (a) forming a mixture of an MgCl2-alcohol adduct in molten form and a liquid which is immiscible with the said adduct in a ratio such that the molten adduct forms the disperse phase, (b) suitably treating the mixture in order to obtain an emulsion, and (c) rapidly cooling the emulsion to solidify the disperse phase and collecting the solid adduct particles, said process being characterized by the fact that at least one of the steps (a) to (c) is carried out in the presence of an applied magnetic or electromagnetic field.

Description

PROCESS FOR THE PREPARATION OF A SPHERICAL SUPPORT COMPRISING MgCl2 AND ALCOHOL

The present invention relates to a process for preparing a support, in the fottn of spherical particles with a narrow size distribution, which can bs used in. the preparation of olefin polymerization supported catalysts. In particular, the present invention relates to a process for preparing the said support, which involves forming an emulsion, in a liquid medium, of a molten adduct of magnesium dihalide and a compound belonging to the group of Lewis bases, followed by rapidly cooling the said emulsion, -under suitably selected conditions for obtaining the solid adduct in the form of spheroidal particles, said process beiwg carried out at least in part in the presence of a magnetic or electromagnetic field.. This process gives support particles capable to generate catalysts that give polymers in higher yields and/or with a better morphology.

The availability of catalysts able to produce polymers with valuable morphology is a fundamental factor in avoiding problems of controlling particularly the gas-phase polymerization process (where usually catalysts having medium-large size is used and where formation of fines is to be avoided) and non-uniformity of the final polymeric product. These properties of the polymer not only allow the entire polymerization process to be controlled with ease, but also allow an improvement in possible treatments after preparation of the polymer, such as granulation, moulding, etc. Often., the morphological properties of the polymers are linked to the morphological properties of the catalyst support or precursor. The reason for this is that a support with these properties allows the preparation of a catalyst which reflects these properties and which in tarn allows the preparation of polymers of high apparent density with good flow properties. However, for polymerization processes carried out in liquid phase, in particular slurry and solution, where usually catalysts of smaller size are used, the need of having improvements in the catalyst activity may be higher than the morphology requirement in order to make polymerization process more efficient

The Ziegler/Natta catalyst components are generally able to combine these characteristics and are customarily used in the industrial polymerization process. They usually comprise a titanium compound supported on magnesium chloride in active form and, when stereospecificity is requested, they also comprise an electron-donating compound. In the polymerization process they are used together with an organo aluminum compound as activato and, when needed, also in combination with an additional stereomodulating agent (external electron donor). In order to impart the good morphological properties the supports comprising MgCl₂ can be prepared by many different processes. Some of these comprise the formation of a molten adduct of magnesium chloride and a Lewis base, followed by spraying in an atmosphere at low temperature (spray-cooling) so as to solidify the adduct.

Another general method widely used in the preparation of spherical supports comprising MgCl₂ consists in melting the adduct described previously, with stirring, in a liquid medium in which the adduct is immiscible, and transferring the mixture into a cooling bath containing a liquid at low temperature, in which the adduct is insoluble, which is capable of bringing about rapid solidification of the adduct in the form of spheroidal particles.

In the attempt to improve the morphology several variations of the above-mentioned process have been proposed. USP 5,500,396 describes a process for preparing spherical particles of MgCl₂-alcohol adduct in a liquid with a viscosity of greater than 50 cSt at 40⁰C, which involves heating the mixture with continuous stirring and finally cooling it to obtain the adduct in the form of solid particles. The cooling is carried out in the same reactor in which the MgCl₂-alcohol adduct in molten form was prepared, while bringing the temperature gradually to 40⁰C by using a jacketed reactor in which a cooling fluid is circulated. By virtue of the intrinsic properties of the high- viscosity liquid and probably also of the long cooling times (of the order of minutes), the experimental conditions are not readily controllable, as a result of which, as is seen from the data reported in the examples, this process leads to results that are not always reproducible and not always optimal in terms of either size distributions or morphology. In addition, given the operating conditions (the entire process is carried out in a single reactor), performing the process on an industrial scale as a continuous process would be highly problematical. USP 4,315,874 describes a process for preparing an MgCl₂-EtOH adduct in the form of spherical particles, which involves (a) forming a suspension of molten drops of adduct in a liquid medium, in the presence of a surfactant, and (b) transferring the said suspension, by means of a transfer tube, into a cooling bath in order to solidify the adduct particles. Good results in terms of particle size distribution are obtained only in the presence of a surfactant that, however, can then interfere in the process for preparing the final catalyst.

Specific conditions have also been proposed in WO 03/82930 for the preparation of adducts able to generate very active catalyst components. Said adducts must have a very narrow composition range (MgCl₂^mEtOH adducts in which m is from 2.5 to 3.2) a maximum amount of water up to l%wt based on the total weight of the adduct, a DSC diagram (profile) in which the highest melting Temperature (Tm) peak is over 109⁰C and has an associated fusion enthalpy (ΔH) of 103J/g or lower. Although the activity of the catalyst is actually increased, the necessity of having a very specified composition and a very carefully controlled amount of water makes the process not so flexible.

Conversely, the applicant has found a versatile and flexible process that allows obtaining on a need-basis MgCl₂-alcohol adducts capable to generate catalysts that give polymers either in higher yields and/or with a better morphology. The process of the present invention for preparing a MgCl₂-alcohol adduct comprises, (a) forming a mixture of an MgCl₂-alcohol adduct in molten form and a liquid which is immiscible with the said adduct, (b) suitably treating the mixture in order to obtain an emulsion, and (c) rapidly cooling the emulsion to solidify the disperse phase and collecting the solid adduct particles, said process being characterized by the fact that at least one of the steps (a) to (c) is carried out in the presence of an applied magnetic or electromagnetic field.

According to the present invention the term "applied magnetic or electromagnetic field" means a magnetic or electromagnetic field in addition to the natural earth's magnetic field. The imposed magnetic or electromagnetic field can be generated either by an electromagnet or by one or more permanent magnets such as magnetite-based materials. It has been found that positive effects on catalyst morphology and/or activities have been obtained by using a magnetic field having maximum intensity of 0.005 T (tesla) or higher. Preferably, the intensity is in the range 0.05 to 1 Tesla. Although not mandatory, when using permanent magnets it is advised to try to reach this intensity possibly by using more than one permanent magnets. The electromagnets are very well known in the art. In their basic set-up they are constituted by a coil wound around a soft iron or steel core; the core becomes therefore strongly magnetized when the current flows through the coil and is almost completely demagnetized when the current is interrupted.

Also the permanent magnets are very well known in the art. The first known permanent magnet was the naturally occurred magnetite, a mineral of approximate composition Fe₃O₄. Subsequently, steel alloy containing various metals took the way. For example, alloys containing, tungsten, chromium, cobalt. Very high magnetic fields are obtainable with alloy of nickel, aluminium, iron and possibly copper. Other usable alloys are those containing copper and cobalt (Alnico series). More recently, the use of steel alloys containing Samarium- Cobalt became spread out.

Depending on where the magnetic field is applied the effects on the characteristics of the adduct may be different. For example, if the magnetic field is applied to step (a) and/or (b), the adduct generated by the process shows a better morphological stability during the catalyst preparation that allows the preparation of catalyst components that, in turn, generate polymers having a very minor fraction of the broken particles that give usually problems in the operability of the plant. If the magnetic field is applied to step (c), the so obtained adduct is able to give catalyst components having a much enhanced catalytic activity.

The liquid medium used in stage (a) can be any liquid medium which is inert with respect to, and substantially immiscible with the adduct of Mg dihalide. Preferably, it is an organic liquid medium in particular selected from the group consisting of aliphatic and aromatic hydrocarbons, silicone oils, liquid polymers or mixtures of the said compounds. Particularly preferred liquid media are paraffin oils and silicone oils having a viscosity of greater than 20 cSt at room temperature and preferably between 30 cSt and 300 cSt. The alcohol forming the adduct with the Mg dihalide is preferably selected from the alcohols of formula ROH in which R is an alkyl group containing from 1 to 10 carbon atoms. The use OfMgCl₂ as a Mg dihalide is preferred. Especially preferred adducts are those of formula MgCl₂-mROH-nH₂O in which m ranges from 0.1 to 6, n ranges from 0 to 0.7 and R has the meaning given above. Among them the adducts particularly preferred are those in which m ranges from 2 to 4, n ranges from 0 to 0.4 and R is ethyl. As regards the spherical morphology, the process of the present invention allows to obtain particles having a ratio between maximum diameter and minimum diameter of less than 1.5 and preferably of less than 1.3.

The formation of the emulsion may be carried out in a mixer, such as for example a static mixer, a rotor-stator mixer or a vessel equipped with a stirring system. In the latter case, for the purpose of forming and maintaining the emulsion it is preferable to work in stage (a) under conditions such that the value λ_k of the emulsion ranges from 5 μm to 150μm and more preferably from 40μm to 130 μm. This parameter, in accordance for example with the description in the book "Mixing in the process industries" by N.Harnby, is defined by the formula λ_k=(v³/3)^1/4 in which v is the kinematic viscosity of the adduct/liquid medium mixture and 3 is the energy supplied by the stirring system. In calculating the value of λ_k according to the present invention, the term 3 is replaced by the power (P) supplied by the stirrer to the system. It is possible to apply the magnetic field in this stage either by fixing (for example via an adhesive tape) on the external or internal surface of the apparatuses one or more permanent magnets, or by placing the entire apparatus inside an hollow metallic member which is provided with an electric winding able to create the magnetic field upon passage of electric current. Preferably, in the mixer, both the value of λ_k and the Reynolds number are kept within a desired range.

The Reynolds number relating to the movement of a fluid inside a tube (Rex) is defined by the formula Re=D-vd/η in which D is the diameter of the tube, v is the linear velocity of the emulsion, d is its density and η is the dynamic viscosity. Generally, values of Re below 2000 correspond to laminar flow, while values of Re above 4000 correspond to turbulent flow. The zone between 2000 and 4000 is the so-called transition zone. The type of flow of a liquid inside a mixer is described by the modified Reynolds number (Rejvi) which is defined by the formula Re=NL²-ά7η in which N is the number of revolutions of the stirrer per unit time, L is the characteristic length of the stirrer while d and η have the meanings given above. It will be clear to a person skilled in the art that the value of ReM may be selected by choosing the most appropriate combination of parameters as necessary. In particular, it will be possible to vary both the specific parameters of the emulsion (density, viscosity and thus also the type of continuous phase) and the operating parameters such as the type and dimensions of container, the type and dimensions of the stirrer, the number of revolutions and the temperature and pressure. In the specific case of an emulsion comprising MgCk-alcohol adducts as the dispersed phase and paraffin oil or silicone oil as the continuous phase, it has been found particularly advantageous by working in the mixer at Re_M values between 10,000 and 80,000, preferably between 15,000 and 50,000 and even more preferably between 15,000 and 30,000. As mentioned above, the formed emulsion is then transferred into the cooling bath. The transfer is preferably carried out under pressure, by using a pipe connected at one end with the cooling bath. The diameter of said pipe is such that the Reynolds number in the pipe (ReT) is higher than 3000, preferably between 3000 and 10000. In any case, the skilled man in the art knows that the value of Rex may be suitably increased or decreased, as a consequence of the value of Re_M selected in the mixer.

The pipe length to connect step a) and b) may be varied within a wide range, bearing in mind, the operating limits caused, on the one hand, by the substantial pressure drops and, on the other hand, by the compactness of the plant.

Also in this step magnetic field can be applied in the same way illustrated for step (a). As mentioned previously, the emulsion is then solidified in the cooling step (b). The cooling step is carried out by immersing one of the ends of the transfer pipe containing the emulsion in the cooling bath wherein the cooling liquid is moving inside a tubular zone. According to the present invention the term "tubular zone" has the ordinary meaning of a zone having the form of a tube. Particularly preferred examples of such zones are pipes or tubular reactors. On coming into contact with the low-temperature liquid, the emulsion containing the droplets of the molten adduct is cooled, bringing about solidification of the droplets in solid particles, which can then be collected for example by means of centrifugation or filtration. The cooling liquid may be any liquid which is inert with respect to the adduct and in which the adduct is substantially insoluble. For example, this liquid can be selected from the group consisting of aliphatic and aromatic hydrocarbons. Preferred compounds are aliphatic hydrocarbons containing from 4 to 12 carbon atoms and in particular hexane and heptane. A cooling liquid temperature of between -20⁰C and 20⁰C gives satisfactory results in terms of rapid solidification of the droplets. In the case of the adduct MgCl₂TiEtC)H, in which n is between 2 and 4, the cooling liquid temperature is preferably between -10⁰C and 20⁰C and more preferably between -5°C and 15°C. Preferably in step (c) the cooling liquid is moving inside a tubular zone and the ratio v_e/v_ref of the velocity of the emulsion (v_e) coming from step (a) to the velocity of the cooling liquid (V_ref) is between 0.25 and 4, preferably between 0.5 and 2, more preferably between 0.75 and 1.5.

In the process of the present invention, with the term "velocity of the emulsion" (v_e) is intended the ratio between the volumetric rate of the emulsion and the section of the tube conveying the emulsion inside the cooling bath.

With the term "velocity of the cooling liquid" (v_ref) is intended the ratio between the volumetric rate of the cooling liquid and the section of the tubular zone conveying the cooling liquid inside the cooling bath.

It has been ascertained that a further improvement in the results of the process of the present invention can be obtained by allowing the emulsion entering the cooling bath at an angle α, which is less than 45°. The angle α is defined as the angle formed by the direction of entry of the emulsion into the cooling bath and by the direction of flow of the cooling liquid inside the tubular zone. Particularly good results are obtained when the said angle α is less than 35° and preferably less than 20°.

Another particularly preferred aspect is that of carrying out the process by combining values for the angle α of less than 20° with values for the ratio v_e/v_ref of between 0.75 and 1.5 and more preferably of unity.

In a preferred embodiment of the present invention, the cooling bath consists of a loop reactor wherein the cooling liquid is circulated, the angle α formed by the direction of entry of the emulsion in the loop and by the direction of flow of the cooling liquid is less than 45° and preferably less than 20°. Also in this step magnetic field can be applied in the same way illustrated for step (a).

As described previously, the supports prepared by the process of the present invention are particularly suitable for preparing catalytic components for the polymerization of olefins. The said catalyst components are obtainable by reacting a transition metal compound of formula MP_x, in which P is a ligand that is coordinated to the metal and x is the valence of the metal M which is an atom selected from the Groups 3 to 11 or the lanthanide or actinide groups of the Periodic Table of the Elements (new IUPAC version), with the supports of the invention. Particularly preferred transition metal compounds are Ti and V halides, alcoholates or haloalcoholates. Other preferred transition metal compounds are the homogeneous ones such as those described in EP 129 368 or the mono-cyclopentadienyl catalyst systems such as those described in EP 416,815 and EP 420,436.

In a preferred embodiment, the adduct can be directly reacted with the Ti compound or it can be previously subjected to thermal controlled dealcoholation (80-130⁰C) so as to obtain an adduct in which the number of moles of alcohol is generally lower than 3 preferably between 0,1 and 2,5. The reaction with the Ti compound, preferably TiCl₄, can be carried out by suspending the adduct (dealcoholated or as such) in cold TiCl₄ (generally 0⁰C); the mixture is heated up to 80-130⁰C and kept at this temperature for 0,5-2 hours. The treatment with TiCl₄ can be carried out one or more times. The maleate can be added during the treatment with TiCl₄. The treatment with the electron donor compound can be repeated one or more times.

The preparation of catalyst components in spherical form is described for example in European

Patent Applications EP-A-395083, EP-A-553805, EP-A-553806, EPA-601525 and

WO98/44009.

The solid catalyst components obtained according to the above method show a surface area (by

B.E.T. method) generally between 20 and 500 m²/g and preferably between 50 and 400 m²/g, and a total porosity (by B.E.T. method) higher than 0,2 cm³/g preferably between 0,2 and 0,6 cm³/g.

The porosity (Hg method) due to pores with radius up to lO.OOOA generally ranges from 0.3 to

1.5 cm³/g, preferably from 0.45 to 1 cm³/g.

In particular, as mentioned above, the process of the present invention is very versatile because, as mentioned above, it allows to easily prepare catalyst components either having improved morphological stability or, simply by varying the step to which the magnetic field is applied, improve the polymerization activity of the catalysts.

The solid catalyst components according to the present invention are converted into catalysts for the polymerization of olefins by reacting them with organoaluminum compounds according to known methods.

In particular, it is an object of the present invention a catalyst for the polymerization of olefins

CH₂=CHR, in which R is hydrogen or a hydrocarbyl radical with 1-12 carbon atoms, comprising the product of the reaction between:

(a) a solid catalyst component as described above;

(b) an alkylaluminum compound and, optionally,

(c) one or more electron-donor compounds (external donor). The alkyl-Al compound (b) is preferably selected from 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 mixtures of trialkylaluminum's with alkylaluminum halides, alkylaluminum hydrides or alkylaluminum sesquichlorides such as AlEt₂Cl and Al₂Et₃Cl₃. The external donor (c) can be of the same type or it can be different from the maleates of formula (I). Suitable external electron-donor compounds include silicon compounds, ethers, esters such as ethyl 4-ethoxybenzoate, amines, heterocyclic compounds and particularly 2,2,6,6-tetramethyl piperidine, and ketones. The examples which follow are given as non- limiting illustrations of the invention. EXAMPLES Characterization Determination of XJ.

2.5 g of polymer were dissolved in 250 ml of o-xylene under stirring at 135°C for 30 minutes, then the solution was cooled to 25°C and after 30 minutes the insoluble polymer was filtered. The resulting solution was evaporated in nitrogen flow and the residue was dried and weighed to determine the percentage of soluble polymer and then, by difference the xylene insoluble fraction

Example 1

Preparation of the MgCl₂-alcohol adduct In a vessel reactor of the capacity of 3 litres equipped with an IKA stirrer providing very efficient suspension of the slurry, 2 litres of freshly produced slurry of MgCl₂ support from SF5 plant were introduced. The reactor was hosted in a hallow cylinder which was in fact a stator with internal diameter of 15 cm, derived from an electric engine to which it was applied a current of 50V and 12.5A. The maximum magnetic field produced was 0.062 Tesla. The reactor contained a heating/cooling tubular circuit so to provide constant temperature conditions during the test. The electro magnet was started up, and so the cooling system, to compensate the heating generated by the electro-magnet under effect of circulating AC current. The slurry/suspension, always kept under stirring, was taken from the starting temperature of 11.8°C up to 20⁰C in about 30 minutes and then kept at this temperature for 3 hrs. After this time elapsed, a portion of the slurry was washed and dried to flowability in a funnel provided with sintered glass filter, always under nitrogen atmosphere. The dried support was then used for catalyst preparation. Preparation of the solid catalyst component

Into a 11 steel reactor provided with stirrer, 800cm³ of TiCl₄ at 0⁰C were introduced; at room temperature and whilst stirring 16 g of the adduct were introduced together with an amount of diisobutylphthalate (DIBP) as internal donor so as to give a donor/Mg molar ratio of 10. The whole was heated to 100⁰C over 90 minutes and these conditions were maintained over 120 minutes. The stirring was stopped and after 30 minutes the liquid phase was separated from the settled solid maintaining the temperature at 100⁰C. Two furthe r treatments of the solid were carried out adding 750 cm³ of TiCl₄ and heating the mixture at 120⁰C over 10 min. and maintaining said conditions for 60 min under stirring conditions (500 rpm). The stirring was then discontinued and after 30 minutes the liquid phase was separated from the settled solid maintaining the temperature at 120⁰C. Thereafter, 3 washings with 500 cm³ of anhydrous hexane at 60⁰C and 3 washings with 500 cm³ of anhydrous hexane at room temperature were carried out. The solid catalyst component obtained was then dried under vacuum in nitrogen environment at a temperature ranging from 40-45⁰C. The analysis showed a titanium content of 2.6%, a Mg content of 19.5%, and a DIBP content of 10.1%. Propylene polymerization test

A 4 litre steel autoclave equipped with a stirrer, pressure gauge, thermometer, catalyst feeding system, monomer feeding lines and thermostatting jacket, was used. The reactor was charged with 0.01 gr. of solid catalyst component 0,76 g of TEAL, 0.076g of dicyclopentyldimetoxy silane, 3.2 1 of propylene, and 1.5 1 of hydrogen. The system was heated to 70⁰C over 10 min. under stirring, and maintained under these conditions for 120 min. At the end of the polymerization, the polymer was recovered by removing any unreacted monomers and was dried under vacuum. The polymerization results are reported in Table 1. Example 2 In a vessel reactor equipped with an IKA RE 166 stirrer 250 g of MgCl₂-EtOH adduct (of the same kind of the support used in example 1) plus extra 13 ml of EtOH were placed. The temperature was raised up to 125°C and kept at this value for 3 hours. After that, 1600 cm³ of OB55 vaseline oil were introduced and, while keeping the temperature at 125°C, the stirring was brought to 1500 rpm and kept at that value for two minutes. The container is then pressurized and the emulsion is transferred into a cooling bath containing hexane at a temperature of 12°C, through a transferring pipe maintained at a temperature of 125⁰C and coupled with a strip/ribbon obtained by a seri es of permanent magnets joined head-tail one to the other. The magnets were of Samarium-Cobalt type having dimensions of 12x4x35 mm and sold by Klaus Union S.r.l. The magnetic field generated was about 0.26 Tesla.

The solid support is then crystallized washed and dried as usual.

The solid catalyst component was prepared by following the same procedure set forth in example 1 with the only difference that only two treatments with the TiCl₄ were carried out. The analysis showed a titanium content of 4.2%, a Mg content of 15.6 and a DIBP content of 16,5%. The obtained catalyst was used in a propylene polymerization test carried out under the same conditions described above. The polymerization results are reported in Table 1. Comparison Example 3

The procedure for preparing the MgC^-alcohol adduct of Example 2 was repeated, with the difference that the magnets were not used.

The solid catalyst component was prepared by following the same procedure set forth in example 2. The analysis showed a titanium content of 3.3%, a Mg content of 18.3%, and a DIBP content of 14.3%. The obtained catalyst was used in a propylene polymerization test carried out under the same conditions described above. The polymerization results are reported in Table 1.

TABLE 1

Claims

1. Process for preparing a MgCl₂-alcohol adduct comprising (a) forming a mixture of an MgCl₂-alcohol adduct in molten form and a liquid which is immiscible with the said adduct, (b) suitably treating the mixture in order to obtain an emulsion, and (c) rapidly cooling the emulsion to solidify the disperse phase and collecting the solid adduct particles, said process being characterized by the fact that at least one of the steps (a) to (c) is carried out in the presence of an applied magnetic or electromagnetic field.

2. Process according to claim 1, characterized in that the magnetic field has intensity in the range 0.05 to 1 Tesla.

3. Process according to claim 1 characterized in that the magnetic field is generated by an electromagnet.

4. Process according to claim 1 characterized in that the magnetic field is generated by one or more permanent n magnets.

5. Process according to claim 4 characterized in that the permanent magnet is selected from Samarium-Cobalt alloy.

6. Process according to claim 1 in which the MgCl₂-alcohol adduct has formula

MgCl₂-HiROH ^nH₂O in which m ranges from 0.1 to 6, n ranges from 0 to 0.7 and R is an alkyl group containing from 1 to 10 carbon atoms.

7. Process according to claim 1 characterized in that the magnetic field is applied to step

(a) and/or (b).

8. Process according to claim 1 characterized in that the magnetic field is applied to step

(C)

9. Spheroidal MgCl₂-alcohol adduct particles obtainable by the process according to anyone of claims 1 -8.

10. Catalyst components for the polymerization of olefins obtained by reacting a transition metal compound of formula MP_x with a spheroidal adduct according to claim 8 , wherein M is a metal selected from the Groups 3 to 11 or the lanthanide or actinide groups of the Periodic Table of the Elements (new IUPAC version), P is a ligand coordinated to the metal M, x is the valence of the metal M.