Catalysts and process for the polymerization of olefins

The invention relates to catalysts and processes for the polymerization of olefins particularly ethylene or a mixture thereof with an alpha-olefih and/or with a diolefin or more than one such comonomer, or for ^;the polymerization of an alpha—olefin such as propylene or butene-l.

The invention provides a .catalyst. for the polymerization of olefins comprising a product of reaction , between a hydride or organo-metallic compound of a metal of Group I, II or III of the Periodic System with the product obtained by contacting a titanium tetra- , . : :, * . ׳ , (except'fluoride) 1 halide with a support comprising an anhydrous magnesium halide/ _;or zino halide in an active form in which the highest intensity, diffraction line in the X-ray powder spectrum Is’ replaced by a halo of lower intensity and/or having a surface area greater than 3 square metres per gram, preferably 10 or even 15 square metres per gram. Such catalysts have valuable properties., in particular a very high activity which in many oases makes it not necessary to purify the polymer at the end, of the polymerization.

Anhydrous magnesium chloride in many active forms has an X-ray spectrum in which the diffraction line appearing • 0 ' at a lattice distance (d.) of 2.56 A, which is the most intense in the spectrum of magnesium chloride of the normal in .

type, becomes less intense while/its place a broadened halo appears which is in the range of d from 2.56 $ to 2.95 A. Likewise the X-ray spectrum of many active forms of magnesium bromide has a diffraction line at d=>2.93 2, ן which is the most intense in the spectrum of magnesium

- ' W bromide of the normal type and which becomes less intense while there appears a broadened halo in the range of d from 2.SO X to 3.25 S .

The supported catalyst components can be prepared by many methods. One consists in contacting, even at room temperature, previously activated anhydrous magnesium or zinc halide with the titanium tetrahalidej for a time sufficient for fixing at least part of titanium compound on the support. The contact is preferably effected by adding the titanium: tetrahalide to a suspension in an inert solvent of the activated anhydrous magnesium or zinc halide and evaporating the solvent at the end of the treatment. The amount of titanium tetrahalide used in this type of preparation is preferably from 0.1% to 5% by weight with respect to the magnesium or zinc halide,

ד , It is however possible, and this is the preferred method, to carry out the preparation of the supported catalyst component by subjecting the anhydrous magnesium or zinc halide to grinding in the presence of the titanium tetrahalide, preferably used in an amount lower than 10% by weight with respect to the support.

It is also possible to obtain the supported catalyst component by heating the anhydrous magnesium or zinc halide, in an active form with the titanium tatroJiR? used in stoichiometric excess with respect to the anhydrous halide at a relatively high ־temperature, generally greater

I than 70°C and cooling the mixture and separating from it . the magnesium or zinc halide carrying the supported tetrahalide. In the case of titanium tetrachloride one operates preferably at the boiling temperature of the halide.

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Th© U.S. Patent Specification No. 2,981,725 discloses a process for polymerizing mono-alpha-olefins of 2 or 3 carbon atoms in the presence of an inert hydrocarbon solvent and with the aid of a catalyst which consists essentially of the product of reaction of an aluminium alkyl or aluminium alkyl halide with a chloride of, inter alia, titanium, formed on the surface of a carrier which may, inter alia, be magnesium chloride. As compared with the yield obtainable by this known process, the yield of the process according to this invention is greater by 1(? -10^ (e.g. 120,000 - 600,000 g of polymer for each gram of titanium in the catalystץ as compared with about 2.5 g of polymer per gram of titanium in the catalyst of the aforesaid known process). In view of the high polymer yield in the process of the invention the residual catalyst or its components need not be removed from the polymer; which has to be done in the known process.

The preparation of the previously activated magnesium and zinc halide can be carried out according to many methods:: one of these consists in subjecting anhydrous magnesium or zinc halide to mechanical treatments such as grinding for a time and under conditions forming the magnesium and zinc halides in to an active form.

Grinding is preferably effected in a ball mill in the absence of any inert solvent.::: The duration of the treatment in general depends on the effectiveness of the grinding apparatus. Just as an example the duration is ‘⁵־ cr t about 1 hour when the support le ground in a centrifugal mill loaded with porcelain balls, Shorter times may be attained when there are used mills with a particularly high grinding efficacy, for instance vibrating ball mins. The grinding conditions suited for the activation of the magnesium or zinc halide in the absence of the titanium tetrahalide are also useful when the magnesium or zinc halides are activated in the presence of the titanium tetrahalide.

According to another method very active forms of magnesium and zinc halides can be obtained by decomposition of an organo-metallic compound of the formula WgX. or RZnX wherein R is alkyl or aryl, X is a halogen, or by reacting the organometallic compound with the stoichiometric or greater than stoichiometric »mount of a halogen-containing compound such as anhydrous gaseous hydrogen chloride.

A further method useful for the preparation of very active forms of magnesium and zinc halides comprises dissolving the halide in an organic solvent such as an alcohol, ether or an amine and then quickly evaporating the solvent, completing the removal of the solvent by heating the halide under reduced pressure at a temperature above 100°C and generally from 100° to 400°C. Thus anhydrous magnesium chloride in an active form has been obtained from a solution in methanol.

The supported catalyst components of the invention generally contain amounts of the titanium compound which vary from very low values, such as 0.01% by weight with

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respect to the support, to higher values which may attain 20$ by weight or more. This amount' is preferably from 0.1$ to 5$ by weight with respect to the magnesium or zinc halide. In addition to the titanium compound bound to the support itself, there may be some in the form of a separable physical phase,

The hydride or organometallic compound of a metal of the Group I, II or III of the Periodic System is preferably of th© following formulae:

. idH ca h₂Al(C₂H_g)₅, A1(C₂H₅)₂C1, Al(iC₄H₉)₃, Al(iC₄H₉)₂Cl,

Al(iC₄H₉)2H, Al(C₂H₅)₂Br, Li-Al(iC₄H_g)₄, LiC₄H₉, MC2H₅)₂/ organometallic The molar ratio between th© ffietelergeMe- compound and the titanium tetrahalide is not critical. In the case of the polymerization of ethylene the molar ratio Al/Ti is preferably from 50 to 1000*

Polymerization can be carried out in a liquid phase, in the presence or absence of an inert solvent or in the gaseous phase. The polymerization temperature may be from -80°C to +200°C, but is preferably between 50° and 100°C, at atmospheric pressure or above. The molecular weight of the polymer may be regulated by carrying out the polymerization in th© presence of an alkyl halide,, or an organometallic cadmium or zinc compound or hydrogen.

The use of such molecular weight regulators tends considerably to lower the catalytic activity of normal Ziegler-type catalysts obtained from a compound of a transition metal and an organometallic compound of a metal of Groups I to III. The catalysts of the invention are little Influenced as to activity by the presence of such substances for the regulation of molecular weight, In the polymerization of ethylene, for instance, it is possible to regulate the molecular weight of the polymer within a range of practical Interest corresponding to values of intrinsic viscosity in tetralin at 135°C, from about 1,5 ¾0 3 dl/g without the yield in polymer dropping to values below which it would be necessary at the end of the polymerization to purify the polymer from the catalyst residues. The polyethylene thus obtained Is generally a substantially linear and highly crystalline

V ־ polymer having density values equal to or greater than 0.96 g/cc and endowed with a processability, in particular with regard to injection moulding, which is very high and in general higher than that of the polyethylene obtained with the aid of normal Ziegler-type catalysts. The titanium content is generally lower than 20 parts per million.

The invention is illustrated by the following Examples; the percentages being by weight where not specifically indicated.

Into a 330 co centrifugal mill loaded with 4 porcelain balls, two with a diameter of 31.9 mm and two with a diameter of 40.9 mm, were introduced 48 g of anhydrous magnesium chloride having a surface area of 1 m²/g together •?8 with 8 g of titanium tetrachloride, and were then ground for 2 hours. Analysis of the ground product showed: fl ® 2,7%, Cl ® 72%. Its surface area was 20 m׳/g. 0*06 g of this ground product were then used in a polymerization test of ethylene. Into a 1,8 litre autoclave of.stainless steel cleansed with nitrogen were introduced 1000 cc of technical heptane and then 2 g of aluminium tri-iso-butyl (Al(iO4H₉)₃).

The temperature was brought up to 75°C and 0.06 g of the ground product suspended in 50 oe of n-heptane were introduced into the autoclave. Immediately hydrogen was introduced Up to a pressure of 3 atm, and then ethylene up to a pressure of 10 atm. The temperature rose to about 85°C. The pressure was maintained constant at this value by continuously feeding ethylene. After 2 hours the suspension was discharged from the autoclave.

. . . . . . . , ' ״ '

The polymer was separated by filtration and dried under vacuum at 100°C. There were obtained 195 S of polyethylene having an Intrinsic viscosity In tetralin at 135⁰¢ of

2.5 dVg׳. The yield in polymer was 121,000 g/g ' of titanium, ,־ '

Example 2.

7.3 g of anhydrous magnesium chloride as used in Example 1 were ground for 1 hour in the ball mill of Example 1 in the presence of 0.5178 g of titanium ־ tetrachloride, The titanium content of the ground product , , □ was 1.4%. Th® surface area of the product was 15 m /g.

- C»

0.0490 g of the ground product were used in the polymerization of the ethylene as in Example 1. After 4 hours there were obtained 395 g of a polymer having an. intrinsic viscosity in tetralin at 135°C of 2.5 dl/g, The yield, in polymer was 570,000 g/g of titanium.

Example g of anhydrous magnesium chloride as used in Example 1 were ground for 3 hours in a bail mill of the type used in this Example. The surface area of the ground product was 22 m²/g. 10 g of this ground product, 50 .cc of n-heptane and 0.590 g of titanium tetrachloride were introduced into a 250 cc flask fitted with a stirrer. This' I suspension was stirred for 1 hour at room temperature after ׳:. which the solvent was evaporated off. In the solid product thus obtained there was present 10 of titanium. 0.133 g of this product were then used in the polymerization of ethylene as in Example 1. After 4 hours, there were obtained 400 g of polymer with an intrinsic viscosity in tetralin at 135°C of 2.1 d׳l/g. The yield in polymer was 300,000 g/g of titanium.

Example

9.25 g of the ground magnesium chloride as used in Example 1, 0.14 g of titanium tetrachloride and 50 cc of n-heptane were treated under the same conditions as in the preceding Example. The surface area of the ground product was 22 m /g. The solid product thus obtained showed on analysis a titanium content of 0.360. 0.0738 g of this product were then used in the polymerization of ethylene as in Example 1. After 4 hours there were obtained 151 g of polymer with, an intrinsic viscosity in tetralin at 135°C of 2.9 d׳l/g. The yield in polymer was 590,000 g/g of titanium.

g of magnesium chloride as used in Example 1 was ground under the same conditions as. in Example 3. The surface area of the ground product was 22 m /g. 0.59 g of titanium tetrachloride and 75 co of n-heptane were treated under the same conditions as in Example 3. The solid product thus obtained contained 0.88% of titaniwu 0.0746 g of this product were used in the polymerization of ethylene as in the preceding Examples. After 4 hours ׳ ׳. there were obtained 182 g of polymer with an intrinsic viscosity in tetralin at 135°C of 2.4 dl/g. The yield in polymer was 277,000 g/g titanium.

Example 6

The solid catalytic product of Example 5 from which the solvent had been removed by evaporation was washed with n-heptane until the disappearance of the reaction of chlorine ions from the liquid. The surface area of the product was 22 m /g. The titanium content of the washed product was 0.16%. 0.4029 g of this product were used in the polymerization of ethylene as in Example 1. After 4 hours of polymerization there were obtained 279 g of polymer. The yield amounted to 435,000 g/g of titanium.

Example 7 g of an anhydrous magnesium chloride which had been ground for 2.5 h. in the ball mill of Example 1, whose surface area was 22 m /g, was Introduced into an autoclave (provided with a stirrer and fitted with a filter plate at th® bottom) containing JOO cc of titanium tetrachloride and heated up to 1J5°C. After 1 hour of heating the excess of titanium tetrachloride was removed by filtering. The solid product left behind in the autoclave was repeatedly washed with cyclohexane until the total disappearance of the. titanium tetrachloride.

Analysis of the solid product thus obtained, showed a titanium content of 0.66% and 72.8% of chloride. 0.170 g of this solid product were then used in the polymerization of ethylene as in the preceding Examples, After 4 hours of this polymerization there were obtained 448 g of polymer with a yield in polymer of 400,000 g/g of titanium. Example 8

7*1 g of magnesium bromide were ground for J hours in the ball mill of Example 1 in the presence of 0.5120 g of titanium tetrachloride. The .titanium content of the ground product was 1.3%.- The surface area of thia product amounted to 27 m^/g. 0.051 g of this product were used in the polymerization of ethylene under the conditions of the preceding Examples. After 4 hours there were obtained 330 g of a polymer having an intrinsic viscosity of 2.3 dtt/g. The yield in polymer amounted to 500,000 g/g titanium.

12.

Example 9

The magnesium chloride used was obtained by reaction of ethyl magnesium chloride (CgH^NgCl) in solution in diethyl ether with anhydrous gaseous hydrogen chloride which was bubbled through the solution until magnesium chloride precipitated which was then filtered and dried at 200°C under vacuum. The surface area of the product was 142 m /g and its X-ray powder, spectrum showed a marked broadening of the diffraction line at d2.56־־ 0 ' Ϊ' .

A. 9.25 g of this product, 0.14 of titanium tetrabromide and 50 cc of n-heptane were introduced into a 250 co flask fitted with a stirrer. The suspension was stirred for !hour at room temperature, ׳after which the solvent was * \ '1 ^,׳fii.

evaporated off. 0.073 g of this product! were used in the polymerization of ethylene under the same conditions as those used in the preceding Examples, obtaining after hours 150 g of polyethylene having an intrinsic viscosity of 2.3 dl/g.

'Exanrolo 10 ”

The magnesium chloride used was obtained by fast evaporating a solution in 200 co of methanol of 15 g of

2 ’ ׳ ' magnesium chloride having a surface area of 1 m 7g and then completing the removal of the alcohol by heating the product at 300°C under vacuum. The magnesium chloride so obtained had a surface area of 32 ־:.jmi/g, its X-ray spectrum showed a marked broadening of the diffraction line which appears at d56*2־־ S in the spectrum of magnesium chloride of the normal type. 9.25 g of this product, 0.14 g titanium tetrachloride and 50 cc of n-heptane were introduced into a

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250 cc flask fitted with a stirrer. The suspension was stirred for 1 hour at room temperature after which the solvent was evaporated off. 0.05 g of this product were used in the polymerization of ethylene as in. the preceding Examples, 150 g of polyethylene having an intrinsic viscosity of 2.1 dd/g» were obtained.

Example 11

8.17 g of anhydrous MgCl, calcined at 45O°C for 48 hours in a stream of gaseous HOI and 0.41 g of 1101¢ were co-ground in a nitrogen atmosphere at 20°C for 16 hours, in a glass mill (100 mm long, 50 mm diameter) containing 550 g of steel balls of a diameter of 9.5 mm each. The surface area of the ground product was 22 m^/g.;

Into a stainless steel autoclave having a capacity of 1.2 liters, fitted with a manometer, and a stirrer and maintained at a temperature of 16°C were introduced 418 g of propylene and then ethylene up to a pressure of 9.7 atm. Then 0.036 g of the ground mixture prepared as described above and having a Ti content of 1.20%, which had been made to react with 1.6 g (2 cc) of Ald-C^Hg)^ and 50 cc of anhydrous n-heptane were introduced under nitrogen pressure into the autoclave.

During the run the pressure of the autoclave was maintained constant by feeding ethylene. The polymerization was interrupted after 4 hours. The mass discharged from the autoclave amounted to 143 g of dried product,

י ) corresponding to a yield of 398,000 g/g of Ti. This product was riain. ethylene-propylene copolymer containing 60.5% by weight of propylene.