DE2234231A1 - PROCESS FOR THE POLYMERIZATION OF AETHYLENE, IF NECESSARY IN A MIXTURE WITH 1-OLEFINS - Google Patents

Description

Gelsenkirchen-Buer, July 3, 1972

Veba-Chemie Aktiengesellschaft Gelsenkirchen-Buer

Process for the polymerization of ethylene, if appropriate

in a mixture with 1-olefins

The invention relates to a process for the production of polyethylene Particularly suitable for processing into finished plastic parts in the extrusion process.

From the German Offenlegungsschrift 1 420 573 it is already known that for the polymerization of aliphatic olefins of the general formula CH ₃ = CHR, in which R denotes a hydrogen atom or an alkyl radical, such catalysts are suitable which are prepared by adding to solid inorganic , optionally calcined, porous carrier materials, compounds of IV. to VI. Subgroups of the periodic table, which contain organic residues bound to the metal via an oxygen atom, are adsorbed and only then with metal alkyl compounds of II. And III. Group of the periodic table converts, the weight ratio of carrier mass to compounds of IV. To VI. Subgroup should be in the range of 1: 1 and 100: 1.

These catalysts have been especially used for polymerization of propylene to predominantly amorphous polymers proved to be suitable. However, the catalyst activity is both in the Polymerization of propylene as well as of ethylene only moderately, so that, apart from an uneconomical high catalyst consumption, cumbersome measures have to be taken,

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in order to remove the heavy metal residues of the catalyst from the polymer again, so that when the polymers are processed Plastic parts discoloration with stabilizers and other packaging surcharges can be avoided. Moreover, it receives with the catalysts belonging to the prior art, ethylene polymers which, because of their relatively narrow molecular weight distribution, are suitable for processing into finished parts in the extrusion process are not very suitable because it is known that if the molecular weight distribution is not sufficiently broad, the output is low and the surfaces of the finished parts have significant defects due to melt fracture. For example, does the Corrugation of the surface of hollow bodies caused by melt fracture easily leads to stress cracking.

In contrast, it has now surprisingly been found that polyethylene with an extremely broad molecular weight distribution, the does not have the deficiencies described above, can be prepared by using a catalyst based on chromium (III) acetylacetonate used, where the catalyst activity is so high, that special measures to remove catalyst components from the polymer are unnecessary.

The invention therefore relates to a process for the polymerization of ethylene, optionally in a mixture with 1-olefins and / or in the presence of hydrogen as molecular weight regulator with catalysts made from compounds of VI. Subgroup of the periodic table and organoaluminum compounds using inert hydrocarbons as diluents or in the gas phase at temperatures between 40 and 110 ⁰ C and pressures between about 10 and 100 atmospheres, which is characterized in that a catalyst is used which in the absence of moisture and molecular oxygen has been produced from chromium (III) acetylacetonate, silica and triisobutylaluminum, with 0.5 to 5% by weight of chromium (III) acetylacetonate being applied to the silica or a material containing silica and then applied with triisobutylaluminum

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has been reacted in molar ratios of aluminum to chromium compound of 10 to 200: 1.

The application of the chromium (III) acetylacetonate to the silica can for example be done so that the silica in a solution of chromium (IIl) acetylacetonate in an aliphatic Hydrocarbon ^ i entered at elevated temperature with stirring will. The chromium compound is adsorbed by the silica, which can be seen from the fact that it can be extracted with a polar solvent such as methanol, can be obtained back unchanged. Another method, silica with chromium (III) ace'tylacetonate to prepare, consists in the fact that a heated solution of the chromium compound in an aromatic hydrocarbon, preferably benzene, onto which the silica is sprayed with stirring or mixing and the solvent evaporates. For example, pyrogenic silica or precipitated silica with a large surface area are suitable as silica, The concentration of the hydroxyl groups on the surface seems to be responsible for the fixation of the chromium (III) acetylacetonate of to be of great importance. On the other hand, water moisture adhering to the surface of the silica is harmful and. must from the use according to the invention of the catalyst support can be removed by drying at elevated temperatures. "Also silica containing support materials, for example cracking catalysts, can be used according to the invention. Furthermore, it is expedient to use a silica with a high bulk density and good flowability to use as a catalyst support if you get polymer powder with the same properties want. The polymerization pressures can be selected from atmospheric pressure to 100 atmospheres, preferably 10-100 atmospheres will.

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example 1

A 250 ml three-necked flask equipped with a stirrer, dropping funnel, capillary and descending condenser was filled with 20 g of dried silica F-5 (manufactured by Koninklijke Zwavelzuurfabrieken v / h KETJEN NV). 41.3 ml of benzene chromium (III) acetylacetonate solution with a concentration of 10.01 g / l were added dropwise to the silica at 110 ^{° C. with vigorous stirring over the course of 70 minutes.} The benzene evaporated immediately and got into the condenser with nitrogen introduced through the capillary and was condensed there. After completion of the dropwise addition, the mixture to completely remove traces still present benzene was heated for 20 minutes at a pressure of 1 Torr to 120 ⁰ C.

In a 2 liter steel autoclave, 0.441 g of the silica loaded with 0.3 μl of ^{chromium were added under nitrogen to a solution, heated to 50 °} C., of 0.5 g of triisobutylaluminum in 1 liter of hexane. The nitrogen was displaced by ethylene. Hydrogen was then injected to a partial pressure of 6.2 atmospheres. Immediately thereafter, the ^{mixture was heated rapidly to 75 °} C. and ethylene was injected in the process until a pressure of 33.6 atmospheres had been reached. The temperature was kept at 75 ^° C. and the pressure was kept constant at 33.6 atmospheres over the further duration of the experiment by adding ethylene. After one hour - calculated from the start of heating - the polymerization was started by cooling and letting down the unreacted ethylene terminated. After cooling to about 50 ⁰ C, the resultant polyethylene was filtered and dried for 3 hours at 80 ⁰ C i. v.
Yield: 70 g;

Reduced specific solution viscosity: 7 »3 dl / g The powdery polymer is very free-flowing and practically free from dust.

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Example 2

In a solution of 0.78 g of chromium (III) acetylacetonate in 500 ml of hexane, 5 g of silica of the type Aerosil 380 (manufactured by DEGUSSA) dried ^{at 110 °} C. were introduced. This suspension was heated to boiling for one hour.

In a 2 liter steel autoclave, 990 ml of hexane, 0.2 g of triisobutylaluminum and 11 ml (= 0.05 mg atom of Cr) of the suspension of the chromium component in hexane prepared in the manner described above were poured in succession under nitrogen. Then the nitrogen was displaced by ethylene at atmospheric pressure, hydrogen was injected up to a pressure of 6.2 atmospheres and then ethylene up to a total pressure of 33.6 atmospheres. The contents of the autoclave were then ^{heated to 75 °} C. with stirring and kept at this temperature for the duration of the experiment. The pressure of 33.6 atmospheres was also kept constant by forcing in more ethylene. After one hour - calculated from the beginning of the ethylene supply - the polymerization was terminated by letting down the unreacted ethylene. The solid was filtered off and i. V. dried at 80 ⁰ C.

Yield: 46.5 g;
reduced specific solution viscosity; 6.5 dl / g

Example 3 '

In a solution of 180 mg of chromium (III) acetylacetonate in 480 ml of hexane at 60 ⁰ C 5 g at 110 ⁰ C dried silica of the type Aerosil 380 (manufactured by DEGUSSA) was added with stirring. The suspension was then heated to the boil for one hour.

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A 2 liter steel autoclave was filled in succession under nitrogen: 950 ml of hexane, 0.2 g of triisobutylaluminum and 48.5 ml (= 0.05 mg atom of Cr) of the suspension of the reaction product of silica and chromium (III) acetylacetonate. The procedure for this mixture was otherwise as in Example 2. Yield: 276 g of polyethylene;
reduced specific solution viscosity: 4.7 dl / g

Example 4

To a warmed at 50 ⁰ C suspension of 5 g of dried silica Silica F-5 (manufactured by Koninklijke Zwavelzuur-. Fabrieken v / h KETJEN NV) in 250 ml of hexane was added a solution of 102 mg of chromium (III) -ac etylacetonat in 150 ml of hexane was added dropwise over 30 minutes with stirring. The mixture was then stirred ^{at 50 °} C. for a further 30 minutes. After cooling, 21.6 ml (= 0.025 mgAtonTCr) of the suspension were stirred with 10 g of free-flowing, powdery polyethylene and evaporated to dryness under reduced pressure. This product was fluidized in a fluidized bed reactor at 75 ^° C., 31 atmospheres and a gas velocity of 0.2 m / sec with ethylene which had been charged with triisobutylaluminum. After 10 hours, the experiment was terminated after the unreacted ethylene was let down.
Yield: 83.5 g;
reduced specific solution viscosity: 9.7 dl / g

example

21.5 ml (= 0.025 mgAtom Cr) of the suspension of the reaction product of silica and chromium acetylacetonate described in Example 4 diluted with hexane to a volume of 1 liter, the hexane being 3 ml of a 10 # strength triisobutylaluminum solution in hexane had been added. Then how

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Proceed in example 2. -

Yield: 224 g of polyethylene;

Reduced specific solution viscosity: 7.7 dl / g The polymer was very free-flowing and practically free of dusty powder components.

Example 6

In a 2 l autoclave, 43 ml (= 0.05 mg of atom Cr) of a suspension of the reaction product of silica with chromium (III) acetylacetonate in hexane were added under nitrogen to a solution of 0.3 g of triisobutylaluminum in 960 ml of hexane, which had been prepared exactly as described in Example 4. The nitrogen was displaced by flushing with ethylene. 20 g of propylene were metered into the autoclave. Polymerization and work-up were then carried out under the conditions specified in Example 2.
Yield: 104 gi

Reduced specific solution viscosity: 3.0 dl / g. As a copolymer, the product had a lower density than the homopolymer of 0.952 g / ml and an increased methyl group content of 13.4 CH ₃ / 1,000 C.

Comparative example 1

A solution of 178 mg of vanadium (III) acetylacetonate in 300 ml of hexane was added dropwise ^{at 50 °} C. with stirring to a suspension of 5 g of dried Aerosil 380 (manufactured by DEGUSSA) in 200 ml of hexane. The suspension was then stirred ^{at 50 ° C. for a further hour.}

980 ml of hexane, 0.2 g of triisobutylaluminum and 24.5 ml (= 0.025 mg of atom V) of the suspension described above were introduced successively into a 2 liter steel autoclave under nitrogen. Exactly as in Example 2 was then followed. Yield: 12 g;
reduced specific solution viscosity: 6.6 dl / g

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Comparison experiment 2

To a suspension of 5 g of dried Aerosil 380 (manufactured by DEGUSSA) in 400 ml of hexane to Hess at 50 ⁰ C with stirring over 30 minutes a solution of 211 mg of tetra-n-propyl titanate in 100 ml of hexane is added dropwise. The suspension was then stirred ^{at 50 ° C. for a further hour.}

22.8 ml (= 0.034 mgAtom Ti) of this suspension were under nitrogen in a 2 liter autoclave to 980 ml of 0.2 g of triisobutylaluminum given parent hexane. Exactly as in Example 2 was then followed. After cooling and letting down the ethylene it was found that the suspension did not contain any polymer powder.

Comparative experiment g

In a solution of 160 nigChrom (III) acetylacetonate in 500 ml of hexane at 60 ⁰ C with stirring within 5 minutes 5 »05 g of ^ - aluminum oxide, which had been obtained by precipitating aluminum hydroxide with carbon dioxide from alkaline aluminate solution and added Calcination of the washed and dried hydroxide at 500 ^° C. The suspension was heated to boiling for a further hour.

955 ml of hexane, 0.2 g of triisobutylaluminum and 48.5 ml (= 0.045 mg of atom Cr) of the suspension described above were introduced successively into a 2 liter steel autoclave under nitrogen. Then the procedure was exactly as in Example 2. Yield: 13 g;
reduced specific solution viscosity: 2.4 dl / g

Claims (3)

P a t e η tan s ρ r u c h; Process for the polymerization of ethylene, optionally in a mixture with! -Olefins and / or in the presence of hydrogen as molecular weight regulator with catalysts made from compounds of VI. Subgroup of the periodic table and organoaluminum compounds using inert hydrocarbons as. Diluent or in the gas phase at temperatures between 40 and 110 ⁰ C and pressures between about 10 and 100 atmospheres, characterized in that a catalyst is used which in the absence of moisture and molecular oxygen from chromium (III) acetylacetonate, silica and triisobutylaluminium has been prepared, with 0.5 to 5 wt .- ^ chromium (III) ~ acetylacetonate applied to the silica or a silica-containing material and then with triisobutylaluminum .in. Molverb? N.tn.isBen from Alu? ⁷¹ \ o .ium- w chrome fore-ness of. until 200: 1 has been implemented. 3 0 9884/1293