HRP930609A2 - A method for preparing low or medium-density straight-chain polyethylene - Google Patents

Description

Technical field of the invention

MPK: C08F 210/02

C08F 4/64

The proposed invention relates to the field of organic chemical technology, particularly to the preparation of linear ethylene polymers of low or medium density by the polymerization process at elevated temperature and under increased pressure, in a tubular reactor, and in the presence of a specific Ziegler-type catalyst.

Technical problem

There was a need for a new, more technologically advanced process for the preparation of linear polyethylene of low or medium density at elevated temperature and under increased pressure in a tubular reactor and with good utilization.

State of the art

Some linear ethylene polymers of densities from about 0.915 to about 0.935, known in the art, are obtained by copolymerizing ethylene with minor amounts of C4-C8-alpha-olefins, and operating at low to medium pressures in the gas phase (fluid or mixed phase) or in the liquid phase (in solution or suspension), usually with a Ziegler-type catalyst, eg as described in Kirk-Othmer, "Encyclopedia of Chemical Technology", 3rd ed., Vol. 16, 1981, p. 385-401.

Also known is the polymerization of ethylene or copolymerization of ethylene with an alpha olefin using a Ziegler-type catalyst, which is carried out at elevated temperatures (typically above approx. 120°C) and under elevated pressures (typically above approx. 1000 bar), similar to tube reactors. and conditions similar to those used in the art for the preparation of low-density polyethylene with the use of radical initiators. Compare the description of BPS 828 828, US PS 3 723 403 and EPA 832 0009. Ziegler catalysts, used for this purpose, usually comprise titanium halide or alkylaluminum, and may also comprise a substrate.

However, the polymerization of ethylene at elevated temperature and under elevated pressure with the use of Ziegler catalysts causes numerous difficulties that have not yet been satisfactorily resolved.

However, these problems are mainly due to controlling the polymerization kinetics of the catalyst, which must act at a maximum level during a short polymerization time, and the instability of the alkylaluminum used as a co-catalyst, which can cause unwanted reactions. If these problems are not satisfactorily solved, polymerization yields are undesirably low and the resulting polymer is contaminated with a high content of residual catalyst.

Description of the solution to the technical problem with practical examples

In accordance with the invention, low or medium density polyethylene is produced by copolymerization of ethylene with C4-C6-alpha-olefin, partially at elevated temperatures and under elevated pressure, in a tubular reactor and in the presence of a Ziegler-type catalyst, wherein the catalyst comprises trialkylaluminum with a short alkyl chain, as a co-catalyst, and a solid component, whereby the solid component is obtained

- by spray drying the ethanol solution of magnesium chloride, so that a substrate of solid particles of magnesium chloride is formed which contains alcoholic hydroxides, where at least 70 wt. % of particles is of the order of size between 0.5 and 10 μm, and the content of alcoholic hydroxyls, expressed as ethanol, ranges from 3 to 15 wt. %;

- by reaction of the substrate with titanium tetrachloride, to create an activated substrate with a content of bound titanium, expressed as metal, from 0.8 to 4.0 wt. %, and the content of alcoholic hydroxyls, expressed as ethanol, from 0.02 to 4 wt. %, i

- by the reaction of the activated substrate with alkyl aluminum chloride, with an atomic ratio between aluminum in the alkyl aluminum chloride and titanium in the activated substrate from 2:1 to 20:1, at a temperature from 0 to 120°C and a time from 100 hours to 15 minutes, to chlorinate titanium and partially or completely reduce titanium from the tetravalent state to the trivalent state and to obtain a solid catalyst component, wherein the atomic ratio between aluminum in the trialkylaluminum and titanium in the solid catalyst component is equal to or greater than 15:1.

Substrate preparation:

The catalytic substrate is prepared by spray drying an ethanol solution of magnesium chloride.

As is known, spray drying is a process by which a solution of a soluble substance is sprayed in a volatile solvent to form droplets of finely distributed liquid and the droplets are brought into contact with an inert (non-reactive) hot gas flowing in the same or opposite direction to the droplets, in which the solvent evaporates and the dissolved material separates as solid particles, usually globules of relatively uniform size.

In accordance with the invention, spray drying is carried out under such conditions as to obtain magnesium chloride with a content of alcoholic hydroxyls in the exact range of values. This can be accomplished by using a spray drying method of the general type disclosed in US-PS 4,421,674, the disclosure of which is incorporated herein by reference, wherein that method is modified to produce a substrate of smaller particle size and relatively lower alcohol group content than required for the proposed catalyst.

Typically, a concentrated solution of magnesium chloride in ethanol is first prepared. It is advantageous that the magnesium chloride used contains water below or approx. 0.7 wt. %. It is also advantageous to prepare the solution by dissolving approximately 40 wt. parts of magnesium chloride per 100 wt. parts of ethanol, which is done at about 130°C and under a nitrogen pressure of about 5 bar.

The solution is then introduced into the spray dryer in the opposite direction to the flow of nitrogen gas, the nitrogen having an inlet temperature of approximately 350°C and an outlet temperature of approximately 230°C. The product obtained under these conditions is a magnesium chloride substrate that contains alcoholic hydroxyls and has the following characteristics:

- shape and size of particles: spherical, with at least 70 wt. % of particles have a diameter of 0.5 to 10 μm;

- content of alcoholic hydroxyls, expressed as ethanol: 3 to 15 wt. %;

- bulk density: 0.3 to 0.5 g/ml;

- porosity: 0.6 to 0.8 ml/g i

- specific area: 2 to 20 m2/year.

In a preferred embodiment at least 90% of the particles have a diameter of 0.5 to 10 μm and an alcohol hydroxyl content, expressed as ethanol, of approximately 10 wt. %.

A characteristic substrate according to the invention contains 23 wt. % Mg, 67 wt. % Cl and 10 wt. % alcohol hydroxyls (expressed as ethanol).

Preparation of the activated substrate:

The activated substrate is prepared by reacting the substrate with titanium tetrachloride until 0.8 to 4.0 wt. % of titanium expressed as metal, and by reducing the content of alcoholic hydroxyls, expressed as ethanol, to a value in the range of 0.02 to 4 wt. %.

In a preferred embodiment, the solid substrate is suspended in liquid titanium tetrachloride; so, for example, 70 to 80 wt. parts of the substrate in 100 wt. parts of titanium tetrachloride. The resulting suspension is then heated to a temperature of 80 to 100°C for 15 to 60 minutes.

The activated substrate is then separated from the excess titanium tetrachloride and the solid is washed until the chlorine disappears from the eluate. For this purpose, liquid paraffin, such as n-decane, can be used.

By working under the above-mentioned conditions, an activated carrier containing titanium and alcohol hydroxyls is obtained, and has the following characteristic properties:

- shape and size of particles: similar to the substrate;

- alcohol hydroxyl content, expressed as ethanol: 0.02 to 4 wt. %;

- content of titanium, expressed as metal: 0.8 to 4 wt. %;

- bulk density: similar to the substrate;

- porosity: 0.7 to 1 ml/g;

- specific area: 10 to 100 m2/year.

In a preferred embodiment, the activated substrate contains 2 to 3 wt. % of bound titanium expressed as metal and 0.6 to 3 wt. % alcoholic hydroxyls expressed as ethanol. A characteristic activated substrate according to the invention contains: 21 wt. % Mg, 74.7 wt. % Cl, 2.3 wt. % Ti and 2 wt. % alcohol hydroxyls (expressed as ethanol).

Preparation of the catalytic component (on the basis of patent application P 695/87);

The catalytic component is prepared by chemical conversion of the activated substrate with alkylaluminum chloride so that titanium is chlorinated and partially or completely reduced from the tetravalent to the trivalent state.

The alkylaluminum chlorides suitable for this purpose are selected from dialkylaluminum chloride, alkylaluminum dichloride and alkylaluminum sesquichloride, wherein the alkyl contains 2 to 4 carbon atoms.

Among them, the substances diethylaluminum chloride, ethylaluminum dichloride and ethylaluminum sesquichloride are of advantage. The most advantageous compound is diethylaluminum chloride.

The reaction is carried out with an atomic ratio between aluminum (in the alkylaluminum chloride) and titanium (in the activated substrate) from 2:1 to 20:1. The reaction conditions between the alkylaluminum chloride and the activated substrate are critical to the preparation of a solid catalytic component suitable for use in accordance with the invention.

The latter found that at a given reaction moment there is a minimum time during which the reagents must remain in contact for the solid catalytic component to acquire the desired characteristics.

Thus, for example, at a reaction temperature of 0°C to room temperature (20 to 25°C), a suitable reaction time is about 100 hours, while when working at 100 to 120°C, to reach the desired effect, it usually only takes about 15 minutes .

The reaction between the alkylaluminum chloride and the activated substrate is typically carried out for about 15 minutes to about 100 hours, and at reaction temperatures of about 120°C to about 0°C.

In the preferred embodiment, the reaction is carried out for 0.5 to 4 hours, at temperatures of 80 to 50°C. In a simplified version, the above ratios between aluminum and titanium from 4:1 to 10:1 are also applied.

During the reaction between the alkylaluminum chloride and the activated substrate, some or all of the titanium is reduced from the tetravalent to the trivalent state and normally the solid catalytic component contains an amount of trivalent titanium equal to 20 to 50% of the total titanium.

Also during the reaction, titanium is chlorinated and binds significant amounts of chlorine, which can be seen from the increase in titanium-chlorine bonds in the ESR spectra.

In any case, when working in the manner described above, the product has a catalytic component with the following properties:

- shape and size of particles: similar to the substrate;

- alcohol hydroxyl content, expressed as ethanol: usually lower than 2 wt. %;

- titanium content, expressed as metal: 0.4 to 4.0 wt. %;

- the ratio between trivalent titanium and the sum of trivalent and tetravalent titanium: from 0.2:1 to 0.5:1;

- bulk density: similar to the substrate;

- attention: 0.6 to 1.2 ml/g;

- specific area: 20 to 120 m2/year.

In a preferred embodiment, the catalytic component contains 2 to 3 wt. % of titanium and 1 wt. % alcoholic hydroxyls expressed as ethanol.

The characteristic catalytic component contains: 21 wt. % Mg, 74 wt. % Cl, 2.4 wt. % Ti, 1.8 wt. % Al and 0.8 wt. % alcohol hydroxyls (expressed as ethanol).

In the best embodiment, the reaction is carried out between the alkylaluminum chloride and the active substrate in an internal solvent, for example in a paraffin carrier, especially liquid paraffinic hydrocarbons containing more than 7 carbon atoms.

The following are examples of the above-mentioned paraffinic hydrocarbons: n-decane, n-undecane, n-dodecane and the commercial product ISOPAR by EXXON, which includes branched C10-C12-isoparaffins.

The presence of the carrier facilitates the control of the reaction heat and the obtaining of the catalytic component in the form of a suspension that can be introduced directly into the tubular reactor.

Catalyst:

The catalyst comprises the solid component mentioned above and trialkylaluminum of a short alkyl chain.

More specifically, trialkylaluminum has 2 to 4 carbon atoms in the alkyl group. Of all the compounds in this class, triethylaluminum is of particular advantage. Trialkylaluminum, which has an alkyl chain, away from the above-mentioned maximum limit, does not give satisfactory results in the process of preparing flat low-density polyethylene.

Both catalyst components are introduced independently into the tubular reactor. In a preferred embodiment, the solid catalytic component is introduced as a suspension in the aforementioned hydrocarbon carrier.

In all examples, both components are fed in an amount such that the atomic ratio between aluminum in the trialkylaluminum and titanium in the solid component is maintained at values typically in the range of 15:1 to 70:1, preferably in the range of 15:1 to 45: 1.

It is convenient to introduce trialkylaluminum into the reactor in the form of a solution in a hydrocarbon solvent, for example in the aforementioned ISOPAR G product.

Polymerization:

In the preparation of linear low-density polyethylene, ethylene is copolymerized with alpha-olefin, which has 4 to 8 carbon atoms in the molecule, in the presence of the previously described catalyst, in a tube reactor operating under high pressure and at elevated temperature, in a relatively short retention time under the conditions polymerization.

In detail, the general reaction conditions are as follows:

- temperature: 100 to 280°C,

- pressure: 1200 to 2000 bar i

- retention time: 25 to 60 seconds.

Under these conditions, and when ethylene-butene-1 comonomer is used as comonomer, low or medium density linear polyethylene can be obtained, which usually has characteristics in the following range of values:

- density: 0.915 to 0.940 g/ml, (ASTM-D 2839 method);

- melt mass flow rate: 0.6 to 25 g/10 min, (conditions E, method ASTM-D 1238, procedure A);

- shear stress: 28 to 23, (ASTM-D 1238 method);

- butene-1 content: from 2 to 8 wt. %, (determined by IR, method ASTM-D 2238-69);

- impact strength: 50 to 100 g, (ASTM-H 1709 method);

- turbidity: 5 - 9, (ASTM-D 1003 method);

- stretching: 4 to 6 (μm);

- color: from A to B.

The stretch value is determined at a constant polymer flow (30 revolutions of the screw per minute) and with a constant increase in the speed of the stretching roller (from 25 rpm to 120 rpm) until the film breaks. The test is then repeated when the speed of the stretching roller is slightly lower than the breaking speed. This speed is maintained for 5 minutes. If at the end of this time there is no break, measure the film with a micrometer and express the measured thickness in micrometers.

The color values are determined according to the modified ASTM-D 1725 method by comparing the tested polyethylene with the polyethylenes of the mentioned known colors, according to the above-mentioned standard method. Reference polyethylenes are usually assigned color values on a scale from A to D.

Finally, let us mention that the linear low-density polyethylene, obtained by the process according to the invention, does not have any odor during the phase of conversion into a film.

When working in accordance with the invention, the density of the resulting polymer in the specified area can also be changed, mainly by changing the alpha-olefin and the quality of the alpha-olefin copolymerized with ethylene. These copolymers usually have an alpha-olefin content that can range from 2 to 8 wt. %.

The alpha-olefin which is preferred for the purpose of the invention is butene-1. In the preferred embodiment, a mixture of ethylene, butene-1 and hydrogen (which acts as a molecular weight regulator) is introduced into the tubular reactor, with the molar ratio between ethylene and butene-1 being 70 to 30 and 40 to 60 .

When operating under the aforementioned general conditions in accordance with the invention, linear low density polyethylenes are produced in an amount of approximately 200,000 g per 1 g of titanium in the catalyst.

The following examples illustrate the invention without the intention of limitation.

Example 1

Substrate preparation

40 g of magnesium chloride in the form of pieces (water content below 0.7 wt. %) is dissolved in 100 kg of ethanol (water content below 0.2 wt. %), at 130°C and under a nitrogen pressure of 5 pond.

At the same temperature and under the same pressure, the solution is fed into a spray drying device of the type "Closed Cycle Drying", company Messrs. NIRO, where it is done in the same flow direction and with complete recovery of the evaporated organic solvent.

In this device, the solution is divided into droplets, it works with a flow of gaseous nitrogen with an inlet temperature of 350°C and an outlet temperature of 225 to 235°C.

Under these conditions, a granular solid substance with the following properties is collected from the bottom of the spray drying device:

- shape and size of particles: spherical, with approximately 90 wt. % of particles have a diameter of 0.5 to 10 micrometers;

- alcohol hydroxyl content, expressed as ethanol: 10 wt. %;

- bulk density: 0.4 g/ml;

- porosity: 0.7 ml/g;

- specific area: 3 m2/year

Preparation of the activated substrate

45 kg of the substrate obtained as described above is suspended in 60 kg of titanium tetrachloride. The mixture is heated for 30 minutes at 100°C. At the end of this time, the mixture is cooled, the chemically unchanged titanium chloride is filtered off and the solid substance is washed with n-decane until the chlorine disappears from the eluate.

The product is an activated substrate with the following features:

- shape and dimensions of the particles: similar to the substrate;

- alcohol hydroxyl content, expressed as ethanol: 2.5 wt. %;

- titanium content, expressed as metal: 2.3 wt. %;

- bulk density: similar to the substrate;

- porosity: similar to the substrate;

- specific area: 18 m2/year.

Preparation of the catalytic component

45 kg of the activated substrate, obtained as described above, is suspended in 100 l of C10-C12-isoparaffin (ISOPAR G). The substance is heated to 70°C and mixed with the gradual addition of 18 kg of diethylaluminum chloride over 1 hour. At the end of this procedure, the substance is kept with stirring for another hour at 70°C.

The obtained substance was a catalytic component in the form of solid particles suspended in a liquid carrier. The solid particles had the following properties:

- shape and size of particles: similar to the substrate;

- alcohol hydroxyl content, expressed as ethanol: 0.8 wt. %.

- titanium content, expressed as metal: 2.3 wt. %;

- the ratio of titanium in the trivalent state to the sum of titanium in the trivalent and tetravalent state: 0.35/1;

- bulk density: similar to the substrate;

- porosity: 0.8 g/ml;

- specific area: 26 m2/year.

Example 2

A steel tube reactor with an inner diameter of 2.54 cm and a length of 460 m was used, equipped with heat exchangers for temperature control.

At one end of the reactor, via an alternative compressor, 12 tons/hour of a mixture of ethylene, butene-1 and hydrogen was introduced, where the molecular ratio of ethylene to butene-1 was approximately 50:50, and the amount of hydrogen was 2000 ppm (number of particles per million in volume ) in the entire amount of gas.

At the same end of the reactor, a suspension of the solid catalytic component, prepared as described in example 1, was introduced by means of a lifting pump, in an amount of 25 1/hour of suspension containing 20 g/l of the catalytic component suspended in a mixture of C10-C12-isoparaffin ISOPAR G .

Above the place for introducing the above-mentioned suspension at the end of the reactor, triethylaluminum in the form of a 10% (wt.) solution in ISOPAR G is introduced, also by means of a lift pump. More specifically, 6 to 8 1/hour of solution are introduced so that at the entrance the atomic ratio of aluminum in triethylaluminum to titanium in the solid catalytic component is approximately 50.

Polymerization is carried out under the following conditions:

- pressure at the entrance to the reactor: 1500 bar;

- pressure drop in the reactor: 200 bar;

- inlet temperature: 60°C;

- activation temperature: 100°C;

- peak temperature: 250°C;

- holding time: 30 seconds.

To deactivate the catalyst, 2.5 1/hour of glycerol is brought near the outlet of the reactor.

When operating under the above conditions, the degree of conversion, calculated as ethylene, is approximately 55 wt. %. At the exit from the reactor, a polymer with a higher degree of decompression is obtained, whereby the polymer is led directly from the decompressor to the extruder.

After cleaning and combining with the aforementioned feed monomers, the chemically unconverted monomers and hydrogen are returned to the reactor inlet.

During the 30-day continuous operation, the average utilization was 2300 kg/hour of linear low-density polyethylene (200,000 g per one g of titanium in the catalyst) with the following characteristics:

- density: 0.9200 to 0.9205 g/ml,

- melt mass flow: 1.0 to 1.1 g/10 min,

- shear stress: 28,

- butene-1 content: 3-3.2 wt. % by mole,

- impact strength: 80 to 10 g,

- blurring: 6 - 8,

- stretching: 5 to 6 micrometers (μm),

- color: from A to B,

- polymer product smell: standard,

- there is no smell during the film formation phase.

Example 3

(comparative)

With respect to substrate preparation and active substrate preparation, the solid catalytic component was prepared in detail in the same manner as described in Example 1.

15 kg of the active substrate was then suspended in 600 l of ISOPAR G. The mixture was kept at room temperature (20 to 25°C) with stirring and 40 l of a 30% (wt.) solution of diethylaluminum chloride in ISOPAR G was added for 1 hour. At the end of that procedure, the substance was kept with stirring for another hour at the same temperature.

A solid catalytic component was obtained in the form of solid particles suspended in a liquid carrier.

The distributed solid had the following characteristics:

- particle shape and size: similar to the substrate;

- alcohol hydroxyl content, expressed as ethanol: 2 wt. %.

- titanium content, expressed as metal: 2.3 wt. %;

- the ratio of titanium in the trivalent state to the sum of titanium in the trivalent and tetravalent state: 0.15/1;

- bulk density: similar to the substrate;

- attention: 1 g/ml;

- specific area: 30 m2/year.

Example 4

(comparison)

Polymerization is carried out similarly to example 2, using the solid catalytic component described in example 3.

At one end of the reactor, 12 tons/hour of a mixture of ethylene, butene-1 and hydrogen is introduced, where the molar ratio of ethylene and butene-1 is 50:50, and the amount of hydrogen is 600 ppm of the entire gas. At the same end of the reactor, a quantity of 20 l/hour of the solid catalytic component suspension, prepared in the manner described in example 3, containing 25 g/l of the solid component, is introduced. Above, a 10% (by mass) solution of triethylaluminum chloride is introduced into ISOPAR G in an amount of 8 to 10 l/hour.

Polymerization is carried out under the following conditions:

- pressure at the entrance to the reactor: 1500 bar;

- pressure drop in the reactor: 200 bar;

- inlet temperature: 60°C;

- activation temperature: 120°C;

- peak temperature: 235°C;

- holding time: 30 seconds.

Near the exit from the reactor, 4 l/hour of glycerol is supplied to deactivate the catalyst.

After cleaning and addition of fresh monomers, chemically unconverted monomers and hydrogen are returned to the reactor inlet.

When operating under the above-mentioned conditions, the initial degree of ethylene conversion was 36% and 1500 kg/hour of polymer (160000 g per g of titanium) was obtained.

In order to maintain this degree of conversion, it was necessary to gradually increase the amount of triethylaluminum only a few hours after the start of the experiment. The amount of 10% triethylaluminum solution in ISOPAR G increased to 18 to 20 l/hour after 10 days when the reaction was stopped.

The polymer obtained at that time had the following characteristics:

- density: 0.921 g/ml,

- melt mass flow: 0.9 to 1 g/10 min,

- butene-1 content: 3.1 % by mole,

- impact strength: 80 to 100 g,

- turbidity: 6.2;

- stretch: 5μm,

- color: from A to B,

- polymer product smell: standard,

- hydrocarbon smell during the formation of the polymer film.

Example 5

(comparative)

The solid catalytic component was prepared exactly as described in Example 1 with respect to substrate preparation and activated substrate preparation.

45 kg of the resulting active substrate is then suspended in 1800 l of the C10-C12-isoparaffin mixture (ISOPAR G).

The substance is kept under stirring at 20 to 25°C and 85 kg of a 30% (w/w) solution of tri-n-octylaluminum is added, followed by 48 kg of a 30% (w/w) solution of diethylaluminum chloride in the same C10 -C12-isoparaffinic solvent.

At the end of the addition process, the substances are kept at the same temperature for 1 hour with stirring.

A solid catalytic component was obtained in the form of solid particles in a liquid carrier.

The solid particles had the following characteristics:

- shape and size of particles: similar to the substrate;

- alcohol hydroxyl content, expressed as ethanol: 1.8 wt. %.

- titanium content, expressed as metal: 2.3 wt. %;

- ratio of titanium in the trivalent state to the sum of titanium in the trivalent and tetravalent state: 0.20/1;

- bulk density: similar to the substrate;

- porosity: 0.9 g/ml;

- specific area: 29 m2/year.

Example 6

(comparison)

A steel tubular reactor with an internal diameter of 3.175 cm and a length of 600 m, equipped with heat exchangers for temperature control, was used. At one end of the reactor, via an alternative compressor, 15,500 kg/hour of a mixture of ethylene, butene-1 and hydrogen was introduced, where the molecular ratio of ethylene to butene-1 was approximately 50:50, and the amount of hydrogen was 1000 ppm with respect to the entire amount of gas .

At the same end of the reactor, a suspension of the solid catalytic component was introduced with a flow rate of 34 1/hour, prepared as described in example 5, which contained 25 g/l of the solid component. At the same time, a 30% (wt.) solution of tri-n-oxylaluminum in C10-C12-isoparaffins was introduced above by means of a lifting pump at a rate of 50 l/hour.

The polymerization was carried out under the following conditions:

- pressure at the entrance to the reactor: 1400 bar;

- pressure drop in the reactor: 200 bar;

- inlet temperature: 60°C;

- activation temperature: 125°C;

- peak temperature: 230°C;

- retention time: 55 seconds.

Near the exit from the reactor, 7 l/hour of diethylene glycol is fed to deactivate the catalyst.

When operating under the above conditions, the initial degree of conversion expressed as ethylene is approximately 34%, and the output was 1900 kg/hour (100000 g per one g of titanium) of polymer with the following characteristics:

- density: 0.9200 g/ml;

- melt mass flow rate: 1.0 g/10 min;

- shear stress: 29.0;

- butene-1 content: 3 mol. %;

- impact strength: 80 g;

- blurring: 15;

- stretching: 5 micrometers (μm);

- color: from C to D, (from yellow to deep yellow);

- the smell of the polymer product: strongly irritating and lasting during the formation of the film.

Citation of the best performance for the economic use of the invention

A steel tube reactor with an inner diameter of 2.54 cm and a length of 460 m was used, equipped with heat exchangers for temperature control. At one end of the reactor, via an alternative compressor, a mixture of ethylene, butene-1 and hydrogen was introduced into the flow of 12 tons/hour, where the molecular ratio of ethylene to butene-1 was approximately 50:50, and the amount of hydrogen was 2000 pm (number particles per million in volume) in the entire amount of gas.

At the same end of the reactor, the suspension of the solid catalytic component prepared as described in example 1 was introduced into the suspension, using a lift pump, in an amount of 25 l/hour of the suspension containing 20 g/l of the catalytic component suspended in the mixture of C10-C12-isoparaffin ISOPAR G .

Above the place for introducing the above-mentioned suspension, at the end of the reactor, triethylaluminum in the form of a 10% (wt.) solution in ISOPAR G. Potanje was introduced, also using a lift pump, 6 to 8 l/hour of solution was introduced, so that at the inlet the atomic ratio of aluminum in triethylaluminum to titanium in the solid catalytic component was approximately 50.

The polymerization was carried out under the following conditions:

- pressure at the entrance to the reactor: 1500 bar;

- pressure drop in the reactor: 200 bar;

- inlet temperature: 60°C;

- activation temperature: 100°C;

- peak temperature: 250°C;

- holding time: 30 seconds.

To deactivate the catalyst near the outlet of the reactor, 2.5 l/hour of glycerol was supplied.

When operating under the above-mentioned conditions, the degree of conversion, calculated as ethylene, was approximately 55 wt. %. At the exit from the reactor, polymer with a higher degree of decompression was obtained, whereby the polymer was led directly from the decompressor to the extruder.

After cleaning and combining with the previously mentioned feed monomers, the chemically unconverted monomers and hydrogen were returned back to the reactor inlet.

During the 30-day continuous operation, the average utilization was 2300 kg/hour of linear low-density polyethylene (200,000 g per one g of titanium in the catalyst) with the following characteristics:

- density: 0.9200 to 0.9205 g/ml;

- melt mass flow: 1.0 to 1.1 g/10 min;

- shear stress: 28;

- butene-1 content: 3.0 – 3.2% per mole;

- impact strength: 80 to 10 g;

- turbidity: 6 – 8;

- stretching 5 to 6 micrometers (µm);

- color: from A to B;

- polymer product smell: standard;

- no smell to us during the making of the film.

Claims (3)

1. Process for the preparation of linear polyethylene of low or medium density by copolymerization of ethylene with C4-C6-alpha-olefinor, characterized in that ethylene is copolymerized with C1-C6-alpha-olefin, such as butene-1, at an elevated temperature, such as e.g. 100 to 280°C, under elevated pressures such as 1200 to 2000 bar and with a residence time of 25 hours to 60 seconds in the reaction phase, was achieved with a tubular reactor and in the presence of a Ziegler catalyst, comprising trialkylaluminum and a solid catalytic component containing titanium and whereby trialkylaluminum contains 2 to 4 carbon atoms in the alkyl group, and the solid component containing titanium is obtained by spray drying an ethanol solution of magnesium chloride so that a substrate of solid magnesium chloride particles containing alcoholic hydroxyls is formed, where at least 70 wt. % of particles of the order of size between 0.5 and 10 pm, and the content of alcoholic hydroxyls, expressed as ethanol, ranges from 3 to 15 wt. %, by reacting the substrate with titanium tetrachloride, to create an activated substrate with a content of bound titanium, expressed as metal, from 0.8 to 4.0 wt. %, and the content of alcoholic hydroxyls, expressed as ethanol, from 0.02 to 4 wt. %, and by chemical conversion of the activated substrate with alkylaluminum chloride with an atomic ratio between aluminum in the alkylaluminum chloride and titanium in the activated substrate from 2:1 to 20:1, at a temperature from 0 to 120°C and a time from 100 hours to 15 minutes , to chlorinate titanium and partially or completely reduce titanium from the tetravalent to the trivalent state, wherein the atomic ratio between the aluminum in the trialkylaluminum and the titanium in the solid catalytic component ranges from 15:1 to 70:1. 2. The process according to claim 1, characterized in that the molar ratio between ethylene and butene-1 in the feed ranges from 70:30 to 40:60. 3. The process according to claim 1, characterized in that it is carried out in the presence of hydrogen.