RU2255095C1 - Method for preparing polyethylene - Google Patents

Abstract

FIELD: organic chemistry, polymers, chemical technology.

SUBSTANCE: invention relates to technology for producing polyethylene by method of radical polymerization in mass under high pressure in the single-zone autoclave reactor. Invention describes a method for preparing polyethylene involving feeding ethylene in the single-zone reactor with stirring device and its polymerization in mass under pressure 140-230 MPa and temperature 210-265°C in the presence of chain-transferring agent - isopropyl alcohol, initiation of polymerization reaction with organic peroxides feeding as solutions in organic solvent at top and bottom parts of reactor and the following two-step separation of synthesized polyethylene from unreacted ethylene in systems of recycles of high and low pressures. Method involves using a mixture of isopropyl alcohol with glycols as the chain-transferring agent that comprise 2-5 carbon atoms in molecule, or with their derivatives - polyglycols with molecular mass 3 000 Da, not above, in the mass ratio isopropyl alcohol and glycol or polyglycol = 1:(0.05-0.25), respectively. Method provides improving strength and optical properties of synthesized polymer, reducing mass part (less 0.65%) extractable substances in it in realization the process of ethylene polymerization in the single-zone autoclave reactor, reducing intensity of gas evolving in processing the synthesized polyethylene and increase of elasticity of film made of polyethylene. Invention can be used in chemical and petroleum chemistry industry.

EFFECT: improved method for producing.

5 cl, 1 tbl, 21 ex

Description

The invention relates to a technology for the production of ethylene polymers by radical polymerization in bulk at high pressure and can be used in the chemical and petrochemical industries.

A known method of producing polyethylene (USSR Patent N1838330, Mcl C 08 F 110/02, 2/38, publ. 30.08.93), including the supply of ethylene in a two-zone autoclave reactor with a stirrer and its polymerization in bulk at a pressure of 135-227 MPa and a temperature of 418-590 K (145-317 ° C) in the presence of radical initiators of the reaction - organic peroxides, which are used tert-butyl peroxypivalate, which is supplied as a solution in an organic solvent to the upper zone of the reactor, and di-tert-butyl peroxide, fed as a solution to the lower zone of the reactor. When using these initiators, the temperature in the upper zone of the reactor is maintained equal to 445-470 K (172-197 ° C); and in the lower zone - 505-543 K (232-270 ° C) (see examples 5-7 of USSR patent N 1838330). As an organic solvent of the initiators, a mixture of n-paraffins (parex) purified on molecular sieves with the number of carbon atoms in the molecule from C ₁₁ to C _{20 is used} ; the concentration of peroxide in the solvent is 1.2-39.5 wt.%, and the mixture of n-paraffins is introduced in an amount of 0.02-0.030 wt.% of the initial reaction mixture. In the synthesis process, regulators can be used, for example hydrogen, ketones or aldehydes, mainly propionaldehyde and methyl ethyl ketone, or hydrocarbons such as propane or propene. The resulting polyethylene and unreacted ethylene are sent through a control valve to a two-stage separation system for the polyethylene from the unreacted reaction mixture. Polyethylene is removed from the recycle system through a discharge extruder and transferred to granulate, and unreacted ethylene after cleaning and cooling is mixed with the original ethylene and sent to the reactor.

The common features of the known technical solution and the present invention are the production of polyethylene in a reactor at high temperatures and pressure by polymerizing it in bulk in the presence of reaction initiators supplied as a solution in an organic solvent to the upper and lower zones of the reactor, and the subsequent two-stage separation of polyethylene from unreacted reaction mixtures.

The polyethylene obtained by this method contains virtually no gel-like inclusions, which is an important positive factor in the production of film. However, the optical and strength characteristics of a film made of this polyethylene have relatively low characteristics (see our test example 20). In addition, the method has a disadvantage inherent in all processes carried out in dual-zone autoclave reactors — a more complex process for controlling the polymerization reaction and the need to disassemble the reactor in case of switching to a single-zone process for producing high-grade polyethylene grades (more than 2 g / 10 min) melt flow rate (MFR).

The closest (prototype) to the claimed method for the combination of essential features and the achieved effect is the method for producing polyethylene described in (High-pressure polyethylene. Scientific and technical foundations of industrial synthesis. / A.V. Polyakov, F.I. Duntov, A.E. Sofiev et al. - L.: Chemistry, 1988, p. 27-37, 44-46).

The method includes feeding ethylene into a single-zone autoclave reactor with a mixing device and polymerizing it in bulk at a pressure of 150-250 MPa and a temperature of 150-280 ° C in the presence of a chain transfer agent - isopropyl alcohol, initiating the polymerization reaction with organic peroxides fed in the form of solutions in organic solvent in the upper and lower parts of the reactor, and the subsequent two-stage separation of the obtained polyethylene from unreacted ethylene in high and low pressure recycling systems. Polyethylene is removed from the recycling systems through a discharge extruder and transferred to granulate, and unreacted ethylene, after purification and cooling, is mixed with the starting ethylene and fed to the reactor. For example, di-lauroyl peroxide, tert-butyl perbenzoate, di-tert-butyl peroxide, and peroxide of fatty acid fractions are used as organic peroxides in the polymerization process, and imported mineral oils Ri-zella-15 and Rizella-17 from the company Shell (see book, High-Pressure Polyethylene, pp. 44-46).

The process for producing polyethylene, implemented in accordance with the prototype method described above, is simpler to control than the polymerization of ethylene in a 2-3-zone reactor, but it has the following disadvantages:

1. Obtained by the prototype polyethylene has a high mass fraction of extractable substances, which limits the scope of its application and worsens the conditions for its processing due to intense gas evolution. So according to GOST 16337-77 (table 5) for premium polyethylene produced in autoclave-type reactors (a list of these grades of polyethylene is given in the book "High-pressure polyethylene", p. 180), the mass fraction of extracted substances can be 0.9 -1.4 wt.%. According to our data, the polyethylene obtained in the conditions of the prototype method has a mass fraction of extractable substances of 0.65 wt.% (See our control example 21).

2. Low tensile strength for a film made from the resulting polyethylene. So, according to the norms for a polyethylene film (GOST 10354-82 - table 3), the strength of a film of the highest quality category when tensile in the longitudinal direction can be 16.1 MPa, and in the transverse direction - 14.7 MPa. According to our data, polyethylene with a PTR of 2 g / 10 min has a tensile strength in the longitudinal direction of 17.1 MPa, and in the transverse - 16.1 MPa (see our control example 21).

3. Low optical properties (gloss and transparency) of the film made from the obtained polyethylene (see our control example 21).

The objective of the invention is:

- Improving the strength and optical properties (gloss and transparency) of the resulting polymer;

- A decrease in the resulting polymer mass fraction of extractable substances;

- Reducing the intensity of gas separation during processing of the obtained polyethylene;

- An increase in the extensibility of a film made from the obtained polyethylene;

- Improving the processing conditions obtained according to the invention of polyethylene due to the elimination of gas separation;

- Expanding the scope of the polyethylene obtained according to the invention by reducing the mass fraction of extractable substances.

The technical result, the achievement of which the claimed method provides, is to improve the strength and optical properties of the obtained polymer, to reduce the mass fraction (less than 0.65%) of extracted substances in it, during the polymerization of ethylene in a single-zone autoclave reactor; in reducing the intensity of gas separation during processing of the obtained polyethylene and in increasing the extensibility of the film made from it.

The claimed technical result in a method for producing polyethylene, comprising feeding ethylene into a single-zone autoclave reactor with a mixing device and polymerizing it in bulk at a pressure of 140-230 MPa and a temperature of 210-265 ° C in the presence of a chain transfer agent - isopropyl alcohol, initiating the polymerization reaction with organic peroxides supplied in the form of solutions in an organic solvent to the upper and lower parts of the reactor, and the subsequent two-stage separation of the obtained polyethylene from unreacted ethylene high and low pressure recycling systems is achieved due to the fact that as a chain transfer agent, a mixture of isopropyl alcohol with glycols containing 2-5 carbon atoms in the molecule, or with their derivatives - polyglycols with a molecular mass (MM) of not more than 3000 at the mass ratio of isopropyl alcohol and glycol or polyglycol equal to 1: (0.05-0.25), a mixture of isopropyl alcohol with glycols or polyglycols is used in an amount of 0.20-3.00% by weight of ethylene fed to the reactor, a mixture solution peroxides consisting of 90-60 m ac.% tert-butylperoxy-3,5,5-trimethylhexanoate and 10-40 wt.% tert-butylperoxybenzoate are fed to the top of the reactor, and a solution of a mixture of peroxides consisting of 10-50 wt.% tert-butylperoxybenzoate and 50- 90 wt.% Di-tert-butyl peroxide to the bottom of the reactor, while the minimum temperature in the upper part of the reactor is maintained in the range of 210-230 ° C, the maximum temperature in the lower part of the reactor is 245-265 ° C, and as an organic solvent peroxides use branched acyclic compounds of the paraffin series with a number of 10-20 carbon atoms Herod in the molecule.

A comparative analysis of the prototype and the present invention shows that common features in the method for producing polyethylene are ethylene supply to a single-zone autoclave reactor and its polymerization in bulk at a pressure of 140-230 MPa and a temperature of 210-265 ° C in the presence of a chain transfer agent - isopropyl alcohol, initiation polymerization reactions with organic peroxides supplied in the form of solutions in an organic solvent to the upper and lower parts of the reactor, and the subsequent two-stage separation of the obtained polyethylene t of unreacted ethylene in high and low pressure recycle systems.

A distinctive feature of the proposed method for producing polyethylene is the use as a chain transfer agent of a mixture of isopropyl alcohol with glycols containing 2-5 carbon atoms in the molecule, or with their derivatives - polyglycols with a molecular weight (MM) of not more than 3000 with a mass ratio of isopropyl alcohol and glycol or polyglycol equal to 1: (0.05-0.25). A mixture of isopropyl alcohol with glycols or polyglycols is used in an amount of 0.20 - 3.00% by weight of ethylene fed to the reactor. A solution of a mixture of peroxides, consisting of 90-60 wt.% Tert-butyl peroxy-3,5,5-trimethylhexanoate and 10-40% by weight of tert-butyl peroxybenzoate, is fed to the top of the reactor, and a solution of a mixture of peroxides consisting of 10-50 wt.% tert-butyl peroxybenzoate and 50-90 wt.% di-tert-butyl peroxide to the bottom of the reactor. In this case, the minimum temperature in the upper part of the reactor is maintained in the range of 210-230 ° С, the maximum temperature in the lower part of the reactor is 245-265 ° С, and branched acyclic compounds of the paraffin series with the number of 10-20 carbon atoms per molecule.

The implementation of the proposed method for producing polyethylene is illustrated by the following examples.

The characteristics of the obtained polyethylene are given in the table. Indicators PT'R of polyethylene (at 190 ° C and a load of 2.16 kgf) and the mass fraction of extractable substances are determined in accordance with GOST 16337-77 (High-pressure polyethylene), the optical properties of the film according to ASTM D1003 methods, the tensile strength of the film according to GOST 10354-82 (polyethylene film). Indicator - the content of gel-like inclusions in the table is not entered due to their absence in the polyethylene obtained in all examples.

Example 1

To obtain polyethylene, a single-zone continuous autoclave reactor with a volume of 250 l is used, equipped with a high-speed mixer, the rotation speed of which is 1000 rpm. Four thermocouples are used to measure the temperature in the reactor, two of which are located at the top of the reactor, and two at the bottom. The first thermocouple is installed in the upper part of the reactor opposite the ethylene inlet, where the temperature of the reaction mixture is minimal; the fourth thermocouple is at the bottom of the reactor, where the temperature of the reaction mixture has a maximum value. The second and third thermocouples are intermediate. The temperature of the outer surface of the wall of the reactor is maintained at 170 ° C with cold air.

10,000 kg / h of ethylene are fed into the reactor at a temperature of 35 ° C. under a pressure of 150 MPa and containing 1.2 wt.% Chain transfer agent. A mixture of isopropyl alcohol and ethylene glycol is used as a chain transfer agent. The mixture contains 85 wt.% Isopropyl alcohol and 15 wt.% Ethylene glycol (mass ratio 1: 0.17). One stream of ethylene in an amount of 500 kg / h passes through the engine casing installed above the reaction space into the upper part of the reactor. A second ethylene stream in an amount of 4,500 kg / h is introduced into the upper part of the reactor opposite the first thermocouple together with the initiating solution. Initial solution formulation: 8% by weight of tert-butyl peroxy-3,5,5-trimethylhexanoate, 2% by weight of tert-butyl peroxybenzoate (weight ratio of peroxides 80:20) and 90% by weight of an acyclic solvent using isododecane (12 carbon atoms in the molecule). The amount of the initiating mixture for the upper zone is controlled by the readings of the first thermocouple, maintaining the temperature of the reaction mixture at the first measurement point by 218 ° C by feeding the initiating mixture. The second thermocouple set the temperature of 243-244 ° C. A third ethylene stream in an amount of 5000 kg / h is fed to the lower part of the reactor opposite the third thermocouple. Before entering the reactor, a solution of an initiating mixture is introduced into the ethylene stream, consisting of 2.5 wt.% Tert-butyl peroxybenzoate, 2.5 wt.% Di-tert-butyl peroxide (mass ratio of peroxides 50:50) and 95 wt.% Solvent - isododecane. The amount supplied to the lower part of the initiating mixture is controlled by a fourth thermocouple. The fourth thermocouple maintains a temperature of 257 ° C. The third thermocouple sets the temperature of 234-235 ° C.

From the reactor, the obtained polyethylene and the unreacted reaction mixture are sent through a throttling valve to a two-stage separation of the polymer from the unreacted reaction mixture in a high and low pressure recycling system. In a high-pressure recycle, a pressure of 25 MPa is maintained, in a low-pressure recycle - 0.13 MPa. The molten polyethylene with a temperature of 250 ° C from the high-pressure separator is fed to the low-pressure separator and then to the unloading extruder, and the ethylene solution with low molecular weight products released in the separators is cooled, refined and mixed with fresh ethylene. The conversion of ethylene in the experiment is 16.5 wt.%, The yield of polyethylene is 1650 kg / h.

Example 2

The method according to example 1 with the difference that 1,5-pentadiol is used as glycol.

Example 3

The method according to example 1 with the difference that polyethylene glycol with MM 3000 is used as a polyglycol.

Example 4

The method according to example 1 with the difference that polypropylene glycol with MM 1000 is used as a polyglycol.

Example 5

The method according to example 1 with the difference that the content of the mixture of isopropyl alcohol with ethylene glycol in the starting ethylene is 0.2 wt.%.

Example 6

The method according to example 1 with the difference that the content of the mixture of isopropyl alcohol with ethylene glycol in the starting ethylene is 3.00 wt.%, And the temperature of the reaction mixture opposite the fourth thermocouple is 252 ° C (maximum temperature in the lower part of the reactor). The conversion of ethylene in the experiment is 16.1 wt.%, The yield of polyethylene is 1610 kg / h.

Example 7

The method according to example 1 with the difference that as a chain transfer agent a mixture of isopropyl alcohol and ethylene glycol of the following composition is used: isopropyl alcohol - 80 wt.%, Ethylene glycol - 20 wt.% (Mass ratio 1: 0.25).

Example 8

The method according to example 1 with the difference that as a chain transfer agent a mixture is used containing 95 wt.% Isopropyl alcohol and 5 wt.% Ethylene glycol (mass ratio 1: 0.05).

Example 9

The method according to example 1 with the difference that the pressure in the polymerization is maintained at 140 MPa, and a mixture of 10 wt.% Initiator solution consisting of 90 wt.% Tert-butyl peroxy-3,5,5-trimethylhexanoate and 10 wt. % by weight of tert-butyl perbenzoate dissolved in isododecane. The minimum temperature in the upper part of the reactor (opposite the first thermocouple) is maintained equal to 210 ° C.

Example 10

The method according to example 1 with the difference that in the upper part of the reactor serves a 10% solution in isododecane initiating mixture of the following composition, wt.%:

tert-butylperoxy-3,5,5 - trimethylhexanoate 60

tert-butyl peroxybenzoate 40

The minimum temperature in the upper part of the reactor is maintained equal to 230 ° C.

Example 11

The method according to example 1 with the difference that in the lower part of the reactor serves a solution of peroxides of the following composition, wt.%:

tert-butyl perbenzoate 10

di-tert-butyl peroxide 90

The maximum temperature in the lower part of the reactor is maintained equal to 265 ° C. The conversion of ethylene in the experiment is 16.4 wt.%, The yield of polyethylene is 1640 kg / h.

Example 12

The method according to example 1 with the difference that in the lower part of the reactor serves a solution of peroxides of the following composition, wt.%:

tert-butyl perbenzoate 60

di-tert-butyl peroxide 40

The maximum temperature in the lower part of the reactor is maintained equal to 245 ° C. The conversion of polyethylene in the experiment is 15.6 wt.%, The yield of polyethylene is 1560 kg / h.

Example 13

The method according to example 1 with the difference that isodecane (10 carbon atoms) is used as a peroxide solvent.

Example 14

The method according to example 1, with the difference that a mixture of branched acyclic hydrocarbons with C ₁₅ -C ₂₀ obtained by thermal degradation of an ethylene copolymer with 20 wt.% Propylene is used as a peroxide solvent.

Example 15

The method according to example 1 with the difference that the process is carried out in a single-zone autoclave reactor with a volume of 6 l, equipped with a high-speed stirrer, rotating at a speed of 1500 rpm, and two thermocouples installed in the upper and lower parts of the reactor. Ethylene is fed into the upper part of the reactor in two streams: 5 wt.% Ethylene is sent to the stirrer motor, and the main amount of ethylene is sent directly to the reactor opposite the upper thermocouple. The supply of initiating mixtures is carried out at two points: one mixture - in the main stream of ethylene before entering the reactor and the second - directly in the lower part of the reactor. The separation of the obtained polyethylene from the unreacted reaction mixture is carried out according to the traditional two-stage scheme at high and low pressure with the release of polyethylene through an extruder and the return of ethylene to the synthesis system.

Polyethylene synthesis conditions:

- the amount of ethylene fed to the reactor is 40 kg / h;

- the content of the chain transfer agent in ethylene is 1.5 wt.%;

- the composition of the chain transfer agent, wt.%: isopropyl alcohol - 90, ethylene glycol - 10;

- pressure in the reactor - 230 MPa;

- the composition of the initiating mixture supplied to the upper part of the reactor, wt.%:

tert-butyl peroxy-3,5,5, trimethylhexanoate 8

tert-butyl peroxybenzoate 2

isododecane 90

- the composition of the initiating mixture supplied to the lower part of the reactor, wt.%:

tert-butyl peroxybenzoate 2.5

di-tert-butyl peroxide 2.5

isododecane 95.0

- the minimum temperature in the upper part of the reactor is 218 ° C;

- the maximum temperature in the lower part of the reactor is 265 ° C.

The conversion of ethylene in the experiment is 16.3 wt.%, The yield of polyethylene is 6.5 kg / h.

Example 16 (control).

The method according to example 1 with the difference that the content of the mixture of isopropyl alcohol with ethylene glycol in the original ethylene goes beyond the stated limits and is 0.1 wt.%. A film made from the obtained polyethylene has deteriorated strength and optical properties (see table).

Example 17 (control)

The method according to example 1 with the difference that the content of the mixture of isopropyl alcohol with ethylene glycol in the starting ethylene is 3.5 wt.%. The resulting polyethylene has a high MFR (13 g / 10 min), and such polyethylene is unsuitable for film production.

Example 18 (control).

The method according to example 1 with the difference that the content of isopropyl alcohol in a mixture with ethylene glycol is 75 wt.%, And ethylene glycol is 25 wt.%, I.e. mass ratio of 1: 0.33. Polyethylene has poor optical properties and an increased mass fraction of extractable substances, which worsens the conditions for its processing, as it leads to the appearance of smoke during the manufacture of the film.

Example 19 (control).

The method according to example 1 with the difference that the content of isopropyl alcohol in a mixture with ethylene glycol is 98%, and ethylene glycol is 2%, i.e. mass ratio of 1: 0.02. A film made from polyethylene obtained under the conditions of this example has a lower optical performance.

Example 20 (control, similar to USSR patent N 1838330).

The process is carried out at the installation described in example 1, with the difference that the single-zone reactor is converted into a dual-zone installation on the shaft of the baffle mixer, which divides the reaction space into two zones - upper and lower. The upper zone covers 56% of the total reaction space, the lower - 44%.

Ethylene divided into three streams in an amount of 10,000 kg / h is fed into the reactor under a pressure of 134 MPa. One partial ethylene stream (500 kg / h) passes through the engine casing installed above the reaction space into the upper zone of the reactor.

The second ethylene stream in an amount of 5000 kg / h is introduced together with the initiator for the upper reaction zone opposite the first thermocouple. As an initiator in the upper zone, a 20% (wt.) Solution of tert-butyl peroxypivalate in dodecane is used. The amount of initiator for the upper zone is controlled by the first thermocouple, constantly maintaining a temperature of 172 ° C (445 K). The second thermocouple sets the temperature at 197 ° C (470 K). The reaction mixture of the upper zone enters the lower zone of the reactor, into which 5000 kg / h of fresh ethylene are additionally fed and, in contrast to the third thermocouple, a 1.2% (wt.) Solution of di-tert-butyl peroxide in dodecane. The amount of initiator is controlled by the fourth thermocouple. The fourth thermocouple maintains a temperature of 270 ° C (543 K). At a third thermocouple located under the deflector, a temperature of 232 ° C. (505 K) is set. The conversion of ethylene in the experiment is 17.5 wt.%, The output of polyethylene 1750 kg / h.

The resulting polymer after reducing the pressure to 26 MPa is sent to a two-stage separation system from unreacted ethylene. Unreacted ethylene after cooling and purification is returned to the reaction unit, and polyethylene is taken out of the system through an unloading extruder. As follows from the table, polyethylene with a PTR equal to 0.3 g / 10 min, obtained under the conditions of USSR patent N 1838330, has lower optical and strength characteristics than polyethylene, with the same PTR obtained by the present method (see example 12).

Example 21 (control prototype).

The method according to example 1 with the difference that only isopropyl alcohol is used as a chain transfer agent. The concentration of isopropyl alcohol in ethylene 0.8 wt.%. An initiating solution of the following composition is fed to the top of the reactor, wt.%:

tert-butylperoxy-3,5,5 - trimethylhexanoate 5

tert-butyl peroxybenzoate 5

Shell Rizella-15 mineral oil 90

The temperature of the reaction mixture, measured by the first thermocouple, 235 ° C, the second thermocouple - 240 ° C.

A 10% (wt.) Solution of tert-butyl peroxybenzoate in Risella oil is fed to the bottom of the reactor. The temperature in the reactor opposite the third thermocouple is 235 ° C, and opposite the fourth thermocouple it is 250 ° C. The conversion of ethylene in the experiment is 16 wt.%, The yield of polyethylene is 1600 kg / h.

As follows from the table, the film of polyethylene obtained in the conditions of the prototype has lower strength and optical properties compared with polyethylene (with PTR 2.0 g / 10 min) obtained in the conditions of the proposed method (see examples 1-4), as well as an increased mass fraction of extractable substances.

According to the claimed method, as glycols containing 2-5 carbon atoms, ethylene glycol, propylene glycol, pentadiols can be used; and polyglycols as polyethylene glycol, polypropylene glycol and other polyglycols with MM no more than 3000. Polyglycols with MM more than 3000 are impractical to use, because they have high viscosity, which makes it difficult to prepare mixtures of them with isopropyl alcohol.

The mass ratio of isopropyl alcohol to glycol or polyglycol should be in a ratio of 1: (0.05-0.25), if this ratio is less than 1: 0.05, then the resulting film has reduced optical performance, and if more than 1 : 0.25, then polyethylene has an increased content of extractable substances in polyethylene, which leads to the appearance of smoke during its processing.

As peroxides fed to the upper part of the reactor, individual peroxides or peroxide mixtures can be used that initiate the ethylene polymerization reaction in the temperature range 210-230 ° С, and for the lower part of the reactor, peroxides or peroxide mixtures can be used that initiate the polymerization of ethylene at 245- 265 ° C.

Branched acyclic paraffin compounds can be used as an organic solvent for peroxides, obtained by the method of oil distillation and subsequent separation of the fraction with the number of carbon atoms in the molecule 10–20, by organometallic synthesis (for example, isododecane from EC Erdolchemie) or by thermal destruction of ethylene copolymers with propylene. These can be either individual compounds, for example, isodecane, isododecane, or mixtures, for example, C ₁₅ –C ₂₀ hydrocarbons, obtained by thermal degradation of ethylene-propylene copolymers.

From (Crystalline polyolefins / edited by Raff R.A. and Duck K.V. M .: Chemistry, T.1, 1970, p. 416) it is known that the use of various alcohols as a chain transfer agent in the synthesis of polyethylene which isopropyl alcohol received the most practical use is explained by its high activity, due to the easy cleavage of the hydrogen atom in the hydroxyl group. The use of mixtures of isopropyl alcohol with glycols or polyglycols as a chain transmitter is not known in the art.

A comparative analysis of the above examples illustrating the implementation of the invention shows that the use of the claimed essential features leads to an unobvious technical result, namely to increase the gloss and transparency of the film, to reduce the content of extractable substances in the polymer, to significantly improve the properties of the obtained polyethylene, which is expressed in an increase film strength under tension in the longitudinal and transverse directions.

The implementation of the proposed method provides for the production of polyethylene in a wide range of MFR (from 0.3 to 7 g / 10 min), practically containing no gel-like inclusions, having higher mechanical and optical properties and having a lower content of extractable substances than polyethylene obtained by known methods . Such polyethylene can be used in the production of films for various purposes, including films for contact with food and medical films, as well as for the manufacture of traditional products: pipes, blow products, fittings, etc.

Claims (5)

1. A method of producing polyethylene, comprising feeding ethylene into a single-zone autoclave reactor and polymerizing it in bulk at high temperatures and pressure in the presence of a chain transfer agent, isopropyl alcohol, initiating the polymerization reaction with organic peroxides fed as solutions in an organic solvent to the upper and lower parts reactor, and the subsequent two-stage separation of the obtained polyethylene from unreacted ethylene in high and low pressure recycling systems, characterized in that as a chain transfer agent, a mixture of isopropyl alcohol with glycols containing 2-5 carbon atoms in the molecule, or with their derivatives - polyglycols with a molecular weight (MM) of not more than 3000 with a mass ratio of isopropyl alcohol and glycol or polyglycol equal to 1 :( 0.05-0.25). 2. The method according to claim 1, characterized in that the mixture of isopropyl alcohol with glycols or polyglycols is used in an amount of 0.20-3.00% by weight of ethylene fed to the reactor. 3. The method according to claim 1, characterized in that the solution of a mixture of peroxides, consisting of 90-60 wt.% Tert-butyl peroxy-3,5,5-trimethylhexanoate and 10-40 wt.% Tert-butyl peroxybenzoate, is fed to the top reactor, and a solution of a mixture of peroxides, consisting of 10-50 wt.% tert-butyl peroxybenzoate and 50-90 wt.% di-tert-butyl peroxide - in the lower part of the reactor. 4. The method according to claim 1, characterized in that the minimum temperature in the upper part of the reactor is maintained in the range of 210-230 ° C, and the maximum temperature in the lower part of the reactor is 245-265 ° C. 5. The method according to claim 1, characterized in that branched acyclic paraffinic compounds with a number of 10-20 carbon atoms in the molecule are used as an organic solvent of peroxides.