The method of producing homopolymers of ethylene and copolymers of ethylene with vinyl acetate

 

(57) Abstract:

The invention can be used in the chemical and petrochemical industries. The invention consists in the process (co)polymerization at a pressure of 1400-3000 ATM, the flow velocity of the reaction mass of 5-10 m/s, using periodic discharge pressure in the reactor when the depth of discharge pressure at the beginning of the reactor 70-150 MPa) and the period between discharges with 100-200 in the presence of a homogenizing hydrocarbon additives. The additive is branched acyclic compounds of the paraffin series with srednekamennogo molecular weight (Mn) 300 to 3000 and a number of 230-400 mesh CH3- groups per 1000 carbon atoms in the mass ratio of the reaction mass to a homogenizing additive(1 : 0,0003)- (1 : 0,002). The process for (co)polymerization in the beginning of one zone of the reactor or at the beginning of the first zone multi-zone reactor is carried out at 160-200°C, and in subsequent sections of the single-band or multi-zone reactor is carried out at 200-320°C, while the specific heat load for the area of the reactor with a temperature of 160-200°With support in the range of 30000-50000 kcal/m2including the Method provides the necessary stability of the synthesis of (co)polymers that allow the sale of way. 1 C.p. f-crystals, 1 table.

The invention relates to the technology of producing homopolymers or copolymers of ethylene with vinyl acetate by the method of high pressure in a tubular reactor and can be used in the chemical and petrochemical industries.

Known (Patent of the USSR N1838330, class C 08 F 110/02, 2/38, publ. 30.08.93) a method of producing polyethylene by polymerization of ethylene in a tubular reactor or a reactor with a stirrer in the presence of oxygen and (or) organic peroxides when pressure 1350-2270 ATM (134-226 MPa) and temperature 145-317oC (418-530 K). To improve the homogeneity and purity of the final product before and / or after the reactor is injected homogenizing additive which is a mixture of normal acyclic compounds of the paraffin series, consisting of 2.5 to 10.0 wt.% n-paraffins C11-C12, 80-90 wt.% n-paraffins C13-C17and 0.5 to 10.0 wt.% n-paraffins C18-C20and n-paraffins enter in the quantity of 0.02 -0,30 wt.% from the original reaction mixture. Introduction in the reaction mass homogenizing additive cleans the walls of the reactor from deposits of high molecular weight products that improves the conditions of heat transfer, increases the conversion of the reaction mass and reduces the number is cyclic compounds, in particular, dodecane, leads to deterioration of the optical properties and strength characteristics of the film made from the obtained in the presence of polyethylene (see reference example 30). Apparently, the marked deterioration in the properties of the polyethylene film is observed with the introduction of the reaction mass of the above mixture of n-paraffins as n-dodecane and a mixture of n-paraffins similar in molecular weight and physico-chemical properties. Correct the mapping properties of polyethylenes obtained with the patent of the USSR N 1838330 and conditions of this application is difficult, as in the patent, there are no data on the optical properties and strength characteristics of plastic film, and experience with use in the polymerization of ethylene mixture of n-paraffins were not conducted because of the lack of commercial production of this product.

There is also known a method of producing polyethylene described in the book "high-pressure Polyethylene. Scientific and technical basis for the industrial synthesis" /Century A. Polyakov, F. I. Duntov, A. E. Sofiev etc.-L.: Chemistry, 1988, 13-37 C. , in accordance with which the polyethylene is obtained by radical polymerization of ethylene in the mass heated single or multi-zone tubular reactor in which the periodical discharge of pressure with depth pressure relief at the beginning of the reactor 200 - 300 atmospheres and the period between discharges with 60-100, initiating the polymerization reaction by oxygen, supplied in a mixture with ethylene in each zone of the reactor. Formed in the polyethylene reactor together with unreacted ethylene is continuously withdrawn from the reactor, cooled and separate the polymer from ethylene. Unreacted ethylene is cooled, cleaned and mixed with fresh ethylene is again fed into the reactor. Due to the low speed of flow of the reaction mass method allows efficient use of the volume of the reactor, but high depth discharge pressure (200-300 bar at the beginning of the reactor and, accordingly, 300-400 ATM at the end of the reactor) at small (60-100) the period between discharges leads to the violation of homogeneity of the reaction mass and, as a consequence, deterioration of quality indicators polyethylene - turbidity film made from such a polymer, and increase the amount of gel-like inclusions (see reference example 22).

Closest to the claimed method according to the totality of the claimed features is a method of producing homopolymers of ethylene or copolymers of ethylene with vinyl acetate, according to the author. mon. The USSR N475861, (M CL C 08 F 110/02, C 08 F 210/02, publ. 05.03.76). In accordance with the specified sposobem single or multi-zone tubular reactor at a pressure of 1200-4000 ATM and a temperature of 100-350oC to initiate the reaction of (co)polymerization by oxygen, supplied in a mixture with ethylene in each zone of the reactor, the introduction into the reaction mass before the reactor hydrocarbon additives (propane) and subsequent separation of the obtained (co)polymer from the unreacted ethylene or mixtures of ethylene with vinyl acetate. (Co)polymerization is carried out at a flow velocity of the reaction mass in the reactor more than 10 m/s (but not higher than 20 m/s). The pressure at any cross section of the reactor to maintain a constant time.

This method provides a high yield of the final product, obtaining high-quality polymer, suitable for transparencies and ease of process control, however, the implementation of the method is associated with high material costs, because, as you know, when the residence time of the reaction mass in the reactor 60-300 and speed 14-20 m/s (see high-pressure Polyethylene. Scientific and technical basis for the industrial synthesis /Century A. Polyakov, F. I. Duntov, A. E. Sofiev etc.-L. Chemistry, 1988, 29 S.) requires the reactor, the minimum length is 840 m

The technical result, which provides the inventive method is to reduce material costs during the implementation process and the technical result is achieved due to the fact, in the method of producing homopolymers of ethylene or copolymers of ethylene with vinyl acetate, comprising the (co)polymerization of ethylene in a heated one - or multi-zone tubular reactor at a pressure and temperature, initiating the reaction of (co)polymerization by oxygen, supplied in a mixture with ethylene in each zone of the reactor, the introduction into the reaction mass before the reactor additives and separating the obtained (co)polymer from the unreacted ethylene or mixtures of ethylene with vinyl acetate, (co)polymerization is carried out at a pressure 1400-3000 ATM, the flow velocity of the reaction mass of 5-10 m/s with the use of periodic discharge pressure at the beginning of the reactor 70-150 ATM with the period between discharges with 100-200, and as an additive used homogenizing hydrocarbon additive, which are branched acyclic compounds of the paraffin series with srednekamennogo molecular weight (Mn) 300 to 3000 and a number of 230-400 mesh CH3-groups per 1000 carbon atoms in the mass ratio of the reaction mass to a homogenizing additive is 1 : 0,0003-1 : 0,002 while before separating the obtained (co)polymer, the reaction mixture is cooled.

The process for (co)polymerization in the beginning of one zone of the reactor or at the beginning of the of kotonoha reactor is carried out at a temperature of 200-320oC, while the specific heat load for the area of the reactor with a temperature of 160-200oC is maintained in the range of 30000-50000 kcal/m2hour.

The process for (co)polymerization of ethylene in a tubular reactor, initiated by oxygen, can be divided into two stages:

1. Stage indolent (co)polymerization occurring at temperatures of 160-200oC;

2.Stage intensive (co)polymerization occurring at temperatures above 200oC.

The polymer obtained in terms of the slow mode (co)polymerization, has a high molecular mass (Mnmore than 100 000).

Such polymer even at pressures up to 3000 bar in a mixture with ethylene or ethylene-vinyl acetate) forms a heterogeneous system consisting of a polymer phase with a small amount dissolved in the ethylene or ethylene-vinyl acetate), and the gaseous phase, representing a solution of ethylene (a mixture of ethylene-vinyl acetate) with a small amount of high molecular weight (co)polymer. At high (>10 m/s) speeds the reaction medium polymer phase is plucked from the walls of the tubular reactor and transferred the reaction stream in the area of intensive (co)polymerization, where smeshivaet is tilen-vinyl acetate. At low (5-10 m/s) speeds the reaction of high molecular weight (co)polymer is deposited on the walls of the reactor, worsens the conditions of heat transfer from the coolant to the reaction mass, and further, as it accumulates, and movement to the area of intensive (co)polymerization creates conditions for heterogeneous (co)polymerization. (Co)polymerization in heterogeneous conditions leads to deterioration of quality of product and to periodic thermal decomposition reaction medium in the reactor. To improve the stability of the polymerization process at low speeds the reaction mixture, the pulsating pressure support mode is periodically through with 60-100 for a short time sharply reduce the pressure at the beginning of the reactor at 200 - 300 ATM. This corresponds to a pressure drop at the end of the reactor to 300 - 400 ATM. Thus, by increasing the speed of the reaction mixture polymer melt from the walls of the reactor breaks down and transferred to the area of intensive (co)polymerization. This technique allows to increase the stability of the process, but leads to a deterioration of the properties of the obtained product, to the extent the discharge pressure of 200-300 bar and associated with the discharge, the effect of lowering the temperature causes the pressure at the small period between discharges have a negative impact on the resource of the reaction equipment.

Introduction in the reaction mass acyclic compounds contributes to the homogenization of the reaction mixture and the improvement of conditions for heat transfer, as is rightly pointed out in the description of the patent of the USSR N 1838330. However, the introduction of n-paraffins in addition to these positive factors has negative consequences: a film made of polyethylene obtained in the presence of n-paraffins, has increased the turbidity and low strength. This is due to the lack of homogenizing ability and reaction inertness of n-paraffins. More effective is the use of branched acyclic compounds which are relatively movable in an atom of hydrogen at a tertiary carbon atom and, therefore, in terms of the (co)polymerization of ethylene are agents of chain transfer. Homogenizing the ability of such compounds to the system ethylene-polyethylene is also higher.

As branched acyclic compounds having srednekamennogo molecular weight of 300 to 3000 and 230-400 mesh CH3- groups per 1000 carbon atoms, there can be used hydrocarbons produced by the method of thermal degradation of copolymers of ethylene with propylene. Introduction in the reaction mass homogenizer the I in reducing the depth of discharge and increasing the period between discharges, to improve the quality characteristics of the obtained product turbidity and the strength of the film in longitudinal and transverse directions.

In addition, the introduction of branched acyclic hydrocarbon in the reaction mass allows on the site of the reactor, corresponding to the slow mode (co)polymerization, to increase the specific heat load up to 30000-50000 kcal/m2the hour that it is impossible for modern tubular reactor having a diameter of 16-70 mm (specific heat load for them is in the range 15000-28000 kcal/m2hour). The increase in the specific heat load for the site is slow (co)polymerization contributes to the stabilization process, reducing the residence time of the reaction mass at this site to 5-10 with and improve the quality of the product.

The invention is illustrated by the following examples.

Example 1.

On entrance one zone of the tubular reactor with a length of 225 m and an inner diameter of 16 mm serves preheated to 160oC under a pressure of 2000 ATM flow of ethylene in the amount of 2700 kg/h containing 0,00027 wt.% oxygen and 0.1 wt.% homogenizing hydrocarbon additive, a mixture of branched acyclic of soedineniya. Homogenizing additive prepared by the method of thermal degradation of high molecular weight copolymer of ethylene with propylene at a temperature of degradation 390oC and residence time of the copolymer in the zone of destruction 10 C.

The mass ratio of the reaction mass to a homogenizing of the hydrocarbon additive is 1:0,001. The additive is introduced into the reaction mass under compression ethylene special pump when this Supplement performs the function of the grease plunger pair of pump. The average speed of the reaction mass in the reactor is 7.5 m/s with its stay in the reactor 30 C. using the valve located at the end of the reactor, set the depth of the periodical discharge pressure at the beginning of the reactor 100 ATM with the period between discharges 130 C. the Specific heat load on the section of the reactor corresponding to the slow polymerization is 40000 kcal/m2hour, the maximum temperature in the reactor 300oC, the conversion of ethylene in a single pass of 15.4 wt.%. The mixture is formed of polyethylene and unreacted ethylene is cooled to a temperature of 280oC and through the regulating valve is removed from the reactor in the system branch of the polyethylene from ethylene.

Properties polyeth CLASS="ptx2">

Examples 2-3.

Experiments are performed in the conditions of example 1, but in example 2, the speed of the reaction mass in the reactor is 5 m/s, as in example 3 - 10 m/s

Examples 4-5.

Experiments are performed in the conditions of example 1, but the mass ratio of the reaction mass to a homogenizing hydrocarbon additive in example 4 is 1 : 0,0003, as in example 5 - 1 : 0,002.

Examples 6-7.

Experiments are performed in the conditions of example 1, but the pressure in the reactor is 2500 ATM, srednekislye molecular mass (Mn) homogenizing the hydrocarbon additive in example 6 is 300, and in example 7 - 3000.

Examples 8-9.

Experiments are performed in the conditions of example 1, but in example 8 acyclic compounds contain 230 CH3- groups per 1000 carbon atoms, and in example 9 - 400.

Examples 10-11.

Experiments are performed in the conditions of example 1, but the depth of the periodic collapses in example 10 is 70 ATM, and in example 11 to 150 ATM.

Examples 12-13.

Experiments are performed in the conditions of example 1, but the period between discharges in example 12 100, as in example 13 - 200 C.

Examples 14-15.

Experiments are performed in the conditions of example 1, but the specific heat load on the site Rimera 15 - 50000 kcal/m2hour.

Example 16.

The experience is conducted under the conditions of example 1, but the reaction mass further comprises 5 wt. % vinyl acetate, the pressure in the reactor 1800 ATM, the maximum temperature in the reactor 268oC, the depth of the periodical discharge pressure of 70 MPa, the mass ratio of the reaction mass to a homogenizing additive is 1 : 0,0003.

Example 17 (control).

Experiments are performed in the conditions of example 1, but the speed of the reaction mass is outside the claimed range and is 3 m/s At this speed the process becomes unstable, periodically occurs explosive decomposition of the reaction mixture.

Example 18 (control).

The experience is conducted under the conditions of example 1, but the speed of the reaction mass is outside the claimed range and is 10 m/s At this speed the maximum temperature is shifted to the end of the reactor, resulting in a temperature output from the reactor of the reaction mixture reaches 310oC. Because the throttling of the reaction mass from 2000 MPa to 250 MPa due to the throttle effect increases the temperature of the mass at ~20oC, leading to thermal decomposition in the system branch of the polyethylene from Nera 1, but the mass ratio of the reaction mass to a homogenizing of the hydrocarbon additive is outside the claimed range and is in example 19 - 1 : is 0.0002, and in example 20 - 1 : 0,003. The polyethylene obtained in example 19, has increased the number of gel-like inclusions (see table), and the polyethylene obtained in example 20 has an increased content of extractable substances in the polymer, which leads to deterioration of its hygienic properties and the processing conditions.

Examples 21-22 (control).

Experiments are performed in the conditions of example 1, but the number of CH3groups in homogenizing additive is outside the claimed range and is in example 21 - 190 per 1,000 carbon atoms, as in example 22 - 500 CH3-groups per 1000 carbon atoms. In example 21 the process is unstable, periodically there is an increase in the temperature of the reaction mixture, leading to its thermal decomposition, and the polyethylene obtained in the conditions of example 22, has a higher melt flow index and low density.

Example 23 (control).

The experience is conducted under the conditions of example 1, but srednekislye molecular mass (Mn) homogenizing the hydrocarbon additive is beyond the claimed within the different inclusions (see table), because of its lack of homogenizing power.

Examples 24-25 (control).

Experiments are performed in the conditions of example 1, but the depth of the periodic discharge pressure is outside the claimed range and is in example 24 - 200 ATM, as in example 25 to 50 ATM. The polyethylene obtained in example 24, has degraded the quality indicators in turbidity and the amount of gel-like inclusions (see table), and experience in the conditions of example 25 was characterized by unstable synthesis process, the rise of temperature at the beginning of the plot, corresponding to the intensive mode of polymerization, which leads to subsequent explosive decomposition of the reaction mixture.

Example 26-27 (control).

The experience is conducted under the conditions of example 1, but the period of the periodic discharge pressure is outside the claimed range and is in example 26 to 80, as in example 27 to 250 C. the Polyethylene obtained in example 26, has worsened the rate of turbidity and the amount of gel-like inclusions. The experience carried out in the conditions of example 27, characterized by unstable synthesis process, leading to explosive decomposition of the reaction mixture.

Example 28 (control).

The experience carried out in conditions of the rights claimed range and is 15000 kcal/m2hour. For a given workload length of the reactor, corresponding to the slow mode of polymerization increases, the maximum temperature is shifted to the end of the reactor, which leads to its thermal decomposition in the system of separation of polyethylene from unreacted ethylene.

Example 29.

At the entrance to the first zone, dual-zone tubular reactor having a length of the first zone 150 m and an internal diameter of 16 mm, serves the first part of the flow of ethylene, preheated to 160oC, under pressure of 2200 psi number 1800 kg/h. The flow of ethylene contains oxygen in the number 0,0026 wt.% and homogenizing the hydrocarbon additive in an amount of 0.1 wt.% (the mass ratio of the reaction mass to a homogenizing additive is 1 : 0,001, the number of CH3groups of 300 to 1000 carbon atoms, the viscosity of the additives 130 SP). Homogenizing additive is introduced at the stage of compression of ethylene special pump. The second part of the flow of ethylene in the amount of 1800 kg/hour and a temperature of 100oC serves under the same pressure in the second zone of the reactor, which has a length of 150 m and an internal diameter of 20 mm, the temperature of the reaction mass after mixing streams of ethylene 200oC. the oxygen Content in the second part of the area is 5 m/s, in the second zone is 6.4 m/s (respectively, the residence time in the first zone 30 and the second zone 23). Set the depth of the periodical discharge pressure at the beginning of the reactor 100 ATM with the period between discharges 130 C. using coolant establish specific heat load on the section of the first zone of the reactor, corresponding to the slow mode of polymerization, 35 000 kcal/m2hour. The maximum temperature in the first zone of the reactor 310oC, in the second zone 300oC. Conversion of ethylene in a single pass through the reactor is 20.6 wt.%. Properties of the resulting polyethylene is shown in the table.

Analogously to example 29 you can process the (co)polymerization in a tubular reactor consisting of three or more zones.

Example 30 (control).

The experience is conducted under the conditions of example 1, but as a homogenizing hydrocarbon additives used n-dodecan. The polyethylene obtained in the presence of dodecane, has degraded performance in terms of turbidity and strength at break in the longitudinal and transverse directions.

Example 31 (control).

The experience is conducted under the conditions of example 1, but homogenizing hydrocarbon additive into a stream of ethylene is not administered. Set the chap who owned the heat load on the section of the reactor, corresponding to the slow mode of polymerization, is 15 000 kcal/m2hour.

The conversion of ethylene in a single pass is 15.4 wt.%. The polyethylene obtained in this example (see table), has degraded optical indicators (turbidity film is 39%), reduced the strength of the film and increased the number of gel-like inclusions (3 pcs. per m2), which reduces consumer properties manufacturing of products.

It should be noted that not been conducted the following experiments with process parameters outside the claimed range:

- experience using as a homogenizing additive hydrocarbons with molecular weight of more than 3000, because the filing of such additive in the reactor requires special equipment;

- experience with thermal load on the site slow polymerization of the above 50000 kcal/m2hour, because it takes a carrier with temperatures above 230oC. For preparation of the carrier with such high temperature also requires special equipment.

Thus, the proposed method of producing polymers of ethylene and copolymers with vinyl acetate provides the necessary stabilizovalo, be reduced in comparison with the prototype material costs for the implementation of the method.

1. The method of producing homopolymers of ethylene or copolymers of ethylene with vinyl acetate, comprising the (co)polymerization of ethylene in a heated one - or multi-zone tubular reactor at a pressure and temperature, initiating the reaction of (co)polymerization by oxygen, supplied in a mixture with ethylene in each zone of the reactor, the introduction into the reaction mass before the reactor additives and separating the obtained (co)polymer from the unreacted ethylene or mixtures of ethylene with vinyl acetate, wherein the (co)polymerization is carried out at a pressure of 1,400 to 3,000 ATM, the flow velocity of the reaction mass 5 - 10 m/s using periodic discharge pressure to the solution when the depth of discharge pressure at the beginning of the reactor 70 - 150 ATM and the period between discharges of 100 - 200, and as an additive used homogenizing hydrocarbon additive, which are branched acyclic compounds of the paraffin series with srednekamennogo molecular weight (Mn) 300 - 3000 and the number 230 - 400 CH3-groups per 1000 carbon atoms in the mass ratio of the reaction mass to a homogenizing additive 1:0,0003 - 1:0,002 while before the m, the process of (co)polymerization in the beginning of one zone of the reactor or at the beginning of the first zone multi-zone reactor is carried out at 160 - 200oC, and in subsequent sections of single-band and multi-zone reactor is carried out at 200 to 320oC, while the specific heat load for the area of the reactor with a temperature of 160 - 200oC is maintained in the range of 30000 - 50000 kcal/m2PM

 

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