CN115197348A - Ethylene polymers and high pressure free radical polymerization process and apparatus for preparing ethylene polymers - Google Patents
Ethylene polymers and high pressure free radical polymerization process and apparatus for preparing ethylene polymers Download PDFInfo
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- CN115197348A CN115197348A CN202110399484.1A CN202110399484A CN115197348A CN 115197348 A CN115197348 A CN 115197348A CN 202110399484 A CN202110399484 A CN 202110399484A CN 115197348 A CN115197348 A CN 115197348A
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- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
- C08F10/00—Homopolymers and copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond
- C08F10/02—Ethene
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J19/00—Chemical, physical or physico-chemical processes in general; Their relevant apparatus
- B01J19/0006—Controlling or regulating processes
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J19/00—Chemical, physical or physico-chemical processes in general; Their relevant apparatus
- B01J19/18—Stationary reactors having moving elements inside
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J19/00—Chemical, physical or physico-chemical processes in general; Their relevant apparatus
- B01J19/24—Stationary reactors without moving elements inside
- B01J19/2415—Tubular reactors
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- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J4/00—Feed or outlet devices; Feed or outlet control devices
- B01J4/001—Feed or outlet devices as such, e.g. feeding tubes
- B01J4/002—Nozzle-type elements
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J4/00—Feed or outlet devices; Feed or outlet control devices
- B01J4/008—Feed or outlet control devices
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
- C08F110/00—Homopolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond
- C08F110/02—Ethene
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
- C08F210/00—Copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond
- C08F210/02—Ethene
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J2204/00—Aspects relating to feed or outlet devices; Regulating devices for feed or outlet devices
- B01J2204/002—Aspects relating to feed or outlet devices; Regulating devices for feed or outlet devices the feeding side being of particular interest
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J2219/00—Chemical, physical or physico-chemical processes in general; Their relevant apparatus
- B01J2219/00002—Chemical plants
- B01J2219/00027—Process aspects
- B01J2219/0004—Processes in series
Abstract
The invention relates to the field of polyolefin, and discloses a high-pressure free radical polymerization method and device for preparing an ethylene polymer, and the ethylene polymer prepared by the method. The method comprises the following steps: feeding the first reaction material into a kettle type reactor, and carrying out a first polymerization reaction to obtain a first polymerization product; separating the first polymerization product to obtain a first material and a second material; the second material is cooled and pressurized by a first jet pump and then returns to the kettle type reactor; cooling the first material, sending the cooled first material into a tubular reactor, and carrying out a second polymerization reaction with a second reaction material to obtain an ethylene polymer and a third material; and cooling the third material, pressurizing by a second jet pump, and returning to the kettle reactor or the tubular reactor. The method can improve the long-chain branching degree and the yield of the ethylene polymer, avoid the fouling and blockage of a circulating pipeline and improve the production capacity. The ethylene polymers thus produced have a high long chain branch content.
Description
Technical Field
The invention relates to the field of polyolefin, in particular to a high-pressure free radical polymerization method and device for preparing an ethylene polymer and the ethylene polymer prepared by the method.
Background
Low Density Polyethylene (LDPE) is an important thermoplastic polymer material, has good chemical stability and electrical insulation, good flexibility, extensibility and transparency, and good processability, and is mainly used for the fields of manufacturing film, coating material of wires and cables, pipes, coating products and the like. Conventional low density polyethylene is produced by free radical polymerization initiated by an initiator at high temperature and high pressure. Autoclave and tubular reactors are two high pressure reactors used primarily for the production of low density polyethylene. Each type of reactor has the advantages of large pressure gradient, wide temperature distribution, short reaction time, no need of stirring, relatively simple process and relatively narrow molecular weight distribution in the tubular process reactor. The materials in the kettle reactor have larger back mixing and longer retention time, and long-chain branches and short-chain branches generated on macromolecules are more and the molecular weight distribution is wider. Based on economics and product design driven improvements, the combined process using reactors can significantly improve the yield and product performance of LDPE. Such improvements have unique advantages for a combination of yield and specificity of the polymerization product.
Disclosure of Invention
The invention aims to overcome the problems of low long-chain branching degree and low yield of low-density polyethylene (LDPE) in the prior art, and provides a high-pressure free radical polymerization method and device for preparing ethylene polymer and the ethylene polymer prepared by the method. The high-pressure free radical polymerization method for preparing the ethylene polymer can improve the long-chain branching degree and the yield of the ethylene polymer, avoid the fouling and blockage of a circulating pipeline and improve the production capacity. The ethylene polymers thus produced have a high long chain branch content.
In order to achieve the above object, a first aspect of the present invention provides a high pressure radical polymerization process for preparing an ethylene polymer, characterized in that the process comprises the steps of:
(1) Conveying a first reaction material containing ethylene, a chain transfer agent and optionally a comonomer into a tank reactor to perform a first polymerization reaction to obtain a first polymerization product;
(2) Separating the first polymerization product to obtain a first material and a second material; the second material is cooled and pressurized by the first jet pump and then returns to the kettle type reactor;
(3) After cooling, the second material is conveyed to a high-pressure tubular reactor and is subjected to a second polymerization reaction with a second reaction material containing ethylene, a chain transfer agent and optionally a comonomer to obtain an ethylene polymer and a third material;
(4) And cooling the third material, pressurizing by a second jet pump, and returning to the kettle reactor or the tubular reactor.
In a second aspect, the present invention provides an ethylene polymer obtainable by the above process.
A third aspect of the invention provides an apparatus for free radical polymerization of ethylene, characterized in that it comprises: at least one tank reactor, at least one tubular reactor, a first jet pump and a second jet pump;
the tank reactor is used for first polymerization of ethylene and optional comonomers to obtain a first polymerization product, and the first polymerization product is separated to obtain a first material and a second material;
the first jet pump is used for returning the second material to the kettle type reactor;
the tubular reactor is used for second polymerization of the first feed, ethylene and optionally comonomer to obtain ethylene polymer and a third stream;
the second jet pump is used to return the third stream to the tank reactor or the tubular reaction.
By the technical scheme, the high-pressure free radical polymerization method for preparing the ethylene polymer and the ethylene polymer prepared by the method provided by the invention have the following beneficial effects:
(1) The ethylene material with lower temperature and the material at the outlet of the kettle reactor with higher temperature are directly mixed by using the jet pump, so that the temperature at the outlet of the kettle reactor can be quickly reduced, the initiator which is not reacted at the outlet of the kettle reactor is prevented from being continuously decomposed in a circulation loop to initiate ethylene polymerization reaction, and the circulation pipeline is prevented from scaling and blocking.
(2) The capacity of the tank reactor is limited by the heat removal capacity of the reaction mass. After the circulation is added to the kettle type reactor, the temperature of the circulating material can be further reduced through the external circulation heat exchanger, so that the heat transfer capacity of the reaction material is improved, and the production capacity of the kettle type reactor can be obviously improved.
(3) By recycling the polyethylene with a large molecular weight back to the reactor inlet, the improvement of the degree of long chain branching is facilitated.
(4) The tubular reactor and the kettle type reactor are combined, the molecular chain structure of the product can be regulated and controlled more flexibly, more new products of polyethylene can be developed, and flexible production can be realized.
Drawings
FIG. 1 is a process flow diagram of a high pressure, free radical polymerization process for preparing an ethylene polymer according to the present invention;
FIG. 2 is a process flow diagram of a high pressure, free radical polymerization process for preparing an ethylene polymer according to the present invention.
Description of the reference numerals
1. A first jet pump; 2. a kettle reactor; 3. a first heat exchanger; 4. a second heat exchanger; 5. a second jet pump; 6. a tubular reactor; 7. a third heat exchanger; 8. a first reaction mass; 9. a second reaction mass; 10. a first stream; 11. a second stream; 12. a third stream; 13. a first material; 14. a second material; 15. a third material; 16. power logistics; 17. a reactant stream; I1-I4, an initiator stream;
101. a first jet pump; 102. a kettle reactor; 103. a first heat exchanger; 104. a second heat exchanger; 105. a second jet pump; 106. a tubular reactor; 107. a third heat exchanger; 108. a first reaction mass; 109. a second reaction mass; 110. a first stream; 111. a second stream; 112. a third stream; 113. a first material; 114. a second stream; 115. a third stream; 116. power logistics; 117. a reactant stream; I101-I104, initiator stream.
Detailed Description
The endpoints of the ranges and any values disclosed herein are not limited to the precise range or value, and such ranges or values should be understood to encompass values close to those ranges or values. For numerical ranges, each range between its endpoints and individual point values, and each individual point value can be combined with each other to give one or more new numerical ranges, and such numerical ranges should be construed as specifically disclosed herein.
The present invention provides in a first aspect a high pressure, free-radical polymerization process for the preparation of an ethylene polymer, characterized in that said process comprises the steps of:
(1) Feeding a first reaction material comprising ethylene, a chain transfer agent and optionally a comonomer into a tank reactor for a first polymerization reaction to obtain a first polymerization product;
(2) Separating the first polymerization product to obtain a first material and a second material; the second material is cooled and pressurized by a first jet pump and then returns to the kettle type reactor;
(3) After cooling, the first material is sent into a tubular reactor and is subjected to a second polymerization reaction with a second reaction material containing ethylene, a chain transfer agent and a comonomer to obtain an ethylene polymer and a third material;
(4) And cooling the third material, pressurizing by a second jet pump, and returning to the kettle reactor or the tubular reactor.
In the invention, in the tank reactor, ethylene and optional comonomer are polymerized to obtain a polymer, and the long-chain branch content of the polymer can be increased, so that the chain transfer reaction is easier to occur in the tubular reactor. And in the tubular reactor, the ethylene is further polymerized, so that the molecular chain structure of the polymer can be adjusted, the residual quantity of the initiator is reduced, and the productivity is increased.
In the present invention, the comonomer is at least one selected from the group consisting of vinyl acetate, methyl acrylate and methyl methacrylate.
According to the invention, the tank reactor comprises more than two reaction zones.
In the present invention, as shown in FIG. 1, the tank reactor 2 comprises a first reaction partition 2a and a second reaction partition 2b located below the first reaction partition 2 a.
In the invention, more than two reaction subareas are arranged in the kettle type reactor, and different polymerization environments can be controlled, so that different polymerization products can be produced in different subareas, and the diversity of the products is realized.
According to the invention, the first reaction mass is divided into three material flows, which enter the tank reactor through the upper feed opening, the middle feed opening and the lower feed opening of the tank reactor.
As shown in fig. 1, a first reaction mass 8 comprising ethylene, initiator, chain transfer agent and optionally comonomer is split into three streams: the device comprises a first material flow 10, a second material flow 11 and a third material flow 12, wherein the three material flows respectively enter the tank reactor through an upper feeding hole, a middle feeding hole and a lower feeding hole of the tank reactor.
According to the invention, the first reaction material is divided into three material flows, and the three material flows are fed into different reaction subareas of the kettle reactor through the feed inlets positioned at different parts of the kettle reactor, so that the accurate control of the temperature in the reaction kettle can be realized.
According to the invention, the tubular reactor comprises more than two reaction zones, each reaction zone being provided with a feed inlet.
As shown in FIG. 1, in the present invention, the tubular reactor 6 comprises a first reaction zone 6a and a second reaction zone 6b, wherein the second reaction zone 6b is located upstream of the first reaction zone 6 a.
In the invention, more than two reaction subareas are arranged in the tubular reactor 6, and the first material and the reaction material are introduced into the tubular reactor 6 from different reaction subareas, so that the reaction temperature in the tubular reactor 6 can be accurately regulated and controlled by fully utilizing the low temperature of the reaction material.
According to the present invention, in the step (1), the conditions of the first polymerization reaction include: the polymerization pressure is 100-350MPa, and the polymer temperature is 100-350 ℃.
In the present invention, the average residence time of the first polymerization reaction can be adjusted according to actual needs, and preferably, the average residence time of the first polymerization reaction is not less than 10 times of the half-life of the initiator used in the polymerization reaction.
In the present invention, homopolymerization or copolymerization of ethylene is achieved under the above-described polymerization conditions, and the long-chain branch content of the produced ethylene polymer can be significantly provided.
Further, in the step (1), the conditions of the first polymerization reaction include: the polymerization pressure is 150-250MPa, and the polymer temperature is 200-300 ℃.
In the present invention, the first polymerization product includes an ethylene homopolymer or an ethylene copolymer, an unreacted initiator, ethylene, a chain transfer agent, and a comonomer.
In the present invention, in the first polymerization product, the ethylene homopolymer or ethylene copolymer has a weight average molecular weight of 5 to 20 ten thousand and a number average molecular weight of 1 to 2 ten thousand.
In the present invention, the first polymerization product may be separated to obtain the first material and the second material in a conventional manner in the art.
In the present invention, the first material comprises mainly an ethylene homopolymer or an ethylene copolymer; the second feed consists essentially of unreacted initiator, ethylene, chain transfer agent and comonomer.
According to the invention, in the step (2), the mass flow ratio of the second material to the first material is 0-2:1.
in the invention, when the mass flow ratio of the second material to the first material is controlled to meet the range, the residence time of the reaction materials in the tank reactor can be prolonged, and the conversion rate of the monomers and the long-chain branching degree of the prepared ethylene polymer are further improved.
Further, the mass flow ratio of the second material to the first material is 0.1-1:1.
according to the invention, the second stream enters the tank reactor through one or more of the upper feed inlet, the middle feed inlet and the lower feed inlet of the tank reactor.
In one embodiment of the present invention, as shown in fig. 1, the second stream 14 is cooled by the second heat exchanger 4, mixed with the first reaction material 8 in the first jet pump 1, pressurized, and divided into a first stream 10, a second stream 11, and a third stream 12, which enter the tank reactor through one or more of the upper feed inlet, the middle feed inlet, and the lower feed inlet of the tank reaction.
According to the invention, in step (2), the cooling is such that the temperature of the second material is reduced by not more than 120 ℃.
In the invention, the temperature of the cooled second material is reduced through the heat exchange of the second heat exchanger 4, and the temperature reduction amplitude is controlled to be not more than 120 ℃, so that the capacity can be remarkably increased on the premise of ensuring that the prepared polymer is not separated from the second material.
Further, in the step (2), the cooling reduces the temperature of the second material by 80-120 ℃.
According to the present invention, in the step (3), the conditions of the second polymerization reaction include: the polymerization pressure is 100-350MPa, and the polymerization temperature is 100-350 ℃.
In the present invention, the average residence time for the second polymerization reaction can be adjusted according to actual needs, and preferably, the average residence time for the second polymerization reaction is not less than 10 times the half-life of the initiator used for the polymerization reaction.
In the present invention, homopolymerization or copolymerization of ethylene is achieved under the above-described polymerization conditions, and the long chain branch content of the produced ethylene polymer can be significantly provided.
Further, in the step (3), the conditions of the second polymerization reaction include: the polymerization pressure is 150-250MPa, and the polymer temperature is 200-300 ℃.
In the invention, the first material and a second reaction material containing ethylene, an initiator, a chain transfer agent and a comonomer are subjected to a second polymerization reaction in a tubular reactor to obtain an ethylene polymer and a third material. Wherein the ethylene polymer is discharged as the final product.
In the present invention, the first reactant 8 and the second reactant 9 may be the same or different.
In a preferred embodiment of the present invention, as shown in FIG. 1, the second reaction mass 9 is divided into a motive stream 16 for powering the second jet pump 5 and a reactant stream 17 for carrying out the second polymerization reaction. After being mixed and pressurized in the second jet pump 5, the power material flow 16 and the third material 15 enter the kettle reactor through one or more of an upper feed inlet, a middle feed inlet and a lower feed inlet of the kettle reactor; reactant stream 17 enters the tank reactor directly through one or more of the upper feed inlet, the middle feed inlet, and the lower feed inlet of the tank reactor.
In the present invention, the flow rates of the motive fluid 16 and the reactant fluid 17 can be adjusted according to actual needs, and preferably, the flow rate ratio of the reactant fluid 17 to the motive fluid 16 is 0:1-1:0, preferably 0.1.
In the present invention, the third material mainly comprises oligomers of ethylene, unreacted ethylene, a comonomer, an initiator and a chain transfer agent.
According to the invention, the ratio of the mass flow of the third material to the mass flow of the first material is 0-2:1.
in the invention, when the mass flow ratio of the third material to the first material is controlled to satisfy the above range, the residence time of the reaction material in the tank reactor can be prolonged, and the conversion rate of the monomer and the long chain branching degree of the prepared ethylene polymer can be further improved.
Further, the mass flow ratio of the third material to the first material is 0.3-1:1.
according to the invention, the third material is returned to the tank reactor via one or more of the upper, middle and lower feed openings of the tank reactor.
In one embodiment of the present invention, as shown in fig. 1, the third stream 15 is cooled by the third heat exchanger 7, mixed with the second reactant 9 in the second jet pump 5, pressurized, and then introduced into the tank reactor through one or more of the upper feed inlet, the middle feed inlet, and the lower feed inlet of the tank reactor.
According to the invention, the third stream is returned to the tube reactor via the feed opening of the first reaction zone of the tube reactor.
In the present invention, as shown in FIG. 1, the third material 15 is returned to the tubular reactor through the first reaction zone 6a of the tubular reactor.
According to the invention, the cooled third material 15 and the second reaction material 9 are mixed in the second jet pump and pressurized and then returned to the tubular reactor through the feed inlet of the first reaction zone of the tubular reactor.
In the present invention, as shown in FIG. 1, the third material 15 is mixed with the motive fluid 16 in the second jet pump 5 and pressurized, and then returned to the tubular reactor through the feed inlet of the first reaction zone 6a of the tubular reactor.
In a preferred embodiment of the invention, the cooled third material 15 is mixed with a motive fluid 16 in the second jet pump 5 and pressurized before being returned to the tubular reactor through the inlet of the second reaction zone 6b of the tubular reactor.
In a preferred embodiment of the present invention, the cooled third material 15 is mixed with the power stream 16 in the second jet pump 5 and pressurized, and then returned to the tubular reactor through the inlet ports of the first reaction zone 6a and the second reaction zone 6b of the tubular reactor.
In a preferred embodiment of the invention, the location of the return of the third material to the tube reactor 6 is upstream of the location of the flow of the third material out of the tube reactor 6.
In a preferred embodiment of the invention, the location of the third stream out of the tubular reactor 6 is located downstream of the temperature peak of the reaction zone (6 a or 6 b) of the tubular reactor.
In the present invention, the temperature peak of the reaction section (6 a, 6 b) of the tubular reactor means the maximum value of the temperature in the reaction section.
In a preferred embodiment of the invention, the process comprises a plurality of tubular reactors. Preferably, the reaction zones of a plurality of tubular reactors constitute one tubular reactor in series.
In a preferred embodiment of the present invention, the ethylene, the chain transfer agent and optionally the comonomer of the tubular reactor obtained by connecting a plurality of tubular reactors in series enter the tubular reactor from the feed inlet of the first reaction zone of a plurality of said tubular reactors.
In a preferred embodiment of the present invention, the ethylene, chain transfer agent and optionally comonomer of a tubular reactor obtained by a cascade of a plurality of tubular reactions are fed into the tubular reactor from the feed inlet of the reaction zone of a plurality of said tubular reactors.
According to the invention, the third material 15 is mixed with the first material 13 and then returned to the tubular reactor through the feed inlet of the first reaction zone of the tubular reactor, and the second polymerization reaction is continued.
In the present invention, as shown in fig. 1, the third material 15 is mixed with the first material 13 from the bottom of the tank reactor cooled by the first heat exchanger 3 by cooling by the third heat exchanger 7 and pressurizing by the second jet pump 5 in this order, and then returned to the pipe reactor through the pipe reactor 6a to continue the second polymerization reaction.
According to the invention, in step (4), the cooling is such that the temperature of the third material does not decrease by more than 120 ℃.
In the present invention, the temperature of the cooled third material is reduced by the heat exchange of the third heat exchanger 7, and the temperature reduction is controlled to be not more than 120 ℃, thereby significantly increasing the productivity while ensuring that the produced polymer is not separated from the third material.
Further, in the step (4), the cooling reduces the temperature of the third material by 80-120 ℃.
According to the invention, the per-pass conversion of the tank reactor is 1-25%, and the per-pass conversion of the tubular reactor is 1-35%.
In the invention, the single-pass conversion rate of the tank reactor is represented by the ratio of the yield of the tank reactor to the atmospheric air quantity of a compressor; the conversion per pass of a tubular reactor is characterized by the ratio of the production of the tubular reactor to the atmospheric gas of the compressor.
Further, the per-pass conversion rate of the tank reactor is 15-20%, and the per-pass conversion rate of the tubular reactor is 20-30%.
In a second aspect, the present invention provides an ethylene polymer obtainable by the above process.
According to the invention, the content of long chain branches is at least 6LCB/1000C, based on the total weight of the ethylene polymer.
In the present invention, the long chain branch means a branch having 6 or more carbons, and LCB/1000C means the number of long chain branches having branched carbons per 1000C in the main chain of the polymer.
In the present invention, the ethylene polymer has a high long chain branch content, so that the ethylene polymer has a significant advantage in the field of coating material production.
According to the invention, the content of long chain branches is 8-10LCB/1000C.
According to the invention, the ethylene polymer has a density of 0.90 to 0.94g/cm 3 The melt index is 0.1-100g/10min.
Further, the ethylene polymer has a density of 0.91 to 0.92g/cm 3 And a melt index at 190 ℃ under a load of 2.16kg of 0.2 to 60g/10min.
In the present invention, the ethylene polymer has a weight average molecular weight of 60,000 to 300,000, a number average molecular weight of 10,000 to 30,000, and a molecular weight distribution of 5 to 15.
A third aspect of the invention provides an apparatus for free radical polymerization of ethylene, characterized in that it comprises: at least one tank reactor, at least one tubular reactor, a first jet pump and a second jet pump;
the tank reactor is used for first polymerization of ethylene and optional comonomers to obtain a first polymerization product, and the first polymerization product is separated to obtain a first material and a second material;
the first jet pump is used for returning the second material to the kettle type reactor;
the tubular reactor is used for second polymerization of the first feed, ethylene and optionally comonomer to obtain ethylene polymer and a third stream;
the second jet pump is used to return the third stream to the tank reactor or the tubular reaction.
In the invention, the device also comprises a first heat exchanger, a second heat exchanger and a third heat exchanger;
the first heat exchanger is used for cooling a first material; the second heat exchanger is used for cooling a second material; the third heat exchanger is used for cooling a third material.
In one embodiment of the present invention, as shown in fig. 1, an apparatus for producing low density polyethylene comprises:
a tank reactor 2 and a tubular reactor 6 for the polymerization of ethylene. The tank reactor 2 comprises a first reaction partition 2a and a second reaction partition 2b positioned below the first reaction partition 2 a; the tubular reactor 6 comprises a first reaction zone section 6a and a second reaction zone section 6b, wherein the second reaction zone section 6b is located upstream of the first reaction zone section 6 a.
A first jet pump 1 for returning the second material 14 to the tank reactor 2.
A second jet pump 5 for returning the third material 15 to the tube reactor 6 or the tank reactor 2.
A first heat exchanger 13 for cooling the first material 13, a second heat exchanger 4 for cooling the second material 14, and a third heat exchanger 7 for cooling the third material 15.
In a preferred embodiment of the present invention, a first reaction mass 8 comprising ethylene, a chain transfer agent and optionally a comonomer is fed into a tank reactor 2, the ethylene and optionally the comonomer being first homopolymerized at a pressure in the range of 100 to 350MPa and a temperature in the range of 100 to 350 ℃ to obtain a first polymer product. The first polymerization product is led out from the bottom outlet of the kettle reactor 2, and is separated to obtain a first material 13 and a second material 14, wherein the first material 13 is cooled by a first heat exchanger 3 and then is led into a tubular reactor 6, and the second material 14 is cooled by a second heat exchanger 4, then is mixed with a first reaction material 8 containing ethylene, a chain transfer agent and optionally a comonomer in a first jet pump 1, is pressurized, and is divided into a first material flow 10, a second material flow 11 and a third material flow 12 to return to the kettle reactor 2 again. The first material 13 and the dynamic stream 16 pressurized by the second ejector pump 5 are fed into the tubular reactor from the feed inlet of the first reaction zone 6a of the tubular reactor 6, the reactive stream 17 is fed into the tubular reactor from the feed inlet of the second reaction zone 6b of the tubular reactor 6, and the ethylene and optionally the comonomer undergo a further homopolymerization reaction at a pressure in the range of 100-350MPa and a temperature in the range of 100-350 ℃ to give an ethylene homopolymer and a third material 15. And a third material 15 is led out from the tubular reactor 6, sequentially cooled by a third heat exchanger 7, pressurized by a second jet pump 5 and returned to the inlet of the kettle reactor 2 or the tubular reactor 6.
Wherein the first reaction mass 8 and the second reaction mass 9 are identical. The initiator is divided into initiator streams I1 to I4, which are introduced into the polymerization system separately.
In one embodiment of the present invention, as shown in fig. 2, an apparatus for producing low density polyethylene comprises:
a tank reactor 102 and a tubular reactor 106 for the polymerization of ethylene. The tank reactor 102 includes a first reaction zone 102a and a second reaction zone 102b located below the first reaction zone 102 a; the tubular reactor 106 includes a first reaction zone section 106a and a second reaction zone section 106b, wherein the second reaction zone section 106b is located upstream of the first reaction zone section 106 a.
A first jet pump 101 for returning the second material 114 to the tank reactor 102.
A second jet pump 105 for returning the third material 115 to the pipe reactor 106 or the tank reactor 102.
A first heat exchanger 103 for cooling a first material 113, a second heat exchanger 104 for cooling a second material 114, and a third heat exchanger 107 for cooling a third material 115.
In a preferred embodiment of the present invention, a first reaction mass 108 comprising ethylene, a chain transfer agent, and optionally a comonomer is fed into the tank reactor 102, and the ethylene and optionally the comonomer are first homopolymerized at a pressure in the range of 100 to 350MPa and a temperature in the range of 100 to 350 ℃ to provide a first polymer product. The first polymerization product is drawn out from the bottom outlet of the tank reactor 102, and separated to obtain a first material 113 and a second material 114, wherein the first material 113 is cooled by the first heat exchanger 103 and introduced into the tubular reactor 106, and the second material 114 is cooled by the second heat exchanger 104, mixed with a first reaction material 108 comprising ethylene, a chain transfer agent, and optionally a comonomer in the first jet pump 101, pressurized, and divided into a first stream 110, a second stream 111, and a third stream 112, and returned to the tank reactor 102. The first material 113 is mixed with a power stream 116 comprising ethylene, chain transfer agent and optionally comonomer pressurized by a second jet pump 105 and enters a first reaction zone 106a of the tubular reactor 106, a reaction stream 117 comprising ethylene, chain transfer agent and optionally comonomer enters a second reaction zone 106b of the tubular reactor 106, and the ethylene and optionally comonomer continue to undergo homopolymerization under the conditions of a pressure range of 100-350MPa and a temperature range of 100-350 ℃ to obtain an ethylene homopolymer and a third material 15. The third material 115 is led out from the tubular reactor 106 and is cooled by the third heat exchanger 107 in sequence, and after being pressurized by the second jet pump 105, the third material returns to the inlet of the tank reactor 102 or the tubular reactor 106.
Wherein the first reaction mass 108 and the second reaction mass 109 are different. The initiator is divided into initiator streams I101-I104, which are introduced into the polymerization system respectively.
The present invention will be described in detail below by way of examples. In the following examples of the present invention, the following examples,
density: the polymer samples were pressed at 190 ℃ and 200MPa for three minutes and subsequently at 21 ℃ and 200MPa for one minute according to GB1033-86 test sample density. The measurements were made within one hour after the preparation of the samples.
Melt index: the polymer samples were measured for melt index at 190 deg.C/2.16 kg according to the melt index of the GB/T3682-2000 test sample.
Molecular weight: the molecular weight and molecular weight distribution of the polymer product were determined on an Alliance GPC2000 type Gel Permeation Chromatography (GPC) instrument from Waters, USA, at a test temperature of 150 ℃, polystyrene as a standard, trichlorobenzene as a solvent, and a flow rate of 1mL/min.
Branched chain content: the polymer branch content was determined on a Brukerav model 400 NMR spectrometer, bruker, germany, weighing about 80mg of the sample dissolved in deuterated o-dichlorobenzene solvent, the determination temperature being 125 ℃ and the number of scans being 5000.
Examples 1 to 8
Pressurizing ethylene, a chain transfer agent and an optional comonomer from a refining area to a pressure required by reaction by an ultrahigh pressure compressor, wherein the pressure of a kettle-type reactor is 200MPa, preheating the reactor to 160 ℃ before injecting raw materials, adding an initiator section by section to establish reaction at the beginning of the reaction, automatically adjusting the injection amount of the initiator after the temperature of the reactor is increased to a required condition, and maintaining the reaction temperature at the required reaction condition, wherein the kettle-type reactor comprises a first reaction subarea and a second reaction subarea positioned below the first reaction subarea, the temperature of the first reaction subarea is 240 ℃, and the temperature of the second reaction subarea is 260 ℃. The fresh ethylene flow, initiator flow, chain transfer agent flow, and recycle flow (mass flow ratio of second feed 14 to first feed 13) for the tank reactor are shown in table 1.
As shown in FIG. 1, the material at the outlet of the tank reactor is divided into a first material 13 and a second material 14, the second material 14 is cooled by a second heat exchanger 4, the temperature is reduced by 100 ℃, the second material is mixed with the first reaction material 8 in a first jet pump 1, the temperature after mixing is 40 ℃, and the mixture is returned to the tank reactor 2. The first material 13 is cooled by the first heat exchanger 3 and mixed with the power material flow 16 pressurized by the second injection pump 5, the temperature of the mixed material is 180 ℃, the mixed material enters the tubular reactor 6 from the first reaction subarea 6a of the tubular reactor to carry out the second polymerization reaction, in the process of the second polymerization reaction, the second reaction subarea 6b of the tubular reactor is supplemented with the reaction material flow 17, and the second polymerization reaction is continuously carried out to obtain the ethylene polymer and a third material flow 15. And cooling the third material 15 by a third heat exchanger 7, reducing the temperature by 100 ℃, pressurizing by a second jet pump 5, and returning to the tank reactor 2 or the tubular reactor 6. The pressure of the tubular reactor 6 is 180MPa, and the inlet temperatures of the three reaction zones are 180 ℃, 200 ℃ and 220 ℃. The temperature and conversion of the tubular reactor 6 were controlled by the heat exchange between the injected amount of initiator and the jacket water, the molecular weight was controlled by the content of chain transfer agent, and the flow rate of fresh ethylene, the flow rate of initiator, the flow rate of chain transfer agent and the circulation flow rate of the tubular reactor (mass flow rate ratio of the third stream 15 to the first stream 13) in the tubular reaction were as shown in table 1. The ethylene polymer produced is discharged from the tubular reactor 6. The ethylene polymers were tested for their properties and the results are shown in table 2.
Comparative example 1
An ethylene polymer was prepared according to the method of example 1, except that: no tubular reactor is included. The process conditions are shown in Table 1, and the properties of the ethylene polymers obtained are shown in Table 2.
Comparative example 2
An ethylene polymer was prepared according to the method of example 1, except that: does not contain a kettle reactor. The process conditions are shown in Table 1, and the properties of the ethylene polymers obtained are shown in Table 2.
Comparative example 3
An ethylene polymer was prepared according to the method of example 5, except that: no tubular reactor is included. The process conditions are shown in Table 1, and the properties of the ethylene polymers obtained are shown in Table 2.
TABLE 1 Process conditions for preparing ethylene polymers
TABLE 1 (continuation)
| Flow rate, kg/h | Fresh ethylene | Initiator | Chain transfer agent | Flow rate of circulation | Vinyl Acetate (EVA) | |
| Example 5 | Kettle type reactor | 15000 | 15 | 10 | 0.2 | 5000 |
| Tubular reactor | 15000 | 10 | 10 | / | 5000 | |
| Comparative example 3 | Kettle type reactor | 30000 | 25 | 20 | 0 | 10000 |
TABLE 2 Properties of the ethylene polymers
Table 2 (continuation)
| Performance of | Example 7 | Example 8 | Comparative example 1 | Comparative example 2 |
| Density (g/cm) 3 ) | 0.923 | 0.921 | 0.919 | 0.920 |
| MFR(g/10min) | 16.7 | 21.2 | 20.3 | 19.8 |
| Mn(10 4 g/mol) | 1.38 | 1.35 | 1.38 | 1.39 |
| Mw(10 4 g/mol) | 17.7 | 17.1 | 14.7 | 8.4 |
| Long chain Length chain (LCB/1000C) | 7.7 | 8.6 | 5.8 | 3.2 |
| Short chain branching content (SCB/1000C) | 12.8 | 15.2 | 10.8 | 7.4 |
Table 2 (continuation)
| Performance of | Example 5 | Comparative example 3 |
| Density (g/cm) 3 ) | 0.940 | 0.938 |
| MFR(g/10min) | 2.2 | 2.3 |
| Mn(10 4 g/mol) | 1.50 | 1.52 |
| Mw(10 4 g/mol) | 15.1 | 14.7 |
| Long chain Length chain (LCB/1000C) | 4.6 | 2.6 |
| Short chain branching content (SCB/1000C) | 15.2 | 10.2 |
As can be seen from tables 1 and 2, the long chain branch content of the polymer can be significantly increased by increasing the circulation flow rates of the tank reactor and the tubular reactor, and the introduction of chain transfer agents into the tank reactor and the tubular reactor, respectively, facilitates the adjustment of the molecular weight of the product to produce diversified products.
Examples 9 to 13
An ethylene polymer was prepared according to the method of example 1, except that: the process conditions are different and are detailed in table 3. The properties of the ethylene polymer obtained are shown in Table 4
TABLE 3
TABLE 4
| Performance of | Example 8 | Example 9 | Example 10 | Example 11 | Example 12 | Example 13 |
| Density (g/cm) 3 ) | 0.921 | 0.918 | 0.916 | 0.917 | 0.92 | 0.915 |
| MFR(g/10min) | 21.2 | 20.1 | 22.1 | 22.6 | 22.2 | 20.3 |
| Mn(10 4 g/mol) | 1.35 | 1.32 | 1.35 | 1.33 | 1.33 | 1.38 |
| Mw(10 4 g/mol) | 17.1 | 16.6 | 14.7 | 15.5 | 15.4 | 14.8 |
| Long chain Length chain (LCB/1000C) | 8.6 | 8.3 | 8.5 | 8.3 | 8.2 | 8.8 |
| Short chain branching content (SCB/1000C) | 15.2 | 14.2 | 15.2 | 14.4 | 13.2 | 15.8 |
As can be seen from tables 3 and 4, by combining different process conditions, we can selectively adjust and control the operation conditions according to the actual requirements of the product, and ethylene polymers with different long chain branch contents can be obtained.
The preferred embodiments of the present invention have been described above in detail, but the present invention is not limited thereto. Within the scope of the technical idea of the invention, many simple modifications can be made to the technical solution of the invention, including combinations of various technical features in any other suitable way, and these simple modifications and combinations should also be regarded as the disclosure of the invention, and all fall within the scope of the invention.
Claims (15)
1. A high pressure, free-radical polymerization process for preparing an ethylene polymer, characterized in that it comprises the steps of:
(1) Feeding a first reaction material comprising ethylene, a chain transfer agent and optionally a comonomer into a tank reactor for a first polymerization reaction to obtain a first polymerization product;
(2) Separating the first polymerization product to obtain a first material and a second material; the second material is cooled and pressurized by a first jet pump and then returns to the kettle type reactor;
(3) After cooling, the first material is sent into a tubular reactor and is subjected to a second polymerization reaction with a second reaction material containing ethylene, a chain transfer agent and optionally a comonomer to obtain an ethylene polymer and a third material;
(4) And cooling the third material, pressurizing by a second jet pump, and returning to the kettle reactor or the tubular reactor.
2. The process of claim 1, wherein the tank reactor comprises two or more reaction zones;
preferably, the first reaction material is divided into three material flows, and the three material flows respectively enter the kettle type reactor through an upper feeding hole, a middle feeding hole and a lower feeding hole of the kettle type reactor;
preferably, the tubular reaction comprises more than two reaction zones, each reaction zone being provided with a feed inlet.
3. The process of claim 1 or 2, step (1), wherein the conditions of the first polymerization reaction comprise: the polymerization pressure is 100-350MPa, and the polymer temperature is 100-350 ℃.
4. The method according to any one of claims 1 to 3, wherein in step (2), the mass flow ratio of the second material to the first material is 0 to 2.
5. The method of any one of claims 2-4, wherein the second stream enters the tank reactor through one or more of an upper feed port, a middle feed port, and a lower feed port of the tank reactor.
6. The method of any one of claims 1-5, wherein in step (2), the cooling reduces the temperature of the second material by ≤ 120 ℃.
7. The process according to any one of claims 1 to 6, wherein in step (3), the conditions of the second polymerization reaction comprise: the polymerization pressure is 100-350MPa, and the polymerization temperature is 100-350 ℃.
8. The method according to any one of claims 1-7, wherein the ratio of the mass flow rates of the third material to the first material is 0-2.
9. The process of any of claims 1-8, wherein the third material is returned to the tank reactor through one or more of the upper, middle, and lower feed ports of the tank reactor;
preferably, the third stream is returned to the tubular reactor through the feed inlet of the first reaction zone of the tubular reactor;
preferably, the cooled third stream is mixed with the second reaction mass in the second jet pump and pressurized before being returned to the tubular reactor through the feed inlet of the first reaction zone of the tubular reactor;
preferably, the third material is mixed with the first material and then returned to the tubular reactor through the feed inlet of the first reaction zone of the tubular reactor.
10. The method of any of claims 1-9, wherein in step (4), the cooling reduces the temperature of the third material by ≤ 120 ℃.
11. The process of any one of claims 1-10, wherein the tank reactor has a per pass conversion of 1-25% and the tubular reactor has a per pass conversion of 1-35%.
12. An ethylene polymer produced by the process of any one of claims 1-11.
13. An ethylene polymer as claimed in claim 12, wherein the amount of long chain branching is at least 6LCB/1000C, preferably from 8 to 10LCB/1000C, based on the total weight of the ethylene polymer.
14. An ethylene polymer as claimed in claim 12 or 13 wherein the ethylene polymer has a density of from 0.90 to 0.94g/cm 3 The melt index at 190 ℃ under a load of 2.16kg is from 0.1 to 100g/10min.
15. An apparatus for free radical polymerization of ethylene, comprising: at least one tank reactor, at least one tubular reactor, a first jet pump and a second jet pump;
the tank reactor is used for first polymerization of ethylene and optional comonomers to obtain a first polymerization product, and the first polymerization product is separated to obtain a first material and a second material;
the first jet pump is used for returning the second material to the kettle type reactor;
the tubular reactor is used for second polymerization of the first feed, ethylene and optionally comonomer to obtain ethylene polymer and a third stream;
the second jet pump is used to return the third stream to the tank reactor or the tubular reaction.
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