CN114939383A - Ethylene polymerization method and device in high-pressure tubular reactor - Google Patents

Ethylene polymerization method and device in high-pressure tubular reactor Download PDF

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CN114939383A
CN114939383A CN202210619111.5A CN202210619111A CN114939383A CN 114939383 A CN114939383 A CN 114939383A CN 202210619111 A CN202210619111 A CN 202210619111A CN 114939383 A CN114939383 A CN 114939383A
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reactor
sub
tubular reactor
ethylene
chain transfer
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CN114939383B (en
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范小强
严翔
任聪静
黄嘉雯
王靖岱
杨遥
黄正梁
蒋斌波
阳永荣
从文杰
尤潇楠
陈言溪
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Zhejiang University Ningbo Five In One Campus Education Development Center
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Zhejiang University Ningbo Five In One Campus Education Development Center
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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
    • B01J3/00—Processes of utilising sub-atmospheric or super-atmospheric pressure to effect chemical or physical change of matter; Apparatus therefor
    • B01J3/04—Pressure vessels, e.g. autoclaves
    • B01J3/042—Pressure vessels, e.g. autoclaves in the form of a tube
    • 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
    • B01J3/00—Processes of utilising sub-atmospheric or super-atmospheric pressure to effect chemical or physical change of matter; Apparatus therefor
    • B01J3/002—Component parts of these vessels not mentioned in B01J3/004, B01J3/006, B01J3/02 - B01J3/08; Measures taken in conjunction with the process to be carried out, e.g. safety measures
    • 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
    • C08F10/00—Homopolymers and copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond
    • C08F10/02—Ethene
    • 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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Abstract

The invention discloses an ethylene polymerization method and a polymerization reaction device in a high-pressure tubular reactor. The polymerization reaction device comprises a tubular reactor formed by sequentially connecting at least 2 sections of sub-reactors in series and at least 1 side stream fed to the inlet of the reactor at the downstream of the first sub-reactor, wherein the temperature and the pressure of the side stream can be controlled. The present invention also relates to a distributed feeding method of chain transfer agent comprising feeding chain transfer agent to any 1 or more locations in the outlet of the main compressor, the outlet of the secondary compressor, the main stream and the side stream, wherein the flow rate of chain transfer agent can be independently controlled. The method and the device can realize the increase of the Molecular Weight Distribution (MWD) width of the low-density polyethylene and have economic benefit.

Description

Method and apparatus for ethylene polymerization in high pressure tubular reactor
Technical Field
The invention belongs to the field of chemical industry, and particularly relates to a method and a device for initiating ethylene homopolymerization or copolymerization of ethylene and other monomers by a free radical polymerization initiator in a high-pressure tubular reactor.
Background
Low Density Polyethylene (LDPE), also known as high pressure polyethylene, is a common commercial polymer, is used as a first plastic for five general purposes, and is mainly used as a film product, and also used for injection molding products, medical appliances, medicine and food packaging materials, blow molding hollow molding products and the like.
Free radical polymerization initiates high pressure tubular reactor produced polyethylene polymers which are branched structures that impart excellent clarity, flexibility and ease of extrusion to LDPE, often by balancing and controlling the molecular weight and Molecular Weight Distribution (MWD) of the product across the different properties. Molecular Weight Distribution (MWD), defined as the ratio of weight average molecular weight to number average molecular weight, reflects primarily flow-related properties. Under the condition of equal average molecular weight, the polyethylene with wide molecular weight distribution has better fluidity than the resin with narrow molecular weight distribution in the processing process, is suitable for various molding processes of thermoplastic molding processing, and has good molding processability.
Currently, Low Density Polyethylene (LDPE) high pressure tubular reactor production processes feed all fresh ethylene (obtained by primary and secondary compressors) to the reactor front end in a manner that produces an extremely broad Molecular Weight Distribution (MWD) while resulting in severe reactor fouling and increased gel levels due to too low a concentration of chain transfer agent in the reactor front end, reducing reactor heat transfer, affecting tubular reactor heat removal capacity and production load. To produce broader molecular weight distribution Low Density Polyethylene (LDPE), methods known in the art include controlling the distribution of fresh ethylene among the different gas paths at the inlet of the secondary machine, controlling the ratio of fresh ethylene to each reaction zone, etc., thereby controlling the concentration of chain transfer agent entering each zone. However, the quality of the product may vary with time due to fluctuations in process conditions within the reaction, and the above method is difficult to control and causes an increase in cost, which makes it difficult to conform to the actual production process.
Disclosure of Invention
According to studies, the Molecular Weight Distribution (MWD) of LDPE is strongly dependent on reaction parameters such as pressure and temperature, the conversion of ethylene in the reaction zone depends on the amount of heat of polymerization that can be removed from the reaction mixture in the reaction zone, and furthermore the addition of chain transfer agents also has an influence on the magnitude of the molecular weight, and the present invention proposes a process and an apparatus for initiating a homopolymerization of ethylene or a copolymerization of ethylene with other monomers in a high pressure tubular reactor by means of a free radical polymerization initiator. According to the invention, by the n (n >1) strand side line ethylene cold charge feeding method and the chain transfer agent/comonomer distributed feeding, the equipment investment can be reduced under the condition that the average molecular weight is unchanged, the low density polyethylene product with wide Molecular Weight Distribution (MWD) is prepared, the product processability is improved, the downstream product requirements are met, and the economic benefit and the scale benefit are achieved.
The scheme of the invention is as follows:
the invention firstly provides an ethylene polymerization method in a high-pressure tubular reactor, which is characterized in that a free radical polymerization initiator initiates ethylene homopolymerization or ethylene and other monomers to carry out copolymerization in a tubular reactor consisting of at least 2 segments of sub-reactors connected in series in turn at the pressure of 170-330MPa and the temperature of 100-350 ℃, wherein the polymerization method comprises the following steps:
(1) providing a high-pressure tubular reactor, dividing the tubular reactor into at least 2 sub-reactors according to a space-divided initiator and/or ethylene feeding point, and sequentially connecting all the sub-reactors in series to form the high-pressure tubular reactor;
(2) after being compressed to reaction pressure by a main compressor and a secondary compressor, fresh ethylene and unreacted reaction materials separated from the outlet of the reactor are divided into a main stream and at least 1 side stream, wherein the main stream is fed to the inlet of the tubular reactor, and the side streams are fed to any one or more of other sub-reactor inlets downstream of the first sub-reactor;
(3) injecting fresh chain transfer agent into at least 1 stream after a high pressure reducing valve at the outlet of the high pressure tubular reactor, the main stream, the side stream and the secondary compressor outlet;
(4) each sub-reactor is provided with at least 1 initiator feeding hole, 1 reactant feeding hole and 1 polymer discharging hole, and ethylene is subjected to homopolymerization or copolymerization with at least one other monomer in each sub-reactor in the presence of an initiator and a chain transfer agent.
Wherein, the material mixed by the chain transfer agent and the ethylene at the injection position of the chain transfer agent is in a single phase state, and the flow rate of the material in the high-pressure tubular reactor is more than 5 m/s.
As a preferred embodiment of the present invention, the chain transfer agent is injected into the main compressor interstage and/or outlet, the secondary compressor outlet, the main stream, and any location after the side stream and high pressure let down valve. Wherein, a part of chain transfer agent is added after the pressure reducing valve, so that the probability of crosslinking reaction caused by temperature rise of polyethylene due to reverse Joule Thomson effect after the pressure reducing valve is reduced.
As a preferred embodiment of the present invention, the chain transfer agent is divided into 2 feeds, and the chain transfer agent is injected into any 2 locations of the outlet of the main compressor, the outlet of the secondary compressor, the main stream, and the side stream.
As a preferable aspect of the present invention, the chain transfer agent is divided into 3 feeds, and the chain transfer agent is injected into any 3 locations of the outlet of the main compressor, the outlet of the secondary compressor, the main stream, and the side stream.
As a preferable scheme of the invention, a preheater is arranged at an inlet of a first sub-reactor of the high-pressure tubular reactor, the preheater is at least 2 sleeve type heat exchange structures which are connected in series or in parallel, wherein the materials in the sleeve type heat exchange structures are reaction materials, the flow speed is 5-25m/s, and the materials in the sleeve are hot water or steam.
As a preferred embodiment of the present invention, the side stream is cooled and then fed to the inlets of the other sub-reactors downstream of the first sub-reactor. Wherein the minimum cooling is to the supercritical temperature of ethylene and the minimum cooling is to 10 ℃ industrially.
As a preferred embodiment of the present invention, when the chain transfer agent is divided into at least 2 feeds, the flow rate of each chain transfer agent can be independently controlled.
As a preferred embodiment of the present invention, the feed streams to the primary and secondary compressors comprise the unreacted mixture separated in the reactor outlet effluent.
As a preferable mode of the present invention, the polymerization temperature of the nth (n.gtoreq.1) sub-reactor of the high-pressure tubular reactor can be independently controlled.
The present invention also provides a polymerization reaction apparatus for carrying out the above method, characterized by comprising:
at least one primary compressor for compressing the gas mixture;
at least one secondary compressor downstream of the primary compressor for compressing the reaction gas mixture;
a high-pressure tubular reactor located downstream of the secondary compressor and used for homopolymerization of ethylene or copolymerization of ethylene and other monomers, the high-pressure tubular reactor is divided into at least 2 sub-reactors according to initiator and/or ethylene feeding points which are divided spatially, all the sub-reactors are connected in series in turn,
a polymer separation system downstream of the high pressure tubular reactor for separating unreacted reactants from the polymer produced by the polymerization in the high pressure tubular reactor effluent;
the outlet of the secondary compressor is provided with a main flow strand connected to the inlet of the tubular reactor; the secondary compressor outlet is also provided with at least 1 side stream that feeds any other sub-reactor inlet or inlets downstream of the first sub-reactor.
In a preferred embodiment of the present invention, the chain transfer agent is one or more of hydrogen, aliphatic hydrocarbon, olefin, ketone, aldehyde, and aliphatic aldehyde. Examples of such hydrocarbons are propane, butane, pentane, hexane, cyclohexane, propylene, 1-butene, 1-pentene or 1-hexene; ketones such as acetone, methyl ethyl ketone (2-butanone), methyl isobutyl ketone, methyl isoamyl ketone, diethyl ketone or diamyl ketone; aldehydes such as formaldehyde, acetaldehyde or propionaldehyde; and saturated aliphatic alcohols such as methanol, ethanol, propanol, isopropanol or butanol. Particular preference is given to using saturated aliphatic aldehydes, in particular propionaldehyde or 1-olefins such as propene, 1-butene or 1-hexene, or aliphatic hydrocarbons such as propane.
In a preferred embodiment of the present invention, the initiator is one or more of oxygen, air, an azo compound or a peroxide polymerization initiator. Examples of suitable organic peroxides are peroxy esters, peroxy ketals, peroxy ketones and peroxy carbonates, such as di-2-ethylhexyl peroxydicarbonate, dicyclohexyl peroxydicarbonate, diacetyl peroxydicarbonate, tert-butyl peroxyisopropylcarbonate, di-sec-butyl peroxydicarbonate, di-tert-butyl peroxide, di-tert-amyl peroxide, tert-butylcumyl peroxide, 2, 5-dimethyl-2, 5-di (tert-butylperoxy) hex-3-yne, 1, 3-diisopropyl hydroperoxide or tert-butyl hydroperoxide, didecanoyl peroxide, 2, 5-dimethyl-2, 5-di (2-ethylhexanoylperoxy) hexane, tert-amyl peroxy-2-ethylhexanoate, dibenzoyl peroxide, tert-butyl peroxy-2-ethylhexanoate, Tert-butylperoxydiethylisobutyrate, tert-butyl peroxy-3, 5, 5-trimethylhexanoate, 1-bis (tert-butylperoxy) -3, 3, 5-trimethylcyclohexane, 1-bis (tert-butylperoxy) cyclohexane, cumyl perneodecanoate, tert-amyl perpivalate, tert-butyl perneodecanoate, tert-butyl permaleate, tert-butyl perpivalate, tert-butyl peroxyisononanoate, cumene hydroperoxide, tert-butyl peroxybenzoate, methyl isobutyl ketone hydroperoxide, 3, 6, 9-triethyl-3, 6, 9-trimethyl-triperoxynonane and 2, 2-bis (tert-butylperoxy) butane. Azoalkanes (diazenes), azodicarboxylates, azodicarboxylic dinitriles, such as azodiisobutyronitrile, and hydrocarbons which decompose into radicals, also referred to as C-C initiators, such as 1, 2-diphenyl-1, 2-dimethylethane derivatives and 1, 1, 2, 2-tetramethylethane derivatives are also suitable.
In a preferred embodiment of the invention, the invention uses the initiator in dissolved form. Examples of suitable initiator solvents are ketones and aliphatic hydrocarbons (octane, decane and isododecane) and other saturated C' s 8 -C 25 A hydrocarbon.
In a preferred embodiment of the invention, the comonomer is used for free radical copolymerization with ethylene under high pressure. Examples of copolymerizable monomers are alpha, beta-unsaturated C 3 -C 8 -carboxylic acid, alpha, beta-unsaturated C 3 -C 8 Derivatives of carboxylic acids, e.g. unsaturated C 3 -C 15 -carboxylic acid esters or anhydrides and 1-olefins. In addition, vinyl carboxylates such as vinyl acetate may be used as comonomers. Propene, 1-butene, 1-hexene, acrylic acid, n-butyl acrylate, tert-butyl acrylate, 2-ethylhexyl acrylate, vinyl acetate or vinyl propionate are particularly suitable as comonomers.
The present invention also provides an ethylene polymerization plant in a high-pressure tubular reactor, comprising at least one main compressor for compressing a gas mixture;
at least one secondary compressor downstream of the primary compressor for compressing the reaction gas mixture;
a high-pressure tubular reactor located downstream of the secondary compressor and used for homopolymerization of ethylene or copolymerization of ethylene and other monomers, the high-pressure tubular reactor is divided into at least 2 sub-reactors according to initiator and/or ethylene feeding points which are divided spatially, all the sub-reactors are connected in series in turn,
a polymer separation system downstream of the high pressure tubular reactor for separating unreacted reactants from the polymer produced by the polymerization in the high pressure tubular reactor effluent;
the outlet of the secondary compressor is provided with a main flow strand connected to the inlet of the tubular reactor; the secondary compressor outlet is also provided with at least 1 side stream that feeds any other sub-reactor inlet or inlets downstream of the first sub-reactor.
In a preferred embodiment of the present invention, the tubular reactor polymerization process can produce broad MWD ethylene homopolymer and copolymer products.
Compared with the prior art, the invention has the following advantages:
(1) the ethylene polymerization method provided by the invention comprises a tubular reactor formed by connecting at least 2 sections of sub-reactors in series in sequence, wherein fresh ethylene and unreacted reaction materials separated from the outlet of the reactor are compressed to reaction pressure by a main compressor and a secondary compressor and then divided into a main stream and at least 1 side stream, the polymerization heat removed from a reaction mixture in a reaction zone can be better reduced by reducing the temperature of the side stream ethylene stream, and the length of the reactor and the equipment cost are reduced under the condition of ensuring that the temperature peak value and the temperature distribution are approximately unchanged.
(2) The ethylene polymerization method provided by the invention comprises a tubular reactor formed by sequentially connecting at least 2 sections of sub-reactors in series, wherein fresh ethylene and unreacted reaction materials separated from the outlet of the reactor are compressed to reaction pressure by a main compressor and a secondary compressor and then divided into a main stream and at least 1 side stream, the flow, temperature and pressure of the side stream can be controlled (such as reducing the concentration of a chain transfer agent in a first zone, the initiation temperature and the initiation pressure in the first zone), a low-density polyethylene product with wide Molecular Weight Distribution (MWD) is produced, and the processing performance of the product is improved.
(3) The ethylene polymerization method provided by the invention comprises the step of feeding the chain transfer agent to any 1 or more positions of an outlet of a main compressor, an outlet of a secondary compressor, a main flow and a side flow, wherein the flow rate of the chain transfer agent can be independently controlled, so that the concentration of the chain transfer agent in each sub-reactor zone can be stably changed, and the adjustment of the Molecular Weight Distribution (MWD) of a product and the stabilization of the product performance are realized.
(4) According to the invention, a chain transfer agent is added after the pressure reducing valve, so that the risk of crosslinking reaction caused by the reverse Joule Thomson effect of ethylene and residual initiator is reduced.
Drawings
The invention is further illustrated with reference to the following figures and examples.
FIG. 1 is a schematic illustration of a polymerization process for initiating homopolymerization of ethylene or copolymerization with other olefinic monomers using a free radical polymerization initiator according to the present invention. In fig. 1, the correspondence between the system combinations and the reference numerals is as follows:
1. a low pressure compressor; 2/13, a high pressure compressor; 3. a preheater; 4/5, precooler; 6. a tubular reactor consisting of at least 2 sub-reactors connected in series; 7. a high pressure relief valve; 8. a cooler; 9. a high pressure separator; 10. a high circulation loop; 11 a low pressure separator; 12. a low circulation loop.
Detailed Description
The invention will be further illustrated and described with reference to specific embodiments. The technical features of the embodiments of the present invention can be combined correspondingly without mutual conflict.
Example 1
The present invention utilizes the polymerization process shown in FIG. 1 and a tubular reactor to continuously polymerize ethylene to produce LDPE. In the process, the secondary compressor was operated at a production of 43.5t/h fresh ethylene, the secondary compressor outlet stream was compressed to 2200bar and preheated to 170 ℃ via a preheater and fed to the tubular reactor inlet, wherein propylene was fed as a chain transfer agent at 0.195t/h downstream of the secondary compressor to be thoroughly mixed with fresh ethylene. The total length of the tubular reactor is 1310m, the inner diameter is 0.045m, the tubular reactor is divided into 4 sub-reactors by four positions of the inlet of the reactor and the downstream of the reactor, namely 110m, 510m and 910m, and all the sub-reactors are sequentially connected in series to form the high-pressure tubular reactor. The mixture from the main compressor is divided into a main stream and 1 side stream, wherein the main stream is fed into the inlet of the tubular reactor (namely, the inlet of the 1 st sub-reactor), the side stream is pre-cooled to 10 ℃ by a pre-cooler and fed into the inlet of the 2 nd sub-reactor, initiator mixtures with different proportions are respectively fed into the inlets of the 4 sub-reactors of the reactor for polymerization, and the using conditions of the initiators are shown in table 1.
The peak temperatures of the 1 st to 4 th sub-reactors of the tubular reactor are controlled to be 295 ℃, 295 ℃, 295 ℃, 295 ℃ and 295 ℃ respectively by adjusting the initiator feeding rate, and the number average polymerization degree, weight average polymerization degree, number average molecular weight, weight average molecular weight, molecular weight distribution index, yield and ethylene conversion rate of the obtained LDPE are given in Table 3.
Example 2
The present invention utilizes the polymerization process shown in FIG. 1 and a tubular reactor to continuously polymerize ethylene to produce LDPE. In the process, the secondary compressor was operated at a production of 43.5t/h fresh ethylene, the secondary compressor outlet stream was compressed to 2200bar, the preheater was preheated to 170 ℃ and fed to the tubular reactor inlet, wherein propylene was fed as chain transfer agent at 0.195t/h downstream of the secondary compressor to be thoroughly mixed with fresh ethylene. The total length of the tubular reactor is 1040m, the inner diameter is 0.045m, the tubular reactor is divided into 4 sub-reactors by four positions of the inlet of the reactor and the downstream of the reactor, namely 110m, 240m and 640m, and all the sub-reactors are connected in series in sequence to form the high-pressure tubular reactor. The mixed material from the main compressor is divided into a main stream and 2 side streams, wherein the main stream is fed into the inlet of the tubular reactor, the 1 st side stream is pre-cooled to 10 ℃ by a pre-cooler and fed into the inlet of the 2 nd sub-reactor, the 2 nd side stream is pre-cooled to 10 ℃ by a pre-cooler and fed into the inlet of the 3 rd sub-reactor, initiator mixtures with different proportions are respectively fed into the inlets of the 4 sub-reactors of the reactor for polymerization, and the using conditions of the initiators are shown in table 2.
The values were obtained by Aspen Plus simulation, the inlet temperatures of the 1 st to 4 th sub-reactors of the tubular reactor were 170 ℃, 186 ℃, 249 ℃, 213 ℃, respectively, the peak temperatures of the 1 st to 4 th sub-reactors were controlled to 295 ℃, 295 ℃, and 295 ℃, respectively, by adjusting the initiator feed rate, and the number average degree of polymerization, weight average degree of polymerization, number average molecular weight, weight average molecular weight, molecular weight distribution index, yield, and ethylene conversion of the obtained LDPE were given in Table 3.
Example 3
The present invention utilizes the polymerization process shown in FIG. 1 and a tubular reactor to continuously polymerize ethylene to produce LDPE. In the process, the secondary compressor was operated at a production of 43.5t/h fresh ethylene, the fluid at the outlet of the secondary compressor was compressed to 2200bar and the preheater was preheated to 170 ℃ and fed to the inlet of the tubular reactor. The total length of the tubular reactor is 1310m, the inner diameter is 0.045m, the tubular reactor is divided into 4 sub-reactors by four positions of the inlet of the reactor and the downstream of the reactor, namely 110m, 510m and 910m, and all the sub-reactors are sequentially connected in series to form the high-pressure tubular reactor. The mixed material from the main compressor was divided into a main stream fed to the tubular reactor inlet and 1 side stream fed to the 2 nd sub-reactor inlet after precooling to 10 ℃ by a precooler. Wherein propylene was fed as chain transfer agent in a portion of 0.180t/h downstream of the secondary compressor to be thoroughly mixed with fresh ethylene and in another portion of 0.015t/h to the side stream. Initiator mixtures with different proportions are respectively fed into 4 sub-reactor inlets of the reactor to carry out polymerization, and the using conditions of the initiators are shown in the table 1.
The peak temperatures of the 1 st to 4 th sub-reactors of the tubular reactor are controlled to be 295 ℃, 295 ℃, 295 ℃, 295 ℃ and 295 ℃ respectively by adjusting the initiator feeding rate, and the number average polymerization degree, weight average polymerization degree, number average molecular weight, weight average molecular weight, molecular weight distribution index, yield and ethylene conversion rate of the obtained LDPE are given in Table 3.
Example 4
The present invention utilizes the polymerization process shown in FIG. 1 and a tubular reactor to continuously polymerize ethylene to produce LDPE. In the process, the secondary compressor was operated at a production of 43.5t/h fresh ethylene, the fluid at the outlet of the secondary compressor was compressed to 2200bar and the preheater was preheated to 170 ℃ and fed to the inlet of the tubular reactor. The total length of the tubular reactor is 1040m, the inner diameter is 0.045m, the tubular reactor is divided into 4 sub-reactors by four positions of the inlet of the reactor and the downstream of the reactor, namely 110m, 240m and 640m, and all the sub-reactors are sequentially connected in series to form the high-pressure tubular reactor. The mixed material from the main compressor is divided into a main stream and 2 side streams, wherein the main stream is fed to the tubular reactor inlet, the 1 st side stream is pre-cooled to 10 ℃ by a pre-cooler and fed to the 2 nd sub-reactor inlet, and the 2 nd side stream is pre-cooled to 10 ℃ by a pre-cooler and fed to the 3 rd sub-reactor inlet. Wherein propylene was fed as a chain transfer agent to the secondary compressor downstream at 0.165t/h in a portion well mixed with fresh ethylene, a portion was fed to the 1 st side stream at 0.015t/h, and another portion was fed to the 2 nd side stream at 0.015 t/h. Initiator mixtures with different proportions are respectively fed into 4 sub-reactor inlets of the reactor to carry out polymerization reaction, and the using conditions of the initiators are shown in the table 2.
The values were obtained by Aspen Plus simulation, the inlet temperatures of the 1 st to 4 th sub-reactors of the tubular reactor were 170 ℃, 186 ℃, 249 ℃, 213 ℃, respectively, the peak temperatures of the 1 st to 4 th sub-reactors were controlled to 295 ℃, 295 ℃, and 295 ℃, respectively, by adjusting the initiator feed rate, and the number average degree of polymerization, weight average degree of polymerization, number average molecular weight, weight average molecular weight, molecular weight distribution index, yield, and ethylene conversion of the obtained LDPE were given in Table 3.
Comparative example 1
In contrast to example 1, comparative example 1 produces LDPE by continuously polymerizing ethylene in a tubular reactor without side feed. In the process, the secondary compressor was operated at 43.5t/h fresh ethylene production, the secondary compressor outlet was fluidly compressed to 2200bar, the preheater was preheated to 170 ℃ and fed to the tubular reactor inlet, with propylene as chain transfer agent fed downstream of the secondary compressor at 0.195t/h to intimately mix with fresh ethylene. The total length of the tubular reactor is 1760m, the inner diameter is 0.045m, the tubular reactor is divided into 4 sub-reactors by four positions of 560m, 960m and 1360m at the inlet of the reactor and at the downstream of the reactor, initiator mixtures with different proportions are respectively fed into the inlets of the 4 sub-reactors of the reactor for polymerization, and the using conditions of the initiators are shown in the table 2.
The peak temperatures of the 1 st to 4 th sub-reactors of the tubular reactor were controlled to 295 ℃, 295 ℃, 295 ℃, 295 ℃ and 295 ℃ by adjusting the initiator feed rate, and the number average degree of polymerization, weight average degree of polymerization, number average molecular weight, weight average molecular weight, molecular weight distribution index, yield, and ethylene conversion of the obtained LDPE were given in Table 3, obtained by Aspen Plus simulation, at 170 ℃, 193 ℃, 210 ℃, and 220 ℃ respectively.
Comparative example 2
In contrast to example 1, comparative example 2 produced LDPE by continuously polymerizing ethylene in a tubular reactor without side feed. In the process, the secondary compressor was operated at a production of 43.5t/h fresh ethylene, the fluid at the outlet of the secondary compressor was compressed to 2200bar and the preheater was preheated to 170 ℃ and fed to the inlet of the tubular reactor. The tubular reactor has a total length of 1760m and an inner diameter of 0.045m, and is divided into 4 sub-reactors at four positions of 560m, 960m and 1360m at the inlet of the reactor and at the downstream of the reactor, wherein propylene is used as a chain transfer agent and is respectively fed into the inlets of the 4 sub-reactors at 0.175t/h, 0.005t/h and 0.005t/h, and initiator mixtures with different proportions are respectively fed into the inlets of the 4 sub-reactors to carry out polymerization, and the use conditions of the initiators are shown in Table 1.
The peak temperatures of the 1 st to 4 th sub-reactors of the tubular reactor are controlled to be 295 ℃, 295 ℃, 295 ℃, 295 ℃ and 295 ℃ respectively by adjusting the initiator feeding rate, and the number average polymerization degree, weight average polymerization degree, number average molecular weight, weight average molecular weight, molecular weight distribution index, yield and ethylene conversion rate of the obtained LDPE are given in Table 3.
TABLE 1
Name of the initiator Abbreviations For R x Zone (x ═ 1/2/3/4)
Di-tert-butyl peroxide DTBP Is/is
Tert-butyl peroxybenzoate TBPB Yes/no
Tert-butyl peroxy-2-ethylhexyl ester TBPEH Yes/no
TABLE 2
Initiator name Abbreviations For R x Zone (x ═ 1/2/3/4)
Di-tert-butyl peroxide DTBP Is/is
Tert-butyl peroxybenzoate TBPB Yes/no
Tert-butylperoxy-2-ethylhexyl ester TBPEH Yes/no
TABLE 3
Figure BDA0003674404620000101
Comparison of examples 1 and 2 with comparative example 1 shows that the use of side-cooling ethylene feed removes part of the heat of polymerization in the reaction zone, reduces the length of the cooling section of the reactor and reduces the equipment cost while ensuring that the temperature peak and the temperature distribution are approximately constant, and simultaneously by controlling the side stream temperature, LDPE polymer with broad Molecular Weight Distribution (MWD) is produced.
Comparison of examples 3, 4 with comparative example 2 shows that by feeding chain transfer agent to any 1 or more of the outlet of the main compressor, the outlet of the secondary compressor, the main stream and the side stream, and controlling the flow rate of each branched chain transfer agent, the concentration of chain transfer agent in each sub-reactor zone can be stably changed, and the Molecular Weight Distribution (MWD) of the product LDPE polymer is significantly improved.
The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the present invention. It should be noted that various changes and modifications can be made by those skilled in the art without departing from the spirit of the invention, and these changes and modifications are all within the scope of the invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.

Claims (10)

1. A process for the polymerization of ethylene in a high-pressure tubular reactor, said process being characterized in that a radical polymerization initiator initiates the homopolymerization of ethylene or the copolymerization of ethylene with other monomers in a tubular reactor consisting of at least 2 sub-reactors connected in series in succession at a pressure of 170-330MPa and a temperature of 100-350 ℃, wherein the process comprises:
(1) providing a high-pressure tubular reactor, dividing the tubular reactor into at least 2 sub-reactors according to a space-divided initiator and/or ethylene feeding point, and sequentially connecting all the sub-reactors in series to form the high-pressure tubular reactor;
(2) after being compressed to reaction pressure by a main compressor and a secondary compressor, fresh ethylene and unreacted reaction materials separated from the outlet of the reactor are divided into a main stream and at least 1 side stream, wherein the main stream is fed to the inlet of the tubular reactor, and the side streams are fed to any one or more of other sub-reactor inlets downstream of the first sub-reactor;
(3) injecting fresh chain transfer agent into at least 1 stream after a high pressure reducing valve at the outlet of the high pressure tubular reactor, the main stream, the side stream and the secondary compressor outlet;
(4) each sub-reactor is provided with at least 1 initiator feeding hole, 1 reactant feeding hole and 1 polymer discharging hole, and ethylene is subjected to homopolymerization or copolymerization with at least one other monomer in each sub-reactor in the presence of an initiator and a chain transfer agent.
Wherein, the material mixed by the chain transfer agent and the ethylene at the injection position of the chain transfer agent is in a single phase state, and the flow rate of the material in the high-pressure tubular reactor is more than 5 m/s.
2. The method of claim 1, wherein the chain transfer agent is injected into the primary compressor interstage and/or outlet, the secondary compressor outlet, the main stream, and any location after the side stream and high pressure let down valve.
3. The method of claim 1, wherein the chain transfer agent is split into 2 feeds and the chain transfer agent is injected into any 2 locations of the outlet of the primary compressor, the outlet of the secondary compressor, the main stream, and the side stream.
4. The method of claim 1, wherein the chain transfer agent is split into 3 feeds and the chain transfer agent is injected into any 3 locations of the outlet of the primary compressor, the outlet of the secondary compressor, the main stream, and the side stream.
5. The method according to claim 1, wherein the high pressure tubular reactor is provided with a preheater at the inlet of the first sub-reactor, the preheater has at least 2 sleeve type heat exchange structures connected in series or in parallel, wherein the material in the sleeve type heat exchange structures is reactant material with a flow rate of 5-25m/s, and the material in the sleeve is hot water or steam.
6. The method according to claim 1, wherein the side stream is cooled and fed to the other sub-reactor inlets downstream of the first sub-reactor.
7. The process of claim 1 wherein when the chain transfer agent is divided into at least 2 feeds, the flow rate of each chain transfer agent can be independently controlled.
8. The process according to any one of claims 1 to 7, wherein the feed streams to the primary and secondary compressors comprise the separated unreacted mixture in the reactor outlet effluent.
9. The process according to any of claims 1 to 7, wherein the polymerization temperature of the nth (n.gtoreq.1) sub-reactor of the high-pressure tubular reactor is independently controllable.
10. A polymerization reaction apparatus for carrying out the process of claim 1, comprising:
at least one main compressor for compressing the gas mixture;
at least one secondary compressor downstream of the primary compressor for compressing the reaction gas mixture;
a high-pressure tubular reactor located downstream of the secondary compressor and used for homopolymerization of ethylene or copolymerization of ethylene and other monomers, the high-pressure tubular reactor is divided into at least 2 sub-reactors according to initiator and/or ethylene feeding points which are divided spatially, all the sub-reactors are connected in series in turn,
a polymer separation system downstream of the high pressure tubular reactor for separating unreacted reactants from the polymer produced by the polymerization in the high pressure tubular reactor effluent;
the outlet of the secondary compressor is provided with a main flow strand connected to the inlet of the tubular reactor; the secondary compressor outlet is also provided with at least 1 side stream that is fed to any other sub-reactor inlet or inlets downstream of the first sub-reactor.
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WO2000010701A1 (en) * 1998-08-20 2000-03-02 Dsm N.V. Tubular reactor, process and installation for high-pressure polymerization
CN104640888A (en) * 2012-09-24 2015-05-20 埃克森美孚化学专利公司 Apparatus and process for making high-pressure polyethylene polymers and copolymers
CN106164110A (en) * 2014-03-31 2016-11-23 沙特基础工业公司 For the method preparing ethylene copolymer in tubular reactor
CN108602043A (en) * 2016-02-26 2018-09-28 埃克森美孚化学专利公司 Device and method for high pressure polymerization of ethylene
US20190322771A1 (en) * 2015-12-22 2019-10-24 Braskem S.A. Tubular reactor polymerization initiator injector device, tubular reactor for continuous polymerization of olefins, and a process for production of polymers and copolymers of ethylene

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2000010701A1 (en) * 1998-08-20 2000-03-02 Dsm N.V. Tubular reactor, process and installation for high-pressure polymerization
CN104640888A (en) * 2012-09-24 2015-05-20 埃克森美孚化学专利公司 Apparatus and process for making high-pressure polyethylene polymers and copolymers
CN106164110A (en) * 2014-03-31 2016-11-23 沙特基础工业公司 For the method preparing ethylene copolymer in tubular reactor
US20190322771A1 (en) * 2015-12-22 2019-10-24 Braskem S.A. Tubular reactor polymerization initiator injector device, tubular reactor for continuous polymerization of olefins, and a process for production of polymers and copolymers of ethylene
CN108602043A (en) * 2016-02-26 2018-09-28 埃克森美孚化学专利公司 Device and method for high pressure polymerization of ethylene

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