CN114939383B - 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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CN114939383B
CN114939383B CN202210619111.5A CN202210619111A CN114939383B CN 114939383 B CN114939383 B CN 114939383B CN 202210619111 A CN202210619111 A CN 202210619111A CN 114939383 B CN114939383 B CN 114939383B
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reactor
sub
tubular reactor
ethylene
transfer agent
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CN114939383A (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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    • 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

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 downstream reactor of the first sub-reactor, wherein the temperature and the pressure of the side stream can be controlled. The invention also relates to a distributed feed method of chain transfer agent comprising feeding chain transfer agent to any 1 or more of the outlet of the primary compressor, the outlet of the secondary compressor, the primary stream and the side stream, wherein the flow rate of chain transfer agent is independently controllable. The method and the device can realize the promotion of the width of the Molecular Weight Distribution (MWD) of the low-density polyethylene, and have economic benefit.

Description

Ethylene polymerization method and device in high-pressure tubular reactor
Technical Field
The invention belongs to the field of chemical industry, and in particular relates to a method and a device for initiating ethylene homopolymerization reaction or ethylene and other monomer copolymerization reaction 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, which is used as a first five-major general purpose plastic, mainly for film products, and also for injection molded articles, medical devices, pharmaceutical and food packaging materials, blow molded hollow molded articles, and the like.
The polyethylene polymers produced in the high pressure tube reactor initiated by free radical polymerization are branched structures which impart excellent clarity, flexibility and ease of extrusion properties to LDPE, typically through the balance of molecular weight and Molecular Weight Distribution (MWD) and control of articles of varying properties. Molecular Weight Distribution (MWD) is defined as the ratio of weight average molecular weight to number average molecular weight, and reflects primarily flow-related properties. Under the condition of equal average molecular weight, the polyethylene with wide molecular weight distribution shows 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.
At present, the preparation method of the low-density polyethylene (LDPE) high-pressure tubular reactor feeds all fresh ethylene (obtained by a primary compressor and a secondary compressor) to the front end of the reactor, and the mode is used for producing extremely wide Molecular Weight Distribution (MWD), and meanwhile, the concentration of the chain transfer agent at the front end of the reactor is too low, so that serious reactor scaling and gel level increase can be caused, the heat transfer of the reactor is reduced, and the heat transfer capacity and the production load of the tubular reactor are influenced. To produce a broader molecular weight distribution Low Density Polyethylene (LDPE), methods known in the art include controlling the distribution of fresh ethylene between the different gas lines at the secondary inlet, controlling the proportion 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-described 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 strongly depends on reaction parameters such as pressure and temperature, the conversion of ethylene in the reaction zone depends on the amount of polymerization heat that can be removed from the reaction mixture in the reaction zone, and the addition of chain transfer agent also has an influence on the molecular weight, so the present invention proposes a method and apparatus for initiating ethylene homo-polymerization or copolymerization of ethylene with other monomers by a radical polymerization initiator in a high pressure tubular reactor. According to the method, the feeding method of the n (n > 1) side line ethylene cold material and the distributed feeding of the chain transfer agent/comonomer can reduce equipment investment under the condition of unchanged average molecular weight, prepare a low-density polyethylene product with wide Molecular Weight Distribution (MWD), improve the processing performance of the product, meet the requirements of downstream products, and have economic benefit and scale benefit.
The scheme of the invention is as follows:
the present invention firstly provides a process for the polymerization of ethylene in a high-pressure tubular reactor, said process being characterized in that in a tubular reactor consisting of at least 2 sub-reactors in series in sequence, a free radical polymerization initiator initiates ethylene homopolymerization or ethylene copolymerization with other monomers at a pressure of 170-330MPa and a temperature of 100-350 ℃, wherein said process comprises:
(1) Providing a high-pressure tubular reactor, dividing the tubular reactor into at least 2 sub-reactors according to the initiator and/or ethylene feeding points which are spatially divided, and sequentially connecting all the sub-reactors in series to form the high-pressure tubular reactor;
(2) Fresh ethylene and unreacted reaction materials separated from the outlet of the reactor are compressed to the reaction pressure by a main compressor and a secondary compressor and then divided into a main flow and at least 1 side flow, wherein the main flow is fed to the inlet of the tubular reactor, and the side flow is fed to any one or more other inlets of the sub-reactors downstream of the first sub-reactor;
(3) Fresh chain transfer agent is injected into at least 1 stream after the main compressor interstage and/or outlet, the secondary compressor outlet, the main stream, the side stream and the high pressure relief valve of the high pressure tubular reactor outlet;
(4) Each sub-reactor is provided with at least 1 initiator feed inlet, 1 reactant feed inlet and 1 polymer discharge outlet, and ethylene is subjected to homopolymerization reaction or ethylene and at least one other monomer are subjected to copolymerization reaction in the presence of an initiator and a chain transfer agent in each sub-reactor.
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 5m/s.
As a preferred aspect of the invention, the chain transfer agent is injected at any point between the primary compressor stages and/or outlets, the secondary compressor outlet, the primary stream, and after the side stream and high pressure relief valve. Wherein, through adding partial chain transfer agent behind the relief pressure valve, reduce the probability of the cross-linking reaction that the temperature rise of polyethylene caused because of anti-Joule Thomson effect behind the relief pressure valve.
As a preferred embodiment of the present invention, the chain transfer agent is split into 2 feeds, and the chain transfer agent is injected into any 2 positions of the outlet of the main compressor, the outlet of the secondary compressor, the main stream, and the side stream.
As a preferred embodiment of the present invention, the chain transfer agent is split into 3 feeds, and the chain transfer agent is injected into any 3 positions 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 the inlet of the first sub-reactor of the high-pressure tubular reactor, the preheater is of at least 2 sleeve-type heat exchange structures which are connected in series or in parallel, the materials in the tubes of the sleeve-type heat exchange structures are reaction materials, the flow rate is 5-25m/s, and the materials in the sleeve-type heat exchange structures are hot water or steam.
As a preferred embodiment of the invention, the side stream is cooled and fed to the inlet of the other sub-reactor downstream of the first sub-reactor. Wherein the minimum cooling is to the supercritical temperature of ethylene, and the minimum cooling is to 10 ℃ in industry.
As a preferred embodiment of the present invention, when the chain transfer agent is split into at least 2 feeds, the flow rate of each chain transfer agent can be independently controlled.
As a preferred embodiment of the invention, the feed streams of the primary compressor and the secondary compressor comprise an unreacted mixture separated from the reactor outlet effluent.
As a preferable scheme of the invention, the polymerization temperature of the nth (n is more than or equal to 1) sub-reactor of the high-pressure tubular reactor can be independently controlled.
The invention also provides a polymerization reaction device for implementing the method, which is characterized by comprising the following steps:
at least one primary compressor for compressing the gas mixture;
at least one secondary compressor downstream of the primary compressor for compressing the reactant gas mixture;
a high-pressure tubular reactor for ethylene homo-polymerization or ethylene copolymerization with other monomers, which is located downstream of the secondary compressor and is divided into at least 2 sub-reactors according to spatially divided initiator and/or ethylene feed points, all sub-reactors being connected in series in sequence,
a polymer separation system downstream of the high pressure tubular reactor for separating unreacted reactants from the polymerization-derived polymer in the high pressure tubular reactor effluent;
the secondary compressor outlet is provided with a main flow connected to the tubular reactor inlet; the secondary compressor outlet is also provided with at least 1 side stream which is fed to any one or more of the other sub-reactor 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 hydrocarbons, olefins, ketones, aldehydes and aliphatic aldehydes. Such as 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 dipentyl ketone; aldehydes such as formaldehyde, acetaldehyde or propionaldehyde; and saturated fatty alcohols such as methanol, ethanol, propanol, isopropanol or butanol. Particular preference is given to using saturated fatty aldehydes, in particular propionaldehyde or 1-olefins such as propylene, 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, azo compounds or peroxidic polymerization initiators. Examples of suitable organic peroxides are peroxy esters, peroxy ketals, peroxy ketones and peroxy carbonates, for example di (2-ethylhexyl) peroxydicarbonate, dicyclohexyl peroxydicarbonate, diacetyl peroxydicarbonate, t-butyl peroxyisopropyl carbonate, di-sec-butyl peroxydicarbonate, di-t-butyl peroxide, di-t-amyl peroxide, t-butylcumyl peroxide, 2, 5-dimethyl-2, 5-di (t-butylperoxy) hex-3-yne, 1, 3-diisopropylmonohydrogen peroxide or t-butylhydroperoxide, didecanoyl peroxide, 2, 5-dimethyl-2, 5-di (2-ethylhexanoylperoxy) hexane, t-amyl peroxy-2-ethylhexanoate, dibenzoyl peroxide, t-butyl peroxy-2-ethylhexanoate tert-butylperoxy diethyl isobutyrate, tert-butyl peroxy-3, 5-trimethylhexanoate, 1-di (tert-butylperoxy) -3, 5-trimethylcyclohexane, 1-di (tert-butylperoxy) cyclohexane, cumyl perneodecanoate, tert-amyl perpivalate tert-butyl perneodecanoate, tert-butyl peroxymaleate, tert-butyl perpivalate, tert-butyl peroxyisononanoate, cumene hydroperoxide, tert-butyl peroxybenzoate, methyl isobutyl ketone hydroperoxide, 3,6, 9-triethyl-3, 6, 9-trimethyl-triperoxycyclononane and 2, 2-di (t-butylperoxy) butane. Azoalkanes (diazenes), azodicarboxylic acid esters, azodicarboxylic acid dinitriles, such as azodiisobutyronitrile, and hydrocarbons which decompose into free radicals, also known as C-C initiators, such as 1, 2-diphenyl-1, 2-dimethylethane derivatives and 1, 2-tetramethylethane derivatives, are also suitable.
In a preferred embodiment of the present invention, the present invention uses an initiator in a dissolved state. Examples of suitable initiator solvents are ketones and aliphatic hydrocarbons (octane, decane and isododecane) and other saturated C' s 8 -C 25 And (3) hydrocarbons.
In a preferred embodiment of the invention, the comonomer is used for 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 esters or anhydrides and 1-olefins. In addition, vinyl carboxylates such as vinyl acetate may be used as comonomers. Propylene, 1-butene, 1-hexene, acrylic acid, n-butyl acrylate, t-butyl acrylate, 2-ethylhexyl acrylate, vinyl acetate or vinyl propionate are particularly suitable as comonomers.
The present invention also provides an ethylene polymerization reaction apparatus in a high pressure tubular reactor, the apparatus comprising at least one primary compressor for compressing a gas mixture;
at least one secondary compressor downstream of the primary compressor for compressing the reactant gas mixture;
a high-pressure tubular reactor for ethylene homo-polymerization or ethylene copolymerization with other monomers, which is located downstream of the secondary compressor and is divided into at least 2 sub-reactors according to spatially divided initiator and/or ethylene feed points, all sub-reactors being connected in series in sequence,
a polymer separation system downstream of the high pressure tubular reactor for separating unreacted reactants from the polymerization-derived polymer in the high pressure tubular reactor effluent;
the secondary compressor outlet is provided with a main flow connected to the tubular reactor inlet; the secondary compressor outlet is also provided with at least 1 side stream which is fed to any one or more of the other sub-reactor 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 homo-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 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 the reaction pressure by a main compressor and a secondary compressor and then are divided into a main flow and at least 1 side flow, and the polymerization heat removed from the reaction mixture in a reaction zone can be better removed by reducing the temperature of the side ethylene flow, so that the length of the reactor is reduced and the equipment cost is reduced under the condition that the temperature peak value and the temperature distribution are kept approximately unchanged.
(2) The ethylene polymerization method 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 the reaction pressure by a main compressor and a secondary compressor and then are divided into a main flow and at least 1 side flow, the temperature and the pressure of the side flow can be controlled (such as reducing the concentration of chain transfer agent in a first area, the initiation temperature and the reduction pressure in the first area), the 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 steps 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, and 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 is stably changed, and the adjustment of the Molecular Weight Distribution (MWD) of a product and the stability of the performance of the product 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 ethylene anti-Joule Thomson effect and residual initiator is reduced.
Drawings
The invention will be further described with reference to the drawings and examples.
FIG. 1 is a schematic illustration of a polymerization process for initiating homo-polymerization 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 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 is further illustrated and described below in connection with specific embodiments. The technical features of the embodiments of the invention can be combined correspondingly on the premise of no 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 run, the secondary compressor was operated at a throughput of 43.5t/h fresh ethylene, the secondary compressor outlet fluid compressed to 2200bar, preheated to 170 ℃ by a preheater fed to the tubular reactor inlet, with propylene as chain transfer agent fed downstream of the secondary compressor at 0.195t/h thoroughly mixed with fresh ethylene. The total length of the tubular reactor is 1310m, the inner diameter of the tubular reactor is 0.045m, the tubular reactor is divided into 4 sub-reactors at four positions of 110m, 510m and 910m at the inlet of the reactor and the downstream of the reactor, and all the sub-reactors are sequentially connected in series to form a high-pressure tubular reactor. The mixture from the main compressor was divided into a main stream fed to the inlet of the tubular reactor (i.e., the inlet of the 1 st sub-reactor) and 1 side stream fed to the inlet of the 2 nd sub-reactor, pre-cooled to 10 c by a pre-cooler, and the initiator mixtures of different ratios were fed to the inlets of the 4 sub-reactors of the reactor respectively for polymerization, with the initiator usage as shown in table 1.
The inlet temperatures of the 1 st to 4 th sub-reactors of the tubular reactor are respectively 170 ℃,170 ℃,203 ℃,248 ℃ and the peak temperatures of the 1 st to 4 th sub-reactors are respectively 295 ℃,295 ℃ and 295 ℃ by adjusting the feeding rate of the initiator, and the number average polymerization degree, the weight average polymerization degree, the number average molecular weight, the weight average molecular weight, the molecular weight distribution index, the yield and the 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 run, the secondary compressor was operated at a throughput of 43.5t/h fresh ethylene, the secondary compressor outlet fluid compressed to 2200bar, the preheater preheated to 170 ℃ was fed to the tubular reactor inlet, with propylene as chain transfer agent fed downstream of the secondary compressor at 0.195t/h thoroughly mixed with fresh ethylene. The full length of the tubular reactor is 1040m, the inner diameter of the tubular reactor is 0.045m, the tubular reactor is divided into 4 sub-reactors at four positions of 110m, 240m and 640m at the inlet of the reactor and at the downstream of the reactor, and all the sub-reactors are sequentially connected in series to form a high-pressure tubular reactor. The mixture from the main compressor was divided into a main stream fed to the inlet of the tubular reactor and 2 side streams, the 1 st side stream was pre-cooled to 10 ℃ by a pre-cooler and fed to the inlet of the 2 nd sub-reactor, the 2 nd side stream was pre-cooled to 10 ℃ by a pre-cooler and fed to the inlet of the 3 rd sub-reactor, and the initiator mixtures of different ratios were fed to the inlets of the 4 sub-reactors of the reactor for polymerization respectively, with the initiator usage as shown in table 2.
The inlet temperatures of the 1 st to 4 th sub-reactors of the tubular reactor are respectively 170 ℃,186 ℃,249 ℃,213 ℃ and the peak temperatures of the 1 st to 4 th sub-reactors are respectively 295 ℃,295 ℃ and 295 ℃ by adjusting the feeding rate of the initiator, and the number average polymerization degree, the weight average polymerization degree, the number average molecular weight, the weight average molecular weight, the molecular weight distribution index, the yield and the ethylene conversion rate of the obtained LDPE are 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 flow, the secondary compressor was operated at a throughput of 43.5t/h fresh ethylene, the secondary compressor outlet fluid was compressed to 2200bar, and the preheater was preheated to 170 ℃ and fed to the tubular reactor inlet. The total length of the tubular reactor is 1310m, the inner diameter of the tubular reactor is 0.045m, the tubular reactor is divided into 4 sub-reactors at four positions of 110m, 510m and 910m at the inlet of the reactor and the downstream of the reactor, and all the sub-reactors are sequentially connected in series to form a high-pressure tubular reactor. The mixture from the main compressor was split into a main stream fed to the tubular reactor inlet and 1 side stream fed to the sub-reactor inlet at 10 ℃ pre-cooled by a pre-cooler. Wherein propylene was fed as a chain transfer agent to the secondary compressor downstream at 0.180t/h and thoroughly mixed with fresh ethylene, and the other was fed to the side stream at 0.015 t/h. The initiator mixtures with different proportions are respectively fed into the inlets of 4 sub-reactors of the reactor for polymerization reaction, and the use conditions of the initiators are shown in table 1.
The inlet temperatures of the 1 st to 4 th sub-reactors of the tubular reactor are respectively 170 ℃,170 ℃,203 ℃,248 ℃ and the peak temperatures of the 1 st to 4 th sub-reactors are respectively 295 ℃,295 ℃ and 295 ℃ by adjusting the feeding rate of the initiator, and the number average polymerization degree, the weight average polymerization degree, the number average molecular weight, the weight average molecular weight, the molecular weight distribution index, the yield and the 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 flow, the secondary compressor was operated at a throughput of 43.5t/h fresh ethylene, the secondary compressor outlet fluid was compressed to 2200bar, and the preheater was preheated to 170 ℃ and fed to the tubular reactor inlet. The full length of the tubular reactor is 1040m, the inner diameter of the tubular reactor is 0.045m, the tubular reactor is divided into 4 sub-reactors at four positions of 110m, 240m and 640m at the inlet of the reactor and at the downstream of the reactor, and all the sub-reactors are sequentially connected in series to form a high-pressure tubular reactor. The mixture from the main compressor is split 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 is fed downstream of the secondary compressor as a portion of chain transfer agent at 0.165t/h and thoroughly mixed with fresh ethylene, one portion being fed to the 1 st side stream at 0.015t/h and the other portion being fed to the 2 nd side stream at 0.015 t/h. The initiator mixtures with different proportions are respectively fed into the inlets of 4 sub-reactors of the reactor for polymerization reaction, and the use conditions of the initiators are shown in table 2.
The inlet temperatures of the 1 st to 4 th sub-reactors of the tubular reactor are respectively 170 ℃,186 ℃,249 ℃,213 ℃ and the peak temperatures of the 1 st to 4 th sub-reactors are respectively 295 ℃,295 ℃ and 295 ℃ by adjusting the feeding rate of the initiator, and the number average polymerization degree, the weight average polymerization degree, the number average molecular weight, the weight average molecular weight, the molecular weight distribution index, the yield and the ethylene conversion rate of the obtained LDPE are given in Table 3.
Comparative example 1
In contrast to example 1, comparative example 1 continuous polymerization of ethylene to produce LDPE in a tubular reactor without side feed. In the process run, the secondary compressor was operated at a throughput of 43.5t/h fresh ethylene, the secondary compressor outlet fluid compressed to 2200bar, the preheater preheated to 170 ℃ was fed to the tubular reactor inlet, with propylene as chain transfer agent fed downstream of the secondary compressor at 0.195t/h thoroughly mixed with fresh ethylene. The total length of the tubular reactor is 1760m, the inner diameter of the tubular reactor is 0.045m, the tubular reactor is divided into 4 sub-reactors by four positions of a reactor inlet and 560m, 960m and 1360m at the downstream of the tubular reactor, initiator mixtures with different proportions are respectively fed into the inlets of the 4 sub-reactors of the tubular reactor for polymerization, and the use conditions of the initiators are shown in table 2.
The inlet temperatures of the 1 st to 4 th sub-reactors of the tubular reactor are respectively 170 ℃,193 ℃,210 ℃,220 ℃ and the peak temperatures of the 1 st to 4 th sub-reactors are respectively 295 ℃,295 ℃ and 295 ℃ by adjusting the feeding rate of the initiator, and the number average polymerization degree, the weight average polymerization degree, the number average molecular weight, the weight average molecular weight, the molecular weight distribution index, the yield and the ethylene conversion rate of the obtained LDPE are given in Table 3.
Comparative example 2
Comparative example 2 LDPE was prepared by continuous polymerization of ethylene in a tubular reactor without side feed, as compared to example 1. In the process flow, the secondary compressor was operated at a throughput of 43.5t/h fresh ethylene, the secondary compressor outlet fluid was compressed to 2200bar, and the preheater was preheated to 170 ℃ and fed to the tubular reactor inlet. The tubular reactor had a total length of 1760m and an internal diameter of 0.045m, and was divided into 4 sub-reactors at four locations of the reactor inlet and 560m, 960m and 1360m downstream of the reactor, wherein propylene was fed as a chain transfer agent to the 4 sub-reactor inlets of the reactor at 0.175t/h, 0.005t/h and 0.005t/h, respectively, and initiator mixtures of different proportions were fed to the 4 sub-reactor inlets of the reactor, respectively, for polymerization, and the initiator usage was as shown in Table 1.
The inlet temperatures of the 1 st to 4 th sub-reactors of the tubular reactor are respectively 170 ℃,198 ℃,211 ℃,220 ℃ and the peak temperatures of the 1 st to 4 th sub-reactors are respectively 295 ℃,295 ℃ and 295 ℃ by adjusting the feeding rate of the initiator, and the number average polymerization degree, the weight average polymerization degree, the number average molecular weight, the weight average molecular weight, the molecular weight distribution index, the yield and the ethylene conversion rate of the obtained LDPE are given in Table 3.
TABLE 1
Initiator name Abbreviations (abbreviations) For R x Zone (x=1/2/3/4)
Di-tert-butyl peroxide DTBP Yes/yes
Tert-butyl peroxybenzoate TBPB Yes/no
Tert-butyl group2-ethylhexyl peroxide TBPEH Yes/no
TABLE 2
Initiator name Abbreviations (abbreviations) For R x Zone (x=1/2/3/4)
Di-tert-butyl peroxide DTBP Yes/yes
Tert-butyl peroxybenzoate TBPB Yes/no
Tert-butyl peroxy-2-ethylhexyl ester TBPEH Yes/no
TABLE 3 Table 3
Figure BDA0003674404620000101
Comparison of example 1, example 2 and comparative example 1 shows that the use of a side-stream cold ethylene feed can remove part of the heat of polymerization in the reaction zone, reducing the length of the reactor cooling section while ensuring that the temperature peaks and temperature distribution are substantially unchanged, reducing equipment costs, and simultaneously producing LDPE polymers with broad Molecular Weight Distribution (MWD) by controlling the side-stream temperature.
Comparison of example 3, example 4 and comparative example 2 shows that the concentration of chain transfer agent in each sub-reactor zone can be stably varied by feeding chain transfer agent to any 1 or more of the primary compressor outlet, secondary compressor outlet, primary stream and side stream and controlling the flow of each branched chain transfer agent, the Molecular Weight Distribution (MWD) of the product LDPE polymer is significantly improved.
The foregoing examples illustrate only a few embodiments of the invention and are described in detail herein without thereby limiting the scope of the invention. It should be noted that it will be apparent to those skilled in the art that several variations and modifications can be made without departing from the spirit of the invention, which are all within the scope of the invention. Accordingly, the scope of protection of the present invention is to be determined by the appended claims.

Claims (9)

1. A process for the polymerization of ethylene in a high pressure tubular reactor, said polymerization process being characterized in that in a tubular reactor consisting of at least 2 sub-reactors in series in sequence, a free radical polymerization initiator initiates ethylene homo-polymerization or ethylene co-polymerization with other monomers at a pressure of 170-330MPa and a temperature of 100-350 ℃, wherein said polymerization process comprises:
(1) Providing a high-pressure tubular reactor, dividing the tubular reactor into at least 2 sub-reactors according to the initiator and/or ethylene feeding points which are spatially divided, and sequentially connecting all the sub-reactors in series to form the high-pressure tubular reactor; the inlet of the first sub-reactor of the high-pressure tubular reactor is provided with a preheater, the preheater is provided with at least 2 sleeve-type heat exchange structures which are connected in series or in parallel, wherein the materials in the tubes of the sleeve-type heat exchange structures are reaction materials, the flow rate is 5-25m/s, and the materials in the sleeve-type heat exchange structures are hot water or steam;
(2) Fresh ethylene and unreacted reaction materials separated from the outlet of the reactor are compressed to the reaction pressure by a main compressor and a secondary compressor and then divided into a main flow and at least 1 side flow, wherein the main flow is fed to the inlet of the tubular reactor, and the side flow is fed to any one or more other inlets of the sub-reactors downstream of the first sub-reactor;
(3) Injecting fresh chain transfer agent into at least the flow after the high-pressure reducing valve at the outlet of the high-pressure tubular reactor;
(4) Each sub-reactor is provided with at least 1 initiator feed inlet, 1 reactant feed inlet and 1 polymer discharge outlet, and ethylene is subjected to homopolymerization reaction or ethylene and at least one other monomer are subjected to copolymerization reaction 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 5m/s.
2. The method of claim 1, wherein in step (3), chain transfer agent is also supplemental injected at any location between the primary compressor stages and/or outlets, the secondary compressor outlets, the primary stream, and the side stream.
3. The method of claim 2, wherein the supplemental injected chain transfer agent is split into 2 feeds, the supplemental injected chain transfer agent being injected into any 2 locations in the outlet of the primary compressor, the secondary compressor outlet, the primary stream, and the side stream.
4. The method of claim 2, wherein the supplemental injected chain transfer agent is split into 3 feeds, the supplemental injected chain transfer agent being injected into any 3 locations in the outlet of the primary compressor, the secondary compressor outlet, the primary stream, and the side stream.
5. The process of claim 1, wherein the side stream is cooled and fed to the other sub-reactor inlets downstream of the first sub-reactor.
6. The process of claim 1 wherein the flow of each chain transfer agent is independently controllable when the chain transfer agent is split into at least 2 feeds.
7. The method of any of claims 1-6, wherein the feed streams of the primary compressor and the secondary compressor comprise a separated unreacted mixture in a reactor outlet effluent.
8. The process according to any of claims 1 to 6, wherein the polymerization temperature of the nth sub-reactor of the high-pressure tubular reactor is independently controllable, n.gtoreq.1.
9. A polymerization apparatus for carrying out the method of claim 1, comprising:
at least one primary compressor for compressing the gas mixture;
at least one secondary compressor downstream of the primary compressor for compressing the reactant gas mixture;
the high-pressure tubular reactor is positioned at the downstream of the secondary compressor and used for ethylene homopolymerization or ethylene copolymerization with other monomers, the high-pressure tubular reactor is divided into at least 2 sub-reactors according to a space-divided initiator and/or ethylene feeding point, all the sub-reactors are sequentially connected in series, a high-pressure reducing valve is arranged at the outlet of the high-pressure tubular reactor, and a fresh chain transfer agent injection port is arranged behind the high-pressure reducing valve;
a polymer separation system downstream of the high pressure tubular reactor for separating unreacted reactants from the polymerization-derived polymer in the high pressure tubular reactor effluent;
the secondary compressor outlet is provided with a main flow connected to the tubular reactor inlet; the secondary compressor outlet is also provided with at least 1 side stream which is fed to any one or more of the other sub-reactor inlets downstream of the first sub-reactor.
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