System for producing high pressure polyethylene and method thereof

Abstract

The application relates to the technical field of chemical synthesis, and discloses a system for preparing high-pressure polyethylene and a method thereof. The system comprises an evaporator (1), a booster (2), a two-stage booster (3) and a tubular reaction unit (4), wherein the tubular reaction unit (4) comprises a first bubble generator (41), a first tubular reactor (42), a first low-pressure separation device (43), a second bubble generator (44), a second tubular reactor (45), a second low-pressure separation device (46) and a two-stage high-pressure separation device (47). According to the technical scheme, the dispersity of the initiator injection system is improved, the conversion rate of ethylene is improved, the prepared high-pressure polyethylene product has high toughness, high notched impact strength and high percentage of breaking strain, and has excellent performance.

Description

Technical Field

[0001] This invention relates to the field of chemical synthesis technology, and more specifically to a system and method for preparing high-pressure polyethylene. Background Technology

[0002] High-density polyethylene (LDPE), also known as high-pressure polyethylene, possesses excellent insulation, ductility, and acid and alkali resistance, and is widely used as a raw material in the preparation of plastic products. The polymerization temperature of LDPE is 150–300℃, the polymerization pressure is 200–330 MPa, and the polymerization time is generally maintained between 0.5 and 120 seconds.

[0003] In the industrial production of high-density polyethylene (HDPE), initiators are required to initiate the polymerization of ethylene monomers. Initiators are typically peroxides and oxidants. During polymerization, the initiator provides active sites for ethylene molecules, thereby accelerating the polymerization process. However, uneven distribution of the initiator in the reaction system can lead to numerous localized hot spots, potentially causing the reaction to runaway. Patent application CN113004439A discloses a method for inhibiting ethylene polymerization in a compressor during HDPE production. While this invention offers advantages such as good polymerization inhibition and ease of operation, uneven initiator injection and distribution can cause explosive polymerization, with the resulting polymers clogging reaction pipelines, leading to system overpressure and posing safety risks such as combustion and explosion. Patent application CN117362494A discloses a system for high-pressure free radical polymerization of ethylene. The system includes a polymerization unit, a fluid suction and delivery unit, an initiator supply unit, and a chain transfer agent supply unit. In this invention, each stage of the reaction, including the subsequent cascade, is a unidirectional flow reaction. At each stage, some reactions are incomplete, and products that do not meet the standards are produced, ultimately affecting the system yield. Moreover, there are problems with uneven initiator distribution and poor catalytic effect, resulting in poor polymerization efficiency of the system and thus affecting product quality.

[0004] Therefore, there is an urgent need to develop a system and method for preparing high-pressure polyethylene that can improve the uniformity of initiator distribution and enhance ethylene conversion and reaction efficiency while ensuring system safety. Summary of the Invention

[0005] The purpose of this invention is to overcome the problems of uneven initiator distribution, low ethylene conversion rate and reaction efficiency, and poor quality of high-pressure polyethylene in the preparation of high-pressure polyethylene in the prior art. This invention provides a system and method for preparing high-pressure polyethylene. This technical solution improves the uniformity of initiator distribution to achieve safe and stable production and operation of high-pressure polyethylene, and also improves the ethylene conversion rate and reaction efficiency, achieving excellent quality, strength, and high fracture strain percentage of high-pressure polyethylene.

[0006] To achieve the above objectives, the present invention provides a system for preparing high-pressure polyethylene. The system includes: an evaporator, a booster compressor, two-stage booster compressors, and a tubular reaction unit. The tubular reaction unit includes a first bubble generator, a first tubular reactor, a first low-pressure separation device, a second bubble generator, a second tubular reactor, a second low-pressure separation device, and two-stage high-pressure separation devices. Initiator is vaporized into a gaseous phase in the evaporator. The vaporized initiator enters the booster compressor for pressurization. The pressurized initiator passes through the first bubble generator and enters the first tubular reactor. The pressurized initiator then passes through the second bubble generator and enters the second tubular reactor. Liquid ethylene enters the two-stage booster for two-stage pressurization. The pressurized ethylene then enters the first tubular reactor for polymerization. The material passing through the first tubular reactor enters the second tubular reactor for polymerization. The material passing through the second tubular reactor enters the second low-pressure separation device for low-pressure separation. The gaseous ethylene after low-pressure separation returns to the first tubular reactor for polymerization again. The material passing through the second tubular reactor sequentially enters the two-stage high-pressure separation device for two-stage high-pressure separation and the first low-pressure separation device for low-pressure separation. The gaseous ethylene after low-pressure separation returns to the first tubular reactor for polymerization again.

[0007] Preferably, the system further includes an ethylene storage tank and a refrigeration unit, wherein the ethylene storage tank is used to store ethylene and the refrigeration unit is used to liquefy ethylene.

[0008] Preferably, the system for preparing high-pressure polyethylene further includes an extrusion granulation device for extruding and granulating the polyethylene that has passed through the first low-pressure separation device.

[0009] Preferably, the tubular reaction unit further includes a third bubble generator, a third tubular reactor, and a third low-pressure separation device. The initiator is vaporized into a gaseous phase in the evaporator. The vaporized initiator enters the booster for pressurization. The pressurized initiator passes through the first bubble generator and enters the first tubular reactor. The pressurized initiator then passes through the second bubble generator and enters the second tubular reactor. The pressurized initiator then passes through the third bubble generator and enters the third tubular reactor. Liquid ethylene enters the two-stage booster for two-stage pressurization. The pressurized ethylene then enters the first tubular reactor for polymerization. The material passing through the first tubular reactor enters the second tubular reactor for polymerization. The polymerization reaction proceeds as follows: the material passing through the second tubular reactor enters the second low-pressure separation device for low-pressure separation; the gaseous ethylene after low-pressure separation returns to the first tubular reactor for another polymerization reaction; the material passing through the second tubular reactor enters the third tubular reactor for another polymerization reaction; the material passing through the third tubular reactor enters the third low-pressure separation device for another low-pressure separation; the gaseous ethylene after low-pressure separation returns to the second tubular reactor for another polymerization reaction; the material passing through the third tubular reactor sequentially enters the two-stage high-pressure separation device for two-stage high-pressure separation and the first low-pressure separation device for low-pressure separation; the gaseous ethylene after low-pressure separation returns to the first tubular reactor for another polymerization reaction.

[0010] Preferably, the tubular reaction unit further includes a fourth bubble generator, a fourth tubular reactor, and a fourth low-pressure separation device. The initiator is vaporized into a gaseous phase in the evaporator. The vaporized initiator enters the booster for pressurization. The pressurized initiator passes through the first bubble generator and enters the first tubular reactor. The pressurized initiator then passes through the second bubble generator and enters the second tubular reactor. The pressurized initiator passes through the third bubble generator and enters the third tubular reactor. The pressurized initiator then passes through the fourth bubble generator and enters the fourth tubular reactor. Liquid ethylene enters the two-stage booster for two-stage pressurization. The pressurized ethylene then enters the first tubular reactor for polymerization. The material passing through the first tubular reactor enters the second tubular reactor for polymerization. The material passing through the second tubular reactor enters the second low-pressure separation device for low-pressure separation. The gaseous ethylene from the second tubular reactor undergoes polymerization again after low-pressure separation. The material from the third tubular reactor then enters the third low-pressure separation unit for further low-pressure separation. The gaseous ethylene from the third tubular reactor then returns to the second tubular reactor for further polymerization. The material from the fourth tubular reactor then enters the fourth low-pressure separation unit for further low-pressure separation. The gaseous ethylene from the fourth tubular reactor then returns to the third tubular reactor for further polymerization. Finally, the material from the fourth tubular reactor sequentially enters the two high-pressure separation units for two-stage high-pressure separation and the first low-pressure separation unit for low-pressure separation. The gaseous ethylene from the low-pressure separation returns to the first tubular reactor for further polymerization.

[0011] Preferably, the first bubble generator, the second bubble generator, the third bubble generator, and the fourth bubble generator each comprise a metal membrane.

[0012] Preferably, the metal film contains copper oxide, aluminum oxide, iron oxide and silicon dioxide.

[0013] Preferably, the pore size of the metal film is 5-10 μm.

[0014] Preferably, the thickness of the metal film is 0.5-3 mm.

[0015] A second aspect of the present invention provides a method for preparing high-pressure polyethylene, the method comprising the following steps:

[0016] (1) The initiator is vaporized into a gas phase in the evaporator. The vaporized initiator enters the booster for pressurization. The pressurized initiator enters the first tubular reactor through the first bubble generator. The pressurized initiator enters the second tubular reactor through the second bubble generator. The pressurized initiator enters the third tubular reactor through the third bubble generator. The pressurized initiator enters the fourth tubular reactor through the fourth bubble generator.

[0017] (2) Ethylene in the ethylene storage tank is liquefied using a refrigeration unit to obtain liquid ethylene. The obtained liquid ethylene enters a two-stage booster for two-stage pressurization. The pressurized ethylene then enters a first tubular reactor for polymerization. The material passing through the first tubular reactor enters a second tubular reactor for polymerization. The material passing through the second tubular reactor enters a second low-pressure separator for low-pressure separation. The gaseous ethylene after low-pressure separation is returned to the first tubular reactor for further polymerization. The material passing through the second tubular reactor enters a third tubular reactor for polymerization. The material passing through the third tubular reactor enters a third low-pressure separator. The material passes through the third tubular reactor and enters the fourth tubular reactor for polymerization. The material then passes through the fourth tubular reactor and enters the fourth low-pressure separation unit for low-pressure separation. The material then passes through the fourth tubular reactor and enters the third tubular reactor for polymerization. The material then passes through the fourth tubular reactor and enters the first low-pressure separation unit for low-pressure separation. The material then passes through the fourth tubular reactor and enters the second high-pressure separation unit for high-pressure separation and the first low-pressure separation unit for low-pressure separation. The material then passes through the first tubular reactor for polymerization.

[0018] (3) The polyethylene that has passed through the first low-pressure separation device is fed into the extrusion granulation device for extrusion granulation to obtain the product.

[0019] Preferably, the initiator is 4,4-di(tert-butylperoxy)valerate n-butyl ester and peroxy(2-ethylhexanoate) tert-butyl ester.

[0020] Preferably, the mass ratio of the amount of 4,4-di(tert-butylperoxy)valerate to the amount of tert-butyl peroxy(2-ethylhexanoate) is (2-3):1.

[0021] Preferably, the mass ratio of the initiator to the ethylene is (1×10⁻⁶). -4 -6×10 -4 ): 1.

[0022] Preferably, the polymerization conditions in the first tubular reactor, the second tubular reactor, the third tubular reactor, and the fourth tubular reactor include: a temperature of 240-250℃, a pressure of 250-260MPa, and a time of 10-90s.

[0023] The above technical solution utilizes metal sintered thin films to prepare microbubbles, which are then added in this form. The large surface area and strong mass and heat transfer characteristics of the microbubbles enhance the polymerization reaction, while the introduction of microbubbles improves the dispersion of the initiator injection system. Furthermore, employing a multi-point initiator injection method with stepwise low-pressure separation and recycling of light components effectively improves the ethylene conversion rate. The prepared high-pressure polyethylene product exhibits high toughness, high notched impact strength, high percentage of fracture strain, excellent performance, and a high ethylene conversion rate.

[0024] The system and method for preparing high-pressure polyethylene described in this invention can be applied not only to the preparation of high-pressure polyethylene, but also to various polymer production systems requiring the addition of initiators, such as polystyrene, polypropylene, and POE elastomers. Furthermore, it can be applied to the preparation and use of various gas-liquid and liquid-liquid mixed-phase reactions. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the process flow of the system for preparing high-pressure polyethylene according to the present invention.

[0026] Explanation of reference numerals in the attached figures

[0027] 1. Evaporator; 2. Booster compressor; 3. Two-stage booster compressor; 4. Tubular reaction unit; 41. First bubble generator; 42. First tubular reactor; 43. First low-pressure separation device; 44. Second bubble generator; 45. Second tubular reactor; 46. Second low-pressure separation device; 47. Two-stage high-pressure separation device; 48. Third bubble generator; 49. Third tubular reactor; 410. Third low-pressure separation device; 411. Fourth bubble generator; 412. Fourth tubular reactor; 413. Fourth low-pressure separation device; 5. Ethylene storage tank; 6. Refrigeration unit; 7. Extrusion granulation device. Detailed Implementation

[0028] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0029] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0030] like Figure 1 As shown, the system for preparing high-pressure polyethylene according to the present invention includes: an evaporator 1, a booster 2, a two-stage booster 3, and a tubular reaction unit 4. The tubular reaction unit 4 includes a first bubble generator 41, a first tubular reactor 42, a first low-pressure separation device 43, a second bubble generator 44, a second tubular reactor 45, a second low-pressure separation device 46, and a two-stage high-pressure separation device 47. The initiator is vaporized into a gaseous phase in the evaporator 1. The vaporized initiator enters the booster 2 for pressurization. The pressurized initiator passes through the first bubble generator 41 and enters the first tubular reactor 42. The pressurized initiator passes through the second bubble generator 44 and enters the second tubular reactor 45. Ethylene enters the two-stage booster 3 for two-stage pressurization. The pressurized ethylene then enters the first tubular reactor 42 for polymerization. The material passing through the first tubular reactor 42 enters the second tubular reactor 45 for polymerization. The material passing through the second tubular reactor 45 enters the second low-pressure separation device 46 for low-pressure separation. The gaseous ethylene after low-pressure separation returns to the first tubular reactor 42 for polymerization again. The material passing through the second tubular reactor 45 sequentially enters the two-stage high-pressure separation device 47 for two-stage high-pressure separation and the first low-pressure separation device 43 for low-pressure separation. The gaseous ethylene after low-pressure separation returns to the first tubular reactor 42 for polymerization again. According to the system described in this invention, microbubbles are prepared using a bubble generator and fed through a multi-stage series tubular reactor, effectively improving the conversion rate of the raw material ethylene. The microbubbles, with their high specific surface area and heat and mass transfer efficiency, significantly improve the polymerization reaction efficiency and effectively solve safety problems such as reaction runaway caused by uneven initiator distribution. Furthermore, the method of injecting initiator at multiple points and performing stepwise low-pressure separation and recycling of light components effectively enhances the ethylene conversion rate. This technical solution is highly operable, achieves a high ethylene conversion rate, and produces high-quality, tough, and high-strength polyethylene with a high percentage of fracture strain, ensuring safe and stable operation in industrial production.

[0031] In the system for preparing high-pressure polyethylene described in this invention, the evaporator 1 can be a thin-film evaporator, which is commercially available or can be referred to the content disclosed in patent application CN202321847313.1.

[0032] In the system for preparing high-pressure polyethylene according to the present invention, the system may further include an ethylene storage tank 5 and a refrigeration unit 6, wherein the ethylene storage tank 5 is used to store ethylene and the refrigeration unit 6 is used to liquefy ethylene.

[0033] In the system for preparing high-pressure polyethylene according to the present invention, the system may further include an extrusion granulation device 7, which is used to extrude and granulate the polyethylene that has passed through the first low-pressure separation device 43. The extrusion granulation device 7 is commercially available, or can be referred to the disclosure in patent application CN202210912859.4.

[0034] In the system for preparing high-pressure polyethylene according to the present invention, the tubular reaction unit 4 may further include a third bubble generator 48, a third tubular reactor 49, and a third low-pressure separation device 410. The initiator is vaporized into a gaseous phase in the evaporator 1. The vaporized initiator enters the booster 2 for pressurization. The pressurized initiator passes through the first bubble generator 41 and enters the first tubular reactor 42. The pressurized initiator passes through the second bubble generator 44 and enters the second tubular reactor 45. The pressurized initiator passes through the third bubble generator 48 and enters the third tubular reactor 49. Liquid ethylene enters the two-stage booster 3 for two-stage pressurization. The two-stage pressurized ethylene enters the first tubular reactor 42 for polymerization. The material passing through the first tubular reactor 42 enters the third low-pressure separation device 410. The polymerization reaction takes place in the two-tube reactor 45. The material passing through the second tube reactor 45 enters the second low-pressure separation device 46 for low-pressure separation. The gaseous ethylene after low-pressure separation returns to the first tube reactor 42 for another polymerization reaction. The material passing through the second tube reactor 45 enters the third tube reactor 49 for another polymerization reaction. The material passing through the third tube reactor 49 enters the third low-pressure separation device 410 for low-pressure separation. The gaseous ethylene after low-pressure separation returns to the second tube reactor 45 for another polymerization reaction. The material passing through the third tube reactor 49 sequentially enters the two-stage high-pressure separation device 47 for two-stage high-pressure separation and the first low-pressure separation device 43 for low-pressure separation. The gaseous ethylene after low-pressure separation returns to the first tube reactor 42 for another polymerization reaction.

[0035] In the system for preparing high-pressure polyethylene according to the present invention, the tubular reaction unit 4 may further include a fourth bubble generator 411, a fourth tubular reactor 412, and a fourth low-pressure separation device 413. The initiator is vaporized into a gaseous phase in the evaporator 1. The vaporized initiator enters the booster 2 for pressurization. The pressurized initiator passes through the first bubble generator 41 into the first tubular reactor 42, then through the second bubble generator 44 into the second tubular reactor 45, then through the third bubble generator 48 into the third tubular reactor 49, and finally through the fourth bubble generator 411 into the fourth tubular reactor 412. Liquid ethylene enters the two-stage booster 3 for two-stage pressurization. The pressurized ethylene then enters the first tubular reactor 42 for polymerization. The material passing through the first tubular reactor 42 enters the second tubular reactor 45 for polymerization. The material passing through the second tubular reactor 45 enters the fourth tubular reactor 412. The second low-pressure separation device 46 performs low-pressure separation. The gaseous ethylene after low-pressure separation is returned to the first tubular reactor 42 for another polymerization reaction. The material passing through the second tubular reactor 45 enters the third tubular reactor 49 for polymerization reaction. The material passing through the third tubular reactor 49 enters the third low-pressure separation device 410 for low-pressure separation. The gaseous ethylene after low-pressure separation is returned to the second tubular reactor 45 for another polymerization reaction. The material passing through the third tubular reactor 49 enters the fourth tubular reactor 412 for polymerization reaction. The material passing through the fourth tubular reactor 412 enters the fourth low-pressure separation device 413 for low-pressure separation. The gaseous ethylene after low-pressure separation is returned to the third tubular reactor 49 for another polymerization reaction. The material passing through the fourth tubular reactor 412 sequentially enters the two-stage high-pressure separation device 47 for two-stage high-pressure separation and the first low-pressure separation device 43 for low-pressure separation. The gaseous ethylene after low-pressure separation is returned to the first tubular reactor 42 for another polymerization reaction.

[0036] In the system for preparing high-pressure polyethylene according to the present invention, the first bubble generator 41, the second bubble generator 44, the third bubble generator 48, and the fourth bubble generator 411 may each include a metal film. The metal film may be a sintered metal film. The sintered metal film is commercially available or can be prepared using conventional methods in the art; specific preparation methods can be found in patent application CN202210511590.9. By using the sintered metal film of the bubble generator to prepare microbubbles, and adding the initiator to the system for preparing high-pressure polyethylene in the form of microbubbles, the polymerization reaction efficiency is effectively improved by the high heat and mass transfer efficiency and large specific surface area of ​​the microbubbles, reducing the risk of reaction runaway caused by local hot spots due to uneven distribution of the initiator during polymerization. The first bubble generator 41, the second bubble generator 44, the third bubble generator 48, and the fourth bubble generator 411 are commercially available or can be found in patent application CN202322669443.7.

[0037] In the system for preparing high-pressure polyethylene described in this invention, in order to improve the polymerization reaction efficiency, the metal film preferably contains copper oxide, aluminum oxide, iron oxide and silicon dioxide.

[0038] In the system for preparing high-pressure polyethylene described in this invention, the pore size of the metal membrane can be 5-10 μm, preferably 6-9 μm. The thickness of the metal membrane can be 0.5-3 mm, preferably 1-2.5 mm. The membrane pressure of the metal membrane can be 100-500 kPa, preferably 200-300 kPa. In this document, pressure refers to gauge pressure.

[0039] In the system for preparing high-pressure polyethylene described in this invention, the first tubular reactor 42, the second tubular reactor 45, the third tubular reactor 49, and the fourth tubular reactor 412 are commercially available, or can be referred to the content disclosed in patent application CN202310430512.0.

[0040] In the system for preparing high-pressure polyethylene according to the present invention, the first low-pressure separation device 43, the second low-pressure separation device 46, the third low-pressure separation device 410, and the fourth low-pressure separation device 413 are depressurized to 0.7-0.9 MPa. The first low-pressure separation device 43, the second low-pressure separation device 46, the third low-pressure separation device 410, and the fourth low-pressure separation device 413 are commercially available, or can be referred to the disclosure in patent application CN202310578311.5.

[0041] In the system for preparing high-pressure polyethylene according to the present invention, the first stage of the two-stage high-pressure separation device 47 is depressurized to 50-60 MPa, and the second stage of the two-stage high-pressure separation device 47 is depressurized to 5-6 MPa. The two-stage high-pressure separation device 47 is commercially available, or can be referred to the content disclosed in patent application CN 202310578329.5.

[0042] In the system for preparing high-pressure polyethylene described in this invention, the number of bubble generators, tubular reactors, and low-pressure separation devices can each be two or more, specifically, two, three, four, five, six, seven, eight, nine, ten, or more. In practical applications, the more bubble generators, tubular reactors, and low-pressure separation devices there are, the higher the ethylene conversion rate of the system for preparing high-pressure polyethylene, but the higher the investment and operating costs of the system. Considering both the ethylene conversion rate and cost of the system for preparing high-pressure polyethylene, the preferred number of bubble generators, tubular reactors, and low-pressure separation devices is four.

[0043] In some embodiments, when the number of the bubble generator, the tubular reactor, and the low-pressure separation device are all four, the system for preparing high-pressure polyethylene according to the present invention includes: an evaporator 1, a booster 2, a two-stage booster 3, a tubular reaction unit 4, an ethylene storage tank 5, a refrigerator 6, and an extrusion granulation device 7. The tubular reaction unit 4 includes a first bubble generator 41, a first tubular reactor 42, a first low-pressure separation device 43, a second bubble generator 44, a second tubular reactor 45, a second low-pressure separation device 46, a third bubble generator 48, a third tubular reactor 49, a third low-pressure separation device 410, a fourth bubble generator 411, a fourth tubular reactor 412, and a fourth low-pressure separation device 410. The device 413 and the two-stage high-pressure separation device 47 are used in the following process: The initiator is vaporized into a gaseous phase in the evaporator 1; the vaporized initiator enters the booster compressor 2 for pressurization; the pressurized initiator passes through the first bubble generator 41 and enters the first tubular reactor 42; the pressurized initiator passes through the second bubble generator 44 and enters the second tubular reactor 45; the pressurized initiator passes through the third bubble generator 48 and enters the third tubular reactor 49; the pressurized initiator passes through the fourth bubble generator 411 and enters the fourth tubular reactor 412; the ethylene in the ethylene storage tank 5 enters the refrigerator 6 for liquefaction; the liquefied ethylene then enters the two-stage booster compressor 3. The ethylene undergoes two-stage pressurization. After pressurization, it enters the first tubular reactor 42 for polymerization. The material passing through the first tubular reactor 42 then enters the second tubular reactor 45 for further polymerization. The material passing through the second tubular reactor 45 then enters the second low-pressure separation device 46 for low-pressure separation. The gaseous ethylene after low-pressure separation returns to the first tubular reactor 42 for polymerization again. The material passing through the second tubular reactor 45 then enters the third tubular reactor 49 for polymerization. The material passing through the third tubular reactor 49 then enters the third low-pressure separation device 410 for low-pressure separation. The gaseous ethylene after low-pressure separation returns to the second tubular reactor 45 for polymerization again. The polymerization reaction proceeds as follows: the material passing through the third tubular reactor 49 enters the fourth tubular reactor 412 for polymerization; the material passing through the fourth tubular reactor 412 enters the fourth low-pressure separation device 413 for low-pressure separation; the gaseous ethylene after low-pressure separation returns to the third tubular reactor 49 for polymerization again; the material passing through the fourth tubular reactor 412 sequentially enters the two-stage high-pressure separation device 47 for two-stage high-pressure separation and the first low-pressure separation device 43 for low-pressure separation; the gaseous ethylene after low-pressure separation returns to the first tubular reactor 42 for polymerization again; and the polyethylene passing through the first low-pressure separation device 43 enters the extrusion granulation device 7 for extrusion granulation.

[0044] The present invention also provides a method for preparing high-pressure polyethylene, the method comprising the following steps:

[0045] (1) The initiator is vaporized into a gas phase in the evaporator 1. The vaporized initiator enters the booster 2 for pressurization. The pressurized initiator enters the first tubular reactor 42 through the first bubble generator 41. The pressurized initiator enters the second tubular reactor 45 through the second bubble generator 44. The pressurized initiator enters the third tubular reactor 49 through the third bubble generator 48. The pressurized initiator enters the fourth tubular reactor 412 through the fourth bubble generator 411.

[0046] (2) Ethylene in ethylene storage tank 5 is liquefied using a chiller 6 to obtain liquid ethylene. The obtained liquid ethylene enters a two-stage booster 3 for two-stage pressurization. The pressurized ethylene then enters a first tubular reactor 42 for polymerization. The material passing through the first tubular reactor 42 enters a second tubular reactor 45 for polymerization. The material passing through the second tubular reactor 45 enters a second low-pressure separator 46 for low-pressure separation. The gaseous ethylene after low-pressure separation is returned to the first tubular reactor 42 for polymerization again. The material passing through the second tubular reactor 45 enters a third tubular reactor 49 for polymerization. The material passing through the third tubular reactor 49 enters a third low-pressure separator. Device 410 performs low-pressure separation. The gaseous ethylene after low-pressure separation is returned to the second tubular reactor 45 for polymerization again. The material passing through the third tubular reactor 49 enters the fourth tubular reactor 412 for polymerization. The material passing through the fourth tubular reactor 412 enters the fourth low-pressure separation device 413 for low-pressure separation. The gaseous ethylene after low-pressure separation is returned to the third tubular reactor 49 for polymerization again. The material passing through the fourth tubular reactor 412 sequentially enters the two-stage high-pressure separation device 47 for two-stage high-pressure separation and the first low-pressure separation device 43 for low-pressure separation. The gaseous ethylene after low-pressure separation is returned to the first tubular reactor 42 for polymerization again.

[0047] (3) The polyethylene that has passed through the first low-pressure separation device 43 is fed into the extrusion granulation device 7 for extrusion granulation to obtain the product.

[0048] According to the method described in this invention, an initiator is added to a high-pressure polyethylene reaction system in the form of microbubbles prepared by a bubble generator. The large specific surface area and strong heat and mass transfer characteristics of microbubbles effectively improve the mixing uniformity between the initiator and ethylene, fundamentally avoiding the generation of local hot spots and the risk of reaction runaway. Furthermore, the method of multi-point initiator injection and stepwise low-pressure separation and recycling of light components effectively improves the ethylene conversion rate and reduces the risk of reaction runaway. The prepared high-pressure polyethylene exhibits excellent quality, high toughness, and a high percentage of fracture strain.

[0049] In the method described in this invention, the initiator can be butyl 4,4-di(tert-butylperoxy)valerate and tert-butyl peroxide (2-ethylhexanoate). The mass ratio of butyl 4,4-di(tert-butylperoxy)valerate to tert-butyl peroxide (2-ethylhexanoate) is (2-3):1. The initiator is used to initiate the polymerization reaction, converting the monomer into the polymer. During the polymerization process, it avoids the formation of local hot spots due to uneven distribution of the initiator, which could lead to runaway reaction.

[0050] In the method described in this invention, in step (1), the gas-liquid separation temperature in the evaporator 1 can be 70-80℃, the evaporation working pressure can be 0.4-0.6MPa, and the steam consumption can be 50-150kg / h.

[0051] In the method described in this invention, in step (1), in order to increase the rate of polymerization, the initiator vaporized into a gaseous phase is preferably pressurized to 4-5 MPa within the pressurizer 2. This is because under high pressure, the intermolecular distance decreases, increasing the chance of collisions and thus improving the reaction rate.

[0052] In the method described in this invention, in step (1), the pressurized initiator is used to prepare microbubbles through metal films in the first bubble generator 41, the second bubble generator 44, the third bubble generator 48, and the fourth bubble generator 411, respectively. The size of the microbubbles can be 50-300 μm, preferably 100-200 μm. The feed flow rate of the microbubbles can be 1-4 m / s, preferably 2-3 m / s.

[0053] In the method described in this invention, in step (2), in order to liquefy ethylene into a liquid phase, the refrigeration temperature of the refrigerator 6 is preferably -20 to -15°C, more preferably -20 to -17°C.

[0054] In the method described in this invention, in step (2), the liquid ethylene is first pressurized to 70-80 MPa in the two-stage booster 3, and then pressurized to 260-270 MPa.

[0055] In the method described in this invention, in step (2), in order to improve the conversion rate of ethylene, the flow rate of ethylene is preferably 3-7 m / s, and more preferably 5-6 m / s.

[0056] In the method described in this invention, in order to increase the polymerization rate, the preferred mass ratio of the initiator to the ethylene is (1 × 10⁻⁶). -4 -6×10 -4 ): 1, more preferably (3×10 -4 -4×10 -4 ): 1.

[0057] In the method described in this invention, the polymerization reaction conditions in the first tubular reactor 42, the second tubular reactor 45, the third tubular reactor 49, and the fourth tubular reactor 412 respectively include: a temperature of 240-250°C, preferably 242-248°C; a pressure of 250-260 MPa, preferably 252-257 MPa; and a time of 10-90 s, preferably 30-40 s.

[0058] In the method described in this invention, in step (2), the mass ratio of gaseous ethylene through the second low-pressure separation device 46 to the stream in the first tubular reactor 42, the mass ratio of gaseous ethylene through the third low-pressure separation device 410 to the stream in the second tubular reactor 45, and the mass ratio of gaseous ethylene through the fourth low-pressure separation device 413 to the stream in the third tubular reactor 49 can each be (1×10) -2 -9×10 -2 ): 1, preferably (4×10 -2 -7×10 -2 ): 1.

[0059] In the method described in this invention, in step (2), the material in the two high-pressure separation devices 47 is first depressurized to 50-60 MPa, and then depressurized to 5-6 MPa. The material in the first low-pressure separation device 43 is depressurized to 0.7-0.9 MPa. The volume ratio of the gaseous ethylene passing through the first low-pressure separation device 43 to the stream in the first tubular reactor 42 can be (2 × 10⁻⁶). -3 -9×10 -3 ): 1, preferably (5×10 -3 -7×10 -3 ): 1.

[0060] In some embodiments, the method for preparing high-pressure polyethylene according to the present invention includes the following steps:

[0061] (1) The initiator is vaporized into a gas phase in the evaporator 1 under the conditions of gas-liquid separation temperature of 70-80℃, evaporation working pressure of 0.4-0.6MPa and steam consumption of 50-150kg / h. The vaporized initiator enters the booster 2 for pressurization to 4-5MPa. The pressurized initiator enters the first tubular reactor 42 through the first bubble generator 41, the second tubular reactor 45 through the second bubble generator 44, the third tubular reactor 49 through the third bubble generator 48, and the fourth tubular reactor 412 through the fourth bubble generator 411. The pressurized initiator is prepared into microbubbles with a size of 50-300μm through metal membranes in the first bubble generator 41, the second bubble generator 44, the third bubble generator 48 and the fourth bubble generator 411 respectively. The feed flow rate of the microbubbles is 1-4m / s.

[0062] (2) Ethylene in ethylene storage tank 5 is liquefied using a refrigeration unit 6 at a temperature of -20 to -15°C to obtain liquid ethylene. The obtained liquid ethylene enters a two-stage booster 3 and is first pressurized to 70-80 MPa, then to 260-270 MPa. The pressurized ethylene then enters a first tubular reactor 42 for polymerization. The material passing through the first tubular reactor 42 enters a second tubular reactor 45 for polymerization. The material passing through the second tubular reactor 45 enters a second low-pressure separation device 46 for low-pressure separation. The gaseous ethylene after low-pressure separation is returned to the first tubular reactor 42 for polymerization again. The material passing through the second tubular reactor 45 enters a third tubular reactor 49 for polymerization. The material passing through the third tubular reactor 49 enters a third low-pressure separation device 410 for low-pressure separation. The gaseous ethylene after low-pressure separation is returned to the second tubular reactor 45 for polymerization again. The polymerization reaction is carried out. The material passing through the third tubular reactor 49 enters the fourth tubular reactor 412 for polymerization. The material passing through the fourth tubular reactor 412 enters the fourth low-pressure separation device 413 for low-pressure separation. The gaseous ethylene after low-pressure separation is returned to the third tubular reactor 49 for polymerization again. The material passing through the fourth tubular reactor 412 sequentially enters two-stage high-pressure separation devices 47 for two-stage high-pressure separation and a first low-pressure separation device 43 for low-pressure separation. In the two-stage high-pressure separation devices 47, the material is first depressurized to 50-60 MPa, then depressurized to 5-6 MPa. In the first low-pressure separation device 43, the material is depressurized to 0.7-0.9 MPa. The gaseous ethylene after low-pressure separation is returned to the first tubular reactor 42 for polymerization again. The flow rate of the ethylene is 3-7 m / s. The mass ratio of the initiator to the ethylene is (1×10⁻⁶ m / s). -4 -6×10-4 ): 1, the conditions for the polymerization reaction include: temperature of 240-250℃, pressure of 250-260MPa, and time of 10-90s;

[0063] (3) The polyethylene that has passed through the first low-pressure separation device 43 is fed into the extrusion granulation device 7 for extrusion granulation to obtain the product.

[0064] The following examples further illustrate the system and method for preparing high-pressure polyethylene according to the present invention. These examples are implemented based on the technical solution of the present invention, providing detailed implementation methods and specific operating procedures; however, the scope of protection of the present invention is not limited to the following examples.

[0065] Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods in the art. Unless otherwise specified, the experimental materials used in the following embodiments are commercially available.

[0066] The following examples illustrate the process of preparing high-pressure polyethylene according to... Figure 1 The system implementation shown specifically includes:

[0067] The system comprises an evaporator 1, a booster compressor 2, a two-stage booster compressor 3, a tubular reaction unit 4, an ethylene storage tank 5, a refrigeration unit 6, and an extrusion granulation device 7. The tubular reaction unit 4 includes a first bubble generator 41, a first tubular reactor 42, a first low-pressure separation device 43, a second bubble generator 44, a second tubular reactor 45, a second low-pressure separation device 46, a third bubble generator 48, a third tubular reactor 49, a third low-pressure separation device 410, a fourth bubble generator 411, a fourth tubular reactor 412, a fourth low-pressure separation device 413, and a two-stage high-pressure separation device 47. The initiator is vaporized into a gaseous phase within the evaporator 1, and the vaporized initiator then enters... The initiator is pressurized by the booster 2, and then passes through the first bubble generator 41 into the first tubular reactor 42. The pressurized initiator then passes through the second bubble generator 44 into the second tubular reactor 45, the third bubble generator 48 into the third tubular reactor 49, and the fourth bubble generator 411 into the fourth tubular reactor 412. The ethylene in the ethylene storage tank 5 is liquefied by the refrigerator 6. The resulting liquid ethylene is then pressurized in two stages by the two-stage booster 3, and finally enters the first tubular reactor 42 for polymerization. The reaction proceeds as follows: the material passing through the first tubular reactor 42 enters the second tubular reactor 45 for polymerization; the material passing through the second tubular reactor 45 enters the second low-pressure separation device 46 for low-pressure separation; the gaseous ethylene after low-pressure separation returns to the first tubular reactor 42 for further polymerization; the material passing through the second tubular reactor 45 enters the third tubular reactor 49 for polymerization; the material passing through the third tubular reactor 49 enters the third low-pressure separation device 410 for low-pressure separation; the gaseous ethylene after low-pressure separation returns to the second tubular reactor 45 for further polymerization; and the material passing through the third tubular reactor... Material 49 enters the fourth tubular reactor 412 for polymerization. The material passing through the fourth tubular reactor 412 then enters the fourth low-pressure separation device 413 for low-pressure separation. The gaseous ethylene after low-pressure separation returns to the third tubular reactor 49 for further polymerization. The material passing through the fourth tubular reactor 412 sequentially enters the two-stage high-pressure separation device 47 for two-stage high-pressure separation and the first low-pressure separation device 43 for low-pressure separation. The gaseous ethylene after low-pressure separation returns to the first tubular reactor 42 for further polymerization. The polyethylene passing through the first low-pressure separation device 43 enters the extrusion granulation device 7 for extrusion granulation. The first bubble generator 41, the second bubble generator 44, the third bubble generator 48, and the fourth bubble generator 411 each include a sintered metal film. The sintered metal film contains copper oxide, aluminum oxide, iron oxide, and silicon dioxide.The pore size of the sintered metal film is 5-10 μm. The thickness of the sintered metal film is 0.5-3 mm. The evaporator 1 is purchased from Hangzhou Anyan Instrument Co., Ltd., brand name AYAN-B60L; the first bubble generator 41, the second bubble generator 44, the third bubble generator 48, and the fourth bubble generator 411 are purchased from Jiangsu Ruke Environmental Protection Equipment Co., Ltd., brand name RWP4000; the first tubular reactor 42, the second tubular reactor 45, the third tubular reactor 49, and the fourth tubular reactor 412 are purchased from Beijing Sixintong Technology Co., Ltd.; the first low-pressure separation device 43, the second low-pressure separation device 46, the third low-pressure separation device 410, and the fourth low-pressure separation device 413 are purchased from Beijing Sixintong Technology Co., Ltd.; the two-stage high-pressure separation device 47 is purchased from Beijing Sixintong Technology Co., Ltd.; the extrusion granulation device 7 is purchased from Beijing Sixintong Technology Co., Ltd.

[0068] Example 1

[0069] (1) The initiator is vaporized into a gaseous phase in evaporator 1 under the conditions of gas-liquid separation temperature of 75℃, evaporation working pressure of 0.5MPa, and steam consumption of 100kg / h. The vaporized initiator enters the booster 2 for pressurization to 4.5MPa. The pressurized initiator passes through the first bubble generator 41 and enters the first tubular reactor 42. The pressurized initiator passes through the second bubble generator 44 and enters the second tubular reactor 45. The pressurized initiator passes through the third bubble generator 48 and enters the third tubular reactor 49. The pressurized initiator passes through the fourth... The bubble generator 411 enters the fourth tubular reactor 412. The initiator is a mixture of 4,4-di(tert-butylperoxy)valerate n-butyl ester and peroxide (2-ethylhexanoate) tert-butyl ester. The mass ratio of 4,4-di(tert-butylperoxy)valerate n-butyl ester and peroxide (2-ethylhexanoate) tert-butyl ester is 3:1. The pressurized initiator is used to prepare microbubbles with a size of 50 μm through metal membranes in the first bubble generator 41, the second bubble generator 44, the third bubble generator 48 and the fourth bubble generator 411, respectively. The feed flow rate of the microbubbles is 1 m / s.

[0070] (2) Ethylene in ethylene storage tank 5 is liquefied by refrigeration unit 6 at a temperature of -15℃ to obtain liquid ethylene. The obtained liquid ethylene enters a two-stage booster 3 and is first pressurized to 75MPa, then to 265MPa. The ethylene after two-stage pressurization enters the first tubular reactor 42 for polymerization. The material passing through the first tubular reactor 42 enters the second tubular reactor 45 for polymerization. The material passing through the second tubular reactor 45 enters the second low-pressure separation device 46 for low-pressure separation. The gaseous ethylene after low-pressure separation returns to the first tubular reactor 42 for polymerization again. The material passing through the second tubular reactor 45 enters the third tubular reactor 49 for polymerization. The material passing through the third tubular reactor 49 enters the third low-pressure separation device 46. Unit 410 performs low-pressure separation. The gaseous ethylene after low-pressure separation is returned to the second tubular reactor 45 for further polymerization. The material passing through the third tubular reactor 49 enters the fourth tubular reactor 412 for polymerization. The material passing through the fourth tubular reactor 412 enters the fourth low-pressure separation unit 413 for low-pressure separation. The gaseous ethylene after low-pressure separation is returned to the third tubular reactor 49 for further polymerization. The mass ratio of gaseous ethylene passing through the second low-pressure separation unit 46 to the material in the first tubular reactor 42, the mass ratio of gaseous ethylene passing through the third low-pressure separation unit 410 to the material in the second tubular reactor 45, and the mass ratio of gaseous ethylene passing through the fourth low-pressure separation unit 413 to the material in the third tubular reactor 49 are all 1×10. -2 1. The material passing through the fourth tubular reactor 412 sequentially enters a two-stage high-pressure separation unit 47 for two-stage high-pressure separation and a first low-pressure separation unit 43 for low-pressure separation. In the two-stage high-pressure separation units 47, the material is first depressurized to 55 MPa, then to 5.5 MPa. In the first low-pressure separation unit 43, the material is depressurized to 0.8 MPa. The gaseous ethylene after low-pressure separation is returned to the first tubular reactor 42 for another polymerization reaction. The volume ratio of the gaseous ethylene passing through the first low-pressure separation unit 43 to the material in the first tubular reactor 42 is 2 × 10⁻⁶. -3 1. The flow rate of ethylene is 3 m / s, and the mass ratio of initiator to ethylene is 1 × 10⁻⁶. -4 1. The polymerization reaction conditions include: temperature of 245℃, pressure of 255MPa, time of 10s, and permeabilization pressure of the metal membrane of 100kPa.

[0071] (3) The polyethylene that has passed through the first low-pressure separation device 43 is fed into the extrusion granulation device 7 for extrusion granulation to obtain the product.

[0072] In Example 1, the ethylene conversion rate was 83%, the microbubble dispersion in the liquid phase was 5.9%, and the resulting high-pressure polyethylene product had a melt index of 16.5 g / 10 min and a density of 0.909 g / cm³.3 The nominal strain at fracture is 470%.

[0073] Example 2

[0074] (1) The initiator is vaporized into a gaseous phase in evaporator 1 under the conditions of gas-liquid separation temperature of 70℃, evaporation working pressure of 0.4MPa and steam consumption of 50kg / h. The vaporized initiator enters the booster 2 for pressurization to 4MPa. The pressurized initiator passes through the first bubble generator 41 and enters the first tubular reactor 42. The pressurized initiator passes through the second bubble generator 44 and enters the second tubular reactor 45. The pressurized initiator passes through the third bubble generator 48 and enters the third tubular reactor 49. The pressurized initiator passes through the fourth bubble generator... The initiator 411 enters the fourth tubular reactor 412. The initiator is a mixture of 4,4-di(tert-butylperoxy)valerate n-butyl ester and peroxide (2-ethylhexanoate) tert-butyl ester. The mass ratio of 4,4-di(tert-butylperoxy)valerate n-butyl ester and peroxide (2-ethylhexanoate) tert-butyl ester is 2:1. The pressurized initiator is used to prepare microbubbles with a size of 100μm through metal membranes in the first bubble generator 41, the second bubble generator 44, the third bubble generator 48 and the fourth bubble generator 411, respectively. The feed flow rate of the microbubbles is 1m / s.

[0075] (2) Ethylene in ethylene storage tank 5 is liquefied by refrigeration unit 6 at a temperature of -20℃ to obtain liquid ethylene. The obtained liquid ethylene enters a two-stage booster 3 and is first pressurized to 70MPa, then to 260MPa. The ethylene after two-stage pressurization enters the first tubular reactor 42 for polymerization. The material passing through the first tubular reactor 42 enters the second tubular reactor 45 for polymerization. The material passing through the second tubular reactor 45 enters the second low-pressure separation device 46 for low-pressure separation. The gaseous ethylene after low-pressure separation returns to the first tubular reactor 42 for polymerization again. The material passing through the second tubular reactor 45 enters the third tubular reactor 49 for polymerization. The material passing through the third tubular reactor 49 enters the third low-pressure separation device 46. Unit 410 performs low-pressure separation. The gaseous ethylene after low-pressure separation is returned to the second tubular reactor 45 for further polymerization. The material passing through the third tubular reactor 49 enters the fourth tubular reactor 412 for polymerization. The material passing through the fourth tubular reactor 412 enters the fourth low-pressure separation unit 413 for low-pressure separation. The gaseous ethylene after low-pressure separation is returned to the third tubular reactor 49 for further polymerization. The mass ratio of gaseous ethylene passing through the second low-pressure separation unit 46 to the material in the first tubular reactor 42, the mass ratio of gaseous ethylene passing through the third low-pressure separation unit 410 to the material in the second tubular reactor 45, and the mass ratio of gaseous ethylene passing through the fourth low-pressure separation unit 413 to the material in the third tubular reactor 49 are all 1×10.-2 1. The material passing through the fourth tubular reactor 412 sequentially enters a two-stage high-pressure separation unit 47 for two-stage high-pressure separation and a first low-pressure separation unit 43 for low-pressure separation. In the two-stage high-pressure separation units 47, the material is first depressurized to 50 MPa, then to 5 MPa. In the first low-pressure separation unit 43, the material is depressurized to 0.7 MPa. The gaseous ethylene after low-pressure separation is returned to the first tubular reactor 42 for another polymerization reaction. The volume ratio of the gaseous ethylene passing through the first low-pressure separation unit 43 to the material in the first tubular reactor 42 is 2 × 10⁻⁶. -3 1. The flow rate of ethylene is 3 m / s, and the mass ratio of initiator to ethylene is 3 × 10⁻⁶. -4 1. The conditions for the polymerization reaction include: temperature of 240℃, pressure of 250MPa, time of 10s, and permeabilization pressure of the metal membrane of 200kPa.

[0076] (3) The polyethylene that has passed through the first low-pressure separation device 43 is fed into the extrusion granulation device 7 for extrusion granulation to obtain the product.

[0077] In Example 2, the ethylene conversion rate was 86%, the microbubble dispersion in the liquid phase was 6.8%, and the resulting high-pressure polyethylene product had a melt index of 17.0 g / 10 min and a density of 0.913 g / cm³. 3 The nominal strain at fracture is 520%.

[0078] Example 3

[0079] (1) The initiator is vaporized into a gaseous phase in evaporator 1 under the conditions of gas-liquid separation temperature of 80℃, evaporation working pressure of 0.6MPa, and steam consumption of 150kg / h. The vaporized initiator enters the booster 2 for pressurization to 5MPa. The pressurized initiator passes through the first bubble generator 41 and enters the first tubular reactor 42. The pressurized initiator passes through the second bubble generator 44 and enters the second tubular reactor 45. The pressurized initiator passes through the third bubble generator 48 and enters the third tubular reactor 49. The pressurized initiator passes through the fourth bubble generator 45. The bubble generator 411 feeds into the fourth tubular reactor 412. The initiator is a mixture of 4,4-di(tert-butylperoxy)valerate n-butyl ester and peroxide (2-ethylhexanoate) tert-butyl ester. The mass ratio of 4,4-di(tert-butylperoxy)valerate n-butyl ester and peroxide (2-ethylhexanoate) tert-butyl ester is 2:1. The pressurized initiator is used to prepare microbubbles with a size of 100μm through metal membranes in the first bubble generator 41, the second bubble generator 44, the third bubble generator 48 and the fourth bubble generator 411, respectively. The feed flow rate of the microbubbles is 1m / s.

[0080] (2) Ethylene in ethylene storage tank 5 is liquefied by refrigeration unit 6 at a temperature of -20℃ to obtain liquid ethylene. The obtained liquid ethylene enters a two-stage booster 3 and is first pressurized to 80MPa, then to 270MPa. The ethylene after two-stage pressurization enters the first tubular reactor 42 for polymerization. The material passing through the first tubular reactor 42 enters the second tubular reactor 45 for polymerization. The material passing through the second tubular reactor 45 enters the second low-pressure separation device 46 for low-pressure separation. The gaseous ethylene after low-pressure separation returns to the first tubular reactor 42 for polymerization again. The material passing through the second tubular reactor 45 enters the third tubular reactor 49 for polymerization. The material passing through the third tubular reactor 49 enters the third low-pressure separation device 46. Unit 410 performs low-pressure separation. The gaseous ethylene after low-pressure separation is returned to the second tubular reactor 45 for further polymerization. The material passing through the third tubular reactor 49 enters the fourth tubular reactor 412 for polymerization. The material passing through the fourth tubular reactor 412 enters the fourth low-pressure separation unit 413 for low-pressure separation. The gaseous ethylene after low-pressure separation is returned to the third tubular reactor 49 for further polymerization. The mass ratio of gaseous ethylene passing through the second low-pressure separation unit 46 to the material in the first tubular reactor 42, the mass ratio of gaseous ethylene passing through the third low-pressure separation unit 410 to the material in the second tubular reactor 45, and the mass ratio of gaseous ethylene passing through the fourth low-pressure separation unit 413 to the material in the third tubular reactor 49 are all 1×10. -2 1. The material passing through the fourth tubular reactor 412 sequentially enters a two-stage high-pressure separation unit 47 for two-stage high-pressure separation and a first low-pressure separation unit 43 for low-pressure separation. In the two-stage high-pressure separation units 47, the material is first depressurized to 60 MPa, then to 6 MPa. In the first low-pressure separation unit 43, the material is depressurized to 0.9 MPa. The gaseous ethylene after low-pressure separation is returned to the first tubular reactor 42 for another polymerization reaction. The volume ratio of the gaseous ethylene passing through the first low-pressure separation unit 43 to the material in the first tubular reactor 42 is 2 × 10⁻⁶. -3 1. The flow rate of ethylene is 3 m / s, and the mass ratio of initiator to ethylene is 3 × 10⁻⁶. -4 1. The polymerization reaction conditions include: temperature of 250℃, pressure of 260MPa, time of 30s, and permeabilization pressure of the metal membrane of 100kPa.

[0081] (3) The polyethylene that has passed through the first low-pressure separation device 43 is fed into the extrusion granulation device 7 for extrusion granulation to obtain the product.

[0082] In Example 3, the ethylene conversion rate was 87%, the microbubble dispersion in the liquid phase was 7.7%, and the resulting high-pressure polyethylene product had a melt index of 18.1 g / 10 min and a density of 0.916 g / cm³.3 The nominal strain at fracture is 550%.

[0083] Example 4

[0084] (1) The initiator is vaporized into a gaseous phase in evaporator 1 under the conditions of gas-liquid separation temperature of 75℃, evaporation working pressure of 0.5MPa, and steam consumption of 100kg / h. The vaporized initiator enters the booster 2 for pressurization to 4.5MPa. The pressurized initiator passes through the first bubble generator 41 and enters the first tubular reactor 42. The pressurized initiator passes through the second bubble generator 44 and enters the second tubular reactor 45. The pressurized initiator passes through the third bubble generator 48 and enters the third tubular reactor 49. The pressurized initiator passes through the fourth... The bubble generator 411 enters the fourth tubular reactor 412. The initiator is a mixture of 4,4-di(tert-butylperoxy)valerate n-butyl ester and peroxide (2-ethylhexanoate) tert-butyl ester. The mass ratio of 4,4-di(tert-butylperoxy)valerate n-butyl ester and peroxide (2-ethylhexanoate) tert-butyl ester is 3:1. The pressurized initiator is used to prepare microbubbles with a size of 100μm through metal membranes in the first bubble generator 41, the second bubble generator 44, the third bubble generator 48 and the fourth bubble generator 411, respectively. The feed flow rate of the microbubbles is 1m / s.

[0085] (2) Ethylene in ethylene storage tank 5 is liquefied by refrigeration unit 6 at a temperature of -15℃ to obtain liquid ethylene. The obtained liquid ethylene enters a two-stage booster 3 and is first pressurized to 75MPa, then to 265MPa. The ethylene after two-stage pressurization enters the first tubular reactor 42 for polymerization. The material passing through the first tubular reactor 42 enters the second tubular reactor 45 for polymerization. The material passing through the second tubular reactor 45 enters the second low-pressure separation device 46 for low-pressure separation. The gaseous ethylene after low-pressure separation returns to the first tubular reactor 42 for polymerization again. The material passing through the second tubular reactor 45 enters the third tubular reactor 49 for polymerization. The material passing through the third tubular reactor 49 enters the third low-pressure separation device 46. Unit 410 performs low-pressure separation. The gaseous ethylene after low-pressure separation is returned to the second tubular reactor 45 for further polymerization. The material passing through the third tubular reactor 49 enters the fourth tubular reactor 412 for polymerization. The material passing through the fourth tubular reactor 412 enters the fourth low-pressure separation unit 413 for low-pressure separation. The gaseous ethylene after low-pressure separation is returned to the third tubular reactor 49 for further polymerization. The mass ratio of gaseous ethylene passing through the second low-pressure separation unit 46 to the material in the first tubular reactor 42, the mass ratio of gaseous ethylene passing through the third low-pressure separation unit 410 to the material in the second tubular reactor 45, and the mass ratio of gaseous ethylene passing through the fourth low-pressure separation unit 413 to the material in the third tubular reactor 49 are all 4 × 10⁻⁶.-2 1. The material passing through the fourth tubular reactor 412 sequentially enters a two-stage high-pressure separation unit 47 for two-stage high-pressure separation and a first low-pressure separation unit 43 for low-pressure separation. In the two-stage high-pressure separation units 47, the material is first depressurized to 55 MPa, then to 5.5 MPa. In the first low-pressure separation unit 43, the material is depressurized to 0.8 MPa. The gaseous ethylene after low-pressure separation is returned to the first tubular reactor 42 for another polymerization reaction. The volume ratio of the gaseous ethylene passing through the first low-pressure separation unit 43 to the material in the first tubular reactor 42 is 5 × 10⁻⁶. -3 1. The flow rate of ethylene is 3 m / s, and the mass ratio of initiator to ethylene is 3 × 10⁻⁶. -4 1. The polymerization reaction conditions include: temperature of 245℃, pressure of 255MPa, time of 10s, and permeabilization pressure of the metal membrane of 200kPa.

[0086] (3) The polyethylene that has passed through the first low-pressure separation device 43 is fed into the extrusion granulation device 7 for extrusion granulation to obtain the product.

[0087] In Example 4, the ethylene conversion rate was 87%, the microbubble dispersion in the liquid phase was 7.1%, and the resulting high-pressure polyethylene product had a melt index of 17.2 g / 10 min and a density of 0.914 g / cm³. 3 The nominal strain at fracture is 530%.

[0088] Example 5

[0089] (1) The initiator is vaporized into a gaseous phase in evaporator 1 under the conditions of gas-liquid separation temperature of 75℃, evaporation working pressure of 0.5MPa, and steam consumption of 100kg / h. The vaporized initiator enters the booster 2 for pressurization to 4.5MPa. The pressurized initiator passes through the first bubble generator 41 and enters the first tubular reactor 42. The pressurized initiator passes through the second bubble generator 44 and enters the second tubular reactor 45. The pressurized initiator passes through the third bubble generator 48 and enters the third tubular reactor 49. The pressurized initiator passes through the fourth... The bubble generator 411 enters the fourth tubular reactor 412. The initiator is a mixture of 4,4-di(tert-butylperoxy)valerate n-butyl ester and peroxide (2-ethylhexanoate) tert-butyl ester. The mass ratio of 4,4-di(tert-butylperoxy)valerate n-butyl ester and peroxide (2-ethylhexanoate) tert-butyl ester is 3:1. The pressurized initiator is used to prepare microbubbles with a size of 100 μm through metal membranes in the first bubble generator 41, the second bubble generator 44, the third bubble generator 48 and the fourth bubble generator 411, respectively. The feed flow rate of the microbubbles is 2 m / s.

[0090] (2) Ethylene in ethylene storage tank 5 is liquefied by refrigeration unit 6 at a temperature of -15℃ to obtain liquid ethylene. The obtained liquid ethylene enters a two-stage booster 3 and is first pressurized to 75MPa, then to 265MPa. The ethylene after two-stage pressurization enters the first tubular reactor 42 for polymerization. The material passing through the first tubular reactor 42 enters the second tubular reactor 45 for polymerization. The material passing through the second tubular reactor 45 enters the second low-pressure separation device 46 for low-pressure separation. The gaseous ethylene after low-pressure separation returns to the first tubular reactor 42 for polymerization again. The material passing through the second tubular reactor 45 enters the third tubular reactor 49 for polymerization. The material passing through the third tubular reactor 49 enters the third low-pressure separation device 46. Unit 410 performs low-pressure separation. The gaseous ethylene after low-pressure separation is returned to the second tubular reactor 45 for further polymerization. The material passing through the third tubular reactor 49 enters the fourth tubular reactor 412 for polymerization. The material passing through the fourth tubular reactor 412 enters the fourth low-pressure separation unit 413 for low-pressure separation. The gaseous ethylene after low-pressure separation is returned to the third tubular reactor 49 for further polymerization. The mass ratio of gaseous ethylene passing through the second low-pressure separation unit 46 to the material in the first tubular reactor 42, the mass ratio of gaseous ethylene passing through the third low-pressure separation unit 410 to the material in the second tubular reactor 45, and the mass ratio of gaseous ethylene passing through the fourth low-pressure separation unit 413 to the material in the third tubular reactor 49 are all 4 × 10⁻⁶. -2 1. The material passing through the fourth tubular reactor 412 sequentially enters a two-stage high-pressure separation unit 47 for two-stage high-pressure separation and a first low-pressure separation unit 43 for low-pressure separation. In the two-stage high-pressure separation units 47, the material is first depressurized to 55 MPa, then to 5.5 MPa. In the first low-pressure separation unit 43, the material is depressurized to 0.8 MPa. The gaseous ethylene after low-pressure separation is returned to the first tubular reactor 42 for another polymerization reaction. The volume ratio of the gaseous ethylene passing through the first low-pressure separation unit 43 to the material in the first tubular reactor 42 is 5 × 10⁻⁶. -3 1. The flow rate of ethylene is 5 m / s, and the mass ratio of initiator to ethylene is 3 × 10⁻⁶. -4 1. The polymerization reaction conditions include: temperature of 245℃, pressure of 255MPa, time of 30s, and permeabilization pressure of the metal membrane of 200kPa.

[0091] (3) The polyethylene that has passed through the first low-pressure separation device 43 is fed into the extrusion granulation device 7 for extrusion granulation to obtain the product.

[0092] In Example 5, the ethylene conversion rate was 92%, the microbubble dispersion in the liquid phase was 8.5%, and the resulting high-pressure polyethylene product had a melt index of 18.6 g / 10 min and a density of 0.919 g / cm³.3 The nominal strain at fracture is 580%.

[0093] Example 6

[0094] (1) The initiator is vaporized into a gaseous phase in evaporator 1 under the conditions of gas-liquid separation temperature of 75℃, evaporation working pressure of 0.5MPa, and steam consumption of 100kg / h. The vaporized initiator enters the booster 2 for pressurization to 4.5MPa. The pressurized initiator passes through the first bubble generator 41 and enters the first tubular reactor 42. The pressurized initiator passes through the second bubble generator 44 and enters the second tubular reactor 45. The pressurized initiator passes through the third bubble generator 48 and enters the third tubular reactor 49. The pressurized initiator passes through the fourth... The bubble generator 411 enters the fourth tubular reactor 412. The initiator is a mixture of 4,4-di(tert-butylperoxy)valerate n-butyl ester and peroxide (2-ethylhexanoate) tert-butyl ester. The mass ratio of 4,4-di(tert-butylperoxy)valerate n-butyl ester and peroxide (2-ethylhexanoate) tert-butyl ester is 3:1. The pressurized initiator is used to prepare microbubbles with a size of 200 μm through metal membranes in the first bubble generator 41, the second bubble generator 44, the third bubble generator 48 and the fourth bubble generator 411, respectively. The feed flow rate of the microbubbles is 3 m / s.

[0095] (2) Ethylene in ethylene storage tank 5 is liquefied by refrigeration unit 6 at a temperature of -15℃ to obtain liquid ethylene. The obtained liquid ethylene enters a two-stage booster 3 and is first pressurized to 75MPa, then to 265MPa. The ethylene after two-stage pressurization enters the first tubular reactor 42 for polymerization. The material passing through the first tubular reactor 42 enters the second tubular reactor 45 for polymerization. The material passing through the second tubular reactor 45 enters the second low-pressure separation device 46 for low-pressure separation. The gaseous ethylene after low-pressure separation returns to the first tubular reactor 42 for polymerization again. The material passing through the second tubular reactor 45 enters the third tubular reactor 49 for polymerization. The material passing through the third tubular reactor 49 enters the third low-pressure separation device 46. Unit 410 performs low-pressure separation. The gaseous ethylene after low-pressure separation is returned to the second tubular reactor 45 for further polymerization. The material passing through the third tubular reactor 49 enters the fourth tubular reactor 412 for polymerization. The material passing through the fourth tubular reactor 412 enters the fourth low-pressure separation unit 413 for low-pressure separation. The gaseous ethylene after low-pressure separation is returned to the third tubular reactor 49 for further polymerization. The mass ratio of gaseous ethylene passing through the second low-pressure separation unit 46 to the material in the first tubular reactor 42, the mass ratio of gaseous ethylene passing through the third low-pressure separation unit 410 to the material in the second tubular reactor 45, and the mass ratio of gaseous ethylene passing through the fourth low-pressure separation unit 413 to the material in the third tubular reactor 49 are all 7 × 10⁻⁶.-2 1. The material passing through the fourth tubular reactor 412 sequentially enters two-stage high-pressure separation devices 47 for two-stage high-pressure separation and a first low-pressure separation device 43 for low-pressure separation. In the two-stage high-pressure separation devices 47, the material is first depressurized to 55 MPa, then to 5.5 MPa. In the first low-pressure separation device 43, the material is depressurized to 0.8 MPa. The gaseous ethylene after low-pressure separation is returned to the first tubular reactor 42 for another polymerization reaction. The volume ratio of the gaseous ethylene passing through the first low-pressure separation device 43 to the material in the first tubular reactor 42 is 7 × 10⁻⁶. -3 1. The flow rate of ethylene is 6 m / s, and the mass ratio of initiator to ethylene is 4 × 10⁻⁶ m / s. -4 1. The polymerization reaction conditions include: temperature of 245℃, pressure of 255MPa, time of 40s, and permeabilization pressure of the metal membrane of 300kPa.

[0096] (3) The polyethylene that has passed through the first low-pressure separation device 43 is fed into the extrusion granulation device 7 for extrusion granulation to obtain the product.

[0097] In Example 6, the ethylene conversion rate was 96%, the microbubble dispersion in the liquid phase was 10.1%, and the resulting high-pressure polyethylene product had a melt index of 19.4 g / 10 min and a density of 0.923 g / cm³. 3 The nominal strain at fracture is 610%.

[0098] Example 7

[0099] (1) The initiator is vaporized into a gaseous phase in evaporator 1 under the conditions of gas-liquid separation temperature of 75℃, evaporation working pressure of 0.5MPa, and steam consumption of 100kg / h. The vaporized initiator enters the booster 2 for pressurization to 4.5MPa. The pressurized initiator passes through the first bubble generator 41 and enters the first tubular reactor 42. The pressurized initiator passes through the second bubble generator 44 and enters the second tubular reactor 45. The pressurized initiator passes through the third bubble generator 48 and enters the third tubular reactor 49. The pressurized initiator passes through the fourth... The bubble generator 411 enters the fourth tubular reactor 412. The initiator is a mixture of 4,4-di(tert-butylperoxy)valerate n-butyl ester and peroxide (2-ethylhexanoate) tert-butyl ester. The mass ratio of 4,4-di(tert-butylperoxy)valerate n-butyl ester and peroxide (2-ethylhexanoate) tert-butyl ester is 3:1. The pressurized initiator is used to prepare microbubbles with a size of 300 μm through metal membranes in the first bubble generator 41, the second bubble generator 44, the third bubble generator 48 and the fourth bubble generator 411, respectively. The feed flow rate of the microbubbles is 3 m / s.

[0100] (2) Ethylene in ethylene storage tank 5 is liquefied by refrigeration unit 6 at a temperature of -15℃ to obtain liquid ethylene. The obtained liquid ethylene enters a two-stage booster 3 and is first pressurized to 75MPa, then to 265MPa. The ethylene after two-stage pressurization enters the first tubular reactor 42 for polymerization. The material passing through the first tubular reactor 42 enters the second tubular reactor 45 for polymerization. The material passing through the second tubular reactor 45 enters the second low-pressure separation device 46 for low-pressure separation. The gaseous ethylene after low-pressure separation returns to the first tubular reactor 42 for polymerization again. The material passing through the second tubular reactor 45 enters the third tubular reactor 49 for polymerization. The material passing through the third tubular reactor 49 enters the third low-pressure separation device 46. Unit 410 performs low-pressure separation. The gaseous ethylene after low-pressure separation is returned to the second tubular reactor 45 for further polymerization. The material passing through the third tubular reactor 49 enters the fourth tubular reactor 412 for polymerization. The material passing through the fourth tubular reactor 412 enters the fourth low-pressure separation unit 413 for low-pressure separation. The gaseous ethylene after low-pressure separation is returned to the third tubular reactor 49 for further polymerization. The mass ratio of gaseous ethylene passing through the second low-pressure separation unit 46 to the material in the first tubular reactor 42, the mass ratio of gaseous ethylene passing through the third low-pressure separation unit 410 to the material in the second tubular reactor 45, and the mass ratio of gaseous ethylene passing through the fourth low-pressure separation unit 413 to the material in the third tubular reactor 49 are all 7 × 10⁻⁶. -2 1. The material passing through the fourth tubular reactor 412 sequentially enters two-stage high-pressure separation devices 47 for two-stage high-pressure separation and a first low-pressure separation device 43 for low-pressure separation. In the two-stage high-pressure separation devices 47, the material is first depressurized to 55 MPa, then to 5.5 MPa. In the first low-pressure separation device 43, the material is depressurized to 0.8 MPa. The gaseous ethylene after low-pressure separation is returned to the first tubular reactor 42 for another polymerization reaction. The volume ratio of the gaseous ethylene passing through the first low-pressure separation device 43 to the material in the first tubular reactor 42 is 7 × 10⁻⁶. -3 1. The flow rate of ethylene is 6 m / s, and the mass ratio of initiator to ethylene is 6 × 10⁻⁶. -4 1. The polymerization reaction conditions include: temperature of 245℃, pressure of 255MPa, time of 40s, and permeabilization pressure of the metal membrane of 500kPa.

[0101] (3) The polyethylene that has passed through the first low-pressure separation device 43 is fed into the extrusion granulation device 7 for extrusion granulation to obtain the product.

[0102] In Example 7, the ethylene conversion rate was 90%, the microbubble dispersion in the liquid phase was 8.1%, and the resulting high-pressure polyethylene product had a melt index of 18.3 g / 10 min and a density of 0.917 g / cm³.3 The nominal strain at fracture is 560%.

[0103] Example 8

[0104] (1) The initiator is vaporized into a gaseous phase in evaporator 1 under the conditions of gas-liquid separation temperature of 75℃, evaporation working pressure of 0.5MPa, and steam consumption of 100kg / h. The vaporized initiator enters the booster 2 for pressurization to 4.5MPa. The pressurized initiator passes through the first bubble generator 41 and enters the first tubular reactor 42. The pressurized initiator passes through the second bubble generator 44 and enters the second tubular reactor 45. The pressurized initiator passes through the third bubble generator 48 and enters the third tubular reactor 49. The pressurized initiator passes through the fourth... The bubble generator 411 enters the fourth tubular reactor 412. The initiator is a mixture of 4,4-di(tert-butylperoxy)valerate n-butyl ester and peroxide (2-ethylhexanoate) tert-butyl ester. The mass ratio of 4,4-di(tert-butylperoxy)valerate n-butyl ester and peroxide (2-ethylhexanoate) tert-butyl ester is 3:1. The pressurized initiator is used to prepare microbubbles with a size of 200 μm through metal membranes in the first bubble generator 41, the second bubble generator 44, the third bubble generator 48 and the fourth bubble generator 411, respectively. The feed flow rate of the microbubbles is 4 m / s.

[0105] (2) Ethylene in ethylene storage tank 5 is liquefied by refrigeration unit 6 at a temperature of -15℃ to obtain liquid ethylene. The obtained liquid ethylene enters a two-stage booster 3 and is first pressurized to 75MPa, then to 265MPa. The ethylene after two-stage pressurization enters the first tubular reactor 42 for polymerization. The material passing through the first tubular reactor 42 enters the second tubular reactor 45 for polymerization. The material passing through the second tubular reactor 45 enters the second low-pressure separation device 46 for low-pressure separation. The gaseous ethylene after low-pressure separation returns to the first tubular reactor 42 for polymerization again. The material passing through the second tubular reactor 45 enters the third tubular reactor 49 for polymerization. The material passing through the third tubular reactor 49 enters the third low-pressure separation device 46. Unit 410 performs low-pressure separation. The gaseous ethylene after low-pressure separation is returned to the second tubular reactor 45 for further polymerization. The material passing through the third tubular reactor 49 enters the fourth tubular reactor 412 for polymerization. The material passing through the fourth tubular reactor 412 enters the fourth low-pressure separation unit 413 for low-pressure separation. The gaseous ethylene after low-pressure separation is returned to the third tubular reactor 49 for further polymerization. The mass ratio of gaseous ethylene passing through the second low-pressure separation unit 46 to the material in the first tubular reactor 42, the mass ratio of gaseous ethylene passing through the third low-pressure separation unit 410 to the material in the second tubular reactor 45, and the mass ratio of gaseous ethylene passing through the fourth low-pressure separation unit 413 to the material in the third tubular reactor 49 are all 7 × 10⁻⁶.-2 1. The material passing through the fourth tubular reactor 412 sequentially enters two-stage high-pressure separation devices 47 for two-stage high-pressure separation and a first low-pressure separation device 43 for low-pressure separation. In the two-stage high-pressure separation devices 47, the material is first depressurized to 55 MPa, then to 5.5 MPa. In the first low-pressure separation device 43, the material is depressurized to 0.8 MPa. The gaseous ethylene after low-pressure separation is returned to the first tubular reactor 42 for another polymerization reaction. The volume ratio of the gaseous ethylene passing through the first low-pressure separation device 43 to the material in the first tubular reactor 42 is 7 × 10⁻⁶. -3 1. The flow rate of ethylene is 7 m / s, and the mass ratio of initiator to ethylene is 4 × 10⁻⁶. -4 1. The polymerization reaction conditions include: temperature of 245℃, pressure of 255MPa, time of 90s, and permeabilization pressure of the metal membrane of 300kPa.

[0106] (3) The polyethylene that has passed through the first low-pressure separation device 43 is fed into the extrusion granulation device 7 for extrusion granulation to obtain the product.

[0107] In Example 8, the ethylene conversion rate was 87%, the microbubble dispersion in the liquid phase was 7.3%, and the prepared high-pressure polyethylene product had a melt index of 17.8 g / 10 min and a density of 0.915 g / cm³. 3 The nominal strain at fracture is 530%.

[0108] Example 9

[0109] (1) The initiator is vaporized into a gaseous phase in evaporator 1 under the conditions of gas-liquid separation temperature of 75℃, evaporation working pressure of 0.5MPa, and steam consumption of 100kg / h. The vaporized initiator enters the booster 2 for pressurization to 4.5MPa. The pressurized initiator passes through the first bubble generator 41 and enters the first tubular reactor 42. The pressurized initiator passes through the second bubble generator 44 and enters the second tubular reactor 45. The pressurized initiator passes through the third bubble generator 48 and enters the third tubular reactor 49. The pressurized initiator passes through the fourth... The bubble generator 411 enters the fourth tubular reactor 412. The initiator is a mixture of 4,4-di(tert-butylperoxy)valerate n-butyl ester and peroxide (2-ethylhexanoate) tert-butyl ester. The mass ratio of 4,4-di(tert-butylperoxy)valerate n-butyl ester and peroxide (2-ethylhexanoate) tert-butyl ester is 3:1. The pressurized initiator is used to prepare microbubbles with a size of 200 μm through metal membranes in the first bubble generator 41, the second bubble generator 44, the third bubble generator 48 and the fourth bubble generator 411, respectively. The feed flow rate of the microbubbles is 3 m / s.

[0110] (2) Ethylene in ethylene storage tank 5 is liquefied by refrigeration unit 6 at a temperature of -15℃ to obtain liquid ethylene. The obtained liquid ethylene enters a two-stage booster 3 and is first pressurized to 75MPa, then to 265MPa. The ethylene after two-stage pressurization enters the first tubular reactor 42 for polymerization. The material passing through the first tubular reactor 42 enters the second tubular reactor 45 for polymerization. The material passing through the second tubular reactor 45 enters the second low-pressure separation device 46 for low-pressure separation. The gaseous ethylene after low-pressure separation returns to the first tubular reactor 42 for polymerization again. The material passing through the second tubular reactor 45 enters the third tubular reactor 49 for polymerization. The material passing through the third tubular reactor 49 enters the third low-pressure separation device 46. Unit 410 performs low-pressure separation. The gaseous ethylene after low-pressure separation is returned to the second tubular reactor 45 for further polymerization. The material passing through the third tubular reactor 49 enters the fourth tubular reactor 412 for polymerization. The material passing through the fourth tubular reactor 412 enters the fourth low-pressure separation unit 413 for low-pressure separation. The gaseous ethylene after low-pressure separation is returned to the third tubular reactor 49 for further polymerization. The mass ratio of gaseous ethylene passing through the second low-pressure separation unit 46 to the material in the first tubular reactor 42, the mass ratio of gaseous ethylene passing through the third low-pressure separation unit 410 to the material in the second tubular reactor 45, and the mass ratio of gaseous ethylene passing through the fourth low-pressure separation unit 413 to the material in the third tubular reactor 49 are all 9 × 10⁻⁶. -2 1. The material passing through the fourth tubular reactor 412 sequentially enters a two-stage high-pressure separation unit 47 for two-stage high-pressure separation and a first low-pressure separation unit 43 for low-pressure separation. In the two-stage high-pressure separation unit 47, the material is first depressurized to 55 MPa, then to 5.5 MPa. In the first low-pressure separation unit 43, the material is depressurized to 0.8 MPa. The gaseous ethylene after low-pressure separation is returned to the first tubular reactor 42 for another polymerization reaction. The volume ratio of the gaseous ethylene passing through the first low-pressure separation unit 43 to the material in the first tubular reactor 42 is 9 × 10⁻⁶. -3 1. The flow rate of ethylene is 6 m / s, and the mass ratio of initiator to ethylene is 4 × 10⁻⁶ m / s. -4 1. The polymerization reaction conditions include: temperature of 245℃, pressure of 255MPa, time of 40s, and permeabilization pressure of the metal membrane of 300kPa.

[0111] (3) The polyethylene that has passed through the first low-pressure separation device 43 is fed into the extrusion granulation device 7 for extrusion granulation to obtain the product.

[0112] In Example 9, the ethylene conversion rate was 89%, the microbubble dispersion in the liquid phase was 7.9%, and the prepared high-pressure polyethylene product had a melt index of 18.0 g / 10 min and a density of 0.916 g / cm³.3 The nominal strain at fracture is 550%.

[0113] Example 10

[0114] (1) The initiator is vaporized into a gaseous phase in evaporator 1 under the conditions of gas-liquid separation temperature of 75℃, evaporation working pressure of 0.5MPa, and steam consumption of 100kg / h. The vaporized initiator enters the booster 2 for pressurization to 4.5MPa. The pressurized initiator passes through the first bubble generator 41 and enters the first tubular reactor 42. The pressurized initiator passes through the second bubble generator 44 and enters the second tubular reactor 45. The pressurized initiator passes through the third bubble generator 48 and enters the third tubular reactor 49. The pressurized initiator passes through the fourth... The bubble generator 411 enters the fourth tubular reactor 412. The initiator is a mixture of 4,4-di(tert-butylperoxy)valerate n-butyl ester and peroxide (2-ethylhexanoate) tert-butyl ester. The mass ratio of 4,4-di(tert-butylperoxy)valerate n-butyl ester and peroxide (2-ethylhexanoate) tert-butyl ester is 3:1. The pressurized initiator is used to prepare microbubbles with a size of 300 μm through metal membranes in the first bubble generator 41, the second bubble generator 44, the third bubble generator 48 and the fourth bubble generator 411, respectively. The feed flow rate of the microbubbles is 4 m / s.

[0115] (2) Ethylene in ethylene storage tank 5 is liquefied by refrigeration unit 6 at a temperature of -15℃ to obtain liquid ethylene. The obtained liquid ethylene enters a two-stage booster 3 and is first pressurized to 75MPa, then to 265MPa. The ethylene after two-stage pressurization enters the first tubular reactor 42 for polymerization. The material passing through the first tubular reactor 42 enters the second tubular reactor 45 for polymerization. The material passing through the second tubular reactor 45 enters the second low-pressure separation device 46 for low-pressure separation. The gaseous ethylene after low-pressure separation returns to the first tubular reactor 42 for polymerization again. The material passing through the second tubular reactor 45 enters the third tubular reactor 49 for polymerization. The material passing through the third tubular reactor 49 enters the third low-pressure separation device 46. Unit 410 performs low-pressure separation. The gaseous ethylene after low-pressure separation is returned to the second tubular reactor 45 for further polymerization. The material passing through the third tubular reactor 49 enters the fourth tubular reactor 412 for polymerization. The material passing through the fourth tubular reactor 412 enters the fourth low-pressure separation unit 413 for low-pressure separation. The gaseous ethylene after low-pressure separation is returned to the third tubular reactor 49 for further polymerization. The mass ratio of gaseous ethylene passing through the second low-pressure separation unit 46 to the material in the first tubular reactor 42, the mass ratio of gaseous ethylene passing through the third low-pressure separation unit 410 to the material in the second tubular reactor 45, and the mass ratio of gaseous ethylene passing through the fourth low-pressure separation unit 413 to the material in the third tubular reactor 49 are all 9 × 10⁻⁶.-2 1. The material passing through the fourth tubular reactor 412 sequentially enters a two-stage high-pressure separation unit 47 for two-stage high-pressure separation and a first low-pressure separation unit 43 for low-pressure separation. In the two-stage high-pressure separation unit 47, the material is first depressurized to 55 MPa, then to 5.5 MPa. In the first low-pressure separation unit 43, the material is depressurized to 0.8 MPa. The gaseous ethylene after low-pressure separation is returned to the first tubular reactor 42 for another polymerization reaction. The volume ratio of the gaseous ethylene passing through the first low-pressure separation unit 43 to the material in the first tubular reactor 42 is 9 × 10⁻⁶. -3 1. The flow rate of ethylene is 7 m / s, and the mass ratio of initiator to ethylene is 6 × 10⁻⁶. -4 1. The polymerization reaction conditions include: temperature of 245℃, pressure of 255MPa, time of 90s, and permeabilization pressure of the metal membrane of 500kPa.

[0116] (3) The polyethylene that has passed through the first low-pressure separation device 43 is fed into the extrusion granulation device 7 for extrusion granulation to obtain the product.

[0117] In Example 10, the ethylene conversion rate was 84%, the microbubble dispersion in the liquid phase was 5.8%, and the resulting high-pressure polyethylene product had a melt index of 17.0 g / 10 min and a density of 0.911 g / cm³. 3 The nominal strain at fracture is 500%.

[0118] Comparative Example 1

[0119] The method of Example 1 was implemented, except that in step (1), the pressurized initiator did not pass through the bubble generator and directly entered the tubular reactor. Specifically, the pressurized initiator directly entered the first tubular reactor 42, the second tubular reactor 45, the third tubular reactor 49, and the fourth tubular reactor 412. In Comparative Example 1, the ethylene conversion rate was 65%, the microbubble dispersion in the liquid phase was 1.3%, and the prepared high-pressure polyethylene product had a melt index of 8.7 g / 10 min and a density of 0.867 g / cm³. 3 The nominal strain at fracture is 330%.

[0120] Comparative Example 2

[0121] The method is implemented according to Example 1, except that in step (1), the pressurized initiator enters the first tubular reactor 42 only through the first bubble generator 41, the pressurized initiator enters the second tubular reactor 45 without passing through the second bubble generator 44, the pressurized initiator enters the third tubular reactor 49 without passing through the third bubble generator 48, and the pressurized initiator enters the fourth tubular reactor 412 without passing through the fourth bubble generator 411. Specifically, the gas-liquid separation temperature of the initiator in evaporator 1 is 75°C, the evaporation working pressure is 0.5 MPa, and the steam consumption is 100 kg / h. Under certain conditions, the initiator is vaporized into a gaseous phase. The vaporized initiator then enters a booster pressurized to 4.5 MPa. After pressurization, the initiator passes through a first bubble generator 41 and enters a first tubular reactor 42. The initiator is a mixture of 4,4-di(tert-butylperoxy)valerate n-butyl ester and tert-butyl peroxide (2-ethylhexanoate), with a mass ratio of 3:1. The pressurized initiator is then processed into microbubbles of 50 μm size through a metal membrane in the first bubble generator 41. The feed flow rate of the microbubbles is 1 m / s. In Comparative Example 2, the ethylene conversion rate is 69%, the microbubble dispersion in the liquid phase is 3.4%, and the resulting high-pressure polyethylene product has a melt index of 12.4 g / 10 min and a density of 0.885 g / cm³. 3 The nominal strain at fracture is 410%.

[0122] Comparative Example 3

[0123] The method of Example 1 was implemented, except that in step (2), the material passing through the tubular reactor did not enter the low-pressure separation device. Specifically, the ethylene after two-stage pressurization entered the first tubular reactor 42 for polymerization, the material passing through the first tubular reactor 42 entered the second tubular reactor 45 for polymerization, the material passing through the second tubular reactor 45 entered the third tubular reactor 49 for polymerization, and the material passing through the third tubular reactor 49 entered the fourth tubular reactor 412 for polymerization. In Comparative Example 3, the ethylene conversion rate was 79%, the dispersion of microbubbles in the liquid phase was 5.0%, and the melt index of the prepared high-pressure polyethylene product was 14.4 g / 10 min, and the density was 0.891 g / cm³. 3 The nominal strain at fracture is 420%.

[0124] Comparative Example 4

[0125] (1) The initiator is vaporized into a gas phase in the evaporator 1 under the conditions of gas-liquid separation temperature of 75℃, evaporation working pressure of 0.5MPa and steam consumption of 100kg / h. The vaporized initiator enters the booster 2 for pressurization to 4.5MPa. The pressurized initiator enters the first tubular reactor 42 through the first bubble generator 41. The initiator is a mixture of 4,4-di(tert-butyl peroxy)valerate n-butyl ester and peroxide (2-ethylhexanoic acid) tert-butyl ester. The mass ratio of 4,4-di(tert-butyl peroxy)valerate n-butyl ester and peroxide (2-ethylhexanoic acid) tert-butyl ester is 3:1. The pressurized initiator is prepared into microbubbles with a size of 50μm through a metal membrane in the first bubble generator 41. The feed flow rate of the microbubbles is 1m / s.

[0126] (2) Ethylene in ethylene storage tank 5 is liquefied using refrigeration unit 6 at a temperature of -15℃ to obtain liquid ethylene. The obtained liquid ethylene enters a two-stage booster 3 and is first pressurized to 75 MPa, then to 265 MPa. The ethylene after two-stage pressurization enters the first tubular reactor 42 for polymerization. The material passing through the first tubular reactor 42 enters a two-stage high-pressure separation device 47 for two-stage high-pressure separation and a first low-pressure separation device 43 for low-pressure separation. In the two-stage high-pressure separation device 47, the material is first depressurized to 55 MPa, then to 5.5 MPa. In the first low-pressure separation device 43, the material is depressurized to 0.8 MPa. The gaseous ethylene after low-pressure separation is returned to the first tubular reactor 42 for polymerization again. The volume ratio of the gaseous ethylene passing through the first low-pressure separation device 43 to the material in the first tubular reactor 42 is 2 × 10⁻⁶. -3 1. The flow rate of ethylene is 3 m / s, and the mass ratio of initiator to ethylene is 1 × 10⁻⁶. -4 1. The polymerization reaction conditions include: temperature of 245℃, pressure of 255MPa, time of 10s, and permeabilization pressure of the metal membrane of 100kPa.

[0127] (3) The polyethylene that has passed through the first low-pressure separation device 43 is fed into the extrusion granulation device 7 for extrusion granulation to obtain the product.

[0128] In Comparative Example 4, the ethylene conversion rate was 80%, the microbubble dispersion in the liquid phase was 5.5%, and the prepared high-pressure polyethylene product had a melt index of 16.0 g / 10 min and a density of 0.902 g / cm³. 3 The nominal strain at fracture is 440%.

[0129] The high-pressure polyethylene prepared according to the system and method for preparing high-pressure polyethylene according to the present invention has excellent quality, high toughness, high percentage of fracture strain, and high ethylene conversion rate.

[0130] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A system for preparing high-pressure polyethylene, characterized in that, The system includes: an evaporator (1), a booster (2), a two-stage booster (3), and a tubular reaction unit (4). The tubular reaction unit (4) includes a first bubble generator (41), a first tubular reactor (42), a first low-pressure separation device (43), a second bubble generator (44), a second tubular reactor (45), a second low-pressure separation device (46), and two-stage high-pressure separation devices (47). In this process, the initiator is vaporized into a gaseous phase in the evaporator (1), and the vaporized initiator enters the booster (2) for pressurization. The pressurized initiator then passes through the first bubble generator (41) and enters the first tubular reactor (42). The pressurized initiator then passes through the second bubble generator (44) and enters the second tubular reactor (45). Liquid ethylene enters the two-stage booster (3) for two-stage pressurization, and the pressurized ethylene then enters the first tubular reactor (42) for polymerization. The material passing through the first tubular reactor (42) enters... The material is fed into the second tubular reactor (45) for polymerization. The material passing through the second tubular reactor (45) enters the second low-pressure separation device (46) for low-pressure separation. The gaseous ethylene after low-pressure separation is returned to the first tubular reactor (42) for polymerization again. The material passing through the second tubular reactor (45) sequentially enters the two-stage high-pressure separation device (47) for two-stage high-pressure separation and the first low-pressure separation device (43) for low-pressure separation. The gaseous ethylene after low-pressure separation is returned to the first tubular reactor (42) for polymerization again.

2. The system according to claim 1, characterized in that, The system also includes an ethylene storage tank (5) and a refrigeration unit (6), wherein the ethylene storage tank (5) is used to store ethylene and the refrigeration unit (6) is used to liquefy ethylene.

3. The system according to claim 1 or 2, characterized in that, The system also includes an extrusion granulation device (7) for extruding and granulating polyethylene that has passed through the first low-pressure separation device (43).

4. The system according to any one of claims 1-3, characterized in that, The tubular reaction unit (4) further includes a third bubble generator (48), a third tubular reactor (49), and a third low-pressure separation device (410). In this process, the initiator is vaporized into a gaseous phase in the evaporator (1). The vaporized initiator enters the booster (2) for pressurization. The pressurized initiator then passes through the first bubble generator (41) and enters the first tubular reactor (42). The pressurized initiator then passes through the second bubble generator (44) and enters the second tubular reactor (45). The pressurized initiator then passes through the third bubble generator (48) and enters the third tubular reactor (49). Liquid ethylene enters the two-stage booster (3) for two-stage pressurization. The ethylene after two-stage pressurization enters the first tubular reactor (42) for polymerization. The material passing through the first tubular reactor (42) enters the second tubular reactor (45) for polymerization. The material passing through the second tubular reactor (45)... The gaseous ethylene enters the second low-pressure separation device (46) for low-pressure separation. After low-pressure separation, the gaseous ethylene returns to the first tubular reactor (42) for polymerization again. The material passing through the second tubular reactor (45) enters the third tubular reactor (49) for polymerization. The material passing through the third tubular reactor (49) enters the third low-pressure separation device (410) for low-pressure separation. After low-pressure separation, the gaseous ethylene returns to the second tubular reactor (45) for polymerization again. The material passing through the third tubular reactor (49) sequentially enters the two-stage high-pressure separation device (47) for two-stage high-pressure separation and the first low-pressure separation device (43) for low-pressure separation. After low-pressure separation, the gaseous ethylene returns to the first tubular reactor (42) for polymerization again.

5. The system according to claim 4, characterized in that, The tubular reaction unit (4) further includes a fourth bubble generator (411), a fourth tubular reactor (412), and a fourth low-pressure separation device (413). In this process, the initiator is vaporized into a gaseous phase in the evaporator (1). The vaporized initiator enters the booster (2) for pressurization. The pressurized initiator passes through the first bubble generator (41) and enters the first tubular reactor (42). The pressurized initiator passes through the second bubble generator (44) and enters the second tubular reactor (45). The pressurized initiator passes through the third bubble generator (48) and enters the third tubular reactor (49). The pressurized initiator passes through the fourth bubble generator (411) and enters the fourth tubular reactor (412). Liquid ethylene enters the two-stage booster (3) for two-stage pressurization. The ethylene after two-stage pressurization enters the first tubular reactor (42) for polymerization. The material passing through the first tubular reactor (42) enters the second tubular reactor (45) for polymerization. The material passing through the second tubular reactor (45) enters the second low-pressure separation device (46) for low-pressure separation. The gaseous ethylene after low-pressure separation returns to the first tubular reactor. The polymerization reaction is carried out again in the second tubular reactor (45). The material passing through the second tubular reactor (45) enters the third tubular reactor (49) for polymerization. The material passing through the third tubular reactor (49) enters the third low-pressure separation device (410) for low-pressure separation. The gaseous ethylene after low-pressure separation is returned to the second tubular reactor (45) for polymerization again. The material passing through the third tubular reactor (49) enters the fourth tubular reactor (412) for polymerization. The material passing through the fourth tubular reactor (412) enters the fourth low-pressure separation device (413) for low-pressure separation. The gaseous ethylene after low-pressure separation is returned to the third tubular reactor (49) for polymerization again. The material passing through the fourth tubular reactor (412) sequentially enters the two-stage high-pressure separation device (47) for two-stage high-pressure separation and the first low-pressure separation device (43) for low-pressure separation. The gaseous ethylene after low-pressure separation is returned to the first tubular reactor (42) for polymerization again.

6. The system according to any one of claims 1-5, characterized in that, The first bubble generator (41), the second bubble generator (44), the third bubble generator (48), and the fourth bubble generator (411) each include a metal film; Preferably, the metal film contains copper oxide, aluminum oxide, iron oxide, and silicon dioxide; Preferably, the pore size of the metal film is 5-10 μm; Preferably, the thickness of the metal film is 0.5-3 mm.

7. A method for preparing high-pressure polyethylene, characterized in that, The method includes the following steps: (1) The initiator is vaporized into a gas phase in the evaporator (1). The vaporized initiator enters the booster (2) for pressurization. The pressurized initiator enters the first tubular reactor (42) through the first bubble generator (41). The pressurized initiator enters the second tubular reactor (45) through the second bubble generator (44). The pressurized initiator enters the third tubular reactor (49) through the third bubble generator (48). The pressurized initiator enters the fourth tubular reactor (412) through the fourth bubble generator (411). (2) Ethylene in the ethylene storage tank (5) is liquefied by a refrigeration unit (6) to obtain liquid ethylene. The obtained liquid ethylene enters a two-stage booster (3) for two-stage pressurization. The ethylene after two-stage pressurization enters the first tubular reactor (42) for polymerization. The material passing through the first tubular reactor (42) enters the second tubular reactor (45) for polymerization. The material passing through the second tubular reactor (45) enters the second low-pressure separator (46) for low-pressure separation. The gaseous ethylene after low-pressure separation is returned to the first tubular reactor (42) for polymerization again. The material passing through the second tubular reactor (45) enters the third tubular reactor (49) for polymerization. The material passing through the third tubular reactor (49) enters the third low-pressure separator. The gaseous ethylene is separated at low pressure by the separation device (410). After low pressure separation, the gaseous ethylene is returned to the second tubular reactor (45) for polymerization again. The material passing through the third tubular reactor (49) enters the fourth tubular reactor (412) for polymerization. The material passing through the fourth tubular reactor (412) enters the fourth low-pressure separation device (413) for low-pressure separation. After low pressure separation, the gaseous ethylene is returned to the third tubular reactor (49) for polymerization again. The material passing through the fourth tubular reactor (412) sequentially enters the two-stage high-pressure separation device (47) for two-stage high-pressure separation and the first low-pressure separation device (43) for low-pressure separation. After low-pressure separation, the gaseous ethylene is returned to the first tubular reactor (42) for polymerization again. (3) The polyethylene that has passed through the first low-pressure separation device (43) is fed into the extrusion granulation device (7) for extrusion granulation to obtain the product.

8. The method according to claim 7, characterized in that, The initiator is 4,4-di(tert-butylperoxy)valerate n-butyl ester and peroxy(2-ethylhexanoate) tert-butyl ester; Preferably, the mass ratio of the amount of 4,4-di(tert-butylperoxy)valerate to the amount of tert-butyl peroxy(2-ethylhexanoate) is (2-3):

1.

9. The method according to claim 7 or 8, characterized in that, The mass ratio of the initiator to the ethylene is (1×10⁻⁶) / ( ... -4 -6×10 -4 ):

1.

10. The method according to any one of claims 7-9, characterized in that, The polymerization conditions in the first tubular reactor (42), the second tubular reactor (45), the third tubular reactor (49), and the fourth tubular reactor (412) respectively include: a temperature of 240-250℃, a pressure of 250-260MPa, and a time of 10-90s.

Images