A method for producing high pressure polyethylene using centrifugation and high pressure polyethylene

Abstract

The present application relates to the technical field of polyethylene synthesis, and particularly relates to a method for preparing high-pressure polyethylene by centrifugation and high-pressure polyethylene. The method comprises the following steps: in the presence of an initiator, raw material gas containing ethylene, a molecular weight regulator and a polymerization catalyst is subjected to a polymerization reaction in a high-pressure autoclave type reactor, and then the mixture obtained by the polymerization reaction is subjected to centrifugation at 170-200 DEG C to obtain high-pressure polyethylene. The method adopts a hot high-temperature centrifugation method to centrifugally treat the discharge of the high-pressure autoclave type reactor, so that the molten oligomer which is not completely reacted can be separated from the polyethylene which is fully reacted, and both the gaseous material and the molten oligomer can be recycled, thereby effectively improving the conversion rate of raw material ethylene and the yield of polyolefin products.

Description

Technical Field

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

[0002] Low-density polyethylene (LDPE), also known as high-pressure polyethylene, is one of the world's major polyolefin polymer products. It possesses excellent insulation, ductility, permeability, and processability, and is resistant to acid and alkali corrosion. It is primarily used in the production of plastic packaging products, injection-molded products, and medical devices. The autoclave process for high-pressure polyethylene, with its in-vessel stirring function, achieves near-complete mixing, ensuring uniform temperature and pressure distribution within the vessel. The polymer produced by this process often has long-chain structures, resulting in superior impact strength. Currently, my country has over a dozen autoclave-process high-pressure polyethylene plants, all maintaining high operating rates to meet market demand.

[0003] The batch reactor process has a low single-pass conversion rate of only 15%–21%, a short residence time, and a maximum single-line capacity of only 18 × 10⁴ t / a, accounting for approximately 33% of domestic production capacity. To improve the single-pass conversion rate and the molecular weight distribution and long-chain content of the product in the batch reactor process for producing high-density polyethylene (HDPE), patent application CN115232233A involves drawing out the material from the outlet of one reaction zone in the reactor and circulating it upstream to contact the first mixture to obtain a second mixture, thereby improving material conversion and yield. Patent application CN111100233A splits the ethylene feed into two streams; 80% of the ethylene gas in the first stream is combined with fresh gas and enters the reactor for polymerization, while the remaining 20% ​​of the ethylene gas is returned to the ethylene refining unit for secondary refining to improve the ethylene feedstock conversion rate. Patent application CN114075309A utilizes a tail gas recovery system to separate and recover the effluent from the polymerization reaction system, which is then recycled back into the reactor to produce polyolefin products. However, these methods offer limited improvement in ethylene conversion and HDPE yield, and the product structure and quality remain relatively poor.

[0004] Therefore, there is a need for a new method that can improve ethylene conversion rate and control the structural quality of high-pressure polyethylene products over a wider range. Summary of the Invention

[0005] The purpose of this invention is to overcome the problems of low ethylene conversion rate and affected product quality in the production process of high-pressure polyethylene, where only the gas phase components are separated and recycled while the molten product is directly discharged. This invention provides a method for preparing high-pressure polyethylene using centrifugation and a high-pressure polyethylene product.

[0006] To achieve the above objectives, the first aspect of the present invention provides a method for preparing high-pressure polyethylene using high-temperature centrifugation. The method includes: in the presence of an initiator, carrying out a polymerization reaction of a raw material gas containing ethylene, a molecular weight regulator and a polymerization catalyst in a high-pressure autoclave reactor, and then centrifuging the mixture obtained from the polymerization reaction at 170-200°C to obtain high-pressure polyethylene.

[0007] Preferably, the centrifugation speed is 900-1100 r / min, and the centrifugation time is 30-60 min.

[0008] Preferably, the molecular weight regulator is propylene, and the polymerization catalyst is air.

[0009] Preferably, the initiator is tert-butyl peroxide-2-ethylhexanoate and 4-tert-butylcyclohexyl peroxide.

[0010] Preferably, the weight ratio of tert-butyl peroxide-2-ethylhexanoate to 4-tert-butylcyclohexyl peroxide is 2-5:1.

[0011] Preferably, the polymerization reaction conditions include: a pressure of 250–260 MPa and a temperature of 250–260 °C.

[0012] Preferably, the raw material gas is prepared according to the following steps:

[0013] The raw material ethylene is pressurized to obtain pressurized ethylene; the pressurized ethylene, molecular weight regulator and polymerization catalyst are introduced into a compressor for compression to obtain raw material gas.

[0014] Preferably, the pressure of the pressurized ethylene is 22-25 MPa;

[0015] Preferably, the compression includes primary compression and secondary compression, wherein the pressure after primary compression is 110-120 MPa, and the pressure after secondary compression is 240-250 MPa.

[0016] Preferably, the volume ratio of the molecular weight regulator to the pressurized ethylene is 1×10⁻⁶. -4 -4×10 -4 :1;

[0017] Preferably, the volume ratio of the polymerization catalyst to the pressurized ethylene is 4 × 10⁻⁶. -3 -8×10 -3 :1.

[0018] Preferably, the volume ratio of initiator to feed gas is 6 × 10⁻⁶. -6 -9×10 -6 :1, more preferably 7×10 -6 -8×10-6 :1.

[0019] Preferably, the method includes the following steps:

[0020] (1) Pressurize the raw material ethylene to obtain pressurized ethylene;

[0021] (2) Pressurized ethylene, molecular weight regulator and polymerization catalyst are introduced into the compressor for compression to obtain raw material gas;

[0022] (3) In the presence of an initiator, the raw material gas obtained in step (2) is subjected to polymerization reaction in a high-pressure autoclave to obtain a mixture and gaseous material;

[0023] (4) The mixture obtained from the polymerization reaction is introduced into a hot high-temperature centrifuge and centrifuged at 170-200℃ to obtain molten oligomers and high-pressure polyethylene;

[0024] (5) The gaseous material obtained in step (3) is returned to step (1) for reuse;

[0025] (6) The molten oligomer obtained in step (4) is returned to the autoclave reactor to participate in the polymerization reaction.

[0026] Preferably, the method further includes: introducing the high-pressure polyethylene obtained in step (3) into an extrusion system for extrusion, and then into a granulation system for granulation.

[0027] Preferably, the extrusion system is a twin-screw extruder, and the extrusion channel is divided into three temperature zones with temperatures of 150–170°C, 170–190°C and 190–210°C, respectively, and the extruder head temperature is 200–210°C.

[0028] A second aspect of the present invention provides high-pressure polyethylene prepared according to the method described above.

[0029] Preferably, the high-pressure polyethylene has a melt index of 17.0–19.8 g / 10 min and a density of 0.907–0.920 g / cm³. 3 The tensile strength is 10.3–12.9 MPa, the elongation at break is 170–310%, and the molecular weight distribution is 4.6–5.9.

[0030] Existing high-pressure polyethylene (HPPE) production processes all employ a method of separating and circulating the gas phase in the reactor under high and low pressures, while the polymerized condensed products are directly discharged into subsequent cycles. However, the polymerized products contain polymers of varying densities, and some polymers do not react completely, affecting the product grade and quality. Therefore, this invention provides a method for preparing HPPE using high-temperature centrifugation.

[0031] The method described in this invention employs high-temperature centrifugation to separate the molten oligomers from the high-molecular-weight polymerized product, polyethylene. Both the unreacted ethylene and the molten oligomers can be recycled, effectively improving the conversion rate of the raw material ethylene and the yield of the polyethylene product. The resulting high-pressure polyethylene product exhibits a wide molecular weight distribution and a high content of long-chain branches, demonstrating high tensile strength, high toughness, and excellent performance. This method has broad application prospects, is highly operable, and is suitable for industrial-scale production. Detailed Implementation

[0032] 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.

[0033] 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.

[0034] The first aspect of the present invention provides a method for preparing high-pressure polyethylene using high-temperature centrifugation. The method includes: in the presence of an initiator, carrying out a polymerization reaction of a raw material gas containing ethylene, a molecular weight regulator and a polymerization catalyst in a high-pressure autoclave reactor, and then centrifuging the mixture obtained from the polymerization reaction at 170-200°C to obtain high-pressure polyethylene.

[0035] In a preferred embodiment, the centrifugation speed is 900-1100 r / min, and the centrifugation time is 30-60 min. Centrifugation under the above conditions facilitates the complete separation of unreacted molten oligomers and fully reacted polymer products (high-pressure polyethylene).

[0036] In a preferred embodiment, the molecular weight regulator is propylene, and the polymerization catalyst is air.

[0037] In a preferred embodiment, the initiator is tert-butyl peroxide-2-ethylhexanoate and 4-tert-butylcyclohexyl peroxide. More preferably, the weight ratio of tert-butyl peroxide-2-ethylhexanoate and 4-tert-butylcyclohexyl peroxide is 2-5:1; specifically, for example, it can be 2:1, 3:1, 4:1 or 5:1.

[0038] In a preferred embodiment, the polymerization reaction conditions include a pressure of 250–260 MPa and a temperature of 250–260 °C. Performing the polymerization reaction under these conditions is beneficial for obtaining high-performance high-pressure polyethylene products.

[0039] According to some preferred embodiments of the present invention, the raw material gas can be prepared according to the following steps:

[0040] The raw material ethylene is pressurized to obtain pressurized ethylene; the pressurized ethylene, molecular weight regulator and polymerization catalyst are introduced into a compressor for compression to obtain raw material gas.

[0041] In the method described in this invention, the purity of the raw material ethylene is ≥99%.

[0042] In a preferred embodiment, the raw ethylene is pressurized to 22–25 MPa, resulting in pressurized ethylene with a pressure of 22–25 MPa. In a specific embodiment, the raw ethylene can be pressurized using a compressor.

[0043] In a preferred embodiment, the compression includes primary compression and secondary compression, wherein the pressure after primary compression is 110-120 MPa, and the pressure after secondary compression is 240-250 MPa. In a specific embodiment, two compressors connected in series can be used for primary and secondary compression.

[0044] In a preferred embodiment, the feed volume ratio of the molecular weight regulator to the pressurized ethylene is 1×10⁻⁶. -4 -4×10 -4 :1, more preferably 2×10 -4 -3×10 -4 1. Introducing the molecular weight regulator and pressurized ethylene into the compressor according to the above volume ratio is beneficial for adjusting the uniformity of the molecular weight of the prepared high-pressure polyethylene, thus ensuring the quality and uniformity of the high-pressure polyethylene product.

[0045] In a preferred embodiment, the feed volume ratio of the polymerization catalyst to the pressurized ethylene is 4 × 10⁻⁶. -3 -8×10 -3 :1, more preferably 5×10 -3 -6×10 -3 1. Introducing the polymerization catalyst and pressurized ethylene into the compressor according to the above volume ratio is beneficial to increasing the polymerization rate of ethylene, improving reaction efficiency and ethylene conversion rate.

[0046] According to some preferred embodiments of the present invention, the method includes the following steps:

[0047] (1) Pressurize the raw material ethylene to obtain pressurized ethylene;

[0048] (2) Pressurized ethylene, molecular weight regulator and polymerization catalyst are introduced into the compressor for compression to obtain raw material gas;

[0049] (3) In the presence of an initiator, the raw material gas obtained in step (2) is subjected to polymerization reaction in a high-pressure autoclave to obtain a mixture and gaseous material;

[0050] (4) The mixture obtained from the polymerization reaction is introduced into a hot high-temperature centrifuge and centrifuged at 170-200℃ to obtain molten oligomers and high-pressure polyethylene;

[0051] (5) Return the gaseous material obtained in step (3) to step (1) for reuse;

[0052] (6) The molten oligomer obtained in step (4) is returned to the autoclave reactor to participate in the polymerization reaction.

[0053] In a preferred embodiment, in step (3), the feed volume ratio of the initiator to the feed gas is 6 × 10⁻⁶. -6 -9×10 -6 :1, more preferably 7×10 -6 -8×10 -6 :1.

[0054] In this invention, step (4) uses a centrifuge to perform high-temperature centrifugation to separate the mixture (molten state) obtained from the polymerization reaction in the autoclave reactor. After centrifugation, the upper layer is unreacted molten oligomer, while the lower layer is a fully reacted high molecular weight polymer (i.e., the target product, high-pressure polyethylene). The upper layer can be returned to step (3) for further polymerization in the autoclave reactor, while the lower layer can be extruded and granulated to obtain a high-performance high-pressure polyethylene product.

[0055] In this invention, the gaseous material obtained after the polymerization reaction is unreacted ethylene. Recycling the gaseous material can further improve the conversion rate of ethylene and the quality of polyethylene products. In a preferred embodiment, by step (5), the gaseous material obtained in step (3) is returned to step (1) for reuse, which can realize the secondary recycling of unreacted ethylene and effectively improve the utilization rate of ethylene. Specifically, the gaseous material can be returned to step (1) for reuse after high-pressure and medium-pressure circulation.

[0056] According to some preferred embodiments of the present invention, when the gaseous material is returned to step (1) for use, the feed volume ratio of the gaseous material to the raw material ethylene is 1×10. -2 -4×10 -2 :1, more preferably 2×10 -2 -3×10 -21. By introducing the gaseous material and raw material ethylene into the booster compressor according to the above volume ratio, the gaseous material can be reused without affecting the quality of the prepared high-pressure polyethylene product.

[0057] In this invention, in step (6), the molten oligomer obtained in step (4) can be returned to step (3) to undergo polymerization with the raw material gas in a high-pressure autoclave reactor, thereby realizing the recycling of the molten oligomer and effectively improving the product quality and molecular weight uniformity. Specifically, the molten oligomer can be returned to the high-pressure autoclave reactor after high-pressure circulation to participate in the polymerization reaction.

[0058] According to some preferred embodiments of the present invention, when the molten oligomer is returned to the autoclave reactor to participate in the polymerization reaction, the volume ratio of the molten oligomer to the reactants in the autoclave reactor is 0.1 to 0.4:1, more preferably 0.2 to 0.3:1. Herein, the volume of the reactants in the autoclave reactor refers to the volume of all materials contained within the reactor.

[0059] In a preferred embodiment, the method further includes: introducing the high-pressure polyethylene (i.e., the lower polymer product) obtained in step (4) into an extrusion system for extrusion, and then into a granulation system for granulation. By extruding and granulating the lower polymer product, a high-pressure polyethylene product can be obtained, which has a wide molecular weight distribution and a high content of long-chain branches. In a preferred case, the high-pressure polyethylene obtained in step (3) can be extruded into an extrusion system after passing through two stages of high-pressure separation and one stage of low-pressure separation, and then granulated underwater in a granulation system and packaged. For example, the high-pressure polyethylene obtained in step (3) can be first subjected to a high-pressure separator with pressure reduced to 140 MPa, then to a high-pressure separator with pressure reduced to 25 MPa, and finally to a low-pressure separator with pressure reduced to 0.8 MPa before entering the extrusion system.

[0060] More preferably, the extrusion system is a twin-screw extruder, the extrusion channel is divided into 3 temperature zones, with temperatures of 150-170°C, 170-190°C and 190-210°C respectively, and the extruder head temperature is 200-210°C.

[0061] In this invention, the granulation system can be a conventional granulation system used in the art, and there are no special requirements for its selection. It is sufficient to granulate the material extruded by the twin-screw extruder.

[0062] The method described in this invention has broad application prospects, high operability, effectively improves the conversion rate of ethylene, and produces high-quality products suitable for industrial-scale production. Besides its application in the preparation of high-pressure polyethylene, it is applicable to various polymer production systems requiring the addition of initiators, such as polystyrene, polypropylene, and POE elastomers. Furthermore, it is suitable for the preparation and application of various gas-liquid and liquid-liquid mixed-phase reactions.

[0063] A second aspect of the present invention provides high-pressure polyethylene prepared according to the method described above.

[0064] Preferably, the high-pressure polyethylene has a melt index of 17.0–19.8 g / 10 min and a density of 0.907–0.920 g / cm³. 3 The tensile strength is 10.3–12.9 MPa, the elongation at break is 170–310%, and the molecular weight distribution is 4.6–5.9.

[0065] The present invention will be described in detail below through embodiments, but the scope of protection of the present invention is not limited thereto.

[0066] Example 1

[0067] (1) The raw material ethylene with a purity of 99% is initially pressurized to 22-25 MPa by a booster press to obtain pressurized ethylene;

[0068] (2) Pressurized ethylene, molecular weight regulator (propylene), and polymerization catalyst (air) are introduced into a first-stage compressor and pressurized to 110-120 MPa, then into a second-stage compressor and pressurized to 240-250 MPa to obtain feed gas; wherein the feed volume ratio of propylene to pressurized ethylene is 1×10 -4 1. The feed volume ratio of air to pressurized ethylene is 4 × 10⁻⁶. -3 :1;

[0069] (3) The raw material gas is introduced into a high-pressure autoclave reactor, and a polymerization reaction is carried out in the presence of an initiator (tert-butyl peroxide-2-ethylhexanoate and 4-tert-butylcyclohexyl peroxide dicarbonate, with a weight ratio of 5:1) to obtain a molten mixture and a gaseous material; wherein the polymerization reaction pressure is 250-260 MPa, the polymerization reaction temperature is 250-260 °C, and the feed volume ratio of initiator to raw material gas is 6 × 10⁻⁶. -6 :1;

[0070] (4) The molten mixture obtained from the polymerization reaction in step (3) is introduced into a centrifuge for high-temperature centrifugation to obtain molten oligomer (upper layer) and high molecular weight polymer (high-pressure polyethylene); wherein the centrifugation temperature is 170℃, the centrifugation speed is 900r / min, and the centrifugation time is 30min.

[0071] (5) The gaseous material obtained in step (3) is mixed with the raw material ethylene after high-pressure and medium-pressure circulation, and then enters the booster for pressurization; wherein the volume ratio of the gaseous material to the raw material ethylene is 1×10 -2 :1;

[0072] (6) The molten oligomer obtained in step (4) is returned to the high-pressure autoclave reactor via high-pressure circulation to participate in the polymerization reaction, wherein the volume ratio of the molten oligomer to the reactants in the high-pressure autoclave reactor is 0.1:1;

[0073] (7) The polymer product obtained in step (4) is first passed through a high-pressure separator to reduce the pressure to 140 MPa, then through a high-pressure separator to reduce the pressure to 25 MPa, and finally through a low-pressure separator to reduce the pressure to 0.8 MPa before entering the twin-screw extruder for extrusion. Then it enters the granulation system for underwater granulation and packaging to obtain high-pressure polyethylene products. The extrusion channel of the twin-screw extruder is divided into three temperature zones: 150~170℃, 170~190℃ and 190~210℃. The extruder head temperature control condition is 200~210℃.

[0074] Example 2

[0075] (1) The raw material ethylene with a purity of 99% is initially pressurized to 22-25 MPa by a booster press to obtain pressurized ethylene;

[0076] (2) The pressurized ethylene, molecular weight regulator (propylene), and polymerization catalyst (air) are introduced into a first-stage compressor for primary compression to a pressure of 110–120 MPa, and then into a second-stage compressor for secondary compression to a pressure of 240–250 MPa to obtain the feed gas; wherein the feed volume ratio of propylene to pressurized ethylene is 2 × 10⁻⁶. -4 1. The feed volume ratio of air to pressurized ethylene is 5 × 10⁻⁶. -3 :1;

[0077] (3) The feed gas is introduced into a high-pressure autoclave reactor, and a polymerization reaction is carried out in the presence of an initiator (tert-butyl peroxide-2-ethylhexanoate and 4-tert-butylcyclohexyl peroxide dicarbonate, with a weight ratio of 4:1) to obtain a molten mixture and a gaseous material; wherein the polymerization reaction pressure is 250-260 MPa, the polymerization reaction temperature is 250-260 °C, and the feed volume ratio of initiator to feed gas is 7 × 10⁻⁶. -6 :1;

[0078] (4) The molten mixture obtained from the polymerization reaction in step (3) is introduced into a centrifuge for high-temperature centrifugation to obtain molten oligomer (upper layer) and high molecular polymer (high-pressure polyethylene). The centrifugation temperature is 170℃, the centrifugation speed is 900r / min, and the centrifugation time is 40min.

[0079] (5) The gaseous material obtained in step (3) is mixed with the raw material ethylene through high-pressure circulation and medium-pressure circulation, and then fed into a booster for pressurization; wherein the volume ratio of the gaseous material to the raw material ethylene is 1×10 -2 :1;

[0080] (6) The molten oligomer obtained in step (4) is returned to the high-pressure autoclave reactor under high pressure to participate in the polymerization reaction. The volume ratio of the molten oligomer to the reactants in the high-pressure autoclave reactor is 0.1:1.

[0081] (7) The polymer product obtained in step (4) is first subjected to a high pressure separator with the pressure reduced to 140 MPa, then subjected to a high pressure separator with the pressure reduced to 25 MPa, and finally subjected to a low pressure separator with the pressure reduced to 0.8 MPa before entering the twin-screw extruder for extrusion. Then it enters the granulation system for underwater granulation and packaging to obtain high-pressure polyethylene products. The extrusion channel of the twin-screw extruder is divided into three temperature zones: 150~170℃, 170~190℃ and 190~210℃. The extruder head temperature control condition is 200~210℃.

[0082] Example 3

[0083] (1) The raw material ethylene with a purity of 99% is initially pressurized to 22-25 MPa by a booster press to obtain pressurized ethylene;

[0084] (2) Pressurized ethylene, molecular weight regulator (propylene), and polymerization catalyst (air) are introduced into a first-stage compressor and pressurized to 110–120 MPa, then into a second-stage compressor and pressurized to 240–250 MPa to obtain feed gas; wherein the feed volume ratio of propylene to pressurized ethylene is 1 × 10⁻⁶. -4 1. The feed volume ratio of air to pressurized ethylene is 4 × 10⁻⁶. -3 :1;

[0085] (3) The feed gas is introduced into a high-pressure autoclave reactor, and a polymerization reaction is carried out in the presence of an initiator (tert-butyl peroxide-2-ethylhexanoate and 4-tert-butylcyclohexyl peroxide dicarbonate, with a weight ratio of 5:1) to obtain a molten mixture and a gaseous material; wherein the polymerization reaction pressure is 250-260 MPa, the polymerization reaction temperature is 250-260 °C, and the feed volume ratio of initiator to feed gas is 6 × 10⁻⁶. -6 :1;

[0086] (4) The molten mixture obtained from the polymerization reaction in step (3) is introduced into a high-temperature centrifuge for high-temperature centrifugation separation to obtain molten oligomer (upper layer) and high molecular weight polymer (high-pressure polyethylene); wherein the centrifugation temperature is 180℃, the centrifugation speed is 1000r / min, and the centrifugation time is 40min.

[0087] (5) The gaseous material obtained in step (3) is mixed with the raw material ethylene through high-pressure circulation and medium-pressure circulation, and then enters the booster for pressurization; wherein, the volume ratio of the gaseous material to the raw material ethylene is 1×10 -2 :1;

[0088] (6) The molten oligomer obtained in step (4) is fed back to the high-pressure autoclave reactor via high-pressure circulation to participate in the polymerization reaction, wherein the volume ratio of the molten oligomer to the reactants in the high-pressure autoclave reactor is 0.1:1.

[0089] (7) The polymer product obtained in step (4) is first passed through a high-pressure separator to reduce the pressure to 140 MPa, then through a high-pressure separator to reduce the pressure to 25 MPa, and finally through a low-pressure separator to reduce the pressure to 0.8 MPa before entering the twin-screw extruder for extrusion. Then it enters the granulation system for underwater granulation and packaging to obtain high-pressure polyethylene products. The extrusion channel of the twin-screw extruder is divided into three temperature zones: 150~170℃, 170~190℃ and 190~210℃. The extruder head temperature control condition is 200~210℃.

[0090] Example 4

[0091] (1) The raw material ethylene with a purity of 99% is initially pressurized to 22-25 MPa by a booster press to obtain pressurized ethylene;

[0092] (2) Pressurized ethylene, molecular weight regulator (propylene), and polymerization catalyst (air) are introduced into a first-stage compressor and pressurized to 110–120 MPa, then into a second-stage compressor and pressurized to 240–250 MPa to obtain feed gas; wherein the feed volume ratio of propylene to pressurized ethylene is 1 × 10⁻⁶. -4 1. The feed volume ratio of air to pressurized ethylene is 4 × 10⁻⁶. -3 :1;

[0093] (3) The raw material gas is introduced into a high-pressure autoclave reactor, and a polymerization reaction is carried out in the presence of an initiator (tert-butyl peroxide-2-ethylhexanoate and 4-tert-butylcyclohexyl peroxide dicarbonate, with a weight ratio of 5:1) to obtain a molten mixture and a gaseous material; wherein the polymerization reaction pressure is 250-260 MPa, the polymerization reaction temperature is 250-260 °C, and the feed volume ratio of initiator to raw material gas is 6 × 10⁻⁶.-6 :1;

[0094] (4) The molten mixture obtained from the polymerization reaction in step (3) is introduced into a centrifuge for high-temperature centrifugation to obtain molten oligomer (upper layer) and high molecular weight polymer (high-pressure polyethylene); wherein the centrifugation temperature is 170℃, the centrifugation speed is 900r / min, and the centrifugation time is 40min.

[0095] (5) The gaseous material obtained in step (3) is mixed with the raw material ethylene after high-pressure and medium-pressure circulation, and then enters the booster for pressurization. The volume ratio of the gaseous material to the raw material ethylene is 2×10. -2 :1;

[0096] (6) The molten oligomer obtained in step (4) is fed back to the high-pressure autoclave reactor via high-pressure circulation to participate in the polymerization reaction, wherein the volume ratio of the molten oligomer to the reactants in the high-pressure autoclave reactor is 0.2:1;

[0097] (7) The polymer product obtained in step (4) is first passed through a high-pressure separator to reduce the pressure to 140 MPa, then through a high-pressure separator to reduce the pressure to 25 MPa, and finally through a low-pressure separator to reduce the pressure to 0.8 MPa before entering the twin-screw extruder for extrusion. Then it enters the granulation system for underwater granulation and packaging to obtain high-pressure polyethylene products. The extrusion channel of the twin-screw extruder is divided into three temperature zones: 150~170℃, 170~190℃ and 190~210℃. The extruder head temperature control condition is 200~210℃.

[0098] Example 5

[0099] (1) The raw material ethylene with a purity of 99% is initially pressurized to 22-25 MPa by a booster press to obtain pressurized ethylene;

[0100] (2) The pressurized ethylene, molecular weight regulator (propylene), and polymerization catalyst (air) are introduced into the pressurized system and then pressurized to 110-120 MPa by a first-stage compressor, and then pressurized to 240-250 MPa by a second-stage compressor. The feed volume ratio of propylene to pressurized ethylene is 2 × 10⁻⁶. -4 1. The feed volume ratio of air to ethylene is 5 × 10⁻⁶. -3 :1;

[0101] (3) The feed gas is introduced into a high-pressure autoclave reactor, and a polymerization reaction is carried out in the presence of an initiator (tert-butyl peroxide-2-ethylhexanoate and 4-tert-butylcyclohexyl peroxide dicarbonate, with a weight ratio of 3:1) to obtain a molten mixture and a gaseous material; wherein the polymerization reaction pressure is 250-260 MPa, the polymerization reaction temperature is 250-260 °C, and the feed volume ratio of initiator to feed gas is 7 × 10⁻⁶. -6 :1;

[0102] (4) The molten mixture obtained from the polymerization reaction in step (3) is introduced into a centrifuge for high-temperature centrifugation to obtain molten oligomer (upper layer) and high molecular weight polymer (high-pressure polyethylene); wherein the centrifugation temperature is 180℃, the centrifugation speed is 900r / min, and the centrifugation time is 60min.

[0103] (5) The gaseous material obtained in step (3) is mixed with the raw material ethylene after high-pressure circulation and medium-pressure circulation, and then enters the booster for pressurization; wherein the volume ratio of the gaseous material to the raw material ethylene is 2×10 -2 :1;

[0104] (6) The molten oligomer obtained in step (4) is returned to the high-pressure autoclave reactor via high-pressure circulation to participate in the polymerization reaction, wherein the volume ratio of the molten oligomer to the reactants in the high-pressure autoclave reactor is 0.2:1;

[0105] (7) The polymer product obtained in step (4) is first passed through a high-pressure separator to reduce the pressure to 140 MPa, then through a high-pressure separator to reduce the pressure to 25 MPa, and finally through a low-pressure separator to reduce the pressure to 0.8 MPa before entering the twin-screw extruder for extrusion. Then it enters the granulation system for underwater granulation and packaging to obtain high-pressure polyethylene products. The extrusion channel of the twin-screw extruder is divided into three temperature zones: 150~170℃, 170~190℃ and 190~210℃. The extruder head temperature control condition is 200~210℃.

[0106] Example 6

[0107] (1) The raw material ethylene with a purity of 99% is initially pressurized to 22-25 MPa by a booster press to obtain pressurized ethylene;

[0108] (2) Pressurized ethylene, molecular weight regulator (propylene), and polymerization catalyst (air) are introduced into a first-stage compressor and pressurized to 110–120 MPa, then into a second-stage compressor and pressurized to 240–250 MPa to obtain feed gas; wherein the feed volume ratio of propylene to pressurized ethylene is 3 × 10⁻⁶. -4 1. The feed volume ratio of air to pressurized ethylene is 6 × 10⁻⁶. -3 :1;

[0109] (3) The feed gas is introduced into a high-pressure autoclave reactor, and a polymerization reaction is carried out in the presence of an initiator (tert-butyl peroxide-2-ethylhexanoate and 4-tert-butylcyclohexyl peroxide, with a weight ratio of 3:1) to obtain a molten mixture and a gaseous material; wherein the polymerization reaction pressure is 250-260 MPa, the polymerization reaction temperature is 250-260 °C, and the feed volume ratio of the initiator to the feed gas is 8 × 10⁻⁶. -6 :1;

[0110] (4) The molten mixture obtained from the polymerization reaction in step (3) is introduced into a centrifuge for high-temperature centrifugation to obtain molten oligomer (upper layer) and high molecular weight polymer (high-pressure polyethylene); wherein, the centrifugation temperature is 190℃, the centrifugation speed is 1000r / min, and the centrifugation time is 50min;

[0111] (5) The gaseous material obtained in step (3) is mixed with the raw material ethylene after high-pressure circulation and medium-pressure circulation, and then enters the booster for pressurization; wherein the volume ratio of the gaseous material to the raw material ethylene is 3×10 -2 :1;

[0112] (6) The molten oligomer obtained in step (4) is fed back to the high-pressure autoclave reactor through high-pressure circulation to participate in the polymerization reaction, wherein the volume ratio of the molten oligomer to the reactants in the high-pressure autoclave reactor is 0.3:1;

[0113] (7) The polymer product obtained in step (4) is first passed through a high-pressure separator to reduce the pressure to 140 MPa, then through a high-pressure separator to reduce the pressure to 25 MPa, and finally through a low-pressure separator to reduce the pressure to 0.8 MPa before entering the twin-screw extruder for extrusion. Then it enters the granulation system for underwater granulation and packaging to obtain high-pressure polyethylene products. The extrusion channel of the twin-screw extruder is divided into three temperature zones: 150~170℃, 170~190℃ and 190~210℃. The extruder head temperature control condition is 200~210℃.

[0114] Example 7

[0115] (1) The raw material ethylene with a purity of 99% is initially pressurized to 22-25 MPa by a booster press to obtain pressurized ethylene;

[0116] (2) Pressurized ethylene, molecular weight regulator (propylene), and polymerization catalyst (air) are introduced into a first-stage compressor and pressurized to 110–120 MPa, then into a second-stage compressor and pressurized to 240–250 MPa to obtain feed gas; wherein the feed volume ratio of propylene to pressurized ethylene is 4 × 10⁻⁶. -41. The feed volume ratio of air to pressurized ethylene is 8 × 10⁻⁶. -3 :1;

[0117] (3) The feed gas is introduced into a high-pressure autoclave reactor, and a polymerization reaction is carried out in the presence of an initiator (tert-butyl peroxide-2-ethylhexanoate and 4-tert-butylcyclohexyl peroxide dicarbonate, with a weight ratio of 3:1) to obtain a molten mixture and a gaseous material; wherein the polymerization reaction pressure is 250-260 MPa, the polymerization reaction temperature is 250-260 °C, and the feed volume ratio of initiator to feed gas is 8 × 10⁻⁶. -6 :1;

[0118] (4) The molten mixture obtained from the polymerization reaction in step (3) is introduced into a centrifuge for high-temperature centrifugation to obtain molten oligomer (upper layer) and high molecular polymer (high-pressure polyethylene). The centrifugation temperature is 190℃, the centrifugation speed is 1000r / min, and the centrifugation time is 60min.

[0119] (5) The gaseous material obtained in step (3) is mixed with the raw material ethylene after high-pressure circulation and medium-pressure circulation, and then enters the booster for pressurization; wherein the volume ratio of the gaseous material to the raw material ethylene is 3×10 -2 :1;

[0120] (6) The molten oligomer obtained in step (4) is returned to the high-pressure autoclave reactor via high-pressure circulation to participate in the polymerization reaction, wherein the volume ratio of the molten oligomer to the reactants in the high-pressure autoclave reactor is 0.3:1;

[0121] (7) The polymer product obtained in step (4) is first passed through a high-pressure separator to reduce the pressure to 140 MPa, then through a high-pressure separator to reduce the pressure to 25 MPa, and finally through a low-pressure separator to reduce the pressure to 0.8 MPa before entering the twin-screw extruder for extrusion. Then it enters the granulation system for underwater granulation and packaging to obtain high-pressure polyethylene products. The extrusion channel of the twin-screw extruder is divided into three temperature zones: 150~170℃, 170~190℃ and 190~210℃. The extruder head temperature control condition is 200~210℃.

[0122] Example 8

[0123] (1) The raw material ethylene with a purity of 99% is initially pressurized to 22-25 MPa by a booster press to obtain pressurized ethylene;

[0124] (2) Pressurized ethylene, molecular weight regulator (propylene), and polymerization catalyst (air) are introduced into a first-stage compressor and pressurized to 110–120 MPa, then into a second-stage compressor and pressurized to 240–250 MPa to obtain feed gas; wherein the feed volume ratio of propylene to pressurized ethylene is 3 × 10⁻⁶. -4 1. The feed volume ratio of air to pressurized ethylene is 6 × 10⁻⁶. -3 :1;

[0125] (3) The feed gas is introduced into a high-pressure autoclave reactor, and a polymerization reaction is carried out in the presence of an initiator (tert-butyl peroxide-2-ethylhexanoate and 4-tert-butylcyclohexyl peroxide dicarbonate, with a weight ratio of 3:1) to obtain a molten mixture and a gaseous material; wherein the polymerization reaction pressure is 250-260 MPa, the polymerization reaction temperature is 250-260 °C, and the feed volume ratio of initiator to feed gas is 8 × 10⁻⁶. -6 :1;

[0126] (4) The molten mixture obtained from the polymerization reaction in step (3) is introduced into a centrifuge for high-temperature centrifugation to obtain molten oligomer (upper layer) and high molecular weight polymer (high-pressure polyethylene); wherein, the centrifugation temperature is 200℃, the centrifugation speed is 1100r / min, and the centrifugation time is 50min;

[0127] (5) The gaseous material obtained in step (3) is mixed with the raw material ethylene after high-pressure circulation and medium-pressure circulation, and then enters the booster for pressurization; wherein the volume ratio of the gaseous material to the raw material ethylene is 3×10 -2 :1;

[0128] (6) The molten oligomer obtained in step (4) is returned to the high-pressure autoclave reactor via high-pressure circulation to participate in the polymerization reaction, wherein the volume ratio of the molten oligomer to the reactants in the high-pressure autoclave reactor is 0.3:1;

[0129] (7) The polymer product obtained in step (4) is first passed through a high-pressure separator to reduce the pressure to 140 MPa, then through a high-pressure separator to reduce the pressure to 25 MPa, and finally through a low-pressure separator to reduce the pressure to 0.8 MPa before entering the twin-screw extruder for extrusion. Then it enters the granulation system for underwater granulation and packaging to obtain high-pressure polyethylene products. The extrusion channel of the twin-screw extruder is divided into three temperature zones: 150~170℃, 170~190℃ and 190~210℃. The extruder head temperature control condition is 200~210℃.

[0130] Example 9

[0131] (1) The raw material ethylene with a purity of 99% is initially pressurized to 22-25 MPa by a booster press to obtain pressurized ethylene;

[0132] (2) Pressurized ethylene, molecular weight regulator (propylene), and polymerization catalyst (air) are introduced into a first-stage compressor and pressurized to 110–120 MPa, then into a second-stage compressor and pressurized to 240–250 MPa to obtain feed gas; wherein the feed volume ratio of propylene to pressurized ethylene is 3 × 10⁻⁶. -4 1. The feed volume ratio of air to pressurized ethylene is 6 × 10⁻⁶. -3 :1;

[0133] (3) The feed gas is introduced into a high-pressure autoclave reactor, and a polymerization reaction is carried out in the presence of an initiator (tert-butyl peroxide-2-ethylhexanoate and 4-tert-butylcyclohexyl peroxide dicarbonate, with a weight ratio of 3:1) to obtain a molten mixture and a gaseous material; wherein the polymerization reaction pressure is 250-260 MPa, the polymerization reaction temperature is 250-260 °C, and the feed volume ratio of initiator to feed gas is 8 × 10⁻⁶. -6 :1;

[0134] (4) The molten mixture obtained from the polymerization reaction in step (3) is introduced into a centrifuge for high-temperature centrifugation to obtain molten oligomer (upper layer) and high molecular weight polymer (high-pressure polyethylene); wherein the centrifugation temperature is 190℃, the centrifugation speed is 1100r / min, and the centrifugation time is 60min.

[0135] (5) The gaseous material obtained in step (3) is mixed with the raw material ethylene after high-pressure and medium-pressure circulation, and then enters the booster for pressurization; wherein the volume ratio of the gaseous material to the raw material ethylene is 4×10 -2 :1;

[0136] (6) The molten oligomer obtained in step (4) is fed back to the high-pressure autoclave reactor through high-pressure circulation to participate in the polymerization reaction, wherein the volume ratio of the molten oligomer to the reactants in the high-pressure autoclave reactor is 0.4:1;

[0137] (7) The polymer product obtained in step (4) is first passed through a high-pressure separator to reduce the pressure to 140 MPa, then through a high-pressure separator to reduce the pressure to 25 MPa, and finally through a low-pressure separator to reduce the pressure to 0.8 MPa before entering the twin-screw extruder for extrusion. Then it enters the granulation system for underwater granulation and packaging to obtain high-pressure polyethylene products. The extrusion channel of the twin-screw extruder is divided into three temperature zones: 150~170℃, 170~190℃ and 190~210℃. The extruder head temperature control condition is 200~210℃.

[0138] Example 10

[0139] (1) The raw material ethylene with a purity of 99% is initially pressurized to 22-25 MPa by a booster press to obtain pressurized ethylene;

[0140] (2) Pressurized ethylene, molecular weight regulator (propylene), and polymerization catalyst (air) are introduced into a first-stage compressor and pressurized to 110–120 MPa, then into a second-stage compressor and pressurized to 240–250 MPa to obtain feed gas; wherein the feed volume ratio of propylene to pressurized ethylene is 4 × 10⁻⁶. -4 1. The feed volume ratio of air to pressurized ethylene is 8 × 10⁻⁶. -3 :1;

[0141] (3) The feed gas is introduced into a high-pressure autoclave reactor, and a polymerization reaction is carried out in the presence of an initiator (tert-butyl peroxide-2-ethylhexanoate and 4-tert-butylcyclohexyl peroxide dicarbonate, with a weight ratio of 2:1) to obtain a molten mixture and a gaseous material; wherein the polymerization reaction pressure is 250-260 MPa, the polymerization reaction temperature is 250-260 °C, and the feed volume ratio of initiator to feed gas is 9 × 10⁻⁶. -6 :1;

[0142] (4) The molten mixture obtained from the polymerization reaction in step (3) is introduced into a centrifuge for high-temperature centrifugation to obtain molten oligomers and high molecular weight polymer products (high-pressure polyethylene); wherein, the centrifugation temperature is 200℃, the centrifugation speed is 1100r / min, and the centrifugation time is 60min;

[0143] (5) The gaseous material obtained in step (3) is mixed with the raw material ethylene after high-pressure and medium-pressure circulation, and then enters the booster for pressurization; wherein the volume ratio of the gaseous material to the raw material ethylene is 4×10 -2 :1;

[0144] (6) The molten oligomer obtained in step (4) is returned to the high-pressure autoclave reactor via high-pressure circulation to participate in the polymerization reaction, wherein the volume ratio of the molten oligomer to the reactants in the high-pressure autoclave reactor is 0.4:1;

[0145] (7) The polymer product obtained in step (4) is first passed through a high-pressure separator to reduce the pressure to 140 MPa, then through a high-pressure separator to reduce the pressure to 25 MPa, and finally through a low-pressure separator to reduce the pressure to 0.8 MPa before entering the twin-screw extruder for extrusion. Then it enters the granulation system for underwater granulation and packaging. The extrusion channel of the twin-screw extruder is divided into three temperature zones: 150~170℃, 170~190℃ and 190~210℃. The extruder head temperature control condition is 200~210℃.

[0146] Comparative Example 1

[0147] The method of Example 1 is implemented, except that the molten mixture obtained in step (3) is not centrifuged, but is directly introduced into the extrusion system for extrusion.

[0148] The specific process is as follows:

[0149] (1) The raw material ethylene with a purity of 99% is initially pressurized to 22-25 MPa by a booster press to obtain pressurized ethylene;

[0150] (2) Pressurized ethylene, molecular weight regulator (propylene), and polymerization catalyst (air) are introduced into a first-stage compressor and pressurized to 110-120 MPa, then into a second-stage compressor and pressurized to 240-250 MPa to obtain feed gas; wherein the feed volume ratio of propylene to pressurized ethylene is 1×10 -4 1. The feed volume ratio of air to pressurized ethylene is 4 × 10⁻⁶. -3 :1;

[0151] (3) The raw material gas is introduced into a high-pressure autoclave reactor, and a polymerization reaction is carried out in the presence of an initiator (tert-butyl peroxide-2-ethylhexanoate and 4-tert-butylcyclohexyl peroxide dicarbonate, with a weight ratio of 5:1) to obtain a molten mixture and a gaseous material; wherein the polymerization reaction pressure is 250-260 MPa, the polymerization reaction temperature is 250-260 °C, and the feed volume ratio of initiator to raw material gas is 6 × 10⁻⁶. -6 :1;

[0152] (5) The gaseous material obtained in step (3) is mixed with the raw material ethylene after high-pressure and medium-pressure circulation, and then enters the booster for pressurization; wherein the volume ratio of the gaseous material to the raw material ethylene is 1×10 -2 :1;

[0153] (6) The molten mixture obtained in step (3) is first passed through a high-pressure separator to reduce the pressure to 140 MPa, then through a high-pressure separator to reduce the pressure to 25 MPa, and finally through a low-pressure separator to reduce the pressure to 0.8 MPa before entering the twin-screw extruder for extrusion. Then it enters the granulation system for underwater granulation and packaging to obtain polyethylene products. The extrusion channel of the twin-screw extruder is divided into three temperature zones: 150~170℃, 170~190℃ and 190~210℃. The extruder head temperature control condition is 200~210℃.

[0154] Test case

[0155] The performance of the polyethylene products prepared in the examples and comparative examples was tested, and the test results are shown in Table 1.

[0156] Melt flow index: Refer to ASTM D1238-13a standard;

[0157] Density: Refer to ASTM D1505;

[0158] Tensile strength: Refer to GB / T 8804.3-2003;

[0159] Elongation at break: Refer to GB / T8804.1-2003;

[0160] Molecular weight distribution: Refer to ASTM 6474-99 (2006).

[0161] Table 1

[0162]

[0163] As shown in Table 1, the method described in this invention can produce high-pressure polyethylene products with high tensile strength, high toughness, and excellent performance, which are suitable for the production of plastic products.

[0164] 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 method for preparing high-pressure polyethylene using centrifugation, characterized in that, The method includes: in the presence of an initiator, carrying out a polymerization reaction in a reactor with a feed gas containing ethylene, a molecular weight regulator and a polymerization catalyst, and then centrifuging the mixture obtained from the polymerization reaction at 170-200°C to obtain high-pressure polyethylene.

2. The method according to claim 1, characterized in that, The centrifugation speed is 900-1100 r / min, and the centrifugation time is 30-60 min.

3. The method according to claim 1 or 2, characterized in that, The molecular weight regulator is propylene, and the polymerization catalyst is air.

4. The method according to claim 1 or 2, characterized in that, The initiator is tert-butyl peroxide-2-ethylhexanoate and 4-tert-butylcyclohexyl peroxide. Preferably, the weight ratio of tert-butyl peroxide-2-ethylhexanoate to 4-tert-butylcyclohexyl peroxide is 2-5:

1.

5. The method according to any one of claims 1-4, characterized in that, The conditions for the polymerization reaction include a pressure of 250–260 MPa and a temperature of 250–260 °C.

6. The method according to claim 1, characterized in that, The raw material gas is prepared according to the following process: The raw material ethylene is pressurized to obtain pressurized ethylene; the pressurized ethylene, molecular weight regulator and polymerization catalyst are introduced into a compressor for compression to obtain raw material gas.

7. The method according to claim 6, characterized in that, The pressure of the pressurized ethylene is 22-25 MPa; Preferably, the compression includes primary compression and secondary compression, wherein the pressure after primary compression is 110-120 MPa, and the pressure after secondary compression is 240-250 MPa.

8. The method according to claim 6, characterized in that, The volume ratio of the molecular weight regulator to pressurized ethylene is 1×10. -4 -4×10 -4 :1; Preferably, the volume ratio of the polymerization catalyst to the pressurized ethylene is 4 × 10⁻⁶. -3 -8×10 -3 :

1.

9. The method according to claim 1 or 6, characterized in that, The volume ratio of initiator to feed gas is 6 × 10⁻⁶. -6 -9×10 -6 :1, more preferably 7×10 -6 -8×10 -6 :

1.

10. The method according to any one of claims 1-9, characterized in that, The method includes the following steps: (1) Pressurize the raw material ethylene to obtain pressurized ethylene; (2) Pressurized ethylene, molecular weight regulator and polymerization catalyst are introduced into the compressor for compression to obtain raw material gas; (3) In the presence of an initiator, the raw material gas obtained in step (2) is subjected to polymerization reaction in a high-pressure autoclave to obtain a mixture and gaseous material; (4) The mixture obtained from the polymerization reaction is introduced into a centrifuge and centrifuged at 170-200℃ to obtain molten oligomers and high-pressure polyethylene; (5) Return the gaseous material obtained in step (3) to step (1) for reuse; (6) The molten oligomer obtained in step (4) is returned to the autoclave reactor to participate in the polymerization reaction.

11. The method according to claim 10, characterized in that, The method further includes: introducing the high-pressure polyethylene obtained in step (3) into the extrusion system for extrusion, and then into the granulation system for granulation.

12. The method according to claim 11, characterized in that, The extrusion system is a twin-screw extruder, and the extrusion channel is divided into three temperature zones with temperatures of 150–170°C, 170–190°C, and 190–210°C, respectively. The extruder head temperature is 200–210°C.

13. High-pressure polyethylene prepared by the method of any one of claims 1-11.

14. The high-pressure polyethylene according to claim 12, characterized in that, The high-pressure polyethylene has a melt flow index of 17.0–19.8 g / 10 min and a density of 0.907–0.920 g / cm³. 3 The tensile strength is 10.3–12.9 MPa, the elongation at break is 170–310%, and the molecular weight distribution is 4.6–5.9.

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