Easily-processable ultra-high molecular weight polyethylene and preparation method thereof

Abstract

The invention relates to ultra-high molecular weight polyethylene easy for subsequent processing and application, which is high in bulk density, narrow in particle size distribution and good in flowability, and comprises two polyethylene components with different molecular weights, one is ultra-high molecular weight polyethylene (called U segment) with viscosity average molecular weight of 2 million-10 million g / mol, and the other is ultra-high molecular weight polyethylene (called U segment) with viscosity average molecular weight of 2 million-10 million g / mol. The other one is low-weight-average molecular weight polyethylene (called L segment) with the weight-average molecular weight of 10,000-50,000 g / mol, and the mass ratio of the U segment to the L segment is (1-50): 1. The preparation method comprises the following steps: by taking a supported polyethylene catalyst as a main catalyst, one or more of alkyl aluminum, halogenated alkyl aluminum or aluminoxane as a cocatalyst and an alkane solvent with a boiling point of 0-90 DEG C or a mixed alkane solvent with saturated vapor pressure of 4-200KPa at 20 DEG C as a polymerization solvent, firstly preparing an ultra-high molecular weight polyethylene component through homopolymerization or copolymerization; and continuously preparing a homopolymerized or copolymerized low-weight-average molecular weight polyethylene component to obtain the ultra-high molecular weight polyethylene disclosed by the invention. The method has the characteristics of flexible production mode, excellent product processability and the like.

Description

Technical Field

[0001] The present invention relates to a ultra-high molecular weight polyethylene with good processability and a preparation method thereof. More specifically, it relates to an easy-to-process powdered ultra-high molecular weight polyethylene and a preparation method thereof. The ultra-high molecular weight polyethylene simultaneously contains an ultra-high molecular weight polyethylene component and a low molecular weight polyethylene component. In the preparation method, an alkane or a mixed alkane is used as a polymerization solvent, a supported polyethylene catalyst is used as a main catalyst, and one or more of an alkyl aluminum, a halogenated alkyl aluminum, and an aluminoxane are used as a cocatalyst to prepare the ultra-high molecular weight polyethylene. Background Art

[0002] The properties of polyethylene mainly depend on its molecular weight and its structural composition distribution. The higher the molecular weight, the higher the mechanical properties and wear resistance of polyethylene. However, as the molecular weight increases, its processability will gradually deteriorate. Especially for ultra-high molecular weight polyethylene with a molecular weight exceeding 3 million g / mol, its processing and application are technical problems in this field.

[0003] Ultra-high molecular weight polyethylene (UHMWPE) generally refers to linear structure polyethylene with a relative molecular weight above 1.5 million g / mol, and has excellent wear resistance, extremely high impact strength, excellent self-lubricating performance, good chemical resistance and low temperature resistance, excellent anti-adhesion, hygienic, non-toxic, pollution-free, recyclable and other advantages that ordinary polyethylene does not have, and has been widely used in textile, papermaking, food, chemical industry, packaging, agriculture, construction, medical treatment, filter element of filtering equipment, sports, entertainment, military and other fields.

[0004] However, the high molecular weight of UHMWPE makes its processing and forming extremely difficult. When processed and melted, it is in a viscoelastic state, with extremely poor fluidity, and the melt flow rate is almost zero. When processed on a screw extruder, the material is difficult to advance along the screw groove, and is easy to block in the screw compression section, making it difficult to process. At the same time, the friction coefficient of UHMWPE is extremely low, and the material is easy to slip during the feeding process, making it difficult to feed; it is easy to occur melt fracture, and its critical shear rate is about 0.01 s -1 , and when extruding and forming, the extrusion rate cannot be too fast, otherwise melt fracture will occur and cracks will appear on the surface. When injection molding, due to the appearance of jet flow state, pores and delamination phenomena are caused, and its molding temperature range is narrow, and it is easy to oxidize and degrade.

[0005] Chinese Patent CN101654492A discloses a ultra-high molecular weight polyethylene. Due to its high molecular weight, the processability of this ultra-high molecular weight polyethylene is poor, and it can only be applied to wear-resistant products such as sintering method molding and extruding pipes at low speed, and its application range is small.

[0006] To overcome the processing difficulties of UHMWPE, the common practice is to improve the processing equipment and processes, such as using compression molding or a new type of plunger extruder for processing, or to enhance the processing performance of UHMWPE raw materials, such as chemically or physically modifying the raw materials, mixing high-density polyethylene, low-density polyethylene, polyamide, nylon, etc. into UHMWPE. As disclosed in US4281070A, JP60240748A, JP57177037A, US5019627A, CN107964163A, CN104884530A, CN102675715A, etc., the processing performance of UHMWPE can be significantly improved. However, the mechanical properties of the blend are much lower than those of the unblended UHMWPE. When applying UHMWPE with a higher viscosity-average molecular weight, a phase separation phenomenon occurs due to the huge molecular weight difference in the components, that is, the added blend preferentially migrates to the surface of the processed product.

[0007] Chinese Patent CN104884530A discloses a method for preparing easy-to-process ultra-high molecular weight polyethylene, which includes adding 66% to 80% by weight of entangled first ultra-high molecular weight polyethylene relative to the total mixture weight, 20 to 60% w / w of disentangled second ultra-high molecular weight polyethylene relative to the entangled first ultra-high molecular weight polyethylene, and a solvent to obtain a mixture. The weight-average molecular weight of the entangled first ultra-high molecular weight polyethylene is higher than 1 million g / mol, and the accumulated melt elastic modulus > 1.0 MPa. The weight-average molecular weight of the disentangled second ultra-high molecular weight polyethylene is at least 2 million g / mol, and the accumulated melt elastic modulus is at most 1.0 MPa. The weight ratio of the solvent ranges from 3% to 20% of the total mixture weight; the mixture is pressurized by melt mixing to obtain a synthesized easy-to-process ultra-high molecular weight polyethylene, and the synthesized ultra-high molecular weight polyethylene has improved processing performance in melt processing compared to the first ultra-high molecular weight polyethylene at a temperature substantially lower than its melting temperature. The solvent used in the mixing process is a high- or boiling-point solvent, such as the group consisting of decalin and paraffin, or the group consisting of acetone, isopropyl alcohol, methyl ethyl ketone, and any combination of the three.

[0008] Chinese Patents CN102219869A, CN102030844A, CN102219869A, etc. disclose the preparation of ultra-low-branched ultra-high molecular weight polyethylene using a specific supported non-metallocene polyolefin catalyst, which is characterized by having 1.8 ± 0.5 branches per 100,000 backbone carbon atoms. Although the extremely low degree of branching can improve the processing performance of UHMWPE, especially being effectively applicable to spinning applications, its improvement effect on aspects such as compression molding and extrusion processing is limited.

[0009] Chinese patents CN107936162A, CN107936163A, CN107936164A, CN107936161A, etc. disclose ultra-high molecular weight polyethylene, its manufacturing method and its applications. Its molecular chain has at least two segments, one of which is composed only of monomer units derived from ethylene (referred to as segment A), and the other is composed of monomer units derived from ethylene and monomer units derived from α-olefins (segment B1) or is composed only of monomer units derived from α-olefins (segment B2). It is in a non-hydrogen atmosphere. First, ethylene is homopolymerized, and then copolymerization of ethylene and α-olefins is carried out continuously. The copolymer ultra-high molecular weight polyethylene provided by the patent has significantly improved processing performance compared with the homopolymer ultra-high molecular weight polyethylene of the prior art. However, both segments are ultra-high molecular weight polyethylene with high molecular weight, and its processing performance is still relatively difficult.

[0010] Therefore, the current situation in this field is that there is still a hope to develop a high-viscosity average molecular weight ultra-high molecular weight polyethylene that is easy to process and apply, has excellent mechanical properties and processing performance, and does not require the addition of processing aids such as high-density polyethylene, low-density polyethylene, polyethylene wax, polyamide, nylon, etc. during the processing. Summary of the Invention

[0011] Based on the prior art, the inventors have conducted in-depth research and found that by using a supported polyethylene catalyst as the main catalyst, one or more of alkyl aluminum, halogenated alkyl aluminum or aluminoxane as the co-catalyst, and an alkane solvent with a boiling point of 0-90 °C or a mixed alkane solvent with a saturated vapor pressure of 4-200 KPa at 20 °C as the polymerization solvent, the ultra-high molecular weight polyethylene prepared can achieve the purpose of the present invention. More specifically, in the preparation method of the ultra-high molecular weight polyethylene of the present invention, under the polyethylene preparation conditions, first, an ultra-high molecular weight polyethylene component is prepared by homopolymerization or copolymerization, and then, on this basis, a homopolymer or copolymer low molecular weight polyethylene component is continuously prepared, thereby forming an in-situ molecular-level mixed ultra-high molecular weight polyethylene, which can solve the above-mentioned existing problems and thus complete the present invention.

[0012] Technical Effects

[0013] The present invention provides an ultra-high molecular weight polyethylene (UHMWPE) with high tensile modulus, elongation at break and Izod notched impact strength, adjustable and controllable density and melting point. The viscosity-average molecular weight of the ultra-high molecular weight polyethylene part in the composition is high, which is beneficial to improving the mechanical properties of the polymer. At the same time, the weight-average molecular weight of the low molecular weight polyethylene part is low, which is beneficial to improving the processing performance of the polymer. Therefore, the ultra-high molecular weight polyethylene of the present invention is easy to process and has excellent mechanical properties.

[0014] More specifically, the present invention provides powdered easy-to-process UHMWPE, which has a high bulk density, a narrow particle size distribution, good fluidity, and is easy to sinter and press into downstream products such as sheets, extrude pipes and profiles for processing applications.

[0015] Under comparable conditions, in extrusion processing applications, for the samples or products processed from the easy-to-process ultra-high molecular weight polyethylene provided by the present invention, compared with the samples or products processed from ultra-high molecular weight polyethylene with the same high viscosity-average molecular weight and added with the same mass of polyethylene wax processing aids, they have a faster extrusion processing rate.

[0016] In addition, through the polymerization method of the present invention, using an alkane solvent with a boiling point of 0-90°C or a mixed alkane solvent with a saturated vapor pressure of 4-200 KPa at 20°C as the polymerization solvent, the selection range of the polymerization solvent is wide, and there are many options for the heat removal method during the polymerization reaction process and the post-treatment method of the obtained polyethylene slurry, and it is easy to carry out.

[0017] Moreover, the present invention uses a supported polyethylene catalyst, especially a supported non-metallocene catalyst, to complete the sequential polymerization preparation of two components. At the same time, according to the performance of different supported polyethylene catalysts, different main catalyst combinations can also be used to sequentially prepare high viscosity-average molecular weight polyethylene components and low weight molecular weight polyethylene components, and the production method is more flexible. Description of the Drawings

[0018] Figure 1 Particle size distribution curve of UHMWPE-1 prepared in Example 1. Detailed Description of the Invention

[0019] The following provides a detailed description of the specific embodiments of the present invention. However, it should be noted that the protection scope of the present invention is not limited by these specific embodiments, but is determined by the appended claims.

[0020] In the context of the present invention, unless otherwise clearly defined or the meaning exceeds the understanding of those skilled in the art, hydrocarbon or hydrocarbon derivative groups with more than 3 carbon atoms (such as propyl, propoxy, butyl, butane, butene, butenyl, hexane, etc.) have the same meaning as when prefixed with the word "n-" when not prefixed with the word "n-". For example, propyl is generally understood as n-propyl, and butyl is generally understood as n-butyl, unless otherwise clearly stated.

[0021] In the context of the present invention, unless otherwise clearly stated, the molecular weight of the ultra-high molecular weight polyethylene (UHMWPE), unless otherwise specified, generally refers to the viscosity-average molecular weight, and its unit is 10,000 g / mol, or 10,000 grams / mole, or 10,000, all regarded as the same molecular weight unit.

[0022] In this specification, to avoid complex expressions, the valence states of individual substituents or groups of the compounds, such as whether they are monovalent, divalent, trivalent or tetravalent, are not explicitly defined. Those skilled in the art can specifically determine based on the positions of these substituents or groups (such as the groups G, D, B, A, and F described or defined in this specification) in the structural formula of the corresponding compound or the substitution situations they exhibit, and select from the definitions given in this specification for these substituents or groups the definitions suitable for the valence states at these positions or substitution situations.

[0023] All publications, patent applications, patents and other references mentioned in this specification are hereby incorporated by reference in their entirety. Unless otherwise defined, all technical and scientific terms used in this specification have the meanings commonly understood by those skilled in the art. In case of conflict, the definitions in this specification shall prevail.

[0024] When this specification uses prefixes such as "known to those skilled in the art", "prior art" or similar terms to introduce materials, substances, methods, steps, devices or components, etc., the objects introduced by these prefixes cover those commonly used in the art at the time when this application is filed, but also include those that are not commonly used at present but will become recognized by the art as suitable for similar purposes.

[0025] In the context of this specification, except for the explicitly stated content, any matters or things not mentioned directly apply to those known in the art without any changes. Moreover, any implementation manner described herein can be freely combined with one or more other implementation manners described herein, and the technical solutions or technical ideas formed thereby shall be regarded as part of the original disclosure or original record of the present invention, and shall not be regarded as new content not disclosed or anticipated herein, unless those skilled in the art consider that the combination is obviously unreasonable.

[0026] Unless otherwise clearly specified, all percentages, parts, ratios, etc. mentioned in this specification are based on weight, unless it does not conform to the common understanding of those skilled in the art when based on weight.

[0027] The following provides a detailed description of the specific implementation manners of the present invention. However, it should be noted that the protection scope of the present invention is not limited by these specific implementation manners, but is determined by the appended claims.

[0028] In the context of the present invention, unless otherwise specifically stated, the physical property values of substances (such as boiling point) are measured values at normal temperature (25°C) and normal pressure (101325 Pa).

[0029] In the present invention, polyethylene is sometimes also referred to as ethylene polymer, including the cases of ethylene homopolymerization and copolymerization of ethylene with comonomers.

[0030] Specifically, the present invention provides an easy-to-process UHMWPE with a bulk density of 0.30 - 0.55 g / cm 3 , preferably 0.33 - 0.50 g / cm 3 , a true density of 0.926 - 0.955 g / cm 3 , preferably 0.930 - 0.950 g / cm 3 , an average particle size of 50 - 2000 μm, preferably 150 - 1000 μm, a melting point of 125 - 137 °C, preferably 128 - 135 °C, a tensile modulus greater than 200 MPa, preferably greater than 220 MPa, more preferably greater than 250 MPa, an elongation at break greater than 500%, preferably greater than 550%, more preferably greater than 600%, and a Charpy notched impact strength greater than 90 KJ / m 2 , preferably greater than 100 KJ / m 2 , more preferably greater than 105 KJ / m 2 , which comprises two polyethylene components, one is ultra-high molecular weight polyethylene with a viscosity-average molecular weight of 2 million - 10 million g / mol (in the present invention, sometimes also referred to as the U segment), preferably with a viscosity-average molecular weight of 2.5 million - 7 million g / mol, preferably 3 million - 5 million g / mol, and the other is low-weight molecular weight polyethylene with a weight-average molecular weight of 10,000 - 50,000 g / mol, preferably 15,000 - 45,000 g / mol, more preferably 20,000 - 40,000 g / mol (in the present invention, sometimes also referred to as the L segment), and the mass ratio of the U segment to the L segment is 1 - 50:1, preferably 3 - 20:1.

[0031] In one embodiment of the present invention, the U segment and the L segment are ethylene homopolymers or copolymers of ethylene and comonomers. Specifically, it can be a combination of an ethylene homopolymer U segment and an ethylene homopolymer L segment, a combination of a copolymer of ethylene and an α-olefin U segment and an ethylene homopolymer L segment, a combination of an ethylene homopolymer U segment and a copolymer of ethylene and a comonomer L segment, and a combination of a copolymer of ethylene and a comonomer U segment and a copolymer of ethylene and a comonomer L segment.

[0032] In one embodiment of the present invention, the comonomer is selected from C3 - C 10 α-olefins, preferably selected from one or more of propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene, and preferably selected from one or more of 1-butene, 1-octene, and 1-hexene.

[0033] In one embodiment of the present invention, the comonomer insertion rate of the U segment is 0 - 1.0 mol%, preferably 0.1 - 0.8 mol%, or 0.2 - 0.6 mol%, or 0.2 - 0.5 mol%.

[0034] In one embodiment of the present invention, the insertion rate of the L-section comonomer is 0-10 mol%, preferably 1.5-8.0 mol%, or 3.0-6.0 mol%, or 3.5-5.5 mol%.

[0035] The present invention also provides a method for polymerizing and preparing easy-to-process UHMWPE. Among them, a supported polyethylene catalyst is used as the main catalyst, preferably a supported non-metallocene catalyst as the main catalyst, and one or more of alkyl aluminum, halogenated alkyl aluminum or aluminoxane are used as the cocatalyst, preferably alkyl aluminum as the cocatalyst, and an alkane solvent with a boiling point of 0-90 °C or a mixed alkane solvent with a saturated vapor pressure of 4-200 KPa at 20 °C is used as the polymerization solvent, preferably an alkane solvent selected from those with a boiling point of 5-55 °C or a mixed alkane solvent with a saturated vapor pressure of 20-150 KPa at 20 °C is used as the polymerization solvent. Among them,

[0036] At a polymerization pressure of 0.5-4.5 MPa, preferably 1.0-3.0 MPa, and a polymerization temperature of 40-80 °C, preferably 50-75 °C, ethylene homopolymerization or copolymerization of ethylene with a comonomer is carried out to prepare the U-section. Then,

[0037] On the basis of the prepared U-section, at a polymerization pressure of 1.0-4.5 MPa, preferably 2.0-3.5 MPa, and a polymerization temperature of 70-95 °C, preferably 78-90 °C, continuous polymerization is carried out to prepare the L-section. Among them, ethylene homopolymerization or copolymerization of ethylene with a comonomer is carried out in the presence of hydrogen.

[0038] In one embodiment of the present invention, in the polymerization reaction for preparing the L-section, the main catalyst and / or cocatalyst are not supplemented and added.

[0039] In one embodiment of the present invention, in the polymerization reaction for preparing the L-section, the main catalyst and / or cocatalyst are supplemented and added; at this time, the supplemented main catalyst and / or cocatalyst may be the same as or different from the main catalyst and / or cocatalyst in the polymerization reaction for preparing the U-section.

[0040] In one embodiment of the present invention, the polymerization preparation method of the UHMWPE of the present invention is carried out by a batch kettle method, and the batch method can be carried out according to the known batch methods in the polyethylene field. In one embodiment of the present invention, after the polymerization reaction for preparing the U-section, the polymerization reaction for continuously preparing the L-section is carried out in the reaction kettle according to the conditions for preparing the L-section described in the present invention. That is, in this method, after the U-section is prepared, the polymerization reaction for preparing the L-section can continue in this reaction kettle.

[0041] In one embodiment of the present invention, the polymerization preparation method of the UHMWPE of the present invention is carried out by a batch continuous method, and the continuous method can be carried out in a continuous manner known in the field of polyethylene. In one embodiment of the present invention, after the polymerization reaction for preparing the U section, the reacted slurry material is transferred according to the existing well-known technology. For example, it enters a material buffer tank connected to the previous reaction kettle in a gas-connected equilibrium manner in an overflow manner to achieve gas-liquid separation, and at least part of the slurry stream in the material buffer tank is continuously transported and transferred to the next reaction kettle by a pump, or at least part of the reacted slurry material is directly continuously transported and transferred to the next reaction kettle by a pump at the lower part or bottom of the previous reaction kettle, and the polymerization reaction for preparing the L section is continued in the next reaction kettle.

[0042] In the preparation method of the present invention, since the reaction conditions for the polymerization reaction for preparing the U section and the polymerization reaction for preparing the L section are different, especially the gas phase conditions are different. For example, the polymerization raw materials in the polymerization reaction for the U section and the polymerization reaction for the L section are different. Therefore, the gas phase components are adjusted as needed after the polymerization reaction for the U section and before the polymerization reaction for the L section. The adjustment method for the gas phase components can be carried out in a conventional manner in the art. For example, in the batch polymerization method, after the polymerization reaction for the U section, at least a part of the gas phase in the reaction kettle is discharged, and then the gas phase for the L section polymerization reaction is introduced to carry out the polymerization reaction for the L section; or in the continuous polymerization method, the slurry material of the U section is introduced into a buffer tank, and then the slurry material is introduced into the reaction kettle of the L section from the lower part or bottom of the buffer tank, and then the gas phase for the L section polymerization reaction is introduced to carry out the polymerization reaction for the L section; or in the continuous polymerization method, the slurry material of the U section is introduced from the bottom of the reaction kettle of the U section polymerization reaction into the reaction kettle of the L section, and then the gas phase for the L section polymerization reaction is introduced to carry out the polymerization reaction for the L section.

[0043] In one embodiment of the present invention, if the batch method is used for the preparation method of the present invention, in order to realize the polymerization process for preparing the L section described in the present invention, optionally, part of the gas in the reaction kettle is discharged to reduce the pressure in the kettle, or it can also not be discharged as long as the polymerization conditions for preparing the L section described in the present invention can be implemented. Then, according to the present invention, optionally, the main catalyst and / or cocatalyst are added again, or it is not necessary to add them. Preferably, the main catalyst and cocatalyst are not added. According to the composition of the polymerization gas phase components for the polymerization reaction for preparing the L section, hydrogen and the required comonomer are added at one time, and then ethylene is continuously introduced, and the polymerization temperature and pressure are adjusted to continue the preparation of the L section. Monitor the progress of the polymerization reaction for the L section. In the present invention, the actual ethylene consumption of each section is displayed by the ethylene mass flowmeter for polymerizing and preparing the U section and the L section to control the quality of the U section and the L section. After the mass ratio of the U section and the L section reaches the mass ratio of the present invention, the addition of ethylene can be stopped to complete the polymerization preparation.

[0044] In one embodiment of the present invention, in the batch process, when preparing the polymerization reaction of the L stage after the polymerization reaction of the U stage, no cocatalyst is added.

[0045] In one embodiment of the present invention, in the batch process, when preparing the polymerization reaction of the L stage after the polymerization reaction of the U stage, no main catalyst is added.

[0046] In one embodiment of the present invention, in the batch process, when preparing the polymerization reaction of the L stage after the polymerization reaction of the U stage, a cocatalyst is added, and the type of the added cocatalyst may be the same as or different from the cocatalyst in the polymerization reaction of the U stage.

[0047] In one embodiment of the present invention, in the batch process, when preparing the polymerization reaction of the L stage after the polymerization reaction of the U stage, no main catalyst is added, and the type of the added main catalyst may be the same as or different from the main catalyst in the polymerization reaction of the U stage.

[0048] In one embodiment of the present invention, if the preparation method of the present invention is carried out by a continuous kettle method, the U stage is continuously polymerized and prepared in the first kettle. At this time, the main catalyst, cocatalyst, solvent and ethylene are continuously added to carry out the polymerization reaction for preparing the U stage to obtain a slurry material. At least part of the slurry material is continuously discharged into the slurry material buffer tank by pumping or by overflow. The gas phase at the top of the slurry material buffer tank is connected to the first reaction kettle, so that the pressure and gas phase composition are the same as those of the first reaction kettle. Then, the slurry material is continuously pumped from the lower part or bottom of the buffer tank into the second reaction kettle to continuously carry out the polymerization reaction for preparing the L stage. Among them, the total volume of the slurry in the first kettle divided by the volume of the part of the slurry material entering the slurry material buffer tank is the average residence time of the first kettle. Under the condition that the overflow mode and stirring speed remain unchanged, the total volume of the slurry in the first kettle is relatively fixed. By controlling the continuous addition amounts of the solvent and ethylene in the first kettle, the overflow slurry discharge amount is further regulated, and thus the average residence time can be controlled. The L stage is continuously polymerized in the second kettle according to the preparation conditions described in the present invention. Similarly, the main catalyst and / or cocatalyst may be added again, or may not be added. Preferably, no main catalyst and cocatalyst are added. Under stable polymerization conditions, the real-time ethylene consumption in the two kettles is the mass ratio of the two-stage components. The mass ratio of the U stage and the L stage can be adjusted and controlled mainly by the average residence times of the two stages, supplemented by adjusting the polymerization pressures of the two stages, or by adjusting the continuous addition amounts of the main catalyst and cocatalyst in the first kettle under the condition of a fixed ratio.

[0049] In one embodiment of the present invention, in the continuous process, when preparing the polymerization reaction of the L stage after the polymerization reaction of the U stage, no cocatalyst is added.

[0050] In one embodiment of the present invention, in the continuous process, when preparing the polymerization reaction of the L section after the polymerization reaction of the U section, the main catalyst is not replenished.

[0051] In one embodiment of the present invention, in the continuous process, when preparing the polymerization reaction of the L section after the polymerization reaction of the U section, a cocatalyst is replenished, and the type of the replenished cocatalyst may be the same as or different from the cocatalyst in the polymerization reaction of the U section.

[0052] In one embodiment of the present invention, in the continuous process, when preparing the polymerization reaction of the L section after the polymerization reaction of the U section, the main catalyst is not replenished, and the type of the replenished main catalyst may be the same as or different from the main catalyst in the polymerization reaction of the U section.

[0053] In the present invention, after the polymerization reaction of the L section is completed, the slurry material enters the slurry and solvent separation section. For example, but not limited to, a centrifuge or a filter press can be used for solid-liquid separation of the free solvent and the wet material containing part of the solvent, and then it enters the dryer to complete the drying of the material, and then enters the bin for blending, degassing, VOCs removal and other treatments, and finally is packaged. The dryer can be, for example but not limited to, an existing drum dryer or a hot nitrogen gas fluidized bed dryer.

[0054] In one embodiment of the present invention, part of steam or nitrogen containing trace steam can be replenished on the pipeline before entering the dryer after solid-liquid separation to inactivate the main catalyst and the cocatalyst.

[0055] According to the present invention, the supported polyethylene catalyst as the main catalyst can be a supported catalyst commonly used in the field for catalyzing ethylene polymerization. For example, it can be a non-metallocene catalyst, a metallocene catalyst, a Ziegler-Natta catalyst, or a composite or composition thereof. Preferably, it is a non-metallocene catalyst and a metallocene catalyst, and most preferably a non-metallocene catalyst.

[0056] The main catalyst added to the reaction kettle can be a solid powder or granule, or can be made into a dispersion with a certain concentration with a polymerization reaction solvent. In this case, generally speaking, the ratio of the main catalyst to the polymerization solvent is 0.001 - 0.500 mmol of polyethylene main catalyst / L of polymerization solvent.

[0057] According to the present invention, considering the existing supported polyethylene catalysts, not all catalysts have the comprehensive function of simultaneously preparing the U section and the L section. Therefore, in one embodiment of the present invention, the same main catalyst can be used for preparing the U section and the L section, which has the function of preparing both the U section and the L section. This catalyst can be added separately when preparing the two sections, or only added when preparing the U section, and preferably only added when preparing the U section.

[0058] In one embodiment of the present invention, two main catalysts can be used. Among them, one main catalyst A has the function of polymerizing to prepare the U section, and the other main catalyst B has the function of polymerizing to prepare the L section. Main catalyst A is added when preparing the U section, and main catalyst B is added when subsequently preparing the L section. At this time, those skilled in the art can select main catalyst A that can prepare the U section with a high viscosity average molecular weight and main catalyst B that can prepare the L section with a low weight average molecular weight. As described above, in one embodiment of the present invention, the same main catalyst can be used to prepare the U section and the L section, which has both the functions of preparing the U section and the L section. This catalyst can be added separately during the preparation of the two sections, or only added during the preparation of the U section, and it is preferably added only during the preparation of the U section.

[0059] As the polyethylene main catalyst, it can be selected from Ziegler-Natta type catalysts supported on a carrier, such as the Ziegler-Natta type catalysts involved in invention patents CN201010522112.5, CN201010240355.X, CN201010502803.9, CN201010511310.1, CN200710121105.2, CN201010502778.4, CN201010502717.8, CN201010240379.5, CN201110148492.5, CN201110148493.X, CN201110148527.5, CN201110148545.3, CN201110306102.2, CN201010240378.0, CN200410086382.0, CN98101108.X, CN200410078280.4, CN200910088546.6, etc. For example, the CM, CMU, BCC, BCH, BCE, BCG, BCS and other series of catalysts of the existing Beijing Aoda Branch of Sinopec Catalyst Co., Ltd. As the Ziegler-Natta type catalyst, CMU is preferably used as the main catalyst for polymerizing to prepare the U section, and BCE is preferably used as the main catalyst for polymerizing to prepare the L section.

[0060] As the polyethylene main catalyst, it can be selected from supported metallocene catalysts, as long as it is a catalyst containing a metallocene catalyst. It can be a single-component metallocene catalyst or a composite catalyst of a metallocene catalyst and other catalysts. Specifically, supported Ziegler-Natta and metallocene composite catalysts, supported double or multi-metallocene catalysts, etc. can be listed.

[0061] More specifically, as the main catalyst for polyethylene, it can be selected from supported metallocene catalysts, such as those described in invention patents CN201110247347.2, CN201110080343.X, CN201010518904.5, CN201010519660.2, CN201210289014.0, CN200910078596.6, CN201310090758.4, CN201310090736.8, 201310521768.9, CN201410589467.4, CN201410590067.5, CN201610835700.1, CN201610944191.6, CN201710959423.X, CN201110247349.1, CN201110080294.X, CN201110080395.7, CN201210289017.4, CN201210289031.4, CN201310091192.7, CN201310540973.X, CN201510724626.1, CN200410086283.2, CN200610137777.8, CN201610944182.7, CN201710312720.5, CN201110080422.0, CN201110080422.0, CN201110080394.2, CN201010519406.2, CN201010519715.X, CN201010519174.0, CN201010519429.3, CN201210289004.7, CN201310090847.9, CN201310091209.9, CN201310540975.9, CN201410554709.6, CN201410513506.2, CN00130388.0, CN200710176589.0, CN201610944083.9, CN201110246705.8, CN201110247085.X, CN2011102914899, CN201010521674.8, CN201310090752.7, CN201310090848.3, CN2013100908483, CN201510624502.6, CN201710166709.2, CN20171031225.2, CN201110246710.9, CN201110080374.5, CN201010519797.8, CN201210289012.1, CN201210418645.8. Supported metallocene catalysts involved in CN201310090998.4, CN201410252254.2, CN201610393399.3, CN201610956141.X, CN201710958837.0, etc., as well as type 101 and 201 supported metallocene catalysts of Grace Davison Company and XCAT type metallocene catalysts of Univation Company.

[0062] As the metallocene catalyst, a supported metallocene catalyst is preferred, and a supported single-component metallocene catalyst is more preferred.

[0063] Among them, the metallocene ligand and metallocene complex structure in the metallocene catalyst can be selected from homoleptic bis-metallocene structures, heteroleptic bis-metallocene structures, chiral metallocene structures, mono / di / multi-bridged, mono-metallocene, constrained geometry mono-metallocene or bis-metallocene, bridged heteroleptic metallocene, cationic types, etc.

[0064] The active metal in the polyethylene main catalyst can be an active metal commonly used in the art. For example, it can be selected from Group IVB elements such as titanium, zirconium or hafnium; Group VB elements such as vanadium; Group VIII elements such as iron, cobalt, nickel, palladium, etc. Group IVB metal elements are preferred, and titanium metal elements are most preferred.

[0065] In one embodiment of the present invention, the present invention preferably uses a supported polyethylene catalyst with specific structure and performance as the main catalyst, such as a supported non-metallocene catalyst, which simultaneously has the polymerization reaction for preparing the U section in the optional presence of a comonomer, and the polymerization reaction for continuously preparing the L section in the presence of hydrogen and in the optional presence of a comonomer.

[0066] Specifically, as a supported non-metallocene catalyst, such as those in invention patents CN200310106156.X, CN200310106157.4, CN200410066068.6, CN200510119401.X, CN200610107651.6, CN200710162677.5, CN200710162667.1, CN200710162672.2, CN200710162675.6, CN200710162676.0, CN200710162666.7, CN200910180100.6, CN200910180607.1, CN200910180601.4, CN200910180606.7, CN200910180602.9, CN200910180605.2, CN200910180603.3, CN200910180604.8, CN200910210988.3, CN200910210984.5, CN200910210989.8, CN200910210986.4, CN200910210985.X, CN200910210990.0, CN200910210987.9, CN200910210991.5, CN201010286008.0, CN201010286012.7, CN201010284870.8, CN201010285982.5, CN201010284856.8, CN201010285970.2, CN201010285956.2, CN201010285969.X, CN201010285958.1, CN201010285967.0, CN201010285994.8, CN201110259336.6, CN201110259219.X, CN201110259330.9, CN201110259327.7, CN201110259367.1, CN201110259289.5, CN201110259359.7, CN201110259282.3, CN201110259318.8, CN201110259258.X, CN201110259300.8, CN201110259254.1, CN001110259299.9, CN201110259245.2, CN201110259296.5, CN201110259338.5, CN201110259370.3, CN201110259339.X, CN201110259293.1. Supported non-metallocene catalysts involved in CN201110259356.3, CN201210063756.1, CN201210063777.3, CN201210063788.1, CN201210063818.9, CN201210063824.4, CN201210063843.7, CN201210063854.5, CN201210063876.1, CN201210063878.0, CN201210063891.6, CN201210063894.X, CN201210063907.3, CN201210063909.2, CN201210063935.5, CN201210063941.0, CN201210063945.9, CN201310189677.X, CN201310227368.7, CN201310227370.4, CN201310227830.3, CN201310227393.5, CN201310452714.1, CN201710814678.7, CN201710814595.8, CN201710814594.3, CN201710814593.9, CN201710814592.4, CN201710814591.X, CN201811144599.0, CN201811144768.0, CN201811139936.7, CN201811140811.6, CN201811139946.0, CN201811139741.2, CN201310091208.4, etc.

[0067] According to the present invention, the term "non-metallocene catalyst" is a single-site olefin polymerization catalyst relative to metallocene catalysts, which does not contain cyclopentadienyl or its derivatives such as metallocene rings, fluorene rings or indene rings in its structure, and is an organometallic compound that can exhibit olefin polymerization catalytic activity when combined with a co-catalyst (such as those described below) (therefore, the non-metallocene catalyst is sometimes also referred to as a non-metallocene complex or a non-metallocene olefin polymerization complex). The compound contains a central metal atom and at least one polydentate ligand (preferably a tridentate ligand or a ligand with more teeth) coordinated to the central metal atom, and the term "non-metallocene ligand" refers to the aforementioned polydentate ligand.

[0068] The non-metallocene catalyst described in the present invention is a supported non-metallocene catalyst, and its active metal element is selected from Group IVB metal elements, preferably titanium metal element. The carrier is selected from one or more of magnesium compounds such as magnesium halide, alkoxy magnesium halide, alkoxy magnesium, alkyl magnesium, alkyl magnesium halide and alkyl alkoxy magnesium, and porous carriers, preferably one or more of magnesium chloride and silica gel. Preferably, the non-metallocene catalyst is selected from one or more of the compounds having the following chemical structural formula:

[0069]

[0070] Based on the total aluminum element in aluminoxane, alkyl aluminum, and halogenated alkyl aluminum in the cocatalyst and the active metal element in the main catalyst, the molar ratio of aluminum to the active metal is 10 - 500:1, preferably 20 - 100:1.

[0071] In one embodiment of the present invention, during the preparation of the U section, in the polymerization gas phase components, the molar content of hydrogen is 0 - 500 ppm, preferably 0 - 200 ppm, and the molar content of the comonomer is 0 - 3.0 mol%, preferably 0.3 - 2.0 mol%, or 0.5 - 1.5 mol%.

[0072] In one embodiment of the present invention, during the preparation of the U section, in the polymerization gas phase components, the content of hydrogen is 0 - 500 ppm, preferably 0 - 200 ppm.

[0073] In one embodiment of the present invention, during the preparation of the L section, in the polymerization gas phase components, the molar content of the comonomer is 0 - 20 mol%, preferably 2.0 - 10 mol%, or 2.5 - 6.0 mol%.

[0074] In one embodiment of the present invention, during the preparation of the L section, in the polymerization gas phase components, the molar content of hydrogen is 30 - 90 mol%, preferably 50 - 85 mol%.

[0075] In one embodiment of the present invention, as the alkane solvent with a boiling point of 0 - 90 °C (preferably 5 - 55 °C), for example, 2,2-dimethylpropane (also known as neopentane, boiling point 9.5 °C, saturated vapor pressure at 20 °C is 146.63 KPa), 2-methylbutane (also known as isopentane, boiling point 27.83 °C, saturated vapor pressure at 20 °C is 76.7 KPa), n-pentane (boiling point 36.1 °C, saturated vapor pressure at 20 °C is 56.5 KPa), cyclopentane (boiling point 49.26 °C, saturated vapor pressure at 20 °C is 34.6 KPa) can be cited. Preferably, the alkane solvent has a boiling point of 25 - 50 °C.

[0076] In one embodiment of the present invention, as the mixed alkane having a saturated vapor pressure of 4 - 200 KPa (preferably 20 - 150 KPa) at 20 °C, more preferably a mixed alkane having a saturated vapor pressure of 40 - 110 KPa at 20 °C, it is a mixed solvent formed by mixing different alkane solvents in proportion, such as a mixed solvent formed by hexane and its isomers, pentane and its isomers solvents, and can also be an alkane mixture obtained by fractionation and extraction from a solvent rectification device. It is preferably a mixed solvent of pentane and its isomers solvents. Specifically, combinations such as n-pentane and isopentane, isopentane and neopentane, n-pentane and cyclopentane, n-pentane and neopentane, isopentane and cyclopentane, neopentane and cyclopentane, n-hexane and cyclopentane, n-hexane and n-pentane, n-pentane - isopentane - cyclopentane, n-pentane - n-hexane - isopentane, etc. can be listed. However, it is not limited thereto. As long as it is a mixed alkane having a saturated vapor pressure of 4 - 200 KPa (preferably 20 - 150 KPa, more preferably 40 - 110 KPa) at 20 °C.

[0077] In one embodiment of the present invention, as the mixed alkane having a saturated vapor pressure of 4 - 200 KPa (preferably 20 - 150 KPa, more preferably 40 - 110 KPa) at 20 °C, it is preferably a mixed alkane having a saturated vapor pressure of 20 - 150 KPa (preferably 40 - 110 KPa) at 20 °C formed by mixing two or more alkanes selected from n-pentane, isopentane, neopentane, and cyclopentane, and more preferably combinations such as n-pentane and isopentane, isopentane and neopentane, n-pentane and cyclopentane, isopentane and cyclopentane, neopentane and cyclopentane, n-pentane - isopentane - cyclopentane, neopentane - isopentane - n-pentane, etc. The proportion of each alkane in the mixed alkane is appropriately selected so that its saturated vapor pressure at 20 °C meets the scope of the present invention. For example, when two alkane solvents are mixed, their molar ratio can be 0.01 - 100:1, preferably 0.1 - 10:1; when three alkane solvents are mixed, their molar ratio can be 0.01 - 100:0.01 - 100:1, preferably 0.1 - 10:0.1 - 10:1. As long as the resulting mixed alkane solvent has a saturated vapor pressure of 4 - 200 KPa (preferably 20 - 150 KPa, more preferably 40 - 110 KPa) at 20 °C.

[0078] According to the present invention, the amount of the supported polyethylene main catalyst can adopt the catalyst amounts commonly used in the art, and its main usage principle is determined based on the ethylene slurry polymerization activity of the catalyst. A low amount of the polyethylene main catalyst is used under high ethylene slurry polymerization activity, and a higher amount of the polyethylene main catalyst is used under low ethylene slurry polymerization activity, so as to achieve the concentration of the slurry meeting the requirements of the present invention.

[0079] It should be noted that in the present invention, unless otherwise specified, the molar amount of the polyethylene main catalyst is based on the active metal element in the polyethylene main catalyst.

[0080] According to the present invention, the cocatalyst is selected from one or more of aluminoxane, alkylaluminum, and haloalkylaluminum, or a mixture thereof.

[0081] Among them, as the aluminoxane serving as the cocatalyst, for example, linear aluminoxane represented by the following general formula (I) can be cited: (R)(R)Al-(Al(R)-O) n -O-Al(R)(R), and cyclic aluminoxane represented by the following general formula (II): -(Al(R)-O-) n+2 -.

[0082]

[0083] In the above general formulas (I) and (II), the groups R are the same as or different from each other (preferably the same), and each independently selected from C1-C8 alkyl groups, preferably methyl, ethyl, propyl, butyl, and isobutyl, most preferably methyl and isobutyl; n is any integer in the range of 1-50, preferably any integer in the range of 10-30.

[0084] As the aluminoxane, methylaluminoxane, ethylaluminoxane, isobutylaluminoxane, and n-butylaluminoxane are preferred, and methylaluminoxane and isobutylaluminoxane are further preferred.

[0085] These aluminoxanes can be used alone or in combination of multiple kinds in any proportion.

[0086] As the alkylaluminum, for example, compounds represented by the following general formula can be cited:

[0087] Al(R)3

[0088] Among them, the groups R are the same as or different from each other (preferably the same), and each independently selected from C1-C8 alkyl groups, preferably methyl, ethyl, propyl, butyl, and isobutyl, most preferably methyl and isobutyl.

[0089] Specifically, as the alkylaluminum, for example, trimethylaluminum (Al(CH3)3), triethylaluminum (Al(CH3CH2)3), tri-n-propylaluminum (Al(C3H7)3), triisopropylaluminum (Al(i-C3H7)3), triisobutylaluminum (Al(i-C4H9)3), tri-n-butylaluminum (Al(C4H9)3), triisopentylaluminum (Al(i-C5H 11 )3), tri-n-pentylaluminum (Al(C5H 11 )3), tri-n-hexylaluminum (Al(C6H 13)3), triisobutylaluminum (Al(i-C6H 13 )3), diethylmethylaluminum (Al(CH3)(CH3CH2)2), and dimethylethylaluminum ((Al(CH3CH2)(CH3)2), etc. Among them, trimethylaluminum, triethylaluminum, tripropylaluminum, and triisobutylaluminum are preferred, and triethylaluminum and triisobutylaluminum are most preferred.

[0090] These alkylaluminums can be used alone or in combination of multiple kinds in any proportion.

[0091] As the haloalkylaluminum, for example, compounds represented by the following general formula can be cited:

[0092] Al(R) n X 3-n

[0093] Among them, the groups R are the same or different from each other (preferably the same), and each independently selected from C1-C8 alkyl groups, preferably methyl, ethyl, propyl, butyl, and isobutyl, most preferably methyl and isobutyl; X represents fluorine, chlorine, bromine, iodine; n represents 1 or 2.

[0094] Specifically, as the haloalkylaluminum, for example, dimethylaluminum chloride (Al(CH3)2Cl), methylaluminum dichloride (Al(CH3)Cl2)), diethylaluminum chloride (Al(CH3CH2)2Cl), ethylaluminum dichloride (Al(CH3CH2)Cl2), dipropylaluminum chloride (Al(C3H7)2Cl), propylaluminum dichloride (Al(C3H7)Cl2)), dibutylaluminum chloride (Al(C4H9)2Cl), butylaluminum dichloride (Al(C4H9)Cl2), diisobutylaluminum chloride (Al(i-C4H9)2Cl), isobutylaluminum dichloride (Al(i-C4H9)Cl2), dipentylaluminum chloride (Al(C5H 11 )2Cl), pentylaluminum dichloride (Al(C5H 11 )Cl2), diisopentylaluminum chloride (Al(i-C5H 11 )2Cl), isopentylaluminum dichloride (Al(i-C5H 11 )Cl2), dihexylaluminum chloride (Al(C6H 13 )2Cl), hexylaluminum dichloride (Al(C6H 13 )Cl2), diisohexylaluminum chloride (Al(i-C6H 13 )2Cl), isohexylaluminum dichloride (Al(i-C6H 13)Cl2), aluminum monochloromethyl ethyl (Al(CH3)(CH3CH2)Cl), aluminum monochloromethyl propyl (Al(CH3)(C3H7)Cl), aluminum monochloromethyl n-butyl (Al(CH3)(C4H9)Cl), aluminum monochloromethyl isobutyl (Al(CH3)(i-C4H9)Cl), aluminum chloroethyl propyl (Al(CH2CH3)(C3H7)Cl), aluminum chloroethyl n-butyl (AlCH2CH3)(C4H9)Cl), aluminum chloroethyl isobutyl (Al(CH2CH3)(i-C4H9)Cl), etc. Among them, aluminum dichloroethyl, dichloroethyl aluminum, aluminum monochloro di-n-butyl, dichloro n-butyl aluminum, aluminum monochloro di-isobutyl, dichloro isobutyl aluminum, aluminum monochloro di-n-hexyl, dichloro n-hexyl aluminum are preferred. Further preferred are chloroethyl aluminum dichloride, dichloroethyl aluminum and aluminum monochloro di-n-hexyl, and most preferred is aluminum dichloroethyl.

[0095] These haloalkyl aluminums can be used alone or in combination of multiple kinds in any proportion.

[0096] According to the present invention, the cocatalyst is generally used in the form of a solution. When preparing the solution of the cocatalyst, there is no particular limitation on the solvent used at this time, as long as it can dissolve the cocatalyst. Generally, alkane solvents such as n-pentane, isopentane, cyclopentane, neopentane, etc. or aromatic solvents such as toluene, ethylbenzene, xylene, etc. are selected. According to the present invention, for the convenience of subsequent separation, a solvent the same as the polymerization solvent is preferred; or a solvent the same as one of the solvents in the polymerization mixed solvent.

[0097] It should be noted that in the present invention, when the cocatalyst is aluminoxane, alkyl aluminum or haloalkyl aluminum, without special instructions, the molar amount of the cocatalyst is calculated based on the molar amount of aluminum (Al) element.

[0098] Specifically, the ratio and addition method of the cocatalyst and the polyethylene main catalyst are described as follows.

[0099] According to the present invention, for the ratio of the cocatalyst to the polyethylene main catalyst, based on the total aluminum element in the aluminoxane, alkyl aluminum, haloalkyl aluminum in the cocatalyst and the active metal element in the polyethylene main catalyst, the molar ratio of aluminum to the active metal is 10 - 500:1, preferably the molar ratio of aluminum to the active metal is 20 - 100:1.

[0100] The addition method of the polyethylene main catalyst and the cocatalyst into the polymerization reaction system is not particularly limited. For batch polymerization, the polyethylene main catalyst can be added first, and then the cocatalyst can be added; or the cocatalyst can be added first, and then the polyethylene main catalyst can be added; or the two can be contacted and mixed first and then added together; or added separately and simultaneously; or part of the cocatalyst can be added first, and then the polyethylene main catalyst and the remaining cocatalyst can be added simultaneously; or part of the polyethylene main catalyst can be added first, and then the remaining polyethylene main catalyst and the cocatalyst can be added simultaneously. When the polyethylene main catalyst and the cocatalyst are added separately, they can be added sequentially in the same feeding pipeline or in multiple feeding pipelines. Among them, when the two are added separately and simultaneously, multiple feeding pipelines are preferably used. For continuous polymerization, when the polyethylene main catalyst and the cocatalyst are added separately, they can be added sequentially in the same feeding pipeline or in multiple feeding pipelines. Among them, when the two are added separately and simultaneously, multiple feeding pipelines are preferably used.

[0101] According to an embodiment of the present invention, the ratio of the polyethylene main catalyst to the polymerization solvent based on the amount of the active metal is 0.001 - 0.500 mmol of polyethylene main catalyst / L of polymerization solvent, preferably 0.005 - 0.200 mmol of polyethylene main catalyst / L of polymerization solvent, and more preferably 0.005 - 0.05 mmol of polyethylene main catalyst / L of polymerization solvent. According to an embodiment of the present invention, the slurry concentration is 50 - 500 g of polymer / L of polymerization solvent, preferably 100 - 400 g of polymer / L of polymerization solvent.

[0102] According to a method for polymerizing and preparing an easy - processing ultra - high - molecular - weight polyethylene provided by the present invention, it is continuously fed with gaseous ethylene or liquid ethylene. If necessary, simultaneously under hydrogen, and gaseous or liquid comonomers, and intermittent or continuous ethylene slurry homopolymerization and / or copolymerization are carried out in a single or two ethylene slurry reactors. The ethylene slurry polymerization reactor can be a single stirred kettle reactor, a series of stirred kettle reactors, etc.

[0103] In an embodiment of the present invention, the description of the kettle slurry polymerization embodiment for preparing the ethylene polymer of the present invention is as follows.

[0104] When preparing the homopolymer U section, when using the batch polymerization method, the supported polyethylene main catalyst, the cocatalyst, the polymerization solvent, and optionally hydrogen are first added into the ethylene slurry polymerization reactor at one time according to the required ratio, and then ethylene is continuously introduced. The polymerization pressure and polymerization temperature are kept constant to carry out the polymerization reaction for preparing the U section. After the reaction is completed, the introduction of ethylene is stopped. To facilitate the polymerization conditions and gas phase composition for continuously preparing the L section described in the present invention, part of the gas in the kettle can be discharged through the vent pipeline to reduce the ethylene concentration in the kettle; or

[0105] When preparing the copolymerized U section by batch polymerization, the supported polyethylene main catalyst, cocatalyst, polymerization solvent, optional hydrogen, and comonomer are first added to the ethylene slurry polymerization reactor at one time according to the required ratio, and then ethylene is continuously introduced, and the polymerization pressure and temperature are kept constant to carry out the polymerization reaction for preparing the U section. After the reaction is completed, the introduction of ethylene is stopped. To facilitate the polymerization conditions and gas phase composition for continuously preparing the L section described in the present invention, part of the gas in the kettle can be discharged through the vent pipeline to reduce the ethylene concentration in the kettle; or

[0106] When preparing the homopolymerized U section by continuous polymerization, the supported polyethylene main catalyst, cocatalyst, polymerization solvent, optional hydrogen, and ethylene are continuously added to the ethylene slurry polymerization reactor at the same time according to the required ratio, and the polymerization reaction for preparing the U section is carried out under constant polymerization pressure and temperature, and the material generated by the polymerization reaction continuously leaves the ethylene slurry stirred kettle; or

[0107] When preparing the copolymerized U section by continuous polymerization, the supported polyethylene main catalyst, cocatalyst, polymerization solvent, optional hydrogen, comonomer, and ethylene are continuously added to the ethylene slurry polymerization reactor at the same time according to the required ratio, and the polymerization reaction for preparing the U section is carried out under constant polymerization pressure and temperature, and the material generated by the polymerization reaction continuously leaves the ethylene slurry stirred kettle.

[0108] Then, enter the polymerization reaction for continuously preparing the L section.

[0109] When continuously preparing the homopolymerized L section by batch polymerization, the polymerization solvent and hydrogen, and optionally the supported polyethylene main catalyst and / or cocatalyst added, are added to the ethylene slurry polymerization reactor at one time according to the required ratio, and then ethylene is continuously introduced, and the polymerization pressure and temperature are kept constant to carry out the polymerization reaction for preparing the L section; or

[0110] When continuously preparing the copolymerized L section by batch polymerization, the polymerization solvent, hydrogen, and comonomer, and optionally the supported polyethylene main catalyst and / or cocatalyst added, are added to the ethylene slurry polymerization reactor at one time according to the required ratio, and then ethylene is continuously introduced, and the polymerization pressure and temperature are kept constant to carry out the polymerization reaction for preparing the L section; or

[0111] When continuously preparing the homopolymerized L section by continuous polymerization, the polymerization solvent, hydrogen, and ethylene, and optionally the supported polyethylene main catalyst and / or cocatalyst added, are continuously added to the ethylene slurry polymerization reactor at the same time according to the required ratio, and the polymerization reaction for preparing the L section is carried out under constant polymerization pressure and temperature; or

[0112] When continuously preparing the copolymerized L segment, in the case of continuous polymerization, the polymerization solvent, hydrogen, the comonomer, ethylene, and optionally the supported polyethylene main catalyst and / or cocatalyst are continuously added into the ethylene slurry polymerization reactor at the required ratios simultaneously. The polymerization reaction for preparing the L segment is carried out under a constant polymerization pressure and polymerization temperature. Among them, the ratio of the partial pressure of hydrogen and the comonomer to the polymerization pressure is the concentration of hydrogen and the concentration of the comonomer when preparing the L segment.

[0113] When preparing the L segment by batch polymerization, after the reaction is completed, the feeding of ethylene is stopped, the temperature of the slurry in the kettle is reduced to room temperature, the pressure in the kettle is released, the slurry material is discharged, and then filtered and dried.

[0114] When continuously preparing the L segment by continuous polymerization, after the reaction is completed, the material generated by the polymerization reaction continuously leaves the ethylene slurry stirring kettle and enters the post-treatment processes such as degassing, desolventizing (such as flash evaporation, centrifugation or filtration), drying, and removing VOCs.

[0115] It should be noted that in the continuous polymerization mode, due to the differences in the polymerization conditions and gas phase composition for preparing the U segment and the L segment, in order to facilitate the balance and stable control of the gas phase composition of the polymerization reaction for continuously preparing the L segment, when using the mode of continuously pumping to the second reactor, at least part of the slurry material can be directly continuously fed into the second reactor by a pump, or at least part of the slurry material can be continuously fed into the material buffer tank by a pump for degassing to reduce the gas holdup and ethylene content of the slurry material, and then the slurry material is introduced into the L segment reaction kettle, and then the hydrogen molar concentration within the total polymerization pressure range when continuously preparing the L segment and the concentration of the optional comonomer are applied, and the required ethylene is continuously introduced or supplemented to carry out the polymerization reaction of the L segment; if the overflow discharging mode is used for preparing the U segment, the gas phase space of the material buffer tank can be connected to the first reactor, gas-liquid separation is achieved in the material buffer tank, and then at least part of the slurry material in the material buffer tank is continuously transported to the second reactor for preparing the L segment by a pump, and the polymerization reaction of the L segment is carried out under the required polymerization conditions.

[0116] In the present invention, in the batch polymerization mode, when using a comonomer in the polymerization reaction of the U segment and the L segment, the partial pressure of the comonomer in the gas phase in the polymerization reaction is the ratio relative to the polymerization pressure, that is, the molar concentration of the comonomer in the gas phase.

[0117] In the present invention, in the batch polymerization mode, during the preparation of the U segment, in the polymerization gas phase components, the content of hydrogen is 0 - 500 ppm, preferably 0 - 200 ppm.

[0118] In the present invention, in the batch polymerization mode, hydrogen is used in the polymerization reaction in the L section. At this time, the partial pressure of hydrogen in the gas phase during the polymerization reaction is the ratio relative to the polymerization pressure, that is, the molar concentration of hydrogen in the gas phase of the L section. In the present invention, in the continuous polymerization mode, when a comonomer is used in the polymerization reaction in the U section and the polymerization reaction in the L section, during the stable polymerization process, in the gas phase components of the reaction kettle, the ratio of the partial pressure of the comonomer in the gas phase to the polymerization pressure is the molar concentration of the comonomer, which can be measured online by a gas chromatograph at the top of the reactor. According to the test results, the continuous addition rate of the comonomer is increased or decreased to meet the requirements of the present invention.

[0119] In the present invention, in the continuous polymerization mode, during the preparation of the U section, in the polymerization gas phase components, the content of hydrogen is 0 - 500 ppm, preferably 0 - 200 ppm.

[0120] In the present invention, in the continuous polymerization mode, hydrogen is used in the polymerization reaction in the L section. At this time, during the stable polymerization process, in the gas phase components of the reaction kettle, the ratio of the partial pressure of hydrogen in the gas phase to the polymerization pressure is the molar concentration of hydrogen when preparing the L section, which can be measured online by a gas chromatograph at the top of the reactor. According to the test results, the continuous addition rate of hydrogen is increased or decreased to meet the requirements of the present invention.

[0121] For the ethylene slurry polymerization conditions with stirring, the stirring method and stirring speed are not particularly limited, as long as it can ensure that the polyethylene main catalyst, cocatalyst, ethylene, hydrogen, comonomer, and slurry in the ethylene slurry reactor can be fully stirred and dispersed. Generally, the stirring method can adopt an anchor type stirring paddle, a screw ribbon type stirring paddle, a paddle type stirring paddle, a turbine type stirring paddle, a propeller type stirring paddle (propeller type), a frame type stirring paddle. When the height-to-diameter ratio of the ethylene slurry polymerization reactor is relatively large (such as greater than 2), multi-layer stirring paddles can be used, and the stirring seal method is not particularly limited. Generally, a mechanical seal type or a magnetic seal type can be adopted. When the volume of the ethylene slurry polymerization reactor is greater than or equal to 10 m 3 ³, it is preferably to adopt a mechanical seal type. When the volume of the ethylene slurry polymerization reactor is less than 10 m 3 ³, it is preferably to adopt a magnetic seal type; the stirring speed is related to the volume of the ethylene slurry reactor and the stirring method. Generally, the smaller the volume of the reactor (such as less than or equal to 5 m 3 ³) or when adopting an anchor type stirring paddle, a paddle type stirring paddle, a turbine type stirring paddle, a propeller type stirring paddle (propeller type), etc., the required stirring speed is greater, and the stirring speed is 200 - 1000 rpm. The larger the volume of the reactor (such as greater than 10 m 3 ³) or when adopting a screw ribbon type stirring paddle, a frame type stirring paddle, etc., the required stirring speed is smaller, and the stirring speed is 10 - 200 rpm. When the volume of the reactor is greater than 5 m3 and less than or equal to 10 m 3 When it is, the stirring speed is 100 - 500 rpm.

[0122] According to the present invention, the polymerization temperature of the polymerization reaction for preparing the U section is 40 - 80 °C, preferably 50 - 75 °C, and ethylene homopolymerization is carried out in the presence of 0 - 500 ppm of hydrogen, preferably 0 - 200 ppm, or copolymerization of ethylene with a comonomer is carried out.

[0123] According to the present invention, the polymerization temperature of the polymerization reaction for preparing the L section is 70 - 95 °C, preferably 78 - 90 °C, and ethylene homopolymerization is carried out in the presence of hydrogen, or copolymerization of ethylene with a comonomer is carried out.

[0124] The polymerization temperature has an impact on aspects such as the polymerization activity of the polyethylene main catalyst, polymerization life, and stability of instantaneous ethylene consumption. Generally speaking, at a relatively high polymerization temperature (such as above 70 °C), the ethylene slurry polymerization activity of the polyethylene main catalyst is relatively high, and the molecular weight of the resulting ethylene polymer is relatively low; while at a relatively low polymerization temperature (such as below 70 °C), the ethylene slurry polymerization activity of the polyethylene main catalyst is relatively low, and the molecular weight of the resulting ethylene polymer is relatively high. Those skilled in the art can select a suitable temperature within the polymerization temperature range of the present invention according to needs.

[0125] The polymerization temperature is mainly the result of the combined action of the heat released by the chain polymerization and combination of ethylene and comonomer during the copolymerization reaction of ethylene in the polymerization solvent in the presence of the polyethylene main catalyst and cocatalyst, as well as heating or heat removal methods such as heating or heat removal by the outer jacket of the ethylene slurry reactor, or by the inner coil, or by external circulation of the slurry, or by vapor evaporation heat removal or heat removal by the latent heat of phase change released from the gas state to the liquid state. In addition, when preparing ethylene polymers from ethylene slurry, when the temperature is difficult to stably control, the polymerization temperature can be assisted in reducing and controlling by reducing the input amount of the polyethylene main catalyst or stopping the input, or reducing the polymerization pressure, to prevent and avoid the occurrence of violent polymerization phenomena such as caking and plasticization of ethylene polymers (such as when the temperature increases by 0.5 - 2 °C per minute when it is 20 °C above or below the preset polymerization temperature). In the most extreme cases, the polymerization pressure can be urgently vented, or a small amount of carbon monoxide, or carbon dioxide, or ethanol, or water vapor, or a mixture thereof and other inactivators or terminators can be introduced to quench the ethylene slurry polymerization activity of the polyethylene main catalyst, to avoid the occurrence of violent polymerization phenomena such as plasticization of ethylene polymers (such as when the temperature increases by more than 2 °C per minute when it is 20 °C above or below the preset polymerization temperature).

[0126] In one embodiment of the present invention, the polymerization temperature of the polymerization reaction for preparing the U section is 40 - 80 °C, preferably 50 - 75 °C.

[0127] In one embodiment of the present invention, the polymerization temperature of the polymerization reaction for preparing the L section is 70 - 95 °C, preferably 78 - 90 °C.

[0128] Among them, the ethylene slurry polymerization pressure for preparing the ethylene polymer is described as follows.

[0129] According to the present invention, the ethylene slurry polymerization pressure for preparing the ethylene polymer is the total pressure of the ethylene slurry polymerization reactor, which is determined by the partial pressures and vapor pressures of ethylene, cocatalyst, dissolved solvent, hydrogen, comonomer, polymerization solvent, etc. in the ethylene slurry polymerization reactor at the polymerization temperature and the optionally added inert gas.

[0130] In one embodiment of the present invention, the polymerization pressure of the polymerization reaction for preparing the U section is 0.5 - 4.5 MPa, preferably 1.0 - 3.0 MPa.

[0131] In one embodiment of the present invention, the polymerization pressure of the polymerization reaction for preparing the L section is 1.0 - 4.5 MPa, preferably 2.0 - 3.5 MPa.

[0132] Similar to the ethylene slurry polymerization temperature, the ethylene slurry polymerization pressure has an impact on aspects such as exerting the polymerization activity of the polyethylene main catalyst and the stability of instantaneous ethylene consumption. Generally speaking, at a relatively high polymerization pressure (such as 2.0 - 4.5 MPa), the ethylene slurry polymerization activity of the polyethylene main catalyst is relatively high; while at a relatively low polymerization pressure (such as 0.5 - 2.0 MPa), the ethylene slurry polymerization activity of the polyethylene main catalyst is relatively low.

[0133] The selection of the ethylene slurry polymerization pressure needs to comprehensively consider various factors and conditions of the ethylene polymer. Generally speaking, when the polymerization solvent is selected as an alkane solvent with a relatively low boiling point or a mixed alkane solvent with a relatively high vapor pressure at 20 °C, a relatively high polymerization pressure can be implemented to exert the ethylene slurry polymerization activity of the polyethylene main catalyst and reduce the polymerization cost. According to the research of the present invention, when using an alkane solvent with a boiling point of 5 - 55 °C at 20 °C such as n - pentane, neopentane, cyclopentane or isopentane, or a mixed alkane solvent with a saturated vapor pressure of 4 - 200 KPa (preferably 20 - 150 KPa) at 20 °C as the polymerization solvent, a polymerization pressure higher than 2.0 MPa can be implemented. The high polymerization pressure can provide a wide space for selecting polymerization conditions for using a relatively large hydrogen molar concentration and comonomer molar concentration under the condition of fully releasing the ethylene slurry polymerization activity of the polyethylene main catalyst, and then ethylene polymers with different molecular weights, different comonomer insertion rates, different true densities, etc. can be regulated within a relatively large range of polymerization process conditions.

[0134] Among them, the comonomer for the ethylene slurry polymerization of preparing the ethylene polymer is described as follows.

[0135] According to the present invention, the comonomer is selected from α-olefins, diolefins, cycloolefins, and other ethylenically unsaturated compounds.

[0136] Specifically, as the α-olefin, it can be C3-C 10 α-olefins, such as propylene, 1-butene, 1-hexene, 1-heptene, 4-methyl-1-pentene, 1-octene, 1-decene, 1-undecene, 1-dodecene, and styrene, etc. As the cycloolefin, such as 1-cyclopentene, ethylidene norbornene, and norbornene, etc. As the diolefin, such as 1,4-butadiene, 2,5-pentadiene, 1,6-heptadiene, vinyl norbornene, norbornadiene, and 1,7-octadiene, etc. As the other ethylenically unsaturated compounds, such as vinyl acetate and (meth)acrylate, etc. Among them, the comonomer is preferably C3-C 10 α-monoolefin, more preferably at least one of propylene, 1-butene, 1-hexene, and 1-octene.

[0137] When carrying out the polymerization reactions of the U-section preparation and the L-section preparation, ethylene and the comonomer are fed into the polymerization kettle and polymerized together. In the present invention, "ethylene and the comonomer are polymerized together (copolymerized)" or "the polymerization reaction (copolymerization) of ethylene and the comonomer is carried out together" means that after ethylene and the comonomer are fed into the reaction kettle, the polymerization reaction is carried out together in the presence of both of them, and there is no step of staged polymerization, that is, there is no staged step of first polymerizing ethylene and then adding the comonomer for polymerization, nor is there a staged step of first homopolymerizing the comonomer and then adding ethylene for polymerization. The obtained polyethylene has a random copolymer structure.

[0138] By copolymerizing ethylene with the above-mentioned comonomer, the true density of the ethylene polymer can be reduced, and the mechanical properties can be improved and enhanced, such as improving the mechanical strength and toughness, and increasing the environmental stress cracking resistance, etc.

[0139] In one embodiment of the present invention, during the preparation of the U-section, the molar content of the comonomer in the polymerization gas phase component is 0-3.0 mol%, preferably 0.3-2 mol%, or 0.5-1.5 mol%.

[0140] In one embodiment of the present invention, during the preparation of the L-section, in the polymerization gas phase component, the molar content of the comonomer is 0-20 mol%, preferably 2.0-10 mol%, or 2.5-6.0 mol%.

[0141] In one embodiment of the present invention, during the preparation of the L-section, in the polymerization gas phase component, the molar content of hydrogen is 30-90 mol%, preferably 50-85 mol%.

[0142] Hydrogen is used as a chain transfer agent and terminator in the slurry polymerization of ethylene. Its main function is to reduce the molecular weight of the resulting ethylene polymer and obtain low molecular weight polyethylene in the L section. Generally, the ethylene polymer obtained under the conditions of ethylene slurry polymerization with a high hydrogen-to-ethylene molar ratio has a lower molecular weight, and vice versa, the ethylene polymer obtained under the conditions of ethylene slurry polymerization with a low hydrogen-to-ethylene molar ratio has a higher molecular weight. Under a certain polymerization pressure condition, the presence of hydrogen will reduce the ethylene partial pressure, thereby reducing the ethylene slurry polymerization activity of the polyethylene main catalyst.

[0143] Regarding the polymerization residence time, the present invention is not particularly limited, and those skilled in the art can select according to needs. As long as the mass ratio of the U section and the L section meets the scope of the present invention. Generally speaking, when polymerizing to prepare the U section, a shorter polymerization time can be selected for high polymerization activity, while when polymerizing to prepare the L section, a longer polymerization time can be selected for low polymerization activity.

[0144] For example, based on the polyethylene main catalyst, when the ethylene slurry polymerization activity is higher than or equal to 20,000 g of polyethylene per gram of polyethylene main catalyst per hour, the polymerization residence time can be selected from 0.5 - 2 h, and when the ethylene slurry polymerization activity is lower than 10,000 g of polyethylene per gram of polyethylene main catalyst per hour, the polymerization residence time can be selected from 1 - 6 h. But it is not limited thereto.

[0145] According to the present invention, the slurry concentration of the ethylene polymer in the ethylene slurry polymerization is an important index reflecting the degree of the ethylene slurry polymerization process. If the concentration is too low, the preparation cost will be high due to the separation of the solvent and the material. If the concentration is too high, it is difficult to disperse evenly by stirring, the heat transfer effect becomes poor, resulting in uneven materials in the kettle, which is not conducive to obtaining the ethylene polymer. According to the present invention, the slurry concentration of the ethylene polymer in the ethylene slurry polymerization reactor is 50 - 500 g of polyethylene per liter of polymerization solvent, preferably 100 - 400 g of polyethylene per liter of polymerization solvent.

[0146] Examples

[0147] The following examples are used to further illustrate the present invention in detail, but the present invention is not limited to these examples.

[0148] The determination of the bulk density (unit: g / cm 3 ) of the ethylene polymer is carried out with reference to the standard GB / T 1636 - 2008, and the true density (unit: g / cm 3 ) of the ethylene polymer is tested in a density tube according to the standard GB / T 1033.2 - 2010.

[0149] Determination of the melting point of the polymer: Referring to the standard GB / T 28724-2012, it is determined by differential scanning calorimetry using a Q1000 type DSC differential scanning calorimeter from TA Instruments, USA.

[0150] The tensile elastic modulus and elongation at break of the polymer are determined with reference to the standard GB / T 1040.5-2008, and the elongation at break is greater than 500%. The Izod notched impact strength is determined with reference to the standard GB / T21461.2-2008.

[0151] The content of the active metal element in the polyethylene main catalyst is determined by ICP-AES method.

[0152] The polymerization activity of the polyethylene main catalyst is calculated as follows: When using the ethylene slurry batch method, after the polymerization reaction is completed, the polymerization product in the reaction kettle is filtered and dried, and then the mass of the polymerization product is weighed. The polymerization activity of the catalyst is expressed as the ratio of the mass of the polymerization product to the mass of the polyethylene main catalyst used (kilograms of ethylene polymer / gram of catalyst or kgPE / gCat). When using the ethylene slurry continuous method, at a steady state (the polymerization pressure, polymerization temperature and gas phase composition are stable), the polymerization activity of the catalyst is expressed as the value of the instantaneous ethylene consumption rate (also known as the absorption rate) divided by the continuous addition rate of the polyethylene main catalyst (the unit is kilograms of ethylene polymer / gram of catalyst or kgPE / gCat).

[0153] The slurry concentration is calculated as follows: After uniformly sampling from the ethylene slurry polymerization reactor and weighing it as m1 (unit: g), and then fully drying to obtain the dried ethylene polymer m2 (unit: g), with the density of the polymerization solvent being ρ (unit: g / ml), the slurry concentration is calculated according to the following formula.

[0154]

[0155] The determination of the average particle size of the polymer is carried out on a Microtrac S3500 type laser particle size analyzer, and the particle size determination range is 0.01 - 10000 μm.

[0156] The viscosity-average molecular weight of the ultra-high molecular weight polyethylene in section U is calculated as follows: Sampling from the slurry material after the polymerization reaction in section U is completed, and according to the standard ASTM D4020-00, using the high-temperature dilution type Ubbelohde viscometer method (capillary inner diameter is 0.44 mm, the constant temperature bath medium is silicone oil No. 300, the dilution solvent is decalin, and the measurement temperature is 135 °C) to measure the intrinsic viscosity of the polymer, and then calculate the viscosity-average molecular weight Mv of the polymer according to the following formula.

[0157] Mv = 5.37×10 4 ×[η]1.37

[0158] Among them, η is the intrinsic viscosity.

[0159] The method for measuring the molecular weight of the low weight-average molecular weight polyethylene in the L section is as follows: According to the same addition amount of the main catalyst and the cocatalyst, or when two different main catalysts and / or cocatalysts are used in the polymerization reaction of the U section and the polymerization reaction of the L section, according to the same addition amount of the main catalyst and / or cocatalyst in the L section, after only carrying out the polymerization reaction in the L section under the polymerization conditions of the L section, a sample is taken for measurement.

[0160] The measurement of the weight-average molecular weight (unit: ten thousand grams / mole) of the low weight-average molecular weight polyethylene in the L section is carried out with reference to the standard GB / T 21864-2005, using the GPC PL220 high-temperature gel chromatography analyzer of Agilent Technologies, Inc. in the United States for measurement. Four Agilent PLgel Olexis type chromatographic columns are selected, and 1,2,4-trichlorobenzene is used as the mobile phase. The temperature during the measurement is 150 °C.

[0161] The measurement of the content of the comonomer in the ultra-high molecular weight polyethylene is calibrated by a copolymer with a known content using a 600M nuclear magnetic resonance spectrometer of Bruck Company, and is measured by a Bruck 66 / S type Fourier transform infrared spectrometer of Bruck Company in Germany.

[0162] The processing performance of the ultra-high molecular weight polyethylene is measured according to the following method: On a plunger-type screw extruder (SJ-45×25, Fengcheng Machinery Manufacturing Co., Ltd., Zhangjiagang City, screw diameter 45 mm, length-diameter ratio 25, heating power 5 kW), 5 kg of ultra-high molecular weight polyethylene is added through the feeding hopper into an extended die with a temperature of 160-220 °C, and the determination is carried out by comparing the extrusion pressure (MPa), the extrusion current (A) and the extrusion rate (m / min).

[0163] In order to more clearly illustrate the ethylene polymer and its preparation method of the present invention, in the specific examples, the following are used as the main catalysts for the ethylene slurry polymerization of polyethylene:

[0164] Supported non-metallocene catalyst (CAT-1), prepared according to Example 1 in Chinese Patent CN110964140B, among which the content of the active metal titanium element is 4.52 wt%;

[0165] Supported non-metallocene catalyst (CAT-2), prepared according to Example 7 in Chinese Patent CN110964136B, among which the content of the active metal titanium element is 4.14 wt%;

[0166] Supported metallocene catalyst (CAT-3), prepared according to Example 1 in Chinese Patent CN102453124B, wherein the content of active metal titanium element is 0.62 wt%.

[0167] Ziegler-Natta catalyst, using CMU and BCE type catalysts produced by Beijing Aoda Branch of Sinopec Catalyst Co., Ltd., wherein the content of active metal titanium element in CMU catalyst is 4.2 wt%, and the content of active metal titanium element in BCE catalyst is 9.5 wt%.

[0168] However, according to the present invention, the main polyethylene catalyst involved includes but is not limited to the above specific catalysts, subject to the claims.

[0169] Example 1

[0170] In a 5L ethylene slurry stirring polymerization kettle, first add 2.5L of polymerization solvent to the polymerization kettle at room temperature, start stirring, with a rotation speed of 300 rpm, then add a mixture of supported polyethylene catalyst and cocatalyst at one time, continuously introduce ethylene for polymerization reaction to prepare the U section. After the ethylene consumption reaches 0.8 kg, vent part of the ethylene, sample and test the viscosity-average molecular weight of the U section. Then add hydrogen at one time, continuously introduce ethylene. After the ethylene consumption reaches a certain mass, vent the gas in the kettle, discharge the polymer in the kettle, and after degassing, desolventizing, drying and post-treatment of removing VOCs, weigh the mass. The ethylene polymer is denoted as UHMWPE-1. The preparation process and conditions of this easy-to-process ultra-high molecular weight polyethylene are shown in Table 1, and the properties of the easy-to-process ultra-high molecular weight polyethylene are shown in Table 2, and the particle size distribution is as Figure 1 shown.

[0171] Among them, the polymerization solvent is n-pentane (boiling point 36.1 °C), with a dosage of 2.5L. The main polyethylene catalyst is a supported non-metallocene catalyst CAT-1 (concentration 0.030 mmol / L), and the cocatalyst is a n-pentane solution of triethylaluminum (TEAL) (concentration 1.0 mol / L). The molar ratio of aluminum to active metal is 80:1. The polymerization pressure for preparing the U section and the L section is both 2.4 MPa. The polymerization temperature for preparing the U section is 70 °C, and the polymerization temperature for preparing the L section is 85 °C. The hydrogen molar content is 75 mol%. The mass ratio of the U section to the L section is 9:1. The final slurry concentration of the polymerization is 288 grams of polyethylene / L of solvent.

[0172] Example 2

[0173] Basically the same as Example 1, but with the following changes:

[0174] The polymerization solvent is changed to cyclopentane, and the cocatalyst solvent is cyclopentane.

[0175] The U section is prepared by copolymerization. The comonomer is propylene, and the molar content of the comonomer in the polymerization gas phase component is 0.5 mol%, and the hydrogen concentration is 50 ppm.

[0176] The ethylene polymer is denoted as UHMWPE-2. The preparation process and conditions of the easy-to-process ultra-high molecular weight polyethylene are shown in Table 1, and the properties of the easy-to-process ultra-high molecular weight polyethylene are shown in Table 2.

[0177] Example 3

[0178] It is basically the same as Example 1, but there are the following changes:

[0179] The polymerization solvent is changed to a mixed alkane solvent with a saturated vapor pressure of 71.65 KPa at 20 °C (a mixed solvent of n-pentane and isopentane in a molar ratio of 25:75), and the cocatalyst solvent is also changed to this mixed alkane solvent.

[0180] The U section is prepared by copolymerization. The comonomer is 1-hexene, the polymerization pressure is 2.5 MPa, the polymerization temperature is 62 °C, and the molar content of the comonomer in the polymerization gas phase component is 1.0 mol%.

[0181] Continue to copolymerize to prepare the L section. The polymerization pressure is 2.8 MPa, the polymerization temperature is 86 °C, the comonomer is 1-hexene, and the molar content of the comonomer in the polymerization gas phase component is 5.0 mol%.

[0182] The ethylene polymer is denoted as UHMWPE-3. The preparation process and conditions of the easy-to-process ultra-high molecular weight polyethylene are shown in Table 1, and the properties of the easy-to-process ultra-high molecular weight polyethylene are shown in Table 2.

[0183] Example 4

[0184] It is basically the same as Example 1, but there are the following changes:

[0185] The polymerization solvent is changed to isopentane (boiling point 27.8 °C), and isopentane is also used as the cocatalyst solvent.

[0186] The molar ratio of aluminum to the active metal is 70:1.

[0187] Prepare the U section. The polymerization pressure is 2.6 MPa and the polymerization temperature is 68 °C.

[0188] Copolymerize to prepare the L section. The polymerization pressure is 2.5 MPa, the polymerization temperature is 87 °C, the comonomer is 1-hexene, the molar content of the comonomer in the polymerization gas phase component is 5.0 mol%, and the hydrogen concentration is 80 mol%.

[0189] The ethylene polymer is denoted as UHMWPE-4. The preparation process and conditions of the easy-to-process ultra-high molecular weight polyethylene are shown in Table 1, and the properties of the easy-to-process ultra-high molecular weight polyethylene are shown in Table 2.

[0190] Example 5

[0191] It is basically the same as Example 1, but with the following changes:

[0192] The polymerization solvent is changed to neopentane (boiling point 7.2 °C), the supported polyethylene catalyst is changed to CAT-2, and the molar ratio of aluminum to the active metal is 60:1.

[0193] For the preparation of the U section, after the ethylene consumption reaches 0.6 kg, copolymerization is continued to prepare the L section. The polymerization pressure is 2.8 MPa, the polymerization temperature is 86 °C, the comonomer is 1-hexene, and the molar content of the comonomer in the polymerization gas phase component is 5.0 mol%, and the hydrogen concentration is 80 mol%.

[0194] The mass ratio of the U section to the L section during preparation is 7:3, and the final polymerization slurry concentration is 214 g of polyethylene / L of solvent.

[0195] The ethylene polymer is denoted as UHMWPE-5. The preparation process and conditions of this easy-to-process ultra-high molecular weight polyethylene are shown in Table 1, and the properties of the easy-to-process ultra-high molecular weight polyethylene are shown in Table 2.

[0196] Example 6

[0197] It is basically the same as Example 1, but with the following changes:

[0198] The polymerization solvent is a mixed alkane solvent composed of n-pentane and isopentane with a saturated vapor pressure of 66.6 KPa at 20 °C in a molar ratio of 1:1. The cocatalyst is a solution of triisobutylaluminum (TIBA) (concentration 2.0 mol / L), and the cocatalyst solvent also uses this mixed alkane solvent. The molar ratio of aluminum to the active metal is 100:1.

[0199] The supported polyethylene catalyst during the preparation of the U section is the CMU catalyst (concentration 0.020 mmol / L), the polymerization pressure is 2.0 MPa, and the polymerization temperature is 70 °C.

[0200] The supported polyethylene catalyst during the copolymerization to prepare the L section is CAT-3 (concentration 0.400 mmol / L), the polymerization pressure is 2.4 MPa, the polymerization temperature is 88 °C, the comonomer is 1-hexene, and the molar content of hydrogen in the polymerization gas phase component is 60 mol%, and the molar content of the comonomer is 3.0 mol%. The mass ratio of the U section to the L section during preparation is 8:2, and the final polymerization slurry concentration is 400 g of polyethylene / L of solvent.

[0201] The ethylene polymer is denoted as UHMWPE-6. The preparation process and conditions of this easy-to-process ultra-high molecular weight polyethylene are shown in Table 1, and the properties of the easy-to-process ultra-high molecular weight polyethylene are shown in Table 2.

[0202] Example 7

[0203] It is basically the same as Example 1, but with the following changes:

[0204] The polymerization solvent is n-hexane (boiling point 68.95 °C), the cocatalyst is a solution of triisobutylaluminum (TIBA) (concentration 2.0 mol / L), and the cocatalyst solvent also uses this mixed alkane solvent.

[0205] 1-Butene is used for preparing both the U-section and L-section comonomers.

[0206] When preparing the U-section, the supported polyethylene catalyst is the CMU catalyst (concentration 0.020 mmol / L), the polymerization pressure is 1.8 MPa, the polymerization temperature is 65 °C, and the comonomer molar concentration is 0.6 mol%.

[0207] When copolymerizing to prepare the L-section, the supported polyethylene catalyst is the BCE catalyst, the polymerization pressure is 2.4 MPa, the polymerization temperature is 90 °C, the molar content of hydrogen in the polymerization gas phase component is 85 mol%, and the comonomer molar content is 4.4 mol%.

[0208] The mass ratio of the U-section to the L-section when preparing is 8:2.

[0209] The ethylene polymer is denoted as UHMWPE-7. The preparation process and conditions of this easy-to-process ultra-high molecular weight polyethylene are shown in Table 1, and the properties of the easy-to-process ultra-high molecular weight polyethylene are shown in Table 2.

[0210] Example 8

[0211] It is basically the same as Example 1, but with the following changes:

[0212] The polymerization solvent is cyclohexane (boiling point 80.72 °C), the cocatalyst solvent also uses cyclohexane, and the molar ratio of aluminum to the active metal is 45:1.

[0213] When copolymerizing to prepare the U-section, the supported polyethylene catalyst is the CMU catalyst (concentration 0.025 mmol / L), the polymerization pressure is 1.8 MPa, the polymerization temperature is 60 °C, the comonomer is 1-butene, and the comonomer molar concentration is 0.3 mol%.

[0214] When homopolymerizing to prepare the L-section, the supported polyethylene catalyst is the BCE catalyst (concentration 0.300 mmol / L), the polymerization pressure is 2.6 MPa, the polymerization temperature is 75 °C, and the molar content of hydrogen in the polymerization gas phase component is 85 mol%.

[0215] The mass ratio of the U-section to the L-section when preparing is 15:1, and the final slurry concentration of the polymerization is 340 g of polyethylene / L of solvent.

[0216] The ethylene polymer is denoted as UHMWPE-8. The preparation process and conditions of this easy-to-process ultra-high molecular weight polyethylene are shown in Table 1, and the properties of the easy-to-process ultra-high molecular weight polyethylene are shown in Table 2.

[0217] Example 9

[0218] It is basically the same as Example 4, but with the following changes:

[0219] The polymerization solvent is a mixed alkane solvent with a saturated vapor pressure of 101.21 KPa at 20 °C (a mixed solvent of n-pentane, isopentane, and neopentane in a molar ratio of 24:34:42), and this mixed alkane solvent is also used as the cocatalyst solvent.

[0220] When preparing the U section, the supported polyethylene catalyst is CMU catalyst (concentration 0.025 mmol / L), the polymerization pressure is 1.5 MPa, the polymerization temperature is 75 °C, and the hydrogen molar content is 150 ppm.

[0221] When copolymerizing to prepare the L section, the supported polyethylene catalyst is CAT-3 (concentration 0.400 mmol / L), the comonomer is 1-octene, the polymerization pressure is 3.0 MPa, the polymerization temperature is 87 °C, the comonomer molar concentration is 3.5 mol%, and the hydrogen molar content is 55 mol%.

[0222] When preparing the U section and the L section, the mass ratio is 19:1, and the final slurry concentration of the polymerization is 356 g of polyethylene / L of solvent.

[0223] The ethylene polymer is denoted as UHMWPE-9. The preparation process and conditions of this easy-to-process ultra-high molecular weight polyethylene are shown in Table 1, and the properties of the easy-to-process ultra-high molecular weight polyethylene are shown in Table 2.

[0224] Example 10

[0225] It is basically the same as Example 2, but with the following changes:

[0226] The polymerization solvent is a mixed alkane solvent with a saturated vapor pressure of 47.48 KPa at 20 °C (a mixed solvent of n-pentane, isopentane, and isohexane in a molar ratio of 40:25:35), and this mixed alkane solvent is also used as the cocatalyst solvent.

[0227] The ethylene polymer is denoted as UHMWPE-10. The preparation process and conditions of this easy-to-process ultra-high molecular weight polyethylene are shown in Table 1, and the properties of the easy-to-process ultra-high molecular weight polyethylene are shown in Table 2.

[0228] Example 11

[0229] It is basically the same as Example 4, but with the following changes:

[0230] The polymerization solvent is a mixed alkane solvent with a saturated vapor pressure of 71.65 KPa at 20 °C (a mixed solvent of n-pentane and isopentane in a molar ratio of 25:75), and this mixed alkane solvent is also used as the cocatalyst solvent.

[0231] The ethylene polymer is denoted as UHMWPE-11. The preparation process and conditions of this easy-to-process ultra-high molecular weight polyethylene are shown in Table 1, and the properties of the easy-to-process ultra-high molecular weight polyethylene are shown in Table 2.

[0232] Example 12

[0233] It is basically the same as Example 5, but with the following changes:

[0234] The polymerization solvent is a mixed alkane solvent with a saturated vapor pressure of 127.38 KPa at 20 °C (a mixed solvent of isopentane and neopentane in a molar ratio of 27.5:72.5), and this mixed alkane solvent is also used as the cocatalyst solvent.

[0235] The ethylene polymer is denoted as UHMWPE-12. The preparation process and conditions of this easy-to-process ultra-high molecular weight polyethylene are shown in Table 1, and the properties of the easy-to-process ultra-high molecular weight polyethylene are shown in Table 2.

[0236] Comparative Example 1

[0237] According to the U-section polymerization preparation conditions in Example 1, the ethylene polymer is denoted as CPE-1.

[0238] The preparation process and conditions of this ultra-high molecular weight polyethylene are shown in Table 1, and the properties of the ultra-high molecular weight polyethylene are shown in Table 2.

[0239] Comparative Example 2

[0240] The U-section polyethylene and L-section polyethylene are obtained respectively according to the U-section polymerization preparation conditions in Example 1. The types and dosages of the main catalyst and cocatalyst in the L-section polymerization reaction are the same as those in the U-section polymerization reaction, and they are mixed according to the mass ratio of the U-section and L-section. The obtained ethylene polymer is denoted as CPE-2.

[0241] The preparation process and conditions of this polymer are shown in Table 1, and the properties of the polymer are shown in Table 2.

[0242] Comparative Example 3

[0243] The U-section polyethylene is obtained according to the U-section polymerization preparation conditions in Example 5. Additionally, polyethylene wax with a molecular weight of 0.2×10⁴ g / mol is independently added and mixed according to the mass ratio of the U-section and L-section. The obtained ethylene polymer is denoted as CPE-3.

[0244] The preparation process and conditions of this polymer are shown in Table 1, and the properties of the polymer are shown in Table 2.

[0245] Comparative Example 4

[0246] It is basically the same as Example 1, but there are the following changes:

[0247] The mass ratio of the U section to the L section is 1.5:1, and the obtained ethylene polymer is denoted as CPE-4.

[0248] The preparation process and conditions of this polymer are shown in Table 1, and the polymer properties are shown in Table 2.

[0249] Comparative Example 5

[0250] It is basically the same as Example 1, but there are the following changes:

[0251] The mass ratio of the U section to the L section is 30:1, and the obtained ethylene polymer is denoted as CPE-5.

[0252] The preparation process and conditions of this polymer are shown in Table 1, and the polymer properties are shown in Table 2.

[0253] Comparative Example 6

[0254] It is basically the same as Example 1, but there are the following changes:

[0255] The hydrogen concentration for preparing the L section is 45 mol%, and the obtained ethylene polymer is denoted as CPE-6.

[0256] The preparation process and conditions of this polymer are shown in Table 1, and the polymer properties are shown in Table 2.

[0257] Comparative Example 7

[0258] It is basically the same as Example 1, but there are the following changes:

[0259] The hydrogen concentration for preparing the L section is 30 mol%, and the obtained ethylene polymer is denoted as CPE-7.

[0260] The preparation process and conditions of this polymer are shown in Table 1, and the polymer properties are shown in Table 2.

[0261]

[0262]

[0263]

[0264] As can be seen from Table 1 and Table 2, an easily processable UHMWPE of the present invention has high tensile modulus, elongation at break, and Izod notched impact strength, adjustable and controllable density and melting point, and high polymer bulk density, which is easy for downstream processing and application. And it can be seen from Figure 1 that the easily processable UHMWPE provided by the present invention has a narrow particle size distribution.

[0265] As can be seen from the comparison between the UHMWPE-1 sample in Table 2 and the CPE-1 sample in Comparative Example 1, it is difficult to extrude and process UHMWPE with only a high viscosity-average molecular weight in the U section for applications.

[0266] As can be seen from Table 1 and Table 2, for the easily processable UHMWPE of the present invention, during the extrusion process, its extrusion current is low and the extrusion rate is high, indicating excellent processability of the UHMWPE of the present invention. Under comparable conditions, for the UHMWPE-1 sample of the present invention in Table 2, the processing extrusion current is significantly lower and the extrusion rate is significantly higher than those of the CPE-2 sample of the U section and L section mixed polymer in Comparative Example 3. For the UHMWPE-6 of the present invention in Table 2, the processing extrusion current is significantly lower and the extrusion rate is significantly higher than those of the CPE-3 sample of the U section plus polyethylene wax in Comparative Example 3. It can be seen that the products processed from the easily processable UHMWPE provided by the present invention have lower extrusion current and higher extrusion rate compared with the samples or products processed from UHMWPE (U section) with the same high viscosity-average molecular weight by adding the same mass of polyethylene wax processing aid.

[0267] In addition, through the polymerization method of the present invention, an alkane solvent with a boiling point of 0-90°C or a mixed alkane solvent with a saturated vapor pressure of 4-200 KPa at 20°C is used as the polymerization solvent. The selection range of the polymerization solvent is wide, and there are more options for the heat removal method during the polymerization reaction process and the post-treatment method of the obtained polyethylene slurry, and it is easy to carry out.

[0268] Moreover, as can be seen from Examples 1-5 in Table 1, the present invention can complete the sequential polymerization preparation of two components by using only one specific supported non-metallocene catalyst. As can be seen from Examples 7-9 in Table 1, different main catalyst combinations can also be used to sequentially prepare high viscosity-average molecular weight polyethylene and low weight-average molecular weight polyethylene, and the production method is more flexible.

Claims

1. Ultra-high molecular weight polyethylene, characterized in that Its bulk density is 0.30-0.55g / cm 3 , true density 0.926-0.955g / cm 3 , average particle size 50-2000μm, melting point 125-137℃, tensile modulus greater than 200MPa, elongation at break greater than 500%, cantilever beam notched impact strength greater than 90KJ / m 2 It contains two polyethylene components, one is an ultra-high molecular weight polyethylene (U segment) with a viscosity-average molecular weight of 2 million to 10 million g / mol, and the other is a low molecular weight polyethylene (L segment) with a weight-average molecular weight of 10,000 to 50,000 g / mol. The mass ratio of U segment to L segment is 1-50:

1.

2. The ultra-high molecular weight polyethylene according to claim 1, characterized in that: Bulk density 0.33-0.50g / cm 3 , true density 0.930-0.950g / cm 3 , average particle size 150-1000μm, melting point 128-135℃, tensile modulus greater than 220MPa, preferably greater than 250MPa, elongation at break greater than 550%, preferably greater than 600%, Izod notched impact strength greater than 100KJ / m 2 , preferably greater than 105KJ / m 2 The U segment is an ultra-high molecular weight polyethylene with a viscosity average molecular weight of 2.5 million to 7 million g / mol, preferably 3 million to 5 million g / mol, and the L segment is a low weight average molecular weight polyethylene with a weight average molecular weight of 15,000 to 45,000 g / mol, preferably 20,000 to 40,000 g / mol. The mass ratio of the U segment to the L segment is 3-20:

1.

3. The ultra-high molecular weight polyethylene according to claim 1, characterized in that: The U segment and the L segment are ethylene homopolymers or copolymers of ethylene and a comonomer, and are preferably selected from the combination of an ethylene homopolymer U segment and an ethylene homopolymer L segment, a combination of an ethylene and a comonomer copolymer U segment and an ethylene homopolymer L segment, a combination of an ethylene homopolymer U segment and an ethylene and a comonomer copolymer L segment, and a combination of an ethylene and a comonomer copolymer U segment and an ethylene and a comonomer copolymer L segment.

4. An ultra-high molecular weight polyethylene according to claim 3, characterized in that: The comonomer is selected from C3-C 10 The α-olefin is preferably selected from one or more of propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, and 1-octene, preferably selected from one or more of 1-butene, 1-octene, and 1-hexene, wherein The U-stage comonomer insertion rate is 0-1.0 mol%, preferably 0.1-0.8 mol%, or 0.2-0.6 mol%, or 0.2-0.5 mol%, and the L-stage comonomer insertion rate is 0-10 mol%, preferably 1.5-8.0 mol%, or 3.0-6.0 mol%, or 3.5-5.5 mol%.

5. A method for preparing ultra-high molecular weight polyethylene by polymerization, characterized in that: A supported polyethylene catalyst is used as the main catalyst, preferably a supported non-metallocene catalyst is used as the main catalyst, an alkyl aluminum, a halogenated alkyl aluminum or one or more of aluminoxanes are used as cocatalysts, preferably an alkyl aluminum is used as a cocatalyst, an alkane solvent with a boiling point of 0-90°C or a mixed alkane solvent with a saturated vapor pressure of 4-200KPa at 20°C is used as a polymerization solvent, preferably an alkane solvent with a boiling point of 5-55°C or a mixed alkane solvent with a saturated vapor pressure of 20-150KPa at 20°C is used as the polymerization solvent, wherein: At a polymerization pressure of 0.5-4.5 MPa, preferably 1.0-3.0 MPa, and a polymerization temperature of 40-80° C., preferably 50-75° C., ethylene homopolymerization or ethylene and comonomer copolymerization is performed to prepare the U segment, and then, Based on the prepared U segment, the L segment is prepared by subsequent polymerization at a polymerization pressure of 1.0-4.5 MPa, preferably 2.0-3.5 MPa, and a polymerization temperature of 70-95°C, preferably 78-90°C, wherein ethylene is homopolymerized or ethylene and a comonomer are copolymerized in the presence of hydrogen.

6. The method for preparing ultra-high molecular weight polyethylene by polymerization according to claim 5, wherein: Meet at least one of the following requirements: In the polymerization reaction for preparing the L stage, a main catalyst and / or a co-catalyst are optionally added; and / or In the polymerization reaction for preparing the L stage, a main catalyst and / or a co-catalyst are added additionally; the main catalyst and / or co-catalyst added additionally may be the same as or different from the main catalyst and / or co-catalyst for the polymerization reaction for preparing the U stage; and / or A polymerization preparation method is carried out by a batch process, wherein after the polymerization reaction of the U stage is prepared, the gas phase in the reactor is optionally vented at least a part, and then the polymerization reaction of the L stage is prepared; and / or The polymerization preparation method is carried out by a continuous kettle method, wherein, after the polymerization reaction of the U stage is prepared, the slurry material after the reaction enters into a material buffer tank which is gas-phase-balanced with the previous reactor in an overflow manner to realize gas-liquid separation, and at least part of the slurry material in the material buffer tank is continuously transported and transferred to the next reactor by a pump, or at least part of the slurry material after the reaction is directly transferred to the next reactor by a pump at the lower part or bottom of the previous reactor, and the polymerization reaction of the L stage is continuously prepared in the next reactor.

7. The method for preparing ultra-high molecular weight polyethylene by polymerization according to any one of claims 5 to 6, characterized in that: The main catalyst is selected from a supported non-metallocene catalyst, the active metal element of the supported non-metallocene catalyst is selected from a metal element of Group IVB, preferably a titanium metal element, the carrier is selected from one or more of magnesium halides, alkoxymagnesium halides, alkoxymagnesium, alkylmagnesium, alkylmagnesium halides and magnesium compounds of alkylalkoxymagnesium and porous carriers, preferably one or more of magnesium chloride and silica gel, and the non-metallocene complex is preferably selected from one or more of the compounds having the following chemical formula:

8. The method for preparing ultra-high molecular weight polyethylene by polymerization according to any one of claims 5 to 7, characterized in that: Calculated on the basis of the total aluminum element in aluminoxane, alkyl aluminum, halogenated alkyl aluminum in the co-catalyst and the active metal element in the main catalyst, the molar ratio of aluminum to active metal is 10-500:1, preferably 20-100:

1.

9. The method for preparing ultra-high molecular weight polyethylene by polymerization according to any one of claims 5 to 8, characterized in that: During the preparation of segment U, the hydrogen content in the polymerization gas phase component is 0-500ppm, preferably 0-200ppm, and the molar content of the comonomer is 0-3.0mol%, preferably 0.3-2.0mol%, or 0.5-1.5mol%. During the preparation of segment L, the molar content of the comonomer in the polymerization gas phase component is 0-20mol%, preferably 2.0-10mol%, or 2.5-6.0mol%, and the molar content of hydrogen is 30-90mol%, preferably 50-85mol%.

10. The method for preparing ultra-high molecular weight polyethylene by polymerization according to any one of claims 5 to 9, characterized in that: The alkane solvent is selected from one of 2,2-dimethylpropane (neopentane), 2-methylbutane (isopentane), n-pentane and cyclopentane; or the mixed alkane is selected from one of the combination of n-pentane and isopentane, the combination of isopentane and neopentane, the combination of n-pentane and cyclopentane, the combination of n-pentane and neopentane, the combination of isopentane and cyclopentane, the combination of neopentane and cyclopentane, the combination of n-hexane and cyclopentane, the combination of n-hexane and n-pentane, the combination of n-pentane-isopentane-cyclopentane and the combination of n-pentane-n-hexane-isopentane.

11. The method for preparing ultra-high molecular weight polyethylene by polymerization according to any one of claims 5 to 10, wherein: The polymerization preparation method is carried out by a batch process. First, a polymerization reaction is carried out to prepare the U segment. When preparing the homopolymer U segment, the supported polyethylene main catalyst, the co-catalyst, the polymerization solvent and the optional hydrogen are first added to the ethylene slurry polymerization reactor, and ethylene is continuously introduced at a constant polymerization pressure and polymerization temperature to carry out the polymerization reaction for preparing the U segment. After the reaction is completed, the introduction of ethylene is stopped, and part of the gas in the reactor can be discharged through a vent line; or When preparing the copolymer U segment, a supported polyethylene main catalyst, a co-catalyst, a polymerization solvent, optional hydrogen and a comonomer are added to an ethylene slurry polymerization reactor, ethylene is continuously introduced, and a polymerization reaction for preparing the U segment is carried out at a constant polymerization pressure and polymerization temperature. After the reaction is completed, the introduction of ethylene is stopped, and part of the gas in the reactor can be discharged through a venting pipeline. Then, the polymerization reaction for preparing the L stage is carried out, wherein: When preparing the homopolymer L stage, a polymerization solvent and hydrogen, and optionally a supported polyethylene main catalyst and / or a co-catalyst, are added to an ethylene slurry polymerization reactor, ethylene is continuously introduced, and the polymerization pressure and polymerization temperature are kept constant to carry out a polymerization reaction for preparing the L stage; or, When preparing the copolymer L stage, the polymerization solvent, hydrogen and comonomer, as well as the optionally added supported polyethylene main catalyst and / or co-catalyst, are added to the ethylene slurry polymerization reactor, and ethylene is continuously introduced at a constant polymerization pressure and polymerization temperature to carry out the polymerization reaction for preparing the L stage.

12. The method for preparing ultra-high molecular weight polyethylene by polymerization according to any one of claims 5 to 10, wherein: The polymerization preparation method is carried out by a continuous batch process. First, a polymerization reaction is carried out to prepare the U segment. When preparing the homopolymer U segment, the supported polyethylene main catalyst, the co-catalyst, the polymerization solvent, the optional hydrogen and the ethylene are continuously added to the ethylene slurry polymerization reactor simultaneously, the polymerization reaction for preparing the U segment is carried out at a constant polymerization pressure and polymerization temperature, and the materials generated by the polymerization reaction are continuously separated from the ethylene slurry stirring tank; or When preparing the copolymerization U segment, a supported polyethylene main catalyst, a cocatalyst, a polymerization solvent, optional hydrogen, a comonomer and ethylene are continuously added to an ethylene slurry polymerization reactor simultaneously, a polymerization reaction for preparing the U segment is carried out at a constant polymerization pressure and polymerization temperature, and the materials generated by the polymerization reaction are continuously separated from the ethylene slurry stirring kettle; Then, the polymerization reaction for preparing the L stage is carried out, wherein: When preparing the homopolymer L stage, the polymerization solvent, hydrogen and ethylene, and the optionally added supported polyethylene main catalyst and / or co-catalyst are continuously added to the ethylene slurry polymerization reactor at the same time, and the polymerization reaction for preparing the L stage is carried out at a constant polymerization pressure and polymerization temperature; or When preparing the copolymerization L stage, the polymerization solvent, hydrogen and comonomer, ethylene, and the optionally added supported polyethylene main catalyst and / or cocatalyst are continuously added to the ethylene slurry polymerization reactor at the same time, and the polymerization reaction for preparing the L stage is carried out at a constant polymerization pressure and polymerization temperature; The polymerization reaction for preparing the U segment and the polymerization reaction for preparing the L segment are connected by one of the following steps: Directly at the bottom or lower part of the polymerization reactor for preparing the U stage, at least part of the slurry material after the reaction is continuously transferred to the polymerization reactor for preparing the L stage by a pump, and the polymerization reaction for preparing the L stage is continued in the polymerization reactor for preparing the L stage; or, After the polymerization reaction of the preparation U stage, the material buffer tank which is in gas-phase balance communication with the polymerization reactor of the preparation U stage is overflowed to achieve gas-liquid separation, and at least part of the slurry material in the material buffer tank is continuously transferred to the polymerization reactor of the preparation L stage by a pump to continue the polymerization reaction of the preparation L stage; or, After the polymerization reaction of the preparation U stage, at least part of the slurry material is continuously sent to the material buffer tank for degassing, and then the slurry material is introduced into the polymerization reactor for preparing the L stage to continue the polymerization reaction of the preparation L stage.

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