Preparation method of ultra-high molecular weight polyethylene

Abstract

The invention relates to a preparation method of ultra-high molecular weight polyethylene, which comprises the following steps: S1, adding raw materials including a diluent, a polyethylene catalyst, a cocatalyst and ethylene into a slurry reactor, and carrying out ethylene polymerization to obtain reacted slurry; s2, concentrating the reacted slurry obtained in the S1, and then adding the concentrated slurry into a stirring container containing an aqueous solution for primary cleaning; and S3, adding the material subjected to primary cleaning in the step S2 into the stirring container containing pure water, carrying out secondary cleaning, then dehydrating and drying to obtain the ultra-high molecular weight polyethylene, and outputting the ultra-high molecular weight polyethylene as a product. Compared with the prior art, the resin preparation process is optimized, so that the cleanliness of the ultra-high molecular weight polyethylene product is greatly improved.

Description

Technical Field

[0001] The invention belongs to the technical field of polymer material preparation, and relates to a method for preparing ultra-high molecular weight polyethylene. Background Art

[0002] Ultra-high molecular weight polyethylene (UHMWPE) has been widely used in lithium battery separators due to its excellent mechanical strength, chemical stability, insulation properties, and controllable porosity. Currently, it is primarily used in the form of dry-laid uniaxially oriented separators, wet-laid separators, composite separators, and coated and modified separators in various applications, including power batteries, energy storage batteries, and consumer electronics batteries. Furthermore, with continuous technological advancements and growing market demand, the depth and breadth of UHMWPE's applications in these fields continues to expand, and new application areas are constantly emerging, demonstrating enormous development potential and market value.

[0003] However, the ultra-high molecular weight polyethylene (UHMWPE) used in these high-end, high-value applications is still largely dependent on imports. This is primarily due to issues such as yarn breakage during the spinning process and excessive metal impurities in the preparation of lithium battery separators. Furthermore, existing UHMWPE typically requires deactivation after the reaction is complete, followed by post-processing such as separation, making the entire process relatively complex.

[0004] Currently, not enough attention has been paid to the post-processing of ultra-high molecular weight polyethylene raw materials, which mainly fall into the following three categories: The first type uses a low-boiling-point diluent, such as isobutane, for slurry polymerization. Flash evaporation is performed after exiting the reactor to remove the diluent and then degas the resin product, as described in Chinese patent CN113845613 B. Analysis shows that this method has a simple post-processing process, but it does not provide sufficient cleanliness for the resin product and is only suitable for products that are not sensitive to impurities.

[0005] The second type uses a C6 or higher diluent for polymerization, uses filter pressing or other methods for solid-liquid separation, and then dries to obtain a resin product, as described in Chinese Patents CN201710998532.2 and CN202210092293.5. This type of product uses a higher-boiling-point diluent, resulting in low reaction pressure and a simple process. While some impurities can be removed through solid-liquid separation, the resulting resin product still lacks sufficient cleanliness, resulting in impurities that cannot meet requirements in fields such as lithium battery separators.

[0006] The third type uses a C6 or higher diluent for polymerization, followed by solvent filtration, washing with an organic solvent such as hexane, and drying after washing. This method, for example, is described in CN119241748A as a method for preparing polyethylene resin for melt spinning. This method can make the resin relatively cleaner, removing some oligomers and organic impurities, but is less effective at removing inorganic impurities and still cannot meet the requirements of fields such as lithium battery separators. Summary of the Invention

[0007] The purpose of the present invention is to provide a method for preparing ultra-high molecular weight polyethylene to improve the cleanliness of the ultra-high molecular weight polyethylene and reduce the impurity content.

[0008] The purpose of the present invention can be achieved by the following technical solutions: Through research, the applicant found that a major cause of broken wires and excessive metal impurity content is the aluminum-containing impurities formed after the co-catalyst is added to the raw materials and the metal impurities in some equipment. These impurities are difficult to remove during the production process of ultra-high molecular weight polyethylene.

[0009] Based on this, in one aspect, the present invention provides a method for preparing ultra-high molecular weight polyethylene, which improves the cleanliness of ultra-high molecular weight polyethylene by optimizing and improving the post-treatment process, and specifically comprises the following steps: S1. Adding raw materials including a diluent, a polyethylene catalyst, a co-catalyst, and ethylene into a slurry reactor (hydrogen may also be added as needed to adjust the molecular weight, for example, 1-10 g hydrogen / t ethylene) to polymerize ethylene to obtain a post-reaction slurry; S2, concentrating the reaction slurry obtained in S1, and then adding it to a stirred container containing an aqueous solution for a first washing; S3, after the solid-liquid separation of the material after the first washing in S2, it is added into a stirring container containing pure water for a second washing, and then dehydrated and dried to obtain ultra-high molecular weight polyethylene, which is output as a product.

[0010] It should be pointed out here that the process of obtaining ultra-high molecular weight polyethylene slurry by polymerization reaction in S1 belongs to the prior art and is not the innovative protection point of the present invention, and will not be described in detail here.

[0011] Furthermore, in S1, the diluent is selected from one or a mixture of n-hexane, cyclohexane, isooctane, isopentane, n-heptane, and n-pentane; The polyethylene catalyst is one or more of a Ziegler-Natta polyethylene catalyst, a metallocene polyethylene catalyst, and a transition metal polyethylene catalyst; The co-catalyst is a combination of one or more of triethylaluminum, triisobutylaluminum, diethylaluminum chloride, methylaluminoxane, modified methylaluminoxane, and triisobutylaluminum. It should be noted that the slurry polymerization step is a conventional technique in the art, i.e., the ratios of the diluent, polyethylene catalyst, co-catalyst, and ethylene and other raw materials used are all conventionally designed in the art. This does not constitute an innovative feature of the present invention and will not be further elaborated upon.

[0012] Furthermore, in S2, the concentration method is to use a cyclone, a centrifuge or a filter press system to perform solid-liquid separation. The purpose of the concentration here is to perform preliminary separation of liquid phase components such as the diluent as much as possible to obtain a polyethylene wet material.

[0013] Furthermore, in S2, the primary cleaning is a chemical cleaning, and the solute in the aqueous solution is a substance that reacts with aluminum hydroxide and aluminum oxide, and the reaction product is soluble in water. Furthermore, in S2, the solute is tartaric acid, citric acid, sodium hydroxide, or other alkaline substances that easily react with impurities.

[0014] Furthermore, in S2, the concentration of the aqueous solution is 0.01 to 40%, and the mass ratio of the material in the stirring container to the aqueous solution is not less than 0.01:1, preferably 0.01 to 0.5:1, and illustratively, it can be 0.01:1, 0.5:1, 0.1:1, etc. The cleaning operation here can be performed intermittently or continuously.

[0015] Furthermore, in S2, the temperature of one washing is 60~98°C, preferably 80~90°C. At this temperature, the diluent in the polyethylene powder can be further removed by azeotropic action, so that the diluent and water are separated in the gas phase, and the mixing of the diluent and the aqueous solution is avoided, which affects the subsequent recycling of the diluent. At the same time, the temperature should not be too high to avoid the aqueous solution from boiling completely and affecting the washing.

[0016] Furthermore, in S3, the mass ratio of the material after one wash to pure water is not less than 0.01:1, preferably 0.01-0.5:1, and illustratively, it can be 0.01:1, 0.5:1, 0.1:1, etc.

[0017] Furthermore, in S3, the temperature of the secondary cleaning is 60-98°C, and can be optionally 80-90°C.

[0018] During the post-treatment process of the present invention, the concentrated material, after entering the aqueous solution kettle, can be converted into a gas phase in an azeotropic form under the action of high-temperature water, thereby removing the diluent. The resin powder is fully contacted with the aqueous solution under the stirring action of the stirring kettle, and the inorganic matter in the powder is stirred into the aqueous solution, fully mixed and reacted with the aqueous solution, which can completely remove the inorganic matter in the pores of the resin powder.

[0019] In addition to removing metallic impurities, the primary cleaning process also simultaneously deactivates the post-reaction slurry, helping to control the polymerization process. The secondary cleaning of the stirred tank removes the solvent from the surface of residual particles and further removes inorganic substances such as aluminum oxide and aluminum hydroxide.

[0020] In a second aspect, the present invention provides a post-treatment method for ultra-high molecular weight polyethylene, comprising: concentrating a polyethylene slurry obtained by a slurry polymerization reaction, washing it once with an aqueous solution, washing it twice with pure water, and then dehydrating and drying it; The solute in the aqueous solution is a substance that reacts with aluminum hydroxide and aluminum oxide, and the reaction product is soluble in water.

[0021] The present invention utilizes an azeotropic solution to effectively remove impurities from the post-reaction slurry. It also effectively prevents the detergent from being carried over into the diluent, hindering its recovery. Furthermore, the two azeotropic washing processes prevent the detergent from remaining in the product and impacting its performance. Overall, this invention allows for effective impurity removal of ultra-high molecular weight polyethylene resin at a low production cost, significantly improving its cleanliness and facilitating its preparation in applications such as lithium battery separators.

[0022] Compared with the existing technology, the process flow of the present invention is easy to implement and can obtain ultra-high molecular weight polyethylene resin products with lower impurity content. It is particularly suitable for preparing lithium battery separators, ultra-high molecular weight polyethylene fibers and other products, and can greatly reduce the spinning breakage rate and the electrical conductivity of lithium battery separators. DETAILED DESCRIPTION

[0023] The present invention is described in detail below with reference to specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0024] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application pertains. The terms used herein in the specification of this application are for the purpose of describing specific embodiments only and are not intended to limit this application.

[0025] The terms "and / or", "or / and", and "and / or" used herein include any one of two or more related listed items, and also include any and all combinations of the related listed items, wherein the any and all combinations include any combination of two related listed items, any more related listed items, or all related listed items. It should be noted that when at least three items are connected by at least two conjunctions selected from "and / or", "or / and", and "and / or", it should be understood that in this application, the technical solution undoubtedly includes technical solutions connected by "logical AND" and technical solutions connected by "logical OR".

[0026] In this application, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0027] In this application, when referring to numerical ranges, unless otherwise specified, the numerical ranges are considered continuous and include the minimum and maximum values ​​of the range, as well as every value between such minimum and maximum values. Further, when a range refers to an integer, every integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe a feature or characteristic, the ranges can be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges subsumed therein.

[0028] Only certain numerical ranges are specifically disclosed herein. However, any lower limit may be combined with any upper limit to form an unspecified range; and any lower limit may be combined with other lower limits to form an unspecified range, and similarly, any upper limit may be combined with any other upper limit to form an unspecified range. In addition, each individually disclosed point or single value may itself serve as a lower limit or upper limit and be combined with any other point or single value, or with other lower limits or upper limits, to form an unspecified range.

[0029] The temperature parameters in this application, unless otherwise specified, allow for both constant temperature treatment and treatment within a certain temperature range. The constant temperature treatment allows for temperature fluctuations within the precision range of instrument control. Fluctuations within the ranges of ±5°C, ±4°C, ±3°C, ±2°C, and ±1°C are permitted.

[0030] Herein, the “suitable” mentioned in “suitable combination”, “suitable method”, “any suitable method”, etc. shall be based on the ability to implement the technical solution of this application, solve the technical problems of this application, and achieve the expected technical effects of this application.

[0031] In this application, "further", "further", "particularly" and the like are used for descriptive purposes to indicate differences in content, but should not be understood as limiting the scope of protection of this application.

[0032] In this application, the terms "optionally," "optional," and "optional" mean optional or dispensable, i.e., they refer to either option being selected from two parallel options: "with" or "without." If a technical solution contains multiple "optional" clauses, each "optional" clause is independent unless otherwise specified and there are no contradictions or constraints.

[0033] In the description of the application, "multiple" means at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0034] Unless otherwise stated, all formulations and tests herein took place at 25°C.

[0035] As used herein, the terms "comprise," "include," "contain," "have," "have," or other variations thereof are intended to encompass non-exclusive inclusions, and no distinction is made between these terms. The term "comprising" means that other steps and ingredients that do not affect the end result may be added. The compositions and methods / processes of the present invention comprise, consist of, and consist essentially of the essential elements and limitations described herein, as well as any additional or optional ingredients, components, steps, or limitations described herein. As used herein, no distinction is made between the terms "efficacy," "performance," "effect," and "efficacy."

[0036] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution. Unless otherwise specified, all technical features and optional technical features of the present application can be combined with each other to form a new technical solution.

[0037] Unless otherwise specified, all steps of the present application can be performed sequentially or randomly, preferably sequentially.

[0038] The polyethylene catalyst used is a Ziegler-Natta polyethylene catalyst, which can be a CMU ultra-high molecular weight polyethylene catalyst produced by Sinopec Beijing Aoda Branch, with a brand name of M-III.

[0039] The metal impurity content analysis method is inductively coupled plasma mass spectrometry, and the metal impurity content test is carried out according to GB5009.268 standard.

[0040] Analysis method of metal foreign matter in lithium battery diaphragm: 1) Sample preparation First, remove a certain amount of separator sample from the lithium-ion battery. Use a blade or scissors to cut the separator sample into appropriate sizes. During this step, care must be taken to maintain sample integrity and avoid contamination.

[0041] 2) Microscopic examination of samples Microscopic examination of samples is an important step in testing for metallic contaminants. A high-magnification microscope is used to examine the sample surface and check for the presence of metallic contaminants. During the inspection, care must be taken to ensure the accuracy and reliability of the information obtained through the microscope. If metallic contaminants are found, their location and quantity should be recorded.

[0042] The preparation method for ultra-high molecular weight polyethylene (UHMWPE) lithium battery separators involves mixing and extruding an UHMWPE resin (viscosity-average molecular weight of approximately 1 million) with white oil (weight ratio of approximately 1:4) at approximately 150°C to produce a gel sheet approximately 125μm thick. This sheet is then biaxially stretched at approximately 60°C (mechanical stretch ratio MD:TD = 5:1) to reduce the thickness to approximately 22μm. The paraffin oil is then extracted with an organic solvent such as n-hexane or dichloromethane at approximately 70°C (for approximately 5 hours) to remove the paraffin oil, resulting in a porous structure. Finally, heat setting is performed at approximately 125°C (for 1-2 minutes) to produce a lithium battery separator with a porosity of approximately 40% and a pore size of approximately 0.06μm. The entire process requires strict control of temperature, stretching rate, and solvent purity to ensure the separator possesses ideal mechanical properties and pore structure.

[0043] Preparation method of ultra-high molecular weight polyethylene fiber: first, ultra-high molecular weight polyethylene resin (viscosity-average molecular weight of about 4 million) and white oil (medical-grade white oil or industrial-grade white oil, concentration controlled at about 5wt%) are stirred and dissolved at about 140°C (stirring speed 100-150rpm, time about 5 hours) to form a uniform and transparent spinning solution; the solution is transported to a spinning box (temperature controlled at about 200°C) through a gear pump (pressure controlled at about 3MPa) and extruded through a spinneret with a pore size of about 0.7mm; the fiber passes through an air layer of about 12cm and enters a cooling bath (temperature about 10°C, using water as a coagulant); the coagulated fiber passes through an extraction device (using n-hexane or dichloromethane, temperature 65°C) to remove the white oil; the treated fiber enters a multi-stage heat stretching zone (first stage temperature about 85°C, second stage temperature about 125°C), with the total stretch ratio controlled at about 35 times; then it is heat-set at about 135°C for 1-2 minutes, finally, obtaining high-strength ultra-high molecular weight polyethylene fiber. The entire process requires key control of solution ratio, temperature, total stretching ratio and extraction effect.

[0044] Example 1 Add polyethylene catalyst, triethylaluminum and n-hexane into 7m3 In a kettle reactor, 30 g of catalyst, 540 g of triethylaluminum, and 3.6 tons of n-hexane were added. After stirring the reactor, the kettle was heated to 80°C and ethylene gas was introduced, maintaining the reactor pressure at 1 MPa. After 3 hours of reaction, the ethylene feed was stopped. Once the pressure dropped, the slurry was transferred to a filter press for solid-liquid separation to produce wet polyethylene. To adjust the molecular weight of the prepared polyethylene material, additional hydrogen gas can be introduced into the reactor, for example, at a rate of 1-10 g of hydrogen per ton of ethylene, to obtain an ultra-high molecular weight polyethylene material of the desired molecular weight.

[0045] The separated polyethylene wet material undergoes a primary cleaning in a stirred tank. A 0.01wt% sodium hydroxide aqueous solution is added to the stirred tank, with a mass ratio of 0.5:1 between the feed volume and the fresh water supply. The water solution is maintained at 80°C and a residence time of approximately 30 minutes. After passing through the stirred tank, the material enters a pure water cleaning tank for a secondary cleaning. The mass ratio of the feed volume to the fresh water supply is 0.01:1, the secondary cleaning temperature is 80°C, and the residence time is approximately 30 minutes. The material is then discharged via a screw belt elevator to a dryer for drying. Testing indicates that the resulting raw material contains less than 15ppm of metallic impurities.

[0046] When the prepared ultra-high molecular weight polyethylene resin is spun downstream, the broken yarn rate is controlled at about 0.3%, and the fiber strength can reach above 32.5 cN / dtex; and when preparing lithium battery separators, no metal foreign matter is detected.

[0047] Example 2 Compared to Example 1, all other conditions were the same, except that in this example: the separated polyethylene wet material was washed once in a stirred tank, a 2 wt% aqueous citric acid solution was added to the stirred tank, and the mass ratio of the material feed to the fresh citric acid solution was 0.1:1; the material after the first wash was then passed into a pure water washing tank, and the mass ratio of the material feed to the fresh pure water added to the washing tank was 0.2:1. The resulting raw material had a metal impurity content of less than 18 ppm.

[0048] During downstream spinning, the broken yarn rate is controlled at about 0.3%, and the fiber strength can reach above 32.2 cN / dtex; when preparing lithium battery separators, no metal foreign matter is detected.

[0049] Example 3 A polyethylene catalyst, triethylaluminum, and n-hexane were added to a 30,000 ton / year slurry loop reactor at a rate of 18 kg / h of catalyst, 0.3 kg / h of triethylaluminum, and 4,000 kg / h of n-hexane. After the axial flow pump was activated, the reactor was heated to 80°C and ethylene gas was introduced, maintaining a pressure of 1 MPa. Hydrogen can also be added to the reactor to adjust the molecular weight of the polyethylene material being produced.

[0050] The slurry is then conveyed to a cyclone for concentration, with a portion of the supernatant returned to the reactor. The concentrated material then enters a ribbon stripper for primary cleaning. A 40wt% tartaric acid aqueous solution is added to the stripper, with a mass ratio of 0.01:1 between the feed and fresh tartaric acid solution, a temperature of 90°C, and a residence time of approximately 30 minutes. After this primary cleaning, the material enters a pure water stripper for secondary cleaning. The mass ratio of the feed to fresh pure water in the stripper is 0.5:1, the pure water temperature is 90°C, and the residence time is approximately 30 minutes. The resulting raw material contains less than 5ppm of metallic impurities.

[0051] During downstream spinning, the broken yarn rate is controlled at about 0.1%, and the fiber strength can reach above 33.3 cN / dtex; when preparing lithium battery separators, no metal foreign matter is detected.

[0052] Example 4 Compared with Example 1, other conditions are the same, except that in this embodiment: the separated polyethylene wet material is washed once by a stirred tank, 5wt% sodium hydroxide aqueous solution is added to the stripping tank, and the mass ratio of the material feed amount to the fresh sodium hydroxide aqueous solution is 0.1:1; the material passes through the aqueous solution stripping tank and then enters the pure water stripping tank for secondary washing, and the mass ratio of the material feed amount to the fresh pure water supply of the pure water stripping tank is 0.4:1; the obtained raw material metal impurity content is less than 3ppm.

[0053] During downstream spinning, there is almost no broken yarn (meaning the broken yarn rate is less than 0.01%), and the fiber strength can reach above 34.0 cN / dtex. When used to prepare lithium battery separators, no metal foreign matter was detected.

[0054] Comparative Example 1 The same polymerization protocol as in Example 1 was used, with solid-liquid separation by filter press followed by drying with hot nitrogen to obtain a raw material with a metal impurity content of approximately 70 ppm. Downstream spinning yielded a high fiber breakage rate of approximately 1.2%, with a fiber strength of 27.8 cN / dtex. Metallic foreign matter was also observed in the preparation of lithium battery separators.

[0055] Comparative Example 2 The same polymerization protocol as in Example 1 was used. After solid-liquid separation by filter press, the resulting material was washed with fresh n-hexane and dried. The metal impurity content of the resulting material was approximately 61 ppm. Downstream spinning revealed a high fiber breakage rate of approximately 1.0%, and a fiber strength of 28.0 cN / dtex. Metallic foreign matter was also observed in the preparation of lithium battery separators.

[0056] Comparative Example 3 The same polymerization protocol as in Example 3 was used, using isobutane as the solvent. After the reactants were discharged, they were flash evaporated and dried with hot nitrogen to obtain the product. The resulting raw material contained approximately 114 ppm of metal impurities. During the ultrahigh-fiber spinning process, post-spinning was not possible. Metallic foreign matter was present during the preparation of lithium battery separators.

[0057] Comparative Example 4 Ultra-high molecular weight polyethylene is polymerized in the gas phase. The reactor is preheated to 80-110°C and the inert gas is replaced with nitrogen. When the reaction conditions are ready, the catalyst and co-catalyst triethylaluminum are introduced into the reactor, and ethylene monomer gas is introduced to start the reaction. During the polymerization reaction stage, the reaction temperature is strictly controlled between 80-110°C and the reaction pressure is maintained at 2MPa to ensure that the bed is in a good fluidized state. During the reaction, polymer particles are continuously discharged from the bottom of the reactor, and the unreacted monomers need to be separated and recovered. Finally, the product is degassed to obtain the raw material. The metal impurity content of the obtained raw material is about 114 ppm. During the ultra-high spinning process of this raw material, the post-spinning process cannot be carried out. Metal foreign matter is present in the preparation of lithium battery separators.

[0058] Comparative Example 5 Compared with Example 1, most of the above are the same, except that the temperature of the aqueous solution for the first cleaning is 100°C. The boiling of the aqueous solution causes the liquid level to be unstable, which affects the solid-liquid separation, making it difficult to obtain a stable output product and the process difficult to proceed smoothly.

[0059] Comparative Example 6 Compared to Example 1, most aspects were identical, except that the temperature of the primary wash aqueous solution was 50°C. The resulting resin contained diluent at a high diluent content exceeding 1%, making subsequent spinning and battery separator processing impossible. This was because the low temperature prevented the water and diluent from reaching azeotropic conditions, preventing the diluent from exiting the system through the liquid-to-vapor phase transition with the water.

[0060] Comparative Example 7 Compared to Example 1, most aspects were identical, except that during the primary wash, the mass ratio of fresh aqueous solution to material feed was 0.001:1, resulting in a raw material metal impurity content of only less than 75 ppm. During downstream spinning, the yarn breakage rate was high, approximately 1.3%. During lithium battery separator preparation, metallic foreign matter was present. The low amount of fresh aqueous solution added resulted in almost no effect during the primary wash, severely reducing the ability to desorb raw metal impurities.

[0061] Table 1 Performance data of the examples and some comparative examples

[0062] It can be found from the above table that after the ultra-high molecular weight polyethylene raw material is processed using the resin preparation technology of the present invention, the obtained raw material has few metal impurities, and during the ultra-high molecular weight polyethylene spinning process, the broken wire rate is low, and the metal impurity content of the lithium battery separator after preparation is low, which can meet the high-end application requirements of lithium battery separators and high-strength fiber products.

[0063] The above description of the embodiments is intended to facilitate understanding and use of the invention by those skilled in the art. It will be apparent that those skilled in the art can readily make various modifications to these embodiments and apply the general principles described herein to other embodiments without requiring inventive effort. Therefore, the present invention is not limited to the above-described embodiments. Improvements and modifications made by those skilled in the art based on the disclosure of the present invention, without departing from the scope of the present invention, should be within the scope of protection of the present invention.

Claims

1. A method for preparing ultra-high molecular weight polyethylene, characterized in that: The following steps are involved: S1, adding raw materials including a diluent, a polyethylene catalyst, a co-catalyst and ethylene into a slurry reactor to carry out ethylene polymerization to obtain a slurry after reaction; S2. Concentrating the reaction slurry obtained in S1, and then adding it to a stirred container containing an aqueous solution for a first wash, wherein the temperature of the first wash is sufficient to produce an azeotropic effect between the residual diluent in the slurry and the aqueous solution; S3. The material after the primary cleaning in S2 is added to a stirring container containing pure water for secondary cleaning, and then dehydrated and dried to obtain ultra-high molecular weight polyethylene, which is output as a product.

2. The method for preparing ultra-high molecular weight polyethylene according to claim 1, wherein: In S1, the diluent is selected from one or a mixture of n-hexane, cyclohexane, isooctane, isopentane, n-heptane, and n-pentane; The polyethylene catalyst is one or more of a Ziegler-Natta polyethylene catalyst, a metallocene polyethylene catalyst, and a transition metal polyethylene catalyst; The co-catalyst is one or a combination of triethylaluminum, triisobutylaluminum, diethylaluminum chloride, methylaluminoxane, modified methylaluminoxane and triisobutylaluminum.

3. The method for preparing ultra-high molecular weight polyethylene according to claim 1, wherein: In S2, the concentration method is to use a hydrocyclone, a centrifuge or a filter press system to separate the solid and liquid.

4. The method for preparing ultra-high molecular weight polyethylene according to claim 1, wherein: In S2, the solute in the aqueous solution is a substance that reacts with aluminum hydroxide and aluminum oxide, and the reaction product is soluble in water.

5. The method for preparing ultra-high molecular weight polyethylene according to claim 4, wherein: In S2, the solutes are tartaric acid, citric acid, and sodium hydroxide.

6. The method for preparing ultra-high molecular weight polyethylene according to claim 1, wherein: In S2, the concentration of the aqueous solution is 0.01-40%, and the mass ratio of the material in the stirring container to the aqueous solution is not less than 0.01:

1.

7. The method for preparing ultra-high molecular weight polyethylene according to claim 1, wherein: In S2, the temperature of the primary cleaning is 80-90°C.

8. The method for preparing ultra-high molecular weight polyethylene according to claim 1, wherein: In S3, the added mass ratio of the material after one cleaning to pure water is not less than 0.01:

1.

9. The method for preparing ultra-high molecular weight polyethylene according to claim 1, wherein: In S3, the temperature of the secondary cleaning is 80~90℃.

10. A post-processing method for ultra-high molecular weight polyethylene, characterized in that: The polyethylene slurry obtained by the slurry polymerization reaction is concentrated, washed once with an aqueous solution, washed twice with pure water, and then dehydrated and dried. The solute in the aqueous solution is a substance that reacts with aluminum hydroxide and aluminum oxide and the reaction product is soluble in water; The temperature of the first cleaning is such that the residual diluent in the slurry produces an azeotropic effect with the aqueous solution.

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