A method for the preparation of ultra-high molecular weight polyethylene

Abstract

The present application relates to a kind of preparation methods of ultra-high molecular weight polyethylene, comprising the following steps: S1, in slurry reactor, diluent, polyethylene catalyst, co-catalyst and raw materials including ethylene are added, ethylene polymerization is carried out, and the slurry material after reaction is obtained;S2, the slurry material after reaction obtained in S1 is concentrated, then is added in the stirring vessel containing aqueous solution and is washed once;S3, the material after washing once in S2 is added in the stirring vessel containing pure water and is washed twice, then is dehydrated and dried, and the ultra-high molecular weight polyethylene is obtained, as product output.Compared with prior art, the present application greatly improves the cleanliness of ultra-high molecular weight polyethylene product by optimizing the resin preparation process.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of polymer material preparation and relates to a preparation method of ultrahigh molecular weight polyethylene. BACKGROUND

[0002] Ultrahigh molecular weight polyethylene has been widely used in the field of lithium battery separators due to its excellent mechanical strength, chemical stability, insulation performance and controllable porosity characteristics. At present, it is mainly in the form of dry single-stretch separator, wet separator, composite separator and coated modified separator, and is applied to power batteries, energy storage batteries, consumer electronic batteries and other fields. Moreover, with the continuous progress of technology and the continuous growth of market demand, the depth and breadth of the application of ultrahigh molecular weight polyethylene in these fields are still expanding, and new application fields are also emerging, showing great development potential and market value.

[0003] However, the ultrahigh molecular weight polyethylene currently applied in the above high-end and high-value fields still depends on imports to a large extent, mainly due to problems such as broken filaments in the spinning process and excessive metal impurity content in the lithium battery separator preparation process. On the other hand, after the reaction is completed, the existing ultrahigh molecular weight polyethylene usually needs to be inactivated before being separated and other post-treatment, and the whole process is relatively complex.

[0004] Currently, there is not enough attention to the post-treatment of the raw material of ultrahigh molecular weight polyethylene, mainly in the following three categories:

[0005] The first category uses low-boiling-point diluents such as isobutane for slurry polymerization, removes the diluents by flashing after leaving the reactor, and obtains resin products by degassing, such as Chinese patent CN113845613B. According to the analysis, this method has a simple post-treatment process, but the cleanliness of the resin product is not enough, and it is only suitable for products that are not sensitive to impurities.

[0006] The second category uses six-carbon and above diluents for polymerization, uses pressure filtration and other means for solid-liquid separation, and then dries to obtain resin products, such as Chinese patent CN201710998532.2 and Chinese patent CN202210092293.5. This product uses a higher-boiling-point diluent, has low reaction pressure, and has a simple process. By solid-liquid separation, part of the impurities can be removed, but the resin product still cannot meet the requirements of fields such as lithium battery separators.

[0007] The third type uses a six-carbon or more diluent to carry out a polymerization reaction, and uses an organic solvent such as hexane to carry out washing on the basis of solvent filtration, and carries out drying after washing, such as the preparation method of a polyethylene resin for melt spinning provided in CN119241748A. This type of method can make the resin relatively cleaner, and can remove part of the oligomers and organic impurities, but the removal effect of inorganic impurities and the like is not good, and still cannot meet the requirements of fields such as lithium battery separators. SUMMARY

[0008] The purpose of the present application is to provide a preparation method of ultra-high molecular weight polyethylene, to improve the cleanliness of ultra-high molecular weight polyethylene, and reduce the impurity content.

[0009] The purpose of the present application can be achieved by the following technical solutions:

[0010] The applicant found that one of the main reasons for filament breakage and excessive metal impurity content is the aluminum-containing impurities formed after the addition of a catalyst promoter to the raw materials and some metal impurities in the equipment, and these impurities are difficult to remove in the production process of ultra-high molecular weight polyethylene.

[0011] Based on this, in one aspect, the present application provides a preparation method of 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 includes the following steps:

[0012] S1, adding raw materials including a diluent, a polyethylene catalyst, a catalyst promoter, and ethylene (hydrogen can also be added as needed to adjust the molecular weight, for example, 1-10 g of hydrogen per ton of ethylene) to a slurry reactor to carry out ethylene polymerization, to obtain a post-reaction slurry;

[0013] S2, concentrating the post-reaction slurry obtained in S1, and then adding it to a stirring container containing an aqueous solution for primary cleaning;

[0014] S3, solid-liquid separation of the material after primary cleaning in S2, and then adding it to a stirring container containing pure water for secondary cleaning, followed by dehydration and drying to obtain ultra-high molecular weight polyethylene as a product.

[0015] Here, it should be pointed out that the process of obtaining ultra-high molecular weight polyethylene slurry in S1 is a prior art, and is not the innovation protection point of the present application, and will not be described here.

[0016] Further, in S1, the diluent is selected from one or a mixture of several of n-hexane, cyclohexane, isooctane, isopentane, n-heptane, and n-pentane;

[0017] The polyethylene catalyst is one or more of Ziegler-Natta polyethylene catalysts, metallocene polyethylene catalysts, and transition metal polyethylene catalysts.

[0018] The co-catalyst is one or a combination of several of triethylaluminum, triisobutylaluminum, diethylaluminum chloride, methylaluminoxane, modified methylaluminoxane, and triisobutylaluminum. It should be noted that the slurry polymerization reaction step described here is a conventional technique in the art; that is, the proportions of the diluent, polyethylene catalyst, co-catalyst, and raw materials such as ethylene used are all conventionally designed in the field and do not constitute an innovative point of this invention, and will not be elaborated further here.

[0019] Furthermore, in S2, the concentration method is to use a hydrocyclone, centrifuge, or filter press system for solid-liquid separation. The purpose of concentration here is to initially separate liquid components such as diluents as much as possible to obtain polyethylene wet material.

[0020] Furthermore, in S2, the first 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. Even further, in S2, the solute is tartaric acid, citric acid, sodium hydroxide, or other alkaline substances that readily react with impurities.

[0021] Furthermore, 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, preferably 0.01~0.5:1. For example, it can be 0.01:1, 0.5:1, 0.1:1, etc. The cleaning operation here can be intermittent or continuous.

[0022] Furthermore, in S2, the temperature of the first cleaning is 60~98℃, preferably 80~90℃. 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 diluent and aqueous solution is avoided, which would affect the subsequent recycling of diluent. At the same time, the temperature should not be too high to avoid the aqueous solution from boiling completely and affecting the cleaning.

[0023] Furthermore, in S3, the mass ratio of the material after one cleaning to pure water is not less than 0.01:1, preferably 0.01~0.5:1, and for example, it can be 0.01:1, 0.5:1, 0.1:1, etc.

[0024] Furthermore, in S3, the temperature for the secondary cleaning is 60~98℃, and can be selected as 80~90℃.

[0025] In the post-processing process of the present application, the concentrated material can be converted into gas phase in the form of azeotrope under the action of high-temperature water after entering the water solution kettle, so as to remove the diluent, and the resin powder is fully contacted with the aqueous solution under the stirring action of the stirred tank, the inorganic substances in the powder are stirred into the aqueous solution, and the inorganic substances are fully mixed and reacted with the aqueous solution, so that the inorganic substances in the pores of the resin powder can be completely removed.

[0026] In addition, in the primary cleaning process, the removal of metal impurities and the like can be realized, and the inactivation treatment of the slurry after the reaction is also realized at the same time, which is helpful to control the progress of the polymerization reaction. The stirred tank for secondary cleaning can clean the solvent on the surface of the residual particles, and further remove the inorganic substances such as aluminum oxide and aluminum hydroxide on the surface of the residual particles.

[0027] In the second aspect, the present application provides a post-processing method of ultra-high molecular weight polyethylene, which comprises the following steps: concentrating the polyethylene slurry obtained by slurry polymerization reaction, and then sequentially using aqueous solution for primary cleaning, pure water for secondary cleaning, and then dehydrating and drying, so as to complete the process.

[0028] 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.

[0029] By using the azeotropic scheme, on the one hand, the impurity components in the slurry after the reaction can be effectively removed, and on the other hand, the cleaning agent can be effectively prevented from being brought into the diluent, which affects the recycling of the diluent. In addition, through the two azeotropic-based washing processes, the cleaning agent can also be prevented from remaining in the product, thereby avoiding its influence on the performance of the product. In general, through the present application, the effective removal of impurities of the ultra-high molecular weight polyethylene resin can be completed at a relatively low production cost, the cleanliness of the product is greatly improved, and the product is beneficial to the preparation in the fields such as lithium battery separator and the like.

[0030] Compared with the prior art, the process flow of the present application is easy to implement, and an ultra-high molecular weight polyethylene resin product with lower impurity content can be obtained, which is especially suitable for preparing lithium battery separators, ultra-high molecular weight polyethylene fibers and the like, and can greatly reduce the yarn breakage rate of spinning and the electrical conductivity of lithium battery separators. DETAILED DESCRIPTION

[0031] The present application will be described in detail below in conjunction with specific embodiments. The present embodiment is implemented on the premise of the technical scheme of the present application, and detailed implementation modes and specific operation processes are given, but the protection scope of the present application is not limited to the following examples.

[0032] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the description of the application herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0033] The selection scope of the terms "and / or", "or / and", "and / or" used in the present application includes any one of two or more relevant listed items, and also includes any and all combinations of the relevant listed items, including any two relevant listed items, any more relevant listed items, or all relevant listed items. It should be noted that when at least two conjunctions selected from "and / or", "or / and", "and / or" are combined to connect at least three items, it should be understood that in the present application, the technical solution undoubtedly includes the technical solution connected by "logical and", and also undoubtedly includes the technical solution connected by "logical or".

[0034] In the present application, the technical features described in an open manner include both the closed technical solution consisting of the listed features and the open technical solution containing the listed features.

[0035] In the present application, if no special description is provided, the numerical interval is considered to be continuous, and includes the minimum value and the maximum value of the range, as well as each value between the minimum value and the maximum value. Further, when the range is an integer, each integer between the minimum value and the maximum value of the range is included. In addition, when multiple ranges are provided to describe a feature or a characteristic, the ranges can be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all sub-ranges therein.

[0036] Only some numerical ranges are specifically disclosed herein. However, any lower limit can be combined with any upper limit to form a range not explicitly recited; and any lower limit can be combined with other lower limits to form a range not explicitly recited, and likewise any upper limit can be combined with any other upper limit to form a range not explicitly recited. In addition, each individual disclosed point or single numerical value can itself be combined as a lower limit or an upper limit with any other point or single numerical value or with other lower limits or upper limits to form a range not explicitly recited.

[0037] In the present application, the temperature parameter, if not specifically limited, allows for constant temperature treatment, and also allows for treatment within a certain temperature range. The constant temperature treatment allows the temperature to fluctuate within the accuracy range controlled by the instrument. Fluctuation within a range such as ±5°C, ±4°C, ±3°C, ±2°C, ±1°C is allowed.

[0038] In the present application, "suitable", "suitable", "any suitable manner", and the like, as described in the present application, are subject to the ability to implement the technical solutions of the present application, solve the technical problems of the present application, and achieve the intended technical effects of the present application.

[0039] In the present application, "further", "furthermore", "in particular" and the like are used to describe purposes and indicate differences in content, but should not be understood as limiting the scope of protection of the present application.

[0040] In the present application, "optionally", "optional" and "optional" mean optional, i.e. selected from either of the two parallel schemes "with" or "without". If there are multiple "options" in a technical solution, unless otherwise specified, and there is no contradictory relationship or mutual restriction, each "option" is independent.

[0041] In the description of the application, "multiple" means at least two, for example, two, three, etc., unless otherwise specified.

[0042] Unless otherwise specified, all formulations and tests in this document occur in an environment of 25°C.

[0043] In this document, "include", "contain", "contain", "contain", "have" or other variants are intended to cover non-closed inclusion, and there is no distinction between these terms. The term "include" means that other steps and ingredients can be added without affecting the final result. The composition and method / process of the present application comprises, consists of and consists essentially of the essential elements and limitations described herein, and any additional or optional ingredients, components, steps or limitations described herein. There is no distinction between the terms "efficiency", "performance", "effect", "efficacy" in this document.

[0044] If not specified, all embodiments and optional embodiments of the present application can be combined to form new technical solutions. If not specified, all technical features and optional technical features of the present application can be combined to form new technical solutions.

[0045] If not specified, all steps of the present application can be performed in sequence or randomly, preferably in sequence.

[0046] The polyethylene catalyst used is a Ziegler Natta polyethylene catalyst, which can use CMU ultra-high molecular weight polyethylene catalyst of Sinopec Beijing Oda Branch, and the brand is M-III, etc.

[0047] The metal impurity content analysis method is inductively coupled plasma mass spectrometry, and the metal impurity content is tested according to GB5009.268 standard.

[0048] Lithium battery diaphragm metal foreign matter analysis method:

[0049] 1) Sample preparation

[0050] First, a certain amount of separator sample needs to be taken out from the lithium-ion battery. A tool such as a blade or scissors can be chosen to cut the separator sample into an appropriate size. Attention should be paid to maintaining the integrity of the sample and avoiding contamination during this step.

[0051] 2) Microscopic examination of the sample

[0052] Microscopic examination of the sample is an important step in testing the metal foreign matter content. A high-power microscope needs to be used to observe the surface of the sample and check for the presence of metal foreign matter. Attention should be paid to the correctness and reliability of the information obtained through the microscope during the examination. If metal foreign matter is found, its location and quantity need to be recorded.

[0053] Method for preparing ultra-high molecular weight polyethylene lithium battery separator: First, mix the ultra-high molecular weight polyethylene resin (viscosity average molecular weight about 1 million) with white oil (weight ratio about 1:4) at about 150°C to obtain a gel sheet with a thickness of about 125 μm; then stretch bidirectionally (mechanical stretching ratio MD:TD=5:1) at about 60°C to reduce the film thickness to about 22 μm; then extract the paraffin oil with an organic solvent such as n-hexane or dichloromethane at about 70°C (extraction time about 5 hours) to obtain a porous structure; finally, heat set at about 125°C (time control at 1-2 minutes) to obtain a lithium battery separator with a porosity of about 40% and a pore size of about 0.06 μm. The entire process needs to be strictly controlled in terms of temperature, stretching rate, and solvent purity to ensure that the separator has ideal mechanical properties and pore structure.

[0054] Method for preparing ultra-high molecular weight polyethylene fiber: First, dissolve the ultra-high molecular weight polyethylene resin (viscosity average molecular weight about 4 million) with white oil (medical grade white oil or industrial grade white oil, concentration controlled at about 5 wt%) at about 140°C by stirring (stirring speed 100-150 rpm, time about 5 hours) to form a uniform transparent spinning solution; deliver the solution through a gear pump (pressure controlled at about 3 MPa) to a spinning box (temperature controlled at about 200°C), and extrude through a spinneret with a pore size of about 0.7 mm; after passing through an air layer of about 12 cm, the fiber 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 a total stretching ratio controlled at about 35 times; then heat set at about 135°C for 1-2 minutes, and finally obtain a high-strength ultra-high molecular weight polyethylene fiber. The entire process needs to be carefully controlled in terms of solution ratio, temperature, total stretching multiple, and extraction effect.

[0055] Example 1

[0056] Polyethylene catalyst, triethylaluminum, n-hexane were added into 7m 3 In the tank reactor, the catalyst dosage was 30 g, the triethylaluminum addition amount was 540 g, and the n-hexane addition amount was 3.6 tons. After the reactor was started to stir, the kettle was heated to 80 ℃, and ethylene gas was introduced to maintain the reactor pressure at 1 MPa. After 3 hours of reaction, the ethylene was stopped, and after the pressure decreased, the slurry reactant was transported to the filter press device for solid-liquid separation to obtain the polyethylene wet material. When it is necessary to adjust the molecular weight of the prepared polyethylene material, hydrogen can be additionally introduced into the reactor, for example, 1-10 g of hydrogen per ton of ethylene, to obtain an ultra-high molecular weight polyethylene material with the desired molecular weight.

[0057] The separated polyethylene wet material was washed once in a stirred tank, 0.01wt% sodium hydroxide aqueous solution was added to the stirred tank, and the mass ratio of the material feed amount in the stirred tank to the fresh aqueous solution supplement amount was 0.5:1. The aqueous solution temperature was 80℃, and the residence time was about 30min. After the material passed through the stirred tank, it was washed twice in a pure water washing kettle, the mass ratio of the material feed amount to the fresh pure water supplement amount was 0.01:1, the second washing temperature was 80℃, and the residence time was about 30min. After that, the material was discharged through a screw belt elevator and dried in a dryer. The detection showed that the content of metal impurities in the obtained raw material was less than 15ppm.

[0058] When the prepared ultra-high molecular weight polyethylene resin is used for downstream spinning, the yarn breakage rate is controlled at about 0.3%, and the fiber strength can reach more than 32.5 cN / dtex; and when used for lithium battery separator preparation, the number of metal foreign matters is not detected.

[0059] Example 2

[0060] Compared with 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, 2wt% citric acid aqueous solution was added to the stirred tank, and the mass ratio of the material feed amount to the fresh citric acid aqueous solution supplement amount was 0.1:1; after the material was washed once, it was washed twice in a pure water washing kettle, and the mass ratio of the material feed amount to the fresh pure water supplement amount was 0.2:1. The content of metal impurities in the obtained raw material was less than 18ppm.

[0061] When used for downstream spinning, the yarn breakage rate was controlled at about 0.3%, and the fiber strength could reach more than 32.2 cN / dtex; and when used for lithium battery separator preparation, the number of metal foreign matters was not detected.

[0062] Example 3

[0063] Polyethylene catalyst, triethylaluminum, n-hexane were added into a slurry loop reactor with a capacity of 30000 tons / year, the catalyst dosage was 18 kg / h, the triethylaluminum dosage was 0.3 kg / h, and the n-hexane dosage was 4000 kg / h. After the reactor was started, the reactor was heated to 80 ℃, and ethylene gas was introduced to maintain the reactor pressure at 1 MPa. Similarly, hydrogen gas can be introduced into the reactor to adjust the molecular weight of the prepared polyethylene material.

[0064] Then the slurry reactants were transported to the cyclone device, the material was concentrated, part of the supernatant was returned to the reactor, and the concentrated material entered the screw belt stripping kettle for primary cleaning. A 40wt% tartaric acid aqueous solution was added to the stripping kettle, and the mass ratio of the material feed amount to the fresh tartaric acid aqueous solution supplement amount was 0.01:1. The aqueous solution temperature was 90℃, and the residence time was about 30 min. After the material was cleaned once, it entered the pure water stripping kettle for secondary cleaning. The mass ratio of the material feed amount to the fresh pure water supplement amount in the cleaning kettle was 0.5:1, the pure water temperature was 90℃, and the residence time was about 30 min. The obtained raw material had a metal impurity content of less than 5 ppm.

[0065] When performing downstream spinning, the breakage rate was controlled at about 0.1%, and the fiber strength could reach more than 33.3 cN / dtex; when preparing lithium battery separators, no metal foreign matter was detected.

[0066] Example 4

[0067] Compared with Example 1, all other conditions were the same, except that in this example: the separated polyethylene wet material was cleaned once in the stirred tank, a 5wt% sodium hydroxide aqueous solution was added to the stripping kettle, and the mass ratio of the material feed amount to the fresh sodium hydroxide aqueous solution supplement amount was 0.1:1. After the material was stripped with the aqueous solution, it entered the pure water stripping kettle for secondary cleaning, and the mass ratio of the material feed amount to the fresh pure water supplement amount in the pure water stripping kettle was 0.4:1. The obtained raw material had a metal impurity content of less than 3 ppm.

[0068] When performing downstream spinning, there was almost no breakage (indicating that the breakage rate was less than 0.01%), and the fiber strength could reach more than 34.0 cN / dtex. When preparing lithium battery separators, no metal foreign matter was detected.

[0069] Comparative Example 1

[0070] The same polymerization scheme as Example 1 was used, and the raw material was obtained by using hot nitrogen gas to dry the solid-liquid separated material after pressure filtration. The obtained raw material had a metal impurity content of about 70 ppm. When performing downstream spinning, the breakage rate was relatively high, about 1.2%, and the fiber strength was 27.8 cN / dtex. When preparing lithium battery separators, metal foreign matter was present.

[0071] Comparative Example 2

[0072] The same polymerization scheme as Example 1 was used, and after solid-liquid separation by pressure filtration, the product was washed with fresh n-hexane and dried. The resulting raw material had a metal impurity content of about 61 ppm. Downstream spinning was performed, with a high yarn breakage rate of about 1.0%, and a fiber strength of 28.0 cN / dtex. Lithium battery separator preparation was performed, with the presence of metal foreign matter.

[0073] Comparative Example 3

[0074] The same polymerization scheme as Example 3 was used, with isobutane used as the solvent. After the reaction was completed, the product was obtained by flash evaporation and drying with hot nitrogen. The resulting raw material had a metal impurity content of about 114 ppm. During the ultra-high spinning process, the post-spinning process could not be performed. Lithium battery separator preparation was performed, with the presence of metal foreign matter.

[0075] Comparative Example 4

[0076] For the gas phase polymerization of ultra-high molecular weight polyethylene, the reactor was preheated to 80-110°C, and inert gas replacement was performed with nitrogen. When the reaction conditions were ready, the catalyst and co-catalyst triethyl aluminum were introduced into the reactor, and ethylene monomer gas was introduced to start the reaction. During the polymerization reaction stage, the reaction temperature was strictly controlled between 80-110°C, and the reaction pressure was maintained at 2 MPa to ensure that the bed was in good fluidization state. During the reaction process, the polymer particles were continuously discharged from the bottom of the reactor, and the unreacted monomer needed to be separated and recovered. Finally, the product was degassed to obtain the raw material, which had a metal impurity content of about 114 ppm. The raw material could not be used for the ultra-high spinning process, and lithium battery separator preparation was performed, with the presence of metal foreign matter.

[0077] Comparative Example 5

[0078] Most of the process was the same as Example 1, except that the temperature of the aqueous solution used for the first washing was 100°C. Due to boiling, the liquid level was unstable, affecting solid-liquid separation, and it was difficult to stably obtain the product. The process was difficult to proceed smoothly.

[0079] Comparative Example 6

[0080] Most of the process was the same as Example 1, except that the temperature of the aqueous solution used for the first washing was 50°C. The resulting resin had a high diluent content of more than 1%, which made it impossible to perform subsequent spinning and battery separator processing. This was because the temperature was too low, and the water and diluent could not reach the azeotropic condition, so the diluent could not be removed from the system with the water through the phase change from liquid to gas.

[0081] Comparative Example 7

[0082] Compared with Example 1, most of them are the same, except that the mass ratio of the amount of fresh water solution supplement to the amount of material feed is 0.001:1 during the first cleaning, and the obtained raw material metal impurity content can only reach less than 75 ppm. Downstream spinning is carried out, and the yarn breakage rate is high, about 1.3%. Lithium battery diaphragm preparation is carried out, and there are metal foreign matters. The low amount of fresh water solution supplement results in almost no effect of the first cleaning, and seriously reduces the ability to remove the raw material metal impurities.

[0083] Table 1 Performance data of examples and part of comparative examples

[0084]

[0085] From the above table, it can be found that after the raw material of ultra-high molecular weight polyethylene is treated by using the resin preparation technology of the present application, the obtained raw material metal impurities are less, and when the process of ultra-high molecular weight polyethylene spinning is carried out, the yarn breakage rate is low, and the metal impurity content after lithium battery diaphragm preparation is less, which can meet the high-end application requirements of lithium battery diaphragm and high-strength fiber products.

[0086] The above description of examples is for the purpose of facilitating the understanding and use of the present application by ordinary skilled persons in the art. Those skilled in the art can obviously make various modifications to these examples, and apply the general principles described herein to other examples without creative labor. Therefore, the present application is not limited to the above examples, and the improvements and modifications made by those skilled in the art according to the disclosure of the present application without departing from the scope of the present application should be within the protection scope of the present application.

Claims

1. A method for preparing ultra-high molecular weight polyethylene, characterized in that, Includes the following steps: S1. Add raw materials including diluent, polyethylene catalyst, co-catalyst and ethylene to the slurry reactor, carry out ethylene polymerization, and obtain the slurry material after reaction. S2. The slurry obtained in S1 after reaction is concentrated and then added to a stirring container containing an aqueous solution for a first wash. The temperature of the first wash is such that the residual diluent in the slurry reacts with the aqueous solution to form an azeotropic reaction. S3. The material that has been washed once in S2 is added to a mixing container containing pure water for a second wash, and then dehydrated and dried to obtain ultra-high molecular weight polyethylene, which is then output as a product. The solute in the aqueous solution is tartaric acid, citric acid, or sodium hydroxide; In S2, the concentration of the aqueous solution is 0.01~40wt%, and the mass ratio of the material in the stirring container to the aqueous solution is not less than 0.01:1; In S3, the mass ratio of the material after one cleaning to pure water added is not less than 0.01:

1.

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

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

4. The method for preparing ultra-high molecular weight polyethylene according to claim 1, characterized in that, In S2, the temperature for one cleaning cycle is 80~90℃.

5. The method for preparing ultra-high molecular weight polyethylene according to claim 1, characterized in that, In S3, the temperature for the second cleaning is 80~90℃.

6. A post-processing method for ultra-high molecular weight polyethylene, characterized in that, After the polyethylene slurry obtained by the slurry polymerization reaction is concentrated, it is washed once with an aqueous solution and then washed twice with pure water. Finally, it is dehydrated and dried to complete the process. The solute in the aqueous solution is tartaric acid, citric acid, or sodium hydroxide; The temperature of the first cleaning is such that the residual diluent in the slurry reacts with the aqueous solution to produce an azeotropic effect. The concentration of the aqueous solution is 0.01~40wt%, and the mass ratio of the material in the stirring container to the aqueous solution is not less than 0.01:1; The mass ratio of the material after one cleaning to pure water should not be less than 0.01:1.

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