A method for preparing polyethylene wax from wet lithium battery separator oil-containing waste material and use of the waste material

Abstract

The present application relates to a kind of polyethylene wax preparation method and waste use of wet lithium battery separator oil-containing waste, belong to lithium battery separator production technical field, the present application includes the following steps: removing surface dust impurities to oil-containing waste film;The oil-containing waste film is continuously carried out twice cracking reaction, the first cracking reaction condition is: feed section 300~350°C, cracking section 450~550°C, screw rotation speed 30~100rpm, until the material viscosity reaches 3000~3500cp after second cracking reaction;Second cracking reaction condition is: feed section 420~500°C, cracking section 400~480°C, screw rotation speed 30~100rpm, reaction to material viscosity is 50~1000cp, obtain polyethylene wax crude product;Two times cracking reaction is carried out in the protection of nitrogen, in screw extruder;Polyethylene wax crude product is successively carried out decoloring treatment and impurity removal treatment.The present application can make full use of white oil and polyethylene in oil-containing waste, by controlling temperature and applied shear stress, white oil and polyethylene cracking and grafting reaction, generate high-quality polyethylene wax.

Description

Technical Field

[0001] This invention relates to the field of lithium battery separator production technology, and in particular to a method for preparing polyethylene wax from oily waste from wet-process lithium battery separators and the uses of the waste. Background Technology

[0002] The wet process is one of the main methods for preparing lithium-ion battery separators. This process involves mixing polyethylene with white oil (paraffin oil) and other materials at high temperatures to form a homogeneous solution, which is then extruded, stretched, and extracted to form a microporous separator. During separator production, a large amount of oil-containing waste membrane, including scraps and defective products, is generated. Statistics show that approximately the same weight of oil-containing waste is generated for every ton of wet-process separator produced, containing a high content of white oil and polyethylene.

[0003] Due to the specific requirements of lithium-ion battery separators, the polyethylene used must have stable molecular weight and extremely low impurity content, while the white oil used must be cosmetic grade with very low impurity content and excellent physicochemical properties. However, current methods for treating oily waste membranes primarily involve landfilling and incineration. Both polyethylene and white oil in these waste membranes are high-value resources; direct disposal not only wastes resources but also pollutes the environment. Therefore, how to achieve the resource utilization, especially the high-value utilization, of oily waste membranes has become an urgent technical problem to be solved in this field.

[0004] To address the aforementioned issues, some scholars have proposed methods for recycling oil-containing waste membranes. For example, Chinese patent CN112622087A discloses a method for recycling and granulating scraps from wet-process lithium-ion battery separators. This method involves mixing oil-containing materials and dry membranes in a 1:1-9 ratio, directly extruding and granulating the mixture at 160-250°C and a screw speed of 60-150 rpm to produce reusable granules for downstream product processing. However, the granules extruded by this method still contain a high content of white oil, limiting their use to low-end filling applications. They cannot meet the strength and quality requirements of most industrial products, and white oil can leach out during storage and transportation, polluting the environment. Chinese patent CN110724360A discloses an elastic material made from waste hydrometallurgical lithium battery separators, its preparation method, and its application. The method involves first removing some of the white oil, and then mixing the oil-containing raw material after white oil removal with elastomers, fillers, and other components to produce an elastic material. The oil film separation process is relatively complex and costly. Furthermore, the production of the elastic material does not fully utilize the unique properties of polyethylene and white oil in the oil-containing waste film, resulting in low resource utilization.

[0005] Furthermore, there are existing reports on the preparation of polyethylene wax from waste plastics. For example, Chinese patent CN112694552A discloses a method for preparing polyethylene wax with a low molecular weight distribution index, including adding polyethylene raw material to a primary screw extruder, setting the primary screw speed to 10-20 r / min and the pyrolysis temperature to 350-380℃, and then extruding it into a secondary screw extruder, setting the secondary screw speed to 5-10 r / min and the pyrolysis temperature to 300-400℃. This method uses pure polyethylene as raw material and is a single pyrolysis process. However, this method is only applicable when the raw material is pure polyethylene. But oily waste film contains polyethylene and white oil, which are difficult to degrade uniformly and controllably under conventional pyrolysis conditions. If the pyrolysis is insufficient, the product has an excessively wide molecular weight distribution and extremely high viscosity, making it unusable as polyethylene wax; if the pyrolysis is excessive, a large amount of small molecule hydrocarbon gas and liquid fuel are generated, resulting in a low yield of the target product.

[0006] In summary, there is currently no effective method for directly preparing polyethylene wax from oily waste materials from wet-process lithium-ion battery separators. Therefore, it is necessary to provide a method for preparing polyethylene wax from oily waste materials with sufficient pyrolysis and a narrow molecular weight distribution, directly converting the white oil and polyethylene inherent in the oily waste materials from lithium-ion battery separators into high-value-added, high-quality polyethylene wax products, thereby achieving high-value resource utilization of the waste materials. Summary of the Invention

[0007] To overcome the problems existing in the background technology, the present invention provides a method for preparing polyethylene wax from oily waste of wet-process lithium battery separators and the use of the waste. It can make full use of the white oil and polyethylene in the oily waste. By controlling the temperature and applying shear stress, the white oil and polyethylene undergo cracking and grafting reactions to generate high-quality polyethylene wax, thereby realizing the high-value resource utilization of oily waste.

[0008] To achieve the above objectives, the present invention is implemented through the following technical solution: This invention provides a method for preparing high-melting-point polyethylene wax using oily waste from wet-process lithium battery separators, specifically including the following steps: (1) Remove surface dust and impurities from the oily waste film; (2) The oily waste film is subjected to two consecutive pyrolysis reactions. The conditions for the first pyrolysis reaction are: 300~350°C in the feed section, 450~550°C in the pyrolysis section, and 30~100 rpm in the screw speed until the material viscosity reaches 3000~3500 cp, and then the second pyrolysis reaction is carried out. The conditions for the second pyrolysis reaction are: 420~500°C in the feed section, 400~480°C in the pyrolysis section, and 30~100 rpm in the screw speed until the material viscosity reaches 50~1000 cp, and crude polyethylene wax is obtained. Both pyrolysis reactions are carried out in a screw extruder under the protection of nitrogen, and a thermo-oxygen stabilizer is added in the feed section of the second pyrolysis reaction. (3) The crude polyethylene wax is subjected to decolorization and impurity removal treatment in sequence, and then cooled to obtain the polyethylene wax product.

[0009] In the above technical solution, the oil-containing waste film has a melting point of 185~195℃ and includes 20%~80% polyethylene with a molecular weight of 200,000-1,600,000 and 20%-80% white oil.

[0010] In the above technical solution, the temperature of the second pyrolysis reaction pyrolysis section is lower than the temperature of the first pyrolysis reaction pyrolysis section.

[0011] In the above technical solution, the thermo-oxidative stabilizer is selected from one or more of antioxidant 330, antioxidant 168, antioxidant 1010 and dioctadecyl thiodipropionate, wherein the mass ratio of oily waste film to thermo-oxidative stabilizer is 10000:5-1000:3.

[0012] In the above technical solution, the decolorization process is carried out by adsorption and decolorization using a physical adsorbent at a temperature of 250±20℃.

[0013] In the above technical solution, the physical adsorbent is selected from one or more combinations of activated clay, activated carbon, and molecular sieves. The amount of physical adsorbent used is 10%-15% of the crude polyethylene wax mass, and the adsorption and decolorization time is 3-5 minutes.

[0014] In the above technical solution, the impurity removal process includes light oil removal and filtration. The light oil removal is carried out by introducing nitrogen gas under vacuum pressure of -1.5 kPa to -2.5 kPa and temperature of 110℃ to 140℃ to remove light oil from the crude polyethylene wax. The filtration is carried out under the condition that the filter pore diameter is 0.5 μm to remove solid impurities from the crude polyethylene wax.

[0015] This technical solution also provides a polyethylene wax, wherein the polyethylene wax has a melting point of 107~135℃, a PDI of 2~7, a penetration of 1~6, and an ash content of <0.0005%.

[0016] This technical solution also provides the use of wet-process lithium battery separator waste in the preparation of polyethylene wax.

[0017] The principle of polyethylene and white oil pyrolysis and grafting reaction: Under the influence of heating and shear stress, polyethylene undergoes the following cracking reactions: At the same time, the white oil also undergoes a cracking reaction: Where a+b=20~40 Under closed conditions, the broken ethylene chain radicals undergo a grafting reaction with the broken white oil chain radicals: Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention has a high resource utilization rate. It directly utilizes oily waste from wet-process diaphragm membranes without the need for pre-separation of white oil and polyethylene, thus reducing the cost of white oil separation. Through the shear stress and temperature generated, the molecular chains of polyethylene and white oil are broken, producing a large number of free radicals. The broken ethylene chain free radicals undergo a grafting reaction with the broken white oil chain free radicals to generate crude polyethylene wax. Then, through a series of refining processes such as decolorization and impurity removal, high-quality polyethylene wax is generated, realizing the high-value resource utilization of waste.

[0018] 2. The polyethylene wax prepared by this invention has a melting point of 107℃~135℃, a wide range of applications, a narrow molecular weight distribution range, a PDI of 2~7, a penetration of 1-6dmm, moderate hardness, and an ash content of <0.0005%, making it of excellent quality and suitable for engineering plastics processing, masterbatch, coatings and other fields where high heat resistance is required.

[0019] 3. This invention controls the degree of pyrolysis of polyethylene and white oil through two-stage temperature-controlled pyrolysis. The first stage involves rapid pyrolysis at high temperature, while the second stage involves lowering the temperature and adding a thermo-oxygen stabilizer to continue slow pyrolysis. This controls the degree of pyrolysis of polyethylene and white oil, making the reaction more uniform and achieving a polyethylene wax yield of over 90%. Detailed Implementation

[0020] To make the objectives, technical solutions and advantages of the present invention clearer, the embodiments of this application will be described in further detail below.

[0021] In the description of this invention, it should be understood that the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance. Those skilled in the art can understand the specific meaning of these terms in this invention based on the specific circumstances. Furthermore, in the description of this invention, unless otherwise stated, "multiple" refers to two or more. "And / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. The character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0022] 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 invention pertains. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0023] Example 1 (1) Raw material preparation: Take 1000 kg of oily waste membrane generated from the production of wet lithium battery separator. Its melting point is 192℃, the molecular weight of polyethylene is 800,000, and the white oil content is 55%. After removing the surface dust, crush it into fragments with a side length of 3×6 mm using a crusher.

[0024] (2) The crushed material was added to the first screw extruder. The temperatures of each heating zone of the first screw extruder were set as follows: 320℃ for the feeding section and 500℃ for the pyrolysis section. The screw speed was 60 rpm / min. The screw length-to-diameter ratio (L / D) was 35, and the die pressure was 100 MPa. Nitrogen gas was introduced throughout the process for protection, with a nitrogen pressure of 0.15 MPa and a flow rate of 5 L / min. The material underwent violent pyrolysis in the barrel, with the polyethylene long chain and white oil molecular chain breaking to generate free radicals, which then underwent grafting reactions. The viscosity of the outlet material was stabilized at 3200 cp by monitoring with an online viscometer.

[0025] (3) The material from the outlet of the first screw extruder is sealed and conveyed to the second screw extruder. The temperatures of each heating zone of the second screw extruder are set as follows: 470℃ in the feed section, 450℃ in the pyrolysis section, and screw speed 60 rpm / min. The screw length-to-diameter ratio (L / D) is 35, and the die pressure is 100 MPa. Nitrogen gas is introduced throughout the process for protection, with a nitrogen pressure of 0.2 MPa and a flow rate of 20 L / min. 1 kg of antioxidant 330 is added at the feed inlet of the second screw extruder. The material reacts more uniformly, and the outlet viscosity drops to 800 cp, yielding crude polyethylene wax.

[0026] (4) The crude polyethylene wax was directly fed into a nitrogen-protected reactor to maintain homogeneity. The material was then transferred to a decolorizing reactor, where 12% activated clay and 3% activated carbon were added by weight. The mixture was stirred and decolorized at 250°C for 4 minutes. It was then transferred to a light oil removal reactor, where light oil was removed under a vacuum of -1.5 kPa and 130°C. Finally, the mixture was filtered through a 0.5 μm plate and frame filter press to remove solid impurities. After cooling, 930 kg of polyethylene wax and 60 kg of light oil were obtained.

[0027] The above technical solution yields 93% polyethylene wax. The polyethylene wax obtained has a melting point of 124.6℃, a molecular weight distribution range of PDI of 2.1, an acid value of 0.03 mgkoH / g, an ash content of 0.0002%, a volatile content of 0.6%, a penetration of 1 dmm, and a grayish-white flake appearance with no visible impurities.

[0028] Example 2 (1) Raw material preparation: Take 1000 kg of oily waste membrane generated from the production of wet lithium battery separator. Its melting point is 185℃, the molecular weight of polyethylene is 200,000, and the white oil content is 20%. Remove surface dust.

[0029] (2) The oily waste film was directly added to the first screw extruder. The temperatures of each heating zone of the first screw extruder were set as follows: 300℃ in the feeding section and 450℃ in the pyrolysis section, with a screw speed of 100 rpm / min. The screw length-to-diameter ratio (L / D) was 35, and the die pressure was 50 MPa. Nitrogen gas was introduced throughout the process for protection, with a nitrogen pressure of 0.15 MPa and a flow rate of 5 L / min. The material underwent violent pyrolysis in the barrel, with the polyethylene long chain and white oil molecular chain breaking to generate free radicals, which then underwent a grafting reaction. The viscosity of the outlet material was stabilized at 3500 cp by online viscometer monitoring.

[0030] (3) The material from the outlet of the first screw extruder is sealed and conveyed to the second screw extruder. The temperatures of each heating zone of the second screw extruder are set as follows: 420℃ for the feed section and 400℃ for the pyrolysis section, with a screw speed of 30 rpm / min. The screw length-to-diameter ratio (L / D) is 35, and the die pressure is 80 MPa. Nitrogen gas is introduced throughout the process for protection, with a nitrogen pressure of 0.2 MPa and a flow rate of 20 L / min. 0.5 kg of antioxidant 1010 is added at the feed inlet of the second screw extruder. The material reacts further, and the outlet viscosity drops to 1000 cp, yielding crude polyethylene wax.

[0031] (4) The crude polyethylene wax was directly fed into a nitrogen-protected reactor to maintain homogeneity. The material was then transferred to a decolorization reactor, where 10% activated clay and 3% molecular sieve were added by mass. The mixture was stirred and decolorized at 250°C for 5 minutes. It was then transferred to a light oil removal reactor, where light oil was removed under a vacuum of -2.0 kPa and a temperature of 130°C. Finally, the mixture was filtered through a 0.5 μm plate and frame filter press to remove solid impurities. After cooling, 920 kg of polyethylene wax and 65 kg of light oil were obtained.

[0032] The above technical solution yields 92% polyethylene wax. The polyethylene wax obtained has a melting point of 126℃, a molecular weight distribution range of PDI of 2, an acid value of 0.06 mgkoH / g, an ash content of 0.0003%, a volatile content of 2.43%, a penetration of 1 dmm, and a grayish-white flake appearance with no visible impurities.

[0033] Example 3 (1) Raw material preparation: Take 500 kg of oily waste film generated from the production of wet lithium battery separator. Its melting point is 195℃, the molecular weight of polyethylene is 1 million, and the white oil content is 80%. After removing the surface dust, it is made into granules.

[0034] (2) The granular material was added to the first screw extruder. The temperatures of each heating zone of the first screw extruder were set as follows: 350℃ for the feeding section and 500℃ for the pyrolysis section. The screw speed was 30 rpm / min. The screw length-to-diameter ratio (L / D) was 35, and the die pressure was 150 MPa. Nitrogen gas was introduced throughout the process for protection, with a nitrogen pressure of 0.15 MPa and a flow rate of 5 L / min. The material underwent violent pyrolysis in the barrel, with the polyethylene long chain and white oil molecular chain breaking to generate free radicals, which then underwent grafting reactions. The viscosity of the outlet material was stabilized at 3000 cp by monitoring with an online viscometer.

[0035] (3) The material from the outlet of the first screw extruder is sealed and conveyed to the second screw extruder. The temperatures of each heating zone of the second screw extruder are set as follows: 480℃ in the feed section, 460℃ in the pyrolysis section, and screw speed 80 rpm / min. The screw length-to-diameter ratio (L / D) is 35, and the die pressure is 80 MPa. Nitrogen gas is introduced throughout the process for protection, with a nitrogen pressure of 0.2 MPa and a flow rate of 20 L / min. 1.5 kg of antioxidant 168 is added at the feed inlet of the second screw extruder. The material undergoes further pyrolysis and grafting, and the outlet viscosity is reduced to 500 cp, yielding crude polyethylene wax.

[0036] (4) The crude polyethylene wax was directly fed into a nitrogen-protected reactor to maintain homogeneity. The material was then transferred to a decolorization reactor, where 8% activated clay, 2% activated carbon, and 1% molecular sieve were added by mass. The mixture was stirred and decolorized at 260°C for 5 minutes. It was then transferred to a light oil removal reactor, where light oil was removed under a vacuum of -2.5 kPa and a temperature of 140°C. Finally, the mixture was filtered through a 0.5 μm plate and frame filter press to remove solid impurities. After cooling, 460 kg of polyethylene wax and 30 kg of light oil were obtained.

[0037] The above technical solution yields 92% polyethylene wax. The polyethylene wax obtained has a melting point of 135℃, a molecular weight distribution range of PDI of 3.2, an acid value of 0.06 mgkoH / g, an ash content of 0.0004%, a volatile content of 0.4%, a penetration of 1 dmm, and a grayish-yellowish-white flake appearance with no visible impurities.

[0038] Example 4 (1) Raw material preparation: Take 500 kg of oily waste film generated from the production of wet lithium battery separator. Its melting point is 192℃, the molecular weight of polyethylene is 1.6 million, and the white oil content is 70%. After removing the surface dust, it is made into scrap.

[0039] (2) The crushed material was added to the first screw extruder. The temperatures of each heating zone of the first screw extruder were set as follows: 350℃ for the feeding section and 550℃ for the pyrolysis section. The screw speed was 100 rpm / min. The screw length-to-diameter ratio (L / D) was 35, and the die pressure was 150 MPa. Nitrogen gas was introduced throughout the process for protection, with a nitrogen pressure of 0.15 MPa and a flow rate of 5 L / min. The material underwent violent pyrolysis in the barrel, with the polyethylene long chain and white oil molecular chain breaking to generate free radicals, which then underwent a grafting reaction. The viscosity of the outlet material was stabilized at 3100 cp by monitoring with an online viscometer.

[0040] (3) The material from the outlet of the first screw extruder is sealed and conveyed to the second screw extruder. The temperatures of each heating zone of the second screw extruder are set as follows: 500℃ in the feed section, 480℃ in the pyrolysis section, and screw speed 80 rpm / min. The screw length-to-diameter ratio (L / D) is 35, and the die pressure is 80 MPa. A total of 1 kg of antioxidant 330 and antioxidant 168 are added at the feed inlet of the second screw extruder. Nitrogen gas is introduced throughout the process for protection, with a nitrogen pressure of 0.2 MPa and a flow rate of 20 L / min. The material is further pyrolyzed and grafted, and the outlet viscosity is reduced to 500 cp, yielding crude polyethylene wax.

[0041] (4) The crude polyethylene wax was directly fed into a nitrogen-protected reactor to maintain homogeneity. The material was then transferred to a decolorization reactor, where 8% activated clay, 2% activated carbon, and 1% molecular sieve were added by mass. The mixture was stirred and decolorized at 260°C for 5 minutes. It was then transferred to a light oil removal reactor, where light oil was removed under a vacuum of -2.5 kPa and a temperature of 140°C. Finally, the mixture was filtered through a 0.5 μm plate and frame filter press to remove solid impurities. After cooling, 455 kg of polyethylene wax and 35 kg of light oil were obtained.

[0042] The above technical solution yields 91% polyethylene wax. The polyethylene wax obtained has a melting point of 115℃, a molecular weight distribution range of PDI of 4, an acid value of 0.06 mgkoH / g, an ash content of 0.0004%, a volatile content of 0.4%, a penetration of 3 dmm, and a grayish-yellowish-white flake appearance with no visible impurities.

[0043] Example 5 The polyethylene wax product obtained in Example 1 and a commercially available polyethylene wax with a melting point of 105.1℃ were used as dispersants for color masterbatches. Example 1 has a melting point of 124.6℃, and when used as a dispersant for color masterbatches, its melting initiation temperature was 120.6℃ and its melting termination temperature was 127.9℃. The commercially available polyethylene wax with a melting point of 120℃ had an actual melting initiation temperature of 81.2℃ and a melting termination temperature of 107.1℃, a difference of 25.9℃, which is significant. When used as a dispersant for color masterbatches, this affects the mixing cycle of the color masterbatch, reduces the activation effect of pigments and other powder materials, hinders the effective dissipation of moisture during mixing, and results in poor lubrication. The produced color masterbatch has relatively poor fluidity and low surface gloss. Using the polyethylene wax obtained in Example 1 to prepare color masterbatches significantly improves the quality of the masterbatch, and the amount used can be reduced by 30%.

[0044] Comparative Example 1 (1) Raw material preparation: Take 500 kg of oily waste film generated from the production of wet lithium battery separator. Its melting point is 190℃, the molecular weight of polyethylene is 600,000, and the white oil content is 60%. After removing the surface dust, it is made into scrap.

[0045] (2) The crushed material was added to the first screw extruder. The temperatures of each heating zone of the first screw extruder were set as follows: 350℃ for the feeding section and 480℃ for the pyrolysis section. The screw speed was 100 rpm / min. The screw length-to-diameter ratio (L / D) was 35, and the die pressure was 150 MPa. Nitrogen gas was introduced throughout the process for protection, with a nitrogen pressure of 0.15 MPa and a flow rate of 5 L / min. The material underwent violent pyrolysis in the barrel, with the polyethylene long chain and white oil molecular chain breaking to generate free radicals, which then underwent grafting reactions. The viscosity of the outlet material was stabilized at 3100 cp by online viscometer monitoring.

[0046] (3) The material from the outlet of the first screw extruder is sealed and conveyed to the second screw extruder. The temperatures of each heating zone of the second screw extruder are set as follows: 460℃ in the feeding section and 430℃ in the pyrolysis section, with a screw speed of 80 rpm / min. The screw length-to-diameter ratio (L / D) is 35, and the die pressure is 80 MPa. Nitrogen gas is introduced throughout the process for protection, with a nitrogen pressure of 0.2 MPa and a flow rate of 20 L / min. The material undergoes further pyrolysis and grafting, and the outlet viscosity is reduced to 50 cp, yielding crude polyethylene wax.

[0047] (4) The crude polyethylene wax was directly fed into a nitrogen-protected reactor to maintain homogeneity. The material was then transferred to a decolorization reactor, where 8% activated clay, 2% activated carbon, and 1% molecular sieve were added by mass. The mixture was stirred and decolorized at 260°C for 5 minutes. It was then transferred to a light oil removal reactor, where light oil was removed under a vacuum of -2.5 kPa and a temperature of 140°C. Finally, the mixture was filtered through a 0.5 μm plate and frame filter press to remove solid impurities. After cooling, 450 kg of polyethylene wax and 40 kg of light oil were obtained.

[0048] The above technical solution yields 90% polyethylene wax. The polyethylene wax obtained has a melting point of 105℃, a molecular weight distribution range of PDI of 7, an acid value of 0.05 mgkoH / g, an ash content of 0.0005%, a volatile content of 0.4%, a penetration of 7 dmm, and a grayish-yellowish-white flake appearance with no visible impurities.

[0049] Comparative Example 2 (1) Raw material preparation: Take 100kg of oily waste film generated from the production of wet lithium battery separator. Its melting point is 192℃, the molecular weight of polyethylene is 600,000, and the white oil content is 55%. After removing the surface dust, crush it into fragments with a side length of 3×6mm using a crusher.

[0050] (2) Add the crushed material to the screw extruder. The temperatures of each heating zone of the extruder are set as follows: 300℃ for the feeding section, 400℃ for the pyrolysis section, screw speed 80 rpm / min, screw length-to-diameter ratio L / D of 35, and die pressure 100 MPa. Nitrogen gas is introduced for protection throughout the process, with a nitrogen pressure of 0.15 MPa and a flow rate of 5 L / min.

[0051] (4) The molten material from the screw extruder is directly fed into a nitrogen-protected reactor to maintain homogeneity. The material is then transferred to a decolorizing reactor, where 12% activated clay and 3% activated carbon (by weight of the material) are added. The mixture is stirred and decolorized at 250°C for 4 minutes. It is then transferred to a light oil removal reactor, where light oils are removed under a vacuum of -2.0 kPa and 120°C. Finally, the material is filtered through a 0.5 μm plate and frame filter press to remove solid impurities. The molten material is cooled to obtain polyethylene wax.

[0052] The polyethylene wax obtained by the above technical solution has a melting point of 152℃, but the polyethylene and white oil failed to degrade effectively. The resulting polyethylene wax is brittle, with a penetration of 0.05dmm, poor wax feel, and no practical value.

[0053] Comparative Example 3 (1) Raw material preparation: Take 100kg of oily waste film generated from the production of wet lithium battery separator. Its melting point is 192℃, the molecular weight of polyethylene is 600,000, and the white oil content is 55%. After removing the surface dust, crush it into fragments with a side length of 3×6mm using a crusher.

[0054] (2) Add the crushed material to the screw extruder. The temperatures of each heating zone of the extruder are set as follows: 400℃ for the feeding section, 580℃ for the pyrolysis section, screw speed 30 rpm / min, screw length-to-diameter ratio L / D of 35, and die pressure 100 MPa. Nitrogen gas is introduced for protection throughout the process, with a nitrogen pressure of 0.15 MPa and a flow rate of 5 L / min.

[0055] (4) The molten material from the screw extruder is directly fed into a nitrogen-protected reactor to maintain homogeneity. The material is then transferred to a decolorizing reactor, where 12% activated clay and 3% activated carbon (by weight of the material) are added. The mixture is stirred and decolorized at 250°C for 4 minutes. It is then transferred to a light oil removal reactor, where light oil is removed under a vacuum of -2.0 kPa and a temperature of 120°C. Finally, the material is filtered through a 0.5 μm plate and frame filter press to remove solid impurities. After cooling, 40 kg of polyethylene wax and 55 kg of light oil are obtained.

[0056] The above technical solution yields only 40% of polyethylene wax. The polyethylene wax obtained has a melting point of 86℃, a penetration of 10dmm, and is relatively soft.

[0057] Finally, it should be noted that the above preferred embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail through the above preferred embodiments, those skilled in the art should understand that various changes can be made to it in form and detail without departing from the scope defined by the claims of the present invention.

Claims

1. A method for preparing polyethylene wax using oily waste from wet-process lithium battery separators, characterized in that: Specifically, the following steps are included: (1) Remove surface dust and impurities from the oily waste film; (2) The oily waste film is subjected to two consecutive pyrolysis reactions. The conditions for the first pyrolysis reaction are: 300~350°C in the feed section, 450~550°C in the pyrolysis section, and 30~100 rpm in the screw speed until the material viscosity reaches 3000~3500 cp, and then the second pyrolysis reaction is carried out. The conditions for the second pyrolysis reaction are: 420~500°C in the feed section, 400~480°C in the pyrolysis section, and 30~100 rpm in the screw speed until the material viscosity reaches 50~1000 cp, and crude polyethylene wax is obtained. Both pyrolysis reactions are carried out in a screw extruder under the protection of nitrogen, and a thermo-oxygen stabilizer is added in the feed section of the second pyrolysis reaction. (3) The crude polyethylene wax is subjected to decolorization and impurity removal treatment in sequence, and then cooled to obtain the polyethylene wax product.

2. The method for preparing polyethylene wax from oily waste from wet-process lithium battery separators according to claim 1, characterized in that: The oil-containing waste film has a melting point of 185~195℃ and includes 20%~80% polyethylene with a molecular weight of 200,000-1,600,000 and 20%-80% white oil.

3. The method for preparing polyethylene wax from oily waste from wet-process lithium battery separators according to claim 1, characterized in that: The temperature of the second pyrolysis reaction pyrolysis section is lower than that of the first pyrolysis reaction pyrolysis section.

4. The method for preparing polyethylene wax from oily waste from wet-process lithium battery separators according to claim 1, characterized in that: The thermo-oxidative stabilizer is selected from one or more of antioxidant 330, antioxidant 168, antioxidant 1010 and dioctadecyl thiodipropionate, wherein the mass ratio of oily waste film to thermo-oxidative stabilizer is 10000:5-1000:

3.

5. The method for preparing polyethylene wax from oily waste from wet-process lithium battery separators according to claim 1, characterized in that: The decolorization process is carried out by adsorption and decolorization using a physical adsorbent at a temperature of 250±20℃.

6. The method for preparing polyethylene wax from oily waste from wet-process lithium battery separators according to claim 1, characterized in that: The physical adsorbent is selected from one or more combinations of activated clay, activated carbon, and molecular sieves. The amount of physical adsorbent used is 10%-15% of the crude polyethylene wax mass, and the adsorption and decolorization time is 3-5 minutes.

7. The method for preparing polyethylene wax from oily waste from wet-process lithium battery separators according to claim 1, characterized in that: The impurity removal process includes light oil removal and filtration. The light oil removal is carried out by introducing nitrogen gas under vacuum pressure of -1.5 kPa to -2.5 kPa and temperature of 110°C to 140°C to remove light oil from the crude polyethylene wax. The filtration is carried out by filtering solid impurities from the crude polyethylene wax under a filter pore diameter of 0.5 μm.

8. A polyethylene wax prepared by the method according to any one of claims 1 to 7, characterized in that: The polyethylene wax has a melting point of 107~135℃, a PDI of 2~7, a penetration of 1~6, and an ash content of <0.0005%.

9. The use of a wet-process lithium battery separator waste in the preparation of polyethylene wax.

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