Chemically recycled polyolefin separator and related methods
By pyrolyzing the waste generated during the manufacturing process of lithium-ion battery separators and converting it into pyrolytic hydrocarbon oil, the problem of waste utilization is solved, efficient chemical recycling and raw material reuse are achieved, the risk of metal pollution is reduced, and the circular economy is supported.
Patent Information
- Application Number
- CN202580026106.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Priority Date
- 2024-05-03
- Filing Date
- 2025-05-02
- Publication Date
- 2026-11-03
AI Technical Summary
The scraps and roll waste generated during the manufacturing process of lithium-ion battery separators are usually discarded, posing a risk of metal pollution. Furthermore, the mechanical recycling process is complex and difficult to utilize effectively.
These wastes are pyrolyzed in an inert atmosphere to form pyrolytic hydrocarbon oil, which can be used in diaphragm manufacturing processes or as input to steam crackers to produce ethylene for polyethylene polymerization.
It enables efficient chemical recycling of waste, reduces the risk of metal pollution, supports the circular economy, provides a source of reusable raw materials, and reduces the amount of waste.
Smart Images
Figure CN123036335A_ABST
Abstract
Description
[0001] Related applications
[0002] This application claims priority to U.S. Provisional Patent Application No. 63 / 642,594, filed May 3, 2024, entitled CHEMICALLY RECYCLEDPOLYOLEFIN SEPARATORS AND RELATED METHODS, which is incorporated herein by reference in its entirety.
[0003] Copyright Notice
[0004] © 2025 Amtek Research International LLC. This patent document contains copyrighted material. The copyright holder does not object to any reproduction of this patent document or its disclosure as presented in the patent files or records of the Patent and Trademark Office, but otherwise reserves all copyright rights. 37 CFR 1.71(d). Technical Field
[0005] This disclosure relates to the chemical recovery (in contrast to mechanical recovery) of oil-filled and / or extracted polyolefin material generated from extrusions, scraps, or roll waste during the manufacture of “wet-process” polyolefin separators used in Li-ion batteries. In this case, the oil-filled or extracted polyethylene is subjected to pyrolysis in an inert atmosphere to convert the waste into pyrolytic hydrocarbon oil. The resulting pyrolysis oil can be reused in the manufacture of polyethylene separators, or it can be used as feedstock to a cracking tower and converted into naphtha or ethylene for polyethylene polymerization. Background Technology
[0006] The separator is an indispensable component affecting the performance, safety, and cost of lithium-ion batteries. During normal operation, the separator's primary function is to prevent electronic conduction (i.e., short circuits or direct contact) between the anode and cathode, while allowing ion conduction via the electrolyte. Under abuse conditions (such as external short circuits or overcharging), the separator is required to shut down at temperatures well below where thermal runaway could occur. Shutdown occurs due to the collapse of pores in the separator caused by the melting and viscous flow of the polymer, thus slowing or stopping ion flow between the electrodes. Almost all Li-ion battery separators contain polyethylene as part of a single-layer or multi-layer structure, causing shunt to begin at approximately 130°C (the melting point of polyethylene).
[0007] Separators for the lithium-ion market are currently manufactured using either a "dry" or "wet" process. In the dry process, polypropylene (PP) or polyethylene (PE) is extruded into thin sheets and subjected to rapid stretching. The sheet is then annealed at 10°C–25°C below the polymer's melting point to control crystallite size and orientation. Next, the sheet is rapidly stretched in the machine orientation (MD) to create slit-like pores or voids. Three-layer PP / PE / PP separators produced via the dry process are commonly used in lithium-ion rechargeable batteries.
[0008] Wet-process separators made of high molecular weight polyethylene are produced by extruding an oil / polymer mixture into oil-filled sheets at high temperatures, followed by phase separation, biaxial stretching, and extraction of the process oil (i.e., plasticizer). The resulting separator has elliptical or spherical pores with good mechanical properties in both the machine direction and transverse direction. PE-based separators manufactured in this way using casting or blown film techniques are already widely used in Li-ion batteries.
[0009] During the simultaneous or sequential biaxial orientation process in cast film manufacturing, oil-filled polyethylene (PE) sheets and extracted PE sheets are held in place by mechanical clamps while the sheets are stretched in the transverse direction at high temperatures. As the sheets leave the transverse orientation (TDO) unit, the damaged area below the clamps is cut off and wound into scrap. Both oil-filled and extracted PE scrap are typically discarded. Recently, some efforts have been made to mechanically recycle scrap by grinding it into powder or flakes, which can then be reused at the extruder in the separator manufacturing process. Because the scrap grinding and sieving processes involve metal parts, there is a potential risk of PE separator contamination, which could lead to short circuits and fires in lithium-ion batteries.
[0010] In this disclosure, pyrolytic hydrocarbon oil is formed from scrap material through chemical recycling via pyrolysis in an inert atmosphere. Similarly, other roll material waste (e.g., non-conforming diaphragm rolls, etc.) can also be chemically recycled into pyrolytic hydrocarbon oil. The resulting pyrolytic hydrocarbon oil can then be reused in the diaphragm manufacturing process, or it can be used as feedstock for a steam cracker to produce ethylene for use in the polymerization of polyethylene. As used herein, pyrolytic hydrocarbon oil refers to hydrocarbon oil produced from the pyrolysis of scrap or roll material waste. Summary of the Invention
[0011] The purpose of this disclosure is to utilize the chemical recovery of oil-filled and extracted scrap or roll waste generated during the manufacture of “wet-process” polyethylene diaphragms. Pyrolysis in an inert atmosphere is used to produce pyrolytic hydrocarbon oil from the waste, which can then be used in diaphragm manufacturing processes (e.g., as process oil), or it can be used as a precursor for a steam cracker to produce ethylene, which is to be used in the polymerization of polyethylene for use in other products (including other diaphragms). This approach supports a “circular economy” and reduces the risk of metal contamination from waste that is ground and screened for reuse in the extrusion process.
[0012] In the wet process for Li-ion membranes, a polyolefin such as polyethylene (e.g., very high molecular weight polyethylene (VHMWPE)) is combined with a process oil (or plasticizer) at high temperature in an extruder (e.g., a twin-screw extruder). The extrudate is pushed through a sheet die and cast onto cooling rollers to form an oil-filled sheet, where the polyethylene undergoes recrystallization and phase separation from the oil. At this point in the process, the oil-filled sheet is then either sequentially biaxially oriented (machine-directed orientation (MDO), followed by transverse orientation (TDO)) or simultaneously biaxially oriented at high temperature. Next, the oil is removed from the sheet using an extraction solvent, which is then evaporated to produce a microporous polyethylene film. The film is then typically slightly stretched in the transverse direction and annealed at high temperature to achieve its final thickness and porosity before being wound into a finished roll. Typically, oil-filled scrap is cut, trimmed, or otherwise removed from the oil-filled sheet at the exit of the transverse orientation (TDO) (or simultaneously biaxial orientation) unit, and extracted scrap is cut, trimmed, or otherwise removed from the extracted film at the exit of the second transverse orientation (TDO) unit. This oil-filled scrap and extracted scrap are commonly referred to as waste scrap and are typically discarded. Similarly, roll waste is also frequently generated and is usually discarded.
[0013] In a first embodiment of this disclosure, oil-filled and / or extracted waste scrap or roll waste is pyrolyzed at a temperature of about 500°C-1000°C or higher to form a pyrolytic hydrocarbon oil. This pyrolytic hydrocarbon oil can be recycled and blended with virgin oil (i.e., virgin process oil) or another recycled process oil (e.g., process oil previously used in a diaphragm manufacturing process, which is extracted and distilled for reuse). In a subsequent diaphragm manufacturing process, this pyrolytic hydrocarbon oil is combined with polyethylene in an extruder (e.g., a twin-screw extruder). In some cases, at least 20% of the oil combined with polyethylene originates from the pyrolytic waste scrap. The resulting oil-filled sheet is then biaxially oriented, followed by solvent extraction and drying to form a self-supporting microporous polyethylene film, which can be further stretched and annealed (according to the previously described diaphragm manufacturing process) before winding. The resulting diaphragm has a thickness between about 3 and about 25 μm, wherein the porosity is in the range of 35%-60%. The term "self-supporting" refers to a thin film possessing sufficient mechanical properties to allow for operations such as winding and unwinding in film form during use in the assembly of energy storage devices. The term "thin film" includes other terms used in scientific and patent literature, such as "membrane," "sheet," and "mesh," and is used interchangeably with such terms throughout this document. The term "microporous" refers to an average pore size of less than about 1 micrometer (e.g., 0.1 to 0.3 micrometers as measured by mercury porosimetry).
[0014] If desired, the additional oil-filled and / or extracted waste scrap generated during the formation of the self-supporting microporous polyethylene film can then be removed and pyrolyzed at approximately 500°C–1000°C or higher to form a pyrolytic hydrocarbon oil. This pyrolytic hydrocarbon oil can be blended with virgin oil (or another recycled process oil, such as a process oil previously used in the diaphragm manufacturing process that is extracted and distilled for reuse) and combined with polyethylene in an extruder (e.g., a twin-screw extruder) to form another self-supporting microporous polyethylene film. In some such embodiments, the continuous processing and pyrolysis of waste scrap can be part of a closed-loop process during “wet” diaphragm manufacturing.
[0015] In a second embodiment, oil-filled and / or extracted waste scraps or roll waste are pyrolyzed at approximately 500°C–1000°C or higher to form pyrolytic hydrocarbon oil. The pyrolytic hydrocarbon oil is then fed into a steam cracker to produce ethylene, which can be polymerized to form polyethylene. The polyethylene can then be used in various products. For example, polyethylene powder or granules can be formed from the ethylene produced during steam cracking. The polyethylene powder or granules can then be used to form various products, including battery separators. Attached Figure Description
[0016] Figure 1This is a schematic diagram of exemplary process steps for manufacturing polyethylene separators.
[0017] Figure 2 It is a graph depicting the carbon distribution of oil obtained from pyrolysis of polyethylene diaphragm scraps. Detailed Implementation
[0018] Polyethylene separators can be produced using various grades of polyethylene with molecular weights ranging from about 500,000 g / mol to about 10,000,000 g / mol. As used herein, ultra-high molecular weight polyethylene (UHMWPE) typically corresponds to a range between about 3,100,000 g / mol and about 10,000,000 g / mol, and very high molecular weight polyethylene (VHMWPE) typically corresponds to a range between about 500,000 g / mol and about 3.1 g / mol. In some embodiments, VHMWPE having a molecular weight between about 500,000 g / mol and about 2,000,000 g / mol is used. Representative polymers include VH035 from KPIC Corporation (Korea), GUR 4102 from Celanese Corporation (USA), and UH650 from Asahi Kasei Corporation (Japan).
[0019] The process oil (i.e., plasticizer) used in this disclosure is a non-evaporative solvent for the polyethylene polymer and is preferably liquid at room temperature. The plasticizer has little or no solvation effect on the polymer at room temperature; it exerts its solvation effect at or above the softening temperature of the polymer. For VHMWPE, the solvation temperature will be above about 180°C, and preferably in the range of about 200°C to about 225°C. Process oils such as paraffin oils, naphthenic oils, aromatic oils, white mineral oils, or mixtures of two or more such oils are preferred. Examples of suitable process oils include Risella 430X from Shell Oil Company and Hydrocal from Calumet Specialty Products. TM 800; and Nytex 820 from Nynas Inc.
[0020] The polyolefin polymer / oil mixture is extruded through a sheet die or annular die and then biaxially oriented to form a thin, oil-filled film. Biaxial orientation can be performed sequentially (machine-oriented (MDO), then transverse-oriented (TDO)) or simultaneously, depending on the requirements. Any solvent compatible with the oil can be used in the extraction step, provided that the boiling point of the solvent makes it practical to separate the solvent from the plasticizer by distillation. Such solvents include 1,1,2-trichloroethylene, perchloroethylene, 1,2-dichloroethane, 1,1,1-trichloroethane, 1,1,2-trichloroethane, dichloromethane, hexane, heptane, decane, toluene, and solvents containing isoparaffins with a flash point of about 38°C to about 66°C (e.g., IsoPar-G). In some cases, it is desirable to select a process oil such that any residual oil in the polymer sheet after extraction is electrochemically inactive.
[0021] Figure 1 The diagram illustrates exemplary process steps for manufacturing polyethylene separators. As shown, common cast film manufacturing processes can include various combinations of: a polymer extruder (such as a twin-screw extruder), a roll stack unit (e.g., a casting roll unit, cooling rolls, etc.), a machine orientation unit (MDO), a first transverse orientation unit (TDO1), a solvent extractor unit, a dryer unit (e.g., an air dryer), a second transverse orientation unit (TDO2), and a winding unit. As will be understood, more or fewer components may be included, and therefore... Figure 1 The diagrams shown are intended to be illustrative only. For example, the process may also include a heat setting unit, a traction roller unit, and a trimming unit.
[0022] In embodiments according to this disclosure, oil-filled scrap can be cut, trimmed, or otherwise removed or taken away at the outlet of the first transverse orientation unit (TDO1), and extracted scrap can be cut, trimmed, or otherwise removed or taken away at the outlet of the second transverse orientation unit (TDO2). Such scrap is commonly referred to as waste scrap and can be the subject of the chemical recycling disclosed herein.
[0023] Non-limiting examples of the chemical recycling of polyethylene membranes are shown below:
[0024] Example 1
[0025] After transverse orientation in a Parkinson tenter frame operating at 130°C, the extracted polyethylene diaphragm scrap was collected. A 500 g sample of scrap was placed in a kiln reactor, which was then heated to 500°C and held at that temperature for 1 hour to convert the scrap into pyrolytic hydrocarbon oil (i.e., the resulting oil). Gas chromatography was used to determine the carbon distribution of the resulting oil. Figure 2As shown, the resulting oil has a carbon profile less than C50, or between C5 and C40. This carbon profile may be further affected by pyrolysis temperature and time.
[0026] Example 2
[0027] A 50 / 20 / 30 ratio of virgin Risella 430X oil (Shell), pyrolytic hydrocarbon oil from Example 1, and VHMWPE (VH035; KPIC) were fed into a twin-screw extruder and processed at approximately 225°C to form an oil-filled sheet 750 µm thick. The resulting sheet was then biaxially stretched at approximately 115°C at 7.0 times in the machine direction (MD) and 7.0 times in the transverse direction (TD) to form an oil-filled sheet approximately 15 µm thick.
[0028] A 100 mm x 100 mm oil-filled sheet was clamped in a metal frame supporting all four sides of the sheet. The sample was then extracted in trichloroethylene, and the frame was placed in a circulating oven at 60°C to dry the resulting microporous membrane. The membrane had a thickness of approximately 12 µm and a Gurley permeability of 160 s / 100 cc air.
Claims
1. A self-supporting microporous polyolefin film derived from the extrusion of a mixture comprising process oil and a polyolefin polymer, wherein at least 20% of the process oil comprises pyrolytic hydrocarbon oil having a carbon distribution of less than C50, the pyrolytic hydrocarbon oil being derived from the pyrolysis of polyolefin scrap or roll waste.
2. The self-supporting microporous polyolefin film of claim 1, wherein, The pyrolysis hydrocarbon oil has a carbon distribution between C5 and C40.
3. A method for recycling polyolefin scraps or roll waste, the method comprising: The mixture containing process oil and polyolefin polymer is extruded into oil-filled sheets; The oil-filled sheet is biaxially oriented. Trim a portion of the biaxially oriented oil-filled sheet; as well as The trimmed portion of a biaxially oriented oil-filled sheet is pyrolyzed to form pyrolytic hydrocarbon oil.
4. The method of claim 3, wherein, The polyolefin polymer includes polyethylene.
5. The method of claim 4, further comprising: The pyrolysis hydrocarbon oil is fed into a steam cracker to produce ethylene.
6. The method of claim 3, further comprising: At least a portion of the process oil is extracted from the oil-filled sheet to form an extracted microporous membrane; Trim a portion of the extracted microporous membrane; as well as The trimmed portion of the extracted microporous membrane is pyrolyzed.
7. The method of claim 6, further comprising: Before pyrolyzing the trimmed portion of the biaxially oriented oil-filled sheet and the trimmed portion of the extracted microporous membrane, the trimmed portion of the extracted microporous membrane is combined with the trimmed portion of the biaxially oriented oil-filled sheet.
8. The method of any one of claims 3-7, wherein, The pyrolysis hydrocarbon oil contains a carbon distribution with a C50 or less.
9. The method of claim 8, wherein, The pyrolysis hydrocarbon oil includes a carbon distribution between C5 and C40.
10. The method of any one of claims 3-9, wherein, The pyrolysis step is carried out at a temperature of at least 500°C for a sufficiently long time to convert the trimmed portion of the biaxially oriented oil-filled sheet into the pyrolytic hydrocarbon oil.
11. The method of claim 10, wherein, The pyrolysis step is carried out at a temperature between approximately 500°C and approximately 1000°C for a sufficiently long period of time to convert the trimmed portion of the biaxially oriented oil-filled sheet into the pyrolytic hydrocarbon oil.
12. A pyrolytic hydrocarbon oil having a carbon distribution of less than C50, derived from the pyrolysis of polyolefin scrap or roll waste generated during the manufacture of wet-process diaphragms.
13. The pyrolysis hydrocarbon oil of claim 12, wherein, The pyrolysis hydrocarbon oil has a carbon distribution between C5 and C40.
14. The pyrolytic hydrocarbon oil of claim 12 or 13, wherein, The polyolefin scrap or roll waste is pyrolyzed at a temperature of at least 500°C for a sufficient period of time in order to convert the scrap or roll waste into the pyrolytic hydrocarbon oil.
15. The pyrolysis hydrocarbon oil of claim 14, wherein, The polyolefin scrap or roll waste is pyrolyzed at a temperature between approximately 500°C and approximately 1000°C for a sufficiently long period of time in order to convert the scrap or roll waste into the pyrolytic hydrocarbon oil.
16. A polyethylene powder, which is polymerized from ethylene produced during the steam cracking of pyrolytic hydrocarbon oil as described in any one of claims 12-15.
17. A closed-loop process for the chemical recovery of polyolefin scrap or roll waste generated during the manufacture of wet-process membranes, the process comprising: The mixture containing process oil and polyolefin polymer is extruded into oil-filled sheets; The oil-filled sheet is biaxially oriented. Trim a portion of the biaxially oriented oil-filled sheet; as well as The trimmed portion of a biaxially oriented oil-filled sheet is pyrolyzed to form pyrolytic hydrocarbon oil.
18. The closed loop process of claim 17, wherein, This biaxial orientation includes sequential biaxial orientation.
19. The closed loop process of claim 17, wherein, This biaxial orientation includes simultaneous biaxial orientation.
20. The closed-loop process according to any one of claims 17-19, further comprising: The pyrolysis hydrocarbon oil is combined with a second volume of process oil to form an oil mixture for subsequent diaphragm manufacturing processes.
21. The closed-loop process according to any one of claims 17-20, further comprising: At least a portion of the process oil is extracted from the oil-filled sheet to form an extracted microporous membrane; Trim a portion of the extracted microporous membrane; as well as The trimmed portion of the extracted microporous membrane is pyrolyzed.
22. The closed-loop process of claim 21, further comprising: Before pyrolyzing the trimmed portion of the biaxially oriented oil-filled sheet and the trimmed portion of the extracted microporous membrane, the trimmed portion of the extracted microporous membrane is combined with the trimmed portion of the biaxially oriented oil-filled sheet.
23. The closed loop process of any of claims 17-22, wherein, The pyrolysis hydrocarbon oil contains a carbon distribution with a C50 or less.
24. The closed loop process of claim 23, wherein, The pyrolysis hydrocarbon oil includes a carbon distribution between C5 and C40.
25. The closed loop process of any one of claims 17-24, wherein, The pyrolysis step is carried out at a temperature of at least 500°C for a sufficiently long time to convert the trimmed portion of the biaxially oriented oil-filled sheet into the pyrolytic hydrocarbon oil.
26. The closed loop process of claim 25, wherein, The pyrolysis step is carried out at a temperature between approximately 500°C and approximately 1000°C for a sufficiently long period of time to convert the trimmed portion of the biaxially oriented oil-filled sheet into the pyrolytic hydrocarbon oil.