Chemically recycled polyolefin separators and related methods

Abstract

Chemical recycling of oil-filled and / or extracted polyolefin materials that result from extrudate, trim, or roll waste during the manufacture of "wet process" polyolefin separators used in Li-ion batteries is disclosed herein. The oil-filled or extracted polyethylene can be subjected to pyrolysis in an inert atmosphere to convert the waste into a pyrolyzed hydrocarbon oil. The resultant oil can be re-used in the manufacture of polyethylene separators, or it can be used as an input to a cracking tower and converted into naphtha or ethylene for use in the polymerization of polyethylene.

Description

CHEMICALLY RECYCLED POLYOLEFIN SEPARATORSAND RELATED METHODSRelated Applications

[0001] This application claims priority to U.S. Provisional Patent Application No. 63 / 642,594, filed on May 3, 2024, and titled CHEMICALLY RECYCLED POLYOLEFIN SEPARATORS AND RELATED METHODS, which is incorporated herein by reference in its entirety.Copyright Notice

[0002] © 2025 Amtek Research International LLC. A portion of the disclosure of this patent document contains material that is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever. 37 CFR § 1.71(d).Technical Field

[0003] The present disclosure relates to the chemical recycling, in contrast to mechanical recycling, of oil-filled and extracted polyolefin materials that result from extrudate, trim, 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 a pyrolyzed hydrocarbon oil. The resultant pyrolyzed oil can be re-used in the manufacture of polyethylene separators or it can be used as an input to a cracking tower and converted into naphtha or ethylene for use in the polymerization of polyethylene.Background

[0004] Separators are an integral part of the performance, safety, and cost of lithium-ion batteries. During normal operation, the principal functions of the separator are to prevent electronic conduction (i.e., shorts or direct contact) between the anode and cathode while permitting ionic conduction via the electrolyte. Under abuse conditions, such as external short circuit or overcharge, the separator is required to shutdown at temperatures well below where thermal runaway can occur Shutdown results from the collapse of pores in the separator due to melting and viscous flow of the polymer, thus slowing down or stopping ion flow between the electrodes Nearly all Li-ion battery separators contain polyethylene as part of a single- or multi-layer construction so that shutdown begins at ~130°C, the melting point of polyethylene

[0005] Separators for the lithium-ion market are presently manufactured via “dry” or “wet” processes. In the dry process, polypropylene (PP) or polyethylene (PE) is extruded into a thin sheet and subjected to rapid drawdown. The sheet is then annealed at 10-25 °C below the polymer melting point such that crystallite size and orientation are controlled. Next, the sheet is rapidly stretched in the machine direction (MD) to achieve slit-like pores or voids. Trilayer PP / PE / PP separators produced by the dry process are commonly used in lithium-ion rechargeable batteries.

[0006] Wet process separators composed of high molecular weight polyethylene are produced by extrusion of an oil / polymer mixture at elevated temperature into an oil-filled sheet, followed by phase separation, biaxial stretching, and extraction of the process oil (i e., plasticizer). The resultantseparators have elliptical or spherical pores with good mechanical properties in both the machine and transverse directions. PE-based separators manufactured this way using cast film or blown film technologies have found wide use in Li-ion batteries

[0007] During simultaneous or sequential biaxial orientation processes in the cast film process, the oil-filled polyethylene sheet and extracted polyethylene sheet are held with mechanical clips as the sheet is stretched in the transverse direction at elevated temperature. As the sheet exits the transverse direction orientation (TDO) units, the damaged areas under the clips are cut off and wound as trim waste. The oil-filled polyethylene trim waste and extracted polyethylene trim waste are typically discarded. Recently, there has been some effort in mechanical recycling of the trim by grinding it into a powder or flake that can be re-used at the extruder in the separator manufacturing process. Because the trim grinding and screening process involves metallic parts, there is the potential risk of contamination of the polyethylene separator which could lead to a short and fire in a lithium-ion battery.

[0008] In this disclosure, a pyrolyzed hydrocarbon oil is formed from the chemical recycling of the trim waste via pyrolysis in an inert atmosphere. Similarly, other roll waste (e.g., separator rolls that don’t meet specifications, etc.) can also be chemically recycled into a pyrolyzed hydrocarbon oil. The resultant pyrolyzed hydrocarbon oil can then be re-used in the separator manufacturing process or it can be used as an input to a steam cracker for the generation of ethylene to be used in the polymerization of polyethylene As used herein, a pyrolyzed hydrocarbon oil refers to a hydrocarbon oil that is the result of the pyrolysis of trim or roll waste.Summary

[0009] An object of the present disclosure is to utilize chemical recycling of oil-filled and extracted trim or roll waste generated during the manufacture of “wet process” polyethylene separators. Pyrolysis in an inert atmosphere is used to create a pyrolyzed hydrocarbon oil from the waste which can subsequently be used in a separator manufacturing process (e.g., as a process oil) or it can be used as a precursor to a steam cracker to produce ethylene to be used in the polymerization of polyethylene for other products (including other separators). This approach supports the “circular economy” and mitigates the risk of metallic contamination from waste that is ground and screened for re-use in the extrusion process.

[0010] In the wet process for Li-ion separators, a polyolefin such as polyethylene (e.g., very high molecular weight polyethylene (VHMWPE)) is combined with a process oil (or plasticizer) in an extruder (e.g., twin-screw extruder) at elevated temperature. The extrudate is pushed through a sheet die and cast onto a chill roll 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 (machine direction orientation (MDO) followed by transverse direction orientation (TDO)) or simultaneously biaxially oriented at elevated temperature. Next, the oil is removed from the sheet using an extraction solvent that is then evaporated to create a microporous polyethylene film. The film is then usually stretched slightly in the transverse direction and annealed at elevated temperature to achieve its final thickness and porosity before being wound into a finished roll. Typically, oil-filled trim is cut, trimmed, or otherwise removed from the oil-filled sheet at the exit of thetransverse direction orientation (TDO) (or simultaneous biaxial orientation) unit, and extracted trim is cut, trimmed, or otherwise removed from the extracted film at the exit of the second transverse direction orientation unit (TDO). This oil-filled trim and extracted trim is often referred to as waste trim and is typically discarded. Similarly, roll waste is also often generated and commonly discarded.

[0011] In a first embodiment of the disclosure, the oil-filled and / or extracted waste trim or roll waste are pyrolyzed at ~ 500-1000 °C or greater to form a pyrolyzed hydrocarbon oil that can be recycled and blended with a virgin oil (i.e., a virgin processing oil) or another recycled processing oil (e.g., a processing oil previously used in a separator manufacturing process that is extracted and distilled for reuse) that is combined with polyethylene in an extruder (e.g., a twin-screw extruder) in a subsequent separator manufacturing process. In some instances, at least 20% of the oil that is combined with the polyethylene is derived from the pyrolyzed waste trim. The resultant oil-filled sheet is then biaxially oriented, followed by solvent extraction and drying to form a freestanding, microporous polyethylene film that may be further stretched and annealed prior to winding (pursuant to the separator manufacturing process previously described). The resultant separator has thickness between about 3 and about 25 pm with porosity in the 35-60% range. The term “freestanding” refers to a film having sufficient mechanical properties that permit manipulation such as winding and unwinding in film form during use in an energy storage device assembly The term “film” is inclusive of other terms used in the scientific and patent literature such as “membrane”, “sheet”, and “web” and can be used interchangeably with such terms throughout this document. The term “microporous” refers to an average pore size less than about 1 micrometer (e.g., 0.1 to 0.3 microns as measured by mercury porosimetry).

[0012] If desired, additional oil-filled and / or extracted waste trim generated in the formation of the freestanding, microporous polyethylene film can thereafter be taken and pyrolyzed at ~ 500-1000 °C or greater to form a pyrolyzed hydrocarbon oil that can be blended with virgin oil (or another recycled processing oil (e g , a processing oil that was previously used in a separator manufacturing process that is extracted and distilled for reuse)) that is combined with polyethylene in an extruder (e.g., a twin-screw extruder) to form another freestanding, microporous polyethylene film In some of such embodiments, continuous processing and pyrolysis of the waste trim can be part of a closed loop process during the manufacture of “wet process” separators.

[0013] In a second embodiment, the oil-filled and / or extracted waste trim or roll waste are pyrolyzed at ~ 500-1000 °C or greater to form a pyrolyzed hydrocarbon oil. The pyrolyzed hydrocarbon oil is then fed to a steam cracker to generate ethylene that can be polymerized to form polyethylene. The polyethylene can then be used in various products For instance, a polyethylene powder or pellets can be formed from the ethylene generated during the steam cracking. The polyethylene powder or pellets can then be used to form various products, including battery separators.Brief Description of the Drawings

[0014] FIG 1 is a schematic of exemplary process steps used in the manufacture of polyethylene separators.

[0015] FIG 2 is graph depicting the carbon distribution of an oil resulting from pyrolyzed polyethylene separator trimDetailed Description

[0016] Polyethylene separators can be produced with various grades of polyethylene that range in molecular weight from about 500,000 g / mol to about 10 million g / mol. As used herein, ultrahigh molecular weight polyethylene (UHMWPE) generally corresponds to a range of between about 3 1 million g / mol to about 10 million g / mol, and very high molecular weight polyethylene (VHMWPE) generally corresponds to a range of between about 500,000 g / mol to about 3.1 g / mol. In some embodiments, VHMWPE having a molecular weight of between about 500,000 g / mol to about 2 million g / mol is used. Representative polymers include VH035 from KPIC (Korea), GUR 4102 from Celanese (USA), and UH650 from Asahi-Kasei (Japan).

[0017] The process oil (i.e. plasticizer) employed in the present disclosure is a nonevaporative solvent for the polyethylene polymer, and is preferably a liquid at room temperature. The plasticizer has little or no solvating effect on the polymer at room temperature; it performs its solvating action at temperatures at or above the softening temperature of the polymer For VHMWPE, the solvating temperature would be above about 180° C, and preferably in the range of between about 200 °C and about 225 °C. It is preferred to use a process oil, such as a paraffinic oil, naphthenic oil, aromatic oil, white mineral oil, or a mixture of two or more such oils. Examples of suitable processing oils include: Risella 430X by Shell Oil Company; and Hydrocal™ 800 by Calumet Specialty Products; and Nytex 820 by Nynas Inc.

[0018] The polyolefin polymer I oil mixture is extruded through a sheet die or annular die, and then it is biaxially-oriented to form a thin, oil-filled film. The biaxial orientation can be performed either sequentially (machine direction orientation (MDO) followed by transverse direction orientation (TDO)) or simultaneously, as desired. Any solvent that is compatible with the oil can be used for the extraction step, provided it has a boiling point that 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, methylene chloride, hexane, heptane, decane, toluene, and isoparaffin containing solvents having a flashpoint of about 38 °C to about 66 °C (e.g., such as IsoPar-G). In some cases, it is desirable to select the processing oil such that any residual oil in the polymer sheet after extraction is electrochemically inactive.

[0019] A schematic of exemplary process steps used in the manufacture of polyethylene separators is shown in FIG 1 As shown, a common cast film manufacturing process can include various combinations of the following: a polymer extruder (such as a twin screw extruder), a roll stack unit (e.g., casting roll unit, chill roll, etc.), a machine direction orientation unit (MDO), a first transverse direction orientation unit (TDO1), a solvent extractor unit, a drier unit (e g., air drier), a second transverse direction orientation unit (TDO2), and a winder unit. As can be appreciated more or less components can be included and thus the schematic in FIG. 1 is intended only to be exemplary. For example, the process may also include a heat setting unit, a pull roll unit, and a trimming unit.

[0020] In embodiments in accordance with the present disclosure, oil-filled trim may be cut, trimmed, or otherwise removed or taken at the exit of the first transverse direction orientation unit (TDO1 ), and extracted trim may be cut, trimmed, or otherwise removed or taken at the exit of second transversedirection orientation unit (TD02). This trim is often referred to as waste trim and may be the subject of the chemical recycling disclosed herein

[0021] Non-limiting examples of the chemical recycling of polyethylene separators are shown below: Example 1

[0022] Extracted polyethylene separator trim was collected after transverse direction orientation in a Parkinson tenter frame operating at 130 °C. A 500 g trim sample was placed in a kiln reactor that was then heated to 500 °C and held at that temperature for 1 hour to convert the trim into a pyrolyzed hydrocarbon oil (i.e., resultant oil). Gas chromatography was used to determine the carbon distribution of the resultant oil, which is shown in FIG. 2. As shown, the carbon distribution of the resultant oil was less than C50, or between C5-C40. This carbon distribution can be further influenced by pyrolysis temperature and time.Example 2

[0023] A 50 / 20 / 30 ratio of virgin Risella 430X oil (Shell), pyrolyzed hydrocarbon oil from Example 1, and VHMWPE (VH035; KPIC) were fed into a twin-screw extruder and processed at ~ 225 °C to form a 750 pm thick oil-filled sheet. The resultant sheet was then biaxially stretched at 7. OX in the machinedirection (MD) and 7. OX in the transverse-direction (TD) at ~ 115 °C to form a ~ 15 pm thick oil-filled sheet

[0024] A 100 mm x 100 mm piece of oil filled sheet was held with clamps in a metal frame that supported all 4 sides of the sheet. The sample was then extracted in trichloroethylene, and the frame was then placed in a circulating oven at 60 °C to dry the resultant microporous membrane. The membrane had ~ 12 pm thickness and a Gurley air permeability of 160 secs / 100 cc air

Claims

What is claimed is:I. A freestanding, microporous polyolefin film derived from the extrusion of a mixture comprising a process oil and a polyolefin polymer, wherein at least 20% of the process oil comprises a pyrolyzed hydrocarbon oil with a carbon distribution less than C50 derived from pyrolysis of polyolefin trim or roll waste.2.. The freestanding, microporous polyolefin film of claim 1, wherein the pyrolyzed hydrocarbon oil has a carbon distribution between C5-C40.

3. A method of recycling polyolefin trim or roll waste, comprising: extruding a mixture comprising a process oil and a polyolefin polymer into an oil-filled sheet; biaxially orienting the oil-filled sheet; trimming a portion of the biaxially oriented oil-filled sheet; and pyrolyzing the trimmed portion of biaxially oriented oil-filled sheet to form a pyrolyzed hydrocarbon oil.

4. The method of claim 3, wherein the polyolefin polymer comprises polyethylene.

5. The method of claim 4, further comprising: feeding the pyrolyzed hydrocarbon oil to a steam cracker to generate ethylene.

6. The method of claim 3, further comprising: extracting at least a portion of the process oil from the oil-filled sheet to form an extracted microporous film; trimming a portion of the extracted microporous film; and pyrolyzing the trimmed portion of extracted microporous film.

7. The method of claim 6, further comprising: combining the trimmed portion of extracted microporous film with the trimmed portion of biaxially oriented oil-filled sheet prior to pyrolyzing the trimmed portion of biaxially oriented oil-filled sheet and trimmed portion of extracted microporous film.

8. The method of any one of claims 3-7, wherein the pyrolyzed hydrocarbon oil comprises a carbon distribution less than C509. The method of claim 8, wherein the pyrolyzed hydrocarbon oil comprises a carbon distribution between C5-C40.

10. The method of any one of claims 3-9, wherein the pyrolyzing step is performed at a temperature of at least 500 °C for a period of time long enough to convert the trimmed portion of biaxially oriented oil-filled sheet into the pyrolyzed hydrocarbon oil.I I . The method of claim 10, wherein the pyrolyzing step is performed at a temperature of between about 500 and about 1000 °C for a period of time long enough to convert the trimmed portion of biaxially oriented oil-filled sheet into the pyrolyzed hydrocarbon oil.

12. A pyrolyzed hydrocarbon oil with a carbon distribution less than C50 derived from pyrolysis of polyolefin trim or roll waste generated during the manufacture of wet process separators13. The pyrolyzed hydrocarbon oil of claim 12, wherein the pyrolyzed hydrocarbon oil has a carbon distribution between C5-C40.

14. The pyrolyzed hydrocarbon oil of claim 12 or 13, wherein the polyolefin trim or roll waste is pyrolyzed at a temperature of at least 500 °C for a period of time long enough to convert the trim or roll waste into the pyrolyzed hydrocarbon oil.

15. The pyrolyzed hydrocarbon oil of claim 14, wherein the polyolefin trim or roll waste is pyrolyzed at a temperature of between about 500 and about 1000 °C for a period of time long enough to convert the trim or roll waste into the pyrolyzed hydrocarbon oil.

16. A polyethylene powder that is polymerized from ethylene generated during steam cracking of the pyrolyzed hydrocarbon oil described in any one of claims 12-15.

17. A closed loop process for the chemical recycling of polyolefin trim or roll waste generated during the manufacture of wet process separators, the process comprising: extruding a mixture comprising a process oil and a polyolefin polymer into an oil-filled sheet; biaxially orienting the oil-filled sheet; trimming a portion of the biaxially oriented oil-filled sheet; and pyrolyzing the trimmed portion of biaxially oriented oil-filled sheet to form a pyrolyzed hydrocarbon oil.

18. The closed loop process of claim 17, wherein the biaxially orienting comprises sequential biaxial orientation.

19. The closed loop process of claim 17, wherein the biaxially orienting comprises simultaneous biaxial orientation.

20. The closed loop process of any one of claims 17-19, further comprising: combining the pyrolyzed hydrocarbon oil with a second volume of process oil to form an oil mixture for use in a subsequent separator manufacturing process.21 . The closed loop process of any one of claims 17-20, further comprising: extracting at least a portion of the process oil from the oil-filled sheet to form an extracted microporous film; trimming a portion of the extracted microporous film; and pyrolyzing the trimmed portion of extracted microporous film.

22. The closed loop process of claim 21 , further comprising: combining the trimmed portion of extracted microporous film with the trimmed portion of biaxially oriented oil-filled sheet prior to pyrolyzing the trimmed portion of biaxially oriented oil-filled sheet and trimmed portion of extracted microporous film.

23. The closed loop process of any one of claims 17-22, wherein the pyrolyzed hydrocarbon oil comprises a carbon distribution of less than 050.

24. The closed loop process of claim 23, wherein the pyrolyzed hydrocarbon oil comprises a carbon distribution between C5-C40.

25. The closed loop process of any one of claims 17-24, wherein the pyrolyzing step is performed at a temperature of at least 500 °C for a period of time long enough to convert the trimmed portion of biaxially oriented oil-filled sheet into the pyrolyzed hydrocarbon oil.

26. The closed loop process of claim 25, wherein the pyrolyzing step is performed at a temperature of between about 500 and about 1000 °C for a period of time long enough to convert the trimmed portion of biaxially oriented oil-filled sheet into the pyrolyzed hydrocarbon oil.AbstractChemical recycling of oil-filled and / or extracted polyolefin materials that result from extrudate, trim, or roll waste during the manufacture of “wet process” polyolefin separators used in Li-ion batteries is disclosed herein. The oil-filled or extracted polyethylene can be subjected to pyrolysis in an inert atmosphere to convert the waste into a pyrolyzed hydrocarbon oil. The resultant oil can be re-used in the manufacture of polyethylene separators, or it can be used as an input to a cracking tower and converted into naphtha or ethylene for use in the polymerization of polyethylene.What is claimed is:I. A freestanding, microporous polyolefin film derived from the extrusion of a mixture comprising a process oil and a polyolefin polymer, wherein at least 20% of the process oil comprises a pyrolyzed hydrocarbon oil with a carbon distribution less than C50 derived from pyrolysis of polyolefin trim or roll waste.2.. The freestanding, microporous polyolefin film of claim 1, wherein the pyrolyzed hydrocarbon oil has a carbon distribution between C5-C40.

3. A method of recycling polyolefin trim or roll waste, comprising: extruding a mixture comprising a process oil and a polyolefin polymer into an oil-filled sheet; biaxially orienting the oil-filled sheet; trimming a portion of the biaxially oriented oil-filled sheet; and pyrolyzing the trimmed portion of biaxially oriented oil-filled sheet to form a pyrolyzed hydrocarbon oil.

4. The method of claim 3, wherein the polyolefin polymer comprises polyethylene.

5. The method of claim 4, further comprising: feeding the pyrolyzed hydrocarbon oil to a steam cracker to generate ethylene.

6. The method of claim 3, further comprising: extracting at least a portion of the process oil from the oil-filled sheet to form an extracted microporous film; trimming a portion of the extracted microporous film; and pyrolyzing the trimmed portion of extracted microporous film.

7. The method of claim 6, further comprising: combining the trimmed portion of extracted microporous film with the trimmed portion of biaxially oriented oil-filled sheet prior to pyrolyzing the trimmed portion of biaxially oriented oil-filled sheet and trimmed portion of extracted microporous film.

8. The method of any one of claims 3-7, wherein the pyrolyzed hydrocarbon oil comprises a carbon distribution less than C509. The method of claim 8, wherein the pyrolyzed hydrocarbon oil comprises a carbon distribution between C5-C40.

10. The method of any one of claims 3-9, wherein the pyrolyzing step is performed at a temperature of at least 500 °C for a period of time long enough to convert the trimmed portion of biaxially oriented oil-filled sheet into the pyrolyzed hydrocarbon oil.I I . The method of claim 10, wherein the pyrolyzing step is performed at a temperature of between about 500 and about 1000 °C for a period of time long enough to convert the trimmed portion of biaxially oriented oil-filled sheet into the pyrolyzed hydrocarbon oil.

12. A pyrolyzed hydrocarbon oil with a carbon distribution less than C50 derived from pyrolysis of polyolefin trim or roll waste generated during the manufacture of wet process separators13. The pyrolyzed hydrocarbon oil of claim 12, wherein the pyrolyzed hydrocarbon oil has a carbon distribution between C5-C40.

614. The pyrolyzed hydrocarbon oil of claim 12 or 13, wherein the polyolefin trim or roll waste is pyrolyzed at a temperature of at least 500 °C for a period of time long enough to convert the trim or roll waste into the pyrolyzed hydrocarbon oil.

15. The pyrolyzed hydrocarbon oil of claim 14, wherein the polyolefin trim or roll waste is pyrolyzed at a temperature of between about 500 and about 1000 °C for a period of time long enough to convert the trim or roll waste into the pyrolyzed hydrocarbon oil.

16. A polyethylene powder that is polymerized from ethylene generated during steam cracking of the pyrolyzed hydrocarbon oil described in any one of claims 12-15.

17. A closed loop process for the chemical recycling of polyolefin trim or roll waste generated during the manufacture of wet process separators, the process comprising: extruding a mixture comprising a process oil and a polyolefin polymer into an oil-filled sheet; biaxially orienting the oil-filled sheet; trimming a portion of the biaxially oriented oil-filled sheet; and pyrolyzing the trimmed portion of biaxially oriented oil-filled sheet to form a pyrolyzed hydrocarbon oil.

18. The closed loop process of claim 17, wherein the biaxially orienting comprises sequential biaxial orientation.

19. The closed loop process of claim 17, wherein the biaxially orienting comprises simultaneous biaxial orientation.

20. The closed loop process of any one of claims 17-19, further comprising: combining the pyrolyzed hydrocarbon oil with a second volume of process oil to form an oil mixture for use in a subsequent separator manufacturing process.21 . The closed loop process of any one of claims 17-20, further comprising: extracting at least a portion of the process oil from the oil-filled sheet to form an extracted microporous film; trimming a portion of the extracted microporous film; and pyrolyzing the trimmed portion of extracted microporous film.

22. The closed loop process of claim 21 , further comprising: combining the trimmed portion of extracted microporous film with the trimmed portion of biaxially oriented oil-filled sheet prior to pyrolyzing the trimmed portion of biaxially oriented oil-filled sheet and trimmed portion of extracted microporous film.

23. The closed loop process of any one of claims 17-22, wherein the pyrolyzed hydrocarbon oil comprises a carbon distribution of less than 050.

24. The closed loop process of claim 23, wherein the pyrolyzed hydrocarbon oil comprises a carbon distribution between C5-C40.

25. The closed loop process of any one of claims 17-24, wherein the pyrolyzing step is performed at a temperature of at least 500 °C for a period of time long enough to convert the trimmed portion of biaxially oriented oil-filled sheet into the pyrolyzed hydrocarbon oil.

726. The closed loop process of claim 25, wherein the pyrolyzing step is performed at a temperature of between about 500 and about 1000 °C for a period of time long enough to convert the trimmed portion of biaxially oriented oil-filled sheet into the pyrolyzed hydrocarbon oil.8

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