Materials and methods for producing carbon fibers from petroleum asphaltenes

Abstract

A method for forming carbon fibers from petroleum asphaltene includes providing a common reaction vessel, introducing a quantity of feed asphaltene into the common reaction vessel, heat-treating the feed asphaltene, and melt-spinning the heat-treated asphaltene. The method further includes the steps of thermally curing the green fibers at a temperature selected to be between 200°C and 500°C in air or oxygen to produce stabilized fibers, and carbonizing the stabilized fibers in an inert atmosphere at a temperature between 1000°C and 2000°C to form asphaltene-derived carbon fibers.

Description

[Technical Field]

[0001] The present disclosure relates generally to methods and uses for producing carbon fibers from petroleum asphaltenes. [Background technology]

[0002] Petroleum asphaltenes are highly heterogeneous in nature and are carbonaceous (approximately 70-90% carbon) polymers with heavy fractions (15% by weight) containing bitumen. Depending on the extraction and / or partial upgrading process, asphaltenes can be amphiphilic in nature. However, most petroleum asphaltenes exhibit hydrophobic properties as bulk materials, are insoluble in n-alkane solvents, and are considered potential precursors for carbon fiber (also hydrophobic) production. After extraction or partial upgrading, petroleum asphaltenes can exist in either solid or liquid form, or a combination of both. Summary of the Invention

[0003] According to a first embodiment, a method for forming carbon fibers from petroleum asphaltene is disclosed, comprising the steps of providing a common reaction vessel, introducing a quantity of feed asphaltene into the common reaction vessel, heat-treating the feed asphaltene, and melt-spinning the heat-treated asphaltene. The method further comprises the steps of heat-setting the raw fibers in air or oxygen at a temperature selected to be between 200°C and 500°C to produce stabilized fibers, and carbonizing the stabilized fibers in an inert atmosphere at a temperature between 1000°C and 2000°C to form asphaltene-derived carbon fibers.

[0004] The method may further include pretreating the feed asphaltenes for removal selected from the group consisting of sieving, solvent extraction, oxidative desulfurization, mixing with additives, and thermal treatment under shear mixing. The pretreatment may be performed prior to introducing the feed fibers into the common reactor vessel.

[0005] The heat treatment may be carried out under N2 and shear mixing for 1 to 15 hours at a temperature selected to be between 100°C and 400°C. The method may further include a step of venting volatiles generated during the heat treatment. The heat treatment may further include mechanical stirring at 50 to 500 rpm.

[0006] The common reaction vessel may include a melt spinning system selected from the group consisting of a plunger or an air pressure reactor. The common reaction vessel may further include a spin box assembly consisting of a spinneret, a distribution plate, a copper cushion, a graphene gasket, and a filtration plate.

[0007] According to a first embodiment, a system for forming carbon fibers from petroleum asphaltenes is disclosed that includes a common reactor vessel including an inlet extending into the common reactor vessel for introducing a quantity of feed asphaltenes into the common reactor vessel, a heat supply for heat treating the feed asphaltenes, a melt spinner for melt spinning the heat-treated asphaltenes, means for heat setting the green fibers to produce stabilized fibers, and means for carbonizing the stabilized fibers to form asphaltene-derived carbon fibers.

[0008] According to a further embodiment, a method for forming carbon fibers from petroleum asphaltenes is disclosed, comprising the steps of receiving a quantity of feed asphaltene; passing the feed asphaltene through a melt spinning system to produce green fibers; soaking the green fibers for a period of time effective with an amount of at least one substance selected to reduce fiber fusion; heat-setting the green fibers in air or oxygen at a temperature selected to be between 200°C and 500°C to produce stabilized fibers; and carbonizing the stabilized fibers in an inert atmosphere at a temperature between 1000°C and 1800°C to form asphaltene-derived carbon fibers.

[0009] The method may further include pretreating the feed asphaltene to adjust the melt viscosity of the asphaltene to improve melt extrusion, as well as to remove clays, dirt, granules, salts, low molecular weight volatile components, and solvent-insoluble particles. The pretreatment step may be selected from the group consisting of sieving, solvent extraction, oxidative desulfurization, mixing with additives, and heat treatment under shear mixing.

[0010] The pretreatment may include, as a first step, sieving the feedstock. The sieving process of the feedstock asphaltenes may be carried out using sieves having mesh sizes in the range of 60 to 120 mesh, which corresponds to particle sizes of 250 μm to 125 μm.

[0011] After the sieving process, the raw asphaltenes may be subjected to solvent extraction and / or oxidative desulfurization. Solvent extraction may involve the use of a solvent selected from the group consisting of toluene, dichloromethane, tetrahydrofuran, and mixtures thereof. Solvent extraction may involve mixing the sieved asphaltenes with a solvent in a ratio selected to provide an asphaltene-to-solvent ratio of 1:5 (w / v) to 1:50 (w / v). The mixture may be stirred by a stirrer until a homogeneous solution is formed, followed by vacuum filtration. The stirrer may be selected from the group consisting of manual and manual, magnetic, or automatic stirrers. Vacuum filtration leaves solvent-insoluble particles on the filter paper, while the asphaltenes dissolved in the solvent pass through. The filtrate may be heated to 50°C to 250°C with continuous stirring at speeds of 100 to 2000 rpm for a period of 2 to 24 hours. Once all the solvent has evaporated, the solid asphaltenes may be dried in a dryer. The dryer may include a vacuum dryer selected to have a temperature of 50-70°C for a period of 2-12 hours.

[0012] Oxidative desulfurization may be carried out at a temperature of 40-70°C to chemically oxidize the feed asphaltene. The oxidized feed asphaltene may have sulfur extracted therefrom after oxidation. Oxidative desulfurization may include mixing the feed asphaltene with hydrogen peroxide for a first period of time, mixing the feed asphaltene and hydrogen peroxide with sodium hydroxide, and settling for a second period of time.

[0013] The hydrogen peroxide may comprise a 20% to 80% (v / v) hydrogen peroxide solution. The hydrogen peroxide may be mixed in a ratio of asphaltene to hydrogen peroxide of 1:10 to 1:80 (w / v). The first time period may be selected to be 1 to 10 hours with continuous stirring at 200 to 2000 rpm and 40 to 80°C. The sodium hydroxide may comprise a 10 to 50% (w / v) saturated sodium hydroxide solution. Sodium hydroxide may be added to the feed asphaltene and hydrogen peroxide mixture in a ratio of feed asphaltene to sodium hydroxide of 1:10 to 1:80 (w / v) to produce a second mixture. The second mixture may be continuously stirred at 100 to 1000 rpm and a temperature of 30 to 100°C until the reaction is complete. The second time period may be selected to be 1 to 12 hours.

[0014] The phase-separated solvent can be removed using a separation filter, followed by washing with deionized water at least 5 to 10 times, and then the solid phase can be vacuum filtered to obtain desulfurized asphaltene.

[0015] The solvent extracted asphaltenes may be dry blended with 1 to 30 wt% of an additive selected from the group consisting of: Following dry blending, the polymer-asphaltene blend may be polymerized and mixed under high shear at a temperature of 100 to 350°C for 1 / 2 to 15 hours.

[0016] The feed asphaltenes after undergoing solvent extraction, and / or oxidative desulfurization, and / or additive incorporation, and / or dry mixing with additives may be subjected to heat treatment under N2 and shear mixing at temperatures between 100 and 400°C for a period of 1 to 15 hours.

[0017] The pretreated asphaltenes can be subjected to thermal treatment under nitrogen at pressures between 10 and 200 kPa, with a vent valve allowing volatile species to exit the system. The pretreated asphaltenes can be subjected to thermal treatment by mechanical stirring in the reactor at 50-500 rpm for uniform mixing and to improve mesophase content.

[0018] The melt spinning system may include a plunger or air-pressurized reactor for producing green fibers at various take-up speeds. The spin box assembly may consist of a spinneret, a distribution plate, a copper cushion, a graphene gasket, and a filtration plate. The spinneret may have an orifice diameter selected to be 100-300 μm, with an orifice length-to-diameter ratio of 1-5 within the spinneret.

[0019] The spinneret may have 1 to 120 orifices for multiple filament drawing. The pretreated asphaltenes may be spun with or without a shear mixer at 20 to 500 rpm under nitrogen pressure of 50 to 2000 kPa at a spinning temperature selected to be 160 to 350°C.

[0020] The pretreated asphaltenes can be spun at take-up speeds ranging from 50 to 4000 rpm to produce green fibers with diameters of 5 to 300 μm.

[0021] According to a further embodiment, a method for forming carbon fibers from petroleum asphaltenes is disclosed, comprising the steps of heat treating raw asphaltene; melt spinning the heat-treated asphaltene to produce green fibers; immersing the green fibers for an effective period of time in an intermediate chamber containing an amount of at least one anti-fusing substance selected to reduce fiber fusing; heat setting the green fibers in air or oxygen at a temperature selected to be between 200°C and 500°C to produce stabilized fibers; and carbonizing the stabilized fibers in an inert atmosphere at a temperature between 1000°C and 2000°C to form asphaltene-derived carbon fibers.

[0022] The intermediate treatment chamber may include a container with organic and inorganic acids, a plasma chamber, a glass chamber, iodine crystals, shelves, or rollers for holding the asphaltene-derived green fiber, and a support for keeping the green fiber fully immersed. The asphaltene-derived green fiber may be fully immersed in the anti-fusing substance in the intermediate treatment chamber. The anti-fusing substance may be provided at a concentration of 5 to 60%. The anti-fusing substance may be selected from the group consisting of nitric acid, sulfuric acid, hydrochloric acid, phosphoric acid, and acetic acid. The green fiber may be immersed in the intermediate chamber for 5 to 120 minutes.

[0023] The asphaltene-derived green fiber may be placed inside a glass quartz tube in an intermediate chamber connected to a vacuum supply containing a quantity of iodine crystals for iodination of the green fiber. The quantity of iodine may range from 100 ml to 100 g. The green fiber and iodine may be heated to 80°C to 120°C. The acid-treated and / or iodine-treated asphaltene-derived green fiber may be dried.

[0024] Asphaltene-derived acid- and / or I2-treated fibers may be subjected to plasma treatment under oxygen to increase the fiber surface roughness and surface oxygen concentration to avoid fiber fusion and shorten stabilization time. Oxygen may be provided at a pressure of 0.1 to 1 Torr. Plasma treatment may involve radio frequency at power levels of 7 W to 30 W (1 MHz to 14 MHz) for 5 to 120 minutes.

[0025] According to a further embodiment, a method for forming carbon fibers from petroleum asphaltenes is disclosed that includes the steps of heat treating raw asphaltenes, melt spinning the heat-treated asphaltenes to produce green fibers, heat setting the green fibers in air or oxygen at a temperature selected to be between 200°C and 500°C to produce stabilized fibers, and carbonizing the stabilized fibers in an inert atmosphere at a temperature between 1000°C and 2000°C to form asphaltene-derived carbon fibers.

[0026] The oxidative stabilization process may involve multiple-stage stabilization in air or oxygen due to the heterogeneity of the precursor material. The green fiber may undergo air or oxygen stabilization at 200-260°C for 0.5-5 hours, followed by 300-400°C for 10-120 minutes. The green fiber may undergo multiple-stage stabilization in air or oxygen at a temperature ramp rate of 0.5-1°C / min from 25°C to 260°C, followed by a temperature ramp rate of 3-5°C / min from 260°C to 350°C.

[0027] The carbonization process may involve using a multi-stage carbonization process, either under tension or without tension, up to 2000°C. The stabilized fibers may be carbonized at temperatures of 400-800°C for 10-30 minutes, followed by carbonization at 1500°C for 1-5 hours and 1700°C for 1-120 minutes.

[0028] Stabilized fibers can be subjected to a multi-stage carbonization process, including low-temperature carbonization at 400-800°C. Carbon fibers may also be subjected to surface treatments for the development of carbon fiber reinforced thermoplastic composites. The surface treatments may be selected from the group consisting of acid oxidation, plasma treatment, silane treatment, and sizing.

[0029] Other aspects and features of the present disclosure will become apparent to those skilled in the art upon review of the following description of specific embodiments in conjunction with the accompanying figures. DETAILED DESCRIPTION OF THE INVENTION

[0030] Aspects of the present disclosure will now be described with reference to exemplary methods and systems. In particular, the present method provides an end-to-end process for producing carbon fibers from petroleum asphaltenes, involving a series of steps including pretreatment, melt spinning, intermediate treatment, oxidative stabilization, and high-temperature carbonization. The present disclosure details all of these steps, which are important for developing asphaltene-derived carbon fibers. In particular, the present disclosure provides a method and system for forming carbon fibers from petroleum asphaltenes. The method includes receiving a quantity of feedstock asphaltene; passing the feedstock asphaltene through a melt spinning system to produce green fibers; immersing the green fibers for an effective period of time in an intermediate chamber containing an amount of at least one substance selected to reduce fiber fusion; thermally curing the green fibers received from the intermediate chamber in air or oxygen at a temperature selected to be between 200°C and 500°C to produce stabilized fibers; and carbonizing the stabilized fibers in an inert atmosphere at a temperature selected to be between 1000°C and 1800°C to form asphaltene-derived carbon fibers. In particular, in some embodiments, the process may include heat treating and melt spinning the asphaltenes in a common vessel to prevent cooling of the asphaltenes therebetween.

[0031] Pretreatment can be important for purifying feed asphaltenes to make them suitable for the spinning process. Pretreatment of feed asphaltenes is useful for removing impurities such as clays, dirt, sand, granules, salts, sulfur, heavy metals, low molecular weight volatiles, and any other type of suspended material that may interfere with the melting and extrudability of the feed asphaltenes. In this disclosure, feed asphaltenes refer to the heavy fraction of bitumen, which can be extracted by several processes, including partial upgrading, solvent extraction, etc. Pretreatment removes clays, dirt, granules, salts, low molecular weight volatiles, and solvent-insoluble particles, as well as adjusts the melt viscosity of the asphaltenes to improve melt extrusion, and consists of sieving, solvent extraction, oxidative desulfurization, mixing with additives (e.g., polymers), and heat treatment under shear mixing.

[0032] In some embodiments, sieving of the feed asphaltene is the first step in the pretreatment technique. The sieving process of the feed asphaltene may be carried out using sieves with mesh sizes ranging from 60 to 120 mesh, which corresponds to particle sizes of 250 μm to 125 μm. Sieving may reduce the amount of clay, dirt, granules, and coarse coagulants in the feed asphaltene that may interfere with melt extrusion. In some embodiments, the feed asphaltene may be subjected to solvent extraction and / or oxidative desulfurization after the sieving process.

[0033] In some embodiments, the feed asphaltenes can be subjected to solvent extraction with toluene, dichloromethane, tetrahydrofuran, etc., and mixtures thereof to remove solvent-insoluble particles that may interfere with melt extrusion. In this embodiment, the sieved asphaltenes can be mixed with toluene, dichloromethane, tetrahydrofuran, or any other similar nonpolar solvent, or mixtures thereof, at asphaltene-to-solvent ratios of 1:5 (w / v), 1:10 (w / v), 1:15 (w / v), 1:20 (w / v), 1:30 (w / v), 1:40 (w / v), or 1:50 (w / v). The mixture can be stirred manually or with a magnetic / automatic stirrer until a homogeneous solution is formed, followed by vacuum filtration. In this embodiment, solvent-insoluble particles may remain on the filter paper, while the asphaltenes dissolved in the solvent pass through the filter paper. The filtrate may then be heated under continuous stirring (100-2000 rpm) at 50-250°C (depending on the boiling point of the solvent) for 2-24 hours overnight. Once all the solvent has evaporated, the solid asphaltenes may be dried overnight for 2-12 hours in a vacuum oven at 50-70°C. The yield of solvent extraction varies from 20% to 99%, depending on the material volume and solvent used.

[0034] In some embodiments, the feed asphaltene may be subjected to oxidative desulfurization, which can remove up to 70% of the sulfur from the feed asphaltene. Most of the sulfur in the feed asphaltene is present as thiophenes, and sulfur (thiophenes and other forms of sulfur) is cleaved from the asphaltene polymer structure. Oxidative desulfurization is a low-temperature (approximately 40-70°C) chemical process in which the feed asphaltene is first chemically oxidized, followed by sulfur extraction.

[0035] In some embodiments, the feed asphaltenes are mixed in a 20-80% (v / v) HO (hydrogen peroxide) solution at asphaltene to HO ratios of 1:10 (w / v), 1:20 (w / v), 1:30 (w / v), 1:40 (w / v), 1:50 (w / v), 1:60 (w / v), 1:70 (w / v), or 1:80 (w / v). The mixture is mixed at about 40-80°C with continuous stirring at 200-2000 rpm for 1-10 hours. Then, 10–50% (w / v) saturated NaOH is added to the asphaltene-HO mixture at asphaltene-to-NaOH ratios of 1:10 (w / v), 1:20 (w / v), 1:30 (w / v), 1:40 (w / v), 1:50 (w / v), 1:60 (w / v), 1:70 (w / v), or 1:80 (w / v). The final mixture is then continuously stirred at 100–1000 rpm at approximately 30–100 °C. Once the reaction is complete, the mixture is allowed to settle for 1–12 h depending on the volume scale for phase separation (e.g., a 200 mL mixture requires 30 min, while a 1 L mixture may take 6–12 h).

[0036] In some embodiments, the phase-separated solvent can be removed using a separation filter, followed by washing with deionized water at least 5-10 times, and then the solid phase can be vacuum filtered to obtain the desulfurized asphaltenes.

[0037] Oxidative desulfurization (two distinct reactions) first oxidizes the sulfur present as thiophenes in asphaltenes to form sulfones (O=S=O), which are more polar than thiophenes and therefore can dissolve in polar phases. Once the thiophenes are oxidized to sulfones, a strong base such as NaOH (sodium hydroxide) extracts the sulfones from the asphaltenes, thus reducing the sulfur content. The superoxide formed during the reaction of NaOH with HO further oxidizes the sulfur in the thiophenes to sulfones.

[0038] In some embodiments, solvent-extracted asphaltenes can be first dry-blended with hydrophobic extrusion-grade polymers / elastomers / additives (e.g., polystyrene, high-impact polystyrene, styrene-ethylene-butylene-styrene, polypropylene, polyester, polymethyl methacrylate, polycarbonate, etc.) at concentrations varying from 1 to 30 wt%. Following dry-blending of the additives / polymers / elastomers, the polymer-asphaltene blend can be polymerized and mixed at temperatures of approximately 100 to 350°C (depending on the glass transition temperature of the polymer / elastomer / additive) under high shear for 0.5 to 15 hours. This melt-blending induces polymerization and cross-linking of molecular chains between the additives / polymers / elastomers and the asphaltenes.

[0039] Dry or wet blending (or a combination of both) and thermal polymerization of modified (with additives / polymers / elastomers) asphaltenes exhibits reduced or increased melt viscosity and improved melt spinnability.

[0040] In some embodiments, feed asphaltenes may undergo physical or chemical pretreatment techniques followed by modified versions of subsequent thermal treatment / blending directly connected to a melt extrusion system. After solvent extraction, oxidative desulfurization, additive incorporation, and / or dry blending with additives, feed asphaltenes may be subjected to thermal treatment under N2 and shear mixing at temperatures between 100°C and 400°C for periods of 1 to 15 hours. The feed asphaltenes may be subjected to thermal treatment to remove low molecular weight volatile components, which can increase the asphaltenes' thermal stability, mesophase content (10-70%), and softening point. Thermal treatment induces polycondensation and the generation of volatile species such as CH4, CO2, CH2, C2O, NO2, HS, H2, and HO, which must be vented during the entire process.

[0041] Pretreated asphaltenes may be subjected to thermal treatment at low N2 pressure (approximately 10-200 kPa) with the exhaust valve partially open, thus allowing volatile species to exit the system. The presence of volatile species during melt spinning can induce voids and defects in the green fiber microstructure. In some embodiments, the pretreated asphaltenes subjected to thermal treatment are carried out in the same reactor. This is particularly to avoid cooling the heat-treated asphaltenes during transfer to a separate reactor under ambient conditions and remelting them in the melt spinner, which could destroy the appropriate rheological properties (e.g., shear viscosity) required for a continuous spinning system. The pretreated asphaltenes (after solvent extraction or oxidative desulfurization or polymerization with additives, polymers, elastomers, etc.) being subjected to thermal treatment are mechanically stirred in the reactor at 50-500 rpm for uniform mixing and improved mesophase content.

[0042] Melt spinning systems for spinning pretreated asphaltenes, which may or may not be pretreated as described above, include either a plunger or air-pressurized reactor to produce green fibers at various take-up speeds.

[0043] Specifically, the spin box assembly may consist of a spinneret, a distribution plate, a copper cushion, a graphene gasket, and a filter plate. The spinneret may have orifice diameters of 100 μm, 150 μm, 200 μm, 250 μm, or 300 μm, and a L / D ratio of 1 to 5. The spinneret may have 1 to 120 orifices for multiple filament drawing.

[0044] Pretreated or raw asphaltenes may be spun at high spinning temperatures ranging from 160°C to 350°C depending on the softening point of the material, at 20-500 rpm with or without a shear mixer, under N2 pressures of 50-2000 kPa. Pretreated or raw asphaltenes were spun at take-up speeds ranging from 50-4000 rpm to produce green fibers with diameters ranging from 5 to 300 μm, depending on the required combination of spinning temperature, spinning pressure, and spinneret size.

[0045] According to some embodiments, the melt spinning system continuously produces green fibers having an average diameter of 10-20 μm using a spinneret orifice of 150-300 μm at a take-up speed of 1500-2700 rpm, a spinning temperature of 200-350°C, and a spinning pressure of 400-800 kPa after heat treatment for 0.5-3 hours at 200-300°C. According to some embodiments, the melt spinning system continuously produces green fibers having an average diameter of 10-15 μm using a spinneret orifice of 150-300 μm at a take-up speed of 1500-3000 rpm, a spinning temperature of 200-400°C, and a spinning pressure of 400-2000 kPa after polymerization under heat treatment for 1-5 hours at 150-300°C.

[0046] Melt spinning systems with spinnerets with multiple orifices (>1) can be used to produce multiple filaments of green fiber that are completely wound through the cycloid. Melt spinning of green fiber can be unstable and discontinuous, with multiple filament breaks occurring at higher spinning temperatures (>280°C) and longer heat treatment times (>3 hours).

[0047] In some embodiments, the green fibers are transferred to an intermediate treatment chamber for treatment to prevent interfiber fusion. In particular, the intermediate treatment chamber may include a large Teflon-based bath, organic and inorganic acids, a plasma chamber, a glass chamber, iodine crystals, shelves, or rollers to hold the asphaltene-derived green fibers and supports to keep the green fibers fully immersed. It will be understood that the use of an intermediate treatment chamber can be performed with or without the use of a common treatment chamber for heat treatment and melt spinning, as well as other embodiments described below.

[0048] In some embodiments, asphaltene-derived green fibers are thoroughly immersed in 5-60% HNO, HSO, HCl, HNO, HPO, CHCOOH, or any combination thereof or any similar class of acid (binary, oxy, etc.) for 5-120 minutes for surface functionalization and nitration.

[0049] In some embodiments, asphaltene-derived green fibers are placed inside a glass quartz tube connected to a vacuum supply containing 100 mg to 100 g of iodine (I) crystals and heated to 80-120°C to form sublimed I vapor for iodination of the green fibers, resulting in 100-200% by weight uptake of the green fibers. It will be appreciated that in some embodiments, acid and / or iodine treatment of the asphaltene-derived green fibers may be necessary to reduce fiber fusion during oxidative stabilization.

[0050] In particular, acid or I2 molecules can act as a surface modifier between individual fibers within a fiber bundle. For example, nitric acid and iodine treatments result in increases in nitrogen and iodine content of 3-15% and 5-30%, respectively. I2 treatment allows for iodine pretreatment (or thermal curing) of the carbon fiber surface, which helps avoid fiber fusion during the subsequent stabilization process.

[0051] In some embodiments, acid- and / or I2-treated asphaltene-derived raw fibers can be dried from excess acid and air-dried for 10-60 minutes before being placed in a stabilization furnace. The asphaltene-derived acid- and / or I2-treated fibers can be subjected to plasma treatment under O2 for 5-120 minutes at pressures of 0.1-1 Torr and radio frequency power levels of 7 W-30 W (1 MHz-14 MHz). This increases the fiber's surface roughness and surface oxygen concentration (e.g., 10-60 atomic %) to avoid fiber fusion and shortens stabilization time by 30-80%. Plasma treatment allows for oxidative pretreatment (or thermal curing) of the carbon fiber surface, which helps avoid fiber fusion during the subsequent stabilization process.

[0052] The oxidative stabilization process involves exposing acid-treated and / or I2-treated and / or plasma-treated raw fibers to temperatures (approximately 200-500 °C) in air or O2 for thermal curing, to avoid melting during the high-temperature carbonization process.

[0053] In some embodiments, the acid- and / or I2-treated or plasma-treated green fibers may be subjected to multi-stage stabilization in air or O2 due to the heterogeneity of the precursor material. In some embodiments, the acid- and / or I2-treated or plasma-treated green fibers may be subjected to air or O2 stabilization at 200°C-260°C for 0.5-5 hours, followed by 300°C-400°C for 10-120 minutes.

[0054] In some embodiments, acid- and / or I2-treated asphaltenes-derived green fibers may undergo multi-stage stabilization in air or O2, starting from 25°C to 260°C at a temperature ramp rate of 0.5-1°C / min, followed by a temperature ramp rate of 3-5°C / min from 260°C to 350°C. In some embodiments, acid- and / or I2-treated and / or plasma-treated green fibers may follow a slow initial temperature ramp rate due to the low softening point of asphaltenes. The first stabilization temperature of the acid- and / or I2-treated and / or plasma-treated green fibers is selected based on the spinning temperature of the precursor material (typically 10-50°C higher than the first stabilization temperature).

[0055] In some embodiments, acid- and / or I2-treated asphaltene-derived green fibers can be subjected to extensive oxidation and crosslinking reactions, including polymerization of small molecules to form larger molecules, formation of active sites by oxidizing alkyl carbons, formation of carbonyl and phenoxy functional groups, etc., thus increasing the melting point of the fibers well beyond the higher carbonization temperatures. In some embodiments, acid- and / or I2-treated asphaltene-derived green fibers can be subjected to multi-stage stabilization in air or O2, through which the bulk oxygen concentration within the fibers increases from 2-5% to 20-40%.

[0056] The high-temperature carbonization process involves exposing the asphaltene-derived stabilized fibers to high temperatures under an inert atmosphere (N or Ar flow) to form asphaltene-derived carbon fibers. In some embodiments, the asphaltene-derived stabilized fibers are carbonized using a multi-stage carbonization process up to 1800°C, either under tension or without tension.

[0057] In some embodiments, the asphaltene-derived stabilized fibers may be carbonized at 400°C to 800°C for 10 to 30 minutes, followed by carbonization at 1500°C for 1 to 5 hours and 1700°C for 1 to 120 minutes.

[0058] In some embodiments, the asphaltene-derived stabilized fibers can be subjected to a multi-stage carbonization process, where low-temperature carbonization between 400 and 800 °C helps to avoid disrupting the fiber microstructure due to the generation of multiple volatile species such as CH, H, etc. below 1000 °C. In some embodiments, the asphaltene-derived stabilized fibers can be subjected to high-temperature carbonization to remove non-carbon elements (e.g., N, O, H, S, etc.) in the stabilized fibers as low-molecular-weight volatile species.

[0059] Asphaltene-derived carbon fibers can exhibit a carbon content of 85-98% after carbonization at 1100-1700°C for 1-6 hours. The sulfur content of asphaltene-derived carbon fibers is reduced by 70-90% with increasing carbonization time (2-3 hours) at 1500-1700°C. Asphaltene-derived carbon fibers can have an average diameter of 3-10 μm without surface or microstructural defects after carbonization at 400-1700°C for 0.5-6 hours.

[0060] Single asphaltene-derived carbon fibers can exhibit tensile strengths of 900-3000 MPa and moduli of 30-250 GPa after carbonization at 400-1700°C for 10 minutes to 6 hours. The asphaltene-derived carbon fibers may be subjected to surface treatments (e.g., acid oxidation, plasma treatment, silane treatment, sizing, etc.) for the development of carbon fiber-reinforced thermoplastic composites. It will be appreciated that the use of multiple-stage stabilization or carbonization processes can be used in conjunction with or without the use of a common processing chamber for heat treatment and melt spinning, as well as other embodiments, or the use of intermediate processing chambers to reduce fiber fusion. It will also be appreciated that each of the multiple-stage stabilization and / or carbonization processes may be used together or separately.

[0061] While particular embodiments have been described and illustrated, such embodiments should be considered as exemplary only and not as limitations on the present disclosure as interpreted according to the appended claims.

Claims

1. 1. A method for forming fibers from a heterogeneous carbonaceous polymer, comprising: placing a heterogeneous carbonaceous polymer in a container; heating the heterogeneous carbonaceous polymer in the vessel; extruding the heterogeneous carbonaceous polymer into the container to form fibers; treating the fibers with an acid; heat setting the fibers; carbonizing the fibers; A method comprising:

2. The method of claim 1, wherein the heating step is carried out at a temperature in the range of about 100°C to about 500°C.

3. The method of claim 1 , wherein the heating step is carried out for about 1 hour to about 15 hours.

4. The method of claim 1 , wherein the heating step is carried out in the presence of an inert atmosphere.

5. The method of claim 1 , wherein the heating step comprises mechanically agitating the heterogeneous carbonaceous polymer.

6. The method of claim 1 further comprising the step of venting the volatile material.

7. The method of claim 1 , wherein the extruding step comprises melt spinning.

8. The method of claim 1 , wherein the container comprises a mixer.

9. The method of claim 1 , wherein the vessel comprises a pressurized reactor.

10. The method of claim 1 , wherein the vessel comprises a spin box assembly.

11. The method of claim 10, wherein the spin box assembly comprises a spinneret.

12. 12. The method of claim 11, wherein the spinneret is a single-hole spinneret.

13. 12. The method of claim 11, wherein the spinneret is a multi-hole spinneret.

14. 14. The method of claim 13, wherein the multi-hole spinneret comprises at least 1 to about 10,000 orifices.

15. The method of claim 10 , wherein the spin box assembly comprises a distribution plate.

16. The method of claim 10, wherein the spin box assembly comprises a metal cushion.

17. The method of claim 10, wherein the spin box assembly comprises a gasket.

18. The method of claim 10 , wherein the spin box assembly comprises a filter plate.

19. The method of claim 1 , wherein the heat curing step is carried out at a temperature in the range of about 200° C. to about 500° C.

20. The method of claim 1 , wherein the heat curing step is carried out in the presence of air.

21. The method of claim 1 , wherein the thermal curing step is carried out in the presence of oxygen.

22. The method of claim 1 , wherein the thermal curing step is carried out in the presence of ozone.

23. The method of claim 1 , wherein the carbonization is carried out in the presence of an inert atmosphere.

24. The method of claim 1, wherein the carbonization is carried out at a temperature in the range of about 800°C to about 1800°C.

25. The method of claim 1 , further comprising pretreating the heterogeneous carbonaceous polymer to remove clay.

26. The method of claim 1 , further comprising pretreating the heterogeneous carbonaceous polymer to remove contaminants.

27. The method of claim 1 , further comprising pre-treating the heterogeneous carbonaceous polymer to remove granules.

28. The method of claim 1 , further comprising pretreating the heterogeneous carbonaceous polymer to remove salts.

29. The method of claim 1 , further comprising pretreating the heterogeneous carbonaceous polymer to remove volatile compounds.

30. The method of claim 1 , further comprising pretreating the heterogeneous carbonaceous polymer to remove insoluble particles.

31. The method of claim 1 , further comprising contacting the heterogeneous carbonaceous polymer with a solvent.

32. 32. The method of claim 31 , wherein the solvent comprises toluene.

33. 32. The method of claim 31 , wherein the solvent comprises dichloromethane.

34. 32. The method of claim 31 , wherein the solvent comprises tetrahydrofuran.

35. 32. The method of claim 31 , wherein the solvent comprises pentane.

36. 32. The method of claim 31 , wherein the solvent comprises heptane.

37. 32. The method of claim 31 , further comprising contacting the heterogeneous carbonaceous polymer in the solvent at a ratio of heterogeneous carbonaceous polymer to solvent of about 1:5 (w / v) to 1:50 (w / v).

38. further comprising oxidative desulfurization of the heterogeneous carbonaceous polymer, wherein the oxidative desulfurization comprises: contacting the heterogeneous carbonaceous polymer with a first reagent; contacting the heterogeneous carbonaceous polymer and the first reagent with a second reagent; recovering the heterogeneous carbonaceous polymer; The method of claim 1 , comprising:

39. 39. The method of claim 38, wherein the first reagent comprises about 20% to about 80% hydrogen peroxide.

40. 39. The method of claim 38, wherein the second reagent comprises about 10% (w / v) to about 50% (w / v) sodium hydroxide.

41. 39. The method of claim 38, wherein the heterogeneous carbonaceous polymer and the first reagent are in a ratio of about 1:10 (w / v) to about 1:80 (w / v).

42. 39. The method of claim 38, wherein the heterogeneous carbonaceous polymer and the first reagent are contacted for about 1 hour to about 10 hours.

43. 39. The method of claim 38, wherein the heterogeneous carbonaceous polymer and the first reagent are contacted with the second reagent in a ratio of about 1:10 (w / v) to about 1:80 (w / v).

44. 39. The method of claim 38, wherein the heterogeneous carbonaceous polymer and the first reagent are contacted with the second reagent for about 1 hour to about 12 hours.

45. recovering the heterogeneous carbonaceous polymer; isolating the phase-separated first and second reagents; filtering to isolate the heterogeneous carbonaceous polymer; 39. The method of claim 38, comprising:

46. The method of claim 1 , further comprising contacting the heterogeneous carbonaceous polymer with an additive.

47. 47. The method of claim 46, wherein the additive comprises polymethyl methacrylate.

48. 47. The method of claim 46, wherein the additive comprises a polycarbonate.

49. 47. The method of claim 46, wherein the concentration of the additive is in the range of about 1% to about 30% by weight.

50. 47. The method of claim 46, wherein the step of contacting the heterogeneous carbonaceous polymer with the additive occurs at a temperature in the range of about 100°C to about 350°C.

51. 47. The method of claim 46, wherein the step of contacting the heterogeneous carbonaceous polymer with the additive occurs for about 0.5 hours to about 15 hours.

52. The method of claim 1 further comprising the step of heat treating.

53. 53. The method of claim 52, wherein the heat treatment is carried out at a pressure in the range of about 0 kPa to about 800 kPa.

54. 53. The method of claim 52, wherein the heat treatment is carried out in the presence of an inert atmosphere.

55. 53. The method of claim 52, further comprising the step of volatile species flowing out of said vessel.

56. 1. A system for forming fibers from a heterogeneous carbonaceous polymer, comprising: a first container; an inlet in communication with the first vessel; a heat supply in communication with the first vessel; an extruder in communication with the first vessel; Acid and a stabilization furnace; A system comprising:

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