Methods of producing carbon fibers from asphaltenes

Abstract

Methods of producing carbon fibers from asphaltenes, and asphaltene-based carbon fibers produced by such method are disclosed. In some embodiments, the method comprises selecting at least one sample comprising asphaltene for supplying as a feedstock, wherein the selecting of the at least one sample comprises determining a melt processing condition of the at least one sample, spinning the feedstock at a melt processing temperature to produce melt-spun fibers, and collecting the melt-spun fibers, stabilizing the melt-spun fibers by subjecting the fibers to an air atmosphere to form stabilized melt-spun fibers, and carbonizing the stabilized melt-spun fibers by subjecting the fibers to an inert atmosphere at a carbonization temperature to produce the carbon fibers.

Description

METHODS OF PRODUCING CARBON FIBERS FROM ASPHALTENESField of the Invention

[0001] This invention relates generally to methods for producing carbon fibers. Specific embodiments provide methods of producing carbon fibers from asphaltenes.Background

[0002] Carbon fibers are widely used as the reinforcing material for high-performance composite materials for both structural and functional applications, and renowned for their outstanding strength-to-weight ratio, making them significantly stronger and lighter than many conventional building materials like steel and aluminum. With comprising over 92 wt.% carbon atoms by definition, and having a unique arrangement of graphitic layers oriented along the fiber axis, carbon fibers possess exceptional mechanical, electrical and thermal properties such as high tensile strength, high stiffness, high fatigue resistance, high chemical resistance, high electrical conductivity, and low thermal expansion. This unique combination of properties makes carbon fibers essential for various industries where high strength and lightweight are required, such as aerospace, automotive, sporting goods, defense, wind turbines, marine, infrastructure, energy storage, and more.

[0003] Currently, polyacrylonitrile (PAN) is the predominant precursor for the commercial-grade carbon fiber production, accounting for over 90% of market volume, while alternative sources such as petroleum pitch and rayon fulfill the remaining demand. However, the high costs associated with the raw materials and energy-intensive production of carbon fibers, especially for the PAN-based precursor fiber, is a major challenge that limit the use of carbon fibers mainly for niche applications. Furthermore, greenhouse gas (GHG) emissions and environmental footprint related to the manufacturing of the raw materials (e.g. acrylonitrile) and PAN- based precursor fibers (e.g. wet spinning using toxic solvents) are problematic in terms of sustainability concerns. A key strategy that has been widely proposed is the adoption of cost-effective precursor materials for carbon fiber production since the precursor cost constitutes more than 50% of the overall cost for the PAN-based carbon fiber. Lowering the cost of carbon fibers holds the potential to significantly broaden their use on a commercial scale, particularly in high-volume applicationssuch as the automotive sector, where there is a pressing need for lightweighting to reduce fuel consumption, enhance electric vehicle performance, and reduce greenhouse gas (GHG) emissions.

[0004] For example, industrial lignin, a byproduct of biorefineries and pulp-paper mills, has been extensively studied as a low-cost renewable feedstock because of its abundance, aromaticity, higher carbon content and thermal stability. However, the tensile strength and modulus of lignin-based carbon fibers to date are still not satisfactory enough to meet the criteria for structural applications and further improvement in properties is needed. Some other alternative precursors that have been explored in both lab-scale and pilot-scale include cellulose and derivatives, polyethylene and melt-spinnable textile-grade acrylic co-polymers.

[0005] Asphaltenes are defined as the heaviest fraction of crude oil or the fraction of bitumen that is soluble in toluene and insoluble in n-alkane solvents. Asphaltenes are generated at considerably large quantities as a by-product of the refining process that transforms bitumen or crude oil into usable fuels. Because of their complex structure, molecular weight, and tendency for aggregation and precipitation, asphaltenes cause issues during both production and transportation of crude oil. Thus, they are considered as a low-value waste, which are either burned for its heat value or disposed of in tailing ponds and landfills. However, these practices are not sustainable, causing environmental problems and increased GHG emissions. There is thus a pressing need to discover innovative value-added applications for asphaltenes, not only to address its economic and environmental consequences but also to mitigate its adverse effects on the oil industry.

[0006] The inventors have recognized a general need for improved methods for producing carbon fibers from asphaltenes. There is a particular need for such methods to produce asphaltene-based carbon fibers with high mechanical properties at low costs.Summary

[0007] One aspect of the invention provides methods for producing carbon fibers from asphaltenes. The method comprises selecting at least one sample comprising asphaltene for supplying as a feedstock, spinning the feedstock at a melt processing temperature to produce melt-spun fibers, and collecting the melt-spun fibers,stabilizing the melt-spun fibers by subjecting the fibers to an air atmosphere to form stabilized melt-spun fibers, and carbonizing the stabilized melt-spun fibers by subjecting the fibers to an inert atmosphere at a carbonization temperature to produce the carbon fibers.

[0008] The selecting of the at least one sample may comprise determining a melt processing condition of the at least one sample. In some embodiments, the melt processing condition is determined by identifying one or more thermal and rheological properties of the sample.

[0009] In some embodiments, the determining of the melt processing condition of the sample comprises identifying one or more of a thermal softening temperature (Ts), thermal transitioning temperature, melt viscosity, Thermogravimetric Analysis (TGA) decomposition temperatures, elemental compositions, and level of aromaticity of the sample.

[0010] In some embodiments, the method comprises stretching the melt-spun fibers to produce drawn melt-spun fibers, prior to the stabilization step.

[0011] In some embodiments, the method comprises applying tension to the melt- spun fibers during the stabilization and / or carbonization steps.

[0012] In some embodiments, the method comprises treating the melt-spun fibers with an acid solution, acid vapor (i.e., the gaseous form of the acid emitted by an acid solution during its evaporation), a gas such as a halogen-containing gas, e.g., iodine gas, bromine gas and / or chlorine gas), and / or oil before the stabilization step. In some embodiments, the treating of the melt-spun fibers with the oil is performed after the spinning step and before the stretching step.

[0013] In some embodiments, the determining of the melt processing condition of an asphaltene sample is performed before the spinning step. The melt processing condition of the sample is adjusted by adding one or more additional samples comprising asphaltene to the sample to create a blend of asphaltenes for supplying as a feedstock.

[0014] In some embodiments, the carbonization step comprises a multi-step heating process. The multi-step heating process may comprise heating the stabilized fibers to a first carbonization temperature at a first heating rate, followed by heating the stabilized fibers to a second carbonization temperature at a second heating rate. Thefirst carbonization temperature may be lower than the second carbonization temperature. The first heating rate may be less than the second heating rate.

[0015] Another aspect of the invention provides asphaltene-based carbon fibers. The asphaltene-based carbon fibers may be produced by the methods of the present disclosure.

[0016] Further aspects and example embodiments are illustrated in the accompanying drawings and / or described in the following description.

[0017] It is emphasized that the invention relates to all combinations of the above features, even if these are recited in different claims.Brief Description of the Drawings

[0018] The accompanying drawings illustrate non-limiting example embodiments of the invention.

[0019] FIG. 1 is a flow chart illustrating the steps of a method for producing carbon fibers according to an example embodiment of the invention.

[0020] FIG. 2A is a plot of heat flow (W / g) measured as a function of temperature (°C) showing the differential scanning calorimetry (DSC) curves of three different asphaltene samples, namely S2, S3 and L3.

[0021] FIG. 2B is a plot of storage modulus (G’), loss modulus (G”), tan delta (tan 5) and complex viscosity (q*) (Pa.s) as a function of temperature (°C) at a heating rate of 20°C / min of the as-received S2 asphaltene sample.

[0022] FIG. 2C is a plot of complex viscosity (q*) (Pa.s) as a function of temperature (°C) at a heating rate of 20°C / min of each of the S2, S3 and L3 asphaltene samples.

[0023] FIG. 2D is a plot of tan delta (tan 5) as a function of temperature (°C) at a heating rate of 20°C / min of each of the S2, S3 and L3 asphaltene samples.

[0024] FIG. 3A is a plot of tan delta (tan 5) as a function of temperature (°C) of the as received S2 sample at different heating rates.

[0025] FIG. 3B is a photograph of a post-rheology-test S2 sample that is heated at 20°C / min. The plates were opened when the temperature is above 300°C, showing the formation of fiber-like spindles.

[0026] FIG. 4A is a plot of complex viscosity (Pa.s) as a function of temperature (°C)of the S2 and L3 asphaltene samples and their blends (S2 / L3 at weight ratios of each of 80 / 20, 70 / 30, and 60 / 40).

[0027] FIG. 4B is a plot of tan delta (tan 5) as a function of temperature (°C) of the S2 and L3 asphaltene samples and their blends (S2 / L3 at weight ratios of each of 80 / 20, 70 / 30, and 60 / 40).

[0028] FIG. 4C is a plot of weight (%) as a function of temperature (°C) showing the Thermogravimetric Analysis (TGA) weight loss curves of the S2 and L3 asphaltene samples and their blends (S2 / L3 at weight ratios of each of 80 / 20, 70 / 30, and 60 / 40).

[0029] FIG. 4D is a plot of intensity (a.u.) as a function of 20 (degrees) showing the X- ray diffraction patterns of the S2 and L3 asphaltene samples and their blends (S2 / L3 at weight ratios of each of 80 / 20, 70 / 30, and 60 / 40). The X-ray diffraction patterns show the peak positions of the y-band (20=19°, d =4.8 A), the 002-band (20=25°, d =3.5 A) and the 10-band (20=43°, d =2.1 A).

[0030] FIG. 5A is a plot of weight (%) as a function of temperature (°C) at 20°C / min heating rate showing the TGA weight loss of the as received S2 sample and the pretreated S2 asphaltene sample.

[0031] FIG. 5B is a plot of derivative weight loss (% / °C) as a function of temperature (°C) at 20°C / min heating rate of the as received S2 sample and the pretreated S2 asphaltene sample.

[0032] FIG. 5C is a plot of complex viscosity (q*) (Pa.s) as a function of temperature (°C) at 20°C / min heating rate of the as received S2 sample and the pretreated S2 asphaltene sample.

[0033] FIG. 5D is a plot of tan (delta) as a function of temperature (°C) at 20°C / min heating rate of the as received S2 sample and the pretreated S2 asphaltene sample.

[0034] FIG. 5E are DSC curves of the as received S2 sample and the pretreated S2 asphaltene sample.

[0035] FIG. 5F are XRD patterns of the as received S2 sample and the pretreated S2 asphaltene sample.

[0036] FIG. 6A is a photograph of continuous melt-spun fibers collected on a 7cm- diameter winder produced from the S2 / L3 asphaltene blend at a blend ratio of 80 / 20.

[0037] FIG. 6B is a photograph of continuous melt-spun fibers collected on a 7cm-diameter winder produced from the S2 / L3 asphaltene blend at a blend ratio of 70 / 30.

[0038] FIG. 60 is a scanning electron microscope (SEM) image of the S2 / L3 asphaltene blend of FIG. 4A.

[0039] FIG. 6D is a SEM image showing a magnified portion of the S2 / L3 asphaltene blend of FIG. 4A.

[0040] FIG. 6E is a SEM image of the S2 / L3 asphaltene blend of FIG. 4B.

[0041] FIG. 6F is a SEM image showing a magnified portion of the S2 / L3 asphaltene blend of FIG. 4B.

[0042] FIG. 6G is a photograph showing continuous melt-spun filaments collected on a 30 cm-diameter winder produced from the as-received S3 asphaltene sample.

[0043] FIG. 6H are SEM images of the S3 melt-spun fibers showing diameters in the range of 15-25 pm.

[0044] FIG. 7A is an image of brittle and thick filaments / rods extruded from the pretreated S2 asphaltene sample.

[0045] FIG. 7B is an optical microscope image of a filament from the pretreated S2 sample.

[0046] FIG. 8 are TGA weight loss curves for the S3 asphaltene meltspun fiber, showing the oxygen uptake during stabilization process in air, and the effect of stabilization on carbon yield.

[0047] FIG. 9A is a SEM image of carbon fibers from S2 / L3 asphaltene blends produced by a single step carbonization method.

[0048] FIG. 9B is a SEM image of carbon fibers from S2 / L3 asphaltene blends produced by a multi-step carbonization method, showing smoother and void-free fiber surfaces.

[0049] FIG. 10 is an image showing stabilized asphaltene fibers prior to carbonization. The fibers were secured by using metal frames and kept under tension during carbonization.

[0050] FIG. 11 is a FTIR spectra of melt-spun and stabilized fibers produced from the S3 asphaltene sample, showing the changes in the functional groups after an oxidative stabilization process at 260°C in the air.

[0051] FIG. 12A is a SEM image of the carbon fibers produced from the S2 / L3 asphaltene blend at a blend ratio of 80 / 20.

[0052] FIG. 12B is a SEM image of the carbon fibers produced from the S2 / L3 asphaltene blend at a blend ratio of 70 / 30.

[0053] FIG. 12C is a SEM image of the carbon fibers produced from the S3 asphaltene sample.

[0054] FIG. 12D is a SEM image showing a cross-section of the carbon fibers produced from the S3 asphaltene sample.

[0055] FIG. 13 are Raman spectra of the carbon fibers produced from different asphaltene samples (S3 and S2 / L3 asphaltene blends at blend ratios of 80 / 20, 70 / 30 and 60 / 40) and carbonized at a carbonization temperature at 1000°C.

[0056] FIG. 14 is a plot of strength (MPa) as a function of fiber diameter (pm), and modulus (GPa) as a function of fiber diameter (pm) showing the effect of fiber diameter on tensile strength and modulus of the carbon fibers produced from the S2 / L3 asphaltene blends.

[0057] FIG. 15A is photograph of non-stretched asphaltene melt-spun fibers mounted between clamps of a dynamic mechanical analyzer (DMA).

[0058] FIG. 15B is photograph of asphaltene melt-spun fibers mounted between clamps of a dynamic mechanical analyzer that were stretched and were subjected to a temperature above the softening temperature of the feedstock during stretching.

[0059] FIG. 15C is an optical microscope image showing melt-spun fibers before stretching. The fibers before stretching have a diameter of 42 pm. The scale bar was set at 50 pm.

[0060] FIG. 15D is an optical microscope image showing melt-spun fibers after stretching. The fibers after stretching have a diameter of 7 pm. The scale bar was set at 50 pm.

[0061] FIG. 15E is a SEM image of the carbon fibers produced from the S3 asphaltene sample. The fibers were stretched after melt-spinning. The resulting carbon fibers have a diameter of 6.4 pm.

[0062] FIG. 15F is another SEM image of the carbon fibers produced from the S3 asphaltene sample.

[0063] FIG. 16A is a plot of modulus (GPa) as a function of fiber diameter (pm), showing the tensile properties of the carbon fibers produced from each of S3 (unstretched), S3 (stretched), and S2 / L3 (70 / 30 and 60 / 40) asphaltene blends. FIG. 16A shows the effect of fiber diameter on tensile strength and modulus.

[0064] FIG. 16B is a plot of strength (MPa) as a function of fiber diameter (pm), showing the tensile properties of the carbon fibers produced from each of S3 (unstretched), S3 (stretched), and S2 / L3 (70 / 30 and 60 / 40) asphaltene blends. FIG. 16B shows the effect of fiber diameter on tensile strength and modulus.Detailed Description

[0065] Throughout the following description, specific details are set forth in order to provide a more thorough understanding of the invention. However, the invention may be practiced without these particulars. In other instances, well known elements have not been shown or described in detail to avoid unnecessarily obscuring the invention. Accordingly, the specification and drawings are to be regarded in an illustrative, rather than a restrictive sense.

[0066] Aspects of the invention relate to methods for producing carbon fibers from asphaltenes. Example methods involve selecting at least one bitumen-derived asphaltene precursor to produce carbon fibers by melt spinning. Proof of concept demonstrations of the methods described herein have shown that carbon fibers with exceptional mechanical properties (e.g., average tensile strength of about 1.1 GPa, and average modulus of about 91 GPa) can be achieved from bitumen-derived asphaltene precursors.

[0067] FIG. 1 is a flow chart illustrating the steps of an example method 10 of producing carbon fibers. Some embodiments of the method begin with selecting at least one sample comprising asphaltene for supplying as a feedstock (block 14). In some embodiments, the sample comprising asphaltene is sourced from oil sands. The sample may be a by-product in oil extraction processes. The sample may be in a form comprising a solid (e.g., powder), liquid and / or a gel. The selecting of the at least one sample may comprise determining a melt processing condition of the sample. In some embodiments, the melt processing condition of the sample is determined by identifying one or more thermal and rheological properties of the sample. Non-limiting examples of thermal and rheological properties that may be useful in determining themelt processing condition of asphaltenes include the thermal softening temperature (Ts), and melt behaviors thereof such as thermal transitioning temperatures, melt viscosity, and Thermogravimetric Analysis (TGA) decomposition temperatures.

[0068] In some example embodiments, the identifying of the one or more thermal and rheological properties of asphaltenes comprises performing one or more of dynamic rheology tests, differential scanning calorimetry (DSC) analysis, Thermogravimetric Analysis (TGA), methods for determining the softening point of bitumen (Ring-and- Ball Apparatus) in accordance with the ASTM D36-06 standard (or other related methods), dilatometry and dynamic mechanical analysis (DMA), methods for determining the viscosity of a sample, e.g., by the use of a rheometer, rotational viscometers and other similar devices.

[0069] In some embodiments, dynamic rheological tests on asphaltene samples are performed to determine one or more of the storage shear modulus (G’), loss shear modulus (G”), loss tangent (tanb), complex viscosity (q*) over a range of temperatures.

[0070] In one non-limiting example dynamic rheology test, the rheological properties of the asphaltene sample are determined under dynamic shear mode using a rheometer. In such example, the test may involve heating a sample from about room temperature to about 350°C at a heating rate of about 20°C / min and an oscillatory strain of about 0.1 % (within the linear viscoelastic range) at a frequency of about 1 Hz.

[0071] In some embodiments, differential scanning calorimetry (DSC) analysis on asphaltene samples is performed to determine the softening temperature (Ts) of the sample. In one non-limiting example, differential scanning calorimetry analysis may involve heating the sample from about -25°C to about 300°C at a heating rate of about 20°C / min to generate a differential scanning calorimetry (DSC) curve. In some embodiments, the softening temperature is measured as the midpoint of the step change in heat capacity in the differential scanning calorimetry (DSC) curve.

[0072] In some embodiments, Thermogravimetric Analysis (TGA) on asphaltene samples is performed to determine the decomposition temperature (i.e., the temperature at which the sample begins to undergo thermal degradation). In some embodiments, the decomposition temperature corresponds to a temperature at which the sample exhibits about 5% to about 10% weight loss before the decompositionbegins. In some embodiments, a DTG curve (derivative thermogravimetric curve) illustrates the rate of material weight changes as a function of temperature, thereby shows how quickly a material loses or gains mass as the temperature changes. The DTG peak temperature indicates the temperature at which the weight loss rate is at a maximum. In one non-limiting example, Thermogravimetric Analysis (TGA) may involve heating the sample from 25°C to about 800°C at a heating rate of about 10°C / min under an inert gas flow. The percent (%) char residue or percent (%) carbon yield is the residual solid mass at elevated temperatures (800°C) after completion of carbonization / pyrolysis.

[0073] In some embodiments, the melt processing condition of the sample is additionally determined by characterizing one or both of elemental compositions and level of aromaticity of the sample.

[0074] The melt processing condition as determined by the identification of the one or more thermal and rheological properties of asphaltenes may be used to determine and / or suggest a melt processing temperature of the sample. In some embodiments, the melt processing temperature is a temperature range within which the asphaltene molecules show fluid-like behavior. In some example embodiments, the melt processing temperature is at a temperature greater than the G7G” crossover points as determined by results of dynamic rheological tests. The G7G” crossover point is the temperature at which G” (loss modulus) begins to become equal to and / or greater than G’ (storage modulus). The G7G” crossover point may provide an indication as to the point at which the transition from solid-like to liquid-like behavior of a sample occurs. For example, the G7G” crossover point is the point at which asphaltene molecules begin to show thermal softening behavior with increased thermal mobility. In some embodiments, the melt processing temperature is at least about 30°C, and in some embodiments, at least about 40°C, and in some embodiments, at least about 50°C, and in some embodiments, between about 60°C and about 70°C above the G7G” crossover points.

[0075] The melt processing condition as determined by the identification of the one or more thermal and rheological properties of asphaltenes may additionally be used to evaluate the melt flow characteristics of the sample. The melt flow characteristics of the sample may be used to inform the suitability or optimality for melt processing.

[0076] Desirable melt flow characteristics of asphaltene may be informed by one ormore of the following thermal and / or rheological properties of the samples:- softening temperature (Ts) between about 45°C and about 125°C, and in some embodiments, less than about 125°C;- thermal transition (G7G” crossover point) between about 150°C and 250°C, and in some embodiments, less than about 250°C;- tan delta values (tan 5) between about 2 and 7, and in some embodiments, more than about 2;- tan delta peak temperatures between about 240°C and 290°C, and in some embodiments, less than about 290°C;- melt viscosity range (as may be informed by q* value determined by dynamic rheology tests) of between about 100 - 1000 Pa.s, and in some embodiments, less than about 1000 Pa.s; and / or- degree of aromaticity in the range of from 0.10 to 0.32 and / or a size of aromatic sheets in the range of from 4.10 A to 4.45 A, etc.

[0077] In some embodiments, the melt flow characteristics of asphaltene samples are adjusted to achieve a melt processing temperature of the sample of less than about 300°C, and in some embodiments, between about 150°C and about 300°C, and in some embodiments, between about 200°C and about 280°C.

[0078] In some embodiments, the melt flow characteristics of the sample are adjusted by pre-treating the sample (block 18).

[0079] In some embodiments, the pre-treating of the sample in block 18 comprises purifying the sample by removing or reducing non-melting aggregates and / or volatile components in the sample. The pre-treating step in block 18 may comprise purifying the sample by one or more chemical treatment processes and thermal treatment processes.

[0080] In some embodiments, the one or more chemical treatment processes comprise a solvent extraction method. The solvent extraction method may comprise dissolving the sample in a solvent and separating a purified sample comprising asphaltene from the solvent. The solvent may in some embodiments comprise an organic solvent. Any suitable organic solvent may be used. Non-limiting examples of suitable organic solvent that may be used include one or more of tetrahydrofuran(THF), N,N-Dimethylformamide (DMF), toluene, hexanes, dichloromethane, diethyl ether, and the like. In some embodiments, the one or more chemical treatment processes additionally comprises a filtration method. The filtration method may for example comprise passing the purified sample through a filter to obtain a further purified sample.

[0081] In some embodiments, the one or more thermal treatment processes comprise heating the sample to a temperature. The sample may be heated to a temperature in the range of from about 100°C to 300°C, and in some embodiments, from about 120°C to about 200°C, and in some embodiments, from about 150°C to about 200°C. In some embodiment, the sample is heated to the temperature under an inert gas atmosphere (e.g., under nitrogen flow). In some embodiments, the sample is maintained at the temperature from about 15 minutes to about 5 hours, and in some embodiments, about 30 minutes to about 2 hours, and in some embodiments, about 45 minutes to 90 minutes.

[0082] In some embodiments, the pre-treating of the sample in block 18 comprises combining two or more samples containing asphaltene to produce a blend for supplying as the feedstock. The two or more samples that are used to produce the blend may each or all be purified by one or more chemical treatment and / or thermal treatment processes prior to or after the combining step.

[0083] In some embodiments, at least one of the two or more samples containing asphaltene exhibit undesirable melt flow characteristics. In some embodiments, the at least one of the two or more samples comprise a low softening temperature having a temperature of less than about 20°C, and in some embodiments, less than about 10°C, and in some embodiments less than about 5°C, and in some embodiments, less than about 3°C, and in some embodiments, less than about 1°C. In some embodiments, the at least one of the two or more samples comprise a low viscosity having a viscosity value of greater than about 0.5 Pa.s at temperatures of greater than 100°C, and in some embodiments, greater than about 1 Pa.s at temperatures of greater than 100°C.

[0084] In some example embodiments, the combining of the two or more samples containing asphaltene to produce a blend is prepared by dissolving each one of the two or more samples in a solvent separately to form a respective two or more solutions. The two or more solutions each comprising the dissolved sample may becombined in predetermined proportions to form a combined solution. The solvent in the combined solution may be separated to obtain the blend comprising the two or more asphaltene samples. The solvent may in some embodiments comprise an organic solvent. Any suitable organic solvent may be used. Non-limiting examples of suitable organic solvents that may be used include one or more of tetrahydrofuran (THF), N,N-Dimethylformamide (DMF), toluene, hexanes, dichloromethane, diethyl ether, and the like.

[0085] The proportions at which the two or more samples containing asphaltene are supplied to produce the blend may be adjusted to achieve the desired melt flow characteristics of the feedstock.

[0086] In block 20, the selected feedstock, optionally pre-treated in block 18, may be supplied to a melt spinner for spinning at the melt processing temperature to produce melt-spun fibers. The melt processing temperature may be informed by results of dynamic rheological tests.

[0087] In some example embodiments, the spinning of the feedstock comprises extruding the feedstock through a spinneret to obtain melt-spun fibers. The melt-spun fibers may then be collected on a take-up winding spool.

[0088] In some embodiments, the spinning of the feedstock is performed in the absence of a solvent.

[0089] In some embodiments, the melt spinner comprises a horizontal melt spinner.

[0090] In some embodiments, the melt spinner comprises a screw extruder. In such embodiments, the spinning of the feedstock comprises passing the feedstock through the screw extruder before extruding through the spinneret. The screw extruder may be a twin screw extruder.

[0091] Some aspects of the invention pertain to producing carbon fibers with reduced diameters. Carbon fibers with reduced diameters may have enhanced mechanical properties, e.g., high strength and modulus. In some embodiments, the method 10 comprises adjusting the size of the take-up winding spool to optimize the average diameter of the produced melt-spun fibers, thereby the average diameter of the resulting carbon fibers. In some embodiments, the adjusting of the size of the take-up winding spool comprises adjusting the diameter thereof to achieve a draw ratio of greater than about 5, and in some embodiments, greater than about 10, and in someembodiments, greater than about 15, and in some embodiments, greater than about 20. The draw ratio may be defined as the diameter of the spinneret to the diameter of the melt-spun fiber.

[0092] In some embodiments, the method 10 optionally comprises an oil treatment step 27. The oil treatment step 27 may in some embodiments, be referred to as a “spin-finish oil application”. The oil treatment step 27 may comprise applying oil to the melt-spun fibers, for example by spraying the oil onto the fibers to immerse the fibers in the oil. In some embodiments, the oil comprises a silicone-based oil. Treating the fibers with oil before stabilization (in block 28) may facilitate the stretching of the fibers and / or assist with producing resultant fibers that comprise more desirable properties (e.g., softer and / or more ductile).

[0093] In some embodiments, the method 10 further comprises drawing or stretching the melt-spun fibers to obtain drawn melt-spun fibers (block 24). In some embodiments, the melt-spun fibers are stretched to a draw ratio in the range of from about 1 .1 to about 2. The draw ratio may be defined as the ratio of drawn fiber length to the starting length.

[0094] In some embodiments, the fibers are subjected to a temperature greater than the thermal softening temperature or the G7G’ crossover point of the feedstock during the stretching step (block 24). In some embodiments, the temperature at which the fibers are subjected to during the stretching step is about 5°C to about 50°C greater than the thermal softening temperature or the G G’ crossover point of the feedstock.

[0095] In some example embodiments, stretching of the melt-spun fibers in block 24 is performed in an oven, such as a steam-heated oven. In some embodiments, the stretching of the melt-spun fibers comprises drawing the fiber tows through the oven and collecting and / or winding the drawn melt-spun fibers at a draw-down device such as a wind-up spool, which may be heated. The wind-up spool may for example comprise a body that is rotatable about a longitudinal axis thereof. The amount of tension applied on the melt-spun fibers may be adjusted by altering the rotational speed at which the drawn-down device collects and / or winds the drawn melt-spun fibers.

[0096] In some example embodiments, the stretching of the melt-spun fibers comprises securing opposing ends of the fibers to a respective support, such as bymounting opposing ends of the fibers to a respective clamp or grip.

[0097] In some embodiments, the oil treatment step 27 is performed after the melt spinning step 20 and before the stretching step 24.

[0098] In some embodiments, the method 10 optionally comprises an acid treatment step 26. The acid treatment step 26 may comprise applying an acid to the melt-spun fibers. The acid may be applied by soaking or dipping the melt-spun fibers in an acid solution, and / or by exposing the melt-spun fibers to an acid vapor. The fibers may be soaked in the acid solution and / or exposed to the acid vapor for less than 30 minutes, and in some embodiments, less than about 15 minutes, and in some embodiments, about 10 minutes or less. In some embodiments, the acid solution which includes the acid solution that the acid vapor is emitted therefrom during evaporation comprises one or more acids. The acid solution may comprise one or more strong acids. Nonlimiting examples of an acid that may be used include nitric acid, sulfuric acid, hydrochloric acid, hydrobromic acid, perchloric acid, and the like. The concentration of the acid may be in the range of from about 5% to about 40%, and in some embodiments, less than 20%, and in some embodiments, about 10% or less. Soaking the fibers with acid solution and / or exposing the fibers to acid vapor before stabilization (in block 28) may advantageously speed up the stabilizing step (e.g., reducing the amount of time and / or heat required to stabilize the melt-spun fibers), and / or prevent or reduce fiber fusion in large-scale production.

[0099] In some embodiments, the method 10 optionally comprises a gas treatment step 29. The gas treatment step 29 may comprise exposing the melt-spun fibers to a gas. In some embodiments, the gas comprises halogen gas such as iodine, chlorine, and / or bromine gas. In some example embodiments, the gas comprises iodine gas. Exposing the fibers to a gas before stabilization (in block 28) may advantageously speed up the stabilizing step.

[0100] The acid and / or gas treatment steps (block 26, 29) may be performed before the stabilization step (block 28) and after the melt-spinning step (block 20).

[0101] In block 28, the melt-spun fibers (i.e. , unstretched melt-spun fibers, or melt- spun fibers which have not undergone stretching in block 24) or drawn melt-spun fibers (in embodiments which the melt-spun fibers have undergone stretching in block 24) are stabilized in an air atmosphere. The stabilization step may comprise heatingthe fibers to a stabilization temperature at a heating rate. Once reached at or near the stabilization temperature, the fibers may be maintained at the stabilization temperature for a time interval.

[0102] In some embodiments, the stabilization temperature is greater than about 250°C, and in some embodiments, in the range of from about 200°C to about 300°C.

[0103] In some embodiments, the heating rate, e.g., the rate at which the fibers are heated to the stabilization temperature such as from room temperature is in the range of from about 0.2°C / min to about 5°C / min, and in some embodiments, in the range of from about 0.2°C / min to about 3°C / min, and in some embodiments, in the range of from about 0.2°C / min to about 1°C / min.

[0104] In some embodiments, the fibers are maintained at the stabilization temperature for a time interval of from about 15 minutes to about 5 hours, and in some embodiments, from about 30 minutes to about 3 hours, and in some embodiments, from about 45 minutes to about 2 hours, and in some embodiments, about 1 hour.

[0105] The stabilized melt-spun fibers may be carbonized in block 32. The carbonizing of the stabilized melt-spun fibers may comprise subjecting the fibers to an inert atmosphere (e.g., a nitrogen flow) at a carbonization temperature to form carbon fibers.

[0106] In some embodiments, the carbonization step 32 comprises a single-step heating process. The single-step heating process may comprise heating the stabilized fibers to one carbonization temperature at a heating rate. The heated stabilized fibers may be maintained at the one carbonization temperature for a time interval.

[0107] In some embodiments, the carbonization step 32 comprises a multi-step heating process. The multi-step heating process may comprise heating the stabilized fibers to a first carbonization temperature at a first heating rate, followed by heating the stabilized fibers to a second carbonization temperature at a second heating rate.

[0108] In some embodiments, the stabilized fibers are maintained at the first carbonization temperature for a time interval before heating to the second carbonization temperature.

[0109] In some embodiments, the stabilized fibers are maintained at the secondcarbonization temperature for a time interval after the fibers are heated to the second carbonization temperature.

[0110] In some embodiments, the first carbonization temperature is lower than the second carbonization temperature. In some example embodiments, the first carbonization temperature is at least about 50% lower than the second carbonization temperature.

[0111] In some embodiments, the first heating rate is lower than the second heating rate. In some embodiments, the first heating rate is at least 50% lower than the second heating rate. In some example embodiments, the first heating rate is at least about two-thirds lower than the second heating rate. A carbonization step 32 which comprises a multi-step heating process comprising a lower first carbonization temperature (i.e., a first carbonization temperature that is lower than the second carbonization temperature) and a slower first heating rate (i.e., a first heating rate that is slower than the second heating rate) may allow for a controlled release of volatile gases during carbonization, which may produce more desirable resulting carbon fibers, such as a greater fraction of carbon fibers that are void-free or substantially void-free. Asphaltenes are heterogeneous in nature and thus could pose challenges in carbonizing such fibers. A multi-step heating process may facilitate in addressing such challenges.

[0112] In some embodiments, the carbonization temperature, the first carbonization temperature, and / or the second carbonization temperature is in the range of from about 500°C to about 2800°C, and in some embodiments, in the range of from about 500°C to about 1800°C, and in some embodiments, in the range of from about 600°C to about 1200°C, and in some embodiments, in the range of from about 800°C to about 1000°C, and in some embodiments, about 1000°C or lower.

[0113] In some embodiments, the rate at which the stabilized fibers are heated is in the range of from about 1°C / min to about 10°C / min, and in some embodiments, in the range of from about 1°C / min to about 8°C / min, and in some embodiments, in the range of from about 2°C / min to about 5°C / min.

[0114] The heated stabilized fibers may be maintained at the carbonization temperature, the first carbonization temperature and / or the second carbonization temperature for a time interval of about 10 minutes to about 2 hours, and in someembodiments, about 15 minutes to about 1 hour. In some example embodiments, the heated stabilized fibers are maintained at the carbonization temperature for about 30 minutes.

[0115] In some embodiments, tension is applied to the melt-spun fibers during the stabilization step 28 and / or the carbonization step 32. Applying tension during one or more of these steps may facilitate in the reduction of the diameters of the resulting carbon fibers.

[0116] In some example embodiments, tension is applied to the melt-spun fibers during the stabilization step 28 and / or the carbonization step 32 by passing the fibers through one or more rollers or godets and the like. The one or more rollers may for example comprise a body that is rotatable about a longitudinal axis thereof. The amount of tension applied on the melt-spun fibers may be controlled to achieve the desired structural integrity and / or alignment of the fibers during the transformation from a precursor material to a carbonized form by adjusting one or more of the following:- the rotational speed of the one or more rollers;- the speed at which the fibers pass through the one or more rollers;- the size of the one or more rollers; and / or- the number of rollers and / or the distance between the rollers; etc.

[0117] In some embodiments, tension is applied to the melt-spun fibers within a furnace. In such embodiments, the one or more rollers are arranged within the furnace.

[0118] Tension may in some embodiments be applied by securing opposing ends of the fibers to a respective support.

[0119] In some embodiments, the stretching of the fibers in block 24 is performed before the stabilization step in block 28, and continues during the stabilization step 28 and / or the carbonization step 32. In some other embodiments, the stretching of the fibers in block 24 may be omitted, and tension is applied to the fibers in one or both of the stabilization step 28 and the carbonization step 32. In some further other embodiments, the fibers may be stretched only in the stretching step 24, and tension is not applied to the fibers in the stabilization step 28 or the carbonization step 32.The stretching of the fibers in block 24 and the applying of tension in the stabilization step 28 and / or the carbonization step 32 are optional.

[0120] Method 10 may be tuned to optimize the melt flow characteristics of the sample and / or the melt processing temperature of the sample and / or the yield of carbon fiber production and / or the mechanical properties of the carbon fibers by adjusting one or more of:- the softening temperature (Ts) of the feedstock;- the melt viscosity of the feedstock;- the levels of aromaticity of the feedstock;- the samples selected to form a blend for supplying as the feedstock, in embodiments in which a blend of asphaltenes is used as a feedstock;- operating conditions used to form the blend of asphaltenes, in embodiments in which a blend of asphaltenes is used as a feedstock;- inclusion / omission of pre-treatment / purification steps and operating conditions used in the purification;- methods, operating conditions and / or apparatus used in the spinning step (e.g., operating temperature, screw speed and / or fiber take-up speed, type and / or size of spinneret and / or screw extruder and / or take-up winding spool, etc.);- inclusion / omission of the stretching step, and methods, operating conditions (e.g., temperature, draw ratio, etc.) and / or apparatus used in the stretching step;- methods, operating conditions and / or apparatus used in the stabilizing step and / or carbonizing step;- inclusion / omission of applying tension to the fibers during the stabilizing and / or carbonizing step and / or methods in applying tension, etc.

[0121] Aspects of the invention pertain to asphaltene-based carbon fibers produced by the method 10. The method 10 may be tuned to advantageously produce asphaltene-based carbon fibers with desirably low average fiber diameters and high mechanical strength and / or modulus.

[0122] In some embodiments, the asphaltene-based carbon fibers produced by the method 10 comprise an average fiber diameter in the range of from about 4 pm to about 200 pm, and in some embodiments in the range of from about 4 pm to about 50 pm, and in some embodiments, in the range of from about 4 pm to about 30 pm, and in some embodiments, less than about 30 pm, and in some embodiments, less than about 20 pm, and in some embodiments, between about 4 pm to about 15 pm.

[0123] In some embodiments, the asphaltene-based carbon fibers produced by the method 10 comprise an average tensile strength in the range from about 300 MPa to about 2,000 MPa, and in some embodiments, in the range of from about 500 MPa to about 1 ,000 MPa, and in some embodiments, greater than about 800 MPa, and in some embodiments, greater than about 1 GPa.

[0124] In some embodiments, the asphaltene-based carbon fibers produced by the method 10 comprise an average modulus in the range from about 30 GPa to about 200 GPa, and in some embodiments, in the range of from about 50 GPa to about 180 GPa, and in some embodiments, greater than about 50 GPa, and in some embodiments, greater than about 80 GPa.

[0125] In some embodiments, the asphaltene-based carbon fibers produced by the method 10 comprise an average strain at break value in the range from about 0.3% to about 2.5%, and in some embodiments, in the range of from about 0.5% to about 2%, and in some embodiments, between about 0.7% to about 1.5%.

[0126] The invention is further described with reference to the following specific examples, which are not meant to limit the invention, but rather to further illustrate it.Examples

[0127] The method illustrated in FIG. 1 was used to produce carbon fibers from asphaltene samples. In these Examples, the asphaltene precursors used to produce carbon fibers were derived from bitumen that were extracted from Alberta oil sands.1. Materials

[0128] In these Examples, Alberta Oil-sands Asphaltenes (AOA), Grade S2, S3, and L3 were used. S2 and S3 samples were received in powder form, and L3 was received in thick gel form. The elemental compositions of the as-received asphaltenes are listed in Table 1 below.Table 1. Elemental compositions of as received asphaltene samples2. Methods2.1 Purification of asphaltene feedstock

[0129] Chemical pre-treatment of the S2 asphaltene sample was conducted using a two-step solvent extraction and filtration method. 30 grams of asphaltene was dissolved in 100 mL of THF (tetrahydrofuran, 99.9%). The solution was stirred overnight and fractionated by centrifugation at 4000 rpm for 10 min. The soluble fraction (supernatant) was collected and then filtered using a filter with a 0.22-micron pore size. THF was recovered by a rotary solvent evaporator. The yield for the pretreated asphaltene sample was about 92 wt.%. The S3 and L3 asphaltene samples were used as received.

[0130] S2 / L3 asphaltene blends were prepared as follows. The purified S2 and L3 blends were prepared at various weight ratios (i.e. , 10, 20, 30 and 40 wt.%). Firstly, each of the asphaltene samples (i.e., S2 and L3) were separately dissolved in THF ata concentration of 30% w / v. The solutions were subsequently blended in pre-defined proportions and agitated at room temperature for one hour using a magnetic stir bar. THF was recovered using a rotary evaporator. The remaining asphaltene sample (S2 / L3 blend) was air-dried in the fume hood overnight to remove residual solvent. Additionally, the solid asphaltene mixture was further heat-treated at 170°C for 1 h under nitrogen flow in a tube furnace to remove volatiles. The resulting S2 / L3 asphaltene blends were crushed into chunks and used for the melt spinning experiments.2.2 Melt spinning of asphaltenes

[0131] Prior to melt spinning, thermal pre-treatment of asphaltenes was performed at 170°C for 1 h under nitrogen flow in a tube furnace to eliminate noxious volatiles and sulfur compounds. Melt spinning of the asphaltene samples was then carried out using a DSM Xplore™ MC15 twin-screw micro compounder / spinner to produce “green fibers.” The diameter of the spinneret used in these Examples was 250 pm with a length / diameter (L / D) ratio of 5. The barrel temperature was adjusted according to the processing window determined by the rheological tests, which was in the range of 220°C-270°C depending on the asphaltene type (S3 only or S2 / L3 blends) and blend weight ratio (w / w %) for asphaltene blends samples. The asphaltene samples in powder form were processed at a screw speed of 50 rpm for 5 minutes under nitrogen flow. The melt-spun fibers were collected on winders with different sizes (7 cm and 30 cm diameter) at fiber take-up speeds ranging from 200-300 m / min.2.3 Production of carbon fibers

[0132] Carbon fibers were produced from the melt spun green fibers, by oxidative thermostabilization in an air atmosphere using a convection oven, where samples were mounted on metal sheets under tension (applied using weights) and heated from room temperature to 260°C with a heating rate of 0.5°C / min followed by an isothermal dwell at 260°C for 1 hour. After thermostabilization, fibers were mounted onto graphite sheets and carbonized in a tube furnace (such as one that is commercially available under the trade name MTI Corp™, Richmond, CA, USA) under nitrogen flow by heating to 1000°C with a heating rate of 3°C / min and holding at 1000°C for 30 min (single step carbonization). For some samples, an alternative carbonization method was tested. In such alternative method, the fibers were carbonized using a multi-step heating process, where samples were first heated to500°C with a slower heating rate (2°C / min) and held isothermally for 30 min and then heated to 1000°C at a faster heating rate (5°C / min) and held at 1000°C for 30 min. Similar to thermo-stabilization, samples were clamped on a metal frame to maintain tension during the carbonization cycle (Figure S6).2.4 Preparation of carbon fibers by the mechanical stretching method

[0133] Stretching of individual melt-spun asphaltene fibers was performed by mounting the fibers on paper frames and fastening them between the clamps of DMA tensile tester with temperature-controlled furnace. Green fibers were heated 20-30°C above their softening temperature, drawn / stretched with a controlled draw ratio of 1.5- 2, and cooled down to room temperature by opening the furnace. Fibers were then thermostabilized in the DMA furnace while being mounted between the clamps, heated to 260°C with a rate of 0.5°C / min, and held at 260°C for 1 hour. Stabilized fibers were removed from the clamps and were then carbonized in a tube furnace at 1000°C as described above.2.5 Dynamic torsional rheology

[0134] The rheological properties of asphaltene samples were investigated under dynamic shear mode using a TA Instruments™ AR2000 rheometer. About 300 mg of finely ground asphaltene powder were loaded between 25 mm diameter stainless steel parallel plates and then heated from room temperature to 350°C with a heating rate of 20 °C / min and an oscillatory strain of 0.1 % (within the linear viscoelastic range) at a frequency of 1 Hz. The change in the complex viscosity (q*), loss tangent (tan6), storage (G’), and loss shear moduli (G”) were recorded as a function of temperature.2.4 Thermal properties

[0135] The softening temperature of asphaltene samples was determined by differential scanning calorimetry (DSC) analysis (TA Instruments™ Q1000). For each sample, 5-7 mg of asphaltene powder was heated from -25°C to 300°C with a heating rate of 20°C / min. The softening temperatures, Ts, of the samples, were measured as the midpoint of the step change in heat capacity in the DSC curve. Thermogravimetric Analysis (TGA) of asphaltenes was carried out by a TA Instruments™ Q500 TGA. About 15 mg samples were loaded in a platinum pan and heated from 25°C to 800°C at a heating rate of 10°C / min under nitrogen gas flow. The software (UniversalAnalysis 2000, TA Instrument™) was used to analyze the DSC curves and TGA thermograms.2.5 Scanning electron microscopy (SEM)

[0136] The surface morphology of carbon fibers was evaluated by scanning electron microscope (Helios NanoLab™ 650 FIB-SEM; FEI, Hillsboro, USA) at an accelerating voltage of 1kV. The samples were mounted onto metal holders with carbon tape and sputter-coated with iridium. Energy-dispersive X-ray (SEM-EDX) analysis was performed on the same instrument at an accelerating voltage of 15 kV.2.6 Tensile tests

[0137] The mechanical properties of the single carbon fibers were measured according to ASTM D3822 with an Instron™ (model 5969), a 50 N load cell, and a crosshead speed of 0.25 mm / min. The samples were glued on a paper frame with a gauge length of 10 mm, and both sides of the paper frame were cut before the experiment. Prior to testing, the diameter of each sample was measured using an optical microscope equipped with an Olympus™ camera software. The tensile strength, Young’s modulus, and strain at break values were reported as the average of at least 15 measurements.2.7 Raman spectroscopy

[0138] Raman spectra of carbon fibers were collected on a Senterra II™ Raman microscope (Bruker™). A 50* objective aperture was used to focus on the fiber surface, and data were collected using a 532 nm laser at 6.25 mW power with a 10 s integration time and 5 co-additions. Baseline correction and Gaussian peak fitting were done using the Origin™ software.2.8 Fourier transform infrared spectroscopy (FTIR)

[0139] For each test, 5 mg of finely ground fiber samples in powder form were thoroughly blended with 500 mg of dried potassium bromide (KBr) and compressed into a pellet using a hydraulic press. FT-IR spectra of melt spun and stabilized fibers samples were collected in transmission mode with an Invenio™ FT-IR Spectrometer (Bruker™, US) in the range of 400-4000 cm-1with a resolution of 4 cm-1for 64 scans.2.9 X-ray powder diffraction (XRD)

[0140] X-ray powder diffraction (XRD) of asphaltene samples was collected on a D8Advance Bragg-Brentano Diffractometer (Bruker™, Billerica, MA, USA) equipped with LynxEye™ silicon strip detector and Fe filter for Co Ka radiation (wavelength A= 1.78897 A) generated at 35 kV and 40 mA. The XRD patterns were obtained in steps of 0.02° in the 20 range of 10° to 80° at a scan rate of 1 ,27min, then shifted to Cu Ka radiation for reference using the WinPlotr™ software. Peak fitting and deconvolution of the recorded patterns were carried out using the Origin software. Peak position, peak intensity, peak area, interplanar distance, and full width at half maximum (FWHM) were used to calculate the structural parameters of asphaltenes.3. Results3.1 Thermo-rheological properties of asphaltene feedstocks

[0141] In this Experiment, melt spinning experiments and subsequent carbon fiber production were conducted using three distinct asphaltene precursors (S2, S3, and L3) extracted from Alberta oilsands bitumen. As shown in Table 1 , elemental analysis of the as-received asphaltenes revealed that all considered samples exhibited a carbon content exceeding 80 wt.% and low H / C molar ratios ranging from 0.82-1.39. The elemental analysis showed that some metal traces (e.g., V, Ni) at the ppm level and heteroatoms (e.g., S, N) were present, which can be considered as impurities.

[0142] The thermal softening behavior of the as-received asphaltene samples were studied by using parallel-plate dynamic torsional rheology and differential scanning calorimetry (DSC) to determine the optimal processing conditions for the melt spinning of asphaltene fibers. FIG. 2A shows the DSC curves of the S2 and S3 samples, which had broad endothermic thermal transition events, with S2 having a less pronounced transition. The midpoint of the step change in heat flow was used to determine the softening temperatures (Ts), which were ~170°C and ~102°C for S2 and S3, respectively. The Ts of the L3 sample was ~0.5°C with a more pronounced step change, which started at sub-zero temperatures. Due to its low Ts, the L3 sample exhibited a viscous, gel-like characteristic at room temperature. The inventors determined that L3 was not suitable in its current state for melt spinning and heat treatment steps in carbon fiber production, while S2 and S3 samples were more suitable having regard to their softening temperatures (Ts). Also as shown in FIG. 2A, the extent of the endothermic transition associated with the S3 sample is more pronounced compared to S2. This may suggest that S3 is easier to melt process at lower temperatures compared to S2.

[0143] Dynamic rheology tests were carried out to identify the melt processing conditions of the samples. FIG. 2B shows the characteristic temperature-dependent dynamic rheological properties of the as-received asphaltene sample (S2) studied by applying a small torsional oscillatory strain (0.1 %). The changes in the storage shear modulus (G’) and loss shear modulus (G”), as well as the loss tangent (tan 5) and complex viscosity (q*), were recorded over a range of temperatures. At the same time, the sample was heated up to 360°C under nitrogen flow. For comparison to the S2 sample, the tan 5 and q* curves of both the S3 and the L3 asphaltene samples are illustrated in FIGS. 2C and 2D.

[0144] As the S2 asphaltene sample was heated between the parallel plates under a compressive normal force, G' and G" slightly increased due to densification below their softening temperature (Ts), but G' remained higher than G", indicating a solidlike behavior. Once the temperature reached around about 200°C, a sudden decrease in G' was observed coinciding with the G" peak maximum temperature (about 205°C), which might be due to the segmental mobility of asphaltene molecules. At the G7G' crossover point (about 228°C), where the G" value became higher than the G' value (tan 6> 1 ), the asphaltene started to show liquid-like behavior. When heated further, tan 5 increased and reached its peak value (~272°C), which indicated that asphaltene molecules could flow freely, showing a fluid-like viscous flow behavior in accordance with the lowest complex viscosity (q*) value at the same peak temperature. The intensity of the tan 5 peak is an indication of the degree of thermal mobility of asphaltene molecules, which was relatively low (about 1.44) for the S2 sample. As the temperature increased above 280°C, G', G", and q* increased, and G' became greater than G" (~302°C, 2ndcrossover point), indicating that the transition from liquid-like to solid-like behavior and loss of melt flow ability due to potential condensation reactions among asphaltene molecules.

[0145] The inventors found that thermal transitioning temperatures and parameters were greatly influenced by the heating rate (FIGS. 3A and 3B, Table S1). The onset softening temperature (G’ drop onset point or G” peak), tan 5 peak temperature (maximum thermal mobility), G7G” crossover points (transition from solid-like to liquid-like behavior and vice versa) and minimum complex viscosity at tan 5 peak temperature as a function of heating rate are summarized in Table S1. When processed at heating rates slower than 10°C / min, the S2 sample did not show anyliquid-like behavior, maintained in its solid form, and tan 5 values were consistently lower than 1 over all temperature ranges up to 360°C. However, when heated at 20 and 40°C / min (the fastest rate achieved by the rheometer and resembles the actual melt spinning conditions), S2 sample showed liquid-like behavior starting from about 220°C (first crossover point where G”>G’) with a peak tan 5 temperature of ~280°C at which the tan 5 value was ~ 1 .8, and q* values reduced to as low as ~5300 Pa.s for the rate of 40 °C / min. The post-rheology-test examination of the asphaltene sample’s appearance revealed that certain portions of the asphaltene sample underwent melting and transformed into fiber-like spindles upon swiftly separating the plates while they were still hot (Figure 3B). However, other segments of the sample retained their powder form and did not undergo melting, even at elevated heating rates exceeding 20°C / min suggesting a second phase in the sample.Table S1. Summary of thermal softening temperatures and rheological properties of as received asphaltene (S2) sample at different heating rates.

[0146] In comparison to the S2 asphaltene, the S3 sample exhibited significantly lower thermal transitioning temperatures (G" and tan 5 peaks, and G7G' crossover point), lower q* values, and higher tan 5 intensity at its peak value. The G’ and q* drop onset point was at about 140°C with a G7G' crossover temperature at about 157°C and a tan 5 peak temperature of about 241°C, which were about 40°C lower than the S2. The intensity of the tan 5 peak was about 9, showing an augmented melt flow behavior for the S3 sample (FIG. 2D). In addition, the q* value at the tan 5 peaktemperature was about 120 Pa.s and dropped an order of magnitude to about 10 Pa.s when the temperature was further increased to 300°C. Beyond the second G7G" crossover point (~310°C), q* slightly increased due to possible condensation reactions. However, the q* values were still lower than ~300 Pa.s at temperatures below 360°C (FIG. 2C). Compared to the S2 sample, which had a q* value of about 12,900 Pa.s at the lowest, the q* of the S3 sample was almost two orders of magnitude lower, revealing the superior melt flow characteristics of the S3 sample. The L3 sample, on the other hand, had q* values less than ~1 Pa.s and tan 5 values more than 100 when heated above 50°C, with a flow behavior like low-viscosity liquids with a lack of melt spinnability with its current form.

[0147] The optimal melt processing window for the S3 sample was identified as the temperature range from ~160°C to ~310°C, corresponding to the first and second G7G" crossover points at which asphaltene molecules show fluid-like behavior. The S3 sample was anticipated to exhibit ideal melt flow characteristics within the temperature range of approximately 230°C to 250°C, as this is the temperature at which the highest tan 5 values are observed along with the lowest q* values.

[0148] The S2 sample displayed a narrower melt processing window, spanning approximately 220°C to 300°C, and exhibited insufficient melt flow characteristics. Preliminary melt-spinning experiments confirmed that the as-received S2 sample had limited melt processability. This limitation may stem from its relatively higher q* values and lower tan 5 values compared to common thermoplastic polymers and other easily melt-processable precursors like petroleum pitch. Furthermore, the restricted melt flow of the S2 sample may be attributed to the presence of non-melting aggregates and particles observed in the post-rheology sample, as was confirmed by the obstruction of the spinning die. Additionally, during the melt extrusion process of the S2 sample, there were notable emissions of unpleasant fumes and odors when temperatures exceeded 160°C, which is likely due to the release of volatiles and sulfur-containing compounds. These volatiles, when present in carbon fiber precursors, may negatively affect the uniformity and strength of melt-spun fibers by creating voids.3.2 Pre-treatment of the S2 asphaltene feedstock prior to melt spinning

[0149] In this Example, a two-step pre-treatment was applied to the S2 sample in an effort to eliminate non-melting aggregates and remove volatile components. The twostep pre-treatment involved solvent extraction using THF and filtration, followed by a mild heat treatment prior to melt spinning. Elemental analysis results confirmed that sulfur and nitrogen contents of the pretreated S2 were significantly lower than those of the as-received S2 (0.96% and 0.0% vs. 7.1 % and 1.7%, respectively). TGA analysis showed that the pretreated S2 had higher onset decomposition temperature (410°C vs. 390°C at 5% weight loss) and similar DTG peak temperature (466°C vs. 459°C) and carbon residue at 800°C (66% vs. 67%) compared to non-pretreated S2. The softening temperature determined by the DSC analysis showed that the pretreated S2 had a lower Ts (122°C vs. 170°C) with a more pronounced endothermic step change (FIGS. 5A-5F). Although the G7 G' crossover (about 246°C vs. about 228°C) and the peak tan 5 temperatures (about 287°C vs. about 272°C) were slightly higher for the pretreated sample, the intensity of tan 5 was also higher (about 1 .9 vs. 1 .4) as well. The q* value at the tan 5 peak were slightly lower compared to the as-received S2 sample. The lowest q* value of the pretreated S2 was about 9900 Pa.s. within the melt processing range (from about 246°C to about 323°C), showing an improvement in the melt flow behavior (FIGS. 5A-5F). Initial melt spinning experiments verified that the pre-treatment of the S2 sample reduced noxious volatiles and enhanced its melt processability. It was possible to extrude uniform and aggregate-free filaments or rods from the pretreated S2 when the spinning temperatures were in the range of 280°C-300°C (FIGS. 7A and 7B). These filaments were however thick (with diameters ranging from 300 to 400 pm) and brittle, and prolonged melt processing at these elevated temperatures posed challenges, primarily due to increased viscosity in the spinning dope and the partial blockage of the spinneret.3.3 Asphaltenes Blends for Melt Spinning

[0150] Blending the pre-treated (chemical and thermal) S2 sample with the L3 asphaltene sample was performed to improve the melt processability of the pretreated S2 by reducing its melt viscosity and processing temperature window. The L3 sample had a very low softening temperature (about 0.5°C by DSC) and low viscosity (greater than 1 Pa.s) at temperatures above 100°C (FIGS. 2C and 2D). The S2 / L3 blends were prepared by mixing the THF solutions of solvent-extracted S2 with as- received L3 at certain weight fractions (10-40 wt.%). The S2 and L3 asphaltene samples showed complete miscibility, and the blends were homogeneous without anyindication of phase separation.

[0151] DSC and dynamic rheology tests indicated good miscibility between the two asphaltene samples, as evidenced by a single endothermic event and thermal transition point for all blend ratios. FIG. 4 shows the change in the q* and tan 5 as a function of temperature for all blend ratios. A summary of thermal properties, including the Ts, G7G" crossover point, tan 5, q* at the tan 5 peak temperature, as well as TGA decomposition temperatures, is listed in Table 2 below.Table 2. Thermal and rheological properties of pretreated-S2 and L3 asphaltene samples and their blends with different weight ratios

[0152] As shown in Table 2, increasing the amount of L3 in the S2 / L3 asphaltene blends decreased the thermal transition and softening temperatures considerably. There was an about 80°C decrease in the Ts and an about 100°C decrease in the G7G" crossover point, while the tan 5 peak temperature decreased by ~50°C when the L3 content increased up to 40 wt.%. More importantly, the intensity of the tan 5 peak tripled, and the q* values decreased more than two orders of magnitude below <150 Pa.s, especially for the 70 / 30 and 60 / 40 S2 / L3 blends (FIGS. 4A and 4B). When the L3 content was 10 wt.%, the q* values and tan 5 peak intensity did not change, despite minor shifts in the softening temperatures. On the other hand, when the L3 content was more than 40 wt.% (data not shown), the thermal transitioning temperatures and the melt viscosity of S2 / L3 asphaltene blends further dropped. TGA analysis of S2 / L3 asphaltene blends revealed that decomposition onset temperature at 5% weight loss and the carbon residue at 800°C reduced from 411°C to 298°C and from 66% to 45%, respectively, as the L3 content increased from 10 wt. % to 40 wt. % (FIG. 4C).

[0153] X-ray diffraction analysis was conducted on asphaltene blends to understand the structural changes and their impact on the melt behavior. The X-ray diffraction patterns of S2 / L3 asphaltene blends showed that the intensity of the 002-band (related to the aromatic groups) reduced while the y-band (related to the aliphatic groups) increased as the L3 ratio increased (FIG. 4D). The structural parameters calculated based on the XRD analysis revealed that the distance between the two aliphatic chains or saturated rings (dr) and the distance between two aromatic sheets (dm) increased from 4.10 A to 4.41 A and from 3.53 A to 3.58 A, respectively, while the aromaticity index (fa) decreased gradually from 0.31 to 0.11 as the L3 ratio increased in the S2 / L3 blends (Table S3). In addition, the size of the aromatic sheets (La) and the number of aromatic rings in each aromatic sheet (Ra) were slightly smaller for the S2 / L3 asphaltene blends compared to the S2 sample. XRD analysis of asphaltene blends suggested that the addition of L3 into the S2 asphaltene sample led to a relatively loose asphaltene structure with a higher free volume, evidenced by the increase in the distance between aliphatic chains and aromatic sheets. In addition, the decrease in the degree of aromaticity and the size of aromatic sheets enabled less restricted thermal mobility of asphaltene molecules, which resulted in moderate softening temperatures and favorable melt flow behavior.

[0154] The distance between the two aliphatic chains or saturated rings (dr), the distance between two aromatic sheets (dm), and the size of the aromatic sheet, La, were obtained from the peak position of the y-band, (002) band, and the (10) band, respectively. The aromaticity index (fa) was calculated from the ratio of the areas under the (002)-band and the y-band. The average number of aromatic rings in each aromatic sheet (Ra), and the number of carbons per aromatic structural unit (CAu) were calculated and listed in Table S3.Table S3. Structural parameters of the asphaltene samples calculated based on XRD analysis.

[0155] The results support that the L3 sample may serve as a “plasticizer” for the S2 sample and / or as a processing aid, which may act to facilitate the lowering of thermal transition temperatures and enhancing the melt processability of S2 through reducing the melt viscosity thereof. Results from the Examples show that the S2 / L3 asphaltene blends at 80 / 20, 70 / 30, and 60 / 40 blend ratios comprise a favorable melt viscosity range (100-1000 Pa.s), possess moderate melt processing temperatures (200- 250°C), may be capable of preventing fiber fusion during oxidative stabilization, and may produce resulting carbon fibers with acceptable carbon yields (>50%).3.4 Melt spinning of asphaltenes

[0156] Melt-spun green fibers from the S2 / L3 asphaltene blends with 80 / 20, 70 / 30, and 60 / 40 blend ratios, as well as from the S3 sample alone, were produced using a twin-screw extruder equipped with a 250pm monofilament spinneret as discussed above. Melt spinning temperatures were chosen in the range of 220-270°C, which was 60-70°C above the G7G" crossover points determined by the dynamic rheology tests, where the q* values were in the range of 100-1000 Pa.s and near the tan 5 peak temperature (tan 5 >3). More specifically, the fiber spinning temperatures used were 270°C, 240°C, and 220°C for the 80 / 20, 70 / 30, and 60 / 40 w / w% S2 / L3 blends, respectively, while the temperature range was 220-230°C for the S3 sample. Continuous fiber spinning was achieved, and uniform melt-spun green fibers were collected from all the asphaltene samples at these temperature ranges (FIG. 6).

[0157] The fibers from the 80 / 20 S2 / L3 blend were larger in diameter (90-150 pm)and quite brittle but were possible to be wound up on a 7 cm-diameter spool, while filaments from the 70 / 30 and 60 / 40 blends had smaller average diameters (40-50 pm) and therefore were less brittle, thus enabling continuous spinning for longer periods. SEM images of melt-spun fibers of both the S2 / L3 80 / 20 and the S2 / L3 70 / 30 blends showed smooth surface morphology without any surface voids or cracks (FIGS. 6C to 6F). Uniform fibers were obtained from the S2 / L3 blends.

[0158] The diameter of the fiber take-up winder was adjusted to 30 cm. This adjustment of the winder may advantageously reduce the tension applied to fibers, enable slower cooling rates, and / or achieve draw ratios exceeding 10 (from a spinneret diameter of 250 pm to meltspun fiber diameters below 25 pm). Fibers that were spun from the S2 / L3 60 / 40 and S2 / L3 70 / 30 blends comprise diameters in the range of 20-25 pm. Due to their reduced diameters, these melt-spun fibers were less brittle and were easy to handle for subsequent thermal processing steps. Likewise, continuous fiber spinning was easily achieved with the S3 sample, which may be the result of its promising melt flow characteristics. Fibers that were spun from the S3 samples were uniform, void-free and thinner with diameters in the range of 15-25 pm (FIG. 6H). Melt processing of S3 was carried out without any pre-treatment (neither solvent extraction nor heat treatment). The S3 sample also had unnoticeable asphaltene odor even at elevated temperatures (200°C-240°C) as compared to S2 and the S2 / L3 asphaltene blends.3.5 Production of carbon fibers

[0159] The melt-spun fibers were subjected to a preliminary oxidative stabilization step at elevated temperatures (200-300°C) in an oxygen-rich environment. The stabilization step may be performed to prevent fiber fusion during the carbonization step. During the stabilization process, oxygen uptake may facilitate various condensation and crosslinking reactions among asphaltene molecules. This, in turn, may enhance the dimensional stability of the fibers and / or elevate their softening points to exceedingly high temperatures (or completely eliminate thermal softening), thus preventing any potential melt flow prior to the onset of carbonization / pyrolysis reactions.

[0160] The asphaltene melt spun fibers were carbonized through a one-step process by heating them to 260°C in an air environment with a heating rate of 0.5°C / min and holding them at 260°C for 1 h. For all the S2 / L3 asphaltene blends and the S3 sample,the stabilized fibers were obtained without melting or fusion. However, fiber fusion and loss of fiber structure was observed when the fibers were stabilized at temperatures below 250°C and at heating rates higher than 0.5°C / min.

[0161] TGA analysis of the melt spun asphaltene fibers in air confirmed the weight gain in fibers during stabilization (FIG. 8); however, the amount of oxygen uptake (<1 %) was low compared to isotropic and mesophase pitch values, which could be attributed to the heterogeneous nature of asphaltenes. Additionally, based on the TGA curves, the stabilized fibers had significantly higher (ranging from 8-18 wt.%) carbon yield at 800°C compared to those that underwent carbonization without prior stabilization (FIGS. 9A and 9B). The overall carbon yields ranged from 58 to 71 wt.% for the S2 / L3 asphaltene blends and approximately 56 wt.% for the S3 sample.

[0162] FTIR spectroscopy was used to evaluate the changes in the functional groups of asphaltene melt-spun fibers after thermal stabilization (FIG. 11). FTIR spectra of the melt spun fiber shows two strong absorption peaks at ~2920 cm-1and ~2850 cm-1for the C-H stretching and two peaks at ~1450 cm-1and ~1375 cm-1for C-H bending which were associated with the aliphatic groups in asphaltene. The peak which appeared at ~1600 cm-1is attributed to the C=C vibrations of the aromatic groups. After stabilization, the intensity of peaks related to C-H vibrations was significantly decreased, and the peak corresponding to the aromatic C=C vibrations shifted. Furthermore, new peaks appeared at the stabilized fiber, which was a broad peak at ~3400 cm-1assigned for the O-H stretching for hydroxyl groups, peaks at ~1700 cm-1and ~1770 cm-1for C=O stretching of carbonyl groups, and the broad peak at ~1300 cm-1for the formation C-O-C linkages. These results validated the oxygen uptake in the stabilized fiber along with chain scission of aliphatic groups and the formation of crosslinked (such as ether linkages) or condensed structures as a result of oxidation reactions during the stabilization process.

[0163] Following stabilization, the fibers were carbonized under a nitrogen atmosphere using a multi-step heating process, initially heating to 500°C at a rate of 2°C / min, followed by a 30-minute isothermal hold, and subsequently heating to 1000°C at a rate of 5°C / min, with another 30-minute hold at 1000°C. Using slower heating rates and incorporating a low-temperature pre-carbonization step may advantageously address the challenges posed by the heterogeneous nature of asphaltenes during pyrolysis reactions. SEM images of the carbon fibers produced inthese Examples further confirmed that the fibers exhibited smoother surfaces and were free of voids and cracks when multi-step carbonization was carried out, as opposed to a single-step carbonization method involving direct heating to 1000°C with a rate of 3°C / min (FIGS. 9A and 9B). FIG. 12 shows the SEM surface morphology of carbon fibers produced from both S2 / L3 asphaltene blends and the S3 asphaltene sample. Uniform and void-free carbon fibers were successfully produced from all asphaltene samples. The cross-section of asphaltene fibers (FIG. 12D) also had a smooth texture, resembling a similarity to isotropic pitch-based carbon fibers without any indication of microcrystal arrangement observed in mesophase carbon fibers. To assess the graphitic structure of asphaltene carbon fibers, Raman spectroscopy was employed. All types of carbon fibers exhibited two characteristic peaks at ~1350 cm-1and ~1580 cm-1■ corresponding to the D and G bands, respectively, which are typically found in disordered carbon materials (FIG. 13, Table S4). The D-band is associated with the disordered regions or defects in the carbon lattice, and the G-band is related to the degree of graphitization and well-ordered regions in the carbon structure. The intensity ratio of these peaks (ID / IG) , a relative indicator for the degree of disorder in the graphitic lattice, was in the range of 0.94-0.96 for the carbon fibers from S2 / L3 asphaltene blends with no significant difference depending on the blending ratio. The carbon fiber produced from the S3 asphaltene had a slightly higher ID / IG ratio (1 .02) compared to S2 / L3 blends, indicating a similar extent of disordered structure. The ID / IG ratios obtained in these Examples are comparable to pitch-based carbon fibers produced at a similar temperature range but lower than the PAN-based carbon fibers with more ordered structures that are graphitized at temperatures above 2000°C.Table S4. Raman peak positions of D and G bands and ID / IG ratios for the carbon fibers from different asphaltene samples carbonized at 1000°C.3.6 Mechanical properties of carbon fibers

[0164] The diameters of the carbon fibers showed a wide range, spanning from 15 to 150 pm. This variation was primarily attributed to the diameter of the precursor fibers, which, in turn, was influenced by the choice of asphaltene source and the dimensions of the fiber take-up winder, as described above. Consequently, the tensile strength and modulus values of the resulting carbon fibers varied significantly with the variation of fiber diameters. These results supported that the strength and modulus of the resulting carbon fibers strongly increased with decreasing fiber diameter (FIG. 14 FIGS. 16A and 16B).

[0165] For example, carbon fibers produced from the S2 / L3 70 / 30 asphaltene blend, which had diameters ranging from 40-50 pm, exhibited average tensile strength, modulus, and strain at break values of 340 ± 55 MPa, 30.1 ± 2.3 GPa, and 1.0 ± 0.3%, respectively. In contrast, carbon fibers from the S2 / L3 80 / 20 asphaltene blend, with larger diameters ranging from 125-150 pm, displayed lower average tensile strength, modulus, and strain at break values of 220 ± 122 MPa, 23.6 ± 5.7 GPa, and 1.0 ± 0.4%, respectively. Smaller fibers were produced from the S2 / L3 70 / 30 and 60 / 40 asphaltene blends through melt-spinning using a larger size take-up winder. This resulted in carbon fibers with diameters ranging from 20-25 pm, which exhibited improved average tensile properties with strength and modulus of 521 ± 99 MPa and 39.7 ± 4.1 GPa, respectively. The thinnest carbon fibers were obtained from the S3 asphaltene fibers, exhibiting diameters ranging from 15-20 pm. Accordingly, the carbon fibers from the S3 asphaltene showed superior tensile properties when compared to the S2 / L3 blends, with values of 567 ± 234 MPa for strength, 63.4 ± 5.9 GPa for modulus, and 0.9 ± 0.3 %, for strain at break.

[0166] The results of these Examples suggested that further enhancements in tensile strength and modulus can be realized by reducing the diameter of the carbon fibers from asphaltene precursors by stretching.

[0167] Proof of concept demonstrations of the method described herein show that the diameter of S3 produced asphaltene-based carbon fibers can be reduced to below 10 pm. The method involved subjecting individual fibers to a stretching process within adynamic mechanical analyzer (DMA) equipped with a temperature-controlled furnace. The fibers were heated above their softening temperature, specifically above the G7G' crossover point and secured within the tensile test frame during this process. Fibers with diameters as low as 7 pm were produced by carefully stretching the filaments in the test frame and subsequently stabilizing under tension within the DMA furnace in an air atmosphere (FIGS. 15A-15F). These stretched and stabilized fibers were then transferred to a tube furnace and carbonized under identical conditions with the non-stretched fibers. Because of the fiber stretching, the carbon fibers produced from the S3 asphaltene sample by this method had diameters ranging from 4-14 pm and an increase in tensile strength and modulus ranging from 77-180 GPa for modulus and 670-1700 MPa for strength, as shown in FIGS. 16A and 16B. The average tensile properties were 1142 ± 97 MPa for strength, 91.1 ± 13.7 GPa for modulus, and 1.1 ± 0.3 % for strain at break.Interpretation of Terms

[0168] Unless the context clearly requires otherwise, throughout the description and the claims:• “comprise”, “comprising”, and the like are to be construed in an inclusive sense, as opposed to an exclusive or exhaustive sense; that is to say, in the sense of “including, but not limited to”;• “connected”, “coupled”, or any variant thereof, means any connection or coupling, either direct or indirect, between two or more elements; the coupling or connection between the elements can be physical, logical, or a combination thereof;• “herein”, “above”, “below”, and words of similar import, when used to describe this specification, shall refer to this specification as a whole, and not to any particular portions of this specification;• “or”, in reference to a list of two or more items, covers all of the following interpretations of the word: any of the items in the list, all of the items in the list, and any combination of the items in the list; the singular forms “a”, “an”, and “the” also include the meaning of any appropriate plural forms. These terms (“a”, “an”, and “the”) mean one or moreunless stated otherwise;• “and / or” is used to indicate one or both stated cases may occur, for example A and / or B includes both (A and B) and (A or B);• “approximately” when applied to a numerical value means the numerical value ± 10%;• where a feature is described as being “optional” or “optionally” present or described as being present “in some embodiments” it is intended that the present disclosure encompasses embodiments where that feature is present and other embodiments where that feature is not necessarily present and other embodiments where that feature is excluded. Further, where any combination of features is described in this application this statement is intended to serve as antecedent basis for the use of exclusive terminology such as "solely," "only" and the like in relation to the combination of features as well as the use of "negative" limitation(s)” to exclude the presence of other features; and• “first” and “second” are used for descriptive purposes and cannot be understood as indicating or implying relative importance or indicating the number of indicated technical features.

[0169] Words that indicate directions such as “vertical”, “transverse”, “horizontal”, “upward”, “downward”, “forward”, “backward”, “inward”, “outward”, “left”, “right”, “front”, “back”, “top”, “bottom”, “below”, “above”, “under”, and the like, used in this description and any accompanying claims (where present), depend on the specific orientation of the apparatus described and illustrated. The subject matter described herein may assume various alternative orientations. Accordingly, these directional terms are not strictly defined and should not be interpreted narrowly.

[0170] Where a range for a value is stated, the stated range includes all sub-ranges of the range. It is intended that the statement of a range supports the value being at an endpoint of the range as well as at any intervening value to the tenth of the unit of the lower limit of the range, as well as any subrange or sets of sub ranges of the range unless the context clearly dictates otherwise or any portion(s) of the stated range is specifically excluded. Where the stated range includes one or both endpoints of the range, ranges excluding either or both of those included endpoints are alsoincluded in the invention.

[0171] Certain numerical values described herein are preceded by "about". In this context, "about" provides literal support for the exact numerical value that it precedes, the exact numerical value ±5%, as well as all other numerical values that are near to or approximately equal to that numerical value. Unless otherwise indicated a particular numerical value is included in “about” a specifically recited numerical value where the particular numerical value provides the substantial equivalent of the specifically recited numerical value in the context in which the specifically recited numerical value is presented. For example, a statement that something has the numerical value of “about 10” is to be interpreted as: the set of statements:• in some embodiments the numerical value is 10;• in some embodiments the numerical value is in the range of 9.5 to 10.5; and if from the context the person of ordinary skill in the art would understand that values within a certain range are substantially equivalent to 10 because the values with the range would be understood to provide substantially the same result as the value 10 then “about 10” also includes:• in some embodiments the numerical value is in the range of C to D where C and D are respectively lower and upper endpoints of the range that encompasses all of those values that provide a substantial equivalent to the value 10.

[0172] Specific examples of systems, methods and apparatus have been described herein for purposes of illustration. These are only examples. The technology provided herein can be applied to systems other than the example systems described above. Many alterations, modifications, additions, omissions, and permutations are possible within the practice of this invention. This invention includes variations on described embodiments that would be apparent to the skilled addressee, including variations obtained by: replacing features, elements and / or acts with equivalent features, elements and / or acts; mixing and matching of features, elements and / or acts from different embodiments; combining features, elements and / or acts from embodiments as described herein with features, elements and / or acts of other technology; and / or omitting combining features, elements and / or acts from described embodiments.

[0173] As will be apparent to those of skill in the art upon reading this disclosure, each of the individual embodiments described and illustrated herein has discrete components and features which may be readily separated from or combined with the features of any other described embodiment(s) without departing from the scope of the present invention.

[0174] Any aspects described above in reference to apparatus may also apply to methods and vice versa.

[0175] Any recited method can be carried out in the order of events recited or in any other order which is logically possible. For example, while processes or blocks are presented in a given order, alternative examples may perform routines having steps, or employ systems having blocks, in a different order, and some processes or blocks may be deleted, moved, added, subdivided, combined, and / or modified to provide alternative or subcombinations. Each of these processes or blocks may be implemented in a variety of different ways. Also, while processes or blocks are at times shown as being performed in series, these processes or blocks may instead be performed in parallel, simultaneously or at different times.

[0176] Various features are described herein as being present in “some embodiments”. Such features are not mandatory and may not be present in all embodiments. Embodiments of the invention may include zero, any one or any combination of two or more of such features. All possible combinations of such features are contemplated by this disclosure even where such features are shown in different drawings and / or described in different sections or paragraphs. This is limited only to the extent that certain ones of such features are incompatible with other ones of such features in the sense that it would be impossible for a person of ordinary skill in the art to construct a practical embodiment that combines such incompatible features. Consequently, the description that “some embodiments” possess feature A and “some embodiments” possess feature B should be interpreted as an express indication that the inventors also contemplate embodiments which combine features A and B (unless the description states otherwise or features A and B are fundamentally incompatible). This is the case even if features A and B are illustrated in different drawings and / or mentioned in different paragraphs, sections or sentences.

[0177] It is therefore intended that the following appended claims and claims hereafter introduced are interpreted to include all such modifications, permutations,additions, omissions, and sub-combinations as may reasonably be inferred. The scope of the claims should not be limited by the preferred embodiments set forth in the examples, but should be given the broadest interpretation consistent with the description as a whole.

Claims

WHAT IS CLAIMED IS:1 . A method of producing carbon fibers, comprising the steps of: selecting at least one sample comprising asphaltene for supplying as a feedstock, wherein the selecting of the at least one sample comprises determining a melt processing condition of the at least one sample; spinning the feedstock at a melt processing temperature to produce melt- spun fibers, and collecting the melt-spun fibers; stabilizing the melt-spun fibers by subjecting the fibers to an air atmosphere to form stabilized melt-spun fibers; and carbonizing the stabilized melt-spun fibers by subjecting the fibers to an inert atmosphere at a carbonization temperature to produce the carbon fibers.

2. The method according to claim 1 , wherein the determining of the melt processing condition of the at least one sample comprises identifying one or more thermal and rheological properties of the sample.

3. The method according to any one of the preceding claims, wherein the determining of the melt processing condition of the at least one sample comprises performing one or both of dynamic rheology tests, differential scanning calorimetry (DSC) analysis, Thermogravimetric Analysis (TGA), dilatometry and thermomechanical analysis (TMA).

4. The method according to any one of the preceding claims, wherein the determining of the melt processing condition of the sample comprises identifying one or more of a thermal softening temperature (Ts), thermal transitioning temperature, melt viscosity, Thermogravimetric Analysis (TGA) decomposition temperatures, elemental compositions, and level of aromaticity of the sample.

5. The method according to any one of the preceding claims, further comprising stretching the melt-spun fibers to produce drawn melt-spun fibers.

6. A method of producing carbon fibers, comprising the steps of: spinning a feedstock comprising at least one sample comprising asphaltene at a melt processing temperature to produce melt-spun fibers,and collecting the melt-spun fibers; stretching the melt-spun fibers to produce drawn melt-spun fibers; stabilizing the drawn melt-spun fibers by subjecting the fibers to an air atmosphere to form stabilized melt-spun fibers; and carbonizing the stabilized melt-spun fibers by subjecting the fibers to an inert atmosphere at a carbonization temperature to produce the carbon fibers.

7. The method according to claim 5 or 6, wherein the stretching of the melt-spun fibers further comprises subjecting the melt-spun fibers to a temperature greater than the thermal softening temperature of the at least one sample.

8. The method according to claim 7, wherein the temperature at which the melt- spun fibers are subjected to in the stretching step is about 5°C to about 50°C greater than the thermal softening temperature of the at least one sample.

9. The method according to any one of claims 5 to 8, wherein the stretching step comprises stretching the melt-spun fibers to a draw ratio in the range of from about 1.1 to about 3.

10. The method according to any one of claims 5 to 9, wherein the stretching step comprises winding the melt-spun fibers around one or more rotatable spools.11 . The method according to any one of claims 5 to 9, wherein the stretching of the melt-spun fibers comprises securing opposing ends of the fibers to a respective support.

12. The method according to any one of claims 5 to 11 , wherein the stretching of the melt-spun fibers is performed prior to the stabilizing step.

13. The method according to any one of the preceding claims, wherein the spinning of the feedstock and / or stabilizing of the melt-spun fibers and / or carbonizing of the melt-spun fibers further comprise applying tension to the melt-spun fibers.

14. The method according to claim 13, wherein the applying of tension to the melt- spun fibers comprises passing the melt-spun fibers through one or more rotatable rollers.

15. The method according to claim 13, wherein the applying of tension to the melt- spun fibers comprises maintaining the fibers in a clamped position with opposing ends of the fibers being secured to a respective support.

16. The method according to any one of the preceding claims, wherein the stabilizing of the melt-spun fiber is performed at a stabilization temperature between about 200°C and about 300°C.

17. The method according to any one of the preceding claims, wherein the stabilizing of the melt-spun fiber is performed at a stabilization temperature greater than about 250°C.

18. The method according to any one of the preceding claims, wherein the stabilizing of the melt-spun fibers comprises:(i) heating the fibers to a stabilization temperature at a heating rate of about 0.2°C / min to about 5°C / min; and(ii) maintaining the fibers at the stabilization temperature for a time interval.

19. The method according to any one of the preceding claims, further comprising applying an acid solution to the melt-spun fibers before stabilizing the melt- spun fibers.

20. The method according to claim 19, wherein the acid solution comprises a strong acid.

21. The method according to claim 19 or 20, wherein the applying of the acid solution comprises dipping the melt-spun fibers into the acid solution.

22. The method according to any one of the preceding claims, further comprising exposing the melt-spun fibers to an acid vapor before stabilizing the melt-spun fibers.

23. The method as defined in claim 22, wherein the acid vapor comprises a gas emitted by the acid solution during evaporation of the acid solution.

24. The method according to any one of the preceding claims, further comprising exposing the melt-spun fibers to a gas before stabilizing the melt-spun fibers.

25. The method according to clam 24, wherein the gas comprises halogen gas.

26. The method according to clam 24 or 25, wherein the gas comprises Iodine gas.

27. The method according to any one of the preceding claims, further comprising applying an oil to the melt-spun fibers before stabilizing the melt-spun fibers.

28. The method according to claim 27, wherein the applying of the oil to the melt- spun fibers is performed after the spinning of the feedstock and prior to the stretching of the melt-spun fibers.

29. The method according to claim 27 or 28, wherein the applying of the oil to the melt-spun fibers comprises spraying the oil to the melt-spun fibers.

30. The method according to any one of the preceding claims, further comprising pre-treating the sample before or after the selecting step.31 . The method according to any one of the preceding claims, wherein the pretreating step is performed before the spinning step.

32. The method according to claim 30 or 31 , wherein the pre-treating step comprises treating the sample by one or more chemical treatment processes and / or one or more thermal treatment processes.

33. The method according to claim 32, wherein the one or more chemical treatment processes comprise dissolving the sample in a solvent, and separating a purified sample comprising the asphaltene from the solvent.

34. The method according to claim 33, wherein the solvent comprises an organic solvent.

35. The method according to any one of claims 32 to 34, wherein the one or more thermal treatment processes comprise heating the sample to a temperature of greater than about 100°C to form a purified sample.

36. The method according to claim 35, wherein the thermal treatment process is performed under an inert gas flow.

37. The method according to any one of claims 30 to 36, wherein the pre-treating step comprises combining two or more samples containing asphaltene to produce a blend for supplying as the feedstock.

38. The method according to claim 37, wherein the combining of the two or more samples containing asphaltene is performed after the determining of the melt processing condition of the at least one sample.

39. The method according to claim 37 or 38, wherein at least one of the two or more samples containing asphaltene used to produce the blend comprises a softening temperature (Ts) of less than about 20°C.

40. The method according to claim 37 or 38, wherein at least one of the two or more samples containing asphaltene used to produce the blend comprises a G7G” crossover temperature of less than about 10°C.41 . The method according to any one of claims 37 to 40, wherein at least one of the two or more samples containing asphaltene used to produce the blend comprises a viscosity of greater than about 1 Pa.s at temperatures of greater than about 100°C.

42. The method according to any one of claims 37 to 41 , wherein the combining step comprises:(i) dissolving a first sample of the two or more samples in a solvent to produce a first solution;(ii) dissolving at least one second sample of the two or more samples in a solvent to produce at least one second solution;(iii) combining the first solution and the at least one second solution to produce a combined solution; and(iv) removing the solvent from the combined solution to produce the blend comprising the first sample and the at least one second sample.

43. The method according to any one of the preceding claims, wherein the carbonizing step comprises:(i) heating the fibers to the carbonization temperature at a heating rate; and(ii) maintaining the fibers at the carbonization temperature for a time interval.

44. The method according to any one of claims 1 to 42, wherein the carbonizing step comprises:(i) heating the fibers to a first carbonization temperature at a first heating rate; and(ii) heating the fibers to a second carbonization temperature at a second heating rate.

45. The method according to claim 44, wherein the first carbonization temperature is lower than the second carbonization temperature.

46. The method according to claim 43 or 44, wherein the first heating rate is lower than the second heating rate.

47. The method according to any one of claims 44 to 46, wherein the fibers are maintained at the first carbonization temperature for a time interval before heating the fibers to the second carbonization temperature.

48. The method according to any one of claims 44 to 47, wherein the fibers are maintained at the second carbonization temperature for a time interval.

49. The method according to any one of claims 43 to 48, wherein the carbonization temperature, the first carbonization temperature, and the second carbonization temperature is between about 300°C and about 1800°C.

50. The method according to any one of claims 43 to 48, wherein the carbonization temperature, the first carbonization temperature, and the second carbonization temperature is not greater than about 1800°C.51 . The method according to any one of the preceding claims, wherein the spinning of the feedstock comprises supplying the feedstock into horizontal melt spinner, wherein the feedstock is substantially free of a solvent.

52. The method according to claim 51 , wherein the horizontal melt spinner comprises a twin screw extruder.

53. The method according to any one of the preceding claims, wherein the collecting of the melt-spun fibers comprises receiving the melt-spun fibers at a take-up winding spool having a diameter to achieve a draw ratio of greater than about 10.

54. The method according to any one of the preceding claims, wherein the at least one sample comprising asphaltene comprises samples obtained from bitumen.

55. The method according to any one of the preceding claims, wherein the at least one sample is in a form comprising a powder, a gel and / or a liquid.

56. The method according to any one of the preceding claims, wherein the melt viscosity of the feedstock is between about 100 Pa.s and about 1 ,000 Pa.s.

57. The method according to any one of the preceding claims, wherein the melt processing temperature applied in the spinning step is between about 200°C and about 250°C.

58. A method of producing carbon fibers, comprising the steps of: determining a melt processing condition of a sample comprising asphaltene; adjusting the melt processing condition of the sample by adding one or more additional samples comprising asphaltene to the sample to create a blend of asphaltenes for supplying as a feedstock; spinning the feedstock at a melt processing temperature to produce melt- spun fibers, and collecting the melt-spun fibers; stabilizing the drawn melt-spun fibers by subjecting the fibers to an air atmosphere to form stabilized melt-spun fibers; and carbonizing the stabilized melt-spun fibers by subjecting the fibers to an inert atmosphere at a carbonization temperature to produce the carbon fibers.

59. Carbon fibers prepared by the method according to any one of the preceding claims, wherein the carbon fibers comprise an average diameter in the range of from about 4 pm to about 200 pm.

60. Carbon fibers prepared by the method according to any one claims 1 to 58 wherein the carbon fibers comprise an average diameter in the range of from about 4 pm to about 15 pm.61 . Carbon fibers prepared by the method according to any one claims 1 to 58, wherein the carbon fibers comprise an average tensile strength in the range of from about 300 MPa to about 2,000 MPa.

62. Carbon fibers prepared by the method according to any one claims 1 to 58, wherein the carbon fibers comprise an average tensile strength greater than about 800 MPa.

63. Carbon fibers prepared by the method according to any one claims 1 to 58, wherein the carbon fibers comprise an average modulus in the range of from about 30 GPa to about 200 GPa.

64. Carbon fibers prepared by the method according to any one claims 1 to 58, wherein the carbon fibers comprise an average modulus in the range of from about 50 GPa to about 180 GPa.

65. Carbon fibers prepared by the method according to any one claims 1 to 58, wherein the carbon fibers comprise an average strain at break value in the range of from about 0.3% to about 2.5%.

66. Carbon fibers prepared by the method according to any one claims 1 to 58, wherein the carbon fibers comprise an average strain at break value in the range of from about 0.5% to about 1 .5%.