Manufacturing carbon fibers with high mechanical properties

Abstract

The method for producing carbon fibers includes the steps of (a) melting asphaltene solids in a closed vessel, (b) spinning the molten asphaltene to produce green fibers, (c) stabilizing the green fibers, (d) carbonizing the stabilized green fibers, and (e) optionally graphitizing the carbonized fibers.

Description

Technical Field

[0001] The present invention relates to a method for producing carbon fibers.

Background Art

[0002] Carbon fibers (CF or graphite fibers) are carbonaceous materials in the form of yarns or filaments typically having a diameter of about 5 to 10 μm and are mainly composed of at least 50% by weight of carbon atoms. Carbon fibers are widely used in aerospace, civil engineering, military, motor sports and sports goods due to many advantages including high rigidity, high tensile strength, low weight, high chemical resistance, high temperature resistance and low thermal expansion.

[0003] Carbon fibers are typically produced using either the use of polyacrylonitrile (PAN) or one of two main methods from pitch. Pitch is a product of the distillation of carbonaceous materials such as plants, crude oil and coal. Pitch is isotropic but can be made anisotropic by heat treatment. However, the most important material in carbon fiber production is mesophase pitch, which results from the ability to melt-spin anisotropic mesophase pitch without filament breakage. Mesophase pitch forms thermotropic crystals, which organize the pitch and enable the formation of straight chains without using tension.

[0004] Mesophase pitch is made by polymerizing isotropic pitch to a high molecular weight. The advantage in the production of pitch-based carbon fibers over PAN carbon fibers is that pitch carbon fibers do not require a constant tension on the fiber at all processing stages.

[0005] Pitch-based carbon fibers have been found to be more sheet-like in crystal structure, in contrast to the more granular PAN-based carbon fibers. The production of carbon fibers from pitch involves six main steps: 1) melt spinning, 2) oxidation, 3) carbonization, 4) graphitization, 5) surface treatment and 6) sizing.

[0006] Melt spinning is a method of forming fibers by rapid cooling of a melt. Due to the high cooling rate, the mesophase pitch can be highly oriented. The mesophase pitch can be melt spun, but due to its flow characteristics, it can be difficult to reliably carry out the process. The viscosity of the mesophase pitch is more sensitive to temperature than other melt spinning materials. Therefore, during the production of pitch-based fibers, the temperature and heat transfer rate must be carefully controlled.

[0007] Oxidation is used to crosslink the molecules to the point where the fibers do not melt or fuse. This is typically carried out in air at about 200 °C to about 400 °C for several hours. This step is extremely important for producing fibers that are stable at the high temperatures of carbonization and graphitization. Without crosslinking, the fibers would be damaged during these process steps.

[0008] Carbonization is achieved by heating the fibers to a high temperature, typically about 1000 °C to about 2000 °C, in an atmosphere free of reactive oxygen. This step removes most of the impurities (e.g., hydrogen, oxygen, nitrogen) from the fibers and leaves mostly crystalline carbon in hexagonal rings.

[0009] Graphitization is a process of treating the fibers at a high temperature to improve the alignment and orientation of the crystalline regions along the main fiber axis. By aligning, stacking, and orienting the crystalline regions along the main fiber axis, the overall strength and stiffness of the carbon fibers increase. To obtain carbon fibers with a higher elastic modulus and a higher carbon content, graphitization is carried out at higher temperatures up to 3000 °C.

[0010] Surface treatment can be applied to improve the adhesion of the carbon fibers to the binding matrix for manufacturing composite materials. Finally, sizing of the carbon fibers includes coating the surface-treated carbon fibers with a polymer to prevent breakage of individual filaments, improve the handling of very fine carbon filaments, and provide compatibility with the molding process.

[0011] The high strength of carbon fibers can be attributed to the six main processes described above. The high level of crystalline regions enables the fibers to withstand large stresses. These crystalline regions are formed by the melt spinning process, and the crystals are rigid regions that do not easily deform when an external stress is applied.

[0012] Asphaltenes are molecular substances found in carbonaceous materials such as bitumen or crude oil, or coal, along with resins, aromatic hydrocarbons, and saturates. Asphaltenes have a complex molecular structure containing aromatic polycyclic structures surrounded by aliphatic chains and heteroatoms, and these are usually insoluble in light n-alkanes (such as n-pentane, nC 5 or n-heptane, nC 7 ), but soluble in aromatic solvents such as toluene. Their molecular weights are usually found in the range of 400 u to 1500 u, but the average and maximum values are difficult to determine due to the aggregation of molecules in solution. Asphaltenes consist mainly of carbon, hydrogen, nitrogen, oxygen, and sulfur, as well as trace amounts of vanadium, nickel, and iron. The C:H ratio is approximately 1:1.2 depending on the asphaltene source.

[0013] Asphaltenes are the main component of the pitch-based precursors of carbon fibers. For example, asphaltenes constitute more than 80% by weight of the entire Ashland 260 petroleum pitch, which is a high-quality pitch precursor for carbon fibers.

[0014] Pure asphaltenes are glassy solids that can be easily pulverized into powder at ambient temperature. No attempts have been made to produce carbon fibers from pure solid asphaltenes. It is known to produce carbon fibers from asphaltenes obtained from the quality improvement of heavy oil. A liquid-phase asphaltene stream at room temperature containing about 60% to about 70% asphaltenes is introduced through a spinneret to obtain carbon-based filaments. When solid asphaltenes are available, before introducing the asphaltene-containing liquid phase through the spinneret to obtain carbon-based filaments, it is necessary to dissolve the solid asphaltene stream in a solvent to obtain an asphaltene solution. In the latter case, the solid asphaltene stream contains about 60% to about 90% asphaltenes when the total weight of the solid asphaltene stream is taken as 100% by weight before being dissolved in the solvent.

[0015] It is also known to use electrospinning to produce both solid and hollow micrometer-sized fibers from asphaltenes. However, no further processing has been carried out to achieve high mechanical properties. Such processing is an essential step for carbon fibers to reach the mechanical properties required for manufacturing composite materials. Furthermore, the fibers after electrospinning appear short, bent, hollow, and branched. These defects do not meet the basic requirements of carbon fibers for structural applications.

[0016] This background information is provided for the purpose of creating known information that the applicant believes may be relevant to the present invention. It is not necessarily intended to be construed as admitting that any of the foregoing information constitutes prior art against the present invention.

Summary of the Invention

[0017] The present invention relates to a method for producing carbon-based fibers by melt spinning of solid asphaltenes, which may preferably be asphaltenes removed by solvent deasphalting of feedstock bitumen or crude oil. The feedstock may be thermally decomposed or non-thermally decomposed. The melt-spun carbon-based fibers are then processed to achieve the desired mechanical properties. One aspect of the present invention is shown below, but the present invention is not limited thereto. [Invention 1] A method for producing carbon fibers, comprising: (a) melting asphaltene solids in a sealed container; (b) spinning the molten asphaltene to produce green fibers; (c) stabilizing the green fibers in a liquid environment or a gaseous environment; and (d) carbonizing the stabilized green fibers. A method comprising the above steps. [Invention 2] The method according to Invention 1, wherein the green fibers are stabilized in air or steam. [Invention 3] The method according to Invention 1 or 2, wherein the asphaltene solids are melted in step (a) at about 150°C to about 550°C in an environment such as nitrogen, hydrogen, steam, or a mixture thereof. [Invention 4] The method according to any one of Inventions 1 to 3, wherein step (a) is extended to about 6 hours. [Invention 5] The method according to Invention 4, wherein step (a) is extended to 0.5 hour to 2 hours. [Invention 6] The method according to any one of Inventions 1 to 5, wherein in step (a), the sealed container is pressurized to a level of 0 to about 1000 kPa during heating. [Invention 7] The method according to any one of Inventions 1 to 6, wherein the spinning step includes pulling the molten asphaltene through a spinneret to produce the green fibers and winding the green fibers around a rotating spool. [Invention 8] The method according to Invention 7, wherein the temperature of the asphaltene during spinning is controlled to about 150°C to about 350°C. [Invention 9] The method according to Invention 7 or 8, wherein the pressure of the sealed container during spinning is controlled to about 100 kPa to about 1000 kPa, preferably about 200 kPa to about 700 kPa. [Invention 10] The method according to any one of Inventions 7 to 9, wherein the speed of the rotating spool is controlled to achieve a fiber pulling speed of 50 to 1000 meters per minute, preferably 100 to 300 meters per minute. [Invention 11] The method according to any one of Inventions 7 to 10, wherein the diameter of the spinneret is selected to be in the range of about 50 to about 300 μm, preferably about 100 to about 200 μm. [Invention 12] The method according to any one of Inventions 1 to 11, wherein the diameter of the green fibers is produced to be in the range of about 1 to about 15 μm, preferably about 7 to about 10 μm. [Invention 13] The method according to any one of Inventions 1 to 12, wherein the green fibers are stabilized by immersing the green fibers in an aqueous solution that coats the green fibers and prevents aggregation between adjacent green fibers. [Invention 14] The method according to Invention 13, wherein the aqueous solution contains hydrochloric acid, nitric acid, sulfuric acid, phytic acid, potassium nitrate, potassium chloride, their derivatives, and / or their mixtures. [Invention 15] The method according to Invention 13 or 14, wherein the aqueous solution can be concentrated or diluted, and the dilution can be in the range of 1 wt% to 100 wt% of the concentrated solution. [Invention 16] The method according to Invention 13, 14 or 15, wherein the immersion time is from 1 second to 100 minutes, preferably from 5 seconds to 50 minutes. [Invention 17] The method according to any one of Inventions 1 to 16, wherein the stabilization step includes at least one-step heat treatment at a temperature of 100°C to 400°C in an air or steam environment. [Invention 18] The method according to Invention 17, wherein the stabilization step includes at least two-step temperature steps, such as 2 to 5 steps, preferably 2 to 3 steps. [Invention 19] The method according to Invention 17 or 18, wherein each temperature step lasts for 0.5 hours to 24 hours. [Invention 20] The method according to any one of Inventions 1 to 19, wherein the carbonization step includes at least one-step heat treatment at a temperature of about 400°C to about 1600°C in an inert environment such as nitrogen gas. [Invention 21] The method according to Invention 20, wherein the at least one-step heat treatment includes at least a low-temperature step and a high-temperature step. [Invention 22] The method according to Invention 20 or 21, wherein the low-temperature step is carried out at about 400°C to about 600°C over a period of about 0.5 to about 3 hours. [Invention 23] The method according to Invention 21 or 22, further including an intermediate temperature step carried out at a temperature of about 700°C to about 900°C over a period of about 0.5 to about 10 hours, preferably about 1 to about 3 hours. [Invention 24] The method according to any one of Inventions 21 to 23, wherein the high-temperature step is carried out at a temperature of about 1300°C to about 1600°C over a period of 0.5 to 10 hours. [Invention 25] The method according to Invention 20, wherein the heat treatment step includes an intermediate temperature step without a low-temperature or high-temperature step. [Invention 26] The method according to Invention 20, wherein the heat treatment step includes a high-temperature step without a low-temperature or intermediate temperature step. [Invention 27] The method according to any one of Inventions 1 to 26, wherein the diameter of the carbon fiber after the final treatment is controlled in the range of about 5 to about 10 μm. [Invention 28] The method according to any one of Inventions 1 to 27, wherein the solid asphaltene is processed to reduce or change the content of sulfur, oxygen, metal species, specific molecular species or groups before melt spinning. [Invention 29] The method according to any one of Inventions 1 to 28, wherein solid asphaltenes are added together with other chemical substances or heat-treated to change the temperature of melt spinning, change the chemical properties of asphaltenes, increase the content of mesophase, and / or change the viscosity of molten asphaltenes. [Invention 30] The method according to any one of Inventions 1 to 29, further comprising the step of graphitizing the carbonized fibers. [Invention 31] Carbon fibers obtained from the method according to any one of Inventions 1 to 29.

[0018] In one aspect, the present invention is a method for producing carbon fibers, comprising: (a) melting the asphaltene solid by heating in a sealed container and pressurizing the container using an inert gas; (b) introducing the molten asphaltene into a spinneret to obtain green fibers; c) To avoid possible fiber fusion during subsequent heat treatment, a step of stabilizing the green fiber with a liquid or gas to perform surface pretreatment on the green fiber, and d) a step of heat-treating the surface-treated green fiber A method including these steps is provided. In some embodiments, the green fiber can be produced with a desired fiber diameter by controlling the pulling speed and diameter of the spinneret.

[0019] Embodiments of the present invention generally relate to a method for directly producing carbon fibers from asphaltene solids without the need to generate a liquid stream containing asphaltenes and introduce the liquid stream into a spinneret to obtain carbon-based fibers. In particular, a solvent for dissolving asphaltenes is not required.

[0020] A more detailed description of the present invention briefly described above will be continued with reference to the following drawings of specific embodiments of the present invention. The drawings show only typical embodiments of the present invention and should not be considered as limiting its scope. The drawings are not necessarily to scale and, in some cases, the ratios may be exaggerated to more clearly show specific features.

Brief Description of the Drawings

[0021] [Figure 1] It is a diagram showing the relationship between the spool winding speed of virgin asphaltenes (referred to as green fibers) established using a melt spinning apparatus for producing asphaltene filaments and the filament diameter.

[0022] [Figure 2] It is a heat flow-temperature diagram of virgin asphaltenes with and without heat treatment at 260°C for 1 hour in nitrogen.

[0023] [Figure 3]It is a diagram showing the effect of the holding time of molten asphaltene before introducing it into the spinneret to obtain raw fibers on the tensile strength of carbon fibers after stabilization at 350 °C for 2 hours in air and carbonization at 800 °C for 2 hours in nitrogen.

[0024] [Figure 4] It is a diagram of an FTIR-ART (Fourier transform infrared spectroscopy using an attenuated total reflection accessory) spectrum showing attenuated infrared light as an interferogram signal after processing raw fibers in the following processes / steps. Upper spectrum: Raw fibers derived from asphaltene after immersion in 17% nitric acid for 10 minutes. Middle spectrum: Raw fibers derived from asphaltene after immersion in 17% nitric acid for 10 minutes and thorough washing with deionized water. Lower spectrum: Raw fibers derived from asphaltene without treatment.

[0025] [Figure 5] It is a diagram showing the tensile strength of carbon fibers after stabilization treatment and carbonization treatment, each carried out at 350 °C for 2 hours in air and 800 °C for 2 hours in nitrogen. The raw fibers were pretreated at 150 °C in air for various times before performing the stabilization treatment and carbonization treatment shown above.

[0026] [Figure 6] It is a diagram showing the tensile modulus of elasticity of carbon fibers after stabilization treatment and carbonization treatment, each carried out at 350 °C for 2 hours in air and 800 °C for 2 hours in nitrogen. The raw fibers were pretreated at 150 °C in air for various times before performing the stabilization treatment and carbonization treatment shown above.

[0027] [Figure 7] It is a diagram of the tensile strength of carbon fibers after stabilization treatment at 350 °C for 2 hours in air, first-stage carbonization treatment at various temperatures in nitrogen for 2 hours, and second-stage carbonization at 800 °C for 2 hours in nitrogen.

[0028] [Figure 8] It is a diagram of the tensile strength of carbon fibers after stabilization treatment at 350 °C for 2 hours in air and carbonization treatment at various temperatures in nitrogen for 2 hours.

[0029] [Figure 9] It is a diagram of the tensile strength of carbon fibers after stabilization treatment at 350°C for 2 hours in air and carbonization treatment at various temperatures in nitrogen for 2 hours.

[0030] [Figure 10] It is a diagram of the tensile modulus of carbon fibers after stabilization treatment at 350°C for 2 hours in air and carbonization treatment at various temperatures in nitrogen for 2 hours.

[0031] [Figure 11] It is an image of the fracture cross-section of carbon fibers after carbonization treatment at 800°C for 8 hours.

[0032] [Figure 12] It shows the melt spinning temperature of the same asphaltene feedstock pretreated at different temperatures up to 350°C for 2 hours in a nitrogen environment before melt spinning to produce green fibers. This treatment increased the melt spinning temperature for producing green fibers. Note that the feedstock used in this study is different from the feedstock used in the study shown in Figure 2.

Mode for Carrying Out the Invention

[0033] The description of the present invention has been presented for purposes of illustration and description, but is not intended to be exhaustive or to limit the invention to the disclosed form. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the present invention. The embodiments were chosen and described in order to best explain the principles of the invention and its practical application, to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated. As far as the following description relates to particular embodiments of the present invention or to particular uses, it is intended for illustration only and is not intended to limit the claimed invention.

[0034] As used herein, "carbon fiber" refers to any yarn or filament material that contains at least 50% (by mass) elemental carbon with a yarn or filament diameter of less than 0.1 mm, which can be controlled to achieve either a higher force or stress against breakage. The term "fiber" can be spelled interchangeably with "fibre".

[0035] The asphaltene solids for producing carbon fibers refer to the solid precipitates obtained by adding solvents such as n-alkanes (such as n-pentane, nC 5 or n-heptane, nC 7 to bitumen or crude oil. This process is generally known to those skilled in the art as solvent deasphalting, is well-known, and does not need further explanation. This deasphalting process can be applied directly to bitumen and crude oil, or can be applied after some thermal conversion processes or cracking, resulting in asphaltene solids that are insoluble in the selected solvent. Asphaltenes have the above-mentioned properties and compositions and are also well-known to those skilled in the art.

[0036] The present invention relates to a method for producing carbon fibers using solid asphaltenes as carbon precursors. Table 1 provides typical compositions of asphaltene solids from different sources. Embodiments of the method disclosed herein can be applied to asphaltenes from any source as long as the asphaltenes are in the solid phase. Preferably, the asphaltenes do not substantially contain solid particles with a melting point higher than about 100 °C or a size larger than about 1 μm. In some preferred embodiments, asphaltene precursors containing relatively low amounts of sulfur, oxygen, any metal species, and fine non-molten particles may be preferred for producing carbon fibers with improved mechanical properties.

Table 1

[0037] The carbon fibers produced by the method disclosed in this specification can achieve high strength. The strength of carbon fibers is very sensitive to the diameter of the carbon fibers. The diameter of the carbon fibers produced by the method disclosed in this specification can be larger than the diameter of commercially available carbon fibers of the prior art, and the diameter of commercially available carbon fibers of the prior art is usually less than 10 μm, and most are in the range of 5 - 7 μm. In contrast, the diameter of the carbon fibers produced herein can be in the range of 10 - 16 μm. These fibers can be tested to demonstrate the effect of heat treatment on the mechanical properties of carbon fibers produced using pure solid asphaltenes as the carbon precursor.

[0038] In some embodiments, solid asphaltenes are added to a sealed chamber and then melted under pressure in an inert atmosphere. For example, in one embodiment, the asphaltenes may be melted at about 190 °C and pressurized to about 0 to about 1000 kPa, preferably about 200 to about 600 kPa, more preferably about 400 kPa using nitrogen gas. A spinneret of appropriate size may be placed at the bottom of the chamber, for example, a spinneret with a diameter of 150 μm may be used. The asphaltene filaments can be drawn from the spinneret and wound around a rotating spool such as a spool with a diameter of 20 cm. The rotational speed of the spool is preferably adjustable. The diameter of the asphaltene filaments or green fibers is inversely proportional to the rotational speed of the spool, as shown in Figure 1.

[0039] The appropriate temperature and pressure for melt spinning can be varied by the temperature and time for which the asphaltenes are held in the melting chamber before spinning into carbon fibers. In one embodiment, the bulk asphaltenes may be held in a sealed chamber at about 260 °C for 1 hour in nitrogen before melt spinning. As can be seen from Figure 2, the temperature point at which the asphaltenes begin to soften rises from about 175 °C to about 245 °C due to such a long heat treatment.

[0040] In one embodiment, bulk asphaltenes were held at 350 °C for 1, 2, and 3 hours, respectively, prior to melt spinning, along with a 0-hour control. The resulting asphaltene fibers were subjected to the same post-melt spinning steps (stabilization treatment and carbonization treatment), each carried out at 350 °C in air for 2 hours and at 800 °C in nitrogen for 2 hours. It was found that the tensile strength of the carbon fibers after all treatments was highest when the treatment of the bulk asphaltenes was maintained at 350 °C for 1 hour prior to melt spinning.

[0041] Figure 12 shows the melt spinning temperatures of the same asphaltene feedstock pretreated for 2 hours at different temperatures up to 350 °C in a nitrogen environment prior to melt spinning into green fibers. This treatment increased the melt spinning temperature for producing green fibers. Note that the feedstock used in this study was different from the feedstock used in the study shown in Figure 2.

[0042] The melt-spun green fibers must be stabilized, for example, by surface treating the green fibers with a liquid or gas, prior to carbonization and / or graphitization. If the stabilization treatment is carried out at a temperature higher than the temperature at which the asphaltenes are melt spun into green fibers, fusion of the green fibers that are physically in contact with each other may occur while heating from ambient temperature to the stabilization temperature.

[0043] In some embodiments, the as-spun raw fibers may be coated on the surface of the raw fibers or immersed in a liquid that interacts with the surface of the raw fibers to prevent fusion between adjacent fibers. Suitable liquids include dilute or concentrated mineral acids such as hydrochloric acid, nitric acid, or sulfuric acid; organic acids such as phytic acid; or solutions of inorganic salts such as potassium salts such as potassium nitrate, potassium chloride; or derivatives of any of the foregoing; and / or mixtures thereof. In a preferred embodiment, the raw fibers can be immersed in a nitric acid solution (17%) for 10 minutes to prevent the physically contacted raw fibers from fusing while heating to a temperature higher than the melt spinning temperature. When immersed in the nitric acid solution, chemical species adhere to the surface of the raw fibers, preventing the raw fibers from fusing with adjacent fibers. When the raw fibers immersed in nitric acid are rinsed with water, the coated chemical species are removed, and the physically adhered raw fibers may fuse again while heating to a temperature higher than the temperature used for melt spinning.

[0044] In some embodiments, the raw fibers may be stabilized or further stabilized in a stepped temperature regime in air. In one embodiment, the raw fibers may first be immersed in 17% nitric acid for 10 seconds and then stabilized at 150°C in air for various times up to a maximum of 24 hours, preferably at least about 16 hours, followed by a second stabilization treatment at 350°C for 2 hours. The stabilized fibers are then carbonized at 800°C for 2 hours. Exemplary results for various treatment times at 150°C are shown in FIG. 5.

[0045] The stabilized raw fibers may be carbonized, for example, at a temperature in the range of about 400°C to about 1600°C, preferably in an inert or nitrogen environment. The carbonization step may be carried out in one step or in multiple steps. For example, a three-step carbonization process having an initial low-temperature step at a temperature in the range of 400°C to 600°C, an intermediate-temperature step in the range of 600°C to about 1200°C (preferably 800°C to 1000°C), and a final high-temperature step in the range of about 1200°C to about 1600°C (preferably about 1500°C) may be suitable. Each step may continue for several minutes to several hours. For example, each step may continue for about 1 hour to about 2 hours.

[0046] In some embodiments where the results are shown in FIG. 7, the raw fibers were carbonized at a low temperature stage and an intermediate temperature stage before the tensile test. The first-stage carbonization was carried out for 2 hours at different temperatures in the range of 400°C to 600°C, and the second-stage carbonization was carried out for 2 hours at 800°C. When the first-stage carbonization was carried out for 2 hours at 500°C, the best tensile strength was achieved. In other embodiments where the results are shown in FIG. 8, after low-temperature carbonization at 500°C for 2 hours, intermediate-temperature carbonization was carried out for 2 hours at a temperature in the range of 800°C to 1000°C. The lowest tensile strength was observed when intermediate carbonization was carried out for 2 hours at 900°C, and the highest tensile strength was observed when intermediate carbonization was carried out at 800°C.

[0047] In some embodiments where the results are shown in FIGS. 9 and 10, the high-temperature carbonization was carried out at 1500°C for various times in the range of 2 hours to 8 hours, regardless of the presence or absence of a prior intermediate temperature stage. The best tensile strength was achieved when carbonization at 1500°C continued for 2 hours without a prior intermediate temperature stage. When the carbonization treatment time at 1500°C was longer than 2 hours, the tensile strength decreased. When intermediate temperature carbonization at 800°C was carried out prior to the high-temperature treatment at 1500°C, the tensile strength decreased compared to the tensile strength obtained when high-temperature carbonization was carried out alone.

[0048] The decrease in strength observed when carbon fibers derived from asphaltenes were carbonized at around 900°C is considered to be due to the formation of aggregates of metal-containing compounds within the fibers. As seen in FIG. 11, after intermediate temperature carbonization treatment at 800°C for 8 hours, the fractured carbon fibers show some aggregates of a metal-containing phase having the chemical composition shown in Table 2. Table 2 is a list of the chemical compositions of the central aggregates shown in FIG. 11.

Table 2

[0049] The treatment of raw fibers may cause changes in the chemical properties of carbon fibers. In one embodiment, the compositions of carbon, nitrogen, hydrogen, and sulfur were analyzed after various treatments, and the results are shown in Table 3. Generally, the carbon content in carbon fibers increased with the increase of treatment temperature and treatment time, while the nitrogen, hydrogen, and sulfur contents decreased with the increase of treatment temperature and treatment time.

[0050] Table 3 is a list of the chemical compositions of asphaltenes and asphaltene-derived carbon fibers after various stages of treatment at different temperatures for different times.

Table 3

[0051] Optionally, the produced carbon fibers may be graphitized. Graphitization is a process of treating the fibers at a high temperature to improve the alignment and orientation of the crystal regions along the main fiber axis. By aligning, laminating, and orienting the crystal regions along the main fiber axis, the overall strength and rigidity of the carbon fibers increase. To obtain carbon fibers with a higher elastic modulus and a higher carbon content, graphitization is carried out at a higher temperature up to about 3000 °C.

[0052] In view of the above description, certain more detailed aspects of the present invention are presented below. However, these detailed aspects should not be construed as having any limiting effect on any different claims containing different or more general teachings described herein, nor should the "specific" aspects be construed as being limited in any way other than the literal meaning of the language used therein.

[0053] Aspect 1: A method for manufacturing carbon fibers, comprising: (a) melting asphaltene solids in a sealed container; (b) spinning the molten asphaltene to produce raw fibers; (c) stabilizing the raw fibers in a liquid environment or a gas environment. (d) The step of carbonizing the stabilized raw fiber, and (e) Optionally, the step of graphitizing the carbonized fiber A method comprising.

[0054] Aspect 2: The method according to claim 1, wherein the raw fiber is stabilized in air or steam.

[0055] Aspect 3: The method according to aspect 1 or 2, wherein the asphaltene solid is melted in step (a) at about 150°C to about 550°C in an environment such as nitrogen, hydrogen, steam, or a mixture thereof.

[0056] Aspect 4: The method according to any one of aspects 1 to 3, wherein step (a) is extended up to about 6 hours.

[0057] Aspect 5: The method according to aspect 4, wherein step (a) is extended to 0.5 hour to 2 hours.

[0058] Aspect 6: The method according to any one of aspects 1 to 5, wherein in step (a), the closed container is pressurized to a level of 0 to about 1000 kPa during heating.

[0059] Aspect 7: The method according to any one of aspects 1 to 6, wherein the spinning step includes pulling molten asphaltene through a spinneret to produce the raw fiber and winding the raw fiber around a rotating spool.

[0060] Aspect 8: The method according to aspect 7, wherein the temperature of the asphaltene during spinning is controlled to about 150°C to about 350°C.

[0061] Aspect 9: The method according to aspect 7 or 8, wherein the pressure of the closed container during spinning is controlled to about 100 kPa to about 1000 kPa, preferably about 200 kPa to about 700 kPa.

[0062] Aspect 10: The method according to aspect 7, 8 or 9, wherein the speed of the rotating spool is controlled to achieve a fiber drawing speed of 50 to 1000 meters per minute, preferably 100 to 300 meters per minute.

[0063] Aspect 11: The method according to any one of aspects 7 to 10, wherein the diameter of the spinneret is selected to be in the range of about 50 to about 300 μm, preferably about 100 to about 200 μm.

[0064] Aspect 12: The method according to any one of aspects 1 to 11, wherein the diameter of the green fiber is produced to be in the range of about 1 to about 15 μm, preferably about 7 to about 10 μm.

[0065] Aspect 13: The method according to any one of aspects 1 to 12, wherein the green fiber is stabilized by immersing the green fiber in an aqueous solution that coats the green fiber and prevents aggregation between adjacent green fibers.

[0066] Aspect 14: The method according to aspect 13, wherein the aqueous solution contains hydrochloric acid, nitric acid, sulfuric acid, phytic acid, potassium nitrate, potassium chloride, their derivatives, and / or mixtures thereof.

[0067] Aspect 15: The method according to aspect 13 or 14, wherein the aqueous solution can be concentrated or diluted, and the dilution can be in the range of 1 wt% to 100 wt% of the concentrated solution.

[0068] Aspect 16: The method according to aspect 13, 14 or 15, wherein the immersion time is 1 second to 100 minutes, preferably 5 seconds to 50 minutes.

[0069] Aspect 17: The method according to any one of aspects 1 to 16, wherein the stabilization step includes at least one-step heat treatment at a temperature of 100°C to 400°C in an air or steam environment.

[0070] Aspect 18: The method according to aspect 17, wherein the stabilization step includes at least two-step temperature steps such as 2 to 5 steps, preferably 2 to 3 steps.

[0071] Aspect 19: The method according to aspect 17 or 18, wherein each temperature stage lasts for about 0.5 hours to about 24 hours.

[0072] Aspect 20: The method according to any one of aspects 1 to 19, wherein the carbonization step includes at least one stage of heat treatment at a temperature of about 400°C to about 1600°C in an inert environment such as nitrogen gas.

[0073] Aspect 21: The method according to aspect 20, wherein the at least one stage of heat treatment includes at least a low-temperature stage and a high-temperature stage.

[0074] Aspect 22: The method according to aspect 20 or 21, wherein the low-temperature stage is carried out at about 400°C to about 600°C over a period of about 0.5 to about 3 hours.

[0075] Aspect 23: The method according to aspect 21 or 22, further including an intermediate temperature stage carried out at a temperature of about 700°C to about 900°C over a period of about 0.5 to about 10 hours, preferably about 1 to about 3 hours.

[0076] Aspect 24: The method according to any one of aspects 21 to 23, wherein the high-temperature stage is carried out at a temperature of about 1300°C to about 1600°C over a period of 0.5 to 10 hours.

[0077] Aspect 25: The method according to aspect 20, wherein the heat treatment stage includes an intermediate temperature stage without a low-temperature or high-temperature stage.

[0078] Aspect 26: The method according to aspect 20, wherein the heat treatment stage includes a high-temperature stage without a low-temperature or intermediate temperature stage.

[0079] Aspect 27: The method according to any one of aspects 1 to 26, wherein the diameter of the carbon fiber after the final treatment is controlled within the range of about 5 to about 10 μm.

[0080] Aspect 28: The method according to any one of aspects 1 to 27, wherein the solid asphaltene is processed to reduce or change the content of sulfur, oxygen, metal species, specific molecular species or groups before melt spinning.

[0081] Aspect 29: The method according to any one of Aspects 1 to 28, wherein solid asphaltenes are added together with other chemical substances or heat-treated to change the temperature of melt spinning, change the chemical properties of asphaltenes, increase the content of mesophase, and / or change the viscosity of molten asphaltenes.

[0082] Aspect 30: The method according to any one of Aspects 1 to 29, modified or added by any step, feature or element described herein.

[0083] Aspect 31: Carbon fibers obtained from the method according to any one of Aspects 1 to 30.

[0084] Definitions and Interpretations References herein to "one embodiment", "an embodiment", etc. indicate that the described embodiment may include a particular aspect, feature, structure, or property, but not all embodiments necessarily include that aspect, feature, structure, or property. Further, such phrases can, but not necessarily, refer to the same embodiment referenced elsewhere in this document. Further, when a particular aspect, feature, structure, or property is described in connection with an embodiment, combining, affecting, or connecting such aspect, feature, structure, or property with other embodiments is within the knowledge of those skilled in the art, whether or not such connection or combination is explicitly described. In other words, any element or feature can be combined with any other element or feature in different embodiments, unless there is an obvious or inherent incompatibility between the two, or unless specifically excluded.

[0085] It should further be noted that the claims can be drafted to exclude any element. Thus, this statement is intended to serve as a preamble for using exclusive terms such as "alone", "only", etc. in relation to the recitation of elements of the claims or the use of "negative" limitations. Terms such as "preferably", "preferred", "prefer", "optionally", "may" and similar terms are used to indicate that the item, condition or step referred to is an optional (not essential) feature of the invention.

[0086] The singular forms "a", "an", and "the" include references to the plural unless the context clearly indicates otherwise. The term "and / or" means any one of the items to which this term relates, any combination of the items, or all of the items.

[0087] As will be understood by those skilled in the art, for all purposes, particularly with respect to providing a written description, all ranges recited herein also include any and all possible subranges and combinations of those subranges, as well as the individual values that make up the range, particularly integer values. The recited ranges (e.g., weight percentages or carbon groups) include each specific value, integer, fraction, or identity within that range. Each of the recited ranges can be readily recognized as being sufficient to describe and enable dividing the same range into at least equal halves, thirds, fourths, fifths, or tenths. By way of non-limiting example, each range described herein can be readily divided into lower thirds, middle thirds, and upper thirds, etc.

[0088] Also, as will be understood by those skilled in the art, all language such as "maximum", "at least", "greater than", "less than", "more than", "above", etc. includes the recited numbers, and such terms refer to ranges that can be divided into sub-ranges later as described above. Similarly, all ratios recited herein also include all sub-ratios within a broader ratio range. References The following documents and any publications referred to therein are indicative of the level of skill of those skilled in the art and, where permitted, are hereby incorporated by reference in their entirety into this specification. TIFF0007679366000004.tif43138 TIFF0007679366000005.tif22134

Claims

1. 1. A method for producing carbon fibers, comprising the steps of: (a) melting in a closed vessel the asphaltene solids obtained from the solvent deasphalting process; (b) spinning the molten asphaltene to produce green fibers; (c) stabilizing the green fiber in a liquid or gas environment; and (d) carbonizing the stabilized green fiber The method includes:

2. The method of claim 1 , wherein the green fibers are stabilized in air or water vapor.

3. 3. The method of claim 1 or 2, wherein the asphaltene solids are melted in step (a) at 150° C. to 550° C. in a gaseous environment comprising nitrogen, hydrogen, or water vapor, or a mixture thereof.

4. The method according to any one of claims 1 to 3, wherein the melting in step (a) is carried out for 0.5 hours to 2 hours.

5. 5. The method of any one of claims 1 to 4, wherein in step (a), the sealed container is pressurized to a level of 200 to 1000 kPa during heating.

6. 6. The method of any one of claims 1 to 5, wherein the spinning step comprises pulling molten asphaltene through a spinneret to produce the green fiber and winding the green fiber onto a rotating spool.

7. The method according to claim 6, wherein the temperature of the asphaltene during spinning is controlled to 150° C. to 350° C., and / or the pressure of the closed vessel during spinning is controlled to 200 kPa to 700 kPa.

8. The method according to claim 6 or 7, wherein the speed of the rotating spool is controlled to achieve a fibre pull speed of from 50 to 1000 metres per minute.

9. The method according to any one of claims 6 to 8, wherein the diameter of the spinneret is selected to a size in the range of 50 to 300 μm and the diameter of the green fibres produced is in the size range of 1 to 15 μm.

10. 10. The method of any one of claims 1 to 9, wherein the biofibers are stabilized by immersion in an aqueous solution that coats the biofibers and prevents agglomeration between adjacent biofibers, the aqueous solution comprising hydrochloric acid, nitric acid, sulfuric acid, phytic acid, potassium nitrate, potassium chloride, derivatives thereof, and / or mixtures thereof.

11. The method of claim 10, wherein the immersion time is from 5 seconds to 50 minutes.

12. A method according to any one of the preceding claims, wherein the stabilisation step comprises or further comprises at least one heat treatment step at a temperature between 100°C and 400°C in an air or water vapour environment.

13. The method of claim 12 , wherein the stabilization step comprises at least two temperature steps.

14. The method according to claim 12 or 13, wherein each temperature step lasts from 0.5 hours to 24 hours.

15. 11. The method of claim 10, wherein the aqueous solution comprises a 17% nitric acid solution.

16. A method according to any one of the preceding claims, wherein the carbonization step comprises at least one heat treatment stage at a temperature between 400°C and 1600°C in an inert environment.

17. 17. The method of claim 16, wherein the at least one stage heat treatment comprises at least one low temperature stage and at least one high temperature stage.

18. The method of claim 17, further comprising an intermediate temperature stage carried out at a temperature of 700° C. to 900° C. for a period of 0.5 to 10 hours.

19. A method according to claim 17 or 18, wherein the at least one high temperature stage is carried out at a temperature of from 1300° C. to 1600° C. for a period of from 0.5 to 10 hours.

20. The method of claim 1, wherein the carbon fibers have a diameter in the range of 5 to 10 μm.

21. The method of any one of claims 1 to 20, wherein a solid asphaltene precursor is used that has been processed to reduce or change the content of sulfur, oxygen, or metal species prior to melt spinning.

22. 22. The method of any one of claims 1 to 21, wherein the solid asphaltene can be added or heat treated with other chemicals to change the melt spinning temperature, change the chemistry of the asphaltene, increase the mesophase content, and / or change the viscosity of the molten asphaltene.

23. A method according to any one of the preceding claims, comprising the further step of graphitising the carbonised fibres.

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