High performance (mesophase) carbon fiber feedstock production

Abstract

Provided is a method for producing an intermediate phase material capable of producing high performance carbon fibers. The intermediate phase is produced after treating heavy hydrocarbons by hydrotreating or quinoline solvent to remove impurities, followed by using toluene solvent to remove light hydrocarbons, and then upgrading by a soaking pit visbreaking step to produce a desired amount of intermediate phase material while preventing coke formation.

Description

[0001] Priority Declaration

[0002] This application claims priority to provisional U.S. application 63 / 435,987, filed December 29, 2022, the entire contents of which are incorporated herein by reference.

[0003] It is known that the production of carbon fibers from low-cost pitch results in carbon fibers with inferior mechanical properties compared to carbon fibers made from polyacrylonitrile materials. Carbon fibers are ideal materials with excellent thermal and electrical conductivity. Due to the low cost of the raw materials compared to PAN, the use of carbon fibers made from pitch offers significant cost savings due to the high availability of feedstock from sources such as FCC slurry oil, solvent deasphalted asphalt, vacuum column bottoms, steam cracker heavy pyrolysis oil (tar), and other types of residues.

[0004] The term "pitch" refers to a broad range of products, including naturally occurring heavy materials and those formed through the thermal polymerization of lighter materials. There are two general grades of carbon fiber produced from pitch. These include the use of isotropic pitch to produce lower-quality, general-performance carbon fibers. These carbon fibers have low strength and stiffness, as well as moderate thermal and electrical conductivity. These carbon fibers are typically used for concrete reinforcement, thermal insulation, and water treatment. Another type of carbon fiber made from pitch is derived from a mesophase derived from pitch to produce high-performance carbon fibers. These carbon fibers have moderate strength and stiffness, with excellent thermal and electrical conductivity. These fibers can be used in energy storage applications such as batteries, fuel cells, supercapacitor electrodes, as well as for rollers in the film and paper industries and in aircraft brake discs. These fibers can be up to three times more expensive than general-performance carbon fibers. Barriers to the widespread adoption of pitch-based carbon fibers include their higher cost compared to glass fiber and steel. Furthermore, pitch-based fibers are very brittle compared to other PAN-based fibers. Potential markets for carbon fibers produced at a lower cost but with superior properties are in the automotive industry and for batteries used in electric vehicles.

[0005] Hydrocarbon mesophase feedstocks are difficult to use to make carbon fibers due to a number of problems, including breakage during spinning to make the fibers and a high degree of brittleness of the fibers. This is due to a lack of optimal, low-cost feedstocks to produce clean mesophase feed for carbon fiber production plants. The present invention produces an optimal feedstock to produce high-performance carbon fibers, thereby improving the mechanical properties of carbon fibers and enabling widespread adoption of carbon fibers for use in composite materials, such as in the automotive industry as a replacement for steel components. The lower weight of carbon fiber composites compared to steel will result in significant advantages for use in vehicles, including electric vehicles. The more economical, high-quality precursor material will also have applications in energy storage, specialty asphalts, and reinforced plastics and concrete.

[0006] Current high-quality carbon fibers are prepared from polyacrylonitrile precursors (PAN). However, using PAN fibers for carbon fiber production is expensive, thus limiting their use to special / high-tech applications such as military aircraft components. Generating an optimal low-cost, high-performance raw material for carbon fiber production would significantly reduce the total production cost and greatly increase the amount of carbon fiber available for production, which is desirable due to the large increase in new applications. At the same time, producing high-performance carbon fibers using low-cost hydrocarbon-based raw materials is an effective means of carbon sequestration and effectively addressing Scope 3 emissions.

[0007] This disclosure will take the product stream of the described SDA unit and further upgrade it to a mesophase to enable high-performance carbon fiber production. The upgrading step will essentially involve sending the SDA product stream to a soaking furnace visbreaking-type step that will operate at a temperature above 800°F and have a residence time greater than 2 minutes to gradually form the desired amount of mesophase while preventing coke formation. Once the desired amount of mesophase is generated, the product stream is fed into a carbon fiber production plant to produce the desired high-performance carbon fibers. Without the final thermal upgrading step described herein, only general performance carbon fibers (GPCF) can be prepared. Note that this thermal upgrading step can consist of a staged heating step to maximize temperature control. Additionally, one or more separation steps can be present downstream of the thermal upgrading step. Summary of the Invention

[0008] A method for producing a hydrocarbon feed for conversion to carbon fiber is provided, the method comprising mixing an untreated crude feed with a solvent to remove solid contaminants and coke insoluble in the solvent, and wherein the hydrocarbons in the untreated crude feed are soluble in the solvent; and then sending the solvent containing the hydrocarbons to a second solvent to remove lighter components; and generating a stream containing heavier hydrocarbon components that is sent to a heat treatment step to increase the molecular weight of the heavier hydrocarbon components and produce pitch to be converted to carbon fiber. The heat treatment step is a soaking furnace visbreaker step operating above 800°F for more than 2 minutes, which produces an increase in the amount of the desired mesophase material without producing coke. The mesophase material can then be converted to carbon fiber.

[0009] In other embodiments of the invention, the feed can be hydrotreated to remove contaminants and then sent to a second solvent to remove lighter components prior to the soaking furnace visbreaking step. Brief Description of the Drawings

[0010] Figure 1 A simplified flow diagram is shown for producing a mesophase material to be used as a raw material for carbon fiber.

[0011] Figure 2 An alternative flow diagram is shown for producing a mesophase material to be used as a raw material for carbon fiber. Detailed implementation mode

[0012] Due to the low raw material cost and high availability of feed components from refinery streams, the production of carbon fibers from petroleum pitch streams for applications such as aircraft brakes, supercapacitors, steel substitutes for automobiles, and other applications has a relatively low production cost. However, due to other components in this type of petroleum pitch stream, compared with polyacrylonitrile (PAN)-based carbon fibers, the carbon fibers produced from petroleum pitch streams generally exhibit poor mechanical properties, thus limiting the market adoption of carbon fibers. These other components include volatile gases, natural components in the oil such as sulfur, nitrogen, and organometallic compounds, and any residual inorganic materials added during processing (FCC catalysts, fines contained in crude oil, etc.). This application provides a method for obtaining an easily accessible petroleum-based stream and processing it into a raw material that will allow for direct carbon fiber production and / or the production of carbon fibers with improved mechanical properties after additional processing.

[0013] Mesophase pitch is an important and relatively recently recognized member of the pitch family. Mesophase pitch has optical properties and can be used to manufacture carbon fibers, carbon foams, and other exotic and valuable materials.

[0014] When natural or synthetic pitch with an aromatic group is heated under static conditions in the temperature range of 350 °C to 500 °C, small insoluble liquid spheres begin to appear in the pitch, and as heating continues, their size gradually increases. When examined by electron diffraction and polarized light techniques, these spheres are shown to consist of oriented molecular layers arranged in the same direction. As these spheres continue to grow with continued heating, they come into contact with each other and gradually coalesce with each other to produce a large number of arranged layers. As coalescence continues, domains of arranged molecules much larger than the molecules of the original spheres are formed. These domains aggregate together to form an overall mesophase, where the transition from one oriented domain to another sometimes occurs smoothly and continuously through gradually curved lamellae and sometimes through more sharply curved lamellae. The orientation differences between domains produce a complex array of polarized light extinction profiles in the overall mesophase, which correspond to various types of linear discontinuities in the molecular arrangement. The final size of the resulting oriented domains depends on the viscosity of the mesophase formed and the rate of viscosity increase, which in turn depends on the specific pitch and heating rate. In some pitches, domains with sizes exceeding two hundred micrometers up to more than one thousand micrometers are produced. In other pitches, the viscosity of the mesophase is such that only limited layer coalescence and structural rearrangement occur, resulting in a final domain size not exceeding one hundred micrometers.

[0015] The highly oriented optically anisotropic insoluble material produced by treating pitch in this manner is given the term "mesophase", and pitch containing such material is called "mesophase pitch". When heated above their softening points, such pitches are mixtures of two essentially immiscible liquids, one liquid being the optically anisotropic oriented mesophase portion and the other liquid being the isotropic non-mesophase portion. The term "mesophase" is derived from the Greek "mesos" or "intermediate", and indicates the pseudo-crystalline nature of this highly oriented optically anisotropic material. Mesophase is essentially a "liquid crystal" because it has an ordered and repeating atomic arrangement, as demonstrated by its X-ray diffraction pattern, and is also capable of flowing when stressed. This seemingly contradictory behavior is due to the rather weak bonding of carbon atoms in adjacent parallel planes.

[0016] In a sense, mesophase pitch is just a stopping point in the thermal condensation of hydrocarbons to coke. As time and temperature increase, aromatic liquid hydrocarbons thermally polymerize, accompanied by some thermal dealkylation. If the atmospheric or vacuum residua of aromatic crude oils are heat-treated, the first stopping point is the visbroken crude oil with lower viscosity and molecular weight than the feedstock. The next stopping point along the heat-treatment route is dominated by the production of petroleum pitch by thermal polymerization. The end of the production line is coke. Mesophase pitch is the penultimate stopping point. Although the thermal method can be briefly explained, numerous methods for preparing mesophase have been proposed or at least patented.

[0017] The term pitch has been used for many heavy products, ranging from the residual fractions of crude oil to the products of thermal polymerization. As used herein, pitch is intended to refer to highly aromatic materials produced by thermal polymerization and having a softening point greater than 100 °C.

[0018] Petroleum pitches have been prepared by refiners for decades. Perhaps the best-known materials are A-240 pitch and / or M-50 produced by Ashland Petroleum Company and subsequently by Marathon Oil Company, respectively. Such pitches with suitable softening points can be satisfactorily used as impregnating materials for electrodes, anodes, and carbon-carbon composites (e.g., carbon-carbon fiber composites such as aircraft brakes and rocket engine nozzles). These pitches can also be used in the nuclear industry for the preparation of fuel rods and control rods for graphite-moderated reactors. In addition, such pitches can be used as starting materials for the production of mesophase pitch, which can be used to produce carbon fiber precursors and carbonized fibers, i.e., carbon fibers and graphite fibers. Carbon foams and other pitch-based products can also be made from mesophase pitch.

[0019] The high strength / weight ratio of single or composite carbon and graphite fibers makes such fibers useful in sports equipment, automotive parts, lightweight aircraft, and several aerospace applications. The high thermal conductivity and strength make carbon foams useful in thermal management applications, etc. The end products (carbon fibers, carbon foams, etc.) are high-value specialty products that are highly dependent on the properties of the starting materials (mesophase pitch).

[0020] Pitch formation is a thermal process involving thermally induced polymerization. The product has a higher molecular weight than the feed. In contrast, there are other thermal refinery processes that use heat to crack or dehydrate the feed. These processes produce products with a lower molecular weight than the feed. Thermal cracking processes such as visbreaking, e.g., the thermal cracking process widely licensed by Universal Oil Products, use high temperatures to thermally crack the high molecular weight components of crude oil to produce their own distillates, thereby reducing the viscosity of the heavy fuel oil product. Steam cracking of naphtha or other light (usually paraffinic) feeds into olefins is an important process for the production of ethylene and other light olefins. Steam and naphtha are mixed together and fed through a heater at ultra-high temperatures of up to 850 °C and at speeds exceeding the speed of sound, and then quenched. Styrene production, although catalytic, uses a large amount of superheated steam to heat the ethylbenzene feed to the temperature at which it can be catalytically and endothermically converted into styrene. The prior art for preparing mesophase pitch can be summarized as follows. There are many methods, most involving relatively long batch processes that allow the formation of the mesophase. Some are continuous and use strong mechanical agitation or agitation by injecting an inert gas after using a wiped film evaporator to remove a large amount of distillate material. All of these are difficult to control, and due to the high temperatures, the mesophase pitch precursors and pitch products can form coke.

[0021] For this discussion, the unconverted oil stream from a hydrocracking unit provides a very good starting point for the production of carbon fibers. The unconverted oil from a hydrocracking unit typically contains a high concentration of heavy polynuclear aromatic hydrocarbons. These need to be removed from the hydrocracking reaction system to prevent catalyst deactivation reactions. In the figure of US8852404, line 26 is the concentrated stream of these heavy polynuclear aromatic hydrocarbons (HPNA). And the typical drag stream from a hydrocracking application (reference line 25 in US8852404) also contains some polynuclear aromatic hydrocarbons before concentration.

[0022] Because the net drag stream from the hydrocracking process has been severely hydrotreated, this HPNA drag stream is typically low in components such as organic sulfur, organic nitrogen, and organometallic compounds. In addition, this stream is free of catalyst fines, which are typically present in other refinery heavy streams that have been examined for carbon fiber production (FCC clarified slurry oil (CSO) and other thermal cracking residues). However, while this stream may be free of typical heavy contaminants, it still contains a certain amount of undesirable lighter materials that can reduce the quality of the final carbon fiber.

[0023] Therefore, it is proposed to direct this HPNA drag stream to a separation process where these light materials can be removed. Solvent extraction is a process step that can be used to recover the light soluble components and exclude the insoluble components. The solvent extraction step can include a step that removes heptane soluble materials such as soft pitch, toluene soluble materials such as asphaltenes, and quinoline soluble materials such as beta resin, leaving a heavy stream of mesophase hydrocarbons.

[0024] Due to the high concentration of heavy polynuclear aromatics, this heavy product stream from the solvent extraction step now becomes an excellent raw material for mesophase production and for the subsequent production of carbon fibers.

[0025] The heavy product stream is held in a soaking furnace visbreaker drum at a temperature above 800°F for more than two minutes to gradually form the desired amount of mesophase material, which can then be fed to the carbon fiber production plant. Visbreaking or thermal cracking achieves moderate conversion of heavy feeds to lighter products, including olefinic naphtha. Coking achieves complete conversion of heavy feeds to lighter products such as coker naphtha, but the olefin content, especially the diene content, of the naphtha is so high that further processing is required. Large integrated refineries have the specialized equipment required to process coker naphtha. Typically, it is either treated at relatively low temperatures over a proprietary catalyst to saturate the dienes, or it is blended with conventional naphtha and hydrotreated at two to three times the pressure required to hydrotreat other refinery naphtha fractions. Severe hydrotreating of coker naphtha saturates the olefins, significantly reducing the octane, and therefore requires further processing such as in a platinum reformer.

[0026] Due to the absence of heavy contaminants and removal of light components, the recycled material can be an excellent feed stream for the production of carbon fibers, such as described in other patents (US9222027 and US10731084).

[0027] Figure 1An embodiment of the present invention is provided. Petroleum feed 10 is sent to a vessel 15 containing quinoline solvent to remove contaminants. Materials insoluble in quinoline are discharged in line 22. Hydrocarbons are soluble in the quinoline solvent and are sent as stream 20 to a second vessel 25 containing toluene solvent. From this toluene solvent, toluene-soluble light hydrocarbons are sent in line 30 for use outside the current process, and a stream 35 of toluene-insoluble β-resin is sent to a soaking pit visbreaking reactor 40 operating at a temperature above 425 °C (800 °F), where the material is retained in the reactor for more than two minutes. Mesophase material 50, as anisotropic pitch, can now be sent for conversion to carbon fiber.

[0028] Figure 2 An embodiment of the method is provided where treatment with quinoline solvent to remove contaminants is not required because contaminant removal is addressed by using a hydrotreating step. In Figure 2 , feed 10 is sent to a hydrocracking unit 60, where the effluent is sent to a separation column 70 to be separated into a product 72 and heavier hydrocarbons 74. A portion of the heavier hydrocarbons is recycled as stream 80, and a second portion of the heavier hydrocarbons is sent to a vessel 30 containing toluene solvent to be separated into a light hydrocarbon stream 30 and a heavy hydrocarbon stream 35, which heavy hydrocarbon stream will be sent to a soaking pit visbreaking reactor 40 to produce mesophase material 50, which will be sent for carbon fiber manufacture.

[0029] The untreated hydrotreated feed (SDA pitch or CSO) is first treated with quinoline to exclude any solid contaminants or coke present in the feedstock. This solid-free oil (quinoline solubles) may or may not require hydrotreating before treatment with toluene to remove the lighter components. The heavy components (β-resin or toluene insolubles) are then directed to a heat treatment step (soaking pit visbreaker) to grow / polymerize the β-resin or small mesophases into larger mosaic mesophases (anisotropic pitch). If isotropic pitch is desired, the heat step can be skipped.

[0030] If the starting material has been hydrotreated (hydrocracker UCO), the first quinoline and hydrotreating steps will not be required because the material is already free of contaminants. In this alternative, the feed is treated with toluene, and the toluene insolubles are sent for heat treatment.

[0031] Embodiment

[0032] In this example, clarified slurry oil (CSO) from fluid catalytic cracking of high molecular weight crude oil is processed using two solvent extraction steps to prepare for further heat treatment. In the first stage extraction, quinoline is added to the CSO at a mass ratio of 10:1 to dissolve the oil. The solution is placed in an oil bath or a controlled heating mantle and on a hot plate with vigorous stirring. A thermocouple is inserted into the solution to measure the solution temperature while a second thermocouple measures the temperature of the oil bath. The solution is heated to 80 °C under reflux and mixed at this temperature for two hours. After two hours, the solution is filtered through a Buchner funnel to separate the quinoline insoluble matter collected on the filter paper and the quinoline soluble matter collected in the filtering flask. The quinoline soluble matter is rotary evaporated to remove quinoline. The collected quinoline insoluble matter and the solvent-free quinoline soluble matter are dried in a vacuum oven at 100 °C for twelve hours.

[0033] The purpose of this extraction is to remove ash / catalyst and particulate matter from the CSO feed. If not removed, ash / catalyst and particulate matter contaminants will cause defects in the microstructure of the carbon fiber, resulting in unacceptable brittleness. Then, a second extraction is performed on the dried solvent-free quinoline soluble matter. In the second stage extraction, heptane is added to the dried solvent-free soluble matter from the first stage extraction at a mass ratio of 10:1 to dissolve the soluble matter. The solution is placed in an oil bath or a controlled heating mantle and on a hot plate with vigorous stirring. A thermocouple is inserted into the solution to measure the solution temperature while a second thermocouple measures the temperature of the oil bath. The solution is heated to 80 °C under reflux and mixed at this temperature for two hours. After two hours, the solution is filtered through a Buchner funnel to separate the heptane insoluble matter collected on the filter paper and the heptane soluble matter collected in the filtering flask. The heptane soluble matter is rotary evaporated to remove heptane. The collected heptane insoluble matter and the solvent-free heptane soluble matter are dried in a vacuum oven at 100 °C for twelve hours. The dried solvent-free heptane insoluble matter is directed for heat treatment. The purpose of this extraction is to remove any volatiles present in the quinoline soluble matter and to concentrate the asphaltenes in the HI. If not removed, the volatile components will cause defects in the microstructure of the carbon fiber, resulting in unacceptable brittleness.

[0034] Then, the dried solvent-free heptane insoluble matter is heat treated at a temperature higher than 426 °C for more than 2 minutes. The heavy hydrocarbons present in the material will form mesophase after treatment and are now a suitable component as a raw material for a carbon fiber production facility.

[0035] Specific implementation

[0036] While the following is described in connection with specific embodiments, it should be understood that the description is intended to be illustrative and not limiting of the scope of the foregoing description and the appended claims. Without further elaboration, it is believed that one skilled in the art can, using the preceding description, utilize the present disclosure to its fullest extent and can readily ascertain the essential characteristics of this disclosure without departing from the spirit and scope of the invention and can make various changes and modifications to the present disclosure and adapt it to various usages and conditions. Accordingly, the foregoing preferred specific embodiments are to be construed as merely illustrative and not in any way limiting the remainder of the disclosure, and are intended to cover various modifications and equivalent arrangements included within the scope of the appended claims.

[0037] In the foregoing, all temperatures are shown in degrees Celsius and all parts and percentages are by weight, unless otherwise indicated. A first embodiment of the present disclosure is a method for producing a hydrocarbon feedstock for conversion into carbon fiber, the method comprising mixing an untreated, crude feedstock with a first solvent to remove contaminants and coke insoluble in the solvent, and wherein the hydrocarbons in the untreated, crude feedstock are soluble in the first solvent; and then sending the first solvent containing the hydrocarbons to a second solvent to remove lighter components; and producing a stream containing heavier hydrocarbon components, which stream is sent to a heat treatment step to increase the molecular weight of the heavier hydrocarbon components to produce pitch; and then converting the pitch into carbon fiber. An embodiment of the present disclosure is one, any, or all of the previous embodiments in this paragraph to the first embodiment in this paragraph, wherein the first solvent is quinoline. An embodiment of the present disclosure is one, any, or all of the previous embodiments in this paragraph to the first embodiment in this paragraph, wherein the second solvent is toluene. An embodiment of the present disclosure is one, any, or all of the previous embodiments in this paragraph to the first embodiment in this paragraph, wherein the heat treatment step is at a temperature above 425 °C for more than 2 minutes. An embodiment of the present disclosure is one, any, or all of the previous embodiments in this paragraph to the first embodiment in this paragraph, wherein the heat treatment step increases the proportion of the heavier hydrocarbon components that are converted to mesophase while reducing the proportion of coke to produce a product stream containing the mesophase. An embodiment of the present disclosure is one, any, or all of the previous embodiments in this paragraph to the first embodiment in this paragraph, further comprising sending the product stream to a carbon fiber production plant to produce carbon fiber having a Young's modulus of at least 200 GPa. An embodiment of the present disclosure is one, any, or all of the previous embodiments in this paragraph to the first embodiment in this paragraph, wherein the untreated, crude feedstock comprises thermally produced pyrolysis oil selected from a steam cracker or a pyrolysis unit or a bio-derived oil from a plant, animal, waste grease, algae, or microbial source. An embodiment of the present disclosure is one, any, or all of the previous embodiments in this paragraph to the first embodiment in this paragraph, wherein after mixing the untreated, crude feedstock with the solvent to remove solid contaminants, the solvent containing the hydrocarbons is sent to a hydrotreating reactor and then to the second solvent extraction. An embodiment of the present disclosure is one, any, or all of the previous embodiments in this paragraph to the first embodiment in this paragraph, wherein the heat treatment step is a soaking pit visbreaking step. An embodiment of the present disclosure is one, any, or all of the previous embodiments in this paragraph to the first embodiment in this paragraph, wherein the heavier hydrocarbon components include β-resin or toluene-insoluble hydrocarbons.Embodiments of the present disclosure are one, any or all of the prior embodiments in this paragraph through the first embodiment in this paragraph wherein the carbon fibers have a Young's modulus of at least 200 GPa. Embodiments of the present disclosure are one, any or all of the prior embodiments in this paragraph through the first embodiment in this paragraph wherein the heavier hydrocarbon component is converted to an anisotropic pitch.

[0038] A second embodiment of the present disclosure is a method for producing a hydrocarbon feed for conversion into carbon fiber, comprising passing a hydrotreated stream to a vessel containing toluene to produce a stream comprising toluene and impurities removed from the hydrotreated asphalt and a solvent-insoluble stream; and passing the solvent-insoluble stream to a heat treatment step to produce anisotropic asphalt.

[0039] A third embodiment of the present disclosure is a method for producing a hydrocarbon feedstock for conversion into carbon fiber, the method comprising mixing a crude, non-hydrotreated feedstock with a first solvent to remove contaminants and coke insoluble in the solvent, wherein hydrocarbons in the crude, non-hydrotreated feedstock are soluble in the first solvent; and then passing the first solvent containing the hydrocarbons to a second solvent to remove lighter components; and producing a stream comprising heavier hydrocarbon components to be converted into carbon fiber. Embodiments of the present disclosure are one, any, or all of the previous embodiments in this paragraph through the first embodiment in this paragraph, wherein the carbon fiber has a Young's modulus of at least 50 GPa.

[0040] A fourth embodiment of the present disclosure is a method for producing a hydrocarbon feed for conversion into carbon fibers, the method comprising passing a non-hydrotreated crude feed to be mixed with a solvent to separate lighter hydrocarbon components from heavier hydrocarbon components and then passing the feed stream containing the heavier hydrocarbon components to a solvent to remove contaminants and coke, thereby producing a clean heavier hydrocarbon feed stream that is insoluble in the solvent; and then converting the heavier hydrocarbon feed stream into carbon fibers.

Claims

1. A method for producing a hydrocarbon feedstock for conversion to carbon fiber, the method comprising mixing an untreated hydrocarbon feedstock with a first solvent to remove contaminants and coke that are insoluble in the solvent, and wherein the hydrocarbons in the untreated hydrocarbon feedstock are soluble in the first solvent; And then sending the first solvent containing the hydrocarbon to a second solvent to remove lighter components; And producing a stream containing heavier hydrocarbon components, which stream is sent to a heat treatment step to increase the molecular weight of the heavier hydrocarbon components to produce pitch; And then converting the pitch into carbon fibers.

2. The method according to claim 1, wherein the first solvent is quinoline.

3. The method according to claim 1, wherein the second solvent is toluene.

4. The method according to claim 1, wherein the heat treatment step increases the proportion of the heavier hydrocarbon components that are converted into mesophase while reducing the proportion of coke to produce a product stream containing the mesophase.

5. The method according to claim 4, further comprising sending the product stream to a carbon fiber production plant to produce carbon fibers having a Young's modulus of at least 200 GPa.

6. The method according to claim 1, wherein the untreated crude feed comprises thermally generated pyrolysis oil selected from a steam cracker or a pyrolysis unit or a bio-derived oil from a plant, animal, waste grease, algae or microbial source.

7. The method according to claim 1, wherein after mixing the untreated crude feed with the solvent to remove solid contaminants, the solvent containing the hydrocarbon is sent to a hydrotreating reactor and then to the second solvent extraction.

8. The method according to claim 1, wherein the heat treatment step is a soaking pit visbreaking step.

9. The method according to claim 1, wherein the heavier hydrocarbon components comprise β-resin or toluene-insoluble hydrocarbons.

10. The method according to claim 1, wherein the heavier hydrocarbon components are converted into anisotropic pitch.

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