System and method for producing carbon fiber from coal

Abstract

Disclosed embodiments relate to a method for processing coal, which includes subjecting raw coal to a liquefaction process to form a pitch resin and purifying the pitch resin to produce a mesophase pitch. The method further includes subjecting the mesophase pitch to a low crystallinity spinning process to form raw fibers. The raw fibers are further subjected to a stabilization process designed to oxygen crosslink the fibers to form stabilized fibers, which are then subjected to a carbonization process to form carbon fibers.

Description

[Technical Field]

[0001] cross reference This application is based on and claims priority to U.S. Provisional Patent Application No. 63 / 051,255, entitled "SYSTEMS AND METHODS FOR MANUFACTURING CARBON FIBER FROM COAL," filed July 13, 2021, the disclosure of which is incorporated by reference in its entirety.

[0002] FIELD OF THE INVENTION The embodiments described herein relate generally to carbon products and methods for processing carbon-based materials. More particularly, the embodiments relate to low-density carbon fibers and systems and methods for producing low-density carbon fibers from coal. [Background technology]

[0003] Fiber materials are used in many different applications across a wide range of industries, including commercial aviation, recreation, industry, and transportation. Carbon fiber is used in a variety of composite materials due to its excellent properties, including high strength, high modulus, and high electrical conductivity. Summary of the Invention [Problem to be solved by the invention]

[0004] Carbon fibers produced using conventional methods, such as conventional carbon fibers that can be produced by carbonizing organic fibers through heat treatment (e.g., polyacrylonitrile (PAN)-based carbon fibers, pitch-based carbon fibers, or cellulose-based carbon fibers), High fever Because of the high electrical conductivity and development costs involved, manufacturers and users of carbon fibers are continually seeking new and improved methods of forming carbon fibers. [Means for solving the problem]

[0005] Embodiments disclosed herein relate to methods for producing carbon fibers from coal. Embodiments herein also relate to producing graphene. The methods disclosed herein can include continuous processes. In one example, the methods disclosed herein can include a direct air capture system including a coal-derived electroactive polymer for capturing CO2 from a gas stream.

[0006] Many of the systems and methods described herein can utilize low-cost, high-yield coal-based pitch precursors, which offer advantages over traditional high-cost, low-yield PAN-based or cellulosic-based insulating fibers. The systems and methods described herein can also provide low-cost pitch-based carbon fibers that offer significant cost savings over current carbon fibers, allowing them to be used in a wide range of useful applications.

[0007] In some embodiments, a method of processing coal can include subjecting raw coal to a liquefaction process to form a pitch resin. The pitch resin can be refined to produce a pitch having a degree of anisotropy of about 20% to about 99%. A method of processing coal can include refining the pitch to produce a mesophase pitch. The mesophase pitch can be subjected to a low crystallinity spinning process to form raw fibers, and the raw fibers can be subjected to a fiber stabilization process using oxygen to produce stabilized carbon fibers. The method can further include subjecting the stabilized carbon fibers to a carbonization process to form carbonized or calcined carbon fibers. In some embodiments, the pitch or pitch resin can have an isotropic pitch.

[0008] In some embodiments, the method of processing coal further includes distilling the coal tar to produce a pitch or pitch resin. In some embodiments, the method of processing coal further includes thermally treating the coal tar to produce a pitch or pitch resin. The method further includes utilizing a machine learning-enabled regression model to optimize parameters for producing the carbon fiber. In some embodiments, the method can further include blending graphene into the mesophase pitch. In some embodiments, the method can include stabilizing the raw fiber. Stabilizing the raw fiber can include heating the pitch to a stabilization temperature of about 280°C and holding the pitch at the stabilization temperature for about 2 hours.

[0009] In some embodiments, subjecting the raw fibers or stabilized fibers to a carbonization process can include heating the raw fibers to a carbonization temperature of about 1000°C and holding the raw fibers at the carbonization temperature for about 30 minutes. In some embodiments, subjecting the raw fibers or stabilized fibers to a carbonization process can include heating the raw fibers in an inert gas environment. Carbon fibers produced by the method of treating coal can include a tensile strength of about 1.51 GPa to about 1.64 GPa and an elastic modulus of about 356 GPa.

[0010] In some embodiments, a method for producing graphene can include mixing coal with cellulose-containing biomass to form a biomass mixture, grinding the biomass mixture to a powder, subjecting the powder to a graphitization process to form graphite, acid-leaching the graphite to remove impurities, and shear-mixing the graphite to form graphene. In some embodiments, the cellulose-containing biomass comprises at least one of wood sawdust, paper waste, and bamboo. In some embodiments, a method for producing graphene can include preheating the cellulose-containing biomass before mixing the coal with the cellulose-containing biomass. Preheating the cellulose-containing biomass can include heating the cellulose-containing biomass to a temperature between about 400°C and about 600°C at atmospheric pressure and holding the temperature for about 1-6 hours.

[0011] In some embodiments, the graphitization process includes evacuating a ceramic container containing the powder, injecting about 0.5% to 10% molar ratio of air into the container, heating the powder in the ceramic container to a temperature of about 1,800°C-2,600°C and holding that temperature for about 18 hours, cooling the powder to ambient temperature, and repeating the heating and cooling process until the coal is graphitized. In some embodiments, the method of producing graphene includes acid-leaching the graphite followed by washing the graphite with distilled water and oven-drying the graphite. In some embodiments, acid-leaching the graphite includes treating the graphite with at least one of sulfuric acid and nitric acid. The impurities can include metal oxides.

[0012] In some embodiments, a method of producing graphene can include separating a graphite anode having a graphite lattice from a used battery, purifying the graphite anode, and shear mixing the graphite lattice to separate graphene sheets from the graphite lattice. In some embodiments, purifying the graphite anode can further include soaking the graphite anode in N-methyl-2-pyrrolidone (NMP).

[0013] Features from any of the disclosed embodiments can be used in combination with each other without limitation. Additionally, other features and advantages of the present disclosure will become apparent to those skilled in the art through a review of the following detailed description and accompanying drawings. [Brief explanation of the drawings]

[0014] The accompanying drawings illustrate several embodiments of the present disclosure, with like reference numerals indicating the same or similar elements or features in different views or embodiments shown in the drawings.

[0015] [Figure 1] 1 is a flowchart of a method for producing coal, according to one embodiment.

[0016] [Figure 2] 1 illustrates a process flow for converting raw coal into carbon fiber, according to one embodiment.

[0017] [Figure 3A] 1 is a flowchart of a method for producing graphene, according to one embodiment.

[0018] [Figure 3B] FIG. 1 illustrates a method for producing graphene, according to one embodiment.

[0019] [Figure 3C] 1 is a transmission electron microscopy (TEM) image of anodic graphite treated with H2SO4.

[0020] [Figure 3D] 1 is a high-resolution transmission electron microscopy (HRTEM) image of shear-mixed graphene.

[0021] [Figure 3E] FIG. 3B is a diagram of the fast Fourier transform (FFT) of FIG. 3D.

[0022] [Figure 4A] 1 is a flowchart of a method for producing graphene, according to one embodiment.

[0023] [Figure 4B] 1 is a flowchart of a graphitization process, according to one embodiment.

[0024] [Figure 4C] FIG. 1 is a schematic diagram of a method for converting coal to graphene, according to one embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0025] This specification presents examples of embodiments of the present invention, and is not intended to limit the scope, application, or configuration of the present invention as defined by the appended claims. Accordingly, it will be understood that changes can be made in the function and arrangement of the disclosed elements, and that steps or components can be omitted, substituted, or added as appropriate in various embodiments, without departing from the spirit and scope of the present disclosure. For example, methods described herein can be performed in an order different from that described, and various steps can be added, omitted, or combined. Additionally, features described with respect to some embodiments can be combined with other embodiments.

[0026] Systems and methods are provided for processing coal to form advanced carbon products. The advanced carbon products can include one or more of carbon fiber, activated carbon, resin, graphene, materials for use in batteries, materials for use in buildings and construction, or combinations thereof. The systems and methods provided herein can include processing pitch made from coal, as well as products formed or produced by the systems and methods. The systems and methods described herein facilitate the production of low-cost, low-thermal-conductivity carbon fiber products. For example, many carbon fiber products produced in accordance with the present disclosure have lower densities than conventional carbon fiber products made from similar materials. Low-density carbon fiber products retain heat, imparting properties to the carbon fiber products that reduce thermal conductivity compared to conventional carbon fibers.

[0027] The low thermal conductivity carbon fiber products produced according to many of the systems and methods described herein are unexpected to those skilled in the art. Many embodiments of the systems and methods described herein improve the conversion of coal-based pitch intermediate products into useful products, such as high-carbon-content pitch fiber products with low thermal conductivity. These products may be suitable as insulation and / or low-density carbon fibers. In particular, the present technology utilizes a specially designed system and one or more blend additives to tailor the physical properties of the carbon fiber, such as at least one of the density (specific gravity) and / or thermal conductivity of the carbonized fiber. Many of the systems and methods described herein can use low-cost, high-yield coal-based pitch precursors, which are advantageous over traditional high-cost, low-yield PAN-based or cellulose-based insulation fibers. The systems and methods described herein can also provide carbon fiber products in a manner that allows low-cost pitch-based carbon fibers to realize all useful applications at a significant cost reduction over current technologies. For example, the systems and methods can produce affordable carbon fiber insulation to improve energy efficiency in the built environment as an alternative to glass fiber insulation.

[0028] FIG. 1 is a flow diagram of a method 100 for processing coal to form low thermal conductivity carbon fibers, according to one embodiment. For example, the method 100 includes step 102, in which raw coal is subjected to a liquefaction process to form a liquid pitch resin. Coal liquefaction is a process in which coal is converted into a liquid. Several processes are used to accomplish this step, with the two most common being the indirect route and the direct route. In some embodiments, the indirect route consists of two steps: first, coal is gasified with steam and oxygen to produce synthesis gas (syngas), which is then scrubbed to remove dust, tar, and acid gases. In the next step, the synthesis gas is reacted with a catalyst via a Fischer-Tropsch process to convert the synthesis gas into various hydrocarbons. For example, the hydrocarbons may include pitch resin. In the direct route, coal is crushed and reacted with a catalyst, followed by the addition of hydrogen at high temperature and pressure in the presence of a solvent to produce hydrocarbons, such as pitch resin. In some embodiments, the pitch resin comprises isotropic pitch.

[0029] Method 100 may also include step 104 of distilling coal tar to produce a pitch resin or step 106 of heat-treating coal tar to produce a pitch resin. Method 100 may also include step 107 of purifying the pitch or pitch resin to produce a pitch having a degree of anisotropy between about 20% and about 99%. In some embodiments, method 100 may also include step 108 of purifying the pitch or pitch resin to produce a mesophase pitch. In some instances, a processing facility may purify coal-derived isotropic pitch to produce a mesophase pitch suitable for melt-spinning a pitch CF precursor. Typically, coal tar pitch can be produced by distillation or heat treatment of coal tar, which is a by-product of coke and coal gas production from coal that can be chemically extracted. Coal tar pitch consists of thousands of compositions with a broad molecular weight distribution and poorly defined chemical structure, making it undesirable for preparing carbon fibers. The processing facilities and procedures described herein can remove impurities such as water, metal oxides, and sulfides from coal and extract value-added carbon materials, graphene, and pitch. Processing parameters such as pyrolysis temperature and duration can be optimized to obtain the highest quality spinnable mesophase pitch possible from an isotropic coal tar pitch suitable for melt spinning carbon fibers. In some instances, graphene oxide obtained from coal can be reduced to graphene by thermal processing methods.

[0030] Carbon fibers produced from mesophase pitch have a highly oriented structure in which the carbon crystallites are preferentially aligned parallel to the fiber axis, and also have high strength and high modulus. In some embodiments, producing mesophase pitch from isotropic coal tar pitch or petroleum pitch involves heating the precursor pitch to a temperature between 350°C and 500°C in an inert environment. A temperature of about 400°C can be used to produce mesophase pitch with the desired rheological properties for spinning. At this temperature, producing mesophase pitch from coal tar or petroleum pitch takes a long time, typically about 24 hours. To produce mesophase pitch suitable for carbon fiber production, it is useful to remove solids, ash-forming materials, and coke, which can lead to defects in the fiber and low tensile strength.

[0031] In some embodiments, the refining step comprises mechanical filtration. In some embodiments, the filtration step comprises chemical filtration. Step 108 may filter the liquid pitch resin to remove minerals and heavy metals present in the raw coal prior to filtration. In some embodiments, the filtration step may be carried out at an elevated temperature. This elevated temperature may include a temperature between about 60°C and about 300°C. In some embodiments, step 108 may include heating the resin pitch temperature to about 60°C or higher, about 100°C or higher, about 150°C or higher, about 200°C or higher, about 300°C or higher, in the range of about 60°C to about 100°C, about 100°C to about 200°C, or about 200°C to about 300°C. The final temperature may be about 200°C or higher, about 250°C or higher, or about 300°C or higher.

[0032] The method 100 also includes, in some embodiments, a step 110 of blending graphene with mesophase pitch. In some examples, the methods described herein can extract valuable advanced carbon products, such as graphene and mesophase pitch, from coal and use them as raw materials to produce high-performance graphene-enhanced carbon fibers (CFs). The methods described herein can prepare high-quality graphene and mesophase pitch from coal and commercial coal-derived isotropic pitch. This graphene and mesophase pitch can be blended to produce low-cost, high-performance pitch-based carbon fibers. In some examples, the production of CFs from coal-based precursors is suitable for automotive structural applications, enabling the development of a wider range of CF composites in next-generation lightweight vehicle designs.

[0033] In some embodiments, pitch / graphene precursor fibers can be prepared by blending 0.1 wt% shear-swollen graphene into mesophase pitch. The resulting pitch and pitch / graphene precursor fibers are then processed using a series of heat treatment steps, including a stabilization step at 280°C for 2 hours in air and carbonization at 1000°C for 30 minutes under Ar gas protection. In some embodiments, pitch / graphene CFs have a fairly dense cross-section, but pitch CFs exhibit several large pores on the cross-section surface, demonstrating the structural improvement function of the added graphene. Pitch / graphene CFs exhibit significantly improved mechanical properties compared to pure pitch CFs, further highlighting this function as the strength increases from 1.51 to 1.64 GPa and the elastic modulus increases from 220 GPa to 356 GPa. The balance between ductility and strength can be further tuned by varying the graphene concentration and other parameters. These successful experiments and promising results give us confidence in carrying out the proposed activities and meeting the established milestones and goals of the proposed project. The resulting high-quality mesophase pitch and graphene can be used as precursor materials to produce pitch / graphene carbon fibers. A series of pitch / graphene mixtures with various graphene concentrations with desired properties can be melt-spun into fibers on a custom spin line. Spinning parameters such as extraction temperature, quench flow rate, take-up speed, and draw rate can be explored to develop the optimal precursor microstructure for conversion to CF.

[0034] Similar results have been reported for carbon nanotubes (CNTs) and other graphene-polymer systems. Some reports have shown that low concentrations (less than 1.0 WT%) of CNTs / graphene can significantly improve mechanical properties. However, after a critical amount, the mechanical properties of the composites begin to deteriorate as the CNT / graphene concentration increases.

[0035] In embodiments, the liquid filtered pitch resin can then be subjected to a low crystallinity spinning process to form raw fibers in step 112. In many embodiments, the present systems and methods include at least one of two steps for disrupting the densified crystalline graphite structure associated with the carbon fibers. The two steps for disrupting the densified crystalline graphite structure can include physically altering the spinning conditions in a variable crystallinity spinning process and chemically altering the pitch composition with one or more blend additives. Spinning conditions can be physically altered in a low crystallinity spinning process to be more conducive to disrupting liquid crystal formation. In some embodiments, spinning conditions can be physically altered by one or more of the following: turbulent spinneret design, low draw ratios for green spun fibers, meltblown solvation spinning systems versus pure resin melt spinning, use of flow inverters or frit flow redistributors in the spinneret capillary channels, creation of voids (such as nano-sized bubbles) in the spun fibers by foaming, and / or use of specialized spinnerets for hollow fiber formation with one or more cross-sectional holes, or a combination thereof.

[0036] In some embodiments, method 100 can also include adding a blend additive to the pitch resin before or during the low-crystallinity spinning step of step 112. In some embodiments, the blend additive can include one or more of an isotropic pitch, a pitch with a level of anisotropy, or a thermoplastic blend additive. Pitch is generally isotropic but can be made anisotropic by heat treatment. Isotropic and anisotropic pitch differ not only in the carbonaceous precursor but also in optical texture, microstructure, and physical properties. The additive can improve the strength and stiffness of the raw fiber. The pitch composition can also be chemically modified with one or more blend additives to make it more conducive to disrupting liquid crystal formation. The inclusion of one or more blend additives can result in carbon fibers having lower densities than conventionally formed carbon fibers. The resulting carbon fibers can include properties more similar to or superior to those of rayon carbon fibers, such as lower thermal conductivity. In some embodiments, the pitch composition can be varied by utilizing isotropic pitch and / or anisotropic pitch having a degree of anisotropy between 0% and 80% as a blend additive (or neat) in place of the highly discotic liquid crystal-containing mesophase pitch. In some embodiments, the blend additive can include one or more of various degrees of anisotropic pitch.

[0037] In some embodiments, the pitch composition can be modified by utilizing an oxygen-containing additive, such as an oxygen-containing polymeric material. In some embodiments, the pitch composition can be modified by utilizing one or more compounds containing heteroatoms such as oxygen or nitrogen. In some embodiments, the pitch composition can be modified by utilizing one or more thermoplastic blending additives (e.g., phenolic resins, lignin, etc.) containing heteroatoms such as oxygen or nitrogen. Mixing materials containing heteroatoms (e.g., oxygen) into the pitch during fiber spinning can reduce the fiber density. Examples of one or more thermoplastic blending additives containing heteroatoms such as nitrogen or oxygen include, but are not limited to, polyphenol-formaldehyde resins, lignin, polyethylene oxide, polyvinyl alcohol, poly DL lactide, polymethyl methacrylate, or combinations thereof. In some embodiments, one or more of the heteroatom-containing additives can be derived from coal. TIFF0007785741000001.tif66168 Polyphenol-formaldehyde resin TIFF0007785741000002.tif64168 Lignin TIFF0007785741000003.tif17168Polyethylene oxide (PEO) TIFF0007785741000004.tif14168 Polyvinyl alcohol TIFF0007785741000005.tif22168Poly DL-lactide (PLA)

[0038] The physical and chemical processes described above to disrupt the dense, crystalline graphite structure associated with carbon fibers can modify pitch-based carbon fibers to approach the microstructural characteristics and resulting density and insulating properties associated with cellulose-based (rayon) carbon fibers. Tables 1 and 2 below provide a comparison of the properties of PAN-, pitch-, and rayon-based carbon fibers. TIFF0007785741000006.tif55169TIFF0007785741000007.tif51168

[0039] In some embodiments, method 100 may also include step 114, which involves subjecting the raw fibers to a stabilization step designed to oxygen crosslink the fibers to form stabilized fibers. In some embodiments, the raw fibers may undergo a stabilization step in which air (oxygen), and in some cases additional gases or steam, are introduced to change the linear atomic bonds of the fibers to a more thermally stable form. The raw carbon fibers must be stabilized in step 114 prior to the calcination step of the overall process, described below. Stabilization prevents the molecules within the carbon fibers from relaxing or becoming misaligned during the calcination step. Stabilization maintains molecular integrity and allows the fibers to maintain their solid form throughout the final processing steps.

[0040] In some embodiments, stabilization of the fibers can be performed at temperatures of 200-300°C and can have a resonance time of 30-120 minutes. In some embodiments, stabilizing the raw fibers involves heating the pitch to a stabilization temperature of about 280°C and holding the pitch at the stabilization temperature for about two hours. During this resonance time, the fibers can be exposed to an air atmosphere containing approximately 21% oxygen. Additional gas or steam can be added to the stabilization atmosphere to alter the reactions occurring within the pitch of the fibers. During step 114, which includes stabilization, the fibers can be maintained under tension to prevent molecular relaxation and imbalance in the pitch. Pitch-based carbon fibers typically form ester and anhydride composites within the pitch during step 114. Pitch-based fibers can also experience a reduction in aromatic content during step 114.

[0041] Method 100 may also include step 116, in which the stabilized fibers may be subjected to a carbonization process to form low thermal conductivity carbon fibers. In some embodiments, carbonization is a process whereby the stabilized fibers are heated to drive off any non-volatile products (liquids and gases) and leave solid, low thermal conductivity carbon fibers. In some embodiments, the carbonization process includes heating the raw fibers to a carbonization temperature of about 1000°C and holding the raw fibers at the carbonization temperature for about 30 minutes. In some embodiments, step 116, of subjecting the raw fibers to a carbonization process, includes heating the raw fibers in an inert gas environment.

[0042] While systems and methods for producing low thermal conductivity carbon fiber insulation have been described above, other systems and methods for producing, generating, or forming various advanced carbon materials are contemplated herein. These advanced carbon materials may include other carbon fibers, activated carbon, resins, graphene, materials for use in batteries, materials for use in buildings and construction, or combinations thereof. Methods for producing carbon fibers, resins, graphene, and other advanced carbon materials (including activated carbon) from coal are disclosed in PCT International Patent Application No. PCT / US2018 / 067341, filed December 21, 2018, the disclosure of which is incorporated herein by reference in its entirety.

[0043] FIG. 2 illustrates a process flow diagram for raw coal to carbon fiber, including an optimization step. In some embodiments, method 100 can include an optimization step 200. Method 100 can include optimizing parameters for producing carbon fiber using a machine learning-enabled regression model. In some examples, a database of properties can be used to develop an ML-enabled regression model to optimize key parameters of the CF conversion process, which typically includes stabilization, carbonization, and graphitization of the precursor fiber, as shown in FIG. 2. The data can be used to train a multivariate regression model. Instead of the typical need for experimental replicates with a significant number of key parameters, such as mixing load, stabilization pretreatment, and stabilization and carbonization duration and temperature, a regression ML model can efficiently deconvolute the effects of each individual variable with a much smaller data set and predict mechanical performance metrics such as elastic modulus, strain, and strength. With a large number of independent predictor variables, multicollinearity will individually limit predictive ability, but this will not harm the overall reliability of the model as a cohesive set of predictors.

[0044] Generally, pitch (coal tar pitch) can be produced by either distillation or thermal treatment of coal tar, a by-product of the production of coke and coal gas from coal, or it can be chemically extracted. In some instances, isotropic pitch from coal can be tailored for mesophase pitch synthesis. Specifically, heating and distillation processes can be optimized to determine which process parameters result in the ideal mesophase pitch material and structure. Because various coal materials have different impurity contents, this process can vary slightly depending on the coal quality and mining source. Parameters critical to this extraction process can be iteratively optimized along with characterization techniques. Using collected data, monitoring feed rate, spinning, and conversion parameters can be used to develop ML-enabled regression models. By predicting the relationship between individual variables and the resulting mechanical properties of the spun fibers, the model will be able to help select key parameters and aid in optimization.

[0045] 3A is a flowchart of a method 300 for producing graphite, according to one embodiment. In some embodiments, method 300 includes separating a graphite anode having a graphite lattice from a used battery, as shown in block 302. In some embodiments, method 300 includes purifying the graphite anode, as shown in block 304. Purifying the graphite anode, in some embodiments, includes soaking the graphite anode in N-methyl-2-pyrrolidone (NMP). Method 300 further includes acid leaching the graphite anode, as shown in block 306. The method further includes shear mixing the graphite lattice to separate graphene sheets from the graphite lattice, as shown in block 308.

[0046] FIG. 3B is a schematic diagram illustrating method 300. In some examples, high-quality graphene can be produced from graphite anodes of used batteries using a cost-effective shear mixing method. A schematic diagram of graphite exfoliation by shear mixing is shown. The separated graphite anode can be purified by soaking in NMP and acid leaching to remove acid-leached impurities. Meanwhile, acid leaching further expands the graphite lattice and provides additives between each layer, which simplifies the separation of graphene sheets. FIG. 3C shows a transmission electron microscopy (TEM) image of anode graphite treated with H2SO4. Examples of graphene sheets obtained by method 300 are shown in FIGS. 3D and 3E. FIG. 3D is a high-resolution transmission electron microscopy (HRTEM) image of shear-mixed graphene. FIG. 3E is a fast Fourier transform (FFT) of FIG. 3D. The time and frequency of shear mixing can be adjusted to control the size of the graphene nanoflakes. In some instances, the combination of acid leaching and shear mixing can improve the efficiency of graphene production, and in some instances, the acid leaching and shear mixing process can have a graphene (i.e., graphite to graphene) productivity of greater than 80%.

[0047] Referring to FIG. 4A, a biomass-assisted method 400 for extracting high-quality graphene from coal is shown. In some embodiments, coal can be mixed with cellulose-containing biomass, as shown in block 402. The cellulose-containing biomass can include at least one of wood sawdust, paper waste, and bamboo. Thereafter, the coal / biomass mixture can be ground into a powder and homogeneously mixed, as shown in block 404. In block 406, the mixture can be subjected to a graphitization process to form graphite. The resulting graphite can be further treated with acid and / or acid leached. In some embodiments, acid leaching the graphite includes treating the graphite with at least one of sulfuric acid and nitric acid to remove residual impurities, often metal oxides derived from the coal and biomass, as shown in block 408. In some embodiments, the graphite can be washed with distilled water until neutral, as shown in block 410. The graphite can then be oven-dried. The dried sample can be transferred to a jar and slurried with distilled water. The jar of graphite suspension is subjected to shear mixing to harvest high quality graphene, as shown in block 412. Through this task, high quality graphene is produced that can be suspended in distilled water for further use.

[0048] In some embodiments, method 400 can further include preheating the cellulose-containing biomass before mixing the coal with the cellulose-containing biomass, as shown in block 414. Preheating the cellulose-containing biomass can include heating the cellulose-containing biomass at atmospheric pressure to a temperature of about 300°C to about 800°C and maintaining that temperature for about 1-6 hours, or until a suitable moisture content is achieved. Preheating is to remove moisture from the biomass. In some embodiments, the cellulose-containing biomass can be preheated to a temperature of about 400°C to about 600°C. In some embodiments, block 414 can include heating the cellulose-containing biomass at atmospheric pressure to a temperature of about 200°C or higher, about 300°C or higher, about 400°C or higher, about 500°C or higher, about 600°C or higher, or in a range of about 200°C to about 400°C, about 400°C to about 600°C, or about 300°C to about 700°C.

[0049] FIG. 4B is a flowchart of the graphitization process 450 of block 406 of FIG. 4A, according to one embodiment. The graphitization process 450 can include evacuating a ceramic container containing the powder, as shown in block 452. In some embodiments, the container can comprise a material other than ceramic. The container material should be an insulator. In some embodiments, the graphitization process 450 can further include injecting a small amount of air into the container, as shown in block 454. The process 450 can include heating the powder in the ceramic container, as shown in block 456. In some embodiments, heating the powder can include heating to a temperature of about 1800° C. to about 2600° C. and holding that temperature for about 1-8 hours or other suitable time. In some embodiments, the powder may be heated to a temperature of about 1500°C or greater, about 1800°C or greater, about 2000°C or greater, about 2200°C or greater, about 2400°C or greater, or in the range of about 1500°C to about 1800°C, about 1800°C to about 2000°C, or about 2000°C to about 2600°C. The graphitization step 450 may further include cooling the powder to ambient temperature, as shown in block 458. The evacuation, air injection, heat treatment, and cooling may be repeated multiple times as a cyclical step, as shown in block 460. The step of block 460 may be repeated until complete graphitization of the coal is achieved, as shown in block 462.

[0050] FIG. 4C is a schematic diagram of a method 400 for converting coal to graphene, according to one embodiment. FIG. 4C includes a schematic diagram of a sample as the method 400 proceeds. Prior to cyclic heating, the ceramic tube is evacuated. In the following steps, a small amount of air can be injected into the system. The system can be heated to a temperature for a period of time and then cooled to room temperature. The cyclic process, including evacuation, air injection, heat treatment, and cooling, can be repeated multiple times until complete graphitization of the coal is achieved.

[0051] In some instances, pitch-based fibers can be obtained by melt-spinning. TGA can be performed to determine the stabilization parameters of the as-spun fibers, including the temperature, heating rate, and holding time, to prevent the as-spun fibers from dissolving during the subsequent carbonization process. To incorporate coal-derived graphene into pitch particles, shear-mixed high-quality graphene can be dispersed in a concentrated polyalcohol (PVA) solution to prevent the graphene nanoparticles from agglomerating. Graphene / pitch mixtures with desired properties can be melt-spun into fibers.

[0052] Low-density or other carbon fibers formed according to one or more of the methods and systems described herein can be utilized in direct air capture (DAC) systems, such as thermoelectric DACs or DACs using coal-derived electroactive polymers (EAPs). Accordingly, DAC systems having low-density carbon fibers according to any of the above-described systems and methods are also disclosed herein. In some embodiments, DAC systems using coal-derived EAPs may not include low-density carbon fibers and may additionally or alternatively include other coal-derived materials, such as coal-derived graphene or graphene oxide.

[0053] Coal-derived EAPs can be formed from anthracene. In some embodiments, coal can be subjected to a liquefaction process to produce anthracene and / or other polycyclic aromatic hydrocarbons (PAHs). Coal-derived anthracene can be oxidized to form anthraquinone or similar products. Anthraquinone can be chlorinated, for example, using hydrochloric acid, to form dichloroanthraquinone. Dichloroanthraquinone can be polymerized to form EAPs.

[0054] Coal-derived EAPs can possess ketone functionality, which promotes carbon dioxide binding to the EAP when a voltage is applied across them. Once the EAP binding sites are saturated with bound or adsorbed carbon dioxide, the polarity of the voltage can be reversed, resulting in the bound carbon dioxide being debound, i.e., released in large quantities from the EAP. Because polarity can be reversed in systems such as batteries comprised of EAPs, separate materials for the anode and cathode within the system are not required. These properties allow the use of feed gases with relatively low concentrations of carbon dioxide (e.g., 415 ppm in air), and the amount of carbon dioxide bound can be increased by passing the feed gas over the EAP multiple times. In some embodiments, carbon nanotubes, graphene, graphene oxide, and / or other coal-derived conductive carbon materials can also be added to the system to enhance the conductivity of elements containing EAPs.

[0055] Thermoelectric DAC systems or DAC systems using coal-derived EAPs can be used in a variety of situations. For example, thermoelectric DAC systems or DAC systems using coal-derived EAPs can be used to combat the harmful effects of carbon dioxide during the construction of new buildings or structures. Panel-like structures including thermoelectric DAC systems or DAC systems using coal-derived EAPs can be added to buildings to capture carbon dioxide during and after the construction of the building. The building can be configured to capture carbon dioxide in the thermoelectric DAC system or DAC system using coal-derived EAPs. The carbon dioxide captured in the thermoelectric DAC system or DAC system using coal-derived EAPs incorporated into a building can be utilized in a number of materials, such as hydrocarbon materials or reverse water gas shift, which converts carbon dioxide into synthesis gas and densified liquids.

[0056] As used herein, the terms "about" or "substantially" refer to a tolerance of ±10% or ±5% of the term modified by "about" or "substantially." Furthermore, the terms "less than," "less than," "greater than," and "more than" include the endpoints modified by those terms.

[0057] Although various aspects and embodiments of the present invention have been disclosed herein, other aspects and embodiments are also contemplated. For purposes of description, specific terms have been used above to provide a thorough understanding of the embodiments. However, it will be apparent to those skilled in the art that the described embodiments need not be limited to these specific terms. That is, the descriptions of specific embodiments set forth herein are presented for purposes of illustration and description. They are not intended to limit the embodiments to the precise forms disclosed. It will be apparent to those skilled in the art that numerous modifications and variations are possible in light of the above teachings.

[0058] Features of any disclosed embodiment can be used in combination with each other without limitation. In addition, other features and advantages of the present disclosure will become apparent to those skilled in the art through a review of the detailed description and accompanying drawings. Various inventions have been described herein with reference to certain specific embodiments and examples. However, those skilled in the art will recognize that many variations are possible without departing from the scope and spirit of the invention disclosed herein, in that the invention as set forth in the following claims is intended to cover all variations and modifications of the disclosed invention without departing from the spirit of the invention. As used in this specification and claims, the terms "including" and "having" shall have the same meaning as the inclusive term "comprising."

[0059] Terms of degree (e.g., "about," "substantially," "generally," etc.) indicate structurally or functionally insignificant variations. As an example, when a term indicating a quantity includes a term of degree, the term of degree is interpreted to mean ±10%, ±5%, or +2% of the term indicating the quantity. As an example, when a term of degree is used to modify a shape, the term of degree indicates that the shape modified by the term of degree has the appearance of the disclosed shape. For example, the term of degree can be used to indicate that a shape has rounded corners instead of sharp corners, curved edges instead of straight edges, one or more protrusions extending therefrom, is rectangular, is the same as the disclosed shape, etc.

Claims

1. 1. A method for producing carbon fibers, comprising: subjecting the raw coal to a liquefaction process to form pitch or pitch resin; purifying the pitch or pitch resin to produce a mesophase pitch having a degree of anisotropy between 20% and 99%; mixing a thermoplastic blending additive into the mesophase pitch; subjecting the mesophase pitch to a low crystallinity spinning process to form raw fibers; subjecting the raw fibers to a fiber stabilization process using oxygen to produce stabilized carbon fibers; subjecting the stabilized carbon fibers to a carbonization process to form carbonized or calcined carbon fibers; A method comprising:

2. 2. The method of claim 1, wherein the pitch or pitch resin comprises an isotropic pitch.

3. 10. The method of claim 1, further comprising distilling coal tar to produce the pitch or pitch resin.

4. 10. The method of claim 1, further comprising heat treating coal tar to produce said pitch or said pitch resin.

5. 10. The method of claim 1, further comprising utilizing a machine learning enabled regression model to optimize parameters for producing the carbon fiber.

6. 10. The method of claim 1, further comprising mixing graphene into the mesophase pitch.

7. 10. The method of claim 1, further comprising stabilizing the raw fibers, wherein stabilizing the raw fibers comprises heating the pitch to a stabilization temperature of 280°C and holding the pitch at the stabilization temperature for 2 hours.

8. 2. The method of claim 1, wherein subjecting the raw fibers or the stabilized carbon fibers to the carbonization process comprises heating the raw fibers to a carbonization temperature of 1000°C and holding the raw fibers at the carbonization temperature for 30 minutes.

9. 10. The method of claim 1, wherein subjecting the raw fibers or the stabilized carbon fibers to the carbonization process comprises heating the raw fibers in an inert gas environment.

10. 10. The method of claim 1, wherein the carbon fibers have a tensile strength of 1.51 GPa to 1.64 GPa and an elastic modulus of 356 GPa.

Images