Carbon fiber production from asphaltene-based precursor material

Abstract

A method of treating a hydrocarbon material including asphaltenes includes heat treatment with a chemical additive such as ammonium sulphate, with subsequent solvent recovery of asphaltenes. The asphaltenes may be spun into precursor fibers or heat treated and then spun into precursor fibers. The precursor fibers may be stabilized and / or oxidized before carbonization into carbon fibers.

Description

CARBON FIBER PRODUCTION FROM ASPHALTENE-BASED PRECURSOR MATERIALField of the Invention

[0001] This disclosure relates to the fabrication of carbon fibers from asphaltene-based precursors derived from asphaltenes-rich hydrocarbon feedstocks.Background

[0002] Asphaltenes are defined operationally as the n-heptane-insoluble, toluene-soluble component of a carbonaceous material, and therefore do not have a specific chemical formula. It has been shown that asphaltenes have a distribution of molecular masses in the range of 400 u to 1500 u, but the average and maximum values are difficult to determine due to aggregation of the molecules in solution (Podgorski, D.C. (2013), Energy & Fuels, 27(3): 1268-1276).

[0003] Many naturally formed hydrocarbon materials are rich in asphaltenes. Crude oils components are customarily divided into saturate, aromatic, resin and asphaltenes (SARA) according to their polarizability and polarity. The saturate fraction consists of nonpolar material including linear, branched, and cyclic saturated hydrocarbons (paraffins). Aromatics, which contain one or more aromatic rings, are slightly more polarized. Both resins and asphaltenes have polar substituents but resins are miscible with heptane or pentane, whereas asphaltenes are insoluble in heptane or pentane.

[0004] The content of asphaltenes in conventional crude oils is usually less than 2%, but can be as high as 20% in heavy oil or bitumen, such as Alberta oilsands bitumen. When bitumen is refined to remove light molecular hydrocarbons, the content of asphaltenes can increase to about30%, for example, in vacuum distillation residues (VDR), also referred to as the bottom-of-the- barrel. These residues are conventionally used to produce asphalt, tar, paraffin wax, lubricating, heavy oils, pitch, and cokes.

[0005] Coal tar is produced as a byproduct when coal is carbonized to make coke or gas. When distilled, coal tar produces creosotes as a product and coal-tar pitch as a residue that can be rich in asphaltenes.

[0006] The extraction of asphaltenes from asphaltene-rich bitumen or residue is conventionally done by a solvent de-asphalting (SDA) process, in which asphaltene-rich feedstocks are mixed with paraffinic solvents which dissolve all components except the asphaltenes, which are precipitated and separated as a solid material.

[0007] It is known that bitumen or residue material such as heavy oil, refinery residues, or coal- derived asphaltene can be processed to produce pitch precursors to fabricate pitch-derived carbon fibers. Different from asphaltene precursors, pitch precursors include aromatic components present in the hydrocarbon feedstocks. The aromatic components in hydrocarbon feedstocks can be processed to produce isotropic pitch and mesophase pitch, which can then be processed into carbon fibers. Asphaltenes in these pitch-based feedstocks are undesirable lower the quality of pitch-derived carbon fibers.

[0008] Asphaltenes are a thermoplastic polymer, where single molecules are linked together by thermosensitive intermolecular attractive forces such as Van der Waals, dipole-dipole, and hydrogen bonding. The softening points and melting points of polymeric materials are generally related to their molecular mass, as well as the intra- and intermolecular forces within thepolymer. Melting points of polymers with a molecular weight of less than 100 mol / g are well below -50° C, while those with a molecular weight greater than 400 mol / g are higher than 50° C. At very low temperatures, thermoplastic polymers are very brittle and exhibit high Young’s modulus, owing to the rigidity of crystalline and amorphous molecules. As temperature rises, there is usually a sudden drop of their rigidity and Young’s modulus, because of activation of molecular movement of the amorphous chain segments. The temperature point at which Young’s modulus drops quickly is termed as the glass point, Tg, which depends on the amorphous / crystalline ratio. Between Tgand Tm(melting temperature) is the rubber-fluid state, known as the softening point, where the polymers are softened and can be pulled into filaments such as fibers.

[0009] The softening points of asphaltenes produced from solvent de-asphalting of Alberta oilsands bitumen is known to be in the range of 160° to 170° C, while those from metallurgic pitch, is well below 150° C. The Tmof these materials are usually about 30-40° C higher than their softening points, which is typically higher than their Tg.

[0010] Asphaltenes can be formed into precursor fibers either by a melt-spinning or wetspinning process. Melt-spinning produces precursor fibers by heating the precursors to temperatures about 30-40° C higher than their softening points and pressing them through nozzles of about 0.3-0.1 mm in diameter. A wet spinning process fabricates precursor fibers at room temperature using a solution of asphaltenes dissolved in a solvent. The precursor fibers are formed after the solvent is removed.

[0011] Precursor fibers can then be turned into carbon fibers with two sequential processes: an initial stage of stabilization / oxidation, and a second stage of carbonization at much highertemperatures, typically about 1000° to 2000° C, in an environment without oxygen. Optionally, carbonized fibers may then be graphitized, typically at temperatures in excess of 3000° C.

[0012] The process of stabilization / oxidation is performed at about 200° to 400° C in a gas including oxygen to cross-link the molecules to the point where the fibers do not melt or fuse together. The time required to achieve stabilization is sensitive to the nature of precursors. In general, the rate of reaction in stabilization becomes meaningful at temperatures above 200° C. At a stabilization lower than 200° C, the reaction is very sluggish and is not economical as a result. On the other hand, higher oxidation temperatures require much shorter time but can lead to overoxidation and poor mechanical properties of the resulting carbon fibers. Generally, a higher softening point requires shorter stabilization times. It is preferred that the softening points of precursor material to be in the range of 230° C to 280° C.

[0013] The softening points of petroleum materials are commonly increased by removing lighter fractions during thermal condensation, at temperatures in excess of 350° C. When temperature is increased, dehydrogenation, cross-linking, and condensation reactions occur, which releases gases such as hydrogen, steam, hydrogen sulphide and low molecular weight hydrocarbons. As a result, the remaining materials will possess a higher average molecular weight with a lower H / C ratio and a higher softening point.

[0014] The prior art discloses several methods developed for increasing softening points of isotropic pitch (Carbon Fibers, Technology (^Engineering, 3rd Edition, J-B Donnet, R. C. Bansal, 1998, page 45). These include reducing pressure thermal condensation, wiped filmevaporator, oxygen containing gas blow oxidation, sulphidation, additive methods and PVC methods.

[0015] Mesophase pitch is made by polymerizing isotropic pitch to a higher molecular weight with its melting point preferably controlled within 230° C to 280° C. Mesophase pitch forms a thermotropic crystal, which allows the pitch to become organized and form linear chains without the use of tension. Many methods are known, as summarized below, for either increasing or reducing the softening point and viscosity of mesophase pitch, depending on the type of raw pitch materials, including thermal modification, solvent modification, hydrogenation methods, and catalyst modifications using Lewis acids (e.g., A1C13, HF / BF3).

[0016] One of the major barriers hindering wider application of carbon fibers is the cost of the preparation of the feedstocks from which the fibers are produced. Most processes commonly require heating of a conventional pitch material at elevated temperatures over a period of several hours (For example, in Lewis et al U.S. Pat. No. 3,967,729, Singer U.S. Pat. No. 4,005,183, and Schulz U.S. Pat. No. 4,014,725), or post-processing filtration to remove additives and solids from reaction.

[0017] Similar to pitch-based precursors, asphaltenes-based precursors for carbon fiber production may not be satisfactory because of their low softening points, which requires uneconomically long periods of oxidation, up to 24 hours.

[0018] Therefore, there is a need in the art for alternative processes to produce precursor material for the fabrication of carbon fibers, which may mitigate at least some of the disadvantages of the prior art.Of the Invention

[0019] This disclosure relates to a process of treating asphaltene-rich hydrocarbon materials of a thermoplastic nature to produce asphaltene-based precursor material to be used for carbon fiber production. In some embodiments, the resulting asphaltene-based precursor material may comprise characteristics more desirable for fabrication of carbon fibers than asphaltenes obtained from a solvent-de-asphalting process.

[0020] In some embodiments, the asphaltene-based precursor material has a softening point of about 300° C, and exhibits excellent spinnability, and a reduced time for stabilization. The material can result in an increased yield of carbon fibers.

[0021] In some embodiments, the process comprises the removal of non-asphaltene molecular constituents such as saturate, aromatic, and resin components. In some embodiments, the removed components may be separated, for example by condensation as distillates, for further processing as hydrocarbons which are free of asphaltenes.

[0022] In one aspect, disclosed is a process of treating a hydrocarbon feedstock comprising asphaltenes, comprising the steps of:(a) mixing the hydrocarbon feedstock with a chemical additive comprising an ammonium-, sulfur- and / or oxygen-containing compound;(b) heating the mixture to a first temperature (Tl) up to about 480° C in a gas flowing environment of air, nitrogen, steam, an oxygen containing gas, or a combination thereof, stirring the mixture during heating, and holding the mixture at about Tl for a first period of time;(c) heating the mixture to a second temperature (T2) in a gas flowing environment of air, nitrogen, steam, an oxygen containing gas, or a combination thereof and holding the mixture at about T2 for a second period of time;(d) optionally, heating the mixture to a third temperature (T3) in a gas flowing environment of air, nitrogen, steam, an oxygen containing gas, or a combination thereof and holding the mixture at about T3 for a third period of time;(e) separating a liquid phase enriched in asphaltenes by filtering the treated mixture; and(f) producing precursor fibers.

[0023] Optionally, the liquid phase recovered from step (e) may be further treated to recover asphaltenes, such as by solvent recovery, and the asphaltenes may be used to fabricate precursor fibers. Therefore, in some embodiments, the liquid phase may be dissolved in a solvent, such as an n-alkane such as pentane or heptane, to precipitate asphaltenes as solids. These asphaltenes may then be spun into precursor fibers, or optionally may be heat treated and then spun into precursor fibers.

[0024] The precursor fibers may be further treated chemically and / or by oxidation prior to being carbonized and optionally graphitized to produce carbon fibers. The temperature required to melt spin the precursor material, the time and temperature required to stabilize the precursor fibers, and the yield of carbon fibers can be controlled through an adjustment of the amounts of chemical additives, the control of resin / asphaltene content in the precursors, and the treatment temperature and time and the type of gas environments being used during the treatment.

[0025] In the drawings, like elements are assigned like reference numerals. The drawings are not necessarily to scale, with the emphasis instead placed upon the principles of the present invention. Additionally, each of the embodiments depicted are but one of a number of possible arrangements utilizing the fundamental concepts of the present invention.

[0026] Figure 1 is a schematic overview of one embodiment of a process to produce precursor fibers from a hydrocarbon feedstock.Detailed Description of Preferred Embodiments

[0027] The present invention relates to a process to produce asphaltene-based precursor material for producing precursor fibers, which may be converted to carbon fibers.

[0028] Embodiments disclosed herein are not limited by the source of the hydrocarbon feedstock. The hydrocarbon feedstock can be any material of a thermoplastic nature that is liquid or becomes liquid upon heating, and comprise asphaltenes, preferably from about 5 % up to about 90 % by weight.

[0029] Hydrocarbon feedstock that can be treated in accordance with the present disclosure includes hydrocarbon material derived from coal, heavy oil or bitumen, such as, for example, coal tar, coal-tar pitch, fluid catalytic cracker (FCC) or residual catalytic cracker (RCC) slurry oil, vacuum distillation residues (VDR) or vacuum refinery residue (VRR), asphalt, petroleum pitch and the like. Preferably, the hydrocarbon feedstock has a high content of asphaltenes, greater than about 5 wt%.

[0030] In preferred embodiments, the hydrocarbon feedstock is treated to increase its softening point. Methods to increase the softening point of a hydrocarbon material are known, and are described in PCT Patent Application No. PCT / CA2021 / 000092 filed on 15 October 2021, the entire contents of which are incorporated herein by reference, where permitted.

[0031] Asphaltenes are a thermoplastic polymer and as such can be used to produce carbon fibers. As used herein, "asphaltenes" are non-polar and non-volatile hydrocarbon compounds present in crude oil such as heavy oil and bitumen, which are insoluble in an n-alkane solvent such as pentane or hexane and are soluble in aromatic solvents such as benzene or toluene. Asphaltene molecules tend to stick together in solution and comprise complex mixtures containing many individual chemical species. Individual asphaltene molecules can vary in the number of atoms contained in the structure, and the average chemical formula can depend on the source - exact molecular structures are difficult to determine. Given this limitation, asphaltenes comprise mainly of polyaromatic carbon ring units with oxygen, nitrogen, and sulfur heteroatoms, combined with trace amounts of heavy metals, particularly chelated vanadium and nickel, and aliphatic side chains of various lengths.

[0032] "Asphaltene-based precursor material" or "precursor material" is the material enriched in asphaltenes and produced by implementing embodiments of the processes disclosed herein. The asphaltenes have been treated to raise their softening point and to be suitable for carbon fiber production. This precursor material can be spun into precursor fibers, which can be carbonized to produce carbon fibers.

[0033] Therefore, in one aspect, a process comprises treating the hydrocarbon feedstock with a chemical additive and heating in at least one heating stage, which will increase the softening point or melting point of the resulting asphaltene-based precursor material, up to about 400° C, through one or a combination of the following process steps. Embodiments disclosed herein include a process which comprises any combination of steps described herein, or omits any optional or preferred step.Chemical Additive

[0034] Initially, the hydrocarbon feedstock is mixed with a chemical additive which serves to increase the softening point through cross-linking reactions in the precursor material, preferably without significantly altering the chemistry of the original hydrocarbon material. It is preferred to control dosage of chemical additives to avoid excessive cross-linking which can convert the material to a thermosetting plastic or coke. In some embodiments, these chemical additives will decompose into intermediate products that catalyze the process of cross-linking. The intermediate products from the decomposition of additives can be further decomposed into gaseous phases that can be easily removed out of the reaction system. As a result, the chemistry of hydrocarbon materials is not altered through chemical bonding with elements of the additives.

[0035] In some embodiments, the chemical additive comprises an ammonium-, sulfur- and / or oxygen-containing-compound. The chemical additive may comprise (NEk^SC (ammonium sulfate), (NH4)2S2C>8 (ammonium persulfate), (NH4)2S2C>3 (ammonium thiosulfate), (NELf^SCh (ammonium sulfite), NH4HSO4 (ammonium hydrogen sulfate), NH4HSO3 (ammonium hydrogen sulfite), and (NH4)2S (ammonium sulfide), or combinations thereof. At elevated temperatures,these ammonium-, sulfur- and oxygen-containing-compounds decompose into such compounds as HSO42', HSO3', S2O?2', S20s2', S2O32', SOs2' containing compounds, SO2, or S, or combinations of such compounds. These decomposition products serve as catalysts, which can cause cross-linking and / or vulcanization of hydrocarbon feedstock material to alter the hydrocarbon feedstock material to have thermoplastic properties and an increased softening or melting point. The vulcanization or cross-linking can also lead to the hydrocarbon feedstock being converted into elastic (rubber), or thermosetting compounds.

[0036] Ammonium sulphate is one preferred chemical additive, which thermally decomposes according to reactions (1) to (3):(NH4)2SO4 = NH4HSO4 +NH3 (1)2 NH4HSO4 = (NH4)2S2O7 + H2O (2)3(NH4)2S2O7= 2NH3+ 2N2 + 6SO2 + 9H2O (3)The overall reaction is 3(NH4)2SO4 = 4NH3 + N2 +3SO2 + 6H2O (4)

[0037] The intermediate products of the reaction include pyrosulfate (S2O?)2' and SO2. These compounds are known to cause vulcanization of a polymer compound (rubber) to an elastic and final end-use product. The above-described reactions occur within a range of temperature from about 250° C to 500° C, which coincides with the temperature range in which depolymerization, cross-linking, chain cleavage, and cracking of hydrocarbon materials can occur. The addition of (NHfkSC or other ammonium-, sulfur- and / or oxygen-containing-compounds can occur atroom temperature or above room temperature, for example, when the hydrocarbon feedstock is at a temperature above room temperature from a previous processing stage.

[0038] The dosage of the chemical additive can range from 0% to 20% (by weight) of the hydrocarbon feedstock to be treated, depending on the initial softening point or melting point of the hydrocarbon feedstock to be treated, the treatment temperature, the gaseous environment, the desired increase in softening point and the desired final rheological properties of the treated materials.

[0039] Further products that result from the decomposition of (NHTkSC or other ammonium-, sulfur- and oxygen-containing-compounds, outside of those listed above are gaseous substances that preferably do not chemically react with hydrocarbon materials being treated.Heat Treatment

[0040] After, before or during mixing with the chemical additive, the feedstock is heated to a first temperature (Tl) and held and stirred for a suitable period of time with a flowing gas environment. The temperature of the hydrocarbon feedstock mixture is then adjusted to a second temperature (T2) which may lower or higher than Tl, and held for a second suitable period of time, again with stirring under a flowing gas environment. Preferably, the stirring is continuous. Optionally, the temperature of the mixture may then be adjusted to a third temperature (T3) which may be lower or higher than T2, and held for a third suitable period of time, again with continuous stirring under a flowing gas environment.

[0041] The treatment temperatures Tl, T2 and T3 must be higher than the thermal decomposition temperature of the chemical additives being added. However, treatment ispreferably performed at a temperature which minimizes or avoids carbonization or coke formation, such as a temperature below 480° C.

[0042] In some embodiments, the holding time for T1 is between about 1 hour to about 4 hours, the holding time at T2 is between about 0 minutes to about 3 hours, and the holding time at T3 is between about 0 minutes to about 3 hours.

[0043] Tl, T2 and optional T3 of treatment are temperatures at which decomposition of the chemical additive takes place, and / or they can be the temperatures at which cross-linking or vulcanization reactions of hydrocarbon materials occur, and / or they can be the temperatures at which reactions between the flowing gases and the hydrocarbon materials take place. It is also possible for all of these events to take place at the same temperature, which can be second or third temperature of the treatment.

[0044] The mixing step can occur at an ambient temperature before the step of heating, or the mixing step can occur after the hydrocarbon feedstocks are heated in the heating step. Stirring can occur after mixing and heating, or stirring can occur during any one or both of mixing and heating. As such, the method can be carried out as separately timed steps, or in different combinations of mixing, heating and stirring.

[0045] In preferred embodiments, processing temperature and time are controlled to control the rate of reaction, which affects the processability of the precursor material for melt-spinning and other activated carbon processing.

[0046] The flowing gas environment in the reactor may comprise air, pure nitrogen, pure steam, an oxygen-containing gas, or combinations thereof. The gas environment serves to modify theinitial hydrocarbon feedstock by attaching to chains of the hydrocarbons and making the chains longer, by cleaving side chains, or cracking heavier molecules when needed. Flowing gas also reduces the incidence of material getting deposited or stuck onto the inner sides of the treatment equipment. Depending on the desired properties of hydrocarbon materials after treatment, the selection of the type of gas streams, the temperature and the residence time can be varied during treatment. The selection of gas environments may change the effectiveness of the chemical additive in achieving cross-linking. It may also affect the alteration of chemical composition of the hydrocarbon feedstock being treated. For example, the gas may facilitate chain cleavage to remove certain side chains or molecular groups, and may facilitate dehydrogenation, leading to a decrease of the H / C ratio, which may be desired or necessary for certain applications of the treated hydrocarbon feedstock. The effectiveness of the above described alteration of chemical composition of the initial hydrocarbon materials is dependent of the type of processing gases.

[0047] It is preferred to continuously stir the mixture of hydrocarbon feedstock and chemical additive while heating and holding the mixture. Stirring improves heat transfer between the feedstock and the reactor wall which is being externally heated, mixing of additives with the feedstock, increases evaporation of volatile components, and encourages mixing of the gaseous medium with the hydrocarbon feedstock.

[0048] The heating of a mixture of the hydrocarbon feedstock with a chemical additive with a flowing gas stream combines various processes of molecular modification (de-polymerization, cross-linking, cleavage and cracking) into a set of single process conditions in a single treatment, which conditions which can be tailored to meet various requirements of the final products.

[0049] The chemical additives thermally decompose to gaseous products, thus making minimum changes to the chemistry of original hydrocarbon feedstock and which facilitates its removal from the hydrocarbon feedstock.

[0050] After at least one heat treatment step with a chemical additive, the hydrocarbon feedstock will have less aliphatic hydrogen present. The resulting higher aromaticity is desirable when using the treated feedstock as a precursor material for making carbon fibers.

[0051] In alternative embodiments, other chemical agents could be added before and / or during each of the stepwise heat treatments for purposes other than the control of softening points and asphaltene content. For example, chemical agents could be added to produce activated carbon fibers, adding solids of any physical form to change the chemical, mechanical, electrical, thermal, and biological properties of the hydrocarbon feedstock. In some embodiments, the chemical agents may comprise a salt such as potassium carbonate, potassium bicarbonate and potassium chloride, lithium acetate, lithium citrate, lithium carbonate, lithium bicarbonate, lithium hydrogen citrate, lithium chloride, sodium oxalate, sodium hydrogen phthalate, sodium hydrogen phthalate, sodium acetate, sodium citrate, sodium carbonate, sodium bicarbonate, sodium hydrogen citrate, sodium chloride, potassium oxalate, potassium hydrogen phthalate, potassium hydrogen phthalate, potassium acetate, potassium citrate, potassium hydrogen citrate, and derivatives thereof, and combinations thereof.

[0052] The asphaltene-based precursor material resulting from the chemical treatment at an elevated temperature is a thermoplastic material which is a liquid at an elevated temperature, but may contain various solid impurities. The solid impurities are preferably removed through usinga liquid-solid separation technique, such as physical, mechanical, chemical, magnetic or electromagnetic methods, or combinations thereof. The precursor material can be dissolved in or mixed with a solvent to liquefy or reduce the viscosity of the thermoplastic precursor material, which can facilitate liquid / solid separation.

[0053] Physical methods include sedimentation, centrifugation or decanting of solid particles that usually have higher density to the bottom of the resulting product and the top portion of the product is removed for further separation.

[0054] Mechanical methods include filtration, which preferably involves a pressure differential to force the liquid to pass through a filter membrane, leaving the solids on the filter and a liquid filtrate. The pressure differential may be created by pressurizing the feedstock above the filter or depressurizing the chamber below the filter (vacuum separation). In some embodiments, the precursor material is filtered through a porous membrane with a pore sizes ranging from 0.1 pm to 500 pm, under pressure up to 100 psi.

[0055] Magnetic and / or electromagnetic methods may be used to remove metal species, usually metal-containing compounds, that are magnetic or can be magnetized by electric current.

[0056] Chemical methods include the addition of chemicals to react with the solid particles to form new compounds that can be easily separated by other methods. Another chemical method involves the use of a solvent to dissolve the thermoplastic portion of the solid feedstock, including asphaltenes, leaving the insoluble particles to be removed by other methods from the bulk material. The precursor material may be recovered by removing the solvent, such as through evaporation. Additionally, or alternatively, a solvent could also be added to precipitateasphaltenes as insoluble to the solvents and to remove soluble components to increase the asphaltene concentrations in the resulting products.

[0057] The asphaltene-based precursor material may be cooled during or after filtration or solids rejection. The end temperature of cooling can be room temperature or an intermediate temperature between the room temperature and the last stage of heating temperature.

[0058] The precursor material remaining after solids removal may then be used to produce precursor fibers, such as by melt-spinning, wet spinning, air-blowing, electrostatic spinning, or a similar method known to those skilled in the art.

[0059] The staged heat treatment with a chemical additive described above produces an asphaltene-based precursor material, with an asphaltene content up to 95%. The softening points of this precursor material can be adjusted for the purpose of enhancing their ability to extrude fibers, processing the precursor fibers more effectively in terms of reducing energy, GHG emissions, and achieving higher mechanical properties.

[0060] In alternative embodiments, the asphaltene-based precursor material, after solids removal, may be further processed to obtain purified asphaltenes, such as by solvent precipitation with n- pentane, hexane or heptane. The solute comprises n-alkane soluble components and can be discarded or recovered for another purpose. The precipitated asphaltenes may then be used for melt spinning into precursor fibers. Optionally, the precipitated asphaltenes may be subjected to one or more stages of heat treatment as described above, preferably without any additional chemical additives.

[0061] In some embodiments, precursor material recovered from different stages of heat treatment may be combined and mixed to produce a mixed precursor material for precursor fiber production. For example, spinnability and / or processability may be improved. In some embodiments, the precursor material may require less time and lower temperature for oxidation and carbonization. In some embodiments, mechanical properties may be improved, for example, higher tensile strength, higher modulus and / or higher elongation before fracture may be achieved.

[0062] The precursor fibers obtained may be stabilized by soaking in an aqueous solution which coats the green precursor fibers and prevents cohesion between adjacent green fibers. The aqueous solution may comprise hydrochloric acid, nitric acid, sulfuric acid, phytic acid, potassium nitrate, potassium chloride, their derivatives, and / or mixtures thereof. The aqueous solution can be concentrated or dilute, a dilution can be in the range of 1 wt.% to 100 wt.% of concentrated solution. The soaking time may range from 1 second to 100 minutes, preferably in the range from 5 seconds to 10 minutes.

[0063] In some embodiments, the stabilized precursor fibers can also be subjected to the process of oxidative stabilization, which is achieved by heating the precursor fiber which has been stabilized by acid soaking to temperatures, for example from about 200° to about 350° C, for a heating period of 1 minute to about 2 hours.

[0064] The stabilized and / or oxidized precursor fibers may then be carbonized and optionally graphitized as is known in the art.

[0065] By way of further description of the process of the present disclosure, reference may be made to the following examples, which are intended to exemplify certain elements of the claimed invention, not limit them. Unless otherwise indicated, all parts and percentages are by weight.

[0066] 20 kg of vacuum refinery residues (VRR) as hydrocarbon feedstock was mixed with different amounts of (NH^SC solid powder, ranging from 3 to 8 wt. % of vacuum refinery residues, as listed in Table 1. The VRR feedstock was a viscous liquid at room temperature and its softening point was below room temperature, but not measured. The mixture was placed in a sealed cylindrical reactor and stirred at a rate of 30 RPM (revolutions per minute) as the mixture was treated with the following sequential steps: a) 1st step of heating to 350°C and held at 350° C for 120 minutes with a flow of N2 gas; b) 2nd step of heating to 420°C and held at 420°C for 60 minutes with a flow of N2 gas; c) 3rd step of heating to 435°C and held at 435°C for 75 minutes with a flow of steam, and d) filtering of the resulting hydrocarbons before cooling the liquid filtrate to room temperature with a flow of nitrogen gas.

[0067] The liquid filtrate comprised asphaltene-based precursor material, which solidified upon cooling to room temperature. This precursor material (Samples A-E) was used to produceprecursor fibers through melt-spinning. The precursor yields and the temperature of meltspinning as affected by different dosage of (NHThSC are listed in Table 1.Table 1 Effect of chemical dosage on the melt-spinning temperature of vacuum refinery residue after the four steps of treatment in Example 1.Example 2

[0068] Precursor Sample C in Table 1, which was produced following the steps in Example 1, was dissolved in pentane with a ratio of 20 liters of pentane to 1 kg of solid Sample C, to precipitate solids insoluble in pentane. The obtained solids were placed in a sealed cylindrical reactor and were then heated to different temperatures as listed in Table 2 for 120 minutes. Stirring at a speed of 30 RPM and a flow of N2 gas were maintained during the treatment. The resulting material (Samples F-J) was used as precursor material to produce precursor fibers through melt-spinning. The temperature of melt-spinning substantially increased depending on the temperature of treatment, as compared to that of Sample C in Table 1 of Example 1Table 2 The melt-spinning temperature of resulting samples after further treatments as described in Example 2Example 3

[0069] Sample C in Table 1, which produced following the steps in Example 1, was dissolved in pentane with different ratios of pentane over Sample C, as listed in Table 3, to produce an asphaltene precipitate. The obtained asphaltene solids were placed in a sealed cylindrical reactor and were then heated to 325° C and held at the temperature for 120 minutes. Stirring at a speed of 30 RPM and a flow of N2 gas were maintained during the treatment. The resulting material was used as precursor material to produce precursor fibers through melt-spinning. The temperature of melt-spinning has been substantially increased depending on the ratio of pentane over Sample C, as compared with that of Sample C in Table 1 of Example 1.Table 3 The melt-spinning temperature of Sample C after further treatments as described in Example 3Example 4

[0070] Samples A to E in Table 1 were further treated following the steps for Sample I of Table 2 in Example 2 (pentane purification and heat treatment at 325° C for 2 hours). The resulted new samples were used as precursor material to produce precursor fibers through melt-spinning. The temperature of melt-spinning of resulted samples are substantially higher than those of SamplesA to E in Table 1 of Example 1Table 4 The melt-spinning temperature of resulted new samples produced by steps described in Example 4Example 5

[0071] Sample K in Table 3 of Example 3 (5: 1 ratio of pentane) was further treated with the conditions listed in Table 5. The resulted new samples (Samples R and S in Table 5) were used as precursors to produce precursor fibers by melt-spinning. The temperature of melt-spinning of resulted samples are substantially higher than those of Sample K of Table 3 in Example 3.Table 5 The melt-spinning temperature of resulted new samples produced by steps described in Example 5Example 6

[0072] The precursor material prepared according to the conditions for Sample I in Table 3 fromExample 3 was used to fabricate precursor fibers through melt-spinning under the conditions listed in Table 6. The precursor was wound into precursor fibers with diameters listed in Table 6,and the variation of resulting precursor fibers was less than 10% of the average diameter of the precursor fibers.Table 6 The melting conditions and the resulting precursor fibers of Sample I in Table 3Example 7

[0073] The precursor material prepared according to the conditions for Sample I in Table 3 of Example 3 was used to determine the condition of stabilization of precursor fiber. Precursor fibers were stabilized in a furnace with flowing hot air. About 10 grams of precursor fibers obtained by melt-spinning Sample I were soaked in various diluted HNO3 solutions with concentrations (vol%) listed in Table 7 for one minute prior to stabilization treatment. The acid- soaked precursor fibers were then dropped directly in the stabilization furnace pre-heated to 200° C, and further heated to 280° C at a heating rate of 3.0° C / min and held at 280° C for 50 minutes. The samples were taken out of the furnace at the end of the hold period and weighed. The weight changes after stabilization are recorded and listed in Table 7. Weight gain is an indication of the degree of oxidation. The highest weight gain is obtained when the concentration of HNO3 solution is 15%. Preferably, oxidation weight gain is in the range of about 2% to about 8 % and in some embodiments, 3% to about 5%.Table 7 Weight changes after stabilization of the precursor fibers with and without acid soaking.Example 8

[0074] The precursor material prepared according to the conditions for Sample I in Table 3 of Example 3 was used to determine the effect of soaking time on the stabilization of precursor fiber. Stabilization is achieved by heating precursor fibers in a furnace with hot air. About 10 grams of precursor fibers obtained by melt-spinning Precursor Sample I was soaked in 15% (vol) HNO3 solution for different periods of time as listed in Table 8. The acid-soaked precursor fibers were then dropped directly in the stabilization furnace pre-heated to 200° C, and further heated to 280° C at a heating rate of 3.0° C / min and held at 280° C for 50 minutes. The samples were taken out of the furnace at the end of the hold period for weight measurements. The weight changes after stabilization are recorded and listed in Table 8. The highest weight gain is obtained when the soaking time is at 1 minute.Table 8 Effect of acid soaking time on weight changes after stabilization of the precursor fibersExample 9

[0075] The precursor material prepared according to the conditions for Sample I in Table 3 of Example 3 was used to determine the effect of stabilization hold temperature and time on the stabilization of precursor fibers. Stabilization is achieved by heating precursor fibers in a furnace with hot air. About 10 grams of precursor fibers obtained by melt-spinning Precursor Sample I was soaked in 15% (vol) HNO3 solution for 1 minute. The acid-soaked precursor fibers were then dropped directly in the stabilization furnace pre-heated to 200° C, and further heated to different temperatures at a heating rate of 3.0° C / min and held at the temperature for different length of time, as detailed in Table 9. The samples were taken out of the furnace at the end of the hold period and weighed. The weight changes after stabilization are recorded and listed in Table9.Table 9 Effect of stabilization temperature and time on weight changes after stabilization of the precursor fibers.Example 10

[0076] Stabilized precursor fibers from Samples I-4-B, I-4-E, and I-4-H listed in Table 9 were carbonized to produce carbon fibers. About 5 grams of the stabilized fibers were carbonized in a furnace with a flow of N2. The samples were heated to 1200° C at a rate of 5° C / min and held at the temperature for 2 hours. The samples were taken out of the furnace after the furnace was cooled to room temperature. The weight changes after carbonization were recorded and the yield of carbonized / carbon fibers is listed in Table 10, which was calculated as a weight percentage of the precursor fiber before acid soaking. The net yield of carbon fibers is as high as 70%.Mechanical properties of the resulting carbon fibers are also determined and included in Table 10.Table 10 Mechanical properties and yield of carbon fibers fabricated from vacuum refinery residues derived precursors.Example 11

[0077] 2 kg of Sample K from Example 3 was added with 40 liters of pentane to reject asphaltenes. The obtained asphaltenes were dried and weighed to determine the concentration of asphaltenes in Sample K, which was determined to be 76% (wt). 2 kg of Sample K was used as feedstock and mixed with 3.5 wt.% (NHTfiSC powder. The mixture was treated following the conditions listed in Table 11. Samples T and U were produced by treating the mixture with twosteps of heating, while Sample U was treated with one additional step of heating as listed in Table 11. Both Sample T and U were also filtered with a removal of potential solid particles larger than 0.5 pm at the end of the treatments listed in Table 11. The treatments and filtration led to an increase of spinning temperature and an improvement in winding speed of the precursor fibers and mechanical properties of resulted carbon fibers, as compared to Sample K.Table 11 Effect of treating conditions on the spinning behaviour of a hydrocarbon feedstock with high asphaltenes content.Example 12

[0078] A vacuum refinery residue feedstock different from that in Example 1 was used as the feedstock hydrocarbon material, having a lower softening point than that used in Example 1. 20 kg of this feedstock was mixed with different amount of (NElfkSC powder, ranging from 0 to 6 wt. % of vacuum refinery residues, as listed in Table 12. The same processing steps and procedures as those in Example 1 were used to process the current mixture. The precursor yields and the temperature of melt-spinning as affected by different dosage of (NHTkSC are listed in Table 12. Lower yields but high melt-spinning temperatures were measured for this feedstockthan the vacuum refinery residues tested in Example 1. Because lower softening points of the current vacuum refinery residues, more components with smaller molecules were evaporated, leading to lower product yield but higher spinning temperature.Table 12 Effect of chemical dosage on the melt-spinning temperature of a different vacuum refinery residue feedstock after the same processing steps and procedures as described in Example 1.Interpretation

[0079] The corresponding structures, materials, acts, and equivalents of all means or steps plus function elements in the claims appended to this specification are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed.

[0080] References in the specification to "one embodiment", "an embodiment", etc., indicate that the embodiment described may include a particular aspect, feature, structure, or characteristic, but not every embodiment necessarily includes that aspect, feature, structure, or characteristic. Moreover, such phrases may, but do not necessarily, refer to the same embodiment referred to in other portions of the specification. Further, when a particular aspect, feature, structure, or characteristic is described in connection with an embodiment, it is within the knowledge of one skilled in the art to affect or connect such module, aspect, feature, structure, or characteristicwith other embodiments, whether or not explicitly described. In other words, any module, element or feature may be combined with any other element or feature in different embodiments, unless there is an obvious or inherent incompatibility, or it is specifically excluded.

[0081] It is further noted that the claims may be drafted to exclude any optional element. As such, this statement is intended to serve as antecedent basis for the use of exclusive terminology, such as "solely," "only," and the like, in connection with the recitation of claim elements or use of a "negative" limitation. The terms "preferably," "preferred," "prefer," "optionally," "may," and similar terms are used to indicate that an item, condition or step being referred to is an optional (not required) feature of the invention.

[0082] The singular forms "a," "an," and "the" include the plural reference unless the context clearly dictates otherwise. The term "and / or" means any one of the items, any combination of the items, or all of the items with which this term is associated. The phrase "one or more" is readily understood by one of skill in the art, particularly when read in context of its usage.

[0083] The term "about" orcan refer to a variation of ± 5%, ± 10%, ± 20%, or ± 25% of the value specified. For example, "about 50" percent can in some embodiments carry a variation from 45 to 55 percent. For integer ranges, the term "about" orcan include one or two integers greater than and / or less than a recited integer at each end of the range. Unless indicated otherwise herein, the term "about" oris intended to include values and ranges proximate to the recited range that are equivalent in terms of the functionality of the composition, or the embodiment.

[0084] As will be understood by one skilled in the art, for any and all purposes, particularly in terms of providing a written description, all ranges recited herein also encompass any and all possible sub-ranges and combinations of sub-ranges thereof, as well as the individual values making up the range, particularly integer values. A recited range includes each specific value, integer, decimal, or identity within the range. Any listed range can be easily recognized as sufficiently describing and enabling the same range being broken down into at least equal halves, thirds, quarters, fifths, or tenths. As a non-limiting example, each range discussed herein can be readily broken down into a lower third, middle third and upper third, etc.

[0085] As will also be understood by one skilled in the art, all language such as "up to", "at least", "greater than", "less than", "more than", "or more", and the like, include the number recited and such terms refer to ranges that can be subsequently broken down into sub-ranges as discussed above. In the same manner, all ratios recited herein also include all sub-ratios falling within the broader ratio.

Claims

CLAIMS1. A process of treating a hydrocarbon feedstock comprising asphaltenes, comprising the steps of:(a) mixing the hydrocarbon feedstock with a chemical additive comprising an ammonium-, sulfur- and / or oxygen-containing-compound;(b) heating the mixture to a temperature (Tl) up to about 480° C in a gas flowing environment of air, nitrogen, steam, an oxygen containing gas, or a combination thereof, and stirring the mixture during heating, and holding the mixture at about Tl for a first period of time;(c) heating the mixture to a second temperature (T2) in a gas flowing environment of air, nitrogen, steam, an oxygen containing gas, or a combination thereof and holding the mixture at about T2 for a second period of time;(d) optionally, heating the mixture to a third temperature (T3) in a gas flowing environment of air, nitrogen, steam, an oxygen containing gas, or a combination thereof and holding the mixture at about T3 for a third period of time;(e) separating a liquid phase enriched in asphaltenes by filtering the treated mixture; and(f) producing precursor fibers.

2. The process of claim 1 wherein Tl, T2 and T3 are between about 300° C to about 450° C.

3. The process of claim 1 or 2 wherein T1<T2 and / or T1<T3.

4. The process of any one of claims 1 to 3, wherein the first period of time is between about 1 hour to about 4 hours, the second period of time is between about 0 minutes and 3 hours, and / or the third period of time is between about 0 minutes and 3 hours.

5. The process of any one of claims 1-4, wherein T1 is about 300° C to about 350° C, for about 90 minutes to about 180 minutes, T2 is about 350° C to about 450° C for about 30 minutes to about 120 minutes, and / or T3 is about 350° C to about 450° C for about 30 minutes to about 120 minutes.

6. The process of claim 5 wherein T1 is about 350°C for about 120 minutes with a flow of N2 gas, T2 is about 420° C, for about 60 minutes with a flow of N2 gas; and T3 is about 435°C, for about 75 minutes with a flow of steam.

7. The process of any one of claims 1 to 6, wherein the chemical additive comprises (NHT SC (ammonium sulfate), (NH4)2S20s (ammonium persulfate), (NH4)2S2C>3 (ammonium thiosulfate), (NH4)2SO3 (ammonium sulfite), NH4HSO4 (ammonium hydrogen sulfate), NH4HSO3 (ammonium hydrogen sulfite), and (NH4)2S (ammonium sulfide), or combinations thereof8. The method of claim 7 wherein the chemical additive comprises (NH4)2SO4.

9. The process of claim 7 or 8 wherein the chemical additive is added in an amount between about 1% and about 15% by weight of the hydrocarbon feedstock.

10. The process of claim 9 wherein the chemical additive is added in an amount between about 3% and 8% by weight of the hydrocarbon feedstock.

11. The process of any one of claims 1 to 10, further comprising the step of rejecting solids from the liquid phase from step (e), such as by filtering the liquid phase through a filter having a pore size between about 0.1 um to about 500 um.

12. The process of any one of claims 1 to 11, comprising the further step of recovering asphaltenes from the product of step (e), and producing precursor fibers from the asphaltenes.

13. The process of claim 10 wherein the asphaltenes are recovered by precipitation by mixing the product of step (e) with n-alkane solvent, such as pentane, in a ratio of about 5: 1 to about 20: 1 litres / kg.

14. The process of claim 13 wherein the precipitated asphaltenes are subjected to at least one stage of heat treatment between about 300° C to about 380° C, for between about 0 minutes to about 3 hours, with or without a chemical additive.

15. The process of any one of claims 1 to 11, wherein the hydrocarbon feedstock comprises a hydrocarbon material derived from coal, heavy oil or bitumen, such as, for example, coal tar, coal-tar pitch, fluid catalytic cracker (FCC) or residual catalytic cracker (RCC) slurry oil, vacuum distillation residue, vacuum refinery residue, asphalt, petroleum pitch; or asphaltenes recovered from the product of step (e) of claim 1.

16. The process of claim 15, wherein the hydrocarbon feedstock comprises asphaltenes precipitated from product of step (e), and the asphaltenes are mixed with (NH^SCh prior to heat treatment at Tl, T2 and T3.

17. The process of any one of claims 1 to 16, wherein the precursor fibers are chemically stabilized or oxidatively stabilized prior to carbonization.

18. The process of claim 17 wherein the precursor fibers are soaked in a nitric acid solution, between about 0% to about 25% vol concentration, for between about 0 minutes and 30 minutes.

19. The process of claim 18 wherein the nitric acid solution has a concentration between about 5% and 25%.

20. The process of claim 18 wherein the soaked precursor fibers are heat treated at between about 200° C to about 350° C, preferably 240° C to about 320° C, for between about 1 minute to about 120 min.

21. A carbon fiber produced by a process comprising the steps of any one of claims 1 to 20.