Method for producing mesophase fibers for carbon fiber production using supercritical carbon dioxide

Abstract

To provide a method for producing a carbon fiber.SOLUTION: The method for producing a carbon fiber, comprises the steps of: contacting a coal-derived material with a mixture of a supercritical fluid solvent and a first cosolvent to remove at least some of a soluble component from the coal-derived material from and obtain an insoluble coal-derived fraction; separating the mixture of the supercritical fluid solvent and the first cosolvent from the insoluble coal-derived fraction; mixing the insoluble coal-derived fraction with the supercritical fluid to obtain a mixture of the supercritical fluid and an insoluble fraction; and separating the supercritical fluid from the insoluble fraction to obtain the carbon fiber.SELECTED DRAWING: Figure 8

Description

Detailed Description of the Invention

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application was filed as a PCT International Patent Application on March 17, 2020, and claims the benefit of U.S. Provisional Patent Application No. 62 / 820,162, filed March 18, 2019, and also claims priority to U.S. Patent Application No. 16 / 532,334, filed August 5, 2019, which applications are incorporated herein by reference.

[0002] [Introduction] Pyrolysis refers to the thermochemical decomposition of organic materials at high temperatures in the absence of oxygen. Different pyrolysis products can be obtained depending on how the pyrolysis system is configured and processed. Systems and methods exist for producing coal tar by pyrolysis of coal using supercritical carbon dioxide. In some of these systems and methods, the resulting coal tar product contains at least some mesophase material that can be used to create mesophase pitch. Mesophase pitch refers to the anisotropic liquid crystal phase of pitch characterized by pre-graphitic order, high density, and a high softening temperature. Mesophase pitch can be used to produce high-performance carbon fibers.

[0003] Improving mesophase pitch for carbon fiber production using supercritical carbon dioxide Embodiments of methods for improving mesophase pitch for carbon fiber production using supercritical carbon dioxide are described. The methods improve the relative quantity and quality of mesophase pitch in a feedstock, such as coal tar, that already contains at least some mesophase pitch. One particular method includes performing an sCO2 / toluene extraction on the coal tar to obtain a toluene-insoluble fraction of the coal tar, mixing the toluene-insoluble fraction with sCO2 to obtain an sCO2 / toluene-insoluble fraction mixture, and extruding the sCO2 / toluene-insoluble fraction mixture, thereby separating the sCO2 from the toluene-insoluble fraction and obtaining mesophase pitch fibers.

[0004] BRIEF DESCRIPTION OF THE DRAWINGS The following drawings that form part of this application are intended to illustrate the described technology and are not meant to limit in any way the scope of the invention as claimed, which scope shall be based on the claims appended hereto.

[0005] FIG. 1 shows a simplified embodiment of a pyrolysis process that, at a high level, improves the relative amount of pitch produced from a given feedstock.

[0006] FIG. 2 shows a more detailed embodiment of the pyrolysis process of FIG.

[0007] FIG. 3 shows an example of a system suitable for the pitch production method described above.

[0008] FIG. 4 shows a process flow diagram of a batch embodiment of a flexible pyrolysis system that can be adjusted to vary the pyrolysis products obtained from a given feedstock.

[0009] 5A-5C illustrate the experimental performance of one embodiment of the system shown in FIG.

[0010] FIG. 6 illustrates an embodiment of a broad process for pyrolyzing a carbonaceous feedstock with CO2 to obtain reaction products.

[0011] FIG. 7 is a more detailed embodiment of a method for pyrolyzing coal using supercritical CO2.

[0012] FIG. 8 illustrates an embodiment of a method for improving mesophase pitch for carbon fiber production using supercritical carbon dioxide.

[0013] Detailed Description Before systems and methods for preparing improved mesophase pitch for carbon fiber production using supercritical carbon dioxide are disclosed and described, it should be understood that the present disclosure is not limited to the specific structures, process steps, or materials disclosed herein and extends to equivalents thereof, as recognized by those skilled in the art. It should also be understood that the terminology used herein is used solely for the purpose of describing particular embodiments and is not intended to be limiting. As used herein, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise; thus, for example, a reference to "one ("a") lithium hydroxide" should not be construed as a quantitative or source limitation; a reference to "one ("a") step" can include multiple steps; a reference to the "product" or "products" of a reaction should not be construed as all of the products of the reaction; and a reference to "reacting" can include reference to one or more of such reaction steps. Thus, a reacting step can include multiple or repeated reactions of similar materials to produce the identified reaction product.

[0014] "Pitch" refers to a collection of hydrocarbons, including polyaromatic hydrocarbons, that can be produced from coal, wood, and other organic materials. Pitch is characterized by a high (>80 wt%) elemental carbon composition, a high concentration of polycyclic aromatic hydrocarbons (PAHs), and a softening temperature that can range from 100°C to over 250°C (measured using Vicat method ASTM-D 1525). Generally, pitches suitable for carbon fiber are capable of forming highly concentrated, anisotropic mesophase pitches. This can be used as a substrate for coatings and paints, in roofing and paving, and as a binder in asphalt products. Pitch can also be used to make carbon fiber, as discussed in more detail below.

[0015] Although the following systems and methods are presented with respect to supercritical carbon dioxide embodiments, any supercritical fluid (e.g., carbon dioxide, water, methane, nitrous oxide, ethane, propane, ethylene, propylene, methanol, ethanol, acetone, etc.) or mixture of supercritical fluids may be used.

[0016] Figure 1 shows a simplified embodiment of a pyrolysis process that, at a high level, improves the relative amount of pitch produced from a given feedstock. In the illustrated process 100, a carbonaceous feedstock material and water are subjected to a two-stage pyrolysis. The water may be present as moisture content within the feedstock. Alternatively, additional water may be added to the feedstock prior to or at some point during pyrolysis.

[0017] The first stage is a low-temperature pyrolysis step (operation, process, work, operation) 102 to remove C1-C4 gases from the feedstock. In this stage 102, pyrolysis occurs at a lower temperature (e.g., 150-350°C at 7-30 MPa). The feedstock is heated to and held at the first-stage temperature to produce and remove C1-C4 gases from the feedstock. In one embodiment, gases in the pyrolysis chamber are monitored, and once the C1-C4 gas concentrations begin to level off based on operator criteria, a high-temperature pyrolysis operation 104 is performed.

[0018] The first stage temperature may be selected based on prior knowledge of the feedstock characteristics or may be automatically determined based on real-time analysis of the pyrolysis reaction and the products produced. Depending on the embodiment, the first stage temperature may have a lower range selected from 150°C, 175°C, 200°C, 225°C, 250°C, 275°C, 300°C, and 325°C, and an upper range selected from 175°C, 200°C, 225°C, 250°C, 275°C, 300°C, 325°C, and 350°C, such that any combination of the aforementioned lower and upper ranges may be used.

[0019] In the second stage pyrolysis step 104, the temperature is increased to 350-550°C at 7-30 MPa, e.g., 7-12 MPa, and held at that temperature for a period sufficient to produce pitch. As with the first stage, the amount of pyrolysis products produced will level off over time as the system reaches equilibrium, and the length of the second pyrolysis step 104 is at the discretion of the operator.

[0020] The second-stage temperature may be selected based on prior knowledge of the feedstock characteristics or may be automatically determined based on real-time analysis of the pyrolysis reaction and the products produced. Depending on the embodiment, the second-stage temperature may have a lower range selected from 350°C, 375°C, 400°C, 425°C, 450°C, and 480°C, or an upper range selected from 375°C, 400°C, 425°C, 450°C, 450°C, 480°C, 500°C, 525°C, and 550°C, such that any combination of the aforementioned lower and upper ranges may be used.

[0021] The pitch is then obtained in an extraction and separation operation 106. In the extraction and separation step 106, the pitch is extracted with a solvent such as supercritical carbon dioxide (sCO), and the solvent and dissolved pitch are removed from the reaction chamber and then separated to produce a pitch product.

[0022] To obtain carbon fibers from the pitch, an optional extrusion step 108 (shown in dashed lines in the drawing) can be performed, in which the pitch can be extruded into fibers of the desired cross-sectional profile and cooled. The pitch may or may not be first washed, for example with toluene or other solvents, to remove unwanted products and further purify the pitch.

[0023] Experimental data for the two-stage process of Figure 1 indicates that the amount of pitch produced for a given feedstock is greater than the amount that would be obtained from the same feedstock using a single-stage pyrolysis at a higher temperature. Without being bound to any particular theory, the two-stage process described above appears to remove lighter hydrocarbons from the feedstock in the first stage, making them unavailable to react with larger hydrocarbon chains and aromatics during the second stage, which improves the relative amount of pitch produced.

[0024] The feedstock material can include any carbonaceous material known in the art. For example, the feedstock material can include, but is not limited to, coal, biomass, mixed-source biomaterial, peat, tar, plastic, garbage, and landfill waste. For example, in the case of coal, the feedstock can include, but is not limited to, bituminous coal, subbituminous coal, lignite, anthracite, etc. As another example, in the case of biomass, the feedstock can include, but is not limited to, wood materials such as softwood or hardwood. In the experiments of the detailed embodiments discussed herein, the feedstock is presented as coal. However, it will be understood that pitch can equally be produced from any other type of feedstock material and then used to produce carbon fibers in the same manner as described for coal.

[0025] It should be noted that any carbonaceous feedstock, such as coal, may contain some amount of water. Additionally, water may be added to the feedstock prior to or during pyrolysis in any of the methods and systems discussed herein to modify the products produced by the reaction. Similarly, the feedstock may be dried prior to pyrolysis to reduce the amount of water available during the pyrolysis process, and such a drying step may be part of any of the methods and systems discussed herein.

[0026] FIG. 2 shows a more detailed embodiment of the pyrolysis method of FIG. 1. Method 200 begins by placing feed material and water into a pyrolysis reaction chamber in a loading step 202. In one embodiment, the feed material and / or water can be preheated before being placed in the pyrolysis reaction chamber. The amount of water used can be between 1% and 1000% of the weight of the dried feed material. In one embodiment, the amount of water can range from 10%, 20%, 30%, 40%, or 50% of the weight of the dried feed material at the bottom to 100%, 200%, or 500% at the top. Water can be added separately or can already be present in the feed material. For example, in one embodiment, the feed material used is coal that is semi-saturated with water, such that more than 10% of the weight of the feed material is water, and the water in the coal is used as water for loading step 202.

[0027] The loading process may also include pressurizing the pyrolysis reaction chamber to operating pressure (e.g., 7-12 MPa). In one embodiment, this may include removing oxygen and adding pressurized CO2 to the reaction chamber. In this embodiment, the pressurized CO2 can later be used as a solvent to extract and remove pitch and other soluble products from the chamber.

[0028] Method 200 also includes heating the pyrolysis reaction chamber to an intermediate temperature of 150-350°C at 7-12 MPa in an initial heating step 204. Narrower temperature ranges can be used, such as from 160, 170, 180, 190, 200, 210, 220, 230, or 240 at the lower end of the range to 250, 260, 270, 280, 290, 300, 310, 320, 330, or 340 at the upper end of the range. Initial heating step 204 can be performed before or after loading step 202. In one embodiment, step 204 can be performed to increase the temperature as fast as practicable with the given equipment, so that reactions below the intermediate temperature are reduced.

[0029] The intermediate temperature is then maintained for a period of time in a first temperature hold step 206. The hold time may be preselected, such as 10 minutes, 15 minutes, 30 minutes, 60 minutes, 120 minutes, or 240 minutes. For example, the preselected hold time may be based on previous experiments. Alternatively, the hold time may be determined by monitoring the gases in the pyrolysis reaction chamber. For example, in one embodiment, the concentration of one or more pyrolysis reaction product gases, such as methane, ethane, butane, propane, or any other light gas reaction product, is monitored. The concentration of the monitored gas(es) initially increases and eventually begins to level off approximately, following an exponential curve. The hold time may be based on the monitored change in the gas or gas concentration over time. For example, in one embodiment, the first temperature hold step 206 may be terminated when the concentration of the monitored gas(es) is observed to have increased by less than a threshold amount (e.g., 2% or 100 ppm) over a predetermined period of time (e.g., 10 seconds, 1 minute, 5 minutes, etc.). In yet another embodiment, the amount of energy input into the chamber to maintain the pyrolysis temperature or any other parameter, such as the visual or physical condition of the feedstock material, can also be monitored to determine when the reaction has progressed to the operator's satisfaction.

[0030] A second heating step 208 then occurs, in which the temperature of the pyrolysis chamber and feedstock material is increased to a pyrolysis temperature of 300° C. to 550° C. For example, the second heating step 208 can include heating the reaction chamber from 325° C., 350° C., 375° C., or 400° C. on the lower end of the range to 425° C., 450° C., 475° C., 500° C., 525° C., or 550° C. on the upper end of the range.

[0031] The pyrolysis temperature, also referred to as the pitch production temperature, is then maintained for a second period of time ranging from 1 minute to 24 hours in a second temperature hold step 210. Again, the second hold time may be preselected, for example, based on previous experimentation. Alternatively, the hold time may be determined by monitoring one or more gases in the pyrolysis reaction chamber, which may or may not be the same one or more gases monitored during the first temperature hold step 206. In yet another embodiment, the amount of energy input to the chamber to maintain the pyrolysis temperature or any other parameter, such as the visual or physical condition of the feedstock material, may also be monitored to determine when the reaction has progressed to the operator's satisfaction.

[0032] At the end of the second retention time, the pitch may be extracted and removed from the pyrolysis chamber in an extraction step 212.

[0033] A separation step 214 can then be performed to separate the extracted pitch from the solvent. In one embodiment, when the solvent is sCO2, separation step 214 can include removing the sCO2 and dissolved pyrolysis reaction products from the chamber and reducing the temperature and pressure of the solvent until pitch is obtained. For example, to differentially remove components of the reaction products, including pitch, that have different solubilities in carbon dioxide, the sCO2 can be passed through successive collection chambers, each at a different pressure-temperature combination. One of the separation chambers can be maintained at a temperature and pressure characteristic of condensing the pitch from the solvent. For example, in one embodiment, pitch is obtained from the CO2 solvent in a chamber maintained at a temperature of 350°C or greater and a pressure of 7.39 MPa or greater.

[0034] To obtain carbon fibers from the pitch, an optional extrusion step 216 (shown in dashed lines in the drawing) can be performed, in which the pitch is extruded into fibers of the desired cross-sectional profile and cooled. The pitch may or may not be first washed to remove unwanted products, further purifying the pitch before or after extrusion. Additionally, the extruded pitch can be stretched, dried, cooled, baked, heat-treated (in an oxidative or inert environment), or otherwise post-treated to improve the properties of the fiber strand.

[0035] The method 200 described above has been described with respect to a batch process in a single pyrolysis reaction chamber. In alternative embodiments, the method can be practiced as a continuous or semi-continuous process using one or more pyrolysis reaction chambers. For example, in one embodiment, the initial heating step 204 and first temperature hold step 206 may be performed in a first reaction chamber, and the contents may then be transferred to a second chamber for a second heating step 208 and second temperature hold step 210.

[0036] Figure 3 is an example of a system 300 suitable for the pitch production method described above. Figure 3 shows a block diagram of a system 300 for converting carbonaceous material into one or more reaction products. In one embodiment, system 300 includes a thermochemical conversion system 302. In one embodiment, thermochemical conversion system 302 includes a thermochemical reaction chamber 304, such as a pyrolysis reaction chamber, suitable for receiving a volume of feed material 305 (e.g., carbonaceous material) and water and converting the feed material into one or more reaction products, including pitch.

[0037] In the illustrated embodiment, the system 300 includes one or more heat sources 308 and a thermal energy transfer system 306 for transferring thermal energy from the one or more heat sources 308 to the volume of feedstock 305 contained within the thermochemical reaction chamber 304. The thermal energy transfer system 306 includes a heat transfer element 307. For example, the heat transfer element 307 may include, but is not limited to, a heat transfer loop, a heat transfer line, or the like. For example, the heat transfer element 307 may include, but is not limited to, a heat transfer loop filled with a supercritical fluid (e.g., sCO2) disposed in thermal communication (e.g., directly or indirectly) with one or more portions of the one or more heat sources 308.

[0038] In one embodiment, the thermal energy transfer system is configured to selectively place a volume of supercritical fluid in thermal communication with a volume of feedstock contained within a thermochemical reaction chamber. In this regard, the thermal energy transfer system 306 can selectively transfer thermal energy from one or more heat sources 308 to a volume of feedstock 305 contained within at least one thermochemical reaction chamber 304. In another embodiment, the thermochemical reaction chamber 304 can use the thermal energy delivered to the feedstock via the supercritical fluid to pyrolyze at least a portion of the feedstock 305 to yield one or more reaction products.

[0039] The supercritical fluid of the system 300 may include any supercritical fluid known in the art suitable for transferring energy from one or more heat sources 308 to the feedstock 305 contained in the thermochemical reaction chamber 304. In one embodiment, the supercritical fluid includes, but is not limited to, sCO2. In another embodiment, the supercritical fluid includes, but is not limited to, water, methanol, ethanol, propanol, and acetone. In another embodiment, the supercritical fluid is pressurized to a high pressure within at least one of the heat transfer element 307 and the thermochemical reaction chamber 304.

[0040] It is noted herein that the supercritical fluid of system 300, such as (but not limited to) CO2, can have low viscosity and surface tension, allowing such supercritical fluid to easily permeate organic materials (e.g., coal). The permeation of the supercritical fluid into the feedstock 305 reduces the need to convert the feedstock 305 into fine particles prior to thermochemical reaction, thereby saving energy in the preparation of the feedstock material. In one embodiment, in the case where the supercritical fluid is supercritical CO2, the supercritical fluid may be pressurized above its critical pressure (7.39 MPa) and critical temperature (31°C). It is noted herein that under these conditions, CO2 exhibits unique solubility characteristics, similar to organic solvents such as hexane, heptane, benzene, and toluene. The non-polar nature of supercritical CO2 can facilitate the control of undesirable secondary ionic reactions that commonly occur in aqueous environments. Furthermore, when the system is depressurized under critical conditions, CO2 volatilizes, facilitating the recovery of low-water-content oils. Again, this can significantly reduce energy consumption during post-pyrolysis reaction product-supercritical fluid separation, as described further herein. Additionally, it should be noted that the supercritical fluid in system 300 adds heated and pressurized CO to feedstock material 305, providing better control of reaction conditions (e.g., time, pressure, and temperature), thereby enabling better selectivity for high-value target compounds or fuel intermediates.

[0041] In another embodiment, a supercritical fluid, such as supercritical CO2, can provide greater temperature and reaction time control via injection of a cooler supercritical fluid into the thermochemical reaction chamber 304 to moderate the reaction, or a hotter supercritical fluid to accelerate the reaction. Additionally, it will be appreciated that because many supercritical fluids, such as supercritical CO2, can be efficiently compressed, the pressurized conditions within the thermochemical reaction chamber 304 can also be used to control the thermochemical reaction within the thermochemical reaction chamber 304.

[0042] In another embodiment, the solubility of one or more reaction products (e.g., pitch) in the supercritical fluid can be controlled by adding or removing polar materials to the supercritical fluid. For example, the solubility of one or more oils in supercritical carbon dioxide can be controlled by adding / removing one or more materials containing polar molecules (e.g., but not limited to, HO, ethanol, methanol, higher alcohols, etc.). As another example, if the feedstock material includes coal, the solubility of one or more oils in sCO can be controlled by adding / removing one or more materials containing hydrogen donor molecules (e.g., but not limited to, HO, HO, formic acid, tetralin, and any other hydrogen donor solvent known in the art).

[0043] It is recognized herein that the feedstock 305 contained within the thermochemical reaction chamber 304 may contain sufficient moisture and polarity to adequately dissolve one or more reaction products (e.g., bio-oil) in the supercritical fluid. As discussed further herein, the "dryness" of the feedstock may be controlled by the thermochemical conversion system 302 (e.g., via the dryer 134), enabling the thermochemical conversion system 302 to maintain a moisture content level within the feedstock 305 at a level sufficient to adequately dissolve one or more reaction products in the supercritical fluid.

[0044] In another embodiment, the supercritical fluid may include one or more materials for facilitating one or more physical or thermochemical reactions in the system 300. For example, the supercritical fluid may contain one or more catalysts, such as, but not limited to, metals, metal salts, and organics. As another example, the supercritical fluid may include one or more solutes, such as, but not limited to, alcohols, oils, hydrogen, and hydrocarbons.

[0045] The one or more heat sources 308 may include any heat source known in the art suitable for providing sufficient thermal energy to heat the feedstock 305 to the selected temperatures used in the two stages of pyrolysis.

[0046] In one embodiment, the one or more heat sources 308 include a non-CO2 emitting heat source. In one embodiment, the one or more heat sources 308 include one or more nuclear reactors. The one or more heat sources 308 may include any nuclear reactor known in the art. For example, the one or more heat sources 308 may include a liquid metal cooled reactor, a molten salt cooled reactor, a high temperature water cooled reactor, a gas cooled reactor, etc. As another example, the one or more heat sources 308 may include a pool reactor. As another example, the one or more heat sources 308 may include a modular reactor.

[0047] It is recognized herein that a nuclear reactor can generate temperatures sufficient to perform thermal decomposition (e.g., fast pyrolysis) of the feedstock 305. For example, a nuclear reactor heat source can generate temperatures in excess of 350-600°C. In this regard, the nuclear reactor can be used to transfer thermal energy (e.g., at temperatures in excess of 350-600°C) to a supercritical fluid. The supercritical fluid can then transfer the thermal energy generated in the reactor to the feedstock 305 contained within the thermochemical reaction chamber 304.

[0048] It is further noted herein that a nuclear reactor heat source may be particularly advantageous as a heat source in connection with system 300 because the thermochemical reaction temperatures of system 300 are within the range of operating temperatures of many nuclear reactors. Because the reactor is operating at the reaction temperature for the thermochemical conversion (i.e., the added heat at the thermochemical reaction temperature provides the necessary reaction enthalpy), the reactor heat can be used to produce reaction products (e.g., pitch) within thermochemical reaction chamber 304 with high efficiency.

[0049] In one embodiment, as shown in FIG. 3 , the thermal energy transfer system 306 includes a direct heat exchange system configured to transfer thermal energy directly from one or more heat sources 308 to a volume of supercritical fluid in the heat transfer element 307. For example, the heat transfer element 307 can be positioned in direct thermal communication with a portion of the one or more heat sources 308. For example, if the one or more heat sources 308 include a nuclear reactor, one or more coolant systems of the reactor can be integrated with the thermal energy transfer system 306. In this regard, the nuclear reactor can utilize supercritical fluid in one or more coolant systems, which can then be directly coupled to the thermochemical reaction chamber 304. For example, the nuclear reactor's primary or intermediate coolant loop can include a coolant fluid comprised of a supercritical fluid, such as supercritical CO2. Furthermore, the reactor's coolant loop can be directly coupled to the thermochemical reaction chamber 304 via the thermal energy transfer system 306 to mix the supercritical fluid in the reactor's coolant loop with the feed material 305 contained within the thermochemical reaction chamber 304. In transferring thermal energy from the reactor to the feedstock material 305, the thermal energy transfer system 306 may then circulate the supercritical fluid coolant back to the reactor via return path 318. It is further contemplated herein that the thermal energy transfer system 306 may include any number of filtration elements to avoid the transfer of feedstock and / or reaction products into the reactor's coolant system.

[0050] In another embodiment, not shown, thermal energy transfer system 306 includes an indirect heat exchange system. In one embodiment, the indirect heat exchange system is configured to indirectly transfer thermal energy from one or more heat sources 308 to a volume of supercritical fluid contained within heat transfer element 307. In one embodiment, the indirect heat exchange system includes an intermediate heat transfer element (not shown) configured to transfer thermal energy from one or more heat sources 308 to the intermediate heat transfer element. The intermediate heat transfer element can then transfer thermal energy from the intermediate heat transfer element to the volume of supercritical fluid contained within heat transfer element 307.

[0051] In one embodiment, the intermediate heat transfer element can include an intermediate heat transfer loop and one or more heat exchangers. The intermediate heat transfer loop can include any working fluid known in the art suitable for transferring thermal energy. For example, the working fluid of the intermediate heat transfer circuit can include, but is not limited to, liquid salt, liquid metal, gas, supercritical fluid (e.g., supercritical CO2), or water.

[0052] Additionally, as previously described herein, the heat transfer element supercritical fluid of the heat transfer system 306 can mix with the feed material 305 contained within the thermochemical reaction chamber 304. Then, upon transferring thermal energy from the heat source 308 through the heat transfer element 307 to the feed material 305, the thermal energy transfer system 306 can recirculate the supercritical fluid coolant via the return path 318.

[0053] It is noted herein that the above description of direct and indirect coupling between one or more heat sources 308 and the feedstock 305 is provided for illustrative purposes only and not limiting. In a general sense, it is recognized that integration between one or more heat sources (e.g., nuclear reactors) and the thermochemical reaction chamber 304 can occur by transferring heat from a primary, intermediate, or tertiary heat transfer system (e.g., a coolant system) of the one or more heat sources 308 to a working fluid, such as supercritical CO2, of the thermochemical conversion system 302. It is further recognized herein that this integration may be performed using any heat transfer system or device known in the art, such as, but not limited to, one or more heat transfer circuits, one or more heat sinks, one or more heat exchangers, etc.

[0054] In one embodiment, the thermal energy transfer system 306 includes a flow control system 310. The flow control system 310 can be configured to selectively place a supercritical fluid in thermal communication with a volume of feedstock contained within the thermochemical reaction chamber 304. In this regard, the flow control system 310 can selectively transfer thermal energy from one or more heat sources 308 to the volume of feedstock contained within the thermochemical reaction chamber 304. For example, the flow control system 310 can be disposed along the heat transfer element 307 (e.g., a heat transfer loop) to control the flow of the supercritical fluid through the heat transfer element 307. In this regard, the flow control system 310 can control the flow rate of the supercritical fluid to the volume of feedstock 305, thereby controlling the transfer of thermal energy to the feedstock 305.

[0055] The flow control system 310 may include any flow control system known in the art suitable for controlling the flow of a supercritical fluid from a first location to a second location. For example, the flow control system 310 may include, but is not limited to, one or more control valves operably coupled to the heat transfer element 307 and suitable for establishing and terminating flow through the heat transfer element 307. For example, the flow control system 310 may include a manual control valve, a valve / valve actuator, etc.

[0056] In another embodiment, the flow control system 310 can couple thermal energy from one or more heat sources 308 to an electricity generation system (not shown). For example, the flow control system 310 can establish a parallel coupling of the generated heat source 308 to the turbine-electric system and the thermochemical conversion system 302. In one embodiment, the thermochemical conversion system 302 can include multiple batch-type reaction systems that can receive heat from one or more heat sources 308 (e.g., nuclear reactors). In this manner, multiple batch processes can be run simultaneously or sequentially, which addresses overall heat and feedstock conversion needs. In another embodiment, heat may be transferred to one or more sequential thermochemical reactors while being coupled in parallel to one or more turbine-electric systems.

[0057] In one embodiment, system 300 includes a feedstock supply system 312. In one embodiment, feedstock supply system 312 is operably coupled to thermochemical reaction chamber 304 of thermochemical conversion system 302. In another embodiment, feedstock supply system 312 supplies a quantity of feedstock material 305 and water to the interior of thermochemical reaction chamber 304. Feedstock supply system 312 may include any supply system known in the art suitable for transporting a selected amount of feedstock material, such as a solid, granular, or liquid material, from one or more sources to the interior of thermochemical reaction chamber 304. For example, feedstock supply system 312 may include, but is not limited to, a conveyor system, a fluid transfer system, etc.

[0058] Feedstock supply system 312 can include separate systems for transferring the feedstock and for transferring the amount of additional water required for the desired reaction. In an alternative embodiment, water can be added to the feedstock prior to transfer of the feedstock into reaction chamber 304. This may be done at feedstock supply system 312 or prior to receipt by feedstock supply system 312.

[0059] A moisture control system (not shown) can be provided to measure the moisture content of the feedstock and add water as needed. Such a system can include a moisture detector that continuously or periodically determines the moisture content of the feedstock, compares the moisture content to a target moisture content range, and adds water if the moisture content is below the target range. A dryer can also be provided if the moisture content is above the target range for drying the feedstock material 305.

[0060] The feedstock material 305 can include any carbonaceous material known in the art. For example, the feedstock material 305 can include, but is not limited to, coal, biomass, mixed-source biomaterial, peat, tar, plastic, trash, and landfill waste. For example, in the case of coal, the feedstock can include, but is not limited to, bituminous coal, sub-bituminous coal, lignite, anthracite, etc. As another example, in the case of biomass, the feedstock can include, but is not limited to, wood material such as softwood or hardwood.

[0061] It is noted herein that the ability to control temperature, pressure, reaction time, pre-treatment options, and post-organic product production options allows for the utilization of multiple types of carbonaceous feedstocks within system 300. Additionally, the ability to simultaneously utilize or switch between feedstock types can improve utilization of available resources and improve overall pitch production economics.

[0062] 3 , thermochemical conversion system 302 includes any thermochemical reaction chamber 304 suitable for carrying out pyrolysis. In one embodiment, thermochemical reaction chamber 304 is configured to carry out a pyrolysis reaction on feedstock 305. In another embodiment, thermochemical reaction chamber 304 includes a pyrolysis chamber. In another embodiment, thermochemical reaction chamber 304 includes a non-combustion or low-combustion pyrolysis chamber. The pyrolysis chamber of system 300 may encompass any thermochemical reaction chamber suitable for carrying out thermochemical decomposition of organic molecules in the absence of oxygen or in a low-oxygen environment.

[0063] In one embodiment, the thermochemical reaction chamber 304 comprises a fast pyrolysis reactor suitable for converting a feedstock 305, such as coal, into reaction products including pitch. A fast pyrolysis reactor can include any thermochemical reaction chamber capable of carrying out the thermochemical decomposition of organic molecules in the absence of oxygen (or in a low-oxygen environment) within approximately two seconds. Fast pyrolysis is generally described by Roel J.M.Westerhof et al. in "Effect of Temperature in Fluidized Bed Fast Pyrolysis of Biomass: Oil Quality Assessment in Test Units," Industrial & Engineering Chemistry Research, Volume 49, Issue 3 (2010), pp. 1160-1168, which is incorporated herein by reference in its entirety. Pyrolysis and fast pyrolysis are also generally described by Ayhan Demirbas et al. in "An Overview of Biomass Pyrolysis," Energy Sources, Volume 24, Issue 3 (2002), pp. 471-482.

[0064] In another embodiment, the thermochemical reaction chamber 304 comprises a supercritical pyrolysis reactor suitable for converting a feedstock 305, such as coal or biomass, into a reaction product, such as pitch. For purposes of this disclosure, "supercritical pyrolysis reactor" is intended to encompass any reactor, reaction vessel, or reaction chamber suitable for carrying out a pyrolysis reaction of a feedstock material using thermal energy provided by a supercritical fluid. In another embodiment, the thermochemical reaction chamber 304 can include, but is not limited to, a fluidized bed reactor.

[0065] In another embodiment, the thermochemical reaction chamber 304 can perform one or more extraction processes on the feedstock. In another embodiment, an extraction chamber operably coupled to the thermochemical reaction chamber 304 can perform one or more extraction processes on the feedstock after either the first or second pyrolysis stage. In one embodiment, the thermochemical reaction chamber 304 is configured to remove additional compounds from the feedstock material prior to pyrolysis. For example, the thermochemical reaction chamber 304 may be configured to remove at least one of oils and lipids, sugars, or other oxygenated compounds. In another embodiment, the extracted compounds can be collected and stored for further bio-based product development.

[0066] It may be advantageous to remove sugars from the feedstock material 305. It is recognized that sugars caramelize at high temperatures and may act to block supercritical fluids, such as supercritical CO2, from entering the cellulosic structure of the feedstock material 305. Additionally, sugars present in the thermochemical conversion system 302 may also act to poison downstream catalyst beds (if present). It is noted herein that removing sugars helps to avoid the formation of oxygenated compounds such as, but not limited to, furfural, hydroxymethylfurfural, vanillin, and the like.

[0067] In one embodiment, the thermochemical conversion system 302 can extract materials from the feedstock 305 at temperatures below 200° C. It is noted that extracting sugars at temperatures below 200° C. is beneficial because fructose, sucrose, and maltose each caramelize at temperatures below about 180° C. In this regard, the supercritical fluid can aid in extracting sugars from the feedstock 305 prior to the temperature increase during pyrolysis by breaking down the cellulosic material and sweeping out the sugars.

[0068] In another embodiment, the thermochemical reaction chamber 304 is configured to preheat the feedstock 305 prior to pyrolysis. In another embodiment, a preheat chamber operably coupled to the thermochemical reaction chamber 304 is configured to preheat the feedstock 305 prior to pyrolysis. For example, the thermochemical reaction chamber 304 (or preheat chamber) can preheat the feedstock material to a temperature at or near the temperature required for liquefaction and / or pyrolysis.

[0069] In another embodiment, the thermochemical reaction chamber 304 is configured to pre-treat the feedstock 305 prior to pyrolysis. For example, the thermochemical reaction chamber 304 can pre-hydrotreat the feedstock material with hydrogen prior to liquefaction and / or pyrolysis. For example, pre-treating the feedstock material with hydrogen can help remove substances such as, but not limited to, sulfur, as well as donate hydrogen to reactive species (i.e., stabilize free radicals).

[0070] In an alternative embodiment not shown, thermochemical conversion system 302 is separated into multiple process chambers for carrying out the various steps of the multi-stage thermochemical process of system 300. For example, in one embodiment, a first chamber is provided for a first stage of pyrolysis at an intermediate temperature, a second stage is provided for a second stage of pyrolysis at a pyrolysis temperature, and an extraction chamber is provided for contacting and extracting the desired pitch products with a solvent. Feedstock 305 may be transferred between the chambers continuously or as a batch process.

[0071] It is noted that while the above description indicates that in some embodiments the pyrolysis reaction chamber and extraction chamber may exist as separate chambers, this should not be construed as limiting. Rather, it is contemplated herein that two or more of the thermochemical processes may each be carried out within a single reaction chamber.

[0072] In one embodiment, the thermochemical reaction chamber 304 comprises a multi-stage single thermochemical reaction chamber. In one embodiment, the thermochemical conversion system 306 is configured to transfer multiple portions of a supercritical fluid over multiple temperature ranges to a volume of feedstock 305 contained within the multi-stage single thermochemical reaction chamber 304 to perform a set of thermochemical reaction processes on at least a portion of the volume of feedstock.

[0073] In another embodiment, the thermal energy transfer system 306 is configured to transfer a first portion of the supercritical fluid in a second temperature range to a volume of feedstock 305 contained within a single thermochemical reaction chamber 304 to perform a preheating process on at least a portion of the volume of feedstock.

[0074] In another embodiment, the thermal energy transfer system 306 is configured to transfer a second portion of the supercritical fluid in the first temperature range to a volume of feedstock 305 contained within the single thermochemical reaction chamber 304 to perform a first stage of pyrolysis on at least a portion of the volume of feedstock.

[0075] In another embodiment, the thermal energy transfer system 306 is configured to transfer a third portion of the supercritical fluid in the second temperature range to a volume of feedstock 305 contained within the single thermochemical reaction chamber 304 to perform a second pyrolysis stage on at least a portion of the volume of feedstock.

[0076] In one embodiment, the flow rate and temperature of the supercritical fluid are spatially varied across the thermochemical reaction chamber 304. For example, to vary the flow rate and / or temperature across the reaction chamber 304, multiple flow rates of supercritical fluid, each at a different temperature, can be established before entering a single reaction chamber. In this regard, a vertical reaction chamber can vary the flow rate and temperature at several spatial locations, corresponding to various thermochemical stages. As another example, the temperature of the supercritical fluid can be varied along the length of the thermochemical reaction chamber 304 by flowing the supercritical fluid along the length of the thermochemical reaction chamber 304. For example, a flow of low-temperature supercritical CO can be combined with a flow of CO at a higher temperature (e.g., 70-150°C) to dissolve sugars. At another downstream point (e.g., 1-3 meters downstream, average flow rate of 0.25-4 m / s), supercritical CO above the pyrolysis temperature is mixed into the chamber. By staging the temperature of the various thermochemical reaction steps along the length, the flow rate can be used to control the reaction time.

[0077] It is further contemplated that two or more thermochemical steps, such as pyrolysis, extraction, and separation, may be performed within the thermochemical chamber 304, while additional processes, such as drying and preheating, may be performed in dedicated chambers operably coupled to the thermochemical reaction chamber 304.

[0078] The reaction chamber may include one or more outlets 319, according to one or more embodiments of the system 300. In the embodiment shown in FIG. 3, the reaction chamber 304 is provided with an outlet for removing the feedstock residue remaining after the second stage of pyrolysis and another outlet for removing the solvent containing pitch and other dissolved pyrolysis reaction products. In one embodiment, the outlet for the feedstock residue remaining after the second stage of pyrolysis is completed is positioned to remove the residue and transport it to a residue storage system 314. In one embodiment, the residue storage system 314 can be as simple as a drum, rail car, Conex box, or other portable container. In an alternative embodiment, the residue may be stored in layers for later transportation.

[0079] Solvent outlet 319 delivers the solvent, which in this embodiment is sCO2, to separation system 320. In one embodiment, the outlet includes a valve that controls the flow of gas from reaction chamber 304 to separation system 320.

[0080] In one embodiment, separation system 320 reduces the temperature and / or pressure in successive steps to obtain different dissolved components. For example, a heat rejection heat exchanger can optionally be used before or after separation system 320. In one of these steps, the pitch is condensed and transferred to pitch extruder 326. The pitch can be intermediately stored in a holding vessel. Alternatively, the pitch can be passed to extruder 326 immediately upon condensation from the sCO2.

[0081] In one embodiment, each step corresponds to a collection chamber maintained at a different temperature and pressure to allow dissolved products to condense from the solvent. Each chamber then collects the products that condense at that chamber's temperature and pressure. In one embodiment, pitch is obtained from a chamber maintained at a temperature of 350°C or greater and a pressure of 7.39 MPa or greater.

[0082] The pitch extruder, as described above, extrudes the pitch into fibers which may then be cooled for use directly or indirectly as carbon fibers.

[0083] Other compounds in the solvent stream removed from the reaction chamber 304 are captured in a product capture system 322 for further processing or sale. In one embodiment, a volatile gas separator and storage system may be provided as part of the product capture system 322 or the separation system 320. The volatile gas separator can separate one or more volatile gases from the remainder of one or more reaction products. For example, the volatile gas separator can separate volatile gases such as, but not limited to, CH, CH, CH, CO, CO, H, and / or HO from solid or liquid reaction products. It is noted herein that the volatile gas separator can include any volatile gas separation device or process known in the art. It is further recognized that these gases may be cooled, scrubbed, captured, and stored for future use. The volatile gases may also be produced to provide a source of hydrogen.

[0084] In the illustrated embodiment, the CO2 is returned 318 to the heat source 308 for reuse after the dissolved products are removed in a closed loop system. In another embodiment, the CO2 is simply vented.

[0085] In another embodiment not shown, system 300 includes a heat recovery system. In the case of recovery, the system can recover heat from the sCO2 prior to or as part of the separation system 320 (or other suitable subsystem of system 300) via a heat transfer loop that acts to thermally couple the sCO2 to the heat recovery system. In one embodiment, the recovered heat can act as a recuperator or regenerator. In another embodiment, energy can be recovered following the thermochemical process performed by chamber 304. In another embodiment, the recovered energy may be used to preheat the feed material prior to thermochemical processing. In another embodiment, the recovered energy may be used to generate power (e.g., mechanical or electrical) incidental to one or more subsystems of system 300.

[0086] Figure 4 shows a process flow diagram for a batch embodiment of a flexible pyrolysis system that can be adjusted to vary the pyrolysis products obtained from a given feedstock. In the illustrated embodiment, the feedstock is provided as coal. However, the reader will understand that any carbonaceous feedstock, such as biomass, can be used.

[0087] FIG. 4 illustrates a closed-loop CO2 pyrolysis system similar in operation to that described above. In the embodiment illustrated in FIG. 4, the pyrolysis chamber is a tower 402 filled with coal 404. An inlet stream of a supercritical fluid, such as sCO2, enters the top of the tower and flows through the coal 404. By controlling the flow rate of the sCO2, the residence or contact time of the sCO2 with the coal can be controlled, as known in the art, to control the amount of dissolved reaction products in the sCO2 observed in the chamber's outlet stream. In one embodiment, the sCO2 entering the pyrolysis chamber 402 can range in temperature from 300 to 600°C and pressure from 7.39 to 12 MPa, such that pyrolysis occurs in a supercritical CO2 atmosphere. Higher temperatures and pressures can also be used.

[0088] In a batch system, the pyrolysis chamber may be a simple cylindrical chamber with no internal parts other than a screen to keep the coal in place. Multiple chambers may be provided in parallel so that one may be in use while the other is emptied of char and refilled with fresh coal. In an alternative embodiment, the chamber may be equipped with an agitator or screw to move the coal during pyrolysis.

[0089] After contacting and pyrolyzing the coal 404, the sCO exits the bottom of the tower 402 along with the dissolved pyrolysis reaction products, as described above. The discharged sCO then passes through a recovery and condensation circuit that removes the dissolved pyrolysis reaction products and then recovers the CO for reuse within the pyrolysis chamber 402. The recovery and condensation circuit includes a series of one or more recuperators 406 that simultaneously cool the CO stream discharged by the pyrolysis chamber 402 while preheating the CO inlet / return stream (in which products have mostly been condensed from the stream) that is fed to the chamber 402. In the illustrated system 400, four recuperators 406 are shown: a first stage recuperator 406a, a second stage recuperator 406b, a third stage recuperator 406c, and a fourth stage recuperator 406d. As described below, more or fewer recuperators 406 can be used as needed.

[0090] The recuperators 406 may be any type of heat exchanger now known or later developed. In one embodiment, for example, the recuperators 406 are each tube-in-tube heat exchangers with the exhaust CO in an outer tube and the cooler inlet CO flowing through an inner tube. However, any type of heat exchanger may be used in any configuration deemed beneficial or desirable.

[0091] In addition to the recuperator 406, an optional final cooling heat exchanger 408 stage may be provided as part of the recuperator and condenser circuit to ultimately reduce the temperature of the CO2 to the desired lower temperature for the circuit. This is accomplished using a coolant, such as chilled water from a chilled water system 424 as shown, to perform the final cooling of the output stream. Similar to the recuperator 406, if utilized, the final heat exchanger 408 may be any type of heat exchanger.

[0092] As noted above, the supercritical state of CO2 is at temperatures above 31.1°C and pressures above 7.39 MPa. In describing the system, CO2 is referred to as supercritical even though at some points in the system, the state may drop below the critical point in either temperature or pressure. It should be understood that at these points, CO2 may be in a gaseous or liquid state, depending on temperature and pressure conditions. Such states may occur downstream of the pyrolyzer 402, for example, in the fourth recuperator 406 or the final heat exchanger 408.

[0093] For example, in one embodiment, the low CO2 circuit temperature can be less than 50°C, such as room temperature (20°C), and the low pressure can be 6-8 MPa. Lower temperatures and pressures can also be used. In this embodiment, the CO2 can be made subcritical to remove as many pyrolysis products as possible. In an alternative embodiment, the circuit temperature and pressure are maintained so that the CO2 remains supercritical throughout the system 400.

[0094] In the illustrated embodiment, after each heat exchanger in the circuit is a condensation collection vessel 410. Each vessel is then at a lower temperature, from left to right. The condensation vessel 410 may be any type of active or passive condensing device. For example, in the illustrated embodiment, the condensation vessel 410 is a cold finger condenser that provides a temperature-controlled surface through which the CO flows. This allows any pyrolysis products that are condensable above the controlled temperature to be collected in the condensation vessel 410. In an alternative embodiment, a cyclone separator could be used in place of the cold finger condenser. Other possible condensation vessels include Liebig condensers, Graham condensers, coil condensers, and Allihn condensers, to name just a few.

[0095] Where appropriate, the term "process stream" will be used to refer to the CO stream of the portion of the CO circuit having CO flowing from the pyrolysis chamber 402 through the final condensation collection vessel 410, and "return stream" or "inlet / return stream" will be used to refer to the CO stream flowing from the final condensation vessel through the circuit, through pump 420, and ultimately back to the pyrolysis chamber 402. Note that the return stream may not be completely pure CO, but will likely contain at least trace amounts of reaction products, water, or other compounds that are not completely captured in the condensation vessels. The process stream, on the other hand, will contain at least some, and possibly very large amounts, of the pyrolysis reaction products that are continuously removed by the various condensation vessels 410, depending on their location in the circuit.

[0096] In the illustrated embodiment, different recuperators can operate at different temperatures. For example, in one embodiment, the first recuperator 406a can receive a process stream of CO and dissolved reaction products at approximately 550°C and discharge it at 450°C. The second recuperator 406b can receive a stream at 450°C and discharge it at 300°C. The third recuperator 406c can receive a stream at 300°C and discharge it at 150°C. The fourth recuperator 406d can receive a stream at 150°C and discharge it at 50°C.

[0097] The CO2 return stream is partially reconditioned by a pump / compressor 420, which returns the CO2 to the operating pressure (e.g., approximately 10 MPa), and a heater 422, which provides additional heat to the CO2 to bring it to the desired pyrolysis temperature. For example, in one embodiment, the pump / compressor 420 receives CO2 at approximately 10 MPa and compresses the stream to approximately 12 MPa, which provides sufficient pressure to maintain flow through the entire CO2 circuit without an additional pump. The heater 422 may be a single heating unit or multiple units in parallel and / or series, depending on the operator's preference. For example, in one embodiment, three separate heaters are provided in series that receive the recovered CO2 stream from the first recuperator 406a and heat the stream from its inlet to a temperature between approximately 450°C and approximately 550°C. Similarly, there may be a single pump 420 as shown, or multiple pumps distributed throughout the CO2 circuit. For example, in embodiments where a portion of the circuit is sub-supercritical, a dedicated heater and / or compressor (not shown) may be provided solely for reconditioning the CO2 to supercritical.

[0098] By providing multiple stages of heat exchanger pairs 406, 408, followed by a condensation vessel 410, the pyrolysis products can be fractionated and collected by condensation temperature. This allows for easy separation of specific desired fractions as part of the recovery process. By providing more or fewer stages, greater or less differentiation of the fractions can be achieved, as well as control over the composition of each fraction.

[0099] In addition to having multiple stages of heat exchangers 406, 408 followed by a condenser vessel 410, further flexibility is achieved by using bypass circuits created by multiple bypass valves 412 for the output CO portion of the circuit and the inlet / return CO portion of the circuit. In one embodiment, one or more of the heat exchangers includes bypass capability, allowing that exchanger to be fully or partially bypassed by either or both the pyrolysis output stream and the inlet / return stream. In the illustrated embodiment, various bypass valves 412 are provided, allowing each of the various stages to be fully or partially bypassed as desired by the operator. At any given bypass valve 412, the operator can select how much of the input stream is directed to either outlet of the valve. This level of flow control provides significant flexibility in the operation of the system 400 and allows for further operational control over where various fractions of pyrolysis products are collected within the system.

[0100] Pyrolysis system 400 may further include an additive injection system for injecting additives into the CO inlet / return stream prior to delivery to pyrolysis chamber 402. In the illustrated embodiment, two additive injection systems are shown, each including an injection pump 414 and an additive supply 416. Examples of additives, as described in more detail above, include H, HO, formic acid, and tetralin. In one embodiment, injection pump 414 is an HPLC injection pump.

[0101] In yet another embodiment (not shown), a bypass valve 412 may be provided to allow for bypassing one or more of the condensation vessels 410. This allows for the collection of reaction products to be combined into fewer vessels, if desired, thus further increasing the flexibility of the system 400.

[0102] A controller 430 is shown in Figure 4. In one embodiment, the controller 430 is a programmable logic controller configured to monitor and control the pyrolysis system 400 to achieve a desired result. The controller can be implemented in many different ways, from a purpose-built hardware controller to a general-purpose computing device running control software. Process controllers are well known in the art, and any suitable controller design or combination of designs now known or later developed can be used.

[0103] The controller 430 controls the flow distribution of the process and return streams through the various stages of the recuperator. In this way, the inlet and outlet temperatures of the streams at each stage can be varied. The heat transfer equations governing the heat exchange between hot and cold streams in heat exchangers are well known, and any form of these equations can be used by the controller to determine the flow distribution between stages to obtain a particular temperature at a particular location in the CO2 circuit. For example, one basic heat exchanger equation that can be used is the general countercurrent heat exchange equation that describes the transfer of heat across a: m a c pa (T a1 -T a2 )=m b c pb (T b2 -T b1 ) where m a is the mass flow rate of the process stream, c pa is the specific heat of the process stream, T a1 is the inlet (high) temperature of the process stream entering the recuperator stage, T a2 is the outlet (low) temperature of the process stream, m b is the mass flow rate of the return flow, c pb is the specific heat of the return flow, T b1 is the inlet (low) temperature of the return stream entering the recuperator stage, T b2is the exit (high) temperature of the return stream. From the above equations, additional equations can be derived that mathematically describe the performance of a recuperator, often in terms of an overall heat transfer coefficient for the recuperator based on its dimensions and characteristics, as is known in the art. In many cases, the performance equations for a heat exchanger may be provided by the manufacturer. Such equations are solved by a controller to determine how to distribute the flow of the stream through the recuperator stages to achieve the goals set by the operator, examples of which are provided below.

[0104] In one embodiment, controller 430 may be connected to and control bypass valve 412, heater 422, chilled water system 424, addition pump 414, and other components of system 400. Additionally, controller 430 may be connected to or receive information or signals from one or more monitoring devices 426, from which controller 430 receives data regarding the status of system 400.

[0105] FIG. 4 shows several monitoring devices 426 at various locations throughout the system 400. The monitoring devices 426 may be any type of process monitor, analyzer, or sensor, such as flow sensors, temperature sensors, pressure sensors, weigh scales, pH sensors, spectrometers, photoionization detectors, gas chromatographs, catalytic sensors, infrared sensors, and flame ionization detectors, to name a few. The monitoring devices 426 may be located anywhere within the system 400 as needed. For example, in one embodiment, a gas chromatograph may be used to periodically or continuously monitor and determine the various compounds and their relative amounts among the reaction products in the sCO2 exiting the reaction chamber 402. Alternatively, liquid level sensors on each condenser vessel may be provided, from which data may be used to determine the relative condensate production rates of each recuperator stage.

[0106] Based on information received from the monitoring device 426, the controller 430 can vary the flow rates through one or more bypass valves and the temperatures of one or more streams to achieve a desired hydrocarbon condensate fraction (i.e., molecular weight range) in one or more condensate vessels. For example, in one embodiment, the controller may be instructed to separate and recover hydrocarbons having boiling points between 300 and 350°C. In this embodiment, the flows through the various bypass valves may be adjusted so that the process stream exits the first recuperator 406a at a temperature of 350°C (as opposed to 450°C as described above) and the second recuperator 406b at a temperature of 300°C. This can be achieved by bypassing a portion of the return stream around the second recuperator 406b, driving a relatively larger and more cooled return stream through the first recuperator 406a, thereby increasing the relative amount of cooling performed by the first stage. In this way, reaction products having a boiling point above 350°C are collected in the condensate container 410 between the first recoverer 406a and the second recoverer 406b, and reaction products having a boiling point between 300 and 350°C are collected in the condensate container 410 following the second recoverer 406b.

[0107] As can be seen from the above example, through the use of controller 430 and the flexibility achieved by the system's design, the operating configuration of system 400 can be changed in real time to achieve different goals. Furthermore, by basing the control of system 400 on real-time knowledge reported by sensors and monitoring devices, system 400 can adjust over time in response to changing conditions, such as changes in feedstock quality. In this manner, through controller 430 and multiple stages of recoverers and condenser vessels, system 400 can be easily configured to separate different fractions of hydrocarbons and collect them in different condenser vessels. By providing more stages, even greater differentiation can be provided as needed. Because controller 430 can easily reconfigure bypass valve 412, system 400 can uniquely handle different power requirements or changes in feedstock characteristics.

[0108] Additionally, the controller 430 can be used to control and optimize the reaction products resulting from the pyrolysis reaction. For example, in one embodiment, the controller 430 can directly or indirectly control the temperature and / or pressure within the reaction chamber 402 to vary the relative amounts of different reaction products. In one embodiment, changes to the temperature or pressure within the reaction chamber can be made in real time based on monitoring information received from sensors and monitoring devices. For example, monitoring data indicating the type and amount of various reaction products in the sCO2 exiting the reaction chamber 402 can be provided to the controller 430. Depending on a preset goal, such as optimizing a subset of reaction products (e.g., maximizing the production of reaction products with boiling points between 250 and 350°C), the controller 430 can then iteratively vary the temperature and / or pressure within the reaction chamber until an optimized profile of reaction products is obtained based on the current goals of the system 400.

[0109] Figures 5A-5C illustrate the experimental performance of one embodiment of the system shown in Figure 4. In the figures, the system is referred to interchangeably as a multi-stage supercritical liquefaction system. In the experiments, the embodiment of the system shown in Figure 4 was constructed at bench scale using four recuperators and a final chilled water heat exchanger as shown. A 1 kg sample of Power River Basin subbituminous coal was placed in the tower and pyrolyzed with sCO2 as described above. A fine mesh screen was installed at the bottom of the tower to prevent solids from exiting the chamber.

[0110] For start-up, a bypass circuit was used to isolate the pyrolysis chamber until the system reached the desired thermal conditions. After the loop reached the test temperature, the bypass was disabled and the pyrolysis chamber was placed in the loop. The outlet temperature of the sCO2 leaving the pyrolysis chamber was approximately 490 °C, and the inlet temperature of the sCO2 fed to the pyrolysis chamber was approximately 500 °C. During the experiment, the pressure of the sCO2 in the pyrolysis chamber was approximately 10 MPa, and the mass flow rate of the sCO2 circulating through the circuit was 4.5–10 kg / min. The system was operated without bypassing any of the five heat exchangers, so that all CO2 flow passed through the respective exchanger / condenser vessel stages. The condenser vessels were cold fingers, designated bottles 1–5, maintained at the temperatures shown in Figure 5. The system was operated for a period of time, and then the condensed pyrolysis products from the condenser vessels were analyzed.

[0111] Figure 5A shows the typical liquid yields (yields) obtained from pyrolyzing a batch of coal by condenser vessel temperature. The condenser vessels are cold fingers, designated as bottles 1 through 5, maintained at the temperatures shown in Figure 5A.

[0112] Mass spectrometry was performed on the condensate fractions obtained from bottles 2 and 5. Figure 5B shows the results for bottle 2, and Figure 5B shows the results for bottle 5. As expected, the results show that a substantially higher molecular weight product distribution was condensed in hot bottle 2 than was obtained in cold bottle 5. This indicates that the multi-stage separation system is successful in producing and fractionating different pyrolysis products from a carbonaceous feedstock.

[0113] Figure 6 illustrates an embodiment of a broad method for pyrolyzing a carbonaceous feedstock with CO to obtain reaction products. The illustrated embodiment is discussed with respect to an ongoing process of reconditioning and recycling the CO for reuse in a closed loop. The process in Figure 6 is shown as beginning with contacting step 602, in which the carbonaceous feedstock is maintained in contact with supercritical carbon dioxide at a pyrolysis temperature and pressure sufficient to maintain the CO in a supercritical state, and for a contact time during which pyrolysis occurs. The resulting pyrolysis converts at least some of the feedstock to char and produces some pyrolysis products that are dissolved in the CO.

[0114] The contact time or residence time used may be selected by the operator. The contacting may be static, in that the CO does not flow through the contact chamber during pyrolysis. Rather, the chamber is charged with CO and the feedstock and then allowed to react, with or without internal stirring or other mixing. In this case, the contact time is the time that the CO is supercritical and in the contact chamber with the feedstock. Alternatively, the contacting may be dynamic, in that the CO is constantly flowing through the chamber containing the feedstock. In dynamic contacting, the residence time is calculated from the CO flow rate and the volume of the contact chamber.

[0115] The chemical composition of the pyrolysis reaction products can be altered to some extent by varying the pyrolysis conditions. For example, the relatively high temperatures and pressures used in contacting step 602 can favor the production of some reaction products (e.g., heavier hydrocarbons such as oil) over others (e.g., medium-weight oil or lighter hydrocarbon gases). Additionally, additives such as water, formic acid, hydrogen, or some other hydrogen donor may be used to increase the availability of hydrogen during pyrolysis, which also alters the chemical composition of the reaction products. Other additives can also be used to affect the pyrolysis reaction and alter the chemical composition of the reaction products.

[0116] After contacting, the supercritical CO2 containing dissolved pyrolysis reaction products is separated from the char in a separation step 604. The separation step can take the form of either removing the char from the CO2 or removing the CO2 from the char.

[0117] After the separation step 604, the supercritical CO is cooled to a first temperature and a first pressure in a first cooling step 606. For example, in one embodiment, the pyrolysis temperature and pressure are 540°C and 11 MPa, respectively, and the first temperature and first pressure are 450°C and 10.9 MPa. The first cooling step 606 can include reducing the temperature or the temperature and pressure of the CO from the pyrolysis temperature and pressure used in the contacting step 602. Furthermore, in one embodiment, although referred to as a cooling step 606, "cooling" may consist solely of reducing the pressure of the CO while maintaining the temperature at or near the pyrolysis temperature. Regardless of whether the temperature, the pressure, or both are reduced, the cooling step 606 alters the solubility of the dissolved reaction products, such that any reaction products that are no longer soluble in CO at the first temperature and pressure condense from the CO as a condensate.

[0118] As part of or after the first cooling step 606, the condensate produced by the first cooling step 606 may be collected and stored for later use. The content of this condensate is determined by the reaction products produced by the pyrolysis reaction and the first temperature and pressure of the first cooling step 606. Therefore, as described above, by selecting the first temperature and pressure, the chemical makeup of the condensate produced by the first cooling step 606 can be controlled to achieve a specific fraction of pyrolysis reaction products. Once the temperatures are known, in one embodiment, heat exchanger equations can be used to determine the relative flow rates of the return and process streams through the different recuperators required to achieve those temperatures and, therefore, the desired condensates. From this information, the controller can then set the position of the bypass valves as necessary to achieve the determined flow rates.

[0119] The CO2 with the remaining reaction products is then subjected to a second cooling step 608. Similar to the first cooling step 606, the second cooling step 608 reduces the CO2 from a first temperature and pressure to a second temperature and pressure. Again, this may include reducing the temperature, pressure, or both of the CO2. The second cooling step may be performed using the same equipment as the first cooling step 606, or by passing the CO2 through a second set of equipment (e.g., heat exchanger, cooling vessel, etc.) in which the second cooling step is performed.

[0120] As part of or after the second cooling step 608, the condensate produced by the second cooling step 608 may be collected and stored for later use. The content of this second condensate is determined by the reaction products produced by the pyrolysis reaction, the first temperature and pressure used in the first cooling step 606, and the second temperature and pressure of the second cooling step 608. Therefore, as described above, by selecting the first and second temperatures and pressures, the chemical makeup of the condensate produced by the second cooling step 606 can be controlled to obtain a specific fraction of the pyrolysis reaction products. Once the temperatures are known, in one embodiment, heat exchanger equations can be used to determine the relative convective flows of the return and process streams through the different recuperators required to achieve those temperatures and, therefore, the desired condensate. From this information, the controller can then set the position of the bypass valves as necessary to obtain the determined convective flows.

[0121] Additional cooling steps (not shown) can be performed. The use of additional cooling steps allows for tighter control over the fractionation and collection of reaction products. For example, 25 cooling steps can be used to obtain a very finely fractionated condensate. Any number of cooling steps can be used as desired, depending on the operator's goals. Referring to Figure 4, which shows a system with five possible cooling steps, the chemical composition of the condensate in each of the five stages can be varied by varying the relative temperatures and pressures of the stages. For example, in one configuration, the first four cooling steps can be performed at very narrow temperature and / or pressure differentials, e.g., the first temperature can be 10°C below the pyrolysis temperature, the second 20°C below, the third 30°C below, and the fourth 40°C below, while the final temperature can be 30°C, allowing for fractionation of higher temperature reaction products (i.e., reaction products that condense from CO2 at higher temperatures). In another configuration, the temperature differential between stages can be more uniform, and in yet another configuration, the temperature can be focused to fractionate lower temperature products. Thus, as part of the process, the temperature and pressure of the different cooling steps can be controlled to obtain specific desired fractions of reaction products.

[0122] Finally, the CO2 is recycled and reused for additional pyrolysis in a recycling step 610. Recycling may be done in a continuous system where the CO2 flows continuously in a loop such as that shown in Figure 4. Alternatively, the CO2 may be stored for later reuse in a batch or semi-batch system.

[0123] As part of method 600, the CO may be maintained in a supercritical state throughout the method, or alternatively, the CO may be brought to a subcritical state, for example in a final cooling step, to condense and remove as many reaction products as possible before the CO is returned to a supercritical state in a recycling step 610.

[0124] Figure 7 is a more detailed embodiment of a method for pyrolysis of coal using supercritical CO. While method 600 of Figure 6 is described more broadly to encompass any batch, semi-batch, or continuous pyrolysis process, method 700 of Figure 7 is more specific to a continuous pyrolysis process in which pyrolysis products are fractionated from coal and CO is recycled in a continuous flow loop.

[0125] 7, the method 700 begins with flowing an inlet stream of carbon dioxide (CO) into a reaction chamber containing coal in a supercritical CO injection step 702. In one embodiment, the inlet CO stream has a temperature of 300-600°C and a pressure of 7-12 MPa.

[0126] The reaction chamber is maintained at a pyrolysis temperature and pressure sufficient to maintain the CO2 in a supercritical state within the reaction chamber. This is illustrated in Figure 7 by pyrolysis step 704. Pyrolysis step 704 may include actively controlling the temperature and pressure of the reaction chamber. For example, heat may be applied directly to the reaction chamber using an internal or external heater to control its temperature. Similarly, pressure can be controlled by adjusting the flow rates of the inlet and outlet CO2 streams. Alternatively, the temperature and pressure of the reaction chamber may be controlled indirectly by simply controlling the temperature and flow rate of the inlet stream. Thus, coal is pyrolyzed in pyrolysis step 704 to obtain char and supercritical CO2, including dissolved pyrolysis reaction products. As discussed above with reference to Figure 6, the chemical composition of the reaction products can be controlled to some extent by varying the temperature and pressure within the reaction chamber and by using certain additives.

[0127] After a contact time determined by the CO flow rate through the reaction chamber and the volume of CO in the chamber, the supercritical CO containing the dissolved pyrolysis reaction products then flows from the reaction chamber through the outlet of outlet stream discharge step 706 as the reactor outlet stream.

[0128] The outlet stream is then passed through a first recuperator in a first recovery and capture step 706a, where the reactor outlet stream is cooled in the first recuperator by transferring heat to the CO return stream on its way back to the reaction chamber. The outlet stream is cooled to a first temperature below the pyrolysis reaction temperature based on the temperatures and flow rates of the two CO streams, the outlet stream and the return stream, passing through the first recuperator.

[0129] The act of cooling the outlet stream condenses from the CO any dissolved reaction products in the outlet stream that condense at temperatures above the first temperature. The first recovery and capture step 706a includes collecting this first-stage condensate in a collector, such as a collection vessel, as shown in Figure 4. It also includes discharging the first-stage CO effluent stream, including any dissolved reaction products not removed as first-stage condensate.

[0130] It should be noted that not all of the outlet stream may be processed in the first recovery and collection step 706a. In one embodiment, a portion of the outlet stream may be sent to a subsequent recovery vessel for processing in a subsequent recovery and collection step. This diversion of a portion of the outlet stream may be performed to control the chemical composition of the condensate obtained from the different stages.

[0131] The first stage CO2 effluent stream is then sent to a second recuperator in a second recovery and capture step 706b. In this step 706b, the reactor first stage CO2 effluent stream is cooled in the second recuperator by transferring heat to the CO2 return stream on its way back to the reaction chamber. The first stage CO2 effluent stream is cooled to a second temperature, lower than the first temperature, based on the temperatures and flow rates of the two CO2 streams, i.e., the first stage CO2 effluent stream and the return stream, and passes through the second recuperator.

[0132] Again, the act of cooling the outlet stream condenses from the CO any dissolved reaction products remaining in the first-stage CO effluent stream that condense at temperatures greater than the second temperature. The second recovery and capture step 706b includes collecting this second-stage condensate in a collector, such as a capture vessel, as shown in Figure 4. It also includes discharging the second-stage CO effluent stream containing any remaining dissolved reaction products not removed as the second-stage condensate.

[0133] Again, not all of the first stage CO2 effluent stream needs to be passed through the second recuperator; a portion of the first stage CO2 effluent stream may be diverted to a subsequent recovery / capture step to alter the chemical composition of the subsequent condensate.

[0134] Any number of additional recovery and capture steps can be performed in method 700. This is indicated in FIG. 7 by an ellipsis and an n-th stage recovery and capture step 706n. Each of the recovery and capture steps 706a-n can be identical except for the process temperature and pressure of the two CO2 streams involved. The condensate recovered from each step 706a-n can be controlled by diverting portions of the process and / or return streams around and to the various steps 706a-n to obtain the desired condensate. The distribution of the flow through the different recovery and capture steps 706a-n can be controlled manually or automatically by a controller to capture different fractions at different stages, as described above.

[0135] Note that one or more of steps 706a-n, such as final recovery and capture step 706n in Figure 4, may not involve recovering heat from the process stream. That is, rather than sending the heat to the CO2 return stream, effectively recycling that energy, the heat may simply be removed, such as by transferring it to a cold water stream, and either wasted or recycled for another purpose.

[0136] Furthermore, not all of the recovery and collection steps 706a-n need involve collection of condensate in a separate vessel. Rather, some condensate may be directed to a subsequent stage recoverer for later collection in a downstream recovery and collection step.

[0137] After the final recovery and capture step 706n, the final CO2 output stream is then reconditioned as a return stream by passing it through various recovery steps in a reconditioning step 708. Reconditioning step 708 may include compressing and / or heating the return stream at one or more points in the system's CO2 return circuit. For example, in FIG. 4, the return stream is compressed by pump 420 immediately after the fifth recovery and capture step (not true recovery, since heat is removed using a cold water stream) and heated by heater 422 immediately before being injected into reaction chamber 402.

[0138] Note that reconditioning step 708 may or may not remove remaining products from the CO. In one embodiment, trace amounts of reaction products and / or other compounds, such as water, remain in the CO return stream when injected into the reaction chamber.

[0139] After reconditioning, the CO2 return stream is injected into the reaction chamber as an inlet stream in injection step 402. This is indicated in Figure 7 by the return arrow from reconditioning step 708 to injection step 702.

[0140] Figure 8 shows an embodiment of a method for improving mesophase pitch for carbon fiber production using supercritical carbon dioxide. The method uses as a feedstock some or all of a coal tar product having at least some mesophase pitch, including those described above. In alternative embodiments, any feedstock having at least some mesophase pitch, whether derived from coal, any other biomass, or hydrocarbon material, can be used as a feedstock. For the remainder of this specification, "coal tar" refers to the material / oil derived from the pyrolysis or coking of coal. Materials extracted from coal tar are referred to as "coal tar pitch."

[0141] Generally, the following method 800 improves the quality of a coal tar product by contacting the feedstock with a mixture of supercritical fluid solvents and co-solvents, for example, by isolating and recovering high molecular weight (MW) coal tar from system 400 as shown in Figure 4 above. High molecular weight is defined as coal tar having a molecular weight of 1,000 amu (atomic mass units) or greater. "supercritical fluid" refers to compounds having a molecular weight of 1000 MW or greater. High MW hydrocarbons from coal tar are mesophase precursor materials. The supercritical fluid can be any supercritical fluid as described above, and the co-solvent can be any co-solvent, including aromatic organic solvents (e.g., benzene, xylene, tetralin, tetrahydrofuran, pyridine, quinoline, isoquinoline, etc.) or mixtures of co-solvents, although the remainder of this specification discusses the specific embodiment of a supercritical carbon dioxide (sCO2) / toluene solvent / co-solvent combination. Those skilled in the art will recognize that the present disclosure is not limited to the specific embodiments described below.

[0142] Method 800 begins with placing feedstock coal tar in a reactor vessel, such as vessel 404 described above (step 802). In one embodiment, any particular fraction or combination of fractions of coal tar can be used as the initial feedstock. For example, in one embodiment, all of the coal tar produced by system 400 of the published application can be used. Alternatively, all of the coal tar that condenses above a certain threshold temperature can be used. For example, all of the coal tar that condenses at or above 50°C, 100°C, 150°C, 200°C, or higher can be used. Alternatively, coal tar that condenses between some defined temperature range can be used.

[0143] The reactor is then raised to process temperature and pressure (as described above), and the sCO / toluene solvent is passed through the reactor 404 and a condensation circuit in an sCO / toluene extraction step 804. The condensation circuit collects and recovers the toluene-soluble (TS) fraction from the flowing sCO / toluene solvent, which then exits the reactor. The flow rate is maintained for a period of time selected by the operator, such as 1 minute, 1 hour, 2 hours, 4 hours, 10 hours, 24 hours, etc. The period may be fixed or determined based on the amount of TS fraction material recovered over time. For example, if the amount of TS fraction material per minute falls below a threshold, the extraction may be considered complete. After this period, the flow is stopped, and the reactor conditions are reduced to below supercritical conditions.

[0144] Optionally, the material remaining in the reaction vessel may then be washed with toluene as a final step in step 804. Alternatively, it may be washed with a solvent other than toluene or a combination of solvents (e.g., toluene and xylene) after the temperature and pressure conditions have been reduced to below supercritical conditions.

[0145] After the sCO / toluene extraction step 804, the toluene-insoluble (TI) fraction remaining in the reaction vessel can be washed with quinoline in a quinoline-soluble fraction extraction step 806. In an alternative embodiment, extraction step 806 may be performed in a different reaction vessel, requiring a transfer step between the vessels.

[0146] In one embodiment of this step 806, quinoline is added to the materials remaining in the vessel and held at a temperature and pressure for a period of time. In an alternative embodiment, quinoline is circulated through the reaction vessel held at a temperature and pressure for a period of time. After the desired period of time, the quinoline is removed for any period of time, e.g., less than or equal to 1 minute, 1 hour, 2 hours, 4 hours, 10 hours, 24 hours, etc., thereby removing any quinoline-soluble (QS) material and leaving quinoline-insoluble (QI) material in the reaction vessel.

[0147] The quinoline, along with the dissolved QS components, is then distilled in a distillation process using, for example, rotary evaporation, to separate the quinoline from the QS compounds. The QS compounds recovered from the distillation of quinoline (referred to herein as the QS fraction) represent an improved coal tar product suitable for the production of anisotropic mesophase pitch suitable for carbon fiber formation / spinning.

[0148] After distillation, the QS fraction is heat-treated to create a mesophase pitch before being added to the extruder. This heat-treatment step 807 creates a mesophase structure, if one is already present, or increases the amount of mesophase material. In one embodiment, heat-treatment step 807 can be performed under reduced, atmospheric, or elevated pressure (e.g., 1.01 atm to 500 atm) and involves heating the QS fraction to 300-400°C and holding at that temperature for a period of time sufficient to create the mesophase structure. For example, in one embodiment, temperature-controlled sCO2 can be used to heat the QS fraction in the reaction vessel. This step creates a mesophase structure (70-100%). Step 807 may also create some additional quinoline-insoluble (QI) material, which can be separated from the QS fraction before the next step, as shown. This can be done by performing another (second) extraction step 806.

[0149] In alternative embodiments, the heat treatment step 807 can heat the QS fraction to any temperature between 200 and 800°C for any period of time selected by the operator, e.g., less than or equal to 1 minute, 1 hour, 2 hours, 4 hours, 10 hours, 24 hours, etc. The period of time can be fixed or determined based on the amount of mesophase produced.

[0150] The QS fractions are then thoroughly mixed and extruded under static conditions in compounding step 808. This can be done, for example, using a HAAKE® MiniLab 3 Micro Compounder or a Pharma 11 Twin-screw extruder (both Thermo Scientific). This process can be carried out using any commercially available compounder or extruder, such as those manufactured by Scientific®. In this process, the QS fraction is thoroughly mixed in a supercritical sCO2 environment for a desired period of time. After the desired amount of mixing, the QS fraction and sCO2 mixture are extruded. As the material leaves the compounder / extruder, at elevated temperatures, the sCO2 solvent evaporates from the mixture, carrying away any compounds dissolved in the sCO2, leaving behind mesophase pitch fibers. The remaining extruded material is believed to be mostly, if not completely, mesophase pitch, and for this reason is referred to as the mesophase fraction. Without being bound by theory, it is believed that extrusion at elevated temperatures with sCO2 could potentially serve as both an oxidant and catalyst for residual undesirable light MW compounds (representing impurities in the mesophase pitch solution) that may ultimately form coke or poor crystallization upon graphitization, resulting in poor carbon fiber quality.

[0151] In the blending step 808 described above, mixing and extrusion occur simultaneously as a combined process. In an alternative embodiment, mixing and extrusion can be performed as separate steps. In this embodiment, mixing occurs under supercritical conditions in an sCO2 environment for a period of time required to determine complete mixing of the QS fraction. After complete mixing, the QS fraction and sCO2 are then passed through an extruder to separate the sCO2 from the mesophase fraction and produce a mesophase fiber fraction. The pressure, partial pressure, and concentration of the sCO2 can be adjusted prior to extrusion. The separated sCO2, which likely contains at least some dissolved low-MW compounds, is removed as the sCO2 fraction.

[0152] In yet another embodiment, an extrusion step can be performed with the mesophase fraction using an amount of CO solvent and a co-solvent (e.g., quinoline or toluene) from the sCO / toluene extraction step 804. The mesophase fraction can then be melt spun or extruded directly into fibers as known in the art.

[0153] In yet another embodiment, the extrusion step can be replaced by a simple separation process to separate the sCO fraction from the mesophase fraction. After this separation, the mesophase fraction can then be melt-spun or extruded directly into fibers, as known in the art. Alternatively, the mesophase fraction can be sold as is or used for purposes other than producing fibers.

[0154] The mesophase fiber fraction may be further stabilized in an optional stabilization step 810. Current stabilization processes involve extruding and pulling the fibers through a series of moderate-temperature (∼200–300°C) oxidation ovens. One purpose of conventional stabilization is to oxidatively remove residual light MW materials prior to graphitization. Because earlier steps in method 800, particularly sCO₂ / toluene extraction step 804 and blending step 808, are expected to remove many, if not most or all, of the low molecular weight compounds, the sCO₂ treatment described above may completely eliminate the need for stabilization step 810 or, alternatively, reduce the time required for sufficient stabilization.

[0155] After stabilization, an optional carbonization step 812 can be performed, as known in the art. Carbonization is a process in which all inorganic elements are removed by heating the fibers in an oxygen-free environment, producing a crystalline carbon structure in the fibers. A prior extraction step can make the mesophase fraction sufficiently devoid of inorganic elements to eliminate the need for a carbonization step or reduce the time required for carbonization.

[0156] A graphitization step 814 can then be performed on the mesophase fraction, as known in the art as the final step in making carbon fibers. Graphitization involves treating the fibers at elevated temperatures to improve the alignment and orientation of the crystalline regions along the fiber direction. Aligning, stacking, and orienting the crystalline regions along the fiber direction increases the overall strength of the carbon fiber.

[0157] The following numbered clauses define further embodiments and features of the present technology: 1. contacting a coal tar containing at least some mesophase pitch precursor with a mixture of supercritical carbon dioxide (sCO2) and toluene, thereby removing at least some toluene-soluble components from the coal tar and obtaining a toluene-insoluble fraction; separating the mixture of sCO and toluene from the toluene-insoluble fraction after the contacting step; washing the toluene-insoluble fraction with quinoline to obtain a mixture of quinoline and a quinoline-soluble fraction of the toluene-insoluble fraction; separating the quinoline from the quinoline-soluble fraction; mixing the quinoline soluble fraction with sCO to obtain an sCO / quinoline soluble fraction mixture; A method comprising: 2. 10. The method of claim 1, wherein the contacting step further comprises passing the sCO2 / quinoline soluble fraction mixture through an extruder, thereby separating the sCO2 from the quinoline soluble fraction to obtain fibers of the mesophase pitch. 3. 3. The method of claim 1 or 2, wherein the method further comprises, after the separating step, subjecting the toluene-insoluble fraction to a toluene wash, thereby removing additional soluble material from the toluene-insoluble fraction. 4. 4. The method of any one of clauses 1 to 3, wherein the step of separating quinoline from the quinoline soluble fraction further comprises distilling the mixture of quinoline and the quinoline soluble fraction. 5. 5. The method of any one of clauses 1 to 4, wherein the step of separating quinoline from the quinoline soluble fraction further comprises evaporating the quinoline to obtain a quinoline soluble fraction mixture. 6. 6. The method of any one of clauses 1 to 5, wherein the method further comprises the step of heating the quinoline soluble fraction to 300 to 400°C. 7. 7. The method of any one of clauses 1 to 6, wherein the method further comprises heating the quinoline soluble fraction to 300-400°C for less than 24 hours. 8. 8. The method of any one of clauses 1 to 7, wherein the method further comprises subjecting the mesophase pitch fibers to a stabilization process. 9. 9. The method of any one of clauses 1 to 8, wherein the method further comprises subjecting the mesophase pitch fibers to a carbonization process. 10. 10. The method of any one of clauses 1 to 9, wherein the method further comprises subjecting the mesophase pitch fibers to a graphitization process. 11. The method further comprises passing the mixture of sCO and toluene through a reaction vessel containing coal tar; 11. The method according to any one of clauses 1 to 10, wherein the washing step comprises washing the toluene-insoluble fraction with the reaction vessel. 12. 12. The method of clause 11, wherein the method further comprises circulating the quinoline in the reaction vessel for up to 24 hours before separating the quinoline from the quinoline soluble fraction. 13. 13. The method of any one of clauses 1 to 12, wherein the method further comprises the step of heating the quinoline soluble fraction to 200 to 800°C. 14. 14. The method of any one of clauses 6 to 13, wherein the heating step further comprises contacting the quinoline-soluble fraction with sCO2 heated to a temperature of 300 to 400°C. 15. 15. The method of any one of clauses 6 to 14, wherein the method further comprises, after the heating step, separating at least a portion of the quinoline-insoluble material from the quinoline-soluble material. 16. A method for producing carbon fibers, comprising: contacting a coal tar containing at least some mesophase pitch precursor with a mixture of supercritical carbon dioxide (sCO2) and toluene, thereby removing at least some toluene-soluble components from the coal tar and obtaining a toluene-insoluble fraction; separating the mixture of sCO and toluene from the insoluble coal tar fraction after the contacting step; After the separation step, mixing the toluene-insoluble fraction with sCO to obtain an sCO / toluene-insoluble fraction mixture; passing the sCO2 / toluene-insoluble fraction mixture through an extruder, thereby separating the sCO2 from the toluene-insoluble fraction to obtain mesophase pitch fibers; A method comprising: 17. The method further includes washing the toluene-insoluble fraction with quinoline to obtain a mixture of quinoline and a quinoline-soluble fraction and a quinoline-insoluble fraction of the toluene-insoluble fraction; separating the quinoline from the quinoline-soluble fraction of the toluene-insoluble fraction; mixing the quinoline soluble fraction of the toluene insoluble fraction with sCO to obtain an sCO / toluene insoluble fraction mixture; 17. The method according to clause 16, comprising: 18. 18. The method of claim 17, further comprising heating the quinoline-soluble fraction of the toluene-insoluble fraction to 300-400°C for less than 24 hours before combining the quinoline-soluble fraction of the toluene-insoluble fraction with sCO. 19. 19. The method of claim 18, wherein the heating step further comprises contacting the quinoline soluble fraction with sCO heated to a temperature of 300-400°C for up to 24 hours. 20. 20. The method of any one of clauses 16 to 19, wherein the method further comprises subjecting the mesophase pitch fibers to a stabilization process. twenty one. 21. The method of any one of clauses 16 to 20, wherein the method further comprises subjecting the mesophase pitch fibers to a carbonization process. twenty two. 22. The method of any one of clauses 16 to 21, wherein the method further comprises subjecting the mesophase pitch fibers to a graphitization process. twenty three. A method for producing carbon fibers, comprising: contacting a coal tar containing at least some mesophase pitch precursor with a mixture of a supercritical fluid solvent and a first co-solvent, thereby removing at least some soluble components from the coal tar and obtaining an insoluble coal tar fraction; separating the mixture of the supercritical fluid solvent and the first co-solvent from the insoluble coal tar fraction after the contacting step; After the separation step, mixing the insoluble coal tar fraction with sCO to obtain an sCO / insoluble fraction mixture; passing the sCO2 / insoluble fraction mixture through an extruder, thereby separating the sCO2 from the insoluble fraction to obtain mesophase pitch fibers; A method comprising: twenty four. The method further includes washing the insoluble fraction with a second co-solvent to obtain a mixture of the second co-solvent and a second co-solvent-soluble fraction and a second co-solvent-insoluble fraction of the first insoluble fraction; separating the second co-solvent from the second co-solvent-soluble fraction of the insoluble fraction; mixing a second co-solvent soluble fraction of the insoluble fraction with sCO to obtain an sCO / insoluble fraction mixture; Including, 24. The method of claim 23, wherein the second co-solvent is selected from one or more of benzene, xylene, tetralin, tetrahydrofuran, pyridine, and quinoline. twenty five. 25. The method of claim 24, further comprising heating the second co-solvent soluble fraction of the insoluble fraction to 300-400°C for less than 24 hours prior to combining the second co-solvent soluble fraction with sCO2. 26. 26. The method of clause 25, wherein the heating step further comprises contacting the second co-solvent soluble fraction with sCO2 heated to a temperature of 300-400°C for up to 24 hours. 27. 27. The method of any one of clauses 23 to 26, further comprising subjecting the mesophase pitch fibers to a stabilization process. 28. 28. The method of any one of clauses 23 to 27, wherein the method further comprises subjecting the mesophase pitch fibers to a carbonization process. 29. 29. The method of any one of clauses 23 to 28, wherein the method further comprises subjecting the mesophase pitch fibers to a graphitization process. 30. 30. The method of any one of clauses 23-29, wherein the supercritical fluid solvent is selected from one or more of carbon dioxide, water, methane, nitrous oxide, ethane, propane, ethylene, propylene, methanol, ethanol, and acetone. 31. 31. The method of any one of clauses 23 to 30, wherein the first co-solvent is an aromatic organic solvent. 31. The method of any one of clauses 24 to 30, wherein the second co-solvent is an aromatic organic solvent. 33. 33. The method of any one of clauses 23 to 32, wherein the first co-solvent is selected from one or more of benzene, xylene, tetralin, tetrahydrofuran, pyridine, and quinoline. 34. 34. The method of any one of clauses 23 to 33, wherein the second co-solvent is selected from one or more of benzene, xylene, tetralin, tetrahydrofuran, pyridine, and quinoline. 35. Coal tar is pyrolyzing a combination of carbonaceous feedstocks at a first temperature and a first pressure for a first period of time to produce C1-C4 gases; increasing the combination to a second temperature greater than the first temperature; pyrolyzing the combination at a second temperature for a second period of time to produce coal tar; extracting coal tar from the combination; 35. The method of any one of clauses 23 to 34, wherein the method is produced by 36. 36. The method of claim 35, wherein the first temperature is 150 to 350°C and the first pressure is 7 to 30 MPa. 37. 37. The method of claim 35 or 36, wherein the second temperature is 350 to 550°C. 38. 39. The method of any one of clauses 35 to 37, wherein the first period of time is 1 to 120 minutes. 39. The method of any one of clauses 35-38, wherein the first period of time is determined based on an amount of at least one C1-C4 gas produced from the carbonaceous feedstock at the first temperature. 40. 40. The method of any one of clauses 35 to 39, wherein the second period of time is from 1 minute to 24 hours. 41. 41. The method of any one of clauses 35-40, wherein the step of pyrolyzing the carbonaceous feedstock at a first temperature and a first pressure occurs in a first pyrolysis reaction chamber. 42. 42. The method of any one of clauses 35-41, wherein pyrolyzing the carbonaceous feedstock at the second temperature occurs in the first pyrolysis reaction chamber. 43. 43. The method of any one of clauses 35-42, wherein pyrolyzing the carbonaceous feedstock at the second temperature occurs in a second pyrolysis reaction chamber different from the first pyrolysis reaction chamber. 44. 44. The method of any one of clauses 35-43, wherein the step of pyrolyzing the carbonaceous feedstock at a first temperature and a first pressure is conducted in a carbon dioxide atmosphere. 45. 45. The method of any one of clauses 35-44, wherein the method further comprises monitoring the concentration of one or more C1-C4 gases in the pyrolysis atmosphere. 46. 46. The method of clause 45, wherein extracting the coal tar comprises transferring the carbon dioxide atmosphere to a separation system. 47. 47. The method of claim 45 or 46, wherein extracting the coal tar comprises reducing at least one of the temperature or pressure of the carbon dioxide atmosphere.

[0158] Unless otherwise indicated, all numbers expressing properties such as quantities of ingredients, molecular weights, reaction conditions, and the like used in the specification and claims are to be understood as being modified in all instances by the term "about." Thus, unless indicated to the contrary, the numerical parameters set forth in the following specification and appended claims are approximations that may vary depending upon the desired properties sought to be obtained.

[0159] Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the present technology are approximations, the numerical values set forth in the specific examples are reported as precisely as possible, however, any numerical value inherently contains certain errors necessarily resulting from the standard deviation found in their respective testing measurements.

[0160] It will be apparent that the systems and methods described herein are well adapted to attain the objects and advantages mentioned, as well as those inherent therein. Those skilled in the art will recognize that the methods and systems herein may be implemented in numerous ways and are thus not limited by the illustrative embodiments and examples set forth above. In this regard, any number of the features of the different embodiments described herein may be combined into one single embodiment, and alternative embodiments having fewer or more than all of the features described herein are possible.

[0161] While various embodiments have been described for purposes of this disclosure, various changes and modifications can be made that are within the scope fully contemplated by this disclosure. For example, in one embodiment, quinoline extraction step 806 can be omitted and the TI fraction can be sent directly to heat treatment step 807. Numerous other modifications can be made that will be readily suggested to those skilled in the art and are encompassed by the spirit of this disclosure. [Brief explanation of the drawings]

[0162] [Figure 1] At a high level, a simplified embodiment of a pyrolysis process that improves the relative amount of pitch produced from a given feedstock is shown. [Figure 2] 2 shows a more detailed embodiment of the pyrolysis method of FIG. 1. [Figure 3] This is an example of a system suitable for the pitch production method described above. [Figure 4] FIG. 1 shows a process flow diagram for a batch embodiment of a flexible pyrolysis system that can be adjusted to vary the pyrolysis products obtained from a given feedstock. [Figure 5A] FIG. 5 illustrates experimental performance of one embodiment of the system shown in FIG. 4. [Figure 5B] FIG. 5 illustrates experimental performance of one embodiment of the system shown in FIG. 4. [Figure 5C] FIG. 5 illustrates experimental performance of one embodiment of the system shown in FIG. 4. [Figure 6] 1 illustrates an embodiment of a broad method for pyrolyzing a carbonaceous feedstock with CO2 to obtain a reaction product. [Figure 7] 1 is a more detailed embodiment of a method for pyrolysis of coal using supercritical CO2. [Figure 8] 1 illustrates an embodiment of a method for improving mesophase pitch for carbon fiber production using supercritical carbon dioxide.

Claims

1. A method for producing mesophase fibers, comprising: contacting the coal-derived material with a mixture of a supercritical fluid solvent and a first co-solvent, thereby removing at least some soluble components from the coal-derived material and obtaining an insoluble coal-derived fraction; separating the mixture of the supercritical fluid solvent and a first co-solvent from the insoluble coal-derived fraction; mixing the insoluble coal-derived fraction with a supercritical fluid to obtain a supercritical fluid / insoluble fraction mixture; separating the supercritical fluid from the insoluble fraction to obtain the mesophase fibers; A method comprising:

2. The method of claim 1 , wherein the coal-derived material comprises coal tar.

3. 10. The method of claim 1, wherein the coal-derived material comprises a mesophase pitch precursor.

4. The supercritical fluid is sCO ２ The method of claim 1 , comprising:

5. 10. The method of claim 1, wherein separating the supercritical fluid from the insoluble fraction comprises passing the supercritical fluid / insoluble fraction mixture through an extruder.

6. The method further comprises: washing the insoluble coal-derived fraction with a second co-solvent to obtain a mixture of a second co-solvent and a second co-solvent-soluble fraction and a second co-solvent-insoluble fraction of the insoluble coal-derived fraction; separating the second co-solvent from the second co-solvent soluble fraction of the insoluble fraction; mixing the second co-solvent soluble fraction of the insoluble fraction with the supercritical fluid to obtain the supercritical fluid / insoluble fraction mixture; The method of claim 1 , comprising:

7. 7. The method of claim 6, wherein the second co-solvent is selected from one or more of benzene, xylene, tetralin, tetrahydrofuran, pyridine, and quinoline.

8. The method further comprises: heating the second co-solvent soluble fraction of the insoluble fraction to 300-400°C for less than 24 hours prior to combining the second co-solvent soluble fraction with the supercritical fluid; contacting the second co-solvent soluble fraction with the supercritical fluid heated to a temperature of 300-400°C for up to 24 hours; The method of claim 6, comprising:

9. A method for producing carbon fiber, comprising: carrying out the method according to any one of claims 1 to 8; a graphitization step for the mesophase fibers obtained by carrying out the method; A method for producing carbon fiber, comprising:

10. 7. The method of claim 6, wherein at least one of the first co-solvent and the second co-solvent comprises an aromatic organic solvent.

11. 7. The method of claim 6, wherein at least one of the first co-solvent and the second co-solvent is selected from one or more of benzene, xylene, tetralin, tetrahydrofuran, pyridine, and quinoline.

12. 10. The method of claim 1, wherein the supercritical fluid solvent is selected from one or more of carbon dioxide, water, methane, nitrous oxide, ethane, propane, ethylene, propylene, methanol, ethanol, and acetone.

13. The coal-derived material Pyrolyzing a combination of carbonaceous feedstocks at a first temperature and a first pressure for a first period of time to produce C １ -C ４ generating a gas; increasing the combination to a second temperature greater than the first temperature; pyrolyzing the combination at a second temperature for a second period of time to produce coal-derived materials; extracting coal-derived materials from the combination; The method of claim 1 , wherein the compound is produced by

14. 14. The method of claim 13, wherein the first temperature is 150 to 350°C, the second temperature is 350 to 550°C, and the first pressure is 7 to 30 MPa.

15. 14. The method of claim 13, wherein the first period of time is from 1 to 120 minutes.

16. 14. The method of claim 13, wherein the second period of time is between 1 minute and 24 hours.

17. 14. The method of claim 13, wherein the step of pyrolyzing the carbonaceous feedstock at the first temperature and first pressure occurs in a first pyrolysis reaction chamber.

18. The method of claim 13 , wherein the step of pyrolyzing the carbonaceous feedstock at the first temperature and first pressure occurs in a carbon dioxide atmosphere.

19. 14. The method of claim 13, wherein the step of extracting the coal-derived material occurs in a carbon dioxide atmosphere, and further comprising the step of transferring the carbon dioxide atmosphere to a separation system.

20. 14. The method of claim 13, wherein the step of extracting the coal-derived material occurs in a carbon dioxide atmosphere, and further comprising reducing at least one of a temperature or a pressure of the carbon dioxide atmosphere.

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