Method for refining pretreatment of coal liquefaction heavy slurry oil and preparation of mesophase pitch

Abstract

The invention relates to a method for refining pretreatment of coal liquefaction heavy oil slurry and preparation of mesophase pitch, the method can remove impurities in the coal liquefaction heavy oil slurry and realize regulation and control of components of the coal liquefaction heavy oil slurry, and the cut narrow fraction refined oil slurry has the characteristics of low ash, low residual carbon value, low asphaltene, high hydrogen-carbon ratio and high aromatic hydrocarbon content; the refined oil slurry is heated to the thermal polycondensation temperature for thermal polycondensation reaction, aromatic ring compound molecules in the refined oil slurry can be subjected to polycondensation to form planar macromolecules, stacking is formed, growth of an intermediate phase is promoted, the intermediate phase pitch with the texture mainly comprising a wide-area streamline structure is obtained, and the technology is suitable for engineering amplification.

Description

Technical Field

[0001] This disclosure relates to the field of bitumen preparation, specifically to a method for refining and pretreating coal liquefaction heavy oil slurry and preparing mesophase bitumen. Background Technology

[0002] Mesophase pitch is a precursor to high-performance carbon materials, and mesophase pitch-based carbon fiber (MPCF) is its main application. The most outstanding properties of mesophase pitch-based carbon fiber are high modulus and high thermal conductivity, and it is widely used in new energy, aerospace, automotive and other fields.

[0003] Mesophase pitch precursors are mainly composed of polycyclic aromatic hydrocarbons extracted from petroleum residue and coal tar. Coal tar and petroleum residue have complex compositions and contain impurities that are difficult to remove, affecting the properties of mesophase pitch. To address the inherent defects of coal tar pitch and petroleum residue pitch, researchers have employed catalytic and polymerization methods to prepare mesophase pitch. The catalytic method uses HF / BF3, which causes severe equipment corrosion, has low yields, and is costly. The polymerization method suffers from poor product uniformity due to the wide molecular distribution of the raw materials and varying polymerization characteristics in different parts, leading to breakage during continuous spinning. Currently, domestically synthesized mesophase pitch has high impurity content, low mesophase content, poor texture morphology, and its continuous spinning performance needs improvement. In actual production, raw material quality is the fundamental factor restricting the production of high-quality mesophase pitch. Shorter side chains, higher H / C ratios, and higher aromatic hydrocarbon content, especially rich in 3-4 ring aromatic hydrocarbons, result in higher yields and better quality mesophase pitch. In order to obtain high-quality, high-performance carbon fibers from raw bitumen, the raw materials must be refined and processed, which greatly increases production costs.

[0004] Direct coal liquefaction (DCL) is an important clean coal conversion and utilization technology in my country. During DCL, the reactor outlet produces a three-phase mixture of solid, liquid, and gas. This mixture is effectively separated using atmospheric and vacuum distillation technology. DCL generates heavy distillate oil rich in aromatics. Compared to the main raw materials for mesophase pitch preparation, such as polyacrylonitrile, refined naphthalene, and refined pitch, heavy distillate oil is cheaper and more abundant. After hydrogenation in the DCL reactor, it has a suitable H / C ratio, fewer heteroatoms, a relatively light composition, and good fluidity. Its high aromatic content makes it a potential carbon source for mesophase pitch. However, the chemical composition and structure of different fractions of heavy distillate oil vary significantly. Directly using it to prepare mesophase pitch results in a wide molecular weight distribution after polymerization, with inconsistent polymerization depths among the components, making it difficult to obtain mesophase pitch with both high mesophase content and a rich flow-like structure. In addition, heavy oil feedstocks usually need to undergo pretreatment to remove impurities. The main pretreatment methods include sedimentation, filtration, centrifugation, extraction and combination techniques. Most of these techniques can only remove impurity components from the feedstock and are difficult to control the composition of heavy oil products while removing impurities. Summary of the Invention

[0005] The purpose of this disclosure is to provide a method for refining and pretreating heavy coal liquefaction oil slurry and preparing mesophase pitch. This method can remove impurities from heavy coal liquefaction oil slurry and control its composition. The narrow-fraction refined oil slurry after cutting has the characteristics of low ash, low residual carbon value, low asphaltenes, high hydrogen-to-carbon ratio and high aromatic content. Its molecular composition is mainly composed of 3-4 ring aromatic compounds. The mesophase pitch prepared by using this refined oil slurry has a high mesophase content and a texture dominated by a wide-area streamline structure, which is a technology suitable for engineering scale-up.

[0006] To achieve the above objectives, this disclosure provides a method for refining and pretreating heavy oil slurry from coal liquefaction and preparing mesophase asphalt, the method comprising: (1) The coal liquefaction heavy oil slurry and the extraction solvent are subjected to supercritical extraction in a supercritical extraction tower to obtain the extract phase collected at the top of the tower and the raffinate phase collected at the bottom of the tower. (2) Separate the refined oil slurry from the extract phase and heat the refined oil slurry to the thermal polycondensation temperature to carry out the thermal polycondensation reaction.

[0007] Optionally, in step (1), the extraction solvent includes aliphatic hydrocarbons with 4 to 10 carbon atoms and / or aromatic hydrocarbons with 6 to 10 carbon atoms, preferably including aliphatic hydrocarbons with 4 to 6 carbon atoms and / or aromatic hydrocarbons with 6 to 8 carbon atoms. Preferably, the aliphatic hydrocarbons having 4 to 6 carbon atoms include one or more of n-butane, n-pentane, n-hexane, and cyclohexane, with n-pentane being the most preferred; the aromatic hydrocarbons having 6 to 8 carbon atoms include one or more of benzene, toluene, and xylene. More preferably, the extraction solvent is n-pentane.

[0008] Optionally, in step (1), the weight ratio of the extraction solvent to the coal liquefaction heavy oil slurry is (1~8):1, preferably (3~5):1; and / or, the temperature of the supercritical extraction treatment is 110~300℃, preferably 170~210℃; and the pressure is 2~10MPa, preferably 3~6MPa.

[0009] Optionally, in step (1), the coal liquefaction heavy oil slurry is heavy oil produced by the direct coal liquefaction process, with a density of 1.0~1.21 g / cm³. 3 The residual carbon content is 40-50% by weight, the ash content is 0.1-1% by weight, the asphaltene content is 10-30% by weight, the aromatic content is 30-60% by weight, and the hydrogen-to-carbon ratio is 0.6-1.0.

[0010] Optionally, in step (2), the density of the refined oil slurry is 0.9~1.2 g / cm³. 3 The residual carbon content is 0.1-45% by weight, the ash content is 0-0.5% by weight, the asphaltene content is 0.1-10% by weight, the aromatic content is 20-80% by weight, the saturated content is 1-15% by weight, and the hydrogen-to-carbon ratio is 0.7-1.12.

[0011] Optionally, in step (2), the separation method includes: sending the extract phase into a solvent separator for solvent flash evaporation to obtain a first solvent collected at the top and the refined oil slurry collected at the bottom; and allowing the first solvent to enter a solvent recovery tank.

[0012] Optionally, the temperature of the solvent separator is 80~300℃, preferably 100~150℃; the pressure is 0~0.20MPa; the solvent separator includes a first heating device, the heating method of the first heating device includes one or more of combustion furnace heating, electric heating and heat transfer oil heating; preferably, the solvent separator includes a stripping tower.

[0013] Optionally, in step (2), the heating is a gradient heating, which includes: in an inert atmosphere, the refined oil slurry is heated to a first temperature at a first heating rate, then heated to a second temperature at a second heating rate, and finally heated to the thermal polycondensation temperature at a third heating rate; optionally, the inert atmosphere includes one or more of nitrogen, argon and helium, preferably nitrogen.

[0014] Optionally, in step (2), the gradient heating satisfies at least one of the following conditions: The first heating rate is 5~12℃ / min, preferably 10℃ / min; The first temperature is 180~220℃; The second heating rate is 1~5℃ / min, preferably 3℃ / min; The second temperature is 330~370℃; The third heating rate is 1~5℃ / min, preferably 2℃ / min; The thermal polycondensation temperature is 470~520℃; and The pressure of the thermal polycondensation reaction is 0.1~1.0 MPa, and the time is 6~20 h.

[0015] Optionally, the method further includes at least one of the following steps: S1. The coal liquefaction heavy oil slurry and the extraction solvent are heated and mixed in a mixer, and the resulting mixture is fed into the supercritical extraction tower for supercritical extraction treatment; or, the coal liquefaction heavy oil slurry is heated and fed into the supercritical extraction tower, where it is countercurrently contacted with the extraction solvent to perform the supercritical extraction treatment. S2. The upper part of the supercritical extraction tower is a cylinder, and the lower part is an inverted cone; optionally, a second heating device is provided on the outside of the inverted cone, and the heating method of the second heating device includes one or more of steam heating, electric heating and heat transfer oil heating; S3. The bottom of the supercritical extraction tower is equipped with a solvent flushing line, a stirring component or a circulating pump; S4. The raffinate phase is introduced into a solvent flash tank for solvent flash evaporation to obtain a second solvent and a solid material; the second solvent is introduced into a solvent recovery tank, and the solid material is introduced into a raffinate tank; preferably, the pressure of the raffinate phase entering the solvent flash tank is 0~0.2MPa; S5. The refined oil slurry undergoes the thermal polycondensation reaction in a reactor, and the reactor is placed in a tin bath for the heating process.

[0016] This disclosure provides a method for refining and pretreating heavy coal liquefaction oil slurry and preparing mesophase pitch using the above technical solutions. The pretreatment employs supercritical fluid extraction technology, utilizing the unique characteristics of supercritical fluids such as low density, high diffusion, high solubility, and high selectivity. This effectively removes impurities such as ash and asphaltenes from the heavy coal liquefaction oil slurry and allows for the control of its composition, resulting in a refined oil slurry with a high aromatic content. Heating the refined oil slurry to its thermal polymerization temperature facilitates the condensation of aromatic ring compounds into planar macromolecules and their stacking, promoting the growth of the mesophase. Ultimately, this yields mesophase pitch with a high mesophase content and a predominantly streamlined structure, with a streamlined structure content as high as 78% to 95.7%, making it an ideal raw material for preparing high-performance carbon fibers. This method provides a new solution for the large-scale production of high-quality spinning-grade mesophase pitch, which is beneficial for preparing high-quality pitch-based carbon fibers and promoting the rapid development of related downstream industries such as mesophase pitch-based carbon fibers.

[0017] Other features and advantages of this disclosure will be described in detail in the following detailed description section. Attached Figure Description

[0018] The accompanying drawings are provided to further illustrate the present disclosure and form part of the specification. They are used together with the following detailed description to explain the present disclosure, but do not constitute a limitation thereof. In the drawings: Figure 1 This is a polarized light microscope image of the mesophase pitch obtained from the refined oil slurry of Example 5 of this disclosure. Figure 2 This is a polarized light microscope image of the mesophase pitch obtained by using the refined oil slurry of Example 5 in Example 8 of this disclosure; Figure 3 This is a polarized light microscope image of the mesophase pitch obtained by using the refined oil slurry of Example 5 in Example 9 of this disclosure. Detailed Implementation

[0019] The specific embodiments of this disclosure will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit this disclosure.

[0020] In this disclosure, unless otherwise specified, the top of the container refers to 0-10% of the container from top to bottom; the upper part of the container refers to 10-40% of the container from top to bottom; the middle part of the container refers to 40-60% of the container from top to bottom; the lower part of the container refers to 60-90% of the container from top to bottom; and the bottom of the container refers to 90-100% of the container from top to bottom.

[0021] This disclosure provides a method for refining and pretreating heavy oil slurry from coal liquefaction and preparing mesophase bitumen, the method comprising: (1) The coal liquefaction heavy oil slurry and the extraction solvent are subjected to supercritical extraction in a supercritical extraction tower to obtain the extract phase collected at the top of the tower and the raffinate phase collected at the bottom of the tower. (2) Separate the refined oil slurry from the extract phase and heat the refined oil slurry to the thermal polycondensation temperature to carry out the thermal polycondensation reaction.

[0022] The method disclosed herein employs supercritical fluid extraction technology, utilizing the unique characteristics of supercritical fluids such as low density, high diffusion, high solubility, and high selectivity. This not only effectively removes impurities from coal liquefaction heavy oil slurry but also allows for the control of its composition, resulting in refined oil slurry with a high aromatic content. Heating the refined oil slurry to its thermal condensation temperature facilitates the condensation of aromatic ring compounds into planar macromolecules and their stacking, promoting the growth of the mesophase. Ultimately, this yields mesophase pitch with a high mesophase content and a predominantly streamlined structure, achieving a streamlined structure of over 78%.

[0023] The coal liquefaction heavy slurry disclosed herein is obtained from direct coal liquefaction technology. This heavy slurry is characterized by high molecular weight, high viscosity, and high density (typically higher than 1.0 g / cm³). 3 The slurry contains a large amount of impurities such as asphaltene, ash, S, and N, and the composition is widely distributed with significant differences in chemical composition and structure among different components. The method provided in this disclosure eliminates the need for hydrogenation control, thus removing the hydrogenation treatment step. It employs a simple supercritical extraction technology to achieve impurity removal and composition control in coal liquefaction heavy oil slurry. The equipment only requires a tower, and the process is simple, low-cost, and suitable for industrial scale-up. It is a simple and efficient pretreatment technology.

[0024] The extraction solvent disclosed herein is a low-boiling-point solvent. Specifically, in step (1), the extraction solvent includes aliphatic hydrocarbons with 4 to 10 carbon atoms and / or aromatic hydrocarbons with 6 to 10 carbon atoms, preferably including aliphatic hydrocarbons with 4 to 6 carbon atoms and / or aromatic hydrocarbons with 6 to 8 carbon atoms. In a specific embodiment, the aliphatic hydrocarbons with 4 to 6 carbon atoms include one or more of n-butane, n-pentane, n-hexane, and cyclohexane, preferably n-pentane; the aromatic hydrocarbons with 6 to 8 carbon atoms include one or more of benzene, toluene, and xylene. In one embodiment, the extraction solvent is n-pentane. In the above embodiments, by selecting the preferred extraction solvent, it is beneficial to further remove solid particles (including unreacted coal, catalyst, ash), residual carbon, ash, asphaltenes, and gums and other impurities from the coal liquefaction heavy slurry, and further regulate the composition of the coal liquefaction heavy slurry, thereby obtaining a refined slurry with a higher aromatic content.

[0025] In one embodiment of this disclosure, in step (1), the weight ratio of the extraction solvent to the coal liquefaction heavy oil slurry is (1~8):1, specifically 1.5:1, 2:1, 3:1, 3.5:1, 4:1, 4.5:1, 5:1, 6:1, 7:1, and any two of these values ​​forming a range, preferably (3~5):1; the temperature of the supercritical extraction treatment is 110~300℃, specifically 120℃, 180℃, 220℃, 250℃, 280℃, and any two of these values ​​forming a range, preferably 170~210℃; the pressure is 2~10 MPa, preferably 3~6 MPa. In the above embodiments, by selecting preferred extraction conditions, the selectivity of the extraction solvent can be further improved, and the heavy oil slurry fraction can be cut. The narrow fraction refined oil slurry obtained after cutting is mainly composed of aromatic compounds with 3 to 4 rings, and has the characteristics of low ash content, low residual carbon value, low asphaltenes, low heteroatoms, high hydrogen-to-carbon ratio and high aromatic content.

[0026] In one embodiment, in step (1), the coal liquefaction heavy oil slurry is heavy oil produced by the direct coal liquefaction process, with a density of 1.0~1.21 g / cm³. 3 The residual carbon content is 40-50% by weight, specifically 41%, 43%, 46%, 49%, or any two of these values; the ash content is 0.1-1% by weight, specifically 0.2%, 0.4%, 0.6%, 0.8%, or any two of these values, preferably 0.15-0.8% by weight; the sulfur content is 0.05-1.1% by weight, specifically 0.1%, 0.3%, 0.6%, 0.8%. The mass content of asphaltene is 10-30% by weight, specifically 11%, 15%, 20%, 25%, 29%, and any two of these values; the mass content of aromatics is 30-60% by weight, specifically 30%, 40%, 50%, 60%, and any two of these values, preferably 40-60% by weight; the hydrogen-to-carbon ratio is 0.6-1.0. In the above embodiments, the coal liquefaction heavy oil slurry contains a large amount of harmful impurities such as ash, residual carbon, asphaltene, and colloids, and also contains a large amount of aromatics with a wide distribution and complex composition.

[0027] In one embodiment, in step (2), the density of the refined oil slurry is 0.9~1.2 g / cm³. 3The residual carbon content is 0.1-45 wt%, specifically 1 wt%, 3 wt%, 6 wt%, 10 wt%, 20 wt%, 40 wt%, and any two of these values, preferably 1-9 wt%; the ash content is 0-0.5 wt%, specifically 0.01 wt%, 0.03 wt%, 0.06 wt%, 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, and any two of these values, preferably 0-0.05 wt%; the sulfur content is 0-0.05 wt%, specifically 0.01 wt%, 0.02 wt%, 0.03 wt%, 0.04 wt%, and any two of these values, preferably 0-0.05 wt%. The asphaltene content is 0.1-10% by weight, specifically 0.2%, 0.5%, 1%, 5%, 9%, or any two of these values, preferably 0.1-0.9% by weight; the aromatic content is 20-80% by weight, specifically 25%, 30%, 50%, 70%, 79%, or any two of these values, preferably 60-78% by weight; the saturated content is 1-15% by weight, specifically 1%, 4%, 8%, 12%, 15%, or any two of these values, preferably 2-8% by weight; and the hydrogen-to-carbon ratio is 0.7-1.12. The refined oil slurry obtained after supercritical extraction of this disclosure has the characteristics of low ash content, low asphaltene content, high hydrogen-to-carbon ratio, and enriched aromatics, which is beneficial for further increasing the mesophase content of mesophase asphalt.

[0028] In this disclosure, aromatic fraction refers to all aromatic hydrocarbons contained in the oil slurry. In one embodiment, the aromatic fraction in the refined oil slurry mainly consists of aromatic compounds with 3 to 4 aromatic rings, such as anthracene, phenanthrene, pyrene, fluoranthene, and benzanthene. The saturated fraction mainly consists of straight-chain and branched aliphatic hydrocarbons, alkyl cyclic hydrocarbons, and some alkyl aromatic hydrocarbons.

[0029] In one embodiment of this disclosure, step (2) includes the following separation method: sending the extract phase into a solvent separator for solvent flash evaporation to obtain a first solvent collected at the top and the refined oil slurry collected at the bottom; and allowing the first solvent to enter a solvent recovery tank.

[0030] In a specific embodiment, the temperature of the solvent separator is 80~300℃, preferably 100~150℃; the pressure is 0~0.20MPa; the solvent separator includes a first heating device, the heating method of which includes one or more of combustion furnace heating, electric heating, and heat transfer oil heating; preferably, the solvent separator includes a stripping tower. In a preferred embodiment, the first solvent is cooled to room temperature, such as 20℃, before entering the solvent recovery tank. In the above embodiments, by selecting the preferred solvent separator and separation conditions, it is beneficial to effectively distill off and recover the solvent in the extract phase, resulting in low energy consumption for solvent recovery; at the same time, the recovered solvent can be recycled back to the supercritical extraction tower for continued use, which helps to reduce solvent consumption and obtain high-purity refined oil slurry.

[0031] In one embodiment of this disclosure, in step (2), the heating is a gradient heating, which includes: in an inert atmosphere, the refined oil slurry is heated to a first temperature at a first heating rate, then heated to a second temperature at a second heating rate, and finally heated to the thermal polycondensation temperature at a third heating rate; optionally, the inert atmosphere includes one or more of nitrogen, argon and helium, preferably nitrogen.

[0032] In the specific implementation, in step (2), the first heating rate is 5~12℃ / min, preferably 10℃ / min; the first temperature is 180~220℃; the second heating rate is 1~5℃ / min, preferably 3℃ / min; the second temperature is 330~370℃; the third heating rate is 1~5℃ / min, preferably 2℃ / min; the thermal polycondensation temperature is 470~520℃, specifically 480℃, 485℃, 495℃, 510℃, 519℃, and any two of these values, preferably 470~500℃; the pressure of the thermal polycondensation reaction is 0.1~1.0MPa, and the time is 6~20h, specifically 8h, 10h, 12h, 15h, 18h, and any two of these values, preferably 8~14h. In the above embodiments, by selecting a preferred heating rate, it is beneficial for the aromatic ring compound molecules in the refined oil slurry to further stack; by selecting preferred thermal polycondensation conditions, it is beneficial for the mesophase to grow and develop more fully, thereby further increasing the mesophase content.

[0033] This disclosure does not limit the order and method of adding coal liquefaction heavy oil slurry and extraction solvent to the supercritical extraction tower. In one embodiment of this disclosure, the coal liquefaction heavy oil slurry is heated and pressurized before entering a mixer, and the extraction solvent is heated before entering the mixer. After being mixed evenly in the mixer, the resulting mixture is entered into the supercritical extraction tower for supercritical extraction treatment.

[0034] In another embodiment, the coal liquefaction heavy oil slurry is heated and pressurized before entering the supercritical extraction tower, and the extraction solvent is also heated before entering the supercritical extraction tower, where they engage in countercurrent contact. Preferably, the coal liquefaction heavy oil slurry is heated and pressurized before entering the supercritical extraction tower from the upper middle part, while the extraction solvent is heated before entering the supercritical extraction tower from the lower part, to achieve the countercurrent contact and realize mixed mass transfer extraction. In a preferred embodiment, the coal liquefaction heavy oil slurry is pressurized to 2~10 MPa by a feed pump.

[0035] In one embodiment, the upper part of the supercritical extraction tower is cylindrical, and the lower part is an inverted cone. In a preferred embodiment, the supercritical extraction tower is an empty barrel tower with an inverted cone at the bottom and a cylindrical upper part, without internal components. A second heating device is provided on the outside of the inverted cone to prevent the raffinate phase from depositing at the bottom of the tower and clogging the discharge pipe. The heating method of the second heating device includes one or more of steam heating, electric heating, and heat transfer oil heating. In the above embodiments, the supercritical extraction tower with the preferred structure is beneficial for uniform mixing of coal liquefaction heavy oil slurry and extraction solvent, and facilitates material flow.

[0036] The raffinate phase disclosed herein contains solid particles (including ash, unreacted coal, and catalyst), asphaltene, colloids, and other impurities insoluble in solvents. Due to its high density, it settles to the bottom of the supercritical extraction tower under gravity, forming a two-phase separation with the extract phase, which contains a large amount of solvent and refined oil slurry. In one embodiment, the bottom of the supercritical extraction tower is equipped with a solvent flushing line, a stirring component, or a circulating pump to facilitate the flow of the raffinate phase and its subsequent discharge treatment.

[0037] In one embodiment, the raffinate phase is depressurized to 0-0.2 MPa via a regulating valve, and then enters a solvent flash evaporator for solvent flash evaporation to obtain a second solvent and the remaining solid phase. The second solvent is then cooled and recovered in a solvent recovery tank, and the solid phase is cooled to below 150°C, becoming solid particles before entering the raffinate tank. The solid particles can be discharged into the raffinate tank via a star-shaped rotary solid particle discharge valve or a gate valve; any method that allows for solid particle discharge is acceptable and not limited in this regard.

[0038] In one embodiment, the refined oil slurry undergoes the thermal polycondensation reaction in a reactor, which is placed in a tin bath for the heating process.

[0039] As is known to those skilled in the art, mesophase pitch is a mixture composed of various flattened disc-shaped polycyclic aromatic hydrocarbons with a relative molecular mass of 370-2000. It exhibits an optically anisotropic, turbid fluid state, possessing both the optical isotropy of a liquid state and the optical anisotropy of a crystal, hence the name mesophase. The higher the mesophase content of mesophase pitch, the better its heat resistance, oxidation resistance, and mechanical strength.

[0040] The morphologies of mesophase asphalt include fluidized bed structures, mosaic structures, spherical structures, fibrous structures, and layered structures. Among these, the fluidized bed structure exhibits good fluidity and displays obvious birefringence under a polarizing microscope, indicating a certain degree of order in the molecular arrangement of the mesophase asphalt, while also possessing good flow properties. When the fluidized bed structure occupies a large area, forming a continuous wide region, it is called a wide-area streamlined structure. The mosaic structure is characterized by the interlocking arrangement of mesophase spheres, forming a mosaic-like pattern. Mosaic structures include mosaic-type structures, which refer to the mesophase asphalt composed of multiple small, discontinuous optically anisotropic regions. These regions are typically small (diameter less than 10 μm) and randomly arranged, resembling a mosaic pattern. This structure indicates that the orientation of asphalt molecules is uneven, and the spheres or lamellar structures have not yet fully merged or aligned, representing a lower degree of mesophase development.

[0041] The mesophase pitch prepared by the method disclosed herein has a high mesophase content and a mesophase texture dominated by a wide-area streamline structure, with a flow-type structure accounting for 78% to 95.7%, making it a high-quality raw material for high-performance carbon fibers.

[0042] The present disclosure will be further illustrated by the following examples, but the present disclosure is not limited thereto.

[0043] The test method for oil slurry density is in accordance with GB / T2450-81, using the specific gravity bottle method at a temperature of 20℃ to determine the density of the distillate oil; the test method for residual carbon is in accordance with SH / T0170-92, using the electric furnace method at 520℃ to determine the residual carbon value; the test method for ash content is in accordance with SH / T0170-92, using the electric furnace method at 900℃ to determine the ash content; the test method for sulfur is in accordance with the literature "GB / T17040-2019 Determination of Sulfur Content in Petroleum and Petroleum Products - Energy Dispersive X-ray Fluorescence Spectrometry"; the test methods for asphaltenes, aromatics, saturates, and resins are in accordance with NB / SH / T 0509-2010, using the four-component method to determine the content of asphaltenes, aromatics, saturates, and resins, using Al2O3 with a water content of 1% by mass as the adsorbent; the test method for hydrogen-to-carbon ratio is in accordance with the method of vario EL (Germany). The cube elemental analyzer detects the mass fraction of carbon, hydrogen, and nitrogen. The hydrogen-to-carbon ratio is carbon mass fraction / 12 : hydrogen mass fraction / 1.

[0044] Example 1 (1) Coal liquefaction heavy distillate oil was used as raw material. The raw material properties were a softening point of 81℃ and a density of 1.21 g / cm³. 3 The residual carbon content was 40.47 wt%, the ash content was 0.39 wt%, the sulfur content was 1.02 wt%, the asphaltene content was 21.74 wt%, the aromatic content was 55.01 wt%, and the H / C ratio was 0.86. After heating the coal liquefaction heavy distillate oil to 150℃, its good fluidity was achieved. The pressure was increased to 4.0 MPa via a feed pump and mixed with n-butane (extraction solvent) heated to 137℃ in a pipeline. The weight ratio of n-butane to coal liquefaction heavy distillate oil (i.e., solvent-to-oil ratio) was 4:1. The resulting mixture entered a supercritical extraction fractionation tower. The extraction solvent selectively extracted and separated the target components in the hot oil slurry within the tower, forming two phases. Due to gravity, heavier components and substances with more impurities settled to the bottom of the extraction fractionation tower, resulting in the raffinate phase collected at the bottom. Most of the extraction solvent and the extracted lighter phase rose to the top of the extraction fractionation tower, resulting in the extract phase collected at the top. The supercritical extraction fractionation tower is a storage tank with an inverted cone at the bottom and a cylinder at the top, which is easy to flow. The bottom of the storage tank is equipped with a stirring component and an external electric heating device to achieve uniform mixing of the raw materials.

[0045] The extract phase enters the solvent separator via a pressure control valve. The solvent separator operates at a pressure of 0.2 MPa and is electrically heated to maintain a temperature of 150°C. Solvent flash separation then occurs, and the product discharged from the bottom of the separator is the refined oil slurry, which is collected in a product tank. The first solvent obtained after flash separation at the top of the separator is condensed and cooled to 20°C before entering a solvent recovery tank for recycling.

[0046] The raffinate phase, carrying a small amount of solvent and containing heavy components such as impurities, solid particles, asphaltenes, and colloids, is discharged from the bottom of the supercritical extraction separation tower. The pressure is reduced to 0.1~0.2 MPa using a regulating valve, and the raffinate phase enters a solvent flash tank to flash out the second solvent. The second solvent is cooled to 20°C by condensation and flows into a solvent recovery tank. The solid phase material at the bottom of the solvent flash tank is cooled to below 150°C, remaining as solid particles. This solid particle discharge is then discharged to the raffinate tank via a star-shaped rotary solid particle discharge valve, protected by nitrogen cooling.

[0047] The refined oil slurry obtained had an extraction yield of 20.23%, an ash content of 0.01 wt%, a density of 1.01 g / cm³, a residual carbon content of 0.45 wt%, an H / C ratio of 1.12, an asphaltenes content of 0.54 wt%, and an aromatic content of 75.49 wt%. It can be used as a high-quality raw material for synthesizing mesophase asphalt. The supercritical extraction conditions used in this example and the properties of the obtained refined oil slurry are shown in Table 1. The extraction yield is calculated as: (Mass of refined oil slurry / Mass of raw coal liquefaction heavy oil slurry) × 100%.

[0048] (2) Take the refined oil slurry raw material and dry it in a drying oven at 90℃ for 2 hours to remove moisture. Weigh about 8g of the refined oil slurry sample and place it in a quartz tube. Wrap the quartz tube with aluminum foil and place it in a high-pressure reactor. Seal the reactor with a pressure indicator and a back pressure valve. Purge the reactor with nitrogen gas for about 1 minute, close the outlet valve, and continue to purge with nitrogen gas until the pressure inside the reactor reaches 0.8MPa. Close the inlet valve and maintain it for 2 minutes to ensure good sealing and stable pressure.

[0049] The reactor was placed in a tin bath, and the temperature was increased gradually from room temperature to a first temperature of 200°C at a first heating rate of 10°C / min. Then, the temperature was increased to a second temperature of 350°C at a second heating rate of 3°C / min. Finally, the temperature was increased to a thermal polycondensation temperature of 490°C at a third heating rate of 2°C / min. The temperature was then maintained at 490°C for 6 hours. During this period, the reaction pressure and the reaction temperature remained constant after each heating to carry out the thermal polycondensation reaction.

[0050] After the reaction is complete, remove the reactor (avoid shaking), cool to room temperature, release the gas inside the reactor, remove the quartz tube and remove the aluminum foil from the outside of the tube. Weigh the total mass of the quartz tube and the solid product, and use the difference method to obtain the mass and yield of the solid product, i.e., the mass and yield of the mesophase pitch. The solid yield is calculated using the following formula: m1 is the mass of the quartz tube (g), m2 is the mass of the refined oil slurry raw material (g), and m3 is the total mass of the quartz tube and solid product (g).

[0051] Characterization of mesophase pitch: Epoxy resin was injected into the mesophase pitch sample and cured. After slicing, the cut surfaces were polished to obtain observable and characterizable resin sections. The morphology of the resin sections was analyzed using a polarizing microscope (200x magnification, Leica DM2700P). ImageJ software was used to perform quantitative statistical analysis on the mesophase content and mesophase texture distribution of the mesophase pitch. The area ratio of the mesophase was calculated using the dot-counting method. The obtained mesophase content data are shown in Table 3.

[0052] Examples 2-7 Step (2) of Examples 2-7 is the same as that of Example 1. The difference is that the extraction solvent, the weight ratio of the extraction solvent to the coal liquefaction heavy distillate oil (i.e., the solvent-oil ratio), the extraction temperature, and the pressure used in Step (1) of Examples 2-7 are different from those in Example 1. The specific conditions and the extraction yield and refined oil slurry properties under different extraction conditions are shown in Table 1. The intermediate phase content data of the obtained intermediate phase pitch are shown in Table 3.

[0053] The polarizing microscope image observed using a polarizing microscope is shown below. Figure 1 As shown, Figure 1 It can be seen that the mesophase asphalt prepared using the refined oil slurry of Example 5 as raw material has a relatively large number of mosaic structures and small watershed structures. This is because the thermal polycondensation reaction temperature of Example 5 is relatively high, which intensifies the intensity of the thermal reaction and promotes the formation of mosaic and small watershed structures, resulting in a relatively low content of mesophase watershed structures.

[0054] Examples 8-9 Examples 8-9 use the refined oil slurry of Example 5 as raw material to prepare mesophase asphalt. The difference is that the thermal polycondensation temperature or time used in step (2) of preparing mesophase asphalt in Examples 8-9 is different from that in Example 5. The specific conditions are shown in Table 2, and the mesophase content data of the obtained mesophase asphalt are shown in Table 3.

[0055] The polarized light microscope images of the mesophase pitch prepared in Examples 8 and 9 are shown below. Figure 2 and Figure 3 As shown, by Figures 2-3 It can be seen that, compared with Example 5, the mesophase pitch of Example 8 has a significantly increased flow domain structure, and the mesophase pitch of Example 9 has a better flow domain structure, indicating that the pitch molecules of Example 9 are more ordered, have better flow properties, and have the potential to prepare high-performance carbon materials.

[0056] Comparative Example 1 Step (2) of Comparative Example 1 is the same as that of Example 5, except that step (1) of Comparative Example 1 does not use supercritical extraction, but conventional extraction is used to remove impurities, and then the components are controlled by hydrogenation. The specific process is as follows: using coal liquefaction heavy oil slurry as raw material, n-pentane is added to the extraction tank as the extraction solvent. After the extraction solvent fully dissolves the components in the raw oil slurry, it enters the continuous separation tank. The extract phase overflows from the top of the separation tank, and the undissolved raffinate phase is deposited to the bottom. After heating, the solvent is flashed back to obtain refined oil slurry. The refined oil slurry is put into a high-pressure hydrogenation kettle for hydrogenation and upgrading to increase the H / C ratio. The hydrogenated refined oil slurry is used as raw material to prepare mesophase pitch. The specific data of the hydrogenated refined oil slurry are shown in Table 1, and the mesophase content data of the prepared mesophase pitch are shown in Table 3.

[0057] Table 1. Supercritical extraction conditions for Examples 1-7 and properties of refined oil slurries obtained in Examples 1-7 and Comparative Example 1.

[0058] As shown in Table 1, supercritical fluid extraction technology can effectively remove impurities and regulate the composition of heavy coal liquefaction slurry, resulting in refined slurry with excellent product properties. Example 1 uses n-butane as the extraction solvent, yielding a refined slurry with low ash content, low asphaltenes, and enriched aromatics. This refined slurry has good product properties, but the yield is low, only 20.23%. Examples 2-7 use n-pentane as the extraction solvent. By changing the solvent-to-oil ratio, extraction temperature, and extraction pressure, refined slurries with different product properties were obtained. Considering factors such as refined slurry yield, low ash content, low impurities, and high aromatic content, Example 5, under conditions of a solvent-to-oil ratio of 4:1, an extraction temperature of 177℃, and an extraction pressure of 4.0 MPa, yielded a refined slurry with a high yield and good properties, an ash content of only 0.03%, near-complete removal of asphaltenes, and an aromatic content reaching a maximum of 76.09%.

[0059] Compared with the refined oil slurry obtained in Example 5, the refined oil slurry obtained in Example 2 had a relatively high saturated content, the refined oil slurry obtained in Example 6 had relatively high residual carbon and asphaltenes content, and the refined oil slurry obtained in Example 7 had a relatively high asphaltenes content. In contrast, Comparative Example 1, which used conventional extraction methods and hydrogenation to treat coal liquefaction heavy oil slurry, resulted in a refined oil slurry with lower aromatic content, higher saturated content, and a significant reduction in aromatic components suitable for mesophase development. In summary, after solvent supercritical extraction, the ash and asphaltenes in the coal liquefaction heavy oil slurry feedstock are significantly removed, while aromatic components are enriched, demonstrating the significant impurity removal and component regulation effects of supercritical extraction technology.

[0060] Table 2 Thermal polycondensation conditions of Examples 5, 8-9

[0061] Table 3 Properties of the mesophase pitches prepared in Examples 1-9 and Comparative Example 1

[0062] As can be seen from the data in Table 3, compared with Example 5, Example 8 lowered the thermal polycondensation temperature to 470℃, which was beneficial to increasing the mesophase content, resulting in a flow-type structure of over 90% in the mesophase pitch. In Example 9, under the thermal polycondensation reaction conditions of 470℃, the isothermal time was extended to 12 hours, which promoted the full development of the mesophase, achieving a flow-type structure of 95.7% in the mesophase, making it a high-quality raw material for high-performance carbon fibers. In contrast, Comparative Example 1 did not use supercritical extraction to prepare the refined oil slurry, and the extracted components contained a large amount of saturated light components. During the mesophase development process, these components rapidly decomposed, generating a large number of volatile free radicals, causing damage to the ordered stacked structure and resulting in a lower flow-type mesophase content.

[0063] The preferred embodiments of this disclosure have been described in detail above with reference to the accompanying drawings. However, this disclosure is not limited to the specific details of the above embodiments. Within the scope of the technical concept of this disclosure, various simple modifications can be made to the technical solutions of this disclosure, and these simple modifications all fall within the protection scope of this disclosure.

[0064] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, this disclosure will not describe the various possible combinations separately.

[0065] Furthermore, various different embodiments of this disclosure can be combined in any way, as long as they do not violate the spirit of this disclosure, they should also be regarded as the content disclosed in this disclosure.

Claims

1. A method for refining and pretreating heavy oil slurry from coal liquefaction and preparing mesophase pitch, characterized in that, The method includes: (1) The coal liquefaction heavy oil slurry and the extraction solvent are subjected to supercritical extraction in a supercritical extraction tower to obtain the extract phase collected at the top of the tower and the raffinate phase collected at the bottom of the tower. (2) Separate the refined oil slurry from the extract phase and heat the refined oil slurry to the thermal polycondensation temperature to carry out the thermal polycondensation reaction.

2. The method according to claim 1, characterized in that, In step (1), the extraction solvent includes aliphatic hydrocarbons with 4 to 10 carbon atoms and / or aromatic hydrocarbons with 6 to 10 carbon atoms, preferably including aliphatic hydrocarbons with 4 to 6 carbon atoms and / or aromatic hydrocarbons with 6 to 8 carbon atoms. Preferably, the aliphatic hydrocarbons having 4 to 6 carbon atoms include one or more of n-butane, n-pentane, n-hexane, and cyclohexane, with n-pentane being the most preferred; the aromatic hydrocarbons having 6 to 8 carbon atoms include one or more of benzene, toluene, and xylene. More preferably, the extraction solvent is n-pentane.

3. The method according to claim 1, characterized in that, In step (1), the weight ratio of the extraction solvent to the coal liquefaction heavy oil slurry is (1~8):1, preferably (3~5):1; and / or, the temperature of the supercritical extraction treatment is 110~300℃, preferably 170~210℃; and the pressure is 2~10Mpa, preferably 3~6Mpa.

4. The method according to claim 1, characterized in that, In step (1), the coal liquefaction heavy oil slurry is heavy oil produced by the direct coal liquefaction process, with a density of 1.0~1.21 g / cm³. 3 The residual carbon content is 40-50% by weight, the ash content is 0.1-1% by weight, the asphaltene content is 10-30% by weight, the aromatic content is 30-60% by weight, and the hydrogen-to-carbon ratio is 0.6-1.

0.

5. The method according to claim 1, characterized in that, In step (2), the density of the refined oil slurry is 0.9~1.2 g / cm³. 3 The residual carbon content is 0.1-45% by weight, the ash content is 0-0.5% by weight, the asphaltene content is 0.1-10% by weight, the aromatic content is 20-80% by weight, the saturated content is 1-15% by weight, and the hydrogen-to-carbon ratio is 0.7-1.

12.

6. The method according to claim 1, characterized in that, In step (2), the separation method includes: sending the extract phase into a solvent separator for solvent flash evaporation to obtain a first solvent collected at the top and the refined oil slurry collected at the bottom; and allowing the first solvent to enter a solvent recovery tank.

7. The method according to claim 6, characterized in that, The solvent separator has a temperature of 80~300℃, preferably 100~150℃; a pressure of 0~0.20MPa; the solvent separator includes a first heating device, the heating method of the first heating device includes one or more of combustion furnace heating, electric heating and heat transfer oil heating; preferably, the solvent separator includes a stripping tower.

8. The method according to claim 1, characterized in that, In step (2), the heating is a gradient heating, which includes: in an inert atmosphere, the refined oil slurry is heated to a first temperature at a first heating rate, then heated to a second temperature at a second heating rate, and finally heated to the thermal polycondensation temperature at a third heating rate; optionally, the inert atmosphere includes one or more of nitrogen, argon and helium, preferably nitrogen.

9. The method according to claim 8, characterized in that, In step (2), the gradient heating satisfies at least one of the following conditions: The first heating rate is 5~12℃ / min, preferably 10℃ / min; The first temperature is 180~220℃; The second heating rate is 1~5℃ / min, preferably 3℃ / min; The second temperature is 330~370℃; The third heating rate is 1~5℃ / min, preferably 2℃ / min; The thermal polycondensation temperature is 470~520℃; and The pressure of the thermal polycondensation reaction is 0.1~1.0 MPa, and the time is 6~20 h.

10. The method according to claim 1, characterized in that, The method further includes at least one of the following steps: S1. The coal liquefaction heavy oil slurry and the extraction solvent are heated and mixed in a mixer, and the resulting mixture is fed into the supercritical extraction tower for supercritical extraction treatment; or, the coal liquefaction heavy oil slurry is heated and fed into the supercritical extraction tower, where it is countercurrently contacted with the extraction solvent to perform the supercritical extraction treatment. S2. The upper part of the supercritical extraction tower is a cylinder, and the lower part is an inverted cone; optionally, a second heating device is provided on the outside of the inverted cone, and the heating method of the second heating device includes one or more of steam heating, electric heating and heat transfer oil heating; S3. The bottom of the supercritical extraction tower is equipped with a solvent flushing line, a stirring component or a circulating pump; S4. The raffinate phase is introduced into a solvent flash tank for solvent flash evaporation to obtain a second solvent and a solid material; the second solvent is introduced into a solvent recovery tank, and the solid material is introduced into a raffinate tank; preferably, the pressure of the raffinate phase entering the solvent flash tank is 0~0.2MPa; S5. The refined oil slurry undergoes the thermal polycondensation reaction in a reactor, and the reactor is placed in a tin bath for the heating process.

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