Method for preparing special pitch by step-by-step separation of coal tar

Abstract

The application discloses a kind of step-by-step separation coal tar preparation special pitch method, belong to coal tar separation and pitch preparation technical field, solve the problem that high energy consumption, many impurities, cannot be used for high-end carbon material raw material of conventional distillation process preparation pitch.The application is under normal temperature and pressure to coal tar in turn three different mixed solvents are added to carry out three-step step-by-step separation: first, add tetrahydrofuran and carbon disulfide mixed solvent, 0.45 microns are filtered and impurities are removed to obtain first separation product;Second, add petroleum ether and washing oil mixed solvent, and separate heavy pitch and light component;Finally, add ethanol and acetone mixed solvent, 0.22 microns are filtered and impurities are removed to obtain target special pitch.By adjusting solvent ratio and reaction time, the molecular weight distribution of pitch can be controlled, and the intermediate phase content of the obtained pitch after polymerization can reach more than 90%.The process equipment of the application is simple, the separation condition is mild, energy is saved, and the product can be used for preparing intermediate phase pitch-based carbon fiber and other high value-added carbon materials.

Description

Technical Field

[0001] This invention relates to the field of coal tar separation and pitch preparation technology, specifically to a method for preparing special pitch by separating coal tar in stages, and particularly to a method for preparing special pitch that can be used to produce mesophase pitch-based carbon fibers. Background Technology

[0002] Coal tar is an important byproduct of coal coking. It is a liquid mixture obtained by washing and capturing the gas after the coal undergoes a dry distillation reaction at 900-1200℃ in the absence of air, using a tar trap. my country is the world's largest producer and consumer of coke, with an annual coal tar production exceeding 20 million tons, accounting for more than 60% of global production. Coal tar contains tens of thousands of organic compounds, of which aromatic compounds account for more than 80%, making it an important raw material for the preparation of high-value-added carbon materials and fine chemical products. However, currently, the deep processing and utilization rate of coal tar in my country is less than 30%. Most coal tar is directly burned as fuel or used to produce low-end bitumen products, resulting in serious resource waste and severe environmental pollution.

[0003] Mesophase pitch-based carbon fiber is a high-performance carbon fiber with excellent properties such as high modulus, high strength, low coefficient of thermal expansion, and good thermal and electrical conductivity. It is widely used in high-end fields such as aerospace, defense, new energy vehicles, and wind power generation. The performance of mesophase pitch-based carbon fiber mainly depends on the quality of the raw pitch, which must have low impurity content, narrow molecular weight distribution, high aromaticity, and good spinnability. Currently, the main raw materials for preparing mesophase pitch include coal tar pitch, petroleum pitch, and synthetic pitch. Among these, coal tar pitch is the most promising raw material due to its wide availability, low price, and high aromaticity.

[0004] Currently, most domestic methods for separating coal tar to produce asphalt employ single-tower or two-tower distillation processes. This process requires high temperatures of 400-500℃, resulting in high energy consumption, complex processes, and significant equipment investment. Statistics show that the energy consumption for producing 1 ton of asphalt by distillation is approximately 1200-1500 kWh, which is 8-10 times that of the process described in this invention. More importantly, the asphalt obtained by distillation contains a large amount of solid impurities such as coal dust and coke particles introduced during coal tar production, as well as secondary polymer impurities generated during high-temperature distillation. These impurities are fine and stable, making them difficult to remove effectively using conventional methods. This limits the asphalt's use to low-end products such as paving and waterproofing, preventing further refinement into raw materials for high-end carbon materials such as carbon fiber and needle coke, severely restricting the high-value utilization of coal tar.

[0005] To address the aforementioned issues, scholars both domestically and internationally have conducted extensive research on the preparation of specialty bitumen using solvent extraction methods. While single-solvent extraction is simple, it suffers from poor separation efficiency, failing to simultaneously remove solid impurities and secondary polymer impurities, and also struggles to effectively control the molecular weight distribution of the bitumen. Although mixed-solvent extraction improves separation efficiency to some extent, existing technologies mostly employ two-stage extraction processes, resulting in insufficient impurity removal precision. The resulting bitumen typically contains less than 80% mesophase, failing to meet the requirements of high-end carbon fiber production. Furthermore, most existing solvent extraction processes require heating and pressurization, still exhibiting problems such as high energy consumption and poor operational safety. Therefore, developing a method for preparing specialty bitumen through the stepwise separation of coal tar under ambient temperature and pressure, with good impurity removal efficiency and controllable molecular weight, has significant practical and economic value. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for preparing special pitch by separating coal tar in stages, solving the problems of high energy consumption, high impurity content and inability to be used as raw material for high-end carbon materials in conventional distillation processes.

[0007] To achieve the above objectives, the present invention provides the following technical solution: A method for preparing special bitumen by stepwise separation of coal tar includes the following steps: Three different mixed solvents were added to coal tar at room temperature and pressure for three-stage separation. After each stage of separation, the filtration was carried out with a corresponding precision. By adjusting the solvent ratio and reaction time of each stage of separation, the molecular weight distribution of the target asphalt was controlled, and finally, a special asphalt was prepared.

[0008] Furthermore, the three mixed solvents are mixed solvent 1, mixed solvent 2 and mixed solvent 3, wherein mixed solvent 1 is a mixture of tetrahydrofuran and carbon disulfide.

[0009] Furthermore, the volume ratio of tetrahydrofuran to carbon disulfide in the mixed solvent 1 is 1:1, and the feed-to-liquid ratio of coal tar to mixed solvent 1 is 1:(5-8).

[0010] Furthermore, after adding mixed solvent 1, the mixture was stirred at a stirring rate of 300 r / min for 30 min, allowed to stand for 15 min to separate into layers, and the upper layer solution was filtered through 0.45 micron filter paper. Mixed solvent 1 was then distilled to recover the primary coal tar product.

[0011] Furthermore, the mixed solvent 2 is a mixture of petroleum ether and wash oil.

[0012] Furthermore, the volume ratio of petroleum ether to wash oil in the mixed solvent 2 is 1:1, and the feed-to-liquid ratio of primary coal tar separator to mixed solvent 2 is 1:(5-8).

[0013] Furthermore, after adding mixed solvent 2, the mixture was stirred at a stirring rate of 300 r / min for 30 min, and then allowed to stand for 15 min to separate into layers. The upper layer was a mixture of mixed solvent 2 and light coal tar components, and the lower layer was heavy pitch. Mixed solvent 2 was then distilled to recover the light coal tar components.

[0014] Furthermore, the mixed solvent 3 is a mixture of ethanol and acetone.

[0015] Furthermore, the volume ratio of ethanol to acetone in the mixed solvent 3 is 1:1, and the material-liquid ratio of heavy asphalt to mixed solvent 3 is 1:(2-5). The upper layer solution is filtered through 0.22-micron filter paper, and mixed solvent 3 is recovered by distillation to obtain the target special asphalt.

[0016] Furthermore, the special pitch can be polymerized to obtain mesophase pitch with a mesophase content of ≥90%, which can be used to prepare mesophase pitch-based carbon fibers.

[0017] The beneficial effects of this invention are as follows: 1. The separation conditions are mild and the energy consumption is low.

[0018] This invention is carried out entirely at room temperature and pressure, eliminating the need for high-temperature distillation equipment, which significantly reduces energy consumption and equipment investment. The process is simple and safe to operate.

[0019] 2. It has a good impurity removal effect and high product purity.

[0020] Through three-stage separation and filtration of varying precision, solid impurities such as coal powder and coke particles, as well as secondary polymer impurities, can be effectively removed from coal tar, resulting in special asphalt with extremely low impurity content.

[0021] 3. Controllable molecular weight, resulting in high added value for the product.

[0022] By adjusting the solvent ratio and reaction time of each separation stage, the molecular weight distribution of the target asphalt can be precisely controlled. After polymerization, the resulting asphalt can be obtained as mesophase asphalt with a mesophase content of ≥90%, which fully meets the requirements for preparing high-value-added carbon materials such as mesophase asphalt-based carbon fibers.

[0023] 4. High resource utilization rate.

[0024] The light components of coal tar obtained from the secondary separation are rich in a variety of organic compounds, which can be further separated and refined to obtain chemical products such as benzene, toluene, and xylene, realizing the high-value utilization of all components of coal tar. Attached Figure Description

[0025] Figure 1 is a process flow diagram of the stepwise separation of coal tar to prepare special bitumen according to the present invention; Figure 2 is a schematic diagram of the three-stage step-by-step separation principle of the present invention; Figure 3 is a schematic diagram showing the characteristics and applications of the separation products at each stage of the present invention.

[0026] Explanation of reference numerals in the attached figures: 1 - Coal tar raw material storage tank; 2 - Primary extraction vessel; 3 - First filter; 4 - First distillation column; 5 - Secondary extraction vessel; 6 - Second distillation column; 7 - Tertiary extraction vessel; 8 - Second filter; 9 - Third distillation column; 10 - Special asphalt product storage tank; 11 - Light component storage tank; 12 - Solvent recovery system. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0028] This invention proposes a method for preparing special asphalt by stepwise separation of coal tar. Under normal temperature and pressure, three different mixed solvents are added to the coal tar in sequence for three-stage stepwise separation. After each stage of separation, filtration with corresponding precision is performed. By adjusting the solvent ratio and reaction time of each stage of separation, the molecular weight distribution of the target asphalt is controlled, and the special asphalt is finally prepared.

[0029] Specifically, the following steps are included: Step 1: Primary separation and impurity removal.

[0030] Tetrahydrofuran and carbon disulfide were mixed in a volume ratio of 1:1 to obtain mixed solvent 1. Under normal temperature and pressure, mixed solvent 1 was added to coal tar at a feed-to-liquid ratio of 1:(5-8). The mixture was stirred at a stirring rate of 300 r / min for 30 min and then allowed to stand for 15 min to allow the system to separate into layers. The lower layer consisted of solid impurities such as coal powder and coke particles introduced during the coal tar production process, while the upper layer was a mixture of mixed solvent 1 and the effective components of coal tar. The upper layer solution was filtered through 0.45 micron filter paper, and the filtrate was distilled to recover mixed solvent 1, yielding the primary coal tar separator. Step 2: Secondary separation of light and heavy components.

[0031] Petroleum ether and wash oil were mixed at a volume ratio of 1:1 to obtain mixed solvent 2. Under normal temperature and pressure, mixed solvent 2 was added to the primary coal tar separator at a feed-to-liquid ratio of 1:(5-8). The mixture was stirred at 300 r / min for 30 min and then allowed to stand for 15 min to allow the system to separate into layers. The upper layer was a mixture of mixed solvent 2 and the light coal tar components, and the lower layer was the heavy asphalt components. After distilling the upper mixture to recover mixed solvent 2, the light coal tar components were obtained, which can be further separated and refined to obtain various organic chemical products. Step 3: Three-stage separation and refining of asphalt.

[0032] Ethanol and acetone were mixed in a volume ratio of 1:1 to obtain mixed solvent 3. Under normal temperature and pressure, mixed solvent 3 was added to the heavy asphalt obtained in step 2 at a material-to-liquid ratio of 1:(2-5). The mixture was stirred at a stirring rate of 300 r / min for 30 min and then allowed to stand for 15 min to allow the system to separate into layers. The lower layer contained residual secondary polymers and other impurities, while the upper layer was a mixture of mixed solvent 3 and the target special asphalt. The upper solution was filtered through 0.22 micron filter paper, and the filtrate was distilled to recover mixed solvent 3, thus obtaining the target special asphalt.

[0033] The present invention will be further described in detail below with reference to specific embodiments and accompanying drawings. The scope of protection of the present invention is not limited to the following embodiments; all equivalent variations and modifications made within the scope of the claims of this invention should be considered within the scope of this invention.

[0034] The coal tar raw material used in this embodiment of the invention comes from a coking plant of a steel company, and its main properties are as follows: Density 1.18 g / cm³ (20℃), ash content 0.32%, quinoline insoluble content 2.8%, toluene insoluble content 12.5%, softening point 35℃; all solvents used are industrial grade with a purity ≥99%. The product performance testing methods are as follows: The softening point was determined by the ring and ball method, the quinoline insoluble content was determined according to GB / T 2293-2008 standard, the toluene insoluble content was determined according to GB / T 2292-2008 standard, and the mesophase content was determined by polarized light microscopy.

[0035] Example 1: At ambient temperature and pressure, coal tar from the coal tar feed tank 1 and mixed solvent 1 (a mixture of tetrahydrofuran and carbon disulfide in equal volume ratio) are added to the primary extraction vessel 2 at a feed-to-liquid ratio of 1:5. The mixture is stirred at 300 r / min for 30 min and then allowed to stand for 15 min to allow the system to separate into layers. The lower layer consists of solid impurities such as coal powder and coke particles, which are discharged from the bottom of the vessel. The upper layer is a mixture of mixed solvent 1 and the effective components of coal tar, which is filtered through the first filter 3 using 0.45 micron filter paper. The filtrate is sent to the first distillation column 4, where mixed solvent 1 is distilled and recovered at 65°C and ambient pressure. The recovered solvent is sent to the solvent recovery system 12 for recycling, and the bottom of the column yields the primary coal tar separator. The primary coal tar fraction is fed into the secondary extraction vessel 5. A mixture of petroleum ether and wash oil in equal volume ratios (1:5) is added to the mixed solvent 2. The mixture is stirred at 300 r / min for 30 min, then allowed to stand for 15 min to allow the system to separate into layers. The upper layer, a mixture of mixed solvent 2 and light coal tar components, is fed into the second distillation column 6. Mixed solvent 2 is recovered by distillation at 90℃ and atmospheric pressure. The recovered solvent is recycled to the solvent recovery system 12. The bottom layer, containing light coal tar components, is sent to the light component storage tank 11. The lower layer, containing heavy asphalt components, is fed into the tertiary extraction vessel 7. Mixed solvent 3, consisting of ethanol and acetone in equal volume ratios, is added to a three-stage extraction vessel 7 at a feed-to-liquid ratio of 1:2 for heavy asphalt and mixed solvent 3. The mixture is stirred at 300 r / min for 30 min and then allowed to stand for 15 min to allow the system to separate into layers. The lower layer, containing residual secondary polymers and other impurities, is discharged from the bottom of the vessel. The upper layer, a mixture of mixed solvent 3 and special asphalt, is sent to a second filter 8 and filtered through 0.22-micron filter paper. The filtrate is then sent to a third distillation column 9, where mixed solvent 3 is recovered by distillation at 75°C and atmospheric pressure. The recovered solvent is then recycled to a solvent recovery system 12. Special asphalt 1 is obtained at the bottom of the column and sent to a special asphalt product storage tank 10. After polymerization, this asphalt yields mesophase asphalt with a mesophase content of 90%.

[0036] Example 2: At ambient temperature and pressure, coal tar from the coal tar feed tank 1 and mixed solvent 1 (a mixture of tetrahydrofuran and carbon disulfide in equal volume ratio) are added to the primary extraction vessel 2 at a feed-to-liquid ratio of 1:6. The mixture is stirred at 300 r / min for 30 min and then allowed to stand for 15 min to allow the system to separate into layers. The lower layer consists of solid impurities such as coal powder and coke particles, which are discharged from the bottom of the vessel. The upper layer is a mixture of mixed solvent 1 and the effective components of coal tar, which is filtered through the first filter 3 using 0.45 micron filter paper. The filtrate is sent to the first distillation column 4, where mixed solvent 1 is distilled and recovered at 65°C and ambient pressure. The recovered solvent is sent to the solvent recovery system 12 for recycling, and the bottom of the column yields the primary coal tar separator. The primary coal tar fraction is fed into the secondary extraction vessel 5. A mixture of petroleum ether and wash oil in equal volume ratios (1:7) is added to the mixed solvent 2. The mixture is stirred at 300 rpm for 30 minutes, then allowed to stand for 15 minutes to allow for stratification. The upper layer, a mixture of mixed solvent 2 and light coal tar components, is fed into the second distillation column 6. Mixed solvent 2 is recovered by distillation at 90°C and atmospheric pressure. The recovered solvent is recycled to the solvent recovery system 12. The bottom layer, containing light coal tar components, is sent to the light component storage tank 11. The lower layer, containing heavy asphalt components, is fed into the tertiary extraction vessel 7. Mixed solvent 3, consisting of ethanol and acetone in equal volume ratios, is added to a three-stage extraction vessel 7 at a feed-to-liquid ratio of 1:4 for heavy asphalt and mixed solvent 3. The mixture is stirred at 300 r / min for 30 min and then allowed to stand for 15 min to allow the system to separate into layers. The lower layer, containing residual secondary polymers and other impurities, is discharged from the bottom of the vessel. The upper layer, a mixture of mixed solvent 3 and special asphalt, is sent to a second filter 8 and filtered through 0.22-micron filter paper. The filtrate is then sent to a third distillation column 9, where mixed solvent 3 is recovered by distillation at 75°C and atmospheric pressure. The recovered solvent is then recycled to a solvent recovery system 12. Special asphalt 2 is obtained at the bottom of the column and sent to a special asphalt product storage tank 10. After polymerization, this asphalt yields mesophase asphalt with a mesophase content of 95%.

[0037] Example 3: At ambient temperature and pressure, coal tar from coal tar feed tank 1 and mixed solvent 1 (a mixture of tetrahydrofuran and carbon disulfide in equal volume ratio) are added to the primary extraction vessel 2 at a feed-to-liquid ratio of 1:8. The mixture is stirred at 300 r / min for 30 min and then allowed to stand for 15 min to allow the system to separate into layers. The lower layer consists of solid impurities such as coal powder and coke particles, which are discharged from the bottom of the vessel. The upper layer is a mixture of mixed solvent 1 and the effective components of coal tar, which is filtered through the first filter 3 using 0.45 micron filter paper. The filtrate is then sent to the first distillation column 4, where mixed solvent 1 is distilled and recovered at 65°C and ambient pressure. The recovered solvent is then recycled to the solvent recovery system 12, and the bottom of the column yields the primary coal tar separator. The primary coal tar fraction is fed into the secondary extraction vessel 5. A mixture of petroleum ether and wash oil in equal volume ratios (1:7) is added to the mixed solvent 2. The mixture is stirred at 300 rpm for 30 minutes, then allowed to stand for 15 minutes to allow for stratification. The upper layer, a mixture of mixed solvent 2 and light coal tar components, is fed into the second distillation column 6. Mixed solvent 2 is recovered by distillation at 90°C and atmospheric pressure. The recovered solvent is recycled to the solvent recovery system 12. The bottom layer, containing light coal tar components, is sent to the light component storage tank 11. The lower layer, containing heavy asphalt components, is fed into the tertiary extraction vessel 7. Mixed solvent 3, consisting of ethanol and acetone in equal volume ratios, is added to a three-stage extraction vessel 7 at a feed-to-liquid ratio of 1:3 for heavy asphalt and mixed solvent 3. The mixture is stirred at 300 r / min for 30 min and then allowed to stand for 15 min to allow the system to separate into layers. The lower layer, containing residual secondary polymers and other impurities, is discharged from the bottom of the vessel. The upper layer, a mixture of mixed solvent 3 and special asphalt, is sent to a second filter 8 and filtered through 0.22-micron filter paper. The filtrate is then sent to a third distillation column 9, where mixed solvent 3 is distilled and recovered at 75°C and atmospheric pressure. The recovered solvent is then recycled to a solvent recovery system 12. Special asphalt 3 is obtained at the bottom of the column and sent to a special asphalt product storage tank 10. After polymerization, this asphalt yields mesophase asphalt with a mesophase content of 92%.

[0038] Comparative Example (Traditional Distillation Process) The same coal tar raw material was fed into a distillation tower and distilled at 450°C and atmospheric pressure. The fraction above 360°C was used to obtain asphalt products. The asphalt had a quinoline insoluble content of 2.1%, a toluene insoluble content of 15.3%, and a softening point of 82°C. After polymerization, the mesophase content was only 72%, which could not meet the requirements for high-end carbon fiber production.

[0039] The process parameters and product performance indicators of each embodiment and comparative embodiment are shown in the table below:

[0040] This invention systematically verifies the feasibility, stability, and technical superiority of a three-stage stepwise separation process for preparing special asphalt at room temperature and pressure through three sets of parallel embodiments, and conducts a comprehensive comparison with the traditional high-temperature distillation process.

[0041] All embodiments used a uniform stirring rate of 300 r / min, reaction time of 30 min, settling time of 15 min, and corresponding precision filtration conditions. Only the material-liquid ratio at each stage was adjusted to examine its impact on product performance.

[0042] The results show that the process of the present invention can stably prepare special asphalt that meets the requirements of high-end carbon materials in different material-liquid ratio ranges. Among them, Example 2 uses the parameter combination of coal tar: mixed solvent 1=1:6, primary separator: mixed solvent 2=1:7, and heavy asphalt: mixed solvent 3=1:4, which has the best comprehensive performance. The obtained special asphalt has a mesophase content of up to 95% after polymerization and a quinoline insoluble content of only 0.05%.

[0043] Compared with traditional high-temperature distillation processes, the process of this invention has significant advantages: The impurity removal efficiency is improved by over 97%, and the quinoline insoluble content is reduced from 2.1% to 0.05%-0.08%; energy consumption is reduced by over 88%, with energy consumption per ton of product decreasing from 1320 kWh to 145-152 kWh; the added value of the product is significantly increased, with the mesophase content increasing from 72% to 90%-95%, fully meeting the production requirements of mesophase pitch-based carbon fiber. Simultaneously, this invention's process can simultaneously recover light components from coal tar, achieving high-value utilization of all components of coal tar. These results fully demonstrate that this invention's process solves the industry pain points of high energy consumption, numerous impurities, and poor product quality associated with traditional distillation processes. It possesses advantages such as simple process flow, safe operation, low cost, and ease of industrial scale-up, showing broad application prospects.

[0044] The above embodiments are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications or equivalent substitutions based on the technical solutions of the present invention without departing from the core ideas of the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for preparing special bitumen by stepwise separation of coal tar, characterized in that, Includes the following steps: Three different mixed solvents were added to coal tar at room temperature and pressure for three-stage separation. After each stage of separation, the filtration was carried out with a corresponding precision. By adjusting the solvent ratio and reaction time of each stage of separation, the molecular weight distribution of the target asphalt was controlled, and finally, a special asphalt was prepared.

2. The method for preparing special bitumen by stepwise separation of coal tar according to claim 1, characterized in that, The three mixed solvents are mixed solvent 1, mixed solvent 2 and mixed solvent 3, wherein mixed solvent 1 is a mixture of tetrahydrofuran and carbon disulfide.

3. The method for preparing special bitumen by stepwise separation of coal tar according to claim 2, characterized in that, The volume ratio of tetrahydrofuran to carbon disulfide in the mixed solvent 1 is 1:1, and the feed-to-liquid ratio of coal tar to mixed solvent 1 is 1:(5-8).

4. The method for preparing special bitumen by stepwise separation of coal tar according to claim 2, characterized in that, After adding mixed solvent 1, the mixture was stirred at a stirring rate of 300 r / min for 30 min, allowed to stand for 15 min to separate into layers, and the upper layer was filtered through 0.45 micron filter paper. Mixed solvent 1 was then distilled to recover the primary coal tar product.

5. The method for preparing special bitumen by stepwise separation of coal tar according to claim 1, characterized in that, The mixed solvent 2 is a mixture of petroleum ether and wash oil.

6. The method for preparing special bitumen by stepwise separation of coal tar according to claim 5, characterized in that, The volume ratio of petroleum ether to wash oil in the mixed solvent 2 is 1:1, and the feed-to-liquid ratio of primary coal tar separator to mixed solvent 2 is 1:(5-8).

7. The method for preparing special bitumen by stepwise separation of coal tar according to claim 5, characterized in that, After adding mixed solvent 2, the mixture was stirred at a stirring rate of 300 r / min for 30 min, and then allowed to stand for 15 min to separate into layers. The upper layer was a mixture of mixed solvent 2 and light coal tar components, and the lower layer was heavy pitch. Mixed solvent 2 was distilled to recover the light coal tar components.

8. The method for preparing special bitumen by stepwise separation of coal tar according to claim 1, characterized in that, The mixed solvent 3 is a mixture of ethanol and acetone.

9. The method for preparing special bitumen by stepwise separation of coal tar according to claim 8, characterized in that, The volume ratio of ethanol to acetone in the mixed solvent 3 is 1:1, and the ratio of heavy asphalt to mixed solvent 3 is 1:(2-5). The upper layer solution is filtered through 0.22-micron filter paper, and mixed solvent 3 is recovered by distillation to obtain the target special asphalt.

10. The method for preparing special bitumen by stepwise separation of coal tar according to claim 1, characterized in that, The special pitch, after polymerization, yields mesophase pitch with a mesophase content of ≥90%, which is used to prepare mesophase pitch-based carbon fibers.

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