A method and apparatus for producing mesophase pitch

Abstract

A method and device for preparing mesophase pitch, the method comprising: feeding a heavy oil raw material into a polymerization reactor after heating by a heating furnace; after reacting at a temperature of 400-480 DEG C for 3-24 hours, feeding into a flash tank to separate a distillate oil with a boiling point less than 350 DEG C, and feeding the rest of the material into a vacuum distillation column to separate a distillate oil with a boiling point less than 480-550 DEG C; feeding the bottom material of the vacuum distillation column into the heating furnace for thermal conversion, and finally feeding into a pitch granulator to contact with nitrogen for jet granulation to obtain mesophase pitch. The method and device provided by the application have the characteristics of simple process flow and easy control of process conditions, and solve the problem of difficult material taking caused by the large viscosity of mesophase pitch.

Description

Technical Field

[0001] This invention relates to a method and apparatus for processing heavy oil, and more specifically, to a method and apparatus for preparing mesophase pitch. Background Technology

[0002] Carbon fibers can be classified into polyacrylonitrile-based carbon fibers and pitch-based carbon fibers based on the different spinning raw materials. Pitch-based carbon fibers can be further divided into general-purpose pitch-based carbon fibers and high-performance pitch-based carbon fibers based on the type of pitch. Polyacrylonitrile-based carbon fibers are currently the most common carbon fiber products. Based on their mechanical properties, they can be divided into strength series (T series) and modulus series (M series). The strength series can reach 3000-11000 MPa depending on its grade. The modulus series can reach 930 GPa depending on its grade. Currently, the production of polyacrylonitrile-based carbon fibers in China is relatively good, and with the continuous development of large-tow carbon fiber technology, production costs are gradually decreasing. General-purpose pitch-based carbon fibers refer to pitch-based carbon fibers using isotropic pitch as the spinning raw material. They have lower mechanical properties, generally with a strength below 1000 MPa and a modulus below 150 GPa, and are usually not used in structural materials. Their cost is low, and due to their corrosion resistance and heat insulation properties, they are generally used in building materials and thermal insulation materials. Currently, large-scale production is possible in China. The main performance characteristic of high-performance pitch-based carbon fiber is its high modulus, which can reach up to 930 GPa. It has the highest modulus among the materials that can be mass-produced at present, reaching more than 90% of the theoretical modulus of graphite materials. It has an irreplaceable position in application scenarios that require high modulus.

[0003] High-performance pitch-based carbon fiber, due to its superior properties such as high strength, high modulus, high temperature resistance, and low density, is widely used in various fields including military, aerospace, electronic devices, and high-end industrial equipment. For these reasons, leading carbon fiber nations such as the US and Japan strictly restrict the export of high-performance pitch-based carbon fiber and its composites, its precursors (spinning pitch), related production technologies, and production equipment to my country. This severely restricts the development of related industries, and its production technology has become a "bottleneck" technology hindering my country's high-end manufacturing. Therefore, independent research and development is imperative.

[0004] my country started research and development in this field relatively early, but industrialization has progressed slowly. Since the 1990s, domestic companies have repeatedly built production lines to attempt production, but all have been forced to halt due to a lack of qualified spinning bitum. Therefore, the current state of production in this industry in my country is that while there are production lines, there is a lack of qualified, high-quality spinning bitum.

[0005] CN201810089036.X discloses a method for refining coal tar pitch for synthesizing mesophase pitch. This method separates the effective components of coal tar pitch from impurities such as coal powder and coke particles remaining in the original coal tar pitch under normal pressure. The refined coal tar pitch obtained can be used as a raw material for high-end carbon materials.

[0006] CN201911039222.3 discloses a method for preparing high thermal conductivity mesophase pitch-based carbon fiber and high-quality mesophase pitch. The method involves mixing graphene, a hydrogen donor, and purified coal tar pitch, and directly carrying out a thermal polycondensation reaction in a high-pressure autoclave to prepare mesophase pitch. The prepared mesophase pitch can be used to produce carbon fibers with excellent mechanical properties and thermal and electrical conductivity.

[0007] CN201910901067.5 discloses a method for preparing spinning-grade synthetic mesophase pitch. The method involves adding ZrCl2 as a catalyst to a pure aromatic compound and reacting it at 200-320℃ for 2-5 hours to obtain an aromatic oligomer. The product is then dissolved in pyridine, and the solid catalyst is removed by filtration. The solvent pyridine is recovered by distillation to obtain an aromatic oligomer without the catalyst. Finally, the aromatic oligomer is subjected to a thermal polycondensation reaction at 390-420℃ for 10-20 hours to obtain mesophase pitch.

[0008] In summary, although there has been a considerable amount of academic research on mesophase pitch preparation methods in China, most of it has focused on chemical methods, reaction processes, and laboratory-level studies. There has been little development on process flow, and no feasible process flow schemes have been provided for Chinese-style scale-up and engineering scale-up. Summary of the Invention

[0009] One of the technical problems to be solved by the present invention is to provide a method for preparing mesophase pitch based on the existing technology. This method has a simple process and the process conditions are easy to control.

[0010] The second technical problem to be solved by the present invention is to provide an apparatus for preparing mesophase pitch, which has a simple structure and can realize the above-mentioned method.

[0011] A method for preparing mesophase asphalt involves heating heavy oil feedstock in a furnace and then feeding it into a polymerization reactor. After reacting at 400-480℃ for 3-24 hours, the feedstock is transferred to a flash tank to separate distillate oil with a boiling point below 350℃. The remaining material is then sent to a vacuum distillation column, where distillate oil with a boiling point below 480-550℃ is separated. The bottom material of the vacuum distillation column is then sent to a furnace for thermal conversion and finally enters an asphalt granulator where it is sprayed and granulated with nitrogen to obtain mesophase asphalt.

[0012] An apparatus for preparing mesophase asphalt includes a raw material pipeline connected to a polymerization reactor, a flash tank, and a vacuum distillation tower via a heating furnace. The bottom outlet of the vacuum distillation tower is connected to an asphalt granulator via the heating furnace. The heating furnace contains two material pipelines: one for raw materials and the other for the bottom outlet of the vacuum distillation tower. The polymerization reactor is equipped with an electric heating rod inside and an electric heating jacket outside. The asphalt granulator has a nitrogen inlet and an outlet.

[0013] The beneficial effects of the method and apparatus for preparing mesophase pitch provided by this invention are as follows:

[0014] The method for preparing mesophase asphalt provided by this invention is adapted to the characteristics of the mesophase asphalt formation process. On the one hand, the high-pressure reaction fully utilizes low-boiling-point components to improve the system viscosity and ensure the growth and coalescence of the mesophase. On the other hand, the high-pressure reaction utilizes the hydrogen transfer reaction of low-boiling-point components to replace the hydrogenation process, which is simple to operate and easy to control the process conditions. Furthermore, it solves the problem of difficulty in material collection caused by the high viscosity of mesophase asphalt. The mesophase asphalt prepared using the method provided by this invention has better quality.

[0015] The apparatus for preparing mesophase pitch provided by the present invention is used to implement the above method and has the advantages of low equipment construction cost, simple process flow and easy control of process conditions. Attached Figure Description

[0016] Figure 1 This is a schematic flowchart of the method for preparing mesophase pitch provided by the present invention.

[0017] Figure 2 This is a flowchart illustrating the process method for comparison.

[0018] in:

[0019] 2-Raw material tank; 2, 6, 8-Heavy oil pumps; 3-Heating furnace; 4-Polymerization reactor; 5-Flash tank; 7-Vacuum distillation tower; 9-Asphalt granulator. Detailed Implementation

[0020] The specific embodiments of the present invention are described in detail below.

[0021] A method for preparing mesophase asphalt involves heating heavy oil feedstock in a furnace and then feeding it into a polymerization reactor. After reacting at 400-480℃ for 3-24 hours, the feedstock is transferred to a flash tank to separate distillate oil with a boiling point below 350℃. The remaining material is then sent to a vacuum distillation column, where distillate oil with a boiling point below 480-550℃ is separated. The bottom material of the vacuum distillation column is then sent to a furnace for thermal conversion and finally enters an asphalt granulator where it is sprayed and granulated with nitrogen to obtain mesophase asphalt.

[0022] In the method for preparing mesophase asphalt provided by the present invention, the heavy oil feedstock is a heavy oil product rich in polycyclic aromatic hydrocarbons, and the polycyclic aromatic hydrocarbon content is greater than 80 wt%.

[0023] Preferably, the heavy oil feedstock is selected from one or a mixture of several of the following: catalytic slurry oil, furfural extract oil, and low-temperature, medium-temperature, and high-temperature coal tar by-products of coal chemical industry.

[0024] Preferably, the heavy oil feedstock has a distillation range of 350-500℃ and is a specific fraction obtained after vacuum distillation of heavy oil products. More preferably, the heavy oil feedstock is a fraction with a distillation range of 350-400℃, 400-450℃, 400-460℃, 450-500℃, 400-430℃, 430-460℃, or 460-490℃. More preferably, it is a fraction with a distillation range of 400-450℃, 400-460℃, 400-430℃, or 430-460℃.

[0025] Heavy oil feedstocks such as catalytic slurry oil, furfural extract oil, and low-temperature, medium-temperature, and high-temperature coal tar byproducts of coal chemical industry contain certain heteroatoms such as sulfur, nitrogen, and oxygen. These atoms are detrimental to the formation and morphology of the mesophase. To improve the quality of the mesophase pitch, preferably, the heavy oil feedstock is subjected to a hydrogenation reaction in a hydrogenation reactor, contacting a hydrogenation catalyst to reduce the heteroatom content. The sulfur content and nitrogen content of the hydrogenated heavy oil feedstock are no more than 0.25% and 0.25%, respectively. More preferably, the oxygen content is no more than 0.4%.

[0026] Optionally, if the raw material has a high solid content, it needs to be desolidified before entering the raw material tank. The solid content of the heavy oil raw material after desolidification is less than 20 μg / g.

[0027] Preferably, the heavy oil feedstock is heated in a heating furnace, and the material temperature at the outlet of the heating furnace is 450-500°C; more preferably, the material temperature at the outlet of the heating furnace is 470-480°C.

[0028] In the method provided by this invention, hydrocarbon cracking and aromatic polymerization occur simultaneously in the polymerization reactor. The hydrocarbon cracking reaction is endothermic, while the aromatic polymerization reaction is exothermic. Previous experimental studies have shown that the reaction in the autoclave is generally endothermic, requiring timely replenishment of heat to maintain a constant temperature. This invention selects an autoclave as the polymerization reactor, with an electric heating rod installed inside and an electric heating jacket outside. The combined effect of internal and external heating maintains a constant temperature for the materials inside the polymerization reactor.

[0029] As the system temperature rises and the reaction proceeds, hydrocarbons are cracked into smaller molecule gases. Due to the closed nature of the high-pressure polymerization reactor, the pressure in the reactor will gradually increase. Because of the higher system temperature, the gasoline, diesel, and wax oil fractions generated from the cracking of heavy oil products will remain in the liquid phase. This helps reduce the viscosity of the liquid phase, prevents localized overheating and coking, and facilitates the coalescence of small intermediate phase spheres. Simultaneously, the lower viscosity facilitates the transport of reaction products to the flash tank.

[0030] The reaction temperature in the polymerization reactor is 400-480℃, preferably 440-460℃. More preferably, the materials are reacted intermittently in the polymerization reactor, with a residence time of 3-24 hours, preferably 3-11 hours. Generally, lower temperatures and longer residence times are beneficial for the growth of mesophase molecular crystal structures, resulting in higher quality mesophase asphalt.

[0031] The apparatus provided by this invention can be a pilot-scale experimental apparatus or an industrial production apparatus.

[0032] Preferably, the vacuum distillation column separates fractions with boiling points below 520-535℃.

[0033] Preferably, the top temperature of the vacuum distillation column is 270-290℃, and the operating pressure is no more than 10 mmHg.

[0034] Preferably, the bottom material of the vacuum distillation column is fed into a heating furnace for short residence time thermal conversion, the outlet temperature of the heating furnace is 460-480℃, and the residence time in the heating furnace is 120-300 seconds.

[0035] Preferably, in the asphalt granulator, the bottom material of the vacuum distillation tower after passing through the heating furnace is sprayed into granulation by contact with low-temperature nitrogen gas. Preferably, the nitrogen gas temperature is room temperature and the operating pressure is 0.2-0.4 MPa.

[0036] In the method provided by this invention, the heating furnace heats two materials: one is raw oil, and the other is asphalt after decompression and deep drawing.

[0037] An apparatus for preparing mesophase asphalt includes a raw material feed pipeline connected to a polymerization reactor, a flash tank, and a vacuum distillation tower via a heating furnace. The bottom outlet of the vacuum distillation tower is connected to an asphalt granulator via the heating furnace. The heating furnace is connected to two pipelines: one for the raw material feed and the other for the material outlet at the bottom of the vacuum distillation tower. The polymerization reactor is equipped with an electric heating rod inside and an electric heating jacket outside. The asphalt granulator has a nitrogen inlet and outlet.

[0038] Preferably, a heavy oil pump is installed on the raw material feed pipeline, the connecting pipeline between the flash tank and the vacuum distillation tower, and the connecting pipeline between the bottom of the vacuum distillation tower and the heating furnace.

[0039] The present invention will be further described below with reference to the accompanying drawings. The drawings are only a preferred embodiment of the present invention and do not constitute a limitation thereof.

[0040] Appendix Figure 1 This is a schematic flowchart illustrating the method for preparing mesophase pitch provided by the present invention. (See attached diagram.) Figure 1 As shown, heavy oil feedstock stored in feedstock tank 1 is pumped by heavy oil pump 2 through pipeline into heater 3. After heating, the temperature is increased, and the outlet temperature of the material in heater 3 is 450-500℃. The heated material enters polymerization reactor 4 for reaction. In polymerization reactor 4, a batch reaction mode is adopted, and the reaction temperature is 400-480℃. After a period of reaction, the temperature of polymerization reactor is reduced to stop the reaction. The generated product enters flash tank 5 through pipeline to flash separate light fractions with boiling points below 350℃. Small molecule hydrocarbons generated by cracking are discharged from the top of flash tank 5, and the material at the bottom of flash tank 5 enters vacuum distillation column 7 through heavy oil pump 6. The material undergoes vacuum distillation in vacuum distillation column 7, with a vacuum cut-off temperature of 480-550℃. Distillate oil is discharged from the top of vacuum distillation column 7, and the material at the bottom of vacuum distillation column 7 enters heater 3 through pipeline via heavy oil pump 8 for short residence time thermal conversion. The outlet temperature of the pipeline in heater 3 is 450-480℃. Then it enters the asphalt granulator 9 and is granulated by contact with low-temperature nitrogen gas to obtain mesophase asphalt products.

[0041] Appendix Figure 1 As shown, the apparatus for preparing mesophase asphalt has a raw material feed pipeline connected to a polymerization reactor 4, a flash tank 5, and a vacuum distillation tower 7 via a heating furnace 3. The bottom outlet of the vacuum distillation tower 7 is connected to an asphalt granulator 9 via the heating furnace 3. The heating furnace 3 heats two separate material streams. The polymerization reactor 4 is equipped with an electric heating rod inside and an electric heating jacket outside. The asphalt granulator 9 is equipped with a low-temperature nitrogen inlet and outlet.

[0042] The following examples further illustrate the effects of the method for preparing mesophase pitch provided by the present invention, but the present invention is not limited thereto.

[0043] In the examples and comparative examples, the heavy feedstock oil was taken from the catalytic slurry by-product of the wax oil catalytic cracking unit of Yanshan Branch of China Petroleum & Chemical Corporation, and was cut into narrow fractions at 400-450℃. The composition is shown in Table 1.

[0044] Analysis method:

[0045] The hydrocarbon composition of the oil was determined in accordance with the petrochemical industry standard "Determination of Hydrocarbons in Saturated Hydrocarbon Fractions of Gas Oil (Mass Spectrometry) (SH / T 0659-1998)".

[0046] The carbon, hydrogen, sulfur and nitrogen content of the petroleum products was determined in accordance with the petrochemical industry standard "Determination of Carbon, Hydrogen and Nitrogen in Petroleum Products and Lubricants by Elemental Analyzer Method (SH / T 0656-2017)".

[0047] The method for determining the oxygen content of petroleum products involves pyrolyzing the sample in a high-temperature pyrolysis tube containing carbon powder, during which oxygen-containing compounds are quantitatively converted into carbon monoxide. The carrier gas carries the pyrolysis products into a series of scrubbers to remove acidic gases and water vapor. Finally, the sample is detected by an infrared detector.

[0048] The determination of carbon residue shall be carried out in accordance with the national standard "Determination of Carbon Residue in Petroleum Products (Trace Method) (GB / T17144-1997)".

[0049] The method for observing the mesophase morphology is as follows: First, take 4-5g of mesophase pitch sample and embed it inside epoxy resin, and add curing agent polyene polyamine; then, after the epoxy resin has cured, polish the surface of the embedded sample by metallographic polishing; finally, use a polarizing microscope to observe the polarization reflection of the polished surface, and determine the mesophase content by image processing software.

[0050] Examples 1-3 illustrate the effectiveness of the method for preparing mesophase pitch provided by the present invention.

[0051] Example 1

[0052] Example 1 uses the attached Figure 1 The process flow illustrates the situation where heavy feedstock oil is used in a polymerization reactor at a temperature of 440℃ for 8 hours.

[0053] Heavy feedstock oil stored in feedstock tank 1 is pumped by heavy oil pump 2 through pipeline into heater 3, where the outlet temperature is 460°C. The material then enters polymerization reactor 4 for reaction at 440°C. After 8 hours of polymerization, the reactor temperature is lowered to stop the reaction. The resulting product enters flash tank 5 via pipeline, operating at 350°C. Small molecule hydrocarbons generated from cracking are discharged from the top of flash tank 5, while the bottom material is pumped by heavy oil pump 6 into vacuum distillation column 7. Vacuum distillation is performed in column 7 at a vacuum cut-off temperature of 535°C. Distillate oil is discharged from the top of column 7, while the bottom material is pumped by heavy oil pump 8 through pipeline back into heater 3 for short-time thermal conversion (100 seconds). The outlet temperature of the bottom material in heater 3 is 480°C. Finally, the material enters asphalt granulator 9 and is granulated by contact with ambient nitrogen gas to obtain mesophase asphalt product.

[0054] Operating conditions are listed in Table 2, and product properties are listed in Table 3.

[0055] Example 2

[0056] Example 2 uses the attached Figure 1 The process describes the situation where heavy feedstock oil is polymerized in a reactor at a temperature of 450℃ for 4 hours.

[0057] Heavy feed oil stored in feed tank 1 is pumped by heavy oil pump 2 through pipeline into heater 3 for heating. The outlet temperature of the material in heater 3 is 460℃. The material enters polymerization reactor 4 for reaction at 450℃. After 4 hours of polymerization, the reactor temperature is reduced to stop the reaction. The product is then piped into flash tank 5 at 350℃. Small molecule hydrocarbons generated by cracking are discharged from the top of flash tank 5, while the remaining material from the bottom is pumped by heavy oil pump 6 into vacuum distillation tower 7. The material undergoes vacuum distillation in vacuum distillation tower 7 at a vacuum cut-off temperature of 530℃. Distillate oil is discharged from the top of vacuum distillation tower 7, while the material from the bottom is pumped by heavy oil pump 8 through pipeline into heater 3 for short-time thermal conversion (90 seconds). The outlet temperature of the bottom material in heater 3 is 470℃. The final product then enters asphalt granulator 9 where it is granulated by contact with ambient nitrogen gas to obtain mesophase asphalt.

[0058] Operating conditions are listed in Table 2, and product properties are listed in Table 3.

[0059] Example 3

[0060] Example 3 uses the attached Figure 1 The process describes the situation where heavy feedstock oil is polymerized in a polymerization reactor at a temperature of 460℃ for 4 hours.

[0061] Heavy feedstock oil stored in feedstock tank 1 is pumped by heavy oil pump 2 through pipeline into heater 3. After heating, the outlet temperature of the material in heater 3 is 480℃. The material enters polymerization reactor 4 for reaction at 460℃. After 4 hours of polymerization, the reactor temperature is reduced to stop the reaction. The product is then piped into flash tank 5, which operates at 350℃. Small molecule hydrocarbons generated by cracking are discharged from the top of flash tank 5, while the material from the bottom of flash tank 5 is pumped by heavy oil pump 6 into vacuum distillation tower 7. The material undergoes vacuum distillation in vacuum distillation tower 7 at a vacuum cut-off temperature of 525℃. Distillate oil is discharged from the top of vacuum distillation tower 7, while the material from the bottom of vacuum distillation tower 7 is pumped by heavy oil pump 8 through pipeline into heater 3 for a short-term thermal conversion with a residence time of 80 seconds. The outlet temperature of the pipeline in heater 3 is 460℃. The product then enters asphalt granulator 12 for granulation to obtain mesophase asphalt. Operating conditions are listed in Table 2, and product properties are listed in Table 3.

[0062] Comparative Example 1

[0063] The process method of Comparative Example 1 is shown in the appendix. Figure 2 The figure shows the case where heavy feedstock oil is produced in a polymerization reactor at a temperature of 440℃ for 8 hours, but without undergoing short-term thermal conversion treatment and asphalt granulation treatment.

[0064] Heavy oil feedstock stored in feed tank 1 is pumped by heavy oil pump 2 through pipeline into heater 3. The outlet temperature of the heated material is 480℃. The material enters polymerization reactor 4 for reaction at 440℃. After 8 hours of polymerization, the reactor temperature is reduced to stop the reaction. The resulting product enters flash tank 5 through pipeline. Flash tank 5 operates at 350℃. Small molecule hydrocarbons generated by cracking are discharged from the top of flash tank 5, and the material from the bottom of flash tank 5 enters vacuum distillation column 7 via heavy oil pump 6. The material undergoes vacuum distillation in vacuum distillation column 7 at a vacuum cut-off temperature of 525℃. Distillate oil is discharged from the top of vacuum distillation column 7, and the material from the bottom of vacuum distillation column 7 is the mesophase asphalt product.

[0065] Operating conditions are listed in Table 2, and product properties are listed in Table 3.

[0066] Table 1 Properties of Heavy Feed Oil

[0067]

[0068] Table 2 Operating Conditions

[0069] Example 1 Example 2 Example 3 Comparative Example 1 Polymerization temperature, °C 440 450 460 440 Aggregation time, h 8 4 4 8

[0070] Table 3 Properties of Mesophase Pitch

[0071] Example 1 Example 2 Example 3 Comparative Example 1 Softening point, ℃ 316 312 340 296 Intermediate phase content, % 92 90 90 78 intermediate phase morphology streamline domain streamline domain streamline domain Uniform sphere Carbon content, wt% 94.14 94.47 94.79 94.20 Hydrogen content, wt% 5.22 4.78 4.82 5.31 Sulfur content, wt% 0.23 0.15 0.21 0.20 Nitrogen content, wt% 0.22 0.38 0.14 0.25

[0072] As can be seen from Table 3, the mesophase asphalt prepared by the method of the present invention has a mesophase content of more than 90% and the mesophase morphology is a streamline domain.

Claims

1. A method for preparing mesophase pitch, characterized in that, Heavy oil feedstock is heated in a furnace and then fed into a polymerization reactor. After reacting at 400-480℃ for 3-24 hours, it enters a flash tank to separate distillate oil with a boiling point below 350℃. The remaining material is sent to a vacuum distillation tower, where distillate oil with a boiling point below 480-550℃ is separated. The bottom material of the vacuum distillation tower is sent to a furnace for thermal conversion and finally enters an asphalt granulator to be sprayed and granulated with nitrogen to obtain mesophase asphalt.

2. The method for preparing mesophase pitch according to claim 1, characterized in that, The heavy oil feedstock is a heavy oil product rich in polycyclic aromatic hydrocarbons (PAHs), with a PAH content greater than 80%. wt %.

3. The method for preparing mesophase pitch according to claim 2, characterized in that, The heavy oil feedstock is selected from one or a mixture of several of the following: catalytic slurry oil, furfural extract oil, and low-temperature, medium-temperature, and high-temperature coal tar by-products of coal chemical industry.

4. The method for preparing mesophase pitch according to claim 2 or 3, characterized in that, The distillation range of the heavy oil feedstock is in the range of 350-500℃.

5. The method for preparing mesophase pitch according to claim 4, characterized in that, The heavy oil feedstock has a distillation range of 350-400℃, 400-450℃, 400-460℃, 450-500℃, 400-430℃, 430-460℃, or 460-490℃.

6. The method for preparing mesophase pitch according to claim 2, characterized in that, The heavy oil feedstock is first contacted with a hydrotreating catalyst in a hydrotreating reactor to remove sulfur and nitrogen impurities.

7. The method for preparing mesophase pitch according to claim 6, characterized in that, The sulfur content in the heavy oil feedstock after hydrogenation is no greater than 0.25%. wt %, nitrogen content not exceeding 0.25%. wt %.

8. The method for preparing mesophase pitch according to claim 1, 2 or 3, characterized in that, The heavy oil feedstock is first treated to remove solids before being introduced into the heating furnace. After the solids removal treatment, the solid content of the heavy oil feedstock is less than 20 μg / g.

9. The method for preparing mesophase pitch according to claim 1, 2 or 3, characterized in that, The heavy oil feedstock is heated in a heating furnace, and the material temperature at the outlet of the heating furnace is 450-500℃.

10. The method for preparing mesophase pitch according to claim 9, characterized in that, The outlet temperature of the heating furnace material is 470-480℃.

11. The method for preparing mesophase pitch according to claim 1, 2 or 3, characterized in that, The materials are reacted in the polymerization reactor in an intermittent manner, with a reaction time of 3-11 hours and a reaction temperature of 440-460℃.

12. The method for preparing mesophase pitch according to claim 1, 2 or 3, characterized in that, The temperature at the top of the vacuum distillation column is 270-290℃, and the operating pressure is no more than 10 mmHg.

13. The method for preparing mesophase pitch according to claim 12, characterized in that, Distillate oils with boiling points below 520-535℃ are separated in a vacuum distillation column.

14. The method for preparing mesophase pitch according to claim 1, 2 or 3, characterized in that, The residence time of the bottom material in the vacuum distillation column is 120-300 seconds in the heating furnace, and the outlet temperature of the heating furnace is 460-480℃.

15. The method for preparing mesophase pitch according to claim 1, 2 or 3, characterized in that, In the aforementioned asphalt granulator, nitrogen gas is introduced at room temperature, and the operating pressure is 0.2-0.4 MPa.

16. An apparatus for preparing mesophase pitch, characterized in that, The heavy oil feedstock pipeline is connected to the polymerization reactor, flash tank, and vacuum distillation tower via a heating furnace. The bottom outlet of the vacuum distillation tower is connected to the asphalt granulator via the heating furnace. The heating furnace contains two material pipelines: one for the heavy oil feedstock and the other for the bottom outlet of the vacuum distillation tower. The polymerization reactor is equipped with an electric heating rod inside and an electric heating jacket outside. The asphalt granulator has a nitrogen inlet and outlet.

17. The apparatus for preparing mesophase pitch according to claim 16, characterized in that, Heavy oil pumps are installed on the heavy oil feed pipeline, the connecting pipeline between the flash tank and the vacuum distillation tower, and the connecting pipeline between the bottom of the vacuum distillation tower and the heating furnace.

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