A method for preparing mesophase pitch based on normal pressure multistage thermal polycondensation

Abstract

The application discloses a method for preparing mesophase pitch based on normal-pressure multistage thermal polycondensation, which comprises the following steps: performing first-stage normal-pressure thermal polycondensation on raw materials and performing thermal filtration to remove high-activity easy-coking pitch and heavy gum and other complex heavy components; and performing second-stage and above normal-pressure thermal polycondensation on the filtrate as raw materials to realize controllable growth and hierarchical regulation of mesophase structures. The whole process of the method is performed under normal-pressure conditions, and no pressure equipment and complex pretreatment are needed, so that the method has low requirements on equipment, high safety, simple process and strong adaptability to raw materials, and can continuously obtain mesophase pitches with different qualities, and is suitable for various heavy raw materials such as coal tar, catalytic cracking slurry oil and vacuum residue, and provides an innovative solution for large-scale and safe production of mesophase pitch.

Description

Technical Field

[0001] This invention belongs to the field of high-performance carbon material precursor preparation technology, and relates to a method for preparing mesophase pitch, specifically, a method for preparing mesophase pitch based on atmospheric pressure multi-stage thermal polycondensation. Background Technology

[0002] Mesophase pitch is a nematic liquid crystal material formed from heavy aromatic oils through a series of reactions including bond breaking, dehydrogenation, and condensation during heat treatment. Its highly ordered molecular structure, good orientation, and ease of graphitization make it a key precursor for the preparation of high-performance carbon materials, widely used in mesophase pitch-based carbon fibers, needle coke, foamed carbon, and C / C composites. With the rapid development of strategic emerging industries such as aerospace, new energy, and high-end equipment, the demand for high-performance carbon materials is increasing. Therefore, developing efficient, controllable, low-cost methods for preparing mesophase pitch suitable for industrial production is of great significance.

[0003] Non-catalytic thermal polycondensation is one of the main methods for preparing mesophase asphalt. Among these methods, pressurized thermal polycondensation can suppress excessive coking and increase yield, but it places extremely high demands on equipment pressure resistance, sealing, and safety. Furthermore, high-viscosity oil and gas can easily clog pipelines, resulting in significant operational risks and poor controllability. Therefore, there is an urgent need for a highly efficient, safe, and controllable mesophase asphalt preparation process under normal pressure.

[0004] CN116023967A discloses a continuous preparation method for spinnable mesophase pitch, which adopts a two-stage thermal reaction series process for continuous production. However, the first-stage reaction still needs to be carried out under pressure (up to 5MPa). Moreover, its purification unit has a complex structure and requires the use of waste catalyst beds and multi-layer screen filtration, resulting in high operation and maintenance requirements.

[0005] CN118185652A discloses a method for simultaneously producing mesophase pitch and COPNA resin from heavy oil. It involves multiple steps such as aromatic enrichment, co-carbonization and pressure polymerization. The process route is complex. In particular, the heavy components need to react with the co-carbonizing agent under pressure. The process is long and energy-intensive. It also faces cost and safety issues caused by high-pressure equipment.

[0006] CN115820289A relates to a method and system for preparing mesophase asphalt, in which the polymerization reactions at each stage still need to be carried out under pressure of 1-3 MPa, which is not a true atmospheric pressure operation, and the process is long and the equipment investment is large.

[0007] CN111548822A discloses a method for purifying and modifying petroleum residue oil, which focuses on the deep pretreatment and purification of raw materials. Although it can obtain high-purity precursors, it involves multiple high-pressure reactions and toxic solvent treatment, which has high requirements for equipment safety, complex process, high cost, low yield and heavy environmental burden.

[0008] In summary, existing mesophase asphalt preparation processes generally rely on pressurization, and their complex flow and low integration require further improvement in terms of equipment safety, ease of operation, investment costs, and process flexibility, thus limiting the large-scale economic production of mesophase asphalt. In particular, how to achieve simple and efficient controllable adjustment of the mesophase asphalt structure under completely atmospheric pressure, while simultaneously considering raw material adaptability, product grading and utilization, and the feasibility of industrial scale-up, has become a pressing technical problem to be solved in this field.

[0009] Therefore, this invention provides a method for preparing mesophase asphalt based on atmospheric pressure multi-stage thermal polycondensation, which significantly improves process safety, economy, operability and raw material applicability, and provides a competitive solution for low-cost, large-scale and flexible production of mesophase asphalt. Summary of the Invention

[0010] The purpose of this invention is to provide a method for preparing mesophase asphalt based on multi-stage thermal polycondensation under normal pressure. The method is characterized by the fact that the entire process is carried out under normal pressure conditions, without the need for pressurization equipment, which significantly reduces equipment investment costs, operational safety risks and maintenance difficulties, and provides an inherently safe process path for industrial-scale production.

[0011] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing mesophase asphalt based on atmospheric pressure multi-stage thermal polycondensation includes the following steps: (S1) Raw material pretreatment: The heavy aromatic feedstock is subjected to desolidification and vacuum distillation to remove insoluble impurities such as catalyst particles, thereby obtaining a pure component for preparing mesophase asphalt; the vacuum distillation range is 380°C to 450°C. The heavy aromatic feedstock is selected from one or more combinations of catalytic cracking slurry, vacuum residue, hydrocracking tail oil, coal tar, medium-temperature coal tar pitch, and high-temperature coal tar pitch.

[0012] (S2) Primary atmospheric pressure thermal polycondensation: The pretreated raw materials are fed into the first-stage atmospheric pressure thermal polycondensation reactor (also known as the first reactor), and a first-stage thermal polycondensation reaction is carried out under atmospheric pressure, inert gas protection and stirring; the reaction is terminated when the amount of solid phase generated in the reaction accounts for 5% to 15% of the total mass of the raw materials. The primary thermopolymerization reaction temperature is 400°C to 520°C, the heating rate is 5 to 10°C / min, the stirring speed is 300 to 800 r / min, and the gas flow rate is 300 to 800 mL / (h·g). The primary thermopolymerization reaction can be carried out using a low-temperature, long-time process or a high-temperature, short-time process. Specifically, when the reaction is carried out at a temperature of 400°C to 470°C, the reaction time is approximately 8 to 24 hours; when the reaction is carried out at a temperature of 480°C to 520°C, the reaction time is approximately 3 to 8 hours.

[0013] The reaction is carried out under inert gas protection (nitrogen or argon) and stirring, ensuring the homogeneity and thermal stability of the reaction system, avoiding local overheating and coking, and improving reaction controllability and product consistency. With a solid phase formation rate of 5% to 15% of the total raw material mass as the reaction endpoint, it can remove poor-quality mesophase asphalt (mesophase content <90%, softening point >340℃, quinoline insolubles >40%) formed by complex heavy components such as highly reactive asphaltenes and heavy resins, which are prone to coking. This acts as a "raw material purification" process, creating a clean reaction environment for the subsequent orderly growth of the mesophase and avoiding excessive coking.

[0014] (S3) Primary heat filtration: The reaction mixture obtained in step (S2) is fed into the first hot filtration unit for hot filtration to separate the first solid phase component and the first liquid phase component. The filter media used has a fineness of 60 to 200 mesh; the filtration temperature is 150°C to 200°C. The first solid phase component is collected as a low-quality mesophase pitch or coke product. The primary thermal filtration step enables online classification of reaction products, effectively removing precursors that are prone to generating coke, preventing them from interfering with the fusion and development of subsequent mesophase structures, and improving product purity and structural controllability.

[0015] (S4) Secondary atmospheric pressure thermal polycondensation: The first liquid phase component obtained in step (S3) is fed into the second-stage atmospheric pressure thermal polycondensation reactor (also known as the second reactor) to carry out a secondary thermal polycondensation reaction under atmospheric pressure, inert gas protection and stirring conditions; The secondary thermal polycondensation reaction temperature is 390℃ to 440℃; the stirring speed is 300 to 800 r / min; and the gas flow rate is 300 to 800 mL / (h·g). (S5) Secondary heat filtration: The reaction product of step (S4) is fed into the second thermal filtration unit for thermal filtration to separate the second solid phase component and the second liquid phase component. The filter media used has a fineness of 60 to 200 mesh; the filtration temperature is 150°C to 200°C. The second solid product has a mesophase pitch content of 93% to 100%, and is a medium-to-high quality mesophase pitch (mesophase content >90%, softening point 270℃ to 340℃, quinoline insolubles 25% to 40%).

[0016] (S6) Optional multi-stage thermal polycondensation and filtration: The liquid phase component obtained from the previous stage of hot filtration is fed into the next stage reactor as raw material. Step (S4) of hot polycondensation and step (S5) of hot filtration are repeated at least once to continue separation to obtain mesophase asphalt. The temperature of the hot polycondensation reaction is controlled within the range of -20 to 20°C based on the temperature of the previous stage. The total number of stages of the multi-stage thermal condensation and thermal filtration is 2 to 4. By repeatedly performing multi-stage thermal condensation and thermal filtration operations, the controllable growth and graded regulation of the mesophase asphalt structure can be achieved, resulting in mesophase asphalt of different qualities.

[0017] (S7) Product collection: The solid components obtained from each stage of thermal filtration were collected to obtain mesophase asphalt products of different qualities.

[0018] In the method of this invention, the thermal filtration unit is a high-temperature filter. In each step, the reaction temperature is independently controlled.

[0019] In the process of preparing mesophase asphalt according to the method of the present invention, the gaseous byproducts generated in each stage (e.g., primary, secondary, and optionally higher-level) of thermal polycondensation reaction are recovered by a condensation recovery unit to obtain light oil products. The solid component byproducts obtained from primary thermal filtration are collected as low-quality mesophase asphalt or coke-like products, realizing the efficient and comprehensive utilization of raw materials and improving the overall economic efficiency and environmental friendliness of the process.

[0020] Compared with existing technologies, the advantages of the method of this invention are as follows: It has wide raw material adaptability, can directly process various industrial heavy aromatics without complex hydrogenation or solvent refining, and has good raw material adaptability and industrial compatibility; it adopts "staged thermal polycondensation + interstage thermal filtration," removing highly active components through a first-stage reaction and subsequent multi-stage controllable polymerization, achieving mesophase structure regulation and online product classification, resulting in high comprehensive utilization; while ensuring product quality, it significantly improves the economy, safety, and operability of the preparation process; the entire process is carried out at atmospheric pressure, eliminating the need for high-pressure equipment, resulting in low equipment investment, high safety, and facilitating industrial-scale application, providing an innovative solution for low-cost, large-scale, flexible production of mesophase asphalt. Attached Figure Description

[0021] Figure 1 This is a schematic flowchart of the mesophase pitch preparation method of the present invention.

[0022] Figure 2 This is a polarized microscope image of the mesophase pitch obtained in Example 1 of the present invention (magnification 10x40).

[0023] Figure 3A This is a scanning electron microscope (SEM) image of the fiber precursor obtained by melt spinning of the mesophase pitch prepared in Example 1 of this invention.

[0024] Figure 3B This is a magnified scanning electron microscope (SEM) image of a single filament in the fiber precursor obtained by melt spinning of the mesophase pitch prepared in Example 1 of this invention. Detailed Implementation

[0025] The present invention will be further described below with reference to specific embodiments. These embodiments are merely illustrative of the technical solutions of the present invention and do not constitute any limitation on the present invention. Within the technical concept of the present invention, those skilled in the art can make various modifications. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] Example 1: Preparation of mesophase asphalt by two-stage thermal polycondensation using catalytic cracking slurry as raw material. The raw material is catalytic cracking slurry from a certain refinery, which has undergone the removal of insoluble impurities and the cutting of components by vacuum distillation.

[0027] Add 1 kg of the oil slurry to the first reactor R1, purge with nitrogen gas at a flow rate of 500 mL / (h·g) and maintain atmospheric pressure. Increase the temperature to 420°C at 5°C / min, start stirring, and rotate at 400 r / min. Maintain the reaction at this temperature until the solid content generated in the reaction system accounts for approximately 8% of the total mass of the raw materials, then terminate the reaction.

[0028] The reaction system was cooled to 180°C and then hot-filtered through a pressure filter with an 80-mesh metal filter screen; approximately 80 g of the first solid phase component and approximately 600 g of the first liquid phase component were obtained.

[0029] Testing revealed that the softening point of the first solid component S1 was approximately 360°C, and the quinoline insoluble matter (QI) was 45 wt%. The first solid component S1 was collected as a byproduct.

[0030] The first liquid phase component L1 was transferred to the second reactor R2, and under nitrogen protection (flow rate 800 mL / (h·g)) and stirring (speed 400 r / min), the temperature was increased to 410℃ at 5℃ / min, and the reaction was carried out at a constant temperature for 18 hours.

[0031] After the reaction is complete, the reactants are cooled to 180°C and then hot-filtered through a pressure filter with an 80-mesh metal screen to obtain a second solid phase component (about 300g) and a second liquid phase component (about 230g).

[0032] The softening point of the second solid phase component S2 was determined to be 320℃; the target product's mesophase pitch content was greater than 95%, and the quinoline insoluble matter (QI) was 38wt%; polarized light microscopy images showed that it exhibited a wide-area streamlined optical structure. Figure 2 ).

[0033] The second liquid phase component L2 can be returned as a primary reaction feedstock or as a heavy fuel oil component. The byproduct light oil is recovered by condensation (approximately 50g).

[0034] Calculations show that the total yield of high-quality mesophase asphalt (based on S2) is 30%. Byproducts are low-quality asphalt (S1) and light oil, and the process is safe and controllable. Example 2: Three-stage thermal polycondensation and product classification using vacuum residue as raw material

[0035] The raw material is vacuum residue oil obtained from a certain refinery after removing insoluble impurities and being processed by vacuum distillation.

[0036] Add 1 kg of the pretreated vacuum residue to R1, and under nitrogen protection (flow rate 600 mL / min), stir (speed 600 r / min), and heat to 480°C at a rate of 5°C / min until the solid content is about 9%, then terminate the reaction.

[0037] The reactants were cooled to 190°C and filtered through a pressure filter equipped with an 80-mesh filter to obtain the first solid phase component S1a (approximately 90g) and the first liquid phase component L1a (approximately 510g).

[0038] Transfer L1a into R2, and heat to 400°C at a rate of 5°C / min under nitrogen (flow rate 600 mL / (h·g)) and stirring (speed 300 r / min), and react at this temperature for 18 hours.

[0039] The reactants were cooled to 180°C and filtered through a pressure filter equipped with an 80-mesh filter to obtain the second solid phase component S2a (approximately 160g, softening point 315°C) and the second liquid phase component L2a (approximately 300g).

[0040] Transfer L2a into R3, and under nitrogen (flow rate 700 mL / min) and stirring (speed 300 r / min), raise the temperature to 410℃ at 5℃ / min and react at a constant temperature for 10 hours.

[0041] The reactants were cooled to 180°C and filtered through a pressure filter equipped with a 60-mesh filter to obtain the third solid phase component S3a (approximately 180g) and a small amount of liquid phase residue.

[0042] The softening point of S2a was determined to be 315℃, with a mesophase bitumen content of 95% and a QI of 35wt%; the softening point of S3a was 295℃, with a mesophase bitumen content of 98% and a QI of 30wt%. The total yield of high-quality mesophase bitumen (based on S2a + S3a) was 34%.

[0043] The two products with high mesophase content and different softening points obtained can be selected for use according to downstream needs.

[0044] In this embodiment, through a three-stage thermal polycondensation reaction, the products are finely graded, and multiple specifications of products are obtained from the same raw material.

[0045] The above embodiments demonstrate that the method of the present invention is carried out entirely under atmospheric pressure, without the need for complicated solvent extraction, hydrogen supply agent pressurization reaction and other cumbersome steps. Through two-stage atmospheric pressure thermal polycondensation and thermal filtration, a high-quality product yield (95% mesophase pitch content) is obtained. The process is simple, with low equipment requirements and low operational risks. The resulting product has an excellent optical structure, which fully meets the requirements for spinning or preparing needle coke. The overall process has significant advantages in terms of economy, safety and efficiency.

Claims

1. A method for preparing mesophase asphalt based on atmospheric pressure multi-stage thermal polycondensation, comprising the following steps: (S1) Raw material pretreatment: The heavy aromatic raw material is subjected to desolidification and vacuum distillation to remove insoluble impurities such as catalyst particles, so as to obtain pure components for preparing mesophase asphalt. (S2) Primary atmospheric pressure thermal polycondensation: The pretreated raw materials are fed into the first reactor and carried out a primary thermal polycondensation reaction under atmospheric pressure, inert gas protection and stirring. The reaction temperature is 400°C to 520°C. When the amount of solid phase generated in the reaction accounts for 5% to 15% of the total mass of the raw materials, the reaction is terminated. (S3) First-stage hot filtration: The reaction mixture obtained in step (S2) is fed into the first hot filtration unit and hot filtered at 150°C to 200°C to separate the first solid phase component and the first liquid phase component. (S4) Secondary atmospheric pressure thermal polycondensation: The first liquid phase component obtained in step (S3) is fed into the second reactor, and the secondary thermal polycondensation reaction is carried out under atmospheric pressure, inert gas protection and stirring. The reaction temperature is 390°C to 440°C. (S5) Secondary thermal filtration: The reaction product obtained in step (S4) is fed into the second thermal filtration unit and thermally filtered at 150°C to 200°C to separate the second solid phase component and the second liquid phase component. (S6) Optional multi-stage thermal polycondensation and filtration: The liquid phase component obtained from the previous stage thermal filtration is fed into the next stage reactor as raw material, and steps (S4) and (S5) are repeated at least once to continue separation to obtain mesophase asphalt; the thermal polycondensation reaction temperature is controlled within the range of -20 to 20°C based on the previous stage temperature. (S7) Product collection: Collect the solid components obtained from each stage of thermal filtration to obtain mesophase asphalt products of different qualities.

2. The method according to claim 1, wherein in step (S1), the heavy aromatic feedstock is selected from one or more combinations of catalytic cracking slurry, vacuum residue, hydrocracking tail oil, coal tar, medium-temperature coal tar pitch, and high-temperature coal tar pitch.

3. The method according to claim 1, wherein in step (S1), the distillation range of the vacuum distillation is 380°C to 450°C.

4. The method according to claim 1, wherein in step (S2), the heating rate of the thermal polycondensation reaction is 5 to 10 °C / min, the stirring speed is 300 to 800 r / min, the inert gas is nitrogen or argon, and the gas flow rate is 300 to 800 mL / (h·g).

5. The method according to claim 1, wherein in step (S3), the first solid phase component is collected as a low-quality mesophase pitch or coke product.

6. The method according to claim 1, wherein in step (S4), the heating rate of the thermal polycondensation reaction is 5 to 10 °C / min, the stirring speed is 300 to 800 r / min, the inert gas is nitrogen or argon, and the gas flow rate is 300 to 800 mL / (h·g).

7. The method according to claim 1, wherein in step (S3), the thermal filtration uses a filter medium with a precision of 60 to 200 mesh and a filtration temperature of 150°C to 200°C.

8. The method according to claim 1, wherein in step (S5), the thermal filtration uses a filter medium with a precision of 60 to 200 mesh and a filtration temperature of 150°C to 200°C.

9. The method according to claim 1, wherein in step (S6), the total number of stages of the multi-stage thermal polycondensation and thermal filtration is 2 to 4 stages.

10. The method according to claim 1, wherein gaseous products generated during each stage of thermal polycondensation reaction are condensed and recovered by a condensation recovery unit to obtain light oil products.

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