High-strength medium-mold carbon fiber and preparation method thereof

Abstract

The application relates to a high-strength medium modulus carbon fiber and a preparation method thereof, and belongs to the technical field of carbon fibers. The application solves the problem of high residual monomer content in a spinning solution, low degree of dense precursor, poor orientation and insufficient strength of the precursor, which further leads to insufficient strength of the carbon fiber in the prior art. The application provides a preparation method of the high-strength medium modulus carbon fiber, and the carbon fiber product is obtained through polymerization, monomer removal, ammoniation, a coagulation bath, washing, hot water drawing, and post-treatment. The weight average molecular weight of the spinning solution / acrylonitrile-based polymerization solution prepared by the preparation method is 200-250 thousand, the polydispersity index PDI is 2.0-3.0, the residual monomer content in the polymerization solution is less than or equal to 350 ppm; the precursor orientation degree is greater than or equal to 93.0%, and the precursor strength is greater than or equal to 7.5 cN / dtex; the carbon fiber elastic modulus is 320-340 GPa, the drawing strength is greater than 6100 MPa, the dimethyl sulfoxide residual amount is less than or equal to 320 ppm, and no obvious defects are observed under a 2000-fold electric microscope.

Description

Technical Field

[0001] This invention relates to the field of carbon fiber materials technology, and in particular to a high-strength intermediate-modulus carbon fiber and its preparation method. Background Technology

[0002] Polyacrylonitrile (PAN) carbon fiber is an inorganic material with a carbon content exceeding 90%. PAN-based carbon fiber has become the mainstream in carbon fiber production due to its superior finished product quality and mechanical properties, as well as its simpler processing. The overall performance of PAN-based carbon fiber largely depends on the quality of the spinning solution and the degree of densification of the precursor fiber.

[0003] Regarding spinning solutions, the preparation of polyacrylonitrile spinning solutions with high molecular weight and narrow molecular weight distribution has always been a research focus, as it can improve the mechanical properties of fibers, reduce fiber breakage in continuous production, and improve the production qualification rate.

[0004] To prepare high molecular weight PAN, scholars at home and abroad have developed a series of polymerization methods. Based on whether the PAN polymer is soluble in solvent, the polymerization methods are divided into two categories: homogeneous polymerization (homogeneous solution polymerization) and heterogeneous polymerization (aqueous precipitation polymerization, mixed solvent precipitation polymerization, aqueous suspension polymerization, etc.). At present, these heterogeneous polymerization methods are difficult to apply in the process because the process flow of these methods is complex and the added reagents such as emulsifiers, dispersants, organometallic reagents, and ionic liquids are difficult to remove, which has an adverse effect on the quality of carbon fibers.

[0005] Currently, the molecular weight of PAN produced by homogeneous solution polymerization, which is the main industrial method, is generally low. Some researchers have attempted to increase the molecular weight of PAN obtained by homogeneous solution polymerization by increasing monomer concentration, decreasing initiator concentration, and lowering reaction temperature. However, these methods have the following problems: excessively high monomer concentration leads to high system viscosity and severe gelation, which is detrimental to subsequent spinning; excessively low initiator concentration leads to a slow reaction rate, which is not conducive to industrial production; lowering the temperature also reduces the reaction rate, and different types of initiators have different optimal decomposition temperatures, so the reaction temperature should not be too low. Therefore, the polyacrylonitrile spinning solutions produced industrially still suffer from problems such as difficulty in increasing molecular weight, wide molecular weight distribution, and unstable viscosity and molecular weight between different batches, ultimately affecting the mechanical properties of carbon fibers.

[0006] Regarding the properties of the precursor fiber (densification), the precursor fiber is made by polymerizing acrylonitrile monomers to form a spinning solution. The spinning solution is then passed through a spinneret to become a single filament stream. The precursor fiber is prepared by the synergistic effect of solidification and double diffusion, as well as water washing and hot water stretching.

[0007] Because spinning solutions of different compositions are highly sensitive to parameters of the coagulation bath and drawing process (temperature, medium, drawing ratio, etc.), defects such as poor orientation consistency of the precursor fibers, numerous pore-type defects, and insufficient densification are prone to occur during the preparation process, which in turn affect the densification degree and strength of the carbon fibers prepared subsequently. Summary of the Invention

[0008] Based on the above analysis, the present invention aims to provide a high-strength intermediate-modulus carbon fiber and its preparation method to solve at least one of the following technical problems: the difficulty in increasing the molecular weight of PAN-based spinning solution, the wide molecular weight distribution, and the instability of viscosity and molecular weight in different batches in the prior art; as well as the poor consistency of precursor fiber orientation, numerous pore-type defects, and insufficient densification, thereby improving the densification degree and strength of carbon fiber.

[0009] This invention provides a method for preparing high-strength intermediate-modulus carbon fiber, specifically including the following steps:

[0010] S1: Add materials containing acrylonitrile, comonomer and solvent to the polymerization device and adjust the target molecular weight of the acrylonitrile-based polymerization solution;

[0011] S2: Perform a monomer removal treatment on acrylonitrile-based polymer solutions that meet the target molecular weight;

[0012] S3: The acrylonitrile-based polymer solution after the single-chain removal treatment is subjected to ammoniation treatment to obtain spinning solution;

[0013] S4: The spinning solution is spun into a coagulation bath after being spun and then drawn to obtain nascent fibers.

[0014] S5: The nascent fibers are washed using a multi-stage washing process with progressively increasing temperatures;

[0015] S6: A multi-stage drawing process is used to draw the washed fibers with hot water and then cool them to obtain a denser filament.

[0016] S7: High-strength intermediate-modulus carbon fiber is made by densifying the precursor yarn.

[0017] Specifically, in step S1, the timing for adding the remaining initiator after polymerization starts and the timing for terminating the reaction are determined based on the viscosity change of the material. The target molecular weight of the acrylonitrile-based polymerization liquid is controlled by the material temperature and the proportion of the remaining initiator in the total amount of initiator.

[0018] Specifically, when the material viscosity reaches the first viscosity threshold, the remaining initiator is added, and when the material viscosity reaches the second viscosity threshold, the reaction is terminated; the first viscosity threshold is 200P to 400P; and / or, the second viscosity threshold is 600P to 1000P; the remaining initiator accounts for 20% to 40% of the total initiator.

[0019] Specifically, the process of finding a partner in step S2 is as follows:

[0020] The polymer liquid undergoes gas-liquid exchange with the countercurrent solvent vapor through multiple layers of perforated partitions. At each layer of perforated partition, the polymer liquid is divided into two parts: one part of the polymer liquid spreads flat on the perforated partition to form a thin liquid layer and flows downward through the holes in the perforated partition, and the other part of the polymer liquid flows downward from the suspended end on the side of the perforated partition.

[0021] Specifically, in step S2, the inlet flow rate Q1 of the acrylonitrile-based polymerization solution entering the depolymerization device and the inlet flow rate Q2 of the solvent vapor entering the depolymerization device satisfy the following:

[0022] Q2≥k×Q1×m×α×1000

[0023] Where Q1 is in meters (m) 3 / h, Q2 is in L / h, m is the mass percentage of residual monomer in the carbon fiber polymerization liquid; α is the flow coefficient of solvent vapor, and the value of α ranges from 1.0 to 1.2; k is the proportionality coefficient, and the value of k ranges from 1.5 to 1.9.

[0024] Specifically, in the ammoniation treatment described in step S3, the mass of ammonia gas M required to be introduced per 1 kg of polymer solution is determined based on the flow rate Q3 of the polymerization liquid and the following relationship: M = Q3 × n; where M is in mg and Q3 is in m³. 3 / h, where n ranges from 1.25 to 3.0.

[0025] Specifically, in step S4, the solidified filaments are stretched during the coagulation bath process, with a stretching ratio of 1.01 to 1.20 times.

[0026] Specifically, in step S5, a flower roller washing method is used. During the washing process, the stretching is distributed. When the washing temperature is ≤45℃, a stretching of 1.01 to 1.03 times is applied; when the washing temperature is >45℃, a stretching of 1.02 to 1.05 times is applied. The temperature and stretching ratio of the next washing stage are not less than the temperature and stretching ratio of the previous washing stage.

[0027] Specifically, in step S6, the hot water temperature is ≥70℃, and the total hot water stretching ratio is 2 to 4 times; the hot water stretching is divided into 2 to 6 segments, with the hot water temperature and stretching ratio gradually increasing in each segment.

[0028] Specifically, the densification process of the precursor fiber in step S6 includes: oiling, drying, and steam drawing.

[0029] Specifically, the densified precursor fiber is processed into carbon fiber through constant tension unwinding, pre-oxidation, low-temperature carbonization, high-temperature carbonization, electrolysis, sizing, drying, and winding.

[0030] The present invention also provides a high-strength intermediate-modulus carbon fiber, wherein the carbon fiber is prepared by the aforementioned preparation method;

[0031] The carbon fiber has an elastic modulus of 320-340 GPa, a tensile strength of >6100 MPa, a dimethyl sulfoxide residue of ≤320 ppm, and no obvious defects when observed under an electron microscope at 2000x magnification.

[0032] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0033] (1) The acrylonitrile-based polymerization solution / spinning solution prepared by the present invention has a high molecular weight, a low molecular weight distribution width, a weight-average molecular weight of 200,000 to 250,000, and a polydispersity index (PDI) of 2.0 to 3.0. The residual monomer content of the spinning solution is ≤350ppm and the amination uniformity is good, which lays a good foundation for the subsequent improvement of carbon fiber performance. The present invention adds the initiator in batches during the polymerization reaction, determines the appropriate time to add the remaining initiator after the polymerization starts according to the change of material viscosity, and effectively controls the molecular weight of the polymer to achieve the target level through the synergistic control of material temperature and the proportion of the remaining initiator in the total initiator. Compared to traditional indicators such as temperature and reaction time, changes in material viscosity more accurately reflect the extent of the reaction. While traditional indicators such as conversion rate can serve as one of the evaluation indicators of the reaction extent, determining the conversion rate is too cumbersome and time-consuming. Obtaining each conversion rate requires sampling the material in the reaction process, drying it for several hours to obtain a solid, and then calculating the conversion rate, which is difficult to apply to industrial production. Compared with traditional indicators such as conversion rate, the viscosity indicator of this invention is more operable. In practical applications, it is possible to easily grasp the optimal timing for adding the initiator, thereby significantly improving the stability of the viscosity and molecular weight of different batches of polymerization solutions, thus laying a solid foundation for the subsequent preparation of high-performance carbon fibers. In some preferred embodiments, based on the advantages of determining the timing of batch initiator addition based on viscosity changes, this invention can effectively reduce the number of end groups of the polymerization reaction molecular chains, increase the molecular chain length, reduce the number of small molecules, obtain high molecular weight polymerization solutions, and reduce the molecular weight distribution width by controlling the viscosity threshold for adding the remaining initiator, the viscosity threshold for termination, the polymerization temperature, the heating to the target temperature, and the proportion of the remaining initiator in the total initiator.

[0034] (2) In some preferred embodiments, during the demonolysis process, by optimizing the flow path of the polymer liquid, it is possible to ensure that the polymer liquid is spread out to form a large-area thin liquid layer, providing sufficient contact area and contact time with the solvent vapor, thereby achieving a good demonolysis effect. Moreover, when dealing with high molecular weight, high-viscosity polymer liquids that are difficult to demonolyze, this invention can also ensure that the polymer liquid flows smoothly to the next layer through the channels reserved at the suspended ends of each partition, thus avoiding problems that are prone to occur in traditional demonolysis processes, such as skinning, coking, or gel formation in the polymer liquid. By further optimizing the flow path of the polymer liquid, the upper layer of polymer liquid flows to the lower partition and continues to spread out, allowing the polymer liquid and solvent vapor to have more opportunities for gas-liquid exchange, thereby improving the demonolysis effect. After demonolysis treatment using the preferred preparation method provided in the embodiments of this invention, the residual monomon content in the polymer liquid is <100ppm, preferably <50ppm, and more preferably <30ppm.

[0035] (3) In some preferred embodiments, during the ammoniation process, the appropriate range of ammonia gas flow rate is set according to the flow rate of the polymerization liquid and in combination with the quantitative relationship, so as to accurately control the ammonia gas flow rate, thereby ensuring the ammoniation effect, improving the uniformity of ammoniation, enhancing the hydrophilicity of polyacrylonitrile, stabilizing the degree of ammoniation, extending the service life of the spinning liquid, and thus improving the performance of carbon fiber.

[0036] (4) The densified precursor prepared by the present invention has high orientation consistency, with a precursor orientation degree ≥91.5% and a precursor strength >6.5cN / dtex; the residual dimethyl sulfoxide in the precursor is significantly reduced, with a residual amount of dimethyl sulfoxide in the precursor <1000ppm, thereby significantly reducing the pore-type defects in the precursor and improving the densification degree and strength of the precursor; thus improving the comprehensive performance of the carbon fibers prepared subsequently.

[0037] Since the precursor fiber is composed of multiple monofilaments, each with a certain diameter, the solidification diffusion of the monofilaments ejected from the spinneret proceeds gradually from the outer surface towards the core. During the double-diffusion solidification process, the outer layer of the monofilament solidifies first, gradually becoming denser, which hinders the double diffusion in the core. Therefore, the dimethyl sulfoxide (DMSO) in the core cannot be released, resulting in defects. This invention first achieves finer denier solidification by adjusting parameters such as the concentration of the solidification solution, solidification temperature, and draw ratio. The fibers become finer in the solidification bath, which is more conducive to the precipitation of DMSO in the core, resulting in better densification of the nascent fibers after solidification (meaning the DMSO content in the nascent fibers is reduced).

[0038] (5) More preferably, when using an annular spinneret, by controlling the concentration and flow rate of the inner ring liquid, the contact between the spinning solution and the coagulation solution (strictly speaking, the inner ring liquid is also part of the coagulation solution) can be more sufficient, the coagulation process is more uniform, which is beneficial to improving the orientation and uniformity of the nascent fibers.

[0039] (6) Furthermore, this invention significantly increases the number of washing stages during the washing phase, particularly preferably 16 stages, and gradually increases the temperature during the washing process, while strictly controlling the draw ratio (slightly increasing according to temperature changes). In this process, the purpose of washing away the coagulant dimethyl sulfoxide and further improving fiber densification is achieved simultaneously, with the residual dimethyl sulfoxide content in the raw yarn <1000ppm. Too few washing stages or too low a temperature will lead to excessively high sulfoxide content in the fiber bundle. Too few washing stages result in insufficient washing time and high sulfoxide residue. Too low a washing temperature leads to poor fiber plasticity, which becomes a defect during draw and affects densification. Too many washing stages will cause resource waste and a lengthy process. The washing temperature should not be too high either. On the one hand, high temperature will cause the residual dimethyl sulfoxide to diffuse rapidly. Although the residual coagulant is removed, it will cause pore-type defects inside or on the surface of the raw yarn. On the other hand, when the washing temperature is >90℃, the crystallinity in the raw yarn will decrease, resulting in changes in the internal structure, which in turn leads to a decrease in the strength of the raw yarn, and also causes energy waste.

[0040] (7) Furthermore, this invention strictly controls the temperature of hot water drawing and divides it into multiple stages / segments, with different draw ratios set for each stage to achieve gradual optimization of the internal structure of the raw filament. Too few segments and too large a draw ratio in each segment will lead to filament breakage and defects. The temperature of each segment is gradually increased, and the draw ratio gradually increases with the temperature. As the temperature gradually increases, the fiber plasticity improves, the draw ratio gradually increases, and the fiber becomes finer and denser step by step.

[0041] Particularly preferred is that the hot water drawing is divided into four stages; wherein, stage 1 is at 70-80℃ with a drawing ratio of 1.1-1.2 times; stage 2 is at 75-85℃ with a drawing ratio of 1.2-1.3 times; stage 3 is at 80-90℃ with a drawing ratio of 1.3-1.4 times; and stage 4 is at 85-95℃ with a drawing ratio of 1.4-1.5 times. This preferred scheme provides a gentler temperature gradient and a gentler drawing ratio, resulting in less damage to the fiber and higher fiber density.

[0042] Through the coordinated operation of the above steps (corresponding to S4, S5, and S6), the technical objectives and parameter designs of each process segment are closely linked and work synergistically to achieve the densification control of the precursor fiber (low residue, reduced porosity defects, and high orientation consistency), thereby improving the performance of the precursor fiber and downstream carbon fiber products.

[0043] The final carbon fiber product has high appearance consistency, high product stability, no structural defects, elastic modulus of 320-340 GPa, tensile strength >6100 MPa, and dimethyl sulfoxide residue ≤320 ppm.

[0044] (8) The preparation method provided by the present invention has high comprehensive performance of the process product, thereby improving the performance and product stability of the final product carbon fiber.

[0045] (9) The equipment involved in the preparation method provided by the present invention is readily available, the process conditions are mild, the energy consumption is low, and it is suitable for large-scale production and widespread promotion.

[0046] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description and drawings. Attached Figure Description

[0047] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0048] Figure 1 This is a flowchart of a method for preparing high-strength intermediate-modulus carbon fiber;

[0049] Figure 2 This is a schematic diagram of the single-person-getting-out-of-singleness device provided in an embodiment of the present invention;

[0050] Figure 3 This is a schematic diagram of the ammoniation apparatus provided in an embodiment of the present invention;

[0051] Figure 4 This is a schematic diagram of the polymerization apparatus provided in an embodiment of the present invention;

[0052] Figure 5 These are actual photos of carbon fiber products.

[0053] Figure label:

[0054] 100-Solvent separation device; A-Tank; B-Solvent vaporizer; C-Real-time viscosity monitoring device; 11-Perforated baffle; 12-Polymerization liquid inlet; 13-Distribution plate; 14-Solvent inlet; 15-Coil; 15a-Coil inlet; 15b-Coil outlet; 16-Solvent vapor; 17-Vacuum port; 18-Polymerization liquid outlet; 200-Ammoniation device; 21-Inclined blade agitator; 21a-Agitator; 21b-Shaft; 22-Ammonia inlet; 23-Polymerization liquid inlet; 24-Polymerization liquid outlet; 25-First motor; 300-Polymerization device; 31-Agitating device; 32-Inert gas inlet; 33-Inert gas outlet; 34-Second motor; 35-Online pressure-viscosity converter; 36-Constant speed gear pump; 37-Circulating water inlet; 38-Circulating water outlet. Detailed Implementation

[0055] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0056] This invention provides a method for preparing high-strength intermediate-modulus carbon fiber, specifically including the following steps:

[0057] S1: Add materials containing acrylonitrile, comonomer and solvent to the polymerization device and adjust the target molecular weight of the acrylonitrile-based polymerization solution;

[0058] S2: Perform a monomer removal treatment on acrylonitrile-based polymer solutions that meet the target molecular weight;

[0059] S3: The acrylonitrile-based polymer solution after the single-chain removal treatment is subjected to ammoniation treatment to obtain spinning solution;

[0060] S4: The spinning solution is spun into a coagulation bath after being spun and then drawn to obtain nascent fibers.

[0061] S5: The nascent fibers are washed using a multi-stage washing process with progressively increasing temperatures;

[0062] S6: A multi-stage drawing process is used to draw the washed fibers with hot water and then cool them to obtain a denser filament.

[0063] S7: High-strength intermediate-modulus carbon fiber is made by densifying the precursor yarn.

[0064] Specifically, in step S1, the timing of adding the remaining initiator after polymerization starts and the timing of terminating the reaction are determined based on the viscosity change of the material. The target molecular weight of the acrylonitrile-based polymerization liquid is controlled by the material temperature and the proportion of the remaining initiator in the total amount of initiator.

[0065] Among these, determining the timing of adding the remaining initiator after polymerization initiation and the timing of terminating the reaction includes:

[0066] Heat to the polymerization temperature and add some initiator;

[0067] Real-time monitoring of material viscosity:

[0068] When the material viscosity reaches the first viscosity threshold, the remaining initiator is added. When the material viscosity reaches the second viscosity threshold, the reaction is terminated to obtain an acrylonitrile-based polymer liquid with the target molecular weight. The first viscosity threshold is less than the second viscosity threshold.

[0069] Specifically, the first viscosity threshold is 200P to 400P; and / or, the second viscosity threshold is 600P to 1000P;

[0070] The polymerization temperature is 50-60°C. When the material viscosity reaches the first viscosity threshold, the material temperature is raised to the target temperature of 60-70°C.

[0071] The remaining initiator accounts for 20% to 40% of the total initiator.

[0072] By controlling the appropriate viscosity threshold, material temperature (polymerization temperature and target temperature to which the temperature is raised when the threshold is reached), and the proportion of the remaining initiator in the total initiator, it is beneficial to obtain a high molecular weight, narrowly distributed acrylonitrile-based polymer solution while increasing the polymerization reaction rate.

[0073] For example, the polymerization temperature is 52°C, 54°C, 56°C, or 58°C. Preferably, the polymerization temperature is 55-60°C.

[0074] For example, the target temperature is 62°C, 64°C, 67°C, or 69°C. Preferably, the target temperature is 66-68°C.

[0075] For example, the first viscosity threshold is 250P, 280P, 330P, 350P, or 380P. More preferably, the first viscosity threshold is 300P-400P.

[0076] For example, the second viscosity threshold is 650P, 700P, 750P, 800P, 850P, 900P, or 950P. Preferably, the second viscosity threshold is 750P-950P.

[0077] For example, the remaining initiator accounts for 23%, 25%, 27%, 30%, 33%, 35%, and 37% of the total initiator. Preferably, the remaining initiator accounts for 30-40% of the total initiator. It should be noted that by precisely controlling the viscosity threshold, material temperature (polymerization temperature and the target temperature to which the temperature is raised when the viscosity threshold is reached), and the percentage of the remaining initiator in the total initiator, a high molecular weight, narrow distribution polymer solution can be obtained while simultaneously achieving micro-tuning of the polymer solution's molecular weight.

[0078] In some embodiments, the polymerization temperature is 50-52°C, the first viscosity threshold is 200P-250P, the target temperature to which the material viscosity is raised is 68-70°C when the material viscosity reaches the first viscosity threshold, the remaining initiator accounts for 35-40% of the total initiator; the second viscosity threshold is 620-650P; the molecular weight (MW) of the obtained acrylonitrile-based polymer solution is 200,000-220,000, and the polydispersity index (PDI) is 2.5-3.0.

[0079] In some embodiments, the polymerization temperature is 54-56°C, the first viscosity threshold is 250P-300P, the target temperature to which the material viscosity is raised is 64-66°C when the material viscosity reaches the first viscosity threshold, the remaining initiator accounts for 35-40% of the total initiator; the second viscosity threshold is 700-750P; the molecular weight (MW) of the obtained acrylonitrile-based polymer solution is 210,000-230,000, and the polydispersity index (PDI) is 2.2-2.7.

[0080] In some embodiments, the polymerization temperature is 58-60°C, the first viscosity threshold is 250P-300P, the target temperature to which the material viscosity is raised is 60-62°C when the material viscosity reaches the first viscosity threshold, the remaining initiator accounts for 35-40% of the total initiator; the second viscosity threshold is 700-750P; the molecular weight (MW) of the obtained acrylonitrile-based polymer solution is 220,000-240,000, and the polydispersity index (PDI) is 2.2-2.7.

[0081] In some embodiments, the polymerization temperature is 54-56°C, the first viscosity threshold is 300P-350P, when the material viscosity reaches the first viscosity threshold, the target temperature to which the temperature is raised is 64-66°C, the remaining initiator accounts for 30-35% of the total initiator; the second viscosity threshold is 800-850P; the molecular weight (MW) of the obtained acrylonitrile-based polymer solution is 230,000-250,000, and the polydispersity index (PDI) is 2.0-2.5.

[0082] In some embodiments, the polymerization temperature is 54-56°C, the first viscosity threshold is 350P-400P, the target temperature to which the material viscosity reaches the first viscosity threshold is 64-66°C, the remaining initiator accounts for 30-35% of the total initiator, the second viscosity threshold is 900-950P, and the molecular weight (MW) of the obtained acrylonitrile-based polymer solution is 230,000-250,000, and the polydispersity index (PDI) is 2.0-2.5.

[0083] In some embodiments, the step of real-time monitoring of material viscosity includes: setting up a material return pipeline, real-time monitoring of the pressure of the material at a fixed position in the return pipeline, and obtaining the real-time monitored material viscosity based on the real-time viscosity value converted from the pressure value.

[0084] Specifically, the material is drawn from the polymerization unit and flows through the return pipeline at a constant temperature and flow rate, eventually converging back into the polymerization unit. By monitoring the pressure of the material at a fixed position in the return pipeline in real time, and combining the pressure-viscosity relationship, the pressure value is converted into a real-time viscosity value.

[0085] Furthermore, the method for determining the pressure-viscosity relationship includes: setting multiple data acquisition times, recording the pressure value and the viscosity value obtained by experimental methods at a fixed position in the return pipeline at each data acquisition time, performing mathematical fitting of the pressure value and viscosity value, and establishing the pressure-viscosity relationship.

[0086] Specifically, the steps for obtaining the viscosity value using the experimental method include: taking a sample from the polymerization apparatus and measuring the viscosity of the sample using a viscosity measuring instrument. Preferably, the sampling location is adjacent to the location where the material is drawn out of the polymerization apparatus. Exemplarily, the viscosity measuring instrument includes a falling ball viscometer and a rotational viscometer.

[0087] To ensure the reliability and consistency of pressure measurement results, ensuring the material flows through the return pipeline at a constant temperature and flow rate includes: placing the return pipeline in a constant-temperature circulating water system and installing a constant-speed gear pump on the return pipeline. The constant-temperature circulating water system ensures that the material temperature remains constant during flow, and by controlling the speed of the gear pump, the material can be ensured to flow through the pipeline at a constant flow rate.

[0088] It is understandable that, under conditions of constant flow rate, constant temperature, and a fixed-length pipeline (with constant pipeline resistance), the viscosity of the material can be obtained by measuring the pressure generated when the polymer flows through a fixed position in the return pipeline and combining this with the pressure-viscosity relationship. Preferably, the above-mentioned real-time monitoring of material viscosity is applicable to materials with a viscosity of 0-1000P.

[0089] Preferably, the length of the return pipe is 0.5-1.5 meters and the diameter is 5-20 mm. For example, the length of the return pipe is 1.0 meter and the diameter is 10 mm.

[0090] In some embodiments, for the acrylonitrile-based polymer solution obtained by polymerizing acrylonitrile and comonomer, the pressure-viscosity relationship is as follows:

[0091] y = -0.045x 2 +13.78x-106.8

[0092] Where y is the viscosity measured by the falling ball method, in units of P; and x is the pressure, in units of kPa.

[0093] For example, the viscosity y is the viscosity measured by the falling ball method at 40-50°C. For instance, within a time range of ±Δ around each data acquisition time t (preferably Δ≤10min), the pressure value at a fixed location on the reflux pipeline is recorded N times. Samples are taken from the polymerization unit at N times at the same time points as the recorded pressure values. Viscosity measurements are performed at N temperature points within the 40-50°C range. The viscosity y and pressure x are fitted using data fitting software (e.g., EXCEL, Matlab, or Python), with the fitting criterion being the coefficient of determination R0.2 ≥95%, preferred R 2 ≥98%, yielding the pressure-viscosity relationship. The model type of this relationship includes at least one of exponential, linear, logarithmic, polynomial (2nd order or higher), and power-law. For example, N is 3, and the test conditions are 40℃, 45℃, and 50℃. For example, Δ = 8 min, 5 min, 2 min, and 1 min.

[0094] Preferably, the constant temperature is 40–50°C; and / or the constant flow rate is 1–2 L / h.

[0095] Preferably, the location where the material is drawn out from the polymerization device is set 10-20 cm below the lower end of the stirring device inside the polymerization device. This location is where the flowability of the polymerization liquid is optimal, which facilitates timely and accurate monitoring of the real-time viscosity of the polymerization liquid in the polymerization reactor.

[0096] In one embodiment, the step of real-time monitoring of the pressure of the material at a fixed position in the return pipeline and converting the pressure value into a real-time viscosity value in conjunction with the pressure-viscosity relationship includes: setting an online pressure-viscosity converter at a fixed position in the return pipeline, the online pressure-viscosity converter including a pressure detector and a processor;

[0097] The pressure detector is used to collect the pressure signal of the polymer liquid in the return pipeline in real time, and transmit the pressure signal to the processor through the line; the processor converts the pressure signal into a viscosity value according to the preset pressure-viscosity relationship, and transmits the viscosity value to the display set outside the polymerization device for real-time display through the line.

[0098] Specifically, the proportions of the materials and the total amount of the initiator, by weight, are as follows: acrylonitrile 20-24 parts, comonomer 1-2 parts, solvent 73.65-78.85 parts, and total initiator 0.15-0.35 parts. Preferably, the total amount of initiator is 0.2-0.3 parts.

[0099] Optionally, the comonomer is one or a combination of itaconic acid, acrylic acid, methyl acrylate, methyl methacrylate, ethyl methacrylate, isobutylacrylic acid, β-butyl itaconic acid, acrylamide, acrylamide oxime, hydroxyethyl acrylonitrile, α-chloroacrylonitrile, or diacetone acrylamide. For example, the comonomer is itaconic acid.

[0100] Optionally, the initiator is at least one selected from azobisisobutyronitrile, azobisisoheptanenitrile, and dimethyl azobisisobutyrate. For example, the initiator is azobisisobutyronitrile (AIBN).

[0101] Optionally, the solvent is at least one selected from dimethyl sulfoxide, sodium thiocyanate, and N,N-dimethylformamide. For example, dimethyl sulfoxide is used as the solvent.

[0102] In some embodiments, the material further includes a molecular weight regulator; exemplarily, the molecular weight regulator is isopropanol; acrylonitrile and comonomer are used as copolymer components, and the amount of molecular weight regulator added is 0.002-0.005% of the total mass of the copolymer components.

[0103] Specifically, after the material is added to the polymerization device, before the polymerization is started, the material is stirred by a stirring device to make it evenly mixed. The stirring device is located in the center of the liquid inside the polymerization vessel and stirs in the same direction.

[0104] Preferably, the stirring device includes a ribbon mixer and a wall-scraping mixer.

[0105] Preferably, before polymerization begins, the stirring speed is 20-80 rpm, and the stirring time is 30-60 min. Exemplarily, the stirring speed is 30 rpm, 40 rpm, 50 rpm, 60 rpm, or 70 rpm, and the stirring time is 35 min, 40 min, 45 min, 50 min, or 55 min.

[0106] (a) For a ribbon agitator, the following conditions must be met: S1 = (50-70%)S2, S1 = Π×(1 / 2D1) 2 D1 is the outer diameter of the helical ribbon, and S2 is the inner cross-sectional area of ​​the polymerization reactor. For example, S1 / S2 = 55%, 60%, and 65%.

[0107] (b) For wall-scraping agitators, the following condition must be met: L ≤ 10 mm, where L represents the gap between the wall-scraping component (such as a scraper or blade) of the wall-scraping agitator and the inner wall of the polymerization reactor. As the polymerization reaction proceeds, the viscosity of the liquid inside the polymerization reactor continuously increases, becoming a high-viscosity liquid. By using a wall-scraping agitator and controlling L, it is possible to effectively prevent the high-viscosity liquid from adhering to the inner wall of the polymerization reactor and forming a sticky residue.

[0108] During the stirring process, the liquid level h in the polymerization reactor accounts for 10%-90% of the total height H of the polymerization reactor. For example, h / H = 20%, 30%, 40%, 50%, 60%, 70%, and 80%. Preferably, h / H = 80-90%.

[0109] By selecting the preferred stirring device and stirring parameters mentioned above, it is possible to ensure that the materials are mixed evenly before polymerization starts in an energy-efficient manner.

[0110] Preferably, by weight, acrylonitrile is 22-24 parts, comonomer is 1-2 parts, solvent is 73.7-76.8 parts, stirring speed is 40-60 rpm, and stirring time is 30-45 min.

[0111] Preferably, by weight, acrylonitrile is 20-22 parts, comonomer is 1-2 parts, solvent is 74.7-77.8 parts, stirring speed is 50-70 rpm, and stirring time is 45-55 min.

[0112] For example, uniformity of the liquid temperature inside the polymerization reactor is used to determine whether the materials are mixed evenly. Specifically, during the stirring process, a temperature difference of ≤1℃ between the liquids inside the polymerization reactor is used as the criterion for determining uniform mixing.

[0113] Specifically, the polymerization reaction is carried out under the protection of an inert gas. The inert gas flow rate is 50-100 L / h; the inert gas pressure is ≤0.1 MPa. Oxygen in the air has an inhibitory effect on polymerization, while inert gas can isolate oxygen. Using an inert gas with appropriate flow rate and pressure is conducive to the polymerization reaction.

[0114] Preferably, the inert gas enters the polymerization reactor from one side of the top and exits from the other side of the top, thus better displacing the original air in the polymerization reactor. The inert gas is selected from at least one of nitrogen, argon, or helium.

[0115] For example, the inert gas flow rate is 60 L / h, 70 L / h, 75 L / h, or 85 L / h.

[0116] For example, the inert gas pressure is 0.07 MPa, 0.05 MPa, 0.04 MPa, 0.02 MPa, or 0.01 MPa.

[0117] Preferably, the inert gas flow rate is 80-90 L / h and the inert gas pressure is 0.06-0.08 MPa. Precise control of the inert gas flow rate and pressure facilitates the polymerization process to obtain a high molecular weight polymer with a narrow distribution.

[0118] Preferably, pre-dissolving the initiator in a solvent before adding it to the polymerization apparatus in batches helps ensure that the initiator achieves a more rapid and uniform distribution throughout the reaction system, improves the uniformity of the polymerization reaction rate at different locations in the polymerization apparatus, and is beneficial for obtaining a high molecular weight polymer solution with a narrow distribution. Preferably, for the case where the initiator is 0.15-0.35 parts, the solvent used to dissolve the initiator is 5-10 parts.

[0119] Specifically, after polymerization starts, the material in the polymerization reactor is continuously stirred at a speed of 30-80 rpm. For example, after polymerization starts, the stirring speed is 35 rpm, 40 rpm, 45 rpm, 50 rpm, 55 rpm, 60 rpm, 65 rpm, 70 rpm, and 75 rpm.

[0120] Preferably, after polymerization starts and before adding the remaining initiator, the stirring speed is 30-60 rpm, more preferably 40-60 rpm. After adding the remaining initiator, the stirring speed is 50-80 rpm, more preferably 50-70 rpm.

[0121] Preferably, the single-person processing in step S2 is as follows:

[0122] The polymer liquid undergoes gas-liquid exchange with the countercurrent solvent vapor through multiple layers of perforated partitions. At each layer of perforated partition, the polymer liquid is divided into two parts: one part of the polymer liquid spreads flat on the perforated partition to form a thin liquid layer and flows downward through the holes in the perforated partition, and the other part of the polymer liquid flows downward from the suspended end on the side of the perforated partition.

[0123] This optimized monomer removal method significantly improves the monomer removal effect and efficiency, effectively preventing skinning or coking inside the monomer removal device and reducing gel formation in the polymer solution during the monomer removal process. After being introduced into the monomer removal device, the polymer solution is evenly distributed on the first perforated partition plate through a porous distribution system, forming a uniform thin liquid layer. The polymer solution mainly flows to the next partition plate through the holes in the partition plate and continues to spread on the lower partition plate to form a thin liquid layer, thus ensuring that the polymer solution thin liquid layer on each partition plate can achieve efficient gas-liquid exchange with solvent vapor. Simultaneously, excess high-viscosity material can flow smoothly to the next partition plate through the channel between the suspended end of the partition plate and the inner wall of the tank. This flow path not only ensures the monomer removal effect but also effectively prevents skinning and coking on the inner wall of the device, reduces gel formation in the polymer solution, and ensures efficient production. Compared with traditional monomer removal methods such as falling film towers and high-gravity rotating beds, the monomer removal process of this invention significantly reduces the stringent requirements on process parameters and equipment processing precision. Especially when dealing with acrylonitrile-based polymer solutions with high viscosity and high molecular weight, this invention exhibits better adaptability and stability, effectively avoiding the coking and skinning problems common in traditional methods, while significantly reducing the formation of gel in the polymer solution during monomer removal.

[0124] More preferably, a portion of the polymer solution flows through the holes in the perforated partition to the next perforated partition or the polymer solution collection area, and the positions of the holes exiting the adjacent perforated partitions are different. The other portion of the polymer solution flows from the suspended end on the side of the perforated partition to the next perforated partition or the polymer solution collection area. In the monomer removal process, by optimizing the polymer solution flow path as described above, the contact time between the polymer solution and solvent vapor is extended, ensuring that unreacted monomers (such as acrylonitrile) are removed more thoroughly, thus meeting the monomer removal requirements for high-viscosity polymer solutions.

[0125] In some embodiments, during the depolymerization process, the polymer solution enters the depolymerization device from the top or upper part, and after passing through a porous distribution plate, it is distributed onto the first layer of perforated partition plates, so that the polymer solution can be more evenly distributed on the first layer of perforated partition plates, thereby improving the depolymerization effect and efficiency.

[0126] It is understood that the monomer removal process includes: the polymerization liquid enters the monomer removal device and flows from top to bottom through multiple layers of perforated baffles to form a continuous liquid film flow; at the same time, solvent vapor enters the monomer removal device and flows from bottom to top through multiple layers of perforated baffles to fully contact the flowing polymerization liquid and perform gas-liquid exchange; the solvent vapor carries the residual volatile monomers in the polymerization liquid and is discharged from the monomer removal device; the polymerization liquid after monomer removal treatment is discharged from the monomer removal device, completing the monomer removal process.

[0127] For example, the single-person removal process is performed under negative pressure. The vacuum degree of the negative pressure is 100-5000 Pa. For example, the vacuum degree is 200 Pa, 500 Pa, 800 Pa, 1000 Pa, 2000 Pa, 3000 Pa, or 4000 Pa. Preferably, the vacuum degree is 500-2000 Pa.

[0128] Preferably, in the monomer removal process, the inlet temperature of the polymerization solution is 50-70°C, more preferably 65-70°C. Exemplarily, the inlet temperature of the polymerization solution is 54°C, 58°C, 62°C, or 66°C.

[0129] Preferably, in the monomer removal process, the influent flow rate of the polymerization solution is 3-5 m³ / h. 3 / h, preferably 3-4m 3 / h. In the monomer removal process, the temperature of the monomer removal system is controlled at 50-70℃, and more preferably, the temperature of the monomer removal system gradually increases from top to bottom. For example, the inlet flow rate of the polymerization solution is 3.3m³. 3 / h, 3.6m 3 / h, 3.9m 3 / h, 4.2m 3 / h, 4.5m 3 / h, 4.8m 3 / h.

[0130] Preferably, in the solvent vapor inlet temperature is 80-100°C; more preferably, it is 90-100°C. Exemplarily, the solvent vapor inlet temperature is 84°C, 88°C, 92°C, or 96°C.

[0131] Preferably, in the solvent vapor inlet pressure is 0.01-0.5 MPa; more preferably 0.2-0.3 MPa. Exemplarily, the solvent vapor inlet pressure is 0.05 MPa, 0.1 MPa, 0.15 MPa, 0.25 MPa, 0.35 MPa, 0.40 MPa, or 0.45 MPa.

[0132] In some embodiments, during the carbon fiber polymerization process, the influent viscosity of the carbon fiber polymer solution is 600-1000P, and the weight-average molecular weight is 200,000-250,000.

[0133] The inventors discovered that in the process of removing monomers, a better monomer removal effect can be obtained when the inlet flow rate of the polymerization liquid and the inlet flow rate of the solvent vapor meet a specific relationship.

[0134] Specifically, in step S2, the inlet flow rate Q1 of the acrylonitrile-based polymerization solution entering the depolymerization device and the inlet flow rate Q2 of the solvent vapor entering the depolymerization device satisfy the following:

[0135] Q2≥k×Q1×m×α×1000

[0136] Where Q1 is in meters (m) 3 / h, Q2 is in L / h, m is the mass percentage of residual monomer in the carbon fiber polymerization liquid; α is the flow coefficient of solvent vapor, and the value of α ranges from 1.0 to 1.2; k is the proportionality coefficient, and the value of k ranges from 1.5 to 1.9.

[0137] For example, k = 1.60, 1.65, 1.70, 1.72, 1.74, 1.75, 1.80, 1.85. For instance, k = 1.737.

[0138] Preferably, Q1 is 3-5m 3 / h.

[0139] When 3.0m 3 / h≤Q1<3.7m 3 / h, preferably, k takes the value of 1.8-1.9.

[0140] When 3.7m 3 / h≤Q1<4.4m 3 / h, preferably, k takes the value of 1.7-1.8.

[0141] When 4.4m 3 / h≤Q1≤5.0m3 / h, preferably, k takes the value of 1.6-1.7.

[0142] In one embodiment, Q1 = 3m 3 With a flow rate of 10%, m = 10%, α = 1.0, and k = 1.9, when Q2 ≥ 570 L / h, the residual acrylonitrile (AN) monomers in the polymer solution after monomer removal are less than 100 ppm, according to the test.

[0143] In one embodiment, Q1 = 4m 3 Given a flow rate of 10%, m = 10%, α = 1.1, and k = 1.73, if Q2 ≥ 760 L / h, the residual acrylonitrile (AN) monomers in the polymer solution after monomer removal are less than 100 ppm, according to the test.

[0144] In one embodiment, Q1 = 5m 3 Given a / h, m=9%, α=1.2, k=1.60, and satisfying Q2≥860L / h, the residual acrylonitrile (AN) monomers in the polymer solution after monomer removal are less than 100ppm according to the test.

[0145] The above embodiments fully verify the reliability of the relation Q2≥k×Q1×m×α×1000.

[0146] In the above embodiments, by precisely controlling the process parameters of the monomer removal process, such as the inlet flow rate of the polymerization liquid, the inlet flow rate of the solvent vapor, the inlet temperature of the polymerization liquid, and the inlet temperature / pressure of the solvent vapor, it is beneficial to improve the monomer removal efficiency and effect, avoid skinning or coking in the monomer removal equipment, and significantly reduce gel formation in the polymerization liquid. In some embodiments, the monomer removal effect is significant, with the residual monomer content after monomer removal being less than 100 ppm, and the monomer removal process is highly efficient and continuous, with the polymerization liquid continuously entering and exiting the monomer removal device according to the operating conditions. In addition, the phenomenon of skinning or coking in the equipment is greatly reduced, and no obvious discoloration is observed on the inner wall of the device through the viewing window on the monomer removal device. In traditional monomer removal devices, due to uneven heating of the polymerization liquid flow, local gelation occurs, and even coking occurs on the inner wall of the device, resulting in the filter replacement cycle for removing gel from the polymerization liquid after monomer removal being only 1-2 months, or even shorter. However, by using the monomer removal treatment of the present invention, gel formation in the polymerization liquid is significantly reduced, extending the filter replacement cycle to more than 3 months, thereby improving the equipment operating efficiency and service life. The above replacement cycle is based on the condition that the filter is replaced when the pressure is increased to half of its pressure resistance rating.

[0147] For example, in the monomer removal process, the solvent vapor is at least one selected from dimethyl sulfoxide, sodium thiocyanate, and N,N-dimethylformamide. The selected solvent vapor is the same as the solvent in the polymerization solution.

[0148] In the ammoniation process, the polymerization liquid is kept flowing and the temperature is controlled at 60-65°C in the storage tank of the ammoniation unit, which is the optimal temperature range for the ammoniation of acrylonitrile-based polymers. Specifically, the polymerization liquid flows in from the top of the storage tank of the ammoniation unit and flows out from the bottom of the tank.

[0149] Specifically, in the ammoniation treatment described in step S3, the mass of ammonia gas M required to be introduced per 1 kg of polymer solution is determined based on the flow rate Q3 of the polymerization liquid and the following relationship: M = Q3 × n; where M is in mg and Q3 is in m³. 3 / h, where n ranges from 1.25 to 3.0.

[0150] For example, n = 1.5, 1.8, 2.1, 2.4, 2.7.

[0151] Preferably, the value of Q3 is in the range of 3-5m. 3 / h.

[0152] When 3.0m 3 / h≤Q3<3.5m 3 / h, preferably, n takes a value in the range of 2.0-2.7.

[0153] When 3.5m 3 / h≤Q3<4.3m 3 / h, preferably, n takes a value in the range of 1.25-1.75.

[0154] When 4.3m 3 / h≤Q3≤5.0m 3 / h, preferably, n takes a value in the range of 1.6-2.0.

[0155] In one embodiment, Q3 = 3m 3 When M is 6-8 mg / h, tests show that the pH of the spinning solution after amination is 8-10, indicating good amination effect.

[0156] In one embodiment, Q3 = 4m 3 When M is 5-7 mg / h, tests show that the pH of the spinning solution after amination is 8-10, indicating good amination effect.

[0157] In one embodiment, Q3 = 5m 3 When M is 8-10 mg / h, tests show that the pH of the spinning solution after amination is 8-10, indicating a good amination effect.

[0158] Preferably, the ammonia gas introduction time is controlled at 5-8 hours.

[0159] In the ammoniation process, based on the material ratio provided by the present invention, the ammonia flow rate is precisely controlled according to the flow rate Q3 of the polymerization liquid and the following relationship: M = Q3 × n, which can not only ensure good ammoniation effect, but also save ammonia and ammoniation time.

[0160] Preferably, in the ammoniation treatment, an inclined blade agitator is used to stir the polymerization liquid. The inclined blade agitator includes multiple inclined blades with an inclination angle of 40-50°. The inclined blades are rectangular and have a length of L that satisfies πL. 2 = (50-70%)S4, where S4 is the cross-sectional area of ​​the storage tank in the ammoniation unit. During ammoniation, the stirring speed is controlled at 30-50 r / min. For example, during ammoniation, the stirring speed is controlled at 35 r / min, 40 r / min, and 45 r / min.

[0161] By employing an inclined blade agitator to lift the polymerization liquid upwards, a strong axial flow is generated, creating a circulating flow between the polymer and the surrounding environment during stirring. This flow pattern helps to better disperse ammonia gas in the polymerization liquid, improving mass transfer efficiency and ammoniation effect. Precise control of the structural parameters of the inclined blade agitator can further promote this circulating flow, thereby enhancing mass transfer efficiency and ammoniation effect.

[0162] Preferably, the ammoniation treatment is carried out under a slightly positive pressure, which allows ammonia gas to diffuse more effectively and come into full contact with the polymerization liquid, while ensuring system safety. Specifically, during the ammoniation process, a pressure slightly higher than the external atmospheric pressure, i.e., a slightly positive pressure, is applied inside the storage tank. The slightly positive pressure is 0-2000 Pa, meaning the pressure inside the storage tank is 0-2000 Pa higher than the external atmospheric pressure. More preferably, the slightly positive pressure is 100-1000 Pa. Exemplarily, the slightly positive pressure is 50 Pa, 200 Pa, 500 Pa, 800 Pa, 1300 Pa, 1500 Pa, or 1800 Pa.

[0163] By employing the ammoniation treatment provided in the above embodiments of the present invention, the pH of the obtained carbon fiber spinning solution can be guaranteed to be between 8 and 10, further between 8.4 and 9.8, and preferably between 8.9 and 9.5.

[0164] Furthermore, the molecular weight M of the acrylonitrile-based polymerization solutions obtained in S1 to S3 is... W The polydispersity index (PDI) is 2.0-3.0, the falling ball viscosity at 40-50℃ is 600-1000 P, the solid content in the polymerization solution is 19.0-21.0%, the polymerization conversion rate is ≥90%, and the residual monomer content of the acrylonitrile-based polymerization solution is ≤10%. After monomer removal treatment, the residual monomer content of the acrylonitrile-based polymerization solution is ≤350 ppm. After ammoniation treatment, the pH of the resulting carbon fiber spinning solution is 8-10.

[0165] In some embodiments, the molecular weight M of the acrylonitrile-based polymer solution obtained by polymerization is... W The polydispersity index (PDI) is 2.1-2.6, the falling ball viscosity at 40-50°C is 620-910P, the solid content in the polymerization solution is 19.2-20.6%, the polymerization conversion rate is 92-95%, and the residual monomer content of the acrylonitrile-based polymer solution is ≤3%, further, ≤2%, and further, ≤1%. After monomer removal treatment, the residual monomer content of the acrylonitrile-based polymer solution is <100ppm, more preferably, less than 50ppm, and further, less than 30ppm. After ammoniation treatment, the pH of the obtained carbon fiber spinning solution is 8.4-9.8, preferably 8.9-9.5.

[0166] The present invention also provides a production equipment for carbon fiber spinning solution, the production equipment being used for the production and preparation of carbon fiber spinning solution (corresponding to steps S1 to S3).

[0167] Specifically, the production equipment includes a desiccant device, an ammoniation device, and a polymerization device.

[0168] (1) Singles-finding device:

[0169] The single-discarding device 100 includes a tank A and multiple perforated baffles 11 disposed inside the tank. The multiple perforated baffles are arranged in layers from top to bottom along the axial direction of the tank, and each layer of perforated baffles is perpendicular to the axial direction of the tank. Each layer of perforated baffles includes a fixed end on one side and a suspended end on the other side. The fixed end is fixed to the inner wall of the tank, and the suspended end on the other side extends freely. The suspended end of the upper layer of perforated baffle is located on one side of the axial direction of the tank, and the suspended end of the lower layer of perforated baffle adjacent to the upper layer of perforated baffle is located on the other side of the axial direction of the tank. The suspended ends of the multiple layers of perforated baffles form an alternating staggered layout in space.

[0170] Compared with existing technologies, this invention incorporates multiple perforated baffles within the monomer removal device. The polymer solution spreads evenly on each baffle to form a thin liquid layer, with the suspended ends of adjacent baffles staggered to ensure smooth flow of the polymer solution. This structural design optimizes the flow path of the polymer solution within the tank. On one hand, the thin liquid layer increases the specific surface area of ​​the material; on the other hand, it extends the residence time of the solution within the equipment, providing more opportunities for solvent vapor to contact residual monomers, thereby significantly improving the monomer removal effect.

[0171] The monomer removal device of this invention designs channels between the suspended end of each perforated baffle and the inner wall of the tank, ensuring that the polymer liquid can flow smoothly to the next layer after forming a thin liquid layer. This structure not only achieves uniform distribution and effective guidance of high molecular weight, high viscosity polymer liquid materials on the baffle, but also significantly reduces problems such as coking, skinning, or gel formation in the polymer liquid that are prone to occur when processing such materials in traditional devices. In addition, it effectively avoids internal blockage of the monomer removal device, improves operational stability, reduces equipment cleaning and maintenance costs, and improves production efficiency.

[0172] Preferably, the area of ​​each perforated baffle layer accounts for 80%-90% of the cross-sectional area of ​​the tank at that layer, with the remaining 10-20% serving as a smooth channel for the flow of the polymer liquid.

[0173] Preferably, the pores of adjacent perforated partitions are staggered, with the position of the pores on each perforated partition offset relative to the position of the pores on its directly adjacent perforated partition. This staggered pore distribution further increases the contact area and time between solvent vapor and the polymerization liquid, thereby improving gas-liquid exchange efficiency and helping the solvent vapor to more effectively remove residual monomers from the polymerization liquid. In addition, the staggered pore distribution can optimize the flow path, making the flow of the polymerization liquid more uniform, reducing local overheating or undercooling, lowering the risk of coking and skinning, and reducing gel formation in the polymerization liquid.

[0174] Preferably, the multi-layer perforated baffles are distributed parallel to each other at equal intervals from top to bottom along the axial direction of the tank. This preferred baffle distribution helps achieve uniform flow of the polymer liquid within the tank, reduces dead zones, lowers the risk of coking and scaling, reduces gel formation in the polymer liquid, and ensures sufficient contact between solvent vapor and the polymer liquid, thereby improving the monomer removal effect and efficiency.

[0175] Preferably, within the tank, the distance between the first and last perforated baffles accounts for 1 / 2 to 4 / 5 of the total height of the tank, more preferably 60%-70%, such as 2 / 3. This allows for more efficient use of the tank space, increases the contact time and area between the polymer liquid and solvent vapor, and improves the polymerization effect and efficiency. The appropriate space at the top and bottom facilitates the heat and mass transfer processes, ensuring uniform distribution of heat and matter throughout the tank, reducing dead zones in the polymer liquid, avoiding local overheating or undercooling, and helping to reduce the risk of coking and skinning, as well as reducing gel formation in the polymer liquid.

[0176] Furthermore, a polymer liquid inlet 12 is provided at the top or upper part of the tank body, and a perforated distribution plate 13 is provided between the polymer liquid inlet 12 and the adjacent first layer perforated partition plate, and the distribution plate 13 is arranged parallel to the first layer perforated partition plate.

[0177] Preferably, the area ratio of the distribution plate 13 to the first perforated partition is 40%-60%, more preferably 45%-55%.

[0178] Preferably, the distance between the upper surface of the distribution plate 13 and the lower end of the polymer inlet 12 is 15%-40% of the distance between the lower end of the polymer inlet 12 and the upper surface of the first perforated partition plate; more preferably, it is 20%-30%.

[0179] The main function of the distribution plate is to distribute the polymer liquid entering from the feed inlet evenly onto the first perforated baffle plate after passing through a porous distribution system, thus forming a uniform, thin layer of polymer liquid on the baffle plate. By controlling the spatial layout of the distribution plate within the tank and its area ratio with adjacent perforated baffle plates, it is beneficial to form a more uniform, thin layer of polymer liquid, increase the contact area and time between the polymer liquid and solvent vapor, and improve the polymerization effect and efficiency.

[0180] By precisely controlling the shape and structural parameters of the perforated baffle and its spatial arrangement within the tank, the monomer removal effect can be improved, while avoiding localized overheating or undercooling, further reducing the risk of coking and skinning, and minimizing gel formation in the polymerization solution. Using the monomer removal device provided by this invention to treat the polymerization solution ensures that the residual monomer content in the polymer solution is reduced to below 100 ppm after monomer removal.

[0181] Specifically, the perforated partition has at least one of the following features:

[0182] (a) The number of layers of the perforated partition is 4-8;

[0183] (b) The aperture size of each perforated partition is 0.5-2 mm and the hole spacing is 10-40 mm; for example, the aperture size is 1 mm or 1.5 mm and the hole spacing is 20 mm or 30 mm.

[0184] (c) The arrangement of the multiple holes on each layer of perforated partition is preferably a ring array; further, the multiple holes cover the entire perforated partition.

[0185] (d) The spacing between two adjacent perforated partitions is 300-800 mm; preferably 400-600 mm, for example 500 mm;

[0186] (e) The thickness of each perforated partition is 6-12 mm;

[0187] (f) The holes of adjacent perforated partitions are staggered, and the offset distance between the corresponding hole centers of adjacent layers is 10-30mm; preferably, they are arranged in an alternating staggered manner: the odd-numbered layers and the even-numbered layers are kept consistent, but the odd-numbered layers and the even-numbered layers are staggered by a certain distance.

[0188] (g) To facilitate better spreading of the polymer solution into a thin film on the perforated partition and thus improve the monomer removal effect, the perforated partition is preferably made of 316L stainless steel, 1Cr18NiMo3 stainless steel, or AL-1100 aluminum alloy. All of these materials are commercially available alloy grades.

[0189] Furthermore, a solvent vapor inlet is provided at the lower part of the tank. The solvent vaporizer also includes a solvent vaporizer B. The upper part of the solvent vaporizer B is connected to the solvent vapor inlet via a pipeline. A solvent inlet 14 is provided at the bottom of the solvent vaporizer B. A coil 15 is provided inside the solvent vaporizer B. One end of the coil 15 is connected to the coil inlet 15a provided at the upper part of the solvent vaporizer B, and the other end of the coil 15 is connected to the coil outlet 15b provided at the lower part of the solvent vaporizer B.

[0190] Understandably, during operation, the solvent enters the solvent vaporizer B through the solvent inlet 14, and water vapor enters the coil through the coil inlet 15a, flows along the coil, and finally flows out through the coil outlet 15b. During the flow of water vapor inside the coil, it transfers heat to the solvent outside the coil, causing it to vaporize into solvent vapor 16. Solvent vapor 16 then flows into the tank A through the solvent vapor inlet.

[0191] For example, the solvent vapor inlet is located below the last layer of perforated baffle and above the liquid surface of the polymerized liquid after depolymerization and the liquefied solvent mixture collected at the bottom of tank A.

[0192] Specifically, a vacuum port 17 is provided at the upper part or top of the tank A; the monomer removal device also includes a liquid ring vacuum jet device, which is connected to the vacuum port 17 via a pipeline, thereby providing a stable negative pressure inside the tank A in the monomer removal device and discharging the solvent vapor carrying the monomer. Specifically, a heating jacket is provided on the outer wall of the tank A to bring the polymerization liquid inside the tank A to the required monomer removal temperature.

[0193] Specifically, a polymer liquid outlet 18 is provided at the lower part or bottom of the tank A.

[0194] (2) Ammoniation unit:

[0195] The ammoniation unit 200 includes a storage tank and an inclined blade agitator 21 disposed inside the storage tank; the inclined blade agitator 21 includes a plurality of agitators 21a arranged in layers along the axial direction of the storage tank, and the plurality of agitators are connected to the same rotating shaft 21b. Preferably, the plurality of agitators are distributed at equal intervals along the axial direction of the storage tank.

[0196] Each agitator includes multiple inclined agitator blades. Preferably, the inclination angle of the inclined agitator blades is 40-50°, and the inclined agitator blades are rectangular blades with a length of L and satisfying πL. 2= (50-70%)S4, where S4 is the cross-sectional area of ​​the storage tank. Preferably, πL 2 = (50-55%)S4.

[0197] For example, the inclined blade agitator includes 2, 3 or 4 agitators, each agitator including at least two inclined agitator blades, for example, each agitator including 3 or 4 inclined agitator blades.

[0198] Preferably, the ammonia inlet 22 is located in the lower 1 / 5 to 2 / 5 height range of the storage tank, that is, in the area between 1 / 5 and 2 / 5 height from the bottom of the storage tank upwards.

[0199] A polymerization liquid inlet 23 is provided at the upper part or top of the storage tank, and a polymerization liquid outlet 24 is provided at the lower part or bottom of the storage tank; the top of the shaft 21b of the inclined blade agitator is driven by a first motor 25.

[0200] (3) Polymerization apparatus:

[0201] The polymerization apparatus 300 includes a polymerization reactor and a stirring device 31 disposed inside the polymerization reactor. The stirring device 31 is selected from a ribbon agitator or a wall scraper agitator.

[0202] For a ribbon agitator, the following conditions must be met: S1 = (50-70%)S2, S1 = Π×(1 / 2D1) 2 D1 is the outer diameter of the helical ribbon, and S2 is the inner cross-sectional area of ​​the polymerization reactor. For example, S1 / S2 = 55%, 60%, and 65%.

[0203] For wall-scraping agitators, the following condition must be met: L≤10mm, where L represents the gap between the wall-scraping component (such as a scraper or blade) of the wall-scraping agitator and the inner wall of the polymerization reactor.

[0204] The polymerization apparatus 300 has an inert gas inlet 32 ​​on one side of its top and an inert gas outlet 33 on the other side. Preferably, both the inert gas inlet 32 ​​and the inert gas outlet 33 are located within 1 / 10 to 1 / 5 of the height of the polymerization apparatus from the top downwards. The stirring device 31 is driven by a second motor 34.

[0205] In some embodiments, the polymerization apparatus further includes a real-time viscosity monitoring device C, which includes a reflux pipeline with both ends connected to the interior of the polymerization reactor. An online pressure-viscosity converter 35 is installed on the reflux pipeline. The online pressure-viscosity converter includes a pressure detector and a processor. The pressure detector is located at a fixed position on the reflux pipeline and is used to collect the pressure signal of the polymerization liquid in the pipeline in real time. The pressure detector is connected to the processor via a line, and the processor is used to convert the collected pressure signal into a viscosity value. Figure 4In this context, T represents the temperature monitoring component, and P represents the pressure monitoring component.

[0206] Furthermore, the processor of the real-time viscosity detection device C is connected to a display located outside the polymerization device via a line. After the processor converts the collected pressure signal into a viscosity value, it transmits the data to the display via the line, thereby displaying the viscosity of the polymerization liquid in real time.

[0207] Preferably, a constant-speed gear pump 36 is installed on the return pipeline, and a circulating water system is installed outside the return pipeline. For example, the circulating water system is a water tank, with constant-temperature circulating water entering from one side and exiting from the other side. Exemplarily, the constant-temperature circulating water enters the water tank from the circulating water inlet 37 at the bottom and exits from the circulating water outlet 38 at the top. The constant-speed gear pump and the circulating water system ensure that the temperature and flow rate of the polymer liquid fluid in the return pipeline remain constant.

[0208] In the method for preparing carbon fiber spinning solution provided in this embodiment of the invention, preferably, a material comprising acrylonitrile, comonomer, and solvent is added to the polymerization apparatus 300 described above. The demonomerization treatment is performed using the demonomerization apparatus 100 described above. The ammoniation treatment is performed using the ammoniation apparatus 200 described above.

[0209] It can be understood that acrylonitrile-based polymer solution refers to a polymer solution formed by polymerization reaction (such as free radical polymerization) with acrylonitrile monomer as the main component.

[0210] For example, one possible dating device 100 is designed as (hereinafter referred to as Type A dating device):

[0211] This embodiment provides a carbon fiber polymer liquid debonding device 100. The debonding device 100 includes a tank A and multiple perforated baffles 11 arranged in the tank A along the horizontal direction (i.e., perpendicular to the tank axis). The multiple perforated baffles are arranged in parallel layers at equal intervals from top to bottom along the tank axis. Each layer of perforated baffle includes a fixed end on one side and a suspended end on the other side. The fixed end is fixed to the inner wall of the tank, and the suspended end on the other side extends freely. The suspended end of one layer of perforated baffle is located on one side of the tank axis, and the suspended ends of adjacent layers of perforated baffle are located on the other side of the tank axis. The suspended ends of the multiple layers of perforated baffles form an alternating staggered layout in space.

[0212] Each layer of perforated baffles occupies 75% of the cross-sectional area of ​​the tank at that location, with the remaining 25% serving as a smooth flow channel for the polymer liquid. The perforations of adjacent layers of perforated baffles are distributed in an alternating staggered pattern, with a misalignment distance of 10 mm between the centers of corresponding perforations in adjacent layers. The perforation diameter of each layer of perforated baffles is 1.0 mm, the spacing between perforations is 20 mm, and the perforations are arranged in a ring array. The thickness of each layer of perforated baffles is 6 mm.

[0213] Inside tank A, the distance between the first layer of perforated baffles and the last layer of perforated baffles accounts for 1 / 2 of the total height of the tank. A polymer liquid inlet 12 is provided at the top of tank A. A perforated distribution plate 13 is provided between the polymer liquid inlet 12 and the adjacent first layer of perforated baffles, and the distribution plate 13 is arranged parallel to the first layer of perforated baffles. The area ratio of the distribution plate 13 to the first layer of perforated baffles is 30%. The ratio of the distance between the upper surface of the distribution plate 13 and the lower end of the polymer liquid inlet 12 to the distance between the lower end of the polymer liquid inlet 12 and the upper surface of the first layer of perforated baffles is 50%.

[0214] A solvent vapor inlet is provided at the lower part of tank A. The monomer removal device also includes a solvent vaporizer B. The top of the solvent vaporizer B is connected to the solvent vapor inlet via a pipeline. A solvent inlet 14 is provided at the bottom of the solvent vaporizer B. A coil 15 is provided inside the solvent vaporizer B. One end of the coil 15 is connected to the coil inlet 15a located at the upper part of the solvent vaporizer, and the other end of the coil 15 is connected to the coil outlet 15b located at the lower part of the solvent vaporizer. A polymerization liquid outlet 18 is provided at the bottom of tank A. The solvent is heated and vaporized into solvent vapor 16 through the solvent vaporizer B and enters the storage tank from the solvent vapor inlet. A vacuum port 17 is provided at the upper part of tank A. The monomer removal device also includes a liquid ring vacuum jet device, which is connected to the vacuum port 17 via a pipeline, thereby providing a stable negative pressure inside tank A in the monomer removal device and discharging the solvent vapor carrying the monomer.

[0215] For example, another possible dating device 100 is designed as follows (hereinafter referred to as Type B dating device):

[0216] The difference between this design and the previous design is that the area of ​​each layer of perforated baffles occupies 85% of the cross-sectional area of ​​the tank at that layer, with the remaining 15% serving as a smooth channel for the flow of polymer liquid; the offset distance between the centers of corresponding holes in adjacent layers is 20mm; inside tank A, the distance between the first layer of perforated baffles and the last layer of perforated baffles accounts for 70% of the total height of the tank; the area ratio of the distribution plate 13 to the first layer of perforated baffles is 50%; and the ratio of the distance between the upper surface of the distribution plate 13 and the lower end of the polymer liquid inlet 12 to the distance between the lower end of the polymer liquid inlet 12 and the upper surface of the first layer of perforated baffles is 30%.

[0217] Furthermore, S4 to S6 are particularly suitable for spinning solutions using dimethyl sulfoxide as the solvent.

[0218] Specifically, the process of the coagulation bath in step S4 is as follows:

[0219] The wet spinning process is employed. The spinning solution is output by a spinning metering pump, flows through a buffer, enters the spinneret, and is ejected into the coagulation solution. The coagulation solution is a mixed solution of dimethyl sulfoxide (DMSO) and water, with a DMSO mass fraction of 60–80%, preferably 70–78%, and a coagulation temperature of 20–60°C. The spinning solution is a mixed solution of DMSO and polyacrylonitrile (PAI), with a solid content of 19–21% representing the PAI content and a DMSO content of 79–81%. The coagulation process is a double diffusion process, with high concentration diffusing to low concentration. That is, DMSO in the spinning stream after the spinneret diffuses into the coagulation solution, and water in the coagulation solution diffuses into the spinning stream after the spinneret. Therefore, the DMSO concentration in the coagulation solution is lower than the corresponding component concentration in the spinning solution. The solidification temperature is generally similar to the spinning solution temperature. The spinning solution temperature is generally controlled below 60 degrees Celsius. If the temperature is too high, the viscosity of the spinning solution is low and the fiber performance is reduced. If the temperature is too low, the viscosity of the spinning solution is too high, and it is not easy to form a fine stream of spinnerets in the spinneret orifice, resulting in poor spinnability. Therefore, the solidification temperature range is 20 to 60 degrees Celsius.

[0220] During the coagulation bath process, the coagulated filaments are drawn with a draw ratio of 1.01 to 1.20. During coagulation and double diffusion fiber formation, the nascent filaments are particularly delicate with very weak intermolecular forces, making them prone to deformation. Applying large uniaxial drawing forces is not advisable, as it can damage the filaments, causing fuzzing and breakage, and resulting in irregular deformation. The stretching tension is controlled below 200 mg / millifilament; a draw ratio of 1.20 corresponds to a millifilament tension of approximately 200 mg / millifilament.

[0221] Furthermore, the spinneret is an annular spinneret, with liquid flowing through its inner ring. The flow rate of the liquid in the inner ring is controlled to be 100-1000 L / h. The liquid in the inner ring is a mixed solution of dimethyl sulfoxide and water, with the mass fraction of dimethyl sulfoxide being 60-80%, preferably 65-75%.

[0222] When using an annular spinneret, by controlling the concentration and flow rate of the inner ring liquid, the contact between the spinning solution and the coagulation solution (strictly speaking, the inner ring liquid is also part of the coagulation solution) can be more thorough, the coagulation process can be more uniform, and this is beneficial to improving the orientation and uniformity of the nascent fibers.

[0223] In this process, the mass fraction of dimethyl sulfoxide (DMSO) in the coagulation solution is greater than that in the inner ring liquid, and the temperatures of the coagulation solution and the inner ring liquid are the same. Driven by a metering pump, the spinning solution is extruded from the spinneret, forming a fine stream that enters the coagulation solution. This fine stream is columnar, and the solvent concentration in the fine stream is greater than that in the coagulation solution. Due to this concentration difference, the solvent in the fine stream diffuses into the coagulation solution. The solvent concentration in the inner ring of the columnar fine stream is higher. To ensure that the coagulation solution concentration in the inner ring is the same as that in the outer ring of the columnar fine stream, the concentration of the coagulation solution (inner ring liquid) in the inner ring must be lower than that in the coagulation solution.

[0224] Since the precursor fiber is composed of multiple monofilaments, each with a certain diameter, the solidification diffusion of the monofilaments ejected from the spinneret proceeds gradually from the outer surface towards the core. During the double-diffusion solidification process, the outer layer of the monofilament solidifies first, gradually becoming denser, which hinders the double diffusion in the core. Therefore, the dimethyl sulfoxide (DMSO) in the core cannot be released, resulting in defects. This invention first achieves finer denier solidification by adjusting parameters such as the concentration of the solidification solution, solidification temperature, and draw ratio. The finer fibers in the solidification bath are more conducive to the precipitation of DMSO in the core, resulting in better densification of the nascent fiber after solidification (meaning the DMSO content in the nascent fiber is reduced). As the solidification bath temperature increases, the density of the nascent fiber first increases and then decreases. At lower temperatures, the double diffusion during solidification is more moderate, forming dense nascent fibers. As the temperature increases, the double diffusion becomes more intense, and the dense surface layer hinders the double diffusion process, thus preventing the release of DMSO from the interior of the monofilament, resulting in void defects. Increasing the coagulation solution concentration reduces the concentration difference between the coagulation bath and the spinning solution, slowing down double diffusion and resulting in a more regular and denser fiber structure. Conversely, decreasing the coagulation solution concentration increases the concentration difference, accelerating double diffusion, but causing the filament to become noticeably opaque and white. This is because excessively rapid coagulation creates defects such as fine pores. The purpose of stretching is to refine the fiber denier. Refined denier fibers facilitate the complete release of sulfoxides from the core of the monofilament, promoting double diffusion and increasing density.

[0225] Specifically, in step S5, a roller washing method is used, with the water flow direction and the fiber direction being countercurrent. The washing temperature is gradually increased, and the washing temperature range is controlled to be 30-80℃.

[0226] During the washing process, stretching is distributed. When the washing temperature is ≤45℃, 1.01 to 1.03 times stretching is applied; when the washing temperature is >45℃, 1.02 to 1.05 times stretching is applied. The temperature and stretching ratio of the next washing stage shall not be less than the temperature and stretching ratio of the previous washing stage.

[0227] This invention significantly increases the number of washing stages, preferably 16 stages, and gradually increases the temperature during washing while strictly controlling the draw ratio (slightly increasing according to temperature changes). This process simultaneously achieves the removal of the coagulant dimethyl sulfoxide (DMSO) and further improves fiber densification, resulting in a DMSO residue content of <1000 ppm in the raw yarn. Too few washing stages or too low a temperature will lead to excessively high DMSO content in the fiber bundles. Insufficient washing stages result in insufficient washing time and high DMSO residue, while low washing temperatures reduce fiber plasticity, creating defects during draw and affecting densification. Too many washing stages lead to resource waste and a lengthy process. Excessive washing temperature is also detrimental. High temperatures cause rapid diffusion of residual DMSO, which, while removing the coagulant, can cause porous defects inside or on the surface of the raw yarn. Furthermore, when the washing temperature exceeds 90°C, the crystallinity of the raw yarn decreases, leading to changes in the internal structure and consequently reducing yarn strength, while also wasting energy.

[0228] Preferably, in step S5, the total number of water washing segments is 16. The first segment is set at 30-40 degrees, and the water washing temperature increases by 2-4 degrees for each subsequent segment. The 16th segment is set at 60-70 degrees.

[0229] Specifically, in step S6, the hot water temperature is ≥70℃, and the total hot water stretching ratio is 2 to 4 times; the hot water stretching is divided into 2 to 6 segments, with the hot water temperature and stretching ratio gradually increasing in each segment.

[0230] This invention strictly controls the temperature of hot water drawing and divides it into multiple stages / segments, with each stage having a different draw ratio to achieve gradual optimization of the internal structure of the raw fiber. Too few segments, or too large a draw ratio per segment, will lead to fiber breakage and defects. The temperature of each segment increases progressively, and the draw ratio gradually increases with temperature. As the temperature increases, the fiber's plasticity improves, and the draw ratio gradually increases, resulting in finer and denser fibers.

[0231] Preferably, the hot water stretching in step S6 is in 4 segments;

[0232] Among them, section 1 has a temperature of 70-80℃ and a draw ratio of 1.1-1.2 times; section 2 has a temperature of 75-85℃ and a draw ratio of 1.2-1.3 times; section 3 has a temperature of 80-90℃ and a draw ratio of 1.3-1.4 times; and section 4 has a temperature of 85-95℃ and a draw ratio of 1.4-1.5 times.

[0233] Specifically, the densification process of the precursor fiber in step S6 includes: oiling, drying, and steam drawing.

[0234] Specifically, the densified precursor fiber has an orientation degree of ≥93.0% and a fiber strength of ≥7.5cN / dtex.

[0235] Specifically, the densified precursor fiber is processed into carbon fiber through constant tension unwinding, pre-oxidation, low-temperature carbonization, high-temperature carbonization, electrolysis, sizing, drying, and winding.

[0236] The present invention also provides a high-strength intermediate-modulus carbon fiber, wherein the carbon fiber is prepared by the aforementioned preparation method;

[0237] The carbon fiber has an elastic modulus of 320-340 GPa, a tensile strength of >6100 MPa, a dimethyl sulfoxide residue of ≤320 ppm, and no obvious defects when observed under an electron microscope at 2000x magnification.

[0238] Spinning solution test group (corresponding to steps S1 to S3)

[0239] Example 1:

[0240] This embodiment provides a method for preparing a binary copolyacrylonitrile-based carbon fiber spinning solution, including the following steps:

[0241] S1: Material preparation: by weight, acrylonitrile is 20 parts, itaconic acid is 1 part, azobisisobutyronitrile (AIBN) is 0.2 parts, and dimethyl sulfoxide is 73.7 parts; 0.2 parts of AIBN are dissolved in 8 parts of dimethyl sulfoxide beforehand as an initiator for free radical polymerization;

[0242] Acrylonitrile, itaconic acid, and dimethyl sulfoxide were added to the polymerization apparatus. The materials in the polymerization apparatus were stirred by a wall-scraping agitator with a height of L = 10 mm, a stirring speed of 20 rpm, and a stirring time of 60 min. The liquid level h in the polymerization apparatus accounted for 80% of the total height H of the polymerization apparatus.

[0243] When the material temperature difference is ≤1℃, when the temperature is raised to 54℃, a portion of the initiator is added first, with the initiator accounting for 60% of the total initiator. The material viscosity is monitored in real time. When the material viscosity reaches the first viscosity threshold of 250P, the material is heated to the target temperature of 64℃, and the remaining 40% of the initiator is added. When the material viscosity reaches the second viscosity threshold of 620P, the reaction is terminated. The polymerization is carried out under nitrogen protection, with a nitrogen flow rate of 50L / h and a pressure of 0.1MPa. During the polymerization, the stirring speed is 30rpm. The molecular weight and PDI of the acrylonitrile-based polymer solution obtained after polymerization are shown in Table 1, which meet the target molecular weight.

[0244] S2. The acrylonitrile-based polymer solution meeting the target molecular weight undergoes a demonolysis treatment. In this treatment, the polymer solution enters from the top of the type A demonolysis device and is evenly distributed on the first perforated partition plate via a porous distribution system. It then sequentially passes through staggered second to fifth perforated partition plates, exchanging gas with the counter-current solvent vapor. At each perforated partition plate, the polymer solution is divided into two parts: one part flows through the holes in the perforated partition plate to the next perforated partition plate or the polymer solution collection area, with the exit positions of the holes on adjacent perforated partition plates differing; the other part flows from the suspended end on the side of the partition plate to the next perforated partition plate or the polymer solution collection area. The demonolysis treatment is carried out at 500 Pa, the inlet temperature of the polymer solution is 50℃, and the inlet flow rate Q1 is 3 m³ / s. 3 The solvent vapor inlet temperature is 80℃. The solvent vapor inlet flow rate is 80 L / h, and the solvent vapor pressure is 0.5 MPa.

[0245] S3: Ammonia bubbling method is used to introduce ammonia gas into the polymer solution after monomer removal for ammoniation treatment. Specifically, the temperature of the polymer solution in the storage tank is adjusted to 60℃, and then ammonia gas is introduced from the lower 1 / 5 of the tank. During the ammoniation process, the temperature is controlled at 60℃, the slight positive pressure is 100 Pa, and a slanted blade agitator is used for stirring at a speed of 55 r / min. The slanted blade agitator includes 3 agitators, each agitator including 3 rectangular slanted blades with an inclination angle of 35°, and their length is L and satisfies πL. 2 =70% × S4, where S4 is the cross-sectional area of ​​the storage tank; the flow rate of the polymer liquid Q3 = 3m³ 3 The required amount of ammonia is calculated based on the amount of ammonia gas introduced into each 1 kg of polymerization liquid at a rate of 4.0 mg / h.

[0246] Example 2:

[0247] The difference between this embodiment and Embodiment 1 is as follows: In step S1, when the material temperature difference is ≤1℃, when the temperature is raised to 58℃, a portion of the initiator is added first, with the portion of the initiator accounting for 65% of the total initiator; the material viscosity is monitored in real time, and when the material viscosity reaches the first viscosity threshold of 300P, the material is heated to the target temperature of 62℃, and the remaining 35% of the initiator is added; when the material viscosity reaches the second viscosity threshold of 710P, the reaction is terminated; in step S2, the solvent vapor inlet flow rate is 100L / h; in step S3, the required amount of ammonia is calculated based on 6mg of ammonia being introduced into each 1kg of polymerization liquid; the remaining steps and parameters are similar to those in Embodiment 1.

[0248] Example 3:

[0249] The difference between this embodiment and Embodiment 1 is as follows: In step S1, when the material temperature difference is ≤1℃, when the temperature is raised to 54℃, a portion of the initiator is added first, with the portion of the initiator accounting for 70% of the total initiator; the material viscosity is monitored in real time, and when the material viscosity reaches the first viscosity threshold of 350P, the material is heated to the target temperature of 66℃, and the remaining 30% of the initiator is added; when the material viscosity reaches the second viscosity threshold of 760P, the reaction is terminated; in step S2, a type B demonolysis device is used for demonolysis treatment, and the inlet flow rate of solvent vapor is 100L / h; in step S3, each stirring paddle includes three rectangular inclined stirring blades with an inclination angle of 35°, and their length is L and satisfies πL. 2 =50%×S4, where S4 is the cross-sectional area of ​​the storage tank. The amount of ammonia required is calculated based on 5mg of ammonia being introduced into each 1kg of polymer solution. The remaining steps and parameters are similar to those in Example 1.

[0250] Example 4:

[0251] The difference between this embodiment and Embodiment 1 is as follows: In step S1, when the material temperature difference is ≤1℃, when the temperature is raised to 55℃, a portion of the initiator is added first, with the portion of the initiator accounting for 68% of the total initiator; the material viscosity is monitored in real time, and when the material viscosity reaches the first viscosity threshold of 320P, the material is heated to the target temperature of 65℃, and the remaining 32% of the initiator is added; when the material viscosity reaches the second viscosity threshold of 840P, the reaction is terminated; in step S2, a type B demonolysis device is used for demonolysis treatment, and the inlet flow rate of solvent vapor is 80L / h; in step S3, each stirring paddle includes three rectangular inclined stirring blades with an inclination angle of 45°, and their length is L and satisfies πL. 2 =60%×S4, where S4 is the cross-sectional area of ​​the storage tank. The amount of ammonia required is calculated based on 5mg of ammonia being introduced into each 1kg of polymer liquid. The remaining steps and parameters are similar to those in Example 1.

[0252] Example 5:

[0253] The difference between this embodiment and Embodiment 1 is as follows: In step S1, when the material temperature difference is ≤1℃, when the temperature is raised to 56℃, a portion of the initiator is added first, with the portion of the initiator accounting for 65% of the total initiator; the material viscosity is monitored in real time, and when the material viscosity reaches the first viscosity threshold of 300P, the material is heated to the target temperature of 64℃, and the remaining 35% of the initiator is added; when the material viscosity reaches the second viscosity threshold of 810P, the reaction is terminated; in step S2, a type B demonolysis device is used for demonolysis treatment, and the inlet flow rate Q1 of the polymerization liquid is 4m. 3 / h, the solvent vapor inlet flow rate is 170L / h; in step S3, the polymerization liquid flow rate Q3 = 4m 3 The required amount of ammonia is calculated based on the rate of ammonia introduced into each 1 kg of polymerization solution at a rate of 6.0 mg / h. The remaining steps and parameters are similar to those in Example 1.

[0254] Example 6:

[0255] The difference between this embodiment and Embodiment 1 is as follows: In step S1, when the material temperature difference is ≤1℃, when the temperature is raised to 54℃, a portion of the initiator is added first, with the portion of the initiator accounting for 75% of the total initiator; the material viscosity is monitored in real time, and when the material viscosity reaches the first viscosity threshold of 350P, the material is heated to the target temperature of 64℃, and the remaining 25% of the initiator is added; when the material viscosity reaches the second viscosity threshold of 910P, the reaction is terminated; in step S2, a type B demonolysis device is used for demonolysis treatment, and the inlet flow rate Q1 of the polymerization liquid is 5m. 3 / h, the solvent vapor inlet flow rate is 250L / h; in step S3, the polymerization liquid flow rate Q3 = 5m 3 The required amount of ammonia is calculated based on the rate of ammonia introduced into each 1 kg of polymerization solution at a rate of 12.0 mg / h. The remaining steps and parameters are similar to those in Example 1.

[0256] Example 7:

[0257] The difference between this embodiment and Embodiment 1 is as follows: In step S1, when the material temperature difference is ≤1℃, when the temperature is raised to 57℃, a portion of the initiator is added first, with the portion of the initiator accounting for 70% of the total initiator. The material viscosity is monitored in real time. When the material viscosity reaches the first viscosity threshold of 350P, the material is heated to the target temperature of 67℃, and the remaining 30% of the initiator is added. When the material viscosity reaches the second viscosity threshold of 620P, the reaction is terminated. Polymerization is carried out under nitrogen protection, with a nitrogen flow rate of 80L / h and a pressure of 0.06Mpa. During polymerization, before adding the remaining initiator, the stirring speed is 50rpm; after adding the remaining initiator, the stirring speed is 60rpm. In step S2, a type B demonolysis device is used for demonolysis treatment. The inlet temperature of the polymerization liquid is 67℃, and the inlet flow rate of the polymerization liquid Q1 is 5m³. 3 / h; the inlet temperature of the solvent vapor is 95℃. The inlet flow rate of the solvent vapor is 100L / h, and the pressure of the solvent vapor is 0.3MPa; in step S3, the flow rate of the polymerization liquid Q3 = 5m 3 The required amount of ammonia is calculated based on the principle of introducing 10.0 mg of ammonia into each 1 kg of polymerization liquid per hour. The remaining steps and parameters are similar to those in Example 1.

[0258] Comparative Example 1:

[0259] The difference between this comparative example and Example 1 is as follows: In step S1, when the material temperature difference is ≤1℃, when the temperature is raised to 70℃, a portion of the initiator is added, with the initiator accounting for 55% of the total initiator. The material viscosity is monitored in real time. When the material viscosity reaches the first viscosity threshold of 150P, the remaining 45% of the initiator is added; when the material viscosity reaches the second viscosity threshold of 630P, the reaction is terminated. The remaining steps and parameters are similar to those in Example 1.

[0260] Comparative Example 2:

[0261] The difference between this comparative example and Example 1 is as follows: In step S1, when the material temperature difference is ≤1℃, when the temperature is raised to 50℃, a portion of the initiator is added, with the initiator accounting for 85% of the total initiator. The material viscosity is monitored in real time. When the material viscosity reaches the first viscosity threshold of 450P, the material is heated to the target temperature of 55℃, and the remaining 15% of the initiator is added. When the material viscosity reaches the second viscosity threshold of 630P, the reaction is terminated. The remaining steps and parameters are similar to those in Example 1.

[0262] Comparative Example 3:

[0263] The difference between this comparative example and Example 1 is as follows: In step S1, when the material temperature difference is ≤1℃, when the temperature is raised to 65℃, a portion of the initiator is added, with the initiator accounting for 90% of the total initiator. The material viscosity is monitored in real time, and when the material viscosity reaches the first viscosity threshold of 450P, the remaining 10% of the initiator is added; when the material viscosity reaches the second viscosity threshold of 560P, the reaction is terminated. The remaining steps and parameters are similar to those in Example 1.

[0264] Comparative Example 4:

[0265] The difference between this comparative example and Example 1 is that in step S3, the required amount of ammonia is calculated based on 2.0 mg of ammonia being introduced into each 1 kg of polymer solution; the remaining steps and parameters are similar to those in Example 1.

[0266] Comparative Example 5:

[0267] The difference between this comparative example and Example 1 is that in step S3, the required amount of ammonia is calculated based on 14.0 mg of ammonia being introduced into each 1 kg of polymer solution; the remaining steps and parameters are similar to those in Example 1.

[0268] Comparative Example 6:

[0269] The difference between this comparative example and Example 1 is that the single-disconnection device used in step S2 differs from the Type A single-disconnection device in that the area of ​​each layer of horizontally perforated partition (hereinafter referred to as horizontal perforated partition) accounts for 50-79% of the cross-sectional area of ​​the tank at that layer, and each layer of horizontal perforated partition is provided with an inclined baffle. The angle between the inclined baffle and the horizontal perforated partition is 10°-60°. The holes on the horizontal perforated partition are within the vertical projection range of the inclined baffle. The line connecting the inclined baffle and the horizontal perforated partition is parallel to the chords corresponding to the two endpoints of the arc on the horizontal perforated partition. The remaining steps and parameters are similar to those in Example 1.

[0270] Table 1 Test results of the examples and comparative examples

[0271]

[0272]

[0273] Test groups for precursor fiber and carbon fiber preparation (corresponding to S4~S7)

[0274] The spinning solutions corresponding to Examples 1 and 4 in the spinning solution test group were selected for the following experiments, that is, five kinds of precursor fibers / carbon fibers were obtained in each group of experiments, for a total of ten kinds.

[0275] Precursor / Carbon Fiber 1

[0276] The spinning solution prepared in Example 1 was used.

[0277] S4: The flow rate of the liquid flowing into the inner ring of the spinneret is 200 L / h, and the mass fraction of the liquid in the inner ring is 70%; the concentration of dimethyl sulfoxide in the coagulation solution is controlled at 75%, the temperature of the coagulation solution is controlled at 35℃; the draw ratio in the coagulation solution is 1.10.

[0278] S5: The washing method adopts a roller washing method, with the water flow direction being countercurrent to the fiber direction. When the washing temperature is ≤45℃, a stretch of 1.02 times is applied, and when the washing temperature is >45℃, a stretch of 1.04 times is applied.

[0279] The washing process consists of 16 stages, with the first stage set at 30 degrees Celsius. Each subsequent stage increases the temperature by 2 degrees Celsius, resulting in a total of 60 degrees Celsius for all 16 stages.

[0280] S6: Hot drawing is performed in 4 stages: stage 1 at 70 degrees Celsius with a draw ratio of 1.1 times; stage 2 at 80 degrees Celsius with a draw ratio of 1.3 times; stage 3 at 90 degrees Celsius with a draw ratio of 1.4 times; and stage 4 at 95 degrees Celsius with a draw ratio of 1.5 times. The finished raw yarn 1 is then obtained by oiling, drying, and steam drawing.

[0281] S7: Carbon fiber is made by unwinding the raw yarn under constant tension, pre-oxidation, low-temperature carbonization, high-temperature carbonization, electrolysis, sizing, drying, and winding.

[0282] Raw silk / carbon fiber 2

[0283] The spinning solution prepared in Example 1 was used.

[0284] S4: The flow rate of the liquid flowing into the inner ring of the spinneret is 500 L / h, and the mass fraction of dimethyl sulfoxide in the inner ring liquid is 75%; the concentration of dimethyl sulfoxide in the coagulation solution is controlled at 78%, the temperature of the coagulation solution is controlled at 40℃; the draw ratio in the coagulation solution is 1.10.

[0285] S5: The washing method adopts a roller washing method, with the water flow direction being countercurrent to the fiber direction. When the washing temperature is ≤45℃, 1.03 times the stretch is applied, and when the washing temperature is >45℃, 1.05 times the stretch is applied.

[0286] The washing process consists of 16 stages, with the first stage set at 45 degrees Celsius. Each subsequent stage increases the temperature by 2 degrees Celsius, resulting in a total washing temperature of 75 degrees Celsius for all 16 stages.

[0287] S6: Hot drawing is performed in 4 stages: stage 1 at 75 degrees with a draw ratio of 1.15 times; stage 2 at 85 degrees with a draw ratio of 1.2 times; stage 3 at 90 degrees with a draw ratio of 1.3 times; and stage 4 at 95 degrees with a draw ratio of 1.4 times. The finished raw yarn 2 is then obtained by oiling, drying, and steam drawing.

[0288] S7: Carbon fiber is made by unwinding the raw yarn under constant tension, pre-oxidation, low-temperature carbonization, high-temperature carbonization, electrolysis, sizing, drying, and winding.

[0289] Raw silk / carbon fiber 3

[0290] The spinning solution prepared in Example 1 was used.

[0291] S4: The flow rate of the liquid flowing into the inner ring of the spinneret is 200 L / h, and the mass fraction of the liquid in the inner ring is 70%; the concentration of dimethyl sulfoxide in the coagulation solution is controlled at 75%, the temperature of the coagulation solution is controlled at 35℃; the draw ratio in the coagulation solution is 1.10.

[0292] S5: The washing method adopts a roller washing method, with the water flow direction being countercurrent to the fiber direction. When the washing temperature is ≤45℃, a stretch of 1.02 times is applied, and when the washing temperature is >45℃, a stretch of 1.04 times is applied.

[0293] The washing process consists of 16 stages, with the first stage set at 35 degrees Celsius. Each subsequent stage increases the temperature by 2 degrees Celsius, resulting in a total washing temperature of 75 degrees Celsius for all 16 stages.

[0294] S6: Hot drawing is performed in 6 sections: section 1 at 75 degrees Celsius with a draw ratio of 1.1 times; section 2 at 80 degrees Celsius with a draw ratio of 1.15 times; section 3 at 85 degrees Celsius with a draw ratio of 1.15 times; section 4 at 90 degrees Celsius with a draw ratio of 1.25 times; section 5 at 95 degrees Celsius with a draw ratio of 1.25 times; and section 6 at 98 degrees Celsius with a draw ratio of 1.3 times. The finished raw yarn is then produced by oiling, drying, and steam drawing.

[0295] S7: Carbon fiber is made by unwinding the raw yarn under constant tension, pre-oxidation, low-temperature carbonization, high-temperature carbonization, electrolysis, sizing, drying, and winding.

[0296] Precursor fiber / carbon fiber 4 (comparative example)

[0297] The spinning solution prepared in Example 1 was used.

[0298] S4: The flow rate of the liquid flowing into the inner ring of the spinneret is 500 L / h, and the mass fraction of dimethyl sulfoxide in the inner ring liquid is 75%; the concentration of dimethyl sulfoxide in the coagulation solution is controlled at 78%, the temperature of the coagulation solution is controlled at 40℃; the draw ratio in the coagulation solution is 1.10.

[0299] S5: The washing method adopts a roller washing method, with the water flow direction being countercurrent to the fiber direction. When the washing temperature is ≤45℃, a stretch of 1.03 times is applied, and when the washing temperature is >45℃, a stretch of 1.05 times is applied.

[0300] The washing process consists of 10 stages, with each stage washing at 65 degrees Celsius and each stage being stretched by 1.03 times.

[0301] S6: Hot drawing is performed in 4 stages: stage 1 at 75 degrees with a draw ratio of 1.15 times; stage 2 at 85 degrees with a draw ratio of 1.4 times; stage 3 at 90 degrees with a draw ratio of 1.3 times; and stage 4 at 95 degrees with a draw ratio of 1.4 times. The finished raw yarn 4 is then obtained by oiling, drying, and steam drawing.

[0302] S7: Carbon fiber is made by unwinding the raw yarn under constant tension, pre-oxidation, low-temperature carbonization, high-temperature carbonization, electrolysis, sizing, drying, and winding.

[0303] Precursor fiber / carbon fiber 5 (comparative example)

[0304] The spinning solution prepared in Example 1 was used.

[0305] S4: The flow rate of the liquid flowing into the inner ring of the spinneret is 500 L / h, and the mass fraction of dimethyl sulfoxide in the inner ring liquid is 75%; the concentration of dimethyl sulfoxide in the coagulation solution is controlled at 78%, the temperature of the coagulation solution is controlled at 40℃; the draw ratio in the coagulation solution is 1.10.

[0306] S5: The washing method adopts a roller washing method, with the water flow direction being countercurrent to the fiber direction. When the washing temperature is ≤45℃, a stretch of 1.03 times is applied, and when the washing temperature is >45℃, a stretch of 1.05 times is applied.

[0307] The washing process consists of 10 stages, each at a temperature of 65 degrees Celsius. The stretching in each stage is 1.03 times.

[0308] S6: Hot drawing is performed in 4 stages: stage 1 at 75 degrees with a draw ratio of 1.4 times; stage 2 at 85 degrees with a draw ratio of 1.4 times; stage 3 at 90 degrees with a draw ratio of 1.2 times; and stage 4 at 95 degrees with a draw ratio of 1.1 times. The finished raw yarn 5 is then obtained through oiling, drying, and steam drawing.

[0309] S7: Carbon fiber is made by unwinding the raw yarn under constant tension, pre-oxidation, low-temperature carbonization, high-temperature carbonization, electrolysis, sizing, drying, and winding.

[0310] Except for the spinning solution prepared in Example 4, the parameters of the precursor / carbon fiber 6 to 10 are the same as those of precursor / carbon fiber 1 to 5, namely 1-6, 2-7, 3-8, 4-9, and 5-10.

[0311] Table 2. Test results of precursor and carbon fiber properties in the precursor and carbon fiber preparation test group.

[0312]

[0313]

[0314] *The porosity defect was evaluated using an electrical microscope at 2000x magnification.

[0315] In precursor fibers 4 and 9, due to the relatively low washing temperature and the absence of gradient heating and increased stretching ratio, the residual amount of dimethyl sulfoxide was relatively high, resulting in a small number of porosity defects in the elements, which in turn led to a decrease in the strength of the precursor fibers and carbon fibers.

[0316] In precursor fibers 5 and 10, the washing parameters were unsatisfactory, and the hot water traction process was not carried out according to the principle of gradually increasing the temperature and the stretching ratio. This resulted in the formation of fuzz and roller entanglement after the first two stretching stages. As a result, the properties of both the precursor fiber and the carbon fiber decreased.

[0317] In summary, precursor fibers / carbon fibers 1, 2, 3, 6, 7, and 8 all possess excellent comprehensive properties. The precursor fibers provided by this invention have an orientation degree ≥93.0% and a strength ≥7.5 cN / dtex. The carbon fibers have an elastic modulus of 320–340 GPa, a tensile strength >6100 MPa, and a dimethyl sulfoxide residue of ≤320 ppm. No obvious defects were observed under an electron microscope at 2000x magnification.

[0318] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing high-strength intermediate-modulus carbon fiber, characterized in that, Specifically, the following steps are included: S1: Add materials containing acrylonitrile, comonomer and solvent to the polymerization device and adjust the target molecular weight of the acrylonitrile-based polymerization liquid; In step S1, determine the timing of adding the remaining initiator after the polymerization starts and the timing of terminating the reaction based on the viscosity change of the material, and adjust the target molecular weight of the acrylonitrile-based polymerization liquid by controlling the material temperature and the proportion of the remaining initiator in the total amount of initiator. The determination of the timing for adding the remaining initiator after polymerization initiation and the timing for terminating the reaction include: Heat to the polymerization temperature and add some initiator; Real-time monitoring of material viscosity: When the material viscosity reaches a first viscosity threshold, the remaining initiator is added; when the material viscosity reaches a second viscosity threshold, the reaction is terminated; the first viscosity threshold is 200P to 400P; and / or, the second viscosity threshold is 600P to 1000P; the remaining initiator accounts for 20% to 40% of the total initiator. S2: Perform a monomer removal treatment on acrylonitrile-based polymer solutions that meet the target molecular weight; S3: The acrylonitrile-based polymer solution after the desiccant treatment is subjected to ammoniation treatment to obtain spinning solution; in the ammoniation treatment in step S3, the mass M of ammonia gas required to be introduced per 1 kg of polymer solution is determined according to the flow rate Q3 of the polymer solution and the following relationship: M=Q3×n; where M is in mg, Q3 is in m³ / h, and n ranges from 1.25 to 3.

0. S4: The spinning solution is spun into a coagulation bath after being spun and then drawn to obtain nascent fibers. S5: The nascent fibers are washed using a multi-stage washing process with progressively increasing temperatures; S5 employs a roller washing method, and stretching is distributed during the washing process, with a total of 16 washing stages; when the washing temperature is ≤45℃, a stretching ratio of 1.01 to 1.03 is applied; when the washing temperature is >45℃, a stretching ratio of 1.02 to 1.05 is applied; wherein, the temperature and stretching ratio of the next washing stage are not less than the temperature and stretching ratio of the previous washing stage; S6: A multi-stage drawing process is used to draw the washed fibers with hot water and then cool them to obtain a denser filament. S7: High-strength intermediate-modulus carbon fiber is made by densifying the precursor yarn.

2. The preparation method according to claim 1, characterized in that, The process of finding a partner in step S2 is as follows: The polymer liquid undergoes gas-liquid exchange with the countercurrent solvent vapor through multiple layers of perforated partitions. At each layer of perforated partition, the polymer liquid is divided into two parts: one part of the polymer liquid spreads flat on the perforated partition to form a thin liquid layer and flows downward through the holes in the perforated partition, and the other part of the polymer liquid flows downward from the suspended end on the side of the perforated partition.

3. The preparation method according to claim 1, characterized in that, In step S2, the inlet flow rate Q1 of the acrylonitrile-based polymerization solution entering the depolymerization device and the inlet flow rate Q2 of the solvent vapor entering the depolymerization device satisfy the following: ； Where Q1 is in meters (m) 3 / h, Q2 is in L / h, m is the mass percentage of residual monomer in the carbon fiber polymerization liquid; α is the flow coefficient of solvent vapor, and the value of α ranges from 1.0 to 1.2; k is the proportionality coefficient, and the value of k ranges from 1.5 to 1.

9.

4. The preparation method according to claim 1, characterized in that, In step S3, the value of n ranges from 1.5 to 2.

7.

5. The preparation method according to claim 1, characterized in that, In step S4, the solidified filaments are stretched during the coagulation bath process, with a stretching ratio of 1.01 to 1.

20.

6. The preparation method according to claim 1, characterized in that, In step S5, the water flow direction is countercurrent to the fiber direction, and the washing temperature is gradually increased, controlling the washing temperature range to be 30-80℃.

7. The preparation method according to claim 1, characterized in that, In step S6, the hot water temperature is ≥70℃, and the total hot water stretching ratio is 2 to 4 times. The hot water stretching is divided into 2 to 6 segments, and the hot water temperature and stretching ratio of each segment gradually increase.

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