A continuous controllable polymerization method of PBO polymer based on online viscosity balance regulation and control

Abstract

The application belongs to the field of high-performance materials, and discloses a PBO polymer continuous controllable polymerization method based on online viscosity balance regulation and control. Through online viscosity monitoring and feedback control in the post-polymerization stage of a double-screw extruder, the end point of polycondensation reaction is accurately regulated, so that stable high-molecular-weight PBO is obtained, and the production efficiency and process flexibility are improved. The system greatly reduces the shutdown and waste caused by process fluctuations, and improves the efficiency and economic benefits of continuous production. By adjusting the target parameters of the control system, the production of PBO polymers with different polymerization degrees can be flexibly adapted, and the process flexibility is significantly enhanced.

Description

Technical Field

[0001] This invention belongs to the field of high-performance materials and relates to a continuous polymerization process for poly(p-phenylenebenzodioxazole) (PBO). In particular, it is a method for obtaining stable high molecular weight PBO by achieving precise control of the polycondensation reaction endpoint through online viscosity monitoring and feedback control in the polymerization stage after a twin-screw extruder. Background Technology

[0002] Poly(p-phenylenebenzodioxazole) (PBO) fiber is one of the best-performing high-performance organic fibers currently available for industrial production. Its strength can reach 5.8 GPa, its modulus can reach 280 GPa, and its thermal decomposition temperature exceeds 650℃. It has excellent impact resistance, heat resistance, and chemical corrosion resistance, and has broad application prospects in both military and civilian fields.

[0003] The synthesis of PBO is typically achieved in a polyphosphoric acid (PPA) solvent via the polycondensation reaction of 4,6-diaminoresorcinol hydrochloride (DAR•HCl) and terephthalic acid (TPA). Established process routes generally involve prepolymerization in a reactor and post-polymerization in a twin-screw extruder. The challenge of this process lies in the post-polymerization stage, which transforms oligomers into ultra-high molecular weight polymers.

[0004] Existing technologies employ a two-step process of "prepolymerization in a reactor + postpolymerization in a twin-screw extruder" to improve mass and heat transfer. However, this system has the following inherent problems: (1) Unknown and uncontrollable degree of reaction: In the continuous, high-shear, and high-viscosity "black box" environment of a twin-screw extruder, it is impossible to directly measure the molecular weight or degree of reaction of the polymer online. Operators usually rely on fixed parameters such as temperature, speed, and residence time for production, but the slight differences in raw materials between batches and fluctuations in equipment status can easily lead to unstable molecular weight of the final product, making it impossible to always reach the theoretical maximum value of the formulation. (2) Viscosity management problem: The viscosity of the PBO polymerization system increases sharply with the increase of molecular weight. Too low viscosity indicates insufficient reaction; too high viscosity leads to overload of screw torque, material blockage, and even equipment shutdown. Existing technologies lack effective online viscosity monitoring and real-time control methods, resulting in poor production stability. (3) Lack of endpoint control and product stability: As a polycondensation reaction, the theoretical upper limit of the molecular weight of PBO is determined by the monomer molar ratio. In order to obtain a stable product with the largest molecular weight, one monomer (usually TPA) needs to be in appropriate excess to achieve "end-capping" of the polymer molecular chain and bring the reaction to equilibrium. However, traditional processes cannot determine when this endpoint is reached in the continuous post-polymerization process, nor can they dynamically adjust the materials to achieve and maintain this end-capping state, which may cause the product to continue to react slowly in subsequent processing or storage, resulting in performance drift. (4) Difficulty in material replenishment: TPA has extremely low solubility in PPA, and its dissolution rate depends on the consumption of dissolved TPA by the polycondensation reaction. If the traditional process feeds in excess at one time, the undissolved TPA is prone to form "nodules", which will destroy the uniformity of the material; while insufficient feeding directly limits the upper limit of molecular weight. If solid TPA is directly added in the post-polymerization stage to adjust the ratio, the undissolved part will also be prone to form "nodules" and affect the product performance. (5) Byproducts and oxygen interference: Small molecule byproducts generated in the reaction (such as water and HCl) and trace amounts of oxygen will inhibit the reaction and hinder the increase of molecular weight.

[0005] The existing technology CN114957663A discloses a continuous polymerization control process for PBO based on temperature and pressure sensor monitoring. However, it only indirectly reflects the viscosity state through pressure changes and does not achieve direct online monitoring of viscosity, resulting in limited control accuracy. Furthermore, this process only corrects the viscosity by adjusting the temperature of the twin-screw reactor shell and does not involve material replenishment. It cannot solve the problem of insufficient molecular weight or overpolymerization caused by monomer imbalance and is difficult to achieve precise control of the reaction endpoint.

[0006] CN118406309A discloses a real-time online monitoring and feedback control system for masterbatch preparation. Its core lies in using a machine learning model to regulate extrusion process parameters to ensure pigment dispersion. The application scenario is the co-extrusion of plastic masterbatch, which differs greatly from the reaction mechanism and material system (high viscosity, strong corrosiveness) of PBO polycondensation reaction. Furthermore, the system does not involve dynamic balance control of monomer replenishment and cannot provide effective technical inspiration for the endpoint control of PBO polymerization reaction.

[0007] Therefore, developing a continuous technology that can respond to viscosity changes, intelligently adjust material balance, and automatically remove interfering factors, ultimately achieving "maximum stable polymerization under formulation conditions," is an urgent need for the industrialization of PBO. Summary of the Invention

[0008] This invention addresses the numerous shortcomings of existing technologies by providing a continuous and controllable polymerization method for PBO polymers based on online viscosity equilibrium regulation. By performing online viscosity monitoring and feedback control during the polymerization stage after a twin-screw extruder, the endpoint of the polycondensation reaction is precisely controlled to obtain stable high-molecular-weight PBO, thus improving production efficiency and process flexibility. This system significantly reduces downtime and scrap caused by process fluctuations, improving the efficiency and economic benefits of continuous production. By adjusting the target parameters of the control system, it can flexibly adapt to the production of PBO polymers with different degrees of polymerization, significantly enhancing process flexibility.

[0009] The specific technical solution of this invention is as follows: A continuous and controllable polymerization method for PBO polymer based on online viscosity equilibrium regulation includes the following steps: S1. Prepolymerization: The PBO monomer is prepolymerized in a polyphosphoric acid solvent. The specific process is as follows: First, 4,6-diaminoresorcinol hydrochloride is dechlorinated at a certain temperature to obtain activated DAR; then, the activated DAR undergoes a polycondensation reaction with terephthalic acid to generate oligomer or oligomer slurry with intrinsic viscosity in the range of 5-20 dL / g as a prepolymer.

[0010] The more specific steps are as follows: First, 4,6-diaminoresorcinol hydrochloride and polyphosphoric acid are added to a prepolymer reactor at a mass ratio of 1:(5-100). High-purity nitrogen is introduced to replace the air in the reactor and maintain a slightly positive pressure inert atmosphere. The temperature is raised to 105-145℃, and the vacuum system is turned on to maintain an absolute pressure of -0.08 to -0.09 MPa. The reaction is carried out at a constant temperature for 1-10 hours. The removed hydrogen chloride gas and trace moisture are collected through the tail gas absorption system to complete the activation of 4,6-diaminoresorcinol hydrochloride, resulting in a reactive DAR / PPA homogeneous system. Subsequently, the activated DAR undergoes a polycondensation reaction with terephthalic acid, wherein the molar ratio of DAR to TPA is controlled at 1:0.88-0.98. The temperature is raised to 120-135℃, and a prepolymerization reaction is carried out for 2-6 hours under normal pressure nitrogen protection to generate an oligomer or oligomer slurry with an intrinsic viscosity in the range of 5-20 dL / g as a prepolymer.

[0011] The reaction-generating intrinsic viscosity of the prepolymer is further controlled at 12-18 dL / g. This viscosity range provides sufficient space for the molecular weight growth in the post-polymerization stage, and the slurry has good conveying fluidity at this viscosity, avoiding screw conveying blockage due to excessive viscosity and uneven post-polymerization reaction due to excessively low viscosity.

[0012] The molar ratio of DAR to TPA in the above reaction differs from the existing technology's method of adding 0.5-1.0% excess TPA. In the prepolymerization stage, TPA is intentionally slightly insufficient, reserving space for monomer replenishment. Dynamic equilibrium of the monomer ratio is achieved through precise addition of a homogeneous TPA / PPA solution in the post-polymerization stage. This fundamentally avoids premature end-capping of oligomer chains caused by excessive TPA in the prepolymerization stage, thus limiting molecular weight increase. Simultaneously, precise closed-loop control of the prepolymer's intrinsic viscosity ensures batch-to-batch consistency. Temperature-vacuum-inert atmosphere coupled degassing ensures more thorough removal of hydrogen chloride gas and small molecule byproducts, while preventing material oxidation. The final prepolymer obtained is a homogeneous oligomer slurry without undissolved monomer particles, solving the problem of poor prepolymer uniformity in existing technologies.

[0013] S2. Conveying and Sealing: The prepolymer slurry is conveyed to a twin-screw extruder. The conveying process and the extruder feed area are sealed with nitrogen to prevent material oxidation and degradation.

[0014] Furthermore, this step employs a corrosion-resistant screw conveyor with an insulated jacket, maintaining the slurry temperature at 80-150℃ during transport to prevent a sudden increase in viscosity that could disrupt the conveying process. An annular chamber nitrogen sealing device is installed between the conveyor outlet and the extruder inlet, introducing high-purity nitrogen and maintaining a slight positive pressure of 20-50Pa to form an air curtain that completely isolates the air, ensuring oxygen-free material transport throughout the process. The sealing device is linked to the extruder feed zone for pressure control, preventing excessive nitrogen intrusion that could disrupt the material flow and ensuring continuous and stable feeding.

[0015] S3. Post-polymerization and online monitoring: The prepolymer undergoes post-polymerization in a twin-screw extruder under high temperature and high shear. An online viscometer and pressure sensor are installed between the end of the homogenization zone and the die head of the twin-screw extruder to monitor the melt viscosity and die head pressure of the material in real time.

[0016] S4. Dynamic Feedback and Balance Control: Based on the online monitoring signal obtained in S3, the following closed-loop control logic is executed to guide the polymerization reaction to the preset endpoint, as follows: The target intrinsic viscosity based on PBO product design was determined through preliminary calibration experiments. The calibration method was as follows: the online viscosity values ​​of PBO polymer melts with different intrinsic viscosities were tested offline at the corresponding process temperatures (200-220℃) to establish the correspondence between "offline intrinsic viscosity" and "online melt viscosity". In this invention, the target intrinsic viscosity is 30-40 dL / g (corresponding to high molecular weight PBO), and the corresponding target online melt viscosity is 30000-40000 Pa·s. The lower limit of the target is set at 95% of the target value (28500-38000 Pa·s), and the upper limit of the target is set at 105% of the target value (31500-42000 Pa·s).

[0017] Meanwhile, under the same process temperature and screw speed, the PBO melt viscosity is strictly positively correlated with the die head pressure. Excessive viscosity will cause the flow resistance of the material at the die head to increase sharply, which is directly reflected in the increase of die head pressure. The system judgment logic is: control is triggered when either of the following conditions is met: ① the real-time viscosity exceeds the target upper limit; ② the die head pressure exceeds the safety threshold (the threshold range is 18-22MPa). If both occur at the same time, the control is prioritized according to "pressure over limit" to avoid equipment safety risks.

[0018] Based on the above, the relevant regulatory strategies are as follows: a) Low viscosity control strategy: When the real-time viscosity is lower than the target lower limit, it indicates that the polymerization reaction is insufficient and the reaction needs to be promoted to a higher molecular weight. The control system automatically starts the replenishment program to quantitatively replenish a homogeneous solution of TPA in PPA to a specific reaction zone of the twin-screw extruder to provide sufficient monomer to promote the continued polycondensation reaction. The replenishment amount is calculated in real time based on the viscosity deviation to ensure that TPA dissolves in time to participate in the reaction and avoids the generation of insoluble substances. At the same time, the screw speed is reduced to prolong the residence time of the material in the reaction zone, the temperature of the screw meshing zone is increased to enhance the reaction activity, and the temperature of the conveying zone is reduced to reduce backmixing and maintain the reaction driving force, all of which jointly promote the increase of molecular weight.

[0019] A more specific approach is as follows: First, obtain a homogeneous TPA / PPA solution. Then, add terephthalic acid and polyphosphoric acid at a mass ratio of 1:(5-10) to a constant-temperature storage tank with a stirrer. Heat the tank to 60-100℃ and start high-speed shear stirring (500-1000 rpm) for 2-10 hours until the terephthalic acid is completely dissolved, resulting in a homogeneous TPA / PPA solution with a mass concentration of 10-20%. At this concentration, the solution has both good fluidity (facilitating precise metering and pumping) and monomer effectiveness, avoiding insufficient dissolution due to excessively high concentration and excessive dilution of the reaction system due to excessively low concentration.

[0020] The specific steps for quantitatively adding a homogeneous TPA / PPA solution to a specific reaction zone of a twin-screw extruder are as follows: A homogeneous TPA / PPA solution is quantitatively added to a specific reaction zone (the primary injection nozzle of the Z2 / Z3 connecting section) of the twin-screw extruder. The calculation method for the addition amount is as follows: The addition amount is based on online viscosity monitoring data and calculated in real time using a preset algorithm of the central control unit. The calculation formula is: The volume of replenishment V (mL / min) = K × (η) 目标 -η 实时 ) / η 目标 ×Q; Where K is the correction factor (specifically 0.8-1.2), η 目标 For the online viscosity target value, η 实时 To monitor viscosity values ​​in real time, Q represents the material feed rate (kg / h). The amount of TPA added is dynamically adjusted according to the viscosity deviation; the greater the viscosity deviation, the greater the addition amount. Furthermore, the addition rate is linked to the screw speed and reaction zone temperature to ensure that the added TPA dissolves quickly and participates in the polycondensation reaction, leaving no undissolved monomer residue. The corresponding strategy is to reduce the screw speed to prolong the residence time of the material in the reaction zone, increase the temperature in the screw meshing zone to enhance reaction activity, and decrease the temperature in the conveying zone to reduce backmixing and maintain the reaction driving force. This combined approach promotes molecular weight growth. Reducing the screw speed by 10-20 rpm from the initial speed can extend the residence time of the material in the reaction zone to 8-12 minutes. Increase the temperature of the screw meshing zone (high shear zone) by 5-10℃ from the initial temperature (e.g., from an initial 190℃ / 205℃ to 195-200℃ / 210-215℃); decrease the temperature of the conveying zone by 10-15℃ from the initial temperature.

[0021] b) High Viscosity / Pressure Control Strategy: When the real-time viscosity is too high or the die pressure exceeds the safety threshold, the system determines that the polymerization reaction has approached or reached the required level, and it needs to move towards equilibrium end-capping and prevent over-polymerization. A homogeneous TPA / PPA solution is added to the reaction zone of the twin-screw extruder to provide excess TPA monomer, allowing it to react with the polymer chain ends, achieving molecular chain end-capping, and promoting the reaction to reach and stabilize at the equilibrium endpoint. Specifically, the addition of the homogeneous TPA / PPA solution to the reaction zone of the twin-screw extruder is as follows: Add homogeneous TPA / PPA solution to the reaction zone (secondary injection nozzle of Z3 / Z4 connecting section) of the twin-screw extruder. Use a fine, small-dose addition method with a addition rate of 1-1.5 mL / min. Add at a constant low flow rate and accurately seal the ends to avoid excessive addition that could lead to system imbalance.

[0022] Simultaneously, increasing the screw speed reduces residence time and reaction depth, while enhancing mixing and conveying to alleviate high viscosity. Lowering the screw meshing zone temperature moderately inhibits reactivity, and increasing the conveying zone temperature reduces melt viscosity and ensures smooth conveying. These combined effects stabilize the system. More specifically, the steps are as follows: Increase the screw speed by 10-25 rpm from the current speed to shorten the residence time of the material in the reaction zone to 4-6 minutes and reduce the reaction depth; reduce the temperature of the screw meshing zone by 8-15°C from the current temperature to moderately inhibit the activity of condensation reaction and prevent excessive polymerization; increase the temperature of the conveying zone by 10-20°C from the current temperature to reduce the melt viscosity, improve the material conveying flowability, and relieve the pressure on the die head.

[0023] The activation and deactivation of the above-mentioned control strategies are solely determined by the real-time monitoring data from the online viscometer and pressure sensor. The central control unit collects data at a 1-second interval. When the data exceeds the target range (lower / upper viscosity limit, pressure safety threshold), the corresponding control strategy is immediately and automatically activated. When the real-time viscosity recovers to within ±5% of the target value and the die head pressure stabilizes within the 5-15MPa safety range, the system automatically stops control and returns to the normal process parameters, achieving closed-loop precise control.

[0024] S5. Online devolatilization and product extrusion: The twin-screw extruder is equipped with a devolatilization zone to continuously remove small molecule byproducts such as water generated in the reaction, as well as excess free monomers entrained therein, promoting the forward reaction.

[0025] The more specific steps are as follows: A three-stage steam jet vacuum pump system is employed, maintaining the absolute pressure in the devolatilization zone at 3-5 kPa, achieving a devolatilization efficiency of ≥99%, thoroughly removing moisture and trace amounts of unremoved hydrogen chloride generated during the polycondensation reaction. The devolatilization zone integrates a high-shear dispersion element, dispersing the material into a thin liquid film, increasing the specific surface area, and enabling rapid removal of small molecule byproducts and free monomers. Devolatilization is linked to material conveying, with the screw speed in the devolatilization zone slightly higher than that in the reaction zone, preventing the material from remaining in the devolatilization zone for too long and causing oxidation. The removed free monomers can be condensed and recovered to prepare a homogeneous TPA / PPA solution, achieving monomer recycling and reducing raw material loss.

[0026] The PBO polymer slurry, after being adjusted to the target viscosity (corresponding to the maximum and stable degree of polymerization) as described above, is extruded from the die head and cooled to obtain a high molecular weight, stable PBO product; the intrinsic viscosity of the obtained PBO product is greater than 25 dL / g, preferably 30-40 dL / g.

[0027] The corresponding reaction system provided in this application is as follows: A reactor for prepolymerization; a material conveying device connected to the reactor outlet, equipped with a nitrogen-sealed interface; a twin-screw extruder with multiple temperature-controlled reaction zones and at least one devolatilization zone in its barrel; an online viscosity monitoring unit and a pressure sensing unit integrated at the end of the twin-screw extruder; a TPA / PPA homogeneous solution replenishment unit, including a storage tank, a precision metering pump, and an injection nozzle leading to the reaction zone of the twin-screw extruder; a central control unit, signal-connected to the online viscosity monitoring unit, the pressure sensing unit, the TPA / PPA solution replenishment unit, and the drive and temperature control system of the twin-screw extruder; the control unit is configured to: control the start-up, shutdown, and acceleration rate of the replenishment unit according to a preset algorithm based on viscosity and pressure signals, and coordinate the adjustment of the twin-screw speed and reaction temperature.

[0028] Compared with the prior art, the main technical effects of this application are as follows: By adding a two-stage replenishment unit for TPA / PPA homogeneous solution, dynamic and precise monomer replenishment is achieved, solving the problem of fixed monomer ratios in existing technologies. An integrated online viscosity-pressure dual monitoring unit enables real-time online monitoring of the reaction process, breaking the "black box" operation of twin-screw extruders. A central closed-loop control unit with four linkages—temperature, rate, replenishment, and devolatilization—is constructed to achieve intelligent dynamic control of process parameters, changing the fixed parameter control of existing technologies. Nitrogen sealing throughout the process ensures oxygen-free transport from prepolymer reactor discharge to extruder feed, preventing material oxidation and degradation. A high-efficiency devolatilization unit completely removes small-molecule byproducts and free monomers, while simultaneously enabling monomer recycling. Ultimately, stable high-molecular-weight PBO products are obtained, improving production efficiency and process flexibility; significantly reducing downtime and scrap caused by process fluctuations, improving the efficiency and economic benefits of continuous production; and by adjusting the target parameters of the control system, it can flexibly adapt to the production of PBO polymers with different polymerization degrees, significantly enhancing process flexibility. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the system configuration and process flow of the present invention; Figure 2 This is a schematic diagram of the process equipment of the present invention. Detailed Implementation

[0030] The present invention will be further described below with reference to specific embodiments, which will enable those skilled in the art to have a more comprehensive understanding of the invention, but will not limit the invention in any way. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention. All reaction raw materials in the following embodiments were purchased directly from the market, and the P2O5 content in the polyphosphoric acid used was 83-85%.

[0031] The PBO continuous controllable polymerization system used in this invention is as follows: Figure 1 and 2 As shown, it specifically includes: 1. Prepolymerization reactor: with a volume of 300 liters, equipped with a frame stirrer, electric heating mantle, temperature sensor, nitrogen inlet valve, vacuum interface and condensation reflux device.

[0032] 2. Screw conveyor: A corrosion-resistant, single-screw conveyor with an insulated jacket, used to steadily and continuously pump prepolymer slurry to a twin-screw extruder.

[0033] 3. Nitrogen sealing device: Installed between the conveyor outlet and the twin-screw extruder inlet, it is an annular chamber structure that can introduce high-purity nitrogen (purity ≥99.999%) and maintain a slight positive pressure of 20-50 Pa to form an air curtain to isolate the air.

[0034] 4. Co-rotating twin-screw extruder: The screw diameter is 58 mm, and the length-to-diameter ratio (L / D) is 52. Its barrel, from the feed inlet to the die head, is divided into: Conveying zone (barrel sections Z1, Z2): its main function is conveying; Reaction zone (barrel sections Z3, Z4): this area's screw configuration includes meshing blocks and reverse thread elements to provide high shear and extended residence time, serving as the main reaction zone; Deviation zone (Zv): equipped with a large-opening exhaust port connected to a three-stage steam jet vacuum pump system, maintaining the system's absolute pressure below 5 kPa; Homogenization and pressurization zone (Z5): performing final homogenization of the melt and establishing extrusion pressure.

[0035] 5. Online monitoring unit: An online melt viscometer and melt pressure sensor are installed between the end of the homogenization zone (Z5) and the die head, perpendicular to the material flow direction.

[0036] 6. TPA / PPA Homogeneous Solution Replenishment Unit: This unit includes a storage tank equipped with a stirrer and a 60°C constant-temperature water bath, containing a 22% (w / w) TPA / PPA homogeneous solution (prepared by mixing TPA and PPA at a mass ratio of 1:4.5 and then high-speed shearing and stirring at 1000 rpm for 3.5 hours at 65°C). The tank outlet is connected via a precision metering pump and pipeline to the primary injection nozzle (Z2 / Z3 connection section) and secondary injection nozzle (Z3 / Z4 connection section) of a twin-screw extruder.

[0037] 7. Central Control Unit: This system combines an Industrial Computer (IPC) and a Programmable Logic Controller (PLC), and is compatible with existing conventional industrial hardware (such as Siemens S7-400 PLC and Mitsubishi Q-series PLC). The IPC has a built-in Human-Machine Interface (HMI) and advanced control algorithm software, while the PLC is responsible for driving the underlying equipment and acquiring data. This unit receives standard signals from the viscometer and pressure sensor in real time and outputs control commands to the metering pump, the twin-screw extruder main drive inverter, the independent temperature control modules for each barrel section, and the vacuum system.

[0038] The TPA / PPA homogeneous solution used is prepared by adding terephthalic acid and polyphosphoric acid at a mass ratio of 1:(5-10) to a constant temperature storage tank with a stirrer, heating to 60-100℃, and stirring at high speed (500-1000 rpm) for 2-10 hours until the terephthalic acid is completely dissolved, resulting in a TPA / PPA homogeneous solution with a mass concentration of 10-20%.

[0039] Example 1: A continuous and controllable polymerization method for PBO polymer based on online viscosity equilibrium regulation, utilizing... Figure 2 The device operates by the following steps: S1. Prepolymerization: Add 150 kg of polyphosphoric acid (PPA, P2O5 content approximately 83%) and 26 kg of 4,6-diaminoresorcinol hydrochloride (DAR•HCl) to the prepolymerization reactor. After purging the air with nitrogen, raise the temperature to 105°C under continuous micro-nitrogen protection. Turn on the vacuum system and react at -0.085 MPa for approximately 2 hours. Collect the removed hydrogen chloride gas and water through the tail gas absorption system. This step ensures that DAR•HCl completely removes hydrogen chloride, converting it into reactive DAR.

[0040] Subsequently, 19 kg of terephthalic acid (TPA) powder was added to the activated DAR / PPA system, with a DAR to TPA molar ratio of 1:0.96. The system temperature was raised to 125°C, and a pre-condensation reaction was carried out for 4 hours under atmospheric pressure and nitrogen protection. After the reaction, a sample was taken, diluted, and tested. Its intrinsic viscosity was approximately 16 dL / g, yielding a PBO oligomer slurry.

[0041] S2. Conveying and Sealing: Start the screw conveyor and twin-screw extruder, and steadily feed the prepolymerized oligomer slurry into the twin-screw extruder at a rate of approximately 8 kg / h. Keep the nitrogen sealing device running throughout the process, introducing high-purity nitrogen and maintaining a slight positive pressure of 30 Pa to ensure that the material transfer process is conducted in an inert atmosphere.

[0042] S3. Post-polymerization initial conditions and online monitoring: The initial process parameters for each zone of the twin-screw extruder are set as follows: Temperature settings: Z1 (120℃), Z2 (160℃), Z3 (190℃), Z4 (205℃), Z5 (210℃); Screw speed: initially set to 70 rpm. Deviation vacuum: The vacuum system is activated, and the absolute pressure in the devolatilization zone (Zv) is maintained at 3 kPa. Control target: The target viscosity value η is set on the central control unit. 目标 For the corresponding online viscosity reading of 36 dL / g, specifically 38000 Pa·s, the upper limit of the die head pressure safety is set to 18 MPa.

[0043] S4. Execution of Dynamic Feedback and Balance Control: The system enters fully automatic operation mode. The central control unit collects viscosity (η) and pressure (P) data in real time at 1-second intervals and executes the following preset algorithm: Scenario A: Triggering the "Low Viscosity Control Strategy" (First Cooperative Operation): At the initial stage of system startup, the online viscometer displays an η value of only 78% of the target value, and the controller determines that it has entered the "low viscosity" state.

[0044] Material replenishment: Calculate the replenishment amount according to the formula (K=1.0, Q=8 kg / h): V = 1.0 × (38000 - 29640) / 38000 × 8 ≈ 1.79 mL / min. The TPA / PPA homogeneous solution is added to the Z2 / Z3 connection section through the primary injection nozzle at the above flow rate.

[0045] Speed ​​adjustment: Gradually reduce the twin screw speed from 70 rpm to 58 rpm.

[0046] Temperature Coordination: The temperature setpoints of the high-shear reaction zones (Z3, Z4) are increased by 8°C (to 198°C and 213°C), respectively, to accelerate the polycondensation reaction kinetics; the temperature setpoints of the conveying zones (Z1, Z2) are decreased by 15°C (to 105°C and 145°C), respectively, to reduce backmixing and pre-reaction of materials in the inlet area, ensuring that the reaction mainly takes place in the set high-temperature reaction zones.

[0047] The core of this combined operation is to promote the reaction; the added TPA, as a reactant monomer, extends the residence time (reduces the rotation speed) and increases the temperature in the reaction zone, which together increase the molecular weight of the polymer.

[0048] Scenario B: Triggering the "High Viscosity / Pressure Control Strategy" (Second Cooperative Operation): After running for about 30 minutes, η rises to 108% of the target value, and the pressure rises to 19.2 MPa, exceeding the safety limit of 18 MPa, which meets the triggering conditions. The controller determines that it enters the "High Viscosity / Pressure Warning" state.

[0049] Material replenishment: Calculate the replenishment amount according to the formula (K=0.8, Q=8 kg / h): V = 0.8 × (38000 - 41040) / 38000 × 8 ≈ -0.51 mL / min. The negative sign indicates that no monomer needs to be added, but capping agent needs to be added. Therefore, switch to fine addition mode and add TPA / PPA homogeneous solution at a low flow rate of 1.2 mL / min. At this time, the added TPA mainly acts as a capping agent.

[0050] Speed ​​adjustment: Quickly increase the screw speed to 85 rpm. Temperature regulation: Reduce the temperature setpoints of the reaction zones (Z3, Z4) by 10°C (to 195°C and 200°C respectively) to moderately suppress over-polymerization. Increase the temperature setpoints of the conveying zones (Z1, Z2) by 20°C (to 140°C and 180°C respectively) to effectively reduce the viscosity of the material in these areas, improve conveying capacity, and alleviate pressure on the die head.

[0051] The control system autonomously and smoothly switches between the two modes, so that the online viscosity η eventually stabilizes within ±5% of the target value, and the die head pressure stabilizes at 12-15 MPa.

[0052] S5. Online Deviation and Product Extrusion: The devolatilization zone (Zv) operates continuously throughout the process, effectively removing moisture generated by the polycondensation reaction and any trace amounts of unreacted monomers that may be entrained, shifting the reaction equilibrium to the right. The high-viscosity PBO polymer melt, intelligently controlled to the desired state, is smoothly extruded from the circular die (3mm in diameter) of the die head, yielding a golden-yellow PBO polymer.

[0053] Results: The PBO resin particles produced during 12 hours of continuous and stable operation in this embodiment were systematically tested. Samples were taken every 1.2 hours during the 12-hour continuous operation, for a total of 10 time points. The intrinsic viscosity was determined using an Ubbelohde viscometer in methanesulfonic acid at 30°C. The IV values ​​of all samples ranged from 35.4 to 36.7 dL / g, with an average of 36.0 dL / g and a relative standard deviation of less than 1.5%. This indicates that the method of this invention can reliably obtain high molecular weight products close to the theoretical maximum value of the formulation.

[0054] Example 2 A continuous and controllable polymerization method for PBO polymer based on online viscosity equilibrium regulation, comprising the following steps: S1. Prepolymerization: Add 300 kg of polyphosphoric acid (PPA, P2O5 content approximately 83%) and 30 kg of 4,6-diaminoresorcinol hydrochloride (DAR•HCl) to the prepolymerization reactor. After purging the air with nitrogen, raise the temperature to 115°C under continuous micro-nitrogen protection. Turn on the vacuum system and react at -0.085 MPa for approximately 2 hours. Collect the removed hydrogen chloride gas and water through the tail gas absorption system. This step ensures that DAR•HCl completely removes hydrogen chloride, converting it into reactive DAR.

[0055] Subsequently, 20 kg of terephthalic acid (TPA) powder was added to the activated DAR / PPA system, with a DAR to TPA molar ratio of 1:0.95. The system temperature was raised to 135°C, and a pre-condensation reaction was carried out for 4 hours under atmospheric pressure and nitrogen protection. After the reaction, a sample was taken, diluted, and tested. Its intrinsic viscosity was approximately 17 dL / g, yielding a PBO oligomer slurry.

[0056] S2. Conveying and Sealing: Start the screw conveyor and twin-screw extruder. Stable feed the prepolymerized oligomer slurry into the twin-screw extruder at a rate of approximately 8 kg / h. Keep the nitrogen sealing device on throughout the process, introduce high-purity nitrogen and maintain a slight positive pressure of 40 Pa to ensure that the material transfer process is in an inert atmosphere.

[0057] S3. Post-polymerization initial conditions and online monitoring: The initial process parameters for each zone of the twin-screw extruder are set as follows: Temperature settings: Z1 (125℃), Z2 (165℃), Z3 (195℃), Z4 (215℃), Z5 (220℃); Screw speed: initially set to 60 rpm; Deviation vacuum: the vacuum system is activated, and the absolute pressure in the devolatilization zone (Zv) is maintained at 3 kPa. Control target: On the central control unit, the target viscosity value η is set. 目标 For the corresponding online viscosity reading of 35 dL / g, specifically 36500 Pa·s, the upper limit of the die head pressure is set to 19 MPa.

[0058] S4. Execution of Dynamic Feedback and Balance Control: The system enters fully automatic operation mode. The central control unit collects viscosity (η) and pressure (P) data in real time at 1-second intervals and executes the following preset algorithm: Scenario A: Triggering the "Low Viscosity Control Strategy" (First Cooperative Operation): At the initial stage of system startup, the online viscometer displays an η value that is only 70% of the target value. The controller determines that it has entered a "low viscosity" state and calculates the replenishment amount according to the formula (K=1.2, Q=8 kg / h): V = 1.2 × (36500 - 25550) / 36500 × 8 ≈ 2.91 mL / min. The TPA / PPA homogeneous solution is added to the Z2 / Z3 connection section through the first-stage injection nozzle at the above flow rate.

[0059] Speed ​​adjustment: Gradually reduce the twin-screw speed from 60 rpm to 48 rpm. Temperature regulation: Increase the temperature setpoints of the high-shear reaction zones (Z3, Z4) by 10°C (to 205°C and 225°C respectively) to accelerate the polycondensation reaction kinetics. Decrease the temperature setpoints of the conveying zones (Z1, Z2) by 10°C (to 115°C and 155°C respectively) to reduce backmixing and pre-reaction of materials in the inlet area, ensuring that the reaction mainly takes place in the set high-temperature reaction zones.

[0060] Scenario B: Triggering the "High Viscosity / Pressure Control Strategy" (Second Cooperative Operation): After running for approximately 30 minutes, η rises to 118% of the target value, and the pressure rises to 22.4 MPa, exceeding the maximum pressure. The controller determines that it has entered the "High Viscosity / Pressure Warning" state and calculates the replenishment amount according to the formula (K=0.9, Q=8 kg / h): V = 0.9 × (36500 - 43070) / 36500 × 8 ≈ -1.3 mL / min. The negative sign indicates that no monomer needs to be added, but capping agent needs to be added. Therefore, switch to fine addition mode and add TPA / PPA homogeneous solution at a low flow rate of 1.2 mL / min. At this time, the added TPA mainly acts as a capping agent.

[0061] Speed ​​adjustment: Quickly increase the screw speed to 75 rpm. Temperature regulation: Reduce the temperature setpoints of the reaction zones (Z3, Z4) by 15°C (to 200°C and 205°C respectively) to moderately suppress over-polymerization. Increase the temperature setpoints of the conveying zones (Z1, Z2) by 10°C (to 135°C and 175°C respectively) to effectively reduce the viscosity of the material in these areas, improve conveying capacity, and alleviate pressure on the die head.

[0062] The control system autonomously and smoothly switches between the two modes, so that the online viscosity η eventually stabilizes within ±5% of the target value, and the die head pressure stabilizes at 12-15 MPa.

[0063] S5. Online Deviation and Product Extrusion: The devolatilization zone (Zv) operates continuously throughout the process, effectively removing moisture generated by the polycondensation reaction and any trace amounts of unreacted monomers that may be entrained, shifting the reaction equilibrium to the right. The high-viscosity PBO polymer melt, intelligently controlled to the desired state, is smoothly extruded from the circular die (3mm in diameter) of the die head, yielding a golden-yellow PBO polymer.

[0064] Results: The PBO resin particles produced during 12 hours of continuous and stable operation in this embodiment were systematically tested. Samples were taken every 1.2 hours during the 12-hour continuous operation, for a total of 10 time points. The intrinsic viscosity was determined using an Ubbelohde viscometer in methanesulfonic acid at 30°C. The IV values ​​of all samples ranged from 34.7 to 35.8 dL / g, with an average of 35.2 dL / g and a relative standard deviation of less than 1.2%. This demonstrates that the method of this invention can stably obtain high molecular weight products close to the theoretical maximum value of the formulation.

[0065] Comparative Example 1: Conventional process without real-time control Using the same raw materials, equipment, and prepolymerization process as in Example 1, but without online viscosity / pressure monitoring during the post-polymerization stage, without adding TPA / PPA homogeneous solution, and with fixed temperature and rotation speed parameters: S1-S2 are completely consistent with Example 1; S3: The process parameters of each zone of the twin-screw extruder are fixed as follows: Z1 (120℃), Z2 (160℃), Z3 (190℃), Z4 (205℃), Z5 (210℃), the screw speed is fixed at 70 rpm, and the absolute pressure in the devolatilization zone is maintained at 3 kPa; S4: There is no dynamic feedback or balance control, and it continues to operate according to fixed parameters; S5 is consistent with Example 1.

[0066] Results: After 12 hours of continuous operation, samples were taken every 1.2 hours, for a total of 10 time points to determine the intrinsic viscosity. The results ranged from 30.2 to 38.7 dL / g, with an average of 34.5 dL / g and a relative standard deviation of ≥8%. During the operation, the die head pressure exceeded the limit (more than 18 MPa) 3 times, resulting in 2 shutdowns for cleaning, with a shutdown rate of ≥15%. Some samples of the product contained undissolved TPA particles, resulting in poor uniformity and failing to meet the requirements for high-performance spinning.

[0067] Comparative Example 2: Process control with only solid TPA addition Using the same raw materials, equipment, monitoring system, and prepolymerization process as in Example 1, solid TPA powder was added instead of a homogeneous TPA / PPA solution when the viscosity was too low. The remaining control strategies (speed and temperature adjustment) were the same as in Example 1. S1-S3: Same as Example 1; S4: In Scenario A, the replenishment method is changed to replenishing solid TPA powder through the feed inlet, and the replenishment amount is equivalent to the molar amount of TPA replenished in Example 1; The control method in Scenario B is the same as in Example 1. S5 is the same as in Example 1.

[0068] Results: After 12 hours of continuous operation, samples were taken every 1.2 hours for a total of 10 time points to determine the intrinsic viscosity. The results ranged from 32.1 to 36.8 dL / g, with an average of 34.3 dL / g and a relative standard deviation of ≥5%. Obvious undissolved TPA particles were detected in the product (observed by optical microscopy). Material adhesion to the screw meshing area was observed. The equipment cleaning time after the operation was 3 times longer than that in Example 1. Some samples showed an increased filament breakage rate during spinning due to undissolved particles.

[0069] As can be seen, the technical solution of this application achieves dynamic and precise monomer replenishment by adding a two-stage replenishment unit for TPA / PPA homogeneous solution, solving the problem of fixed monomer ratios in existing technologies; it integrates an online viscosity-pressure dual monitoring unit to achieve real-time online monitoring of the reaction process, breaking the "black box" operation of twin-screw extruders; it constructs a central closed-loop control unit with four linkages of temperature, speed, replenishment, and devolatilization, realizing intelligent dynamic control of process parameters, changing the fixed parameter control of existing technologies; nitrogen sealing throughout the process ensures oxygen-free transport from prepolymer reactor discharge to extruder feed, avoiding material oxidation and degradation; and a high-efficiency devolatilization unit achieves complete removal of small molecule byproducts and free monomers, while simultaneously enabling monomer recycling. Ultimately, a stable high molecular weight PBO product is obtained, improving production efficiency and process flexibility; it significantly reduces downtime and scrap caused by process fluctuations, improving the efficiency and economic benefits of continuous production; and by adjusting the target parameters of the control system, it can flexibly adapt to the production of PBO polymers with different polymerization degrees, significantly enhancing process flexibility.

[0070] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A continuous and controllable polymerization method for PBO polymer based on online viscosity equilibrium regulation, characterized in that, Includes the following steps: S1. Prepolymerization: The PBO monomer is prepolymerized in a polyphosphoric acid solvent. The specific process is as follows: First, 4,6-diaminoresorcinol hydrochloride is dehydrochlorinated at a certain temperature to obtain activated DAR; then, the activated DAR undergoes a polycondensation reaction with terephthalic acid to generate an oligomer or oligomer slurry with an intrinsic viscosity in the range of 5-20 dL / g as a prepolymer. S2. Conveying and Sealing: The prepolymer slurry is conveyed to a twin-screw extruder. The conveying process and the extruder feed area are sealed with nitrogen to prevent material oxidation and degradation. S3. Post-polymerization and online monitoring: The prepolymer undergoes post-polymerization in a twin-screw extruder under high temperature and high shear. An online viscometer and pressure sensor are installed at the end of the homogenization zone and between the die head of the twin-screw extruder to monitor the melt viscosity and die head pressure of the material in real time. S4. Dynamic Feedback and Balance Control: Based on the online monitoring signal obtained in S3, execute closed-loop control logic to guide the polymerization reaction to the preset endpoint; S5. Online devolatilization and product extrusion: The twin-screw extruder is equipped with a devolatilization zone to continuously remove small molecule byproducts such as water generated in the reaction, as well as excess free monomers entrained therein, promoting the forward reaction.

2. The method for continuous and controllable polymerization of PBO polymer based on online viscosity equilibrium control according to claim 1, characterized in that, The specific steps of the S4 dynamic feedback and balance control are as follows: By offline testing of the online viscosity values ​​of PBO polymer melts with different intrinsic viscosities at corresponding process temperatures, a correspondence between "offline intrinsic viscosity" and "online melt viscosity" was established. The target intrinsic viscosity of high molecular weight PBO is 30-40 dL / g, corresponding to an online melt viscosity target of 30,000-40,000 Pa·s. The lower limit of the target is set at 95% of the target value, and the upper limit of the target is set at 105% of the target value. The safe threshold for head pressure is 18-22 MPa; The judgment logic in the closed-loop control logic is as follows: regulation is triggered when any of the following conditions are met: ① real-time viscosity exceeds the target upper limit; ② head pressure exceeds the safety threshold; if both occur at the same time, regulation is prioritized based on "pressure exceeding the limit".

3. The continuous and controllable polymerization method for PBO polymer based on online viscosity equilibrium control according to claim 2, characterized in that, The relevant control strategies in the closed-loop control logic are as follows: a) Low viscosity control strategy: When the real-time viscosity is lower than the target lower limit, it indicates that the polymerization reaction is insufficient and the reaction needs to be promoted to a higher molecular weight. The control system automatically starts the replenishment program to quantitatively replenish a homogeneous solution of TPA in PPA to a specific reaction zone of the twin-screw extruder to provide sufficient monomer to promote the continued polycondensation reaction. The replenishment amount is calculated in real time based on the viscosity deviation to ensure that TPA dissolves in time to participate in the reaction and avoids the generation of insoluble substances. At the same time, the screw speed is reduced to prolong the residence time of the material in the reaction zone, the temperature of the screw meshing zone is increased to enhance the reaction activity, and the temperature of the conveying zone is reduced to reduce backmixing and maintain the reaction driving force, all of which jointly promote the increase of molecular weight.

4. The continuous and controllable polymerization method for PBO polymer based on online viscosity equilibrium control according to claim 3, characterized in that, First, a homogeneous TPA / PPA solution is obtained by adding terephthalic acid and polyphosphoric acid at a mass ratio of 1:5-10 to a constant temperature storage tank with a stirrer, heating to 60-100℃, and stirring with a high-speed shear stirrer for 2-10 hours until the terephthalic acid is completely dissolved, thus obtaining a homogeneous TPA / PPA solution with a mass concentration of 10-20%. The specific steps for quantitatively adding a homogeneous TPA / PPA solution to a specific reaction zone of a twin-screw extruder are as follows: A quantitative amount of homogeneous TPA / PPA solution is added to the primary injection nozzle of the Z2 / Z3 connecting section of the twin-screw extruder. The calculation method for the addition amount is as follows: The addition amount is based on online viscosity monitoring data and is calculated in real time using a preset algorithm of the central control unit. The calculation formula is: Additional volume V = K × (η) 目标 -η 实时 ) / η 目标 ×Q; Where K is a correction factor, specifically 0.8-1.2, and η 目标 For the online viscosity target value, η 实时 To monitor viscosity values ​​in real time, Q represents the material feed rate; The amount of TPA added is dynamically adjusted according to the viscosity deviation; the greater the viscosity deviation, the greater the amount added. Furthermore, the addition rate is linked to the screw speed and reaction zone temperature to ensure that the added TPA dissolves quickly and participates in the polycondensation reaction, leaving no undissolved monomer residue. The specific strategy is as follows: Reducing the screw speed by 10-20 rpm from the initial speed can extend the residence time of the material in the reaction zone to 8-12 minutes; increasing the temperature of the screw meshing zone by 5-10℃ from the initial temperature; and reducing the temperature of the conveying zone by 10-15℃ from the initial temperature.

5. The continuous and controllable polymerization method for PBO polymer based on online viscosity equilibrium control according to claim 2, characterized in that, The relevant control strategies in the closed-loop control logic are as follows: b) High Viscosity / Pressure Control Strategy: When the real-time viscosity is too high or the die pressure exceeds the safety threshold, the system determines that the polymerization reaction has approached or reached the required level, and it needs to move towards equilibrium end-capping and prevent over-polymerization. A homogeneous TPA / PPA solution is added to the reaction zone of the twin-screw extruder to provide excess TPA monomer, allowing it to react with the polymer chain ends, achieving molecular chain end-capping, and promoting the reaction to reach and stabilize at the equilibrium endpoint. Specifically, the addition of the homogeneous TPA / PPA solution to the reaction zone of the twin-screw extruder is as follows: A homogeneous TPA / PPA solution was added to the secondary injection nozzle of the Z3 / Z4 connecting section of the reaction zone of the twin-screw extruder. The addition was carried out in a fine, small-dose manner at a rate of 1-1.5 mL / min and at a constant low flow rate.

6. The continuous and controllable polymerization method for PBO polymer based on online viscosity equilibrium control according to claim 5, characterized in that, b) In the high viscosity / pressure control strategy, simultaneously increase the screw speed by 10-25 rpm from the current speed to shorten the residence time of the material in the reaction zone to 4-6 min; reduce the temperature of the screw meshing zone by 8-15℃ from the current temperature; and increase the temperature of the conveying zone by 10-20℃ from the current temperature.

7. The continuous and controllable polymerization method for PBO polymer based on online viscosity equilibrium control according to claim 2, characterized in that, The activation and deactivation of the control strategy are solely determined by real-time monitoring data from the online viscometer and pressure sensor. The central control unit collects data at a 1-second interval. When the data exceeds the target range, the corresponding control strategy is automatically activated immediately. When the real-time viscosity recovers to within ±5% of the target value and the die head pressure stabilizes within the safe range of 5-15MPa, the system automatically stops control and returns to the normal process parameters, achieving closed-loop precise control.

8. The continuous and controllable polymerization method for PBO polymer based on online viscosity equilibrium control according to claim 1, characterized in that, S1. The specific steps of prepolymerization are as follows: First, 4,6-diaminoresorcinol hydrochloride and polyphosphoric acid are added to a prepolymer reactor at a mass ratio of 1:(5-100). High-purity nitrogen is introduced to replace the air in the reactor and maintain a slightly positive pressure inert atmosphere. The temperature is raised to 105-145℃, and the vacuum system is turned on to maintain an absolute pressure of -0.08 to -0.09 MPa. The reaction is carried out at a constant temperature for 1-10 hours. The removed hydrogen chloride gas and trace moisture are collected through the tail gas absorption system to complete the activation of 4,6-diaminoresorcinol hydrochloride, resulting in a reactive DAR / PPA homogeneous system. Subsequently, the activated DAR undergoes a polycondensation reaction with terephthalic acid, wherein the molar ratio of DAR to TPA is controlled at 1:0.88-0.

98. The temperature is raised to 120-135℃, and a prepolymerization reaction is carried out for 2-6 hours under normal pressure nitrogen protection to generate an oligomer or oligomer slurry with an intrinsic viscosity in the range of 5-20 dL / g as a prepolymer.

9. The continuous and controllable polymerization method for PBO polymer based on online viscosity equilibrium control according to claim 1, characterized in that, S2. A corrosion-resistant screw conveyor with an insulation jacket is used for conveying and sealing. The slurry temperature is maintained at 80-150℃ during the conveying process. An annular chamber nitrogen sealing device is installed between the conveyor outlet and the extruder inlet. High-purity nitrogen is introduced and maintained at a slight positive pressure of 20-50Pa to form an air curtain that completely isolates the air.

10. The continuous and controllable polymerization method for PBO polymer based on online viscosity equilibrium control according to claim 1, characterized in that, S5. A three-stage steam jet vacuum pump system is used in online devolatilization and product extrusion. The absolute pressure in the devolatilization zone is maintained at 3-5 kPa, and the devolatilization efficiency is ≥99%.

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