Integrated polymerization production system for flame-retardant nylon chip

Abstract

The application provides an integrated polymerization production system of flame-retardant nylon chip, which comprises a flame retardant preparation unit, a raw material mixing unit, a prepolymerization unit, a post-polymerization unit, a cutting unit, an extraction unit and a drying unit connected in series, wherein the prepolymerization unit is connected with the raw material mixing unit and used for carrying out a multi-stage pressure-temperature controlled prepolymerization reaction on the pre-reaction substance to generate a prepolymer; the post-polymerization unit is connected with the prepolymerization unit and used for carrying out a pressure-vacuum pulse controlled post-polymerization reaction on the prepolymer to generate a polymer; and the prepolymerization unit and the post-polymerization unit are provided with pressure gradient linkage control and temperature curve matching.

Description

Technical Field

[0001] This invention relates to the field of plastic processing technology, and in particular to an integrated polymerization production system for flame-retardant nylon chips. Background Technology

[0002] Currently, the industrial production of flame-retardant nylon chips mainly relies on a two-stage continuous polymerization system. This system consists of a raw material preparation unit, a prepolymerization unit, a postpolymerization unit, a pelletizing unit, an extraction unit, and a drying unit connected in series. Among these, the prepolymerization unit and the postpolymerization unit are the core links, playing a decisive role in the molecular weight and distribution of the polymer.

[0003] However, existing prepolymerization units generally employ isothermal and pressure control, maintaining the temperature at 240-250 degrees Celsius and the pressure at a constant range of 0.1-0.3 MPa throughout the entire reaction cycle, which lasts 6-8 hours. This static operation mode cannot adapt to the dynamic requirements of different stages of the polymerization reaction: higher pressure is needed in the initial stage to effectively suppress monomer volatilization, the pressure needs to be moderately reduced in the middle stage to promote molecular chain growth, and further depressurization is required in the later stage to fully remove small molecule byproducts. Static control leads to insufficient optimization of the reaction process, affecting polymer uniformity.

[0004] Similarly, post-polymerization units typically employ isothermal and pressure control or constant vacuum control. In isothermal mode, the temperature is kept constant at 250 to 260 degrees Celsius, and the pressure is maintained at a slightly positive pressure. In constant vacuum mode, a vacuum level of -0.06 to -0.1 MPa is maintained. These single-parameter operating mechanisms make it difficult to achieve a smooth transition between the chain growth stage and the deep devolatilization stage, limiting the fine-tuning of polymer properties. These issues constrain the product quality of flame-retardant nylon chips. Summary of the Invention

[0005] The present invention aims to solve the above-mentioned technical problems by providing an integrated polymerization production system for flame-retardant nylon chips.

[0006] The technical solution of this invention is an integrated polymerization production system for flame-retardant nylon chips, comprising the following components connected in series:

[0007] A flame retardant preparation unit includes a preparation tank, which is used to mix and react a nitrogen-based flame retardant precursor with demineralized water to generate a flame retardant intermediate.

[0008] The raw material mixing unit is connected to the flame retardant preparation unit and is used to mix the flame retardant intermediate with caprolactam, hexamethylenediamine adipate, and terephthalic acid to prepare a pre-reactant.

[0009] The prepolymerization unit, connected to the raw material mixing unit, is used to perform a multi-stage pressure-temperature controlled prepolymerization reaction on the pre-reactant to generate a prepolymer.

[0010] The post-polymerization unit, connected to the prepolymerization unit, is used to perform a pressure-vacuum pulse controlled post-polymerization reaction on the prepolymer to generate a polymer;

[0011] A pelletizing unit, connected to the post-polymerization unit, is used to pelletize the polymer melt into slices;

[0012] An extraction unit, connected to the pelletizing unit, is used to perform desalination extraction on the slices to remove unreacted monomers;

[0013] A drying unit, connected to the extraction unit, is used to dry the extracted wet slices to obtain flame-retardant nylon slice products.

[0014] The prepolymerization unit and the postpolymerization unit are equipped with pressure gradient linkage control and temperature curve matching.

[0015] In one embodiment, the nitrogen-based flame retardant precursor is melamine and cyanuric acid.

[0016] In one embodiment, the preparation tank is used to mix melamine, cyanuric acid and deionized water at a predetermined molar ratio, and react them under heating and stirring conditions to generate a flame-retardant intermediate.

[0017] In one embodiment, in the raw material mixing unit, the weight ratio of caprolactam, hexamethylenediamine adipate, flame retardant intermediate, and terephthalic acid is 1:0.1~0.2:0.15~0.25:0.005~0.01.

[0018] In one embodiment, the prepolymerization unit includes a prepolymerization reactor, which sequentially performs three stages during the prepolymerization reaction, with each stage lasting for one-third of the total prepolymerization reaction time.

[0019] The first stage has a pressure of 0.25–0.3 MPa and a temperature of 235–240℃, the second stage has a pressure of 0.15–0.2 MPa and a temperature of 240–245℃, and the third stage has a pressure of -0.1–0.05 MPa and a temperature of 245–250℃.

[0020] In one embodiment, the post-polymerization unit includes a post-polymerization reactor, and the post-polymerization unit is configured to achieve a viscosity of 2.4-2.8 for the resulting polymer.

[0021] The post-polymerization unit is executed sequentially within a total reaction time of 10 hours:

[0022] The first stage lasts 0-4 hours, with a pressure of 0.05-0.10 MPa and a temperature of 250-255℃.

[0023] The second stage lasts 4-10 hours, with each pulse cycle lasting 60 minutes. Within each cycle: for the first 40 minutes, the vacuum level is -0.06 to -0.08 MPa, and the temperature is 255 to 258°C; for the next 20 minutes, the pressure is 0.02 to 0.04 MPa, and the temperature is 252 to 255°C.

[0024] In one implementation, a controller is provided between the prepolymerization unit and the postpolymerization unit. The controller adjusts the inlet pressure of the postpolymerization unit according to the outlet pressure of the prepolymerization unit so that the pressure difference between the two is ≤0.05MPa, and adjusts the inlet temperature of the postpolymerization unit according to the outlet temperature of the prepolymerization unit so that the temperature change rate between the two is ≤5℃ / h.

[0025] In one embodiment, the extraction unit includes a pre-extraction tank and an extraction tower for extracting demineralized water from the slices under heating conditions, and the extraction unit is configured to ensure that the monomer content of the extracted slices is ≤0.1%.

[0026] In one embodiment, the drying unit includes a drying tower for drying wet slices in a nitrogen atmosphere with segmented temperature control, and the drying unit is configured to ensure that the moisture content of the dried slices is ≤500ppm.

[0027] As one implementation, a cooling silo is also included, which is connected to the drying tower and is used to cool the dried slices to room temperature.

[0028] The advantages of this invention compared to the prior art are that the integrated polymerization production system for flame-retardant nylon chips includes a flame retardant preparation unit, a raw material mixing unit, a prepolymerization unit, a postpolymerization unit, a pelletizing unit, an extraction unit, and a drying unit connected in series. By coordinating the operating parameters of the prepolymerization unit and the postpolymerization unit through pressure gradient linkage control and temperature curve matching, sudden pressure drops and temperature changes are avoided. This system has the advantages of improving the viscosity stability of the chip products, reducing the amount of unreacted monomer residue, and improving the uniformity of flame retardant dispersion. Attached Figure Description

[0029] Figure 1 A view of an integrated polymerization production system for flame-retardant nylon chips provided in an embodiment of the present invention.

[0030] In the diagram: 10, flame retardant preparation unit; 20, raw material mixing unit; 30, prepolymerization unit; 40, postpolymerization unit; 50, pelletizing unit; 60, extraction unit; 70, drying unit; 80, cooling silo. Detailed Implementation

[0031] The above and other embodiments and advantages of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0032] In one implementation, such as Figure 1 As shown.

[0033] The integrated polymerization production system for flame-retardant nylon chips provided in this embodiment includes a flame retardant preparation unit 10, a raw material mixing unit 20, a prepolymerization unit 30, a postpolymerization unit 40, a pelletizing unit 50, an extraction unit 60, and a drying unit 70 connected in series. The flame retardant preparation unit 10 includes a preparation tank for mixing and reacting a nitrogen-based flame retardant precursor with demineralized water to generate a flame-retardant intermediate. The raw material mixing unit 20 is connected to the flame retardant preparation unit 10 and is used to mix the flame-retardant intermediate with caprolactam, hexamethylenediamine adipate, and terephthalic acid to prepare a pre-reactant. The prepolymerization unit 30 is connected to the raw material mixing unit 20 and is used to perform a multi-stage pressure-temperature controlled prepolymerization reaction on the pre-reactant to generate a prepolymer. Multi-stage pressure-temperature control refers to dividing the entire reaction process into multiple stages in the prepolymerization unit 30 and setting different pressure and temperature conditions in each stage for control. This control method aims to optimize the polymerization process to adapt to the process parameter requirements of different polymerization stages. The post-polymerization unit 40 is connected to the pre-polymerization unit 30 and is used to perform a pressure-vacuum pulse-controlled post-polymerization reaction on the prepolymer to generate the polymer. Pressure-vacuum pulse control refers to controlling the reaction environment in the post-polymerization unit 40 by periodically switching between positive pressure and vacuum. This pulsed control strategy aims to promote the removal of small molecules and the growth of molecular chains to achieve the desired polymer properties. The pelletizing unit 50 is connected to the post-polymerization unit 40 and is used to pelletize the polymer melt into chips. The extraction unit 60 is connected to the pelletizing unit 50 and is used to perform demineralized water extraction on the chips to remove unreacted monomers. The drying unit 70 is connected to the extraction unit 60 and is used to dry the extracted wet chips to obtain flame-retardant nylon chip products. A pressure gradient linkage control and temperature profile matching are provided between the pre-polymerization unit 30 and the post-polymerization unit 40. Pressure gradient linkage control and temperature profile matching refer to a synergistic control mechanism between the pre-polymerization unit 30 and the post-polymerization unit 40. This mechanism ensures a smooth material transition and avoids polymer performance fluctuations caused by sudden changes in process parameters by monitoring and adjusting the pressure difference and temperature change rate between the two units in real time.

[0034] In this embodiment, the integrated polymerization production system for flame-retardant nylon chips first involves adding melamine and cyanuric acid, as nitrogen-based flame retardant precursors, to a preparation tank along with deionized water at a predetermined molar ratio in the flame retardant preparation unit 10. Under heating and stirring conditions, these precursors react to generate a flame-retardant intermediate. This process ensures the precise preparation and activation of the flame-retardant components. Subsequently, the flame-retardant intermediate is conveyed to the raw material mixing unit 20. In this raw material mixing unit 20, the flame-retardant intermediate is thoroughly mixed with caprolactam, hexamethylenediamine adipate, and terephthalic acid at a specific weight ratio, for example, the weight ratio of caprolactam, hexamethylenediamine adipate, flame-retardant intermediate, and terephthalic acid is 1:0.1~0.2:0.15~0.25:0.005~0.01. This is prepared as a pre-reactant. The prepared pre-reactant then enters the pre-polymerization unit 30 for a pre-polymerization reaction. The prepolymerization unit 30 comprises a prepolymerization reactor that sequentially executes multi-stage pressure-temperature control over a total reaction time of 6 hours. Specifically, the first stage lasts for 2 hours, with pressure controlled at 0.25–0.3 MPa and temperature at 235–240°C. At this stage, high pressure helps suppress monomer volatilization. The second stage lasts for 2 hours, with pressure decreasing to 0.15–0.2 MPa and temperature increasing to 240–245°C. Moderate pressure reduction promotes molecular chain growth. The third stage lasts for 2 hours, with pressure further decreasing to -0.1–0.05 MPa and temperature increasing to 245–250°C. Low pressure facilitates the removal of small molecules. This segmented dynamic control mode, unlike the static temperature and pressure control mode in existing technologies, can better match the process parameter requirements of different stages of the polymerization reaction and optimize prepolymer formation. The prepolymer generated in the prepolymerization unit 30 then enters the postpolymerization unit 40 for postpolymerization. A key innovation of this integrated polymerization production system is the pressure gradient linkage control and temperature curve matching between the prepolymerization unit 30 and the postpolymerization unit 40. Specifically, this is achieved through a controller: this controller adjusts the inlet pressure of the post-polymerization unit 40 in real time based on the outlet pressure of the pre-polymerization unit 30, ensuring that the pressure difference between the two does not exceed 0.05 MPa. Simultaneously, the controller also adjusts the inlet temperature of the post-polymerization unit 40 based on the outlet temperature of the pre-polymerization unit 30, ensuring that the temperature change rate between the two does not exceed 5 °C / h. This coordinated control effectively avoids bubble defects caused by sudden pressure changes and molecular chain structure fluctuations caused by excessive temperature differences, as is present in existing technologies, thus ensuring the quality and stability of the polymer. The post-polymerization unit 40 contains a post-polymerization reactor designed to achieve a polymer viscosity of 2.4-2.8. During the total 10-hour reaction time, the post-polymerization unit 40 also implements staged control. The first stage is 0-4 hours, with pressure controlled at 0.05–0.10 MPa and temperature controlled at 250–255 °C.The second stage lasts 4-10 hours and employs a pulse control mode: each pulse cycle is 60 minutes. For the first 40 minutes, a vacuum of -0.06 to -0.08 MPa and a temperature of 255 to 258°C are maintained to promote deep devolatilization and chain growth. For the next 20 minutes, the pressure is increased to 0.02 to 0.04 MPa and the temperature is decreased to 252 to 255°C to stabilize the system. This pressure-vacuum pulse control mode, compared to the single constant pressure or constant vacuum mode in existing technologies, achieves a dynamic switch between chain growth and deep devolatilization, further improving the molecular weight and viscosity of the polymer. The polymer melt after polymerization is transported to pelletizing unit 50, where it is pelletized into chips. The chips then enter extraction unit 60. This extraction unit 60 includes a pre-extraction water tank and an extraction tower for demineralized water extraction of the chips under heating conditions to remove unreacted monomers. By optimizing the extraction conditions, the monomer content of the extracted chips can be reduced to below 0.1%, significantly better than the potentially higher monomer residues found in existing technologies. The extracted wet chips are sent to drying unit 70. Drying unit 70 includes a drying tower where the wet chips are dried in a segmented, temperature-controlled nitrogen atmosphere. The drying process is precisely controlled to ensure that the moisture content of the dried chips is below 50 ppm, thus meeting the product's stringent moisture content requirements. Finally, the dried chips enter a cooling silo 80 and are cooled to room temperature, ultimately yielding the flame-retardant nylon chip product. The entire integrated polymerization production system, through the close connection of its units and the coordinated control of key processes, effectively solves the quality problems caused by the independent control of pre-polymerization and post-polymerization in existing technologies. It improves the viscosity stability of the flame-retardant nylon chips, reduces monomer residue, and promotes the uniform dispersion of the flame retardant.

[0035] In one embodiment, the nitrogen-based flame retardant precursor of the integrated polymerization production system for flame-retardant nylon chips is melamine and cyanuric acid.

[0036] In this embodiment, melamine is rich in nitrogen, which decomposes at high temperatures and releases a large amount of non-flammable gas, thus playing a flame-retardant role. Cyanuric acid, a hydrolysis product of melamine, combines with melamine to form stable melamine cyanurate. This salt undergoes endothermic decomposition upon heating, further releasing non-flammable gas and enhancing the flame-retardant effect. Therefore, specifically limiting the nitrogen-based flame retardant precursor to melamine and cyanuric acid can significantly improve flame-retardant efficiency and thermal stability.

[0037] In one embodiment, the preparation tank of the integrated polymerization production system for flame-retardant nylon chips is used to mix melamine, cyanuric acid, and demineralized water at a predetermined molar ratio, and react them under heating and stirring conditions to generate a flame-retardant intermediate. Specifically, the molar ratio of melamine, cyanuric acid, and demineralized water is 1:1:2.5, the reaction temperature is 95°C, the stirring time is 30 min, and the holding time is 4 h.

[0038] In this embodiment, by controlling the molar ratio of melamine, cyanuric acid, and deionized water, the reactants can be fully and efficiently converted into the target flame-retardant intermediate, minimizing side reactions and unreacted monomer residues. Simultaneously, conducting the reaction under heating conditions provides the necessary activation energy, significantly accelerating the reaction rate. Combined with stirring conditions, localized overheating or uneven concentration is avoided, improving the yield and purity of the flame-retardant intermediate.

[0039] In one embodiment, the weight ratio of caprolactam, hexamethylenediamine adipic acid salt, flame retardant intermediate, and terephthalic acid in the integrated polymerization production system for flame-retardant nylon chips is 1:0.1~0.2:0.15~0.25:0.005~0.01.

[0040] In this embodiment, by controlling the weight ratio of caprolactam, hexamethylenediamine adipate, flame-retardant intermediate, and terephthalic acid, the problems of low polymerization efficiency and unstable product performance caused by improper raw material ratio can be effectively solved. This optimized ratio ensures the smooth progress of the polymerization reaction, allowing the flame-retardant intermediate to be uniformly dispersed, thereby improving its flame-retardant properties.

[0041] In one embodiment, the prepolymerization unit 30 of the integrated polymerization production system for flame-retardant nylon chips includes a prepolymerization reactor, which sequentially performs the following stages during a total reaction time of 6 hours: a first stage with a pressure of 0.25–0.3 MPa and a temperature of 235–240°C; a second stage with a pressure of 0.15–0.2 MPa and a temperature of 240–245°C; and a third stage with a pressure of -0.1–0.05 MPa and a temperature of 245–250°C; wherein the duration of the first, second, and third stages each accounts for one-third of the total prepolymerization reaction time.

[0042] In this embodiment, the prepolymerization reactor can adopt a stirred tank or tower structure, and is equipped with a stirring device, heating / cooling jacket, feed port, discharge port, and pressure and temperature sensors to ensure precise control of reaction conditions. Its main function is to convert the pre-reactants configured in the raw material mixing unit 20 into a prepolymer with a certain degree of polymerization through polymerization, laying the foundation for subsequent post-polymerization reactions. The prepolymerization reactor performs multi-stage pressure-temperature control sequentially over a total reaction time of 6 hours. The total reaction time is 6 hours, and by dividing the total reaction time into three stages and setting specific pressure and temperature ranges for each stage, fine control of the polymerization process can be achieved. In the first stage, the pressure is controlled at 0.25–0.3 MPa, and the temperature is controlled at 235–240°C. This stage is usually the initial stage of the polymerization reaction; higher pressure helps suppress monomer volatilization and promotes the initial stage of polymerization, while moderate temperature ensures a smooth start-up of the reaction. In the second stage, the pressure is reduced to 0.15–0.2 MPa, and the temperature is increased to 240–245°C. As the polymerization reaction proceeds, the system viscosity gradually increases. Appropriately reducing the pressure facilitates the escape of small-molecule byproducts generated during the reaction, thereby shifting the polymerization equilibrium towards polymer formation. Simultaneously, increasing the temperature accelerates the reaction rate and improves monomer conversion. In the third stage, the pressure is further reduced to -0.1 to 0.05 MPa, and the temperature is increased to 245 to 250 °C. In the later stages of the polymerization reaction, to further increase the degree of polymerization, it is necessary to remove reaction byproducts more effectively. Lower pressure significantly promotes the removal of byproducts, while higher temperature maintains sufficient reactivity to ensure the prepolymer reaches the target molecular weight. The duration of the first, second, and third stages each accounts for one-third of the total prepolymerization reaction time. This uniform time allocation helps ensure a smooth transition and full progress of each stage, avoiding the impact of insufficient time in any stage on the overall polymerization effect. Through the above technical solution, the prepolymerization unit 30 can optimize the prepolymerization process by precisely controlling the pressure and temperature of multiple stages and rationally allocating the reaction time of each stage. This not only solves the problem of difficult precise control of the degree of polymerization in traditional prepolymerization processes but also provides high-quality prepolymers for the subsequent postpolymerization unit 40.

[0043] In one embodiment, the post-polymerization unit 40 of the integrated polymerization production system for flame-retardant nylon chips includes a post-polymerization reactor, and the post-polymerization unit 40 is configured to achieve a viscosity of 2.4-2.8 for the resulting polymer. The post-polymerization unit 40 performs the following sequentially over a total reaction time of 10 hours: a first stage of 0-4 hours, with a pressure of 0.05-0.10 MPa and a temperature of 250-255°C; a second stage of 4-10 hours, with a pulse cycle every 60 minutes, wherein in each cycle: the vacuum degree is -0.06--0.08 MPa and the temperature is 255-258°C for the first 40 minutes; and the pressure is 0.02-0.04 MPa and the temperature is 252-255°C for the last 20 minutes.

[0044] In this embodiment, the post-polymerization reactor is typically equipped with a stirring device, a heating jacket or coil, inlet and outlet ports, and a vacuum system interface. The post-polymerization unit 40 sequentially performs staged, pulsed pressure-temperature control over a total reaction time of 10 hours. In the first stage, the pressure inside the reactor is maintained at 0.05–0.10 MPa, and the temperature is controlled at 250–255°C. This initial stage, conducted at relatively high pressure and moderate temperature, primarily aims to promote further polymerization of the prepolymer, achieve initial molecular weight growth, and homogenize the system, preparing for the subsequent vacuum stage. In the second stage, the reaction operates using a pulse cycle of 60 minutes. For the first 40 minutes of each pulse cycle, a vacuum condition is introduced into the reactor, with a vacuum level of -0.06–-0.08 MPa, and the temperature is raised to 255–258°C. The introduction of a vacuum facilitates the rapid removal of small molecule byproducts, thereby promoting the polymerization reaction towards higher molecular weights and accelerating molecular weight growth, while the higher temperature further increases the reaction rate. In the last 20 minutes of each pulse cycle, the pressure inside the reactor recovers to 0.02–0.04 MPa, and the temperature slightly decreases to 252–255 °C. This stage helps to suppress excessive polymer degradation, stabilize the polymer structure, and provide a buffer for the next vacuum pulse cycle, preventing excessive system fluctuations. This staged, pulsed operation is achieved through a precise automated control system, including an online viscometer, pressure sensor, temperature sensor, vacuum pump, heating / cooling system, and control valves. This system automatically switches pressure and temperature conditions according to a preset program, ensuring the reaction proceeds according to the predetermined curve. By controlling the reaction conditions in the first stage and the pulse cycle, and supplementing this with real-time monitoring of the polymer viscosity using an online viscometer, the reaction process is automatically adjusted when the viscosity reaches the target range, ensuring that the viscosity of the resulting polymer remains stable between 2.4 and 2.8.

[0045] In one embodiment, a controller is provided between the prepolymerization unit 30 and the postpolymerization unit 40 of the integrated polymerization production system for flame-retardant nylon chips. The controller adjusts the inlet pressure of the postpolymerization unit 40 according to the outlet pressure of the prepolymerization unit 30 so that the pressure difference between the two is ≤0.05MPa, and adjusts the inlet temperature of the postpolymerization unit 40 according to the outlet temperature of the prepolymerization unit 30 so that the temperature change rate between the two is ≤5℃ / h.

[0046] In this embodiment, the controllers are a PLC and a DCS. Their signal input terminals are connected to a pressure sensor and a temperature sensor located at the outlet of the pre-polymerization unit, respectively, and their signal output terminals are connected to the control terminals of the pressure regulating valve and the heater located at the inlet of the post-polymerization unit. Based on the received pressure signal from the pre-polymerization unit outlet, the PLC adjusts the opening of the pressure regulating valve at the inlet of the post-polymerization unit using a PID algorithm, ensuring that the pressure difference between the two units is ≤0.05MPa. Simultaneously, based on the received temperature signal from the pre-polymerization unit outlet, it adjusts the power of the heater at the inlet of the post-polymerization unit, ensuring that the temperature change rate is ≤5℃ / h. By precisely controlling the pressure difference and temperature change rate between the two units, the problems of unstable material transfer and fluctuating reaction conditions during polymerization can be effectively solved. Specifically, by controlling the pressure difference between the outlet of the pre-polymerization unit 30 and the inlet pressure of the post-polymerization unit 40 to within 0.05MPa, and controlling the temperature change rate between the two units to within 5℃ / h, a smooth transition of the material between different polymerization stages is ensured, avoiding flash evaporation, thermal degradation, or molecular chain damage caused by sudden pressure or temperature changes. This coordinated control helps to obtain flame-retardant nylon chip products with more uniform molecular weight distribution and superior performance.

[0047] In one embodiment, the extraction unit 60 of the integrated polymerization production system for flame-retardant nylon chips includes a pre-extraction water tank and an extraction tower for extracting the chips with demineralized water under heating conditions, and the extraction unit 60 is configured to ensure that the monomer content of the extracted chips is ≤0.1%.

[0048] In this embodiment, the pre-extraction tank can initially remove a large amount of monomers from the surface of the slices, effectively reducing the load on the subsequent extraction tower. The extraction tower further removes monomers from the interior of the slices through multi-stage countercurrent contact. Heating conditions significantly improve the solubility and diffusion rate of monomers, accelerating the extraction process, while the use of demineralized water avoids the introduction of impurities, ensuring product purity. During the extraction process, by controlling the extraction temperature, water-to-solid ratio, and time, and by periodically monitoring the monomer content of the extracted slices, it is ensured to be ≤0.1%, thereby significantly improving the thermal stability of the product.

[0049] In one embodiment, the drying unit 70 of the integrated polymerization production system for flame-retardant nylon chips includes a drying tower for drying wet chips in a segmented temperature-controlled nitrogen atmosphere, and the drying unit 70 is configured to ensure that the moisture content of the dried chips is ≤50ppm.

[0050] In this embodiment, a drying tower is used to dry the wet slices in a nitrogen atmosphere with segmented temperature control, which effectively solves the problems of incomplete drying or product degradation during the drying process. By controlling the nitrogen temperature, flow rate, and drying time, and monitoring the moisture content of the slices online, it is ensured that the moisture content of the dried slices is ≤50ppm, thus ensuring that the flame-retardant nylon slices will not undergo hydrolysis during subsequent processing.

[0051] In one embodiment, the integrated polymerization production system for flame-retardant nylon chips also includes a cooling silo 80, which is connected to a drying tower for cooling the dried chips to room temperature.

[0052] In this embodiment, after the flame-retardant nylon chips are dried, their temperature can be effectively reduced to room temperature.

[0053] The specific embodiments described above further illustrate the inventive purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the scope of protection of the present invention. In particular, it should be noted that any modifications, equivalent substitutions, or improvements made by those skilled in the art within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An integrated polymerization production system for flame-retardant nylon chips, characterized in that, Including those connected in series: A flame retardant preparation unit includes a preparation tank, which is used to mix and react a nitrogen-based flame retardant precursor with demineralized water to generate a flame retardant intermediate. The raw material mixing unit is connected to the flame retardant preparation unit and is used to mix the flame retardant intermediate with caprolactam, hexamethylenediamine adipate, and terephthalic acid to prepare a pre-reactant. The prepolymerization unit, connected to the raw material mixing unit, is used to perform a multi-stage pressure-temperature controlled prepolymerization reaction on the pre-reactant to generate a prepolymer. The post-polymerization unit, connected to the prepolymerization unit, is used to perform a pressure-vacuum pulse controlled post-polymerization reaction on the prepolymer to generate a polymer; A pelletizing unit, connected to the post-polymerization unit, is used to pelletize the polymer melt into slices; An extraction unit, connected to the pelletizing unit, is used to perform desalination extraction on the slices to remove unreacted monomers; A drying unit, connected to the extraction unit, is used to dry the extracted wet slices to obtain flame-retardant nylon slice products. The prepolymerization unit and the postpolymerization unit are equipped with pressure gradient linkage control and temperature curve matching; The prepolymerization unit includes a prepolymerization reactor, which sequentially executes three stages during the prepolymerization reaction, with each stage lasting one-third of the total prepolymerization reaction time. Specifically, the first stage has a pressure of 0.25–0.3 MPa and a temperature of 235–240°C; the second stage has a pressure of 0.15–0.2 MPa and a temperature of 240–245°C; and the third stage has a pressure of -0.1–0.05 MPa and a temperature of 245–250°C. The post-polymerization unit includes a post-polymerization reactor, and is configured to achieve a polymer viscosity of 2.4-2.

8. The post-polymerization unit executes the following sequentially over a total reaction time of 10 hours: Phase 1 (0-4 hours): pressure 0.05-0.10 MPa, temperature 250-255°C; Phase 2 (4-10 hours): each phase consists of a 60-minute pulse cycle. Within each cycle: the first 40 minutes have a vacuum of -0.06-0.08 MPa and a temperature of 255-258°C; the last 20 minutes have a pressure of 0.02-0.04 MPa and a temperature of 252-255°C. A controller is provided between the prepolymerization unit and the postpolymerization unit. The controller adjusts the inlet pressure of the postpolymerization unit according to the outlet pressure of the prepolymerization unit so that the pressure difference between the two is ≤0.05MPa, and adjusts the inlet temperature of the postpolymerization unit according to the outlet temperature of the prepolymerization unit so that the temperature change rate between the two is ≤5℃ / h.

2. The integrated polymerization production system for flame-retardant nylon chips according to claim 1, characterized in that, The precursors of the nitrogen-based flame retardant are melamine and cyanuric acid.

3. The integrated polymerization production system for flame-retardant nylon chips according to claim 2, characterized in that, The preparation tank is used to mix melamine, cyanuric acid and demineralized water at a predetermined molar ratio, and react them under heating and stirring conditions to generate a flame-retardant intermediate.

4. The integrated polymerization production system for flame-retardant nylon chips according to claim 1, characterized in that, In the raw material mixing unit, the weight ratio of caprolactam, hexamethylenediamine adipate, flame retardant intermediate, and terephthalic acid is 1:0.1~0.2:0.15~0.25:0.005~0.

01.

5. The integrated polymerization production system for flame-retardant nylon chips according to claim 1, characterized in that, The extraction unit includes a pre-extraction tank and an extraction tower for extracting demineralized water from the slices under heating conditions, and the extraction unit is configured to ensure that the monomer content of the extracted slices is ≤0.1%.

6. The integrated polymerization production system for flame-retardant nylon chips according to claim 1, characterized in that, The drying unit includes a drying tower for drying wet slices in a nitrogen atmosphere with segmented temperature control, and the drying unit is configured to ensure that the moisture content of the dried slices is ≤500ppm.

7. The integrated polymerization production system for flame-retardant nylon chips according to claim 6, characterized in that, It also includes a cooling silo, which is connected to the drying tower and is used to cool the dried slices to room temperature.

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