Bio-based polyamide in-situ polymerization process based on deep eutectic solvent, molecular weight regulation and control system and bio-based polyamide resin

Abstract

The invention relates to the technical field of high polymer material synthesis, in particular to a bio-based polyamide in-situ polymerization process based on a deep eutectic solvent, a molecular weight regulation and control system and bio-based polyamide resin.The process comprises the steps that bio-based monomers and DES with specific composition are mixed and subjected to polycondensation in a double-screw reaction extruder through microwave heating and pressure reduction, and the bio-based polyamide resin is obtained; in the reaction process, carboxyl consumption is monitored in real time by utilizing online near infrared spectroscopy, and itaconic acid monomers are accurately supplemented at a key conversion point, so that in-situ accurate regulation and control on the molecular weight of the polymer are realized; after the reaction, the DES skeleton can be recycled; the invention also protects the narrow-distribution bio-based polyamide resin prepared by the process and a special molecular weight regulation and control system for realizing the process. The technology solves the problems that a traditional technology is not environmentally friendly, molecular weight control is extensive, and bio-based monomers are easy to degrade.

Description

Technical Field

[0001] This invention relates to the field of polymer material synthesis technology, specifically to a bio-based polyamide in-situ polymerization process based on a deep eutectic solvent, a molecular weight control system, and a bio-based polyamide resin. Background Technology

[0002] Polyamide, as an important engineering plastic, has attracted much attention for its bio-based derivatives due to their green sustainability. Among them, rigid bio-based monomers, represented by 2,5-furandimethylamine, can endow polyamide with excellent heat resistance and mechanical properties, and are currently a research hotspot. However, there are still several technical problems that need to be solved in its synthesis process.

[0003] First, the solvent problem is prominent in traditional polymerization processes. Currently, the synthesis of bio-based polyamides mostly adopts high-temperature melt polycondensation or uses toxic, high-boiling-point organic solvents such as m-cresol as reaction media. These solvents are not only environmentally unfriendly, but also require complex purification steps to remove residual solvents in the post-processing, and are difficult to recycle, which contradicts the concept of green chemistry. Deep eutectic solvent DES, as a novel green solvent, is widely used in the field of biomass pretreatment, but its direct use as a reaction media for the in-situ polymerization of bio-based polyamides, especially aromatic polyamides containing furan ring structures, is still a blank. How to design a DES system that combines the functions of a reaction media and a specific function is a challenge.

[0004] Secondly, the molecular weight control precision in the polymerization process is insufficient. In polycondensation reactions, precise control of molecular weight and its distribution is crucial for obtaining high-performance resins. Current technologies often achieve rough molecular weight regulation by adding excess monomer at the initial stage of the reaction or by adding monofunctional end-capping agents, such as acetic acid or laurylamine, at the later stage. This method relies on ring-opening control and cannot respond to molecular weight fluctuations caused by side reactions or uneven monomer consumption during the reaction. This results in a wide molecular weight distribution in the final product, typically with a low molecular weight distribution index. This affects the uniformity and reliability of material properties;

[0005] Third, there is a lack of efficient and mild polymerization processes suitable for bio-based monomers. Bio-based aromatic monomers such as 2,5-furandimethylamine have poor thermal stability. Under traditional high-temperature conditions, usually exceeding 250°C, long-term polymerization can easily lead to side reactions such as furan ring opening and yellowing, resulting in darker product color and decreased performance. Therefore, developing a polymerization process that can be carried out under relatively mild conditions and can achieve precise monitoring and control of the process is crucial for the preparation of high-quality bio-based polyamides.

[0006] In summary, existing technologies lack a complete technical solution that can organically combine green solvents, in-situ polymerization, precise molecular weight control, and mild reaction conditions specifically for the preparation of high-performance bio-based polyamides. Summary of the Invention

[0007] The purpose of this invention is to provide a bio-based polyamide in-situ polymerization process, a molecular weight control system, and a bio-based polyamide resin based on a deep eutectic solvent;

[0008] The first aspect provides a bio-based polyamide in-situ polymerization process based on a deep eutectic solvent, comprising the following steps:

[0009] S1, 2,5-furandimethylamine and sebacic acid from a bio-based source are mixed with a deep eutectic solvent at a total molar ratio of 1:1:2.5 and stirred and dehydrated at 75°C and 10 kPa absolute pressure for 45 minutes to form a homogeneous salt solution;

[0010] The eutectic solvent is composed of choline chloride, itaconic acid and 1,3-propanediol in a molar ratio of 1:1:1;

[0011] S2, the homogeneous salt solution obtained in step S1 is pumped into a twin-screw reactive extruder, heated to 195°C under microwave frequency of 2.45 GHz and power density of 3.2 kW / kg material, and polycondensation reaction is carried out under an absolute pressure of 1.5 kPa;

[0012] S3, when the polycondensation reaction has proceeded for 75 minutes, the 1710 cm⁻¹ chromatogram is monitored using an online near-infrared spectrometer integrated into the extruder reaction section. -1 The peak area of ​​the characteristic carboxyl group is measured. When the peak area drops to 25%-35% of the initial value, itaconic acid monomer is added to the system in an amount equal to 1.0% of the initial sebacic acid mass.

[0013] S4, after a total reaction time of 120 minutes, the melt was extruded and cooled to 80°C, so that the choline chloride dissociated in the eutectic solvent could recombine with 1,3-propanediol to form a liquid phase; the recombined liquid phase complex was collected; the product was cooled in a water bath and pelletized to obtain bio-based polyamide resin.

[0014] Preferably, microwave irradiation employs segmented power control:

[0015] From the start of the reaction to 30 minutes, the power density was 3.2 kW / kg;

[0016] The reaction time was 30 to 90 minutes, and the power density was adjusted to 2.6 kW / kg.

[0017] After 90 minutes of reaction, the power density was maintained at 2.1 kW / kg until the reaction was completed.

[0018] Preferably, the screw configuration of the twin-screw reactive extruder, from the feed section to the devolatilization section, includes:

[0019] The conveying element section, the kneading block assembly section, the reverse thread element section, and the toothed disc element section located before the devouring section;

[0020] The shear rate of the kneading block assembly segment is controlled between 180-220 s. -1 The probe of the online near-infrared spectrometer is located at the end of the anti-threaded element section.

[0021] Preferably, after water bath cooling and pelletizing in step S4, a solid-phase thickening step is further included:

[0022] The obtained polyamide resin particles were treated at 170°C under inert gas protection for 8 hours.

[0023] The second aspect provides a bio-based polyamide resin prepared by a process, wherein the resin has a number-average molecular weight of 30,000-32,000 g / mol and a molecular weight distribution index of [missing information]. ;

[0024] The third aspect provides a molecular weight control system for a process, comprising:

[0025] The premixing unit includes a premixing vessel equipped with a vacuum degassing device and a temperature control system, used to prepare the deep eutectic solvent and homogeneous salt solution;

[0026] It is equipped with a vacuum degassing device and a temperature control system for preparing deep eutectic solvents and homogeneous salt solutions;

[0027] The twin-screw reactive extruder is sequentially configured with a feeding section, a microwave-heated reaction section, a molecular weight control section, and a devolatilization section along the material conveying direction.

[0028] The microwave-heated reaction section is equipped with a microwave magnetron;

[0029] The molecular weight control section integrates an online near-infrared probe and a linked micro-feed pump;

[0030] A solvent recovery unit, connected via pipeline to the outlet of the devolatilization section, is used to collect the liquid-phase complex formed by the recombination of choline chloride and 1,3-propanediol.

[0031] Preferably, the solvent recovery device is a receiving vessel.

[0032] The beneficial effects of this invention are as follows:

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] High catalytic efficiency and high coenzyme utilization are achieved by co-immobilizing 7α-hydroxysteroid dehydrogenase and coenzyme regeneration enzyme on the same carrier, creating a microreactor environment that allows for efficient NAD+ catalysis. + This method enables efficient in-situ cycling and regeneration between the active sites of two enzymes, using a low concentration of NAD+ (0.02 mg / mL). + It can achieve a conversion rate of up to 88.5%, and the amount of coenzyme used is 1 / 5 of that of the traditional free enzyme system, thus reducing production costs;

[0035] The catalyst is recyclable and has good operational stability. The enzyme complex uses magnetic mesoporous silica microspheres as a carrier. After the reaction, the catalyst can be quickly and completely separated by simply applying an external magnetic field. As shown in Experiment 2, after the enzyme complex is reused 10 times, the relative enzyme activity is still maintained at 86.5%, which effectively solves the industrialization problem of free enzymes being used once and costly.

[0036] The process is green and economical, and suitable for industrialization. This invention uses a one-step enzyme-catalyzed reaction under mild conditions, avoiding the environmental pollution and safety risks caused by the use of toxic oxidants in traditional chemical methods. At the same time, the reusability of the catalyst and the low coenzyme consumption reduce the overall production cost. Attached Figure Description

[0037] Figure 1 A process flow diagram of a bio-based polyamide in-situ polymerization process based on a deep eutectic solvent provided in Embodiment 1 of the present invention;

[0038] Figure 2 This is a comparison chart of the molecular weight distribution GPC curves of the bio-based polyamide resins obtained in Example 1 and Comparative Example 1 of the present invention.

[0039] Figure 3 This is a bar chart comparing the recovery rates of the eutectic solvent in Example 1 and Comparative Example 1 of the present invention.

[0040] Figure 4 The molecular weight distribution index of the resin in Examples 1, 2 and Comparative Example 1 of the present invention under different feed trigger points and deep eutectic solvent compositions. Comparison chart;

[0041] Figure 5 This is a DSC thermal analysis diagram of the bio-based polyamide resin in Example 1 of the present invention;

[0042] Figure 6 This is a schematic diagram of a bio-based polyamide in-situ polymerization process based on a deep eutectic solvent, provided in Embodiment 3 of the present invention. Detailed Implementation

[0043] To further illustrate the technical means and effects adopted by the present invention to achieve its intended purpose, exemplary embodiments will be described in detail below, examples of which are illustrated in the accompanying drawings. In the following description relating to the drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this application. Rather, they are merely examples of methods and systems consistent with some aspects of this application as detailed in the appended claims.

[0044] The terminology used in this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The singular forms “a,” “the,” and “the” used in this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used herein refers to and includes any or all possible combinations of one or more of the associated listed items.

[0045] To better illustrate the purpose, technical solution, and advantages of this application, the following detailed description, in conjunction with specific embodiments and experimental examples, aims to provide a thorough understanding of the application's content, rather than limiting it. All other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this application. Unless otherwise specified, the experimental reagents and instruments involved in the implementation of this application are commonly used and ordinary reagents and instruments. In this application, the open-ended technical features include both closed-ended technical solutions comprised of the listed features and open-ended technical solutions that include the listed features.

[0046] The following detailed description of the specific implementation methods, features, and effects of the present invention, in conjunction with the accompanying drawings and preferred embodiments, is provided in detail.

[0047] Example 1

[0048] Please refer to Figure 1-5 This embodiment provides a bio-based polyamide in-situ polymerization process based on a deep eutectic solvent;

[0049] Bio-based aromatic diamine, 2,5-furan dimethylamine, with a bio-based carbon content ≥98%, dried by molecular sieve before use;

[0050] Bio-based aliphatic dicarboxylic acid, sebacic acid, with a bio-based carbon content ≥99%;

[0051] The components of the deep eutectic solvent DES are: choline chloride (ChCl) ≥99%, itaconic acid ≥99%, and 1,3-propanediol ≥99%.

[0052] The twin-screw reactive extruder has a length-to-diameter ratio of 52:1. The screw configuration includes, in sequence: a conveying element section, a kneading block assembly section, a reverse thread element section, and a toothed disc element section.

[0053] The shear rate γ of the kneading block assembly segment is controlled between 180-220 s. -1 ;

[0054] The shear rate γ is calculated using the following formula:

[0055]

[0056] Where D is the screw diameter, N is the screw speed, and h is the screw groove depth. In this embodiment, the screw speed is controlled between 200-240 rpm.

[0057] Equipped with a microwave heating system with a frequency of 2.45 GHz and an online near-infrared monitoring probe, the probe is located at the end of the anti-threaded element section;

[0058] Vacuum drying oven, vacuum pump, analytical balance, receiving vessel;

[0059] Weigh out 100g of each component in a molar ratio of choline chloride:itaconic acid:1,3-propanediol = 1:1:1 and place it in a 250mL round-bottom flask.

[0060] At 75°C and 10 kPa absolute pressure, mechanically stir at 200 rpm for 45 minutes until a homogeneous and transparent liquid is formed, which is the desired DES. Cool to room temperature for later use.

[0061] 0.1 mol of bio-based 2,5-furandimethylamine and 0.1 mol of bio-based sebacic acid were added to 0.25 mol of the DES prepared above, based on the total molar amount of DES;

[0062] The total molar ratio of this bio-based diamine, bio-based dicarboxylic acid, and DES is 1:1:2.5;

[0063] The mixture was stirred at 75°C and 10 kPa absolute pressure for 45 minutes to dehydrate it and form a homogeneous salt solution.

[0064] Feeding and initial reaction: The resulting homogeneous salt solution is pumped into a twin-screw reactive extruder at a rate of 5 kg / h using a metering pump;

[0065] Microwave heating and polycondensation reaction: The microwave heating system is activated at a frequency of 2.45 GHz, using segmented power control.

[0066] From the start of the reaction to 30 minutes, the power density was 3.2 kW / kg of material;

[0067] The reaction time was 30 to 90 minutes, and the power density was adjusted to 2.6 kW / kg.

[0068] After 90 minutes of reaction, the power density was maintained at 2.1 kW / kg until the reaction was completed;

[0069] The reaction temperature was maintained at 195℃, the absolute pressure of the reaction system was controlled at 1.5 kPa, and the total reaction time was 120 minutes.

[0070] Online monitoring and molecular weight control are achieved through an online near-infrared spectrometer integrated at the end of the reverse thread element section of the reactive extruder, enabling real-time monitoring at 1710 cm⁻¹. -1 Changes in the peak area of ​​the characteristic carboxyl peak;

[0071] When the reaction proceeded for 75 minutes and the area of ​​the carboxyl peak decreased to 25% of the initial value, the system automatically triggered a micro-plunger pump to add itaconic acid monomer to the reaction system. The amount added was 1.0% of the initial sebacic acid mass.

[0072] After the reaction is complete, the molten polymer is extruded and cooled by a two-roller cooling belt;

[0073] DES recovery involves collecting the extruded material and cooling it to 80°C. At this temperature, the dissociated choline chloride recombines with 1,3-propanediol to form a liquid phase. This recombined DES liquid complex is collected in a receiving vessel. The calculated recovery rate of DES is 92%.

[0074] The polymer was processed, and the remaining polymer was cooled in a water bath and pelletized to obtain bio-based polyamide resin particles. The obtained resin particles were then treated at 170°C under high-purity nitrogen, i.e., inert gas protection, for 8 hours to perform solid-phase thickening.

[0075] The obtained bio-based polyamide resin was tested:

[0076] Molecular weight and distribution: The number-average molecular weight was determined by gel permeation chromatography (GPC) to be 31,500 g / mol, and the molecular weight distribution index was [not specified]. It is 1.52;

[0077] The bio-based carbon content, measured according to ASTM D6866-22 standard, is 65%.

[0078] Thermal properties, determined by differential scanning calorimetry (DSC), show a melting point of 128℃.

[0079] Example 2

[0080] The difference between this embodiment and Embodiment 1 is that the timing of the online monitoring for material replenishment is adjusted, as follows:

[0081] In-situ polymerization and molecular weight control: The homogeneous salt solution prepared as described in Example 1 was pumped into a twin-screw reactive extruder, and the microwave heating and polycondensation reaction conditions were the same as in Example 1.

[0082] The peak area change of the carboxyl characteristic peak at 1710 cm⁻¹ was monitored in real time by an online near-infrared spectrometer integrated at the end of the anti-thread element section of the reactive extruder.

[0083] When the reaction proceeded for 60 minutes, the area of ​​the carboxyl peak was observed to decrease to 35% of the initial value. The system automatically triggered a feed replenishment, adding itaconic acid monomer to the system. The amount added was 1.0% of the initial sebacic acid mass, the same as in Example 1.

[0084] The subsequent DES recovery, polymer treatment, and solid-phase thickening steps are the same as in Example 1;

[0085] The final bio-based polyamide resin was characterized as follows:

[0086] Molecular weight and distribution: Number average molecular weight is 30,800 g / mol, molecular weight distribution index is [not specified]. It is 1.54;

[0087] The bio-based carbon content is 63%;

[0088] As in Example 1, when the carboxyl peak area decreased to 30%, feed was added. In comparison, in this embodiment, when the carboxyl peak area decreased to 35%, i.e., when the feed was added earlier, the molecular weight distribution of the resulting polymer was slightly broadened. .

[0089] Comparative Example 1

[0090] The difference between this embodiment and Embodiment 1 is that the molar ratio of each component in the deep eutectic solvent DES is changed, as follows:

[0091] Weigh out 100g of each component in a molar ratio of choline chloride:itaconic acid:1,3-propanediol = 1:1.2:0.8, place them in a 250mL round-bottom flask, and mechanically stir at 200rpm for 45 minutes at 75℃ and 10kPa absolute pressure until a homogeneous and transparent liquid is formed. This is the desired DES. Cool to room temperature for later use.

[0092] 0.1 mol of bio-based 2,5-furandimethylamine and 0.1 mol of bio-based sebacic acid were added to the DES prepared above, totaling 0.25 mol, based on the total molar amount of DES.

[0093] The total molar ratio of this bio-based diamine, bio-based dicarboxylic acid, and DES is 1:1:2.5;

[0094] The mixture was stirred at 75°C and 10 kPa absolute pressure for 45 minutes to dehydrate it and form a homogeneous salt solution.

[0095] Feeding and reaction: The resulting homogeneous salt solution is pumped into a twin-screw reactive extruder at a rate of 5 kg / h using a metering pump;

[0096] Microwave heating and polycondensation reaction: The microwave heating system is activated at a frequency of 2.45 GHz, using segmented power control.

[0097] From the start of the reaction to 30 minutes, the power density was 3.2 kW / kg of material;

[0098] The reaction time was 30 to 90 minutes, and the power density was adjusted to 2.6 kW / kg.

[0099] After 90 minutes of reaction, the power density was maintained at 2.1 kW / kg until the reaction was completed;

[0100] The reaction temperature was maintained at 195℃, the absolute pressure of the reaction system was controlled at 1.5 kPa, and the total reaction time was 120 minutes.

[0101] Online monitoring and molecular weight control are achieved through an online near-infrared spectrometer integrated at the end of the reverse thread element section of the reactive extruder, enabling real-time monitoring at 1710 cm⁻¹. -1 Changes in the peak area of ​​the characteristic carboxyl peak;

[0102] When the reaction proceeded for 70 minutes, the area of ​​the carboxyl peak was observed to decrease to 35% of the initial value. The system automatically triggered a micro-plunger pump to add itaconic acid monomer to the reaction system, with the added amount being 1.0% of the initial sebacic acid mass.

[0103] After the reaction is complete, the molten polymer is extruded;

[0104] DES recovery involves collecting the extruded material and cooling it to 80°C. At this temperature, the dissociated choline chloride recombines with 1,3-propanediol to form a liquid phase. This recombined DES liquid complex is collected in a receiving vessel. The calculated recovery rate of DES is 88%.

[0105] Polymer treatment and solid-phase thickening: The remaining polymer is cooled in a water bath and granulated to obtain bio-based polyamide resin particles. The obtained resin particles are treated at 170°C and under high-purity nitrogen protection for 8 hours to perform solid-phase thickening.

[0106] Tests were conducted on the solid-phase thickened bio-based polyamide resin:

[0107] Molecular weight and distribution were determined by gel permeation chromatography (GPC). The number-average molecular weight (Mn) was 29,800 g / mol, and the molecular weight distribution index was [not specified]. It is 1.68;

[0108] The bio-based carbon content, measured according to ASTM D6866-22 standard, is 61%.

[0109] Thermal properties, measured by differential scanning calorimetry (DSC), show a glass transition temperature of 125°C.

[0110] This comparative example demonstrates that simply changing the molar ratio of the DES components from 1:1:1 to 1:1.2:0.8, even with all other process parameters remaining identical, leads to a deterioration in the molecular weight distribution of the product and a broadening of the molecular weight distribution of the resulting polymer. Furthermore, the DES recovery rate decreased by 88%, indicating that the specific composition of DES (1:1:1) is a key factor in achieving molecular weight control and efficient solvent recovery.

[0111] Comparative Example 2

[0112] Please refer to Figure 2-4 This comparative example follows the steps of Example 1, but step S3 is not performed during the reaction process. Specifically:

[0113] The area of ​​the carboxyl characteristic peak at 1710 cm⁻¹ was monitored without activating the online near-infrared monitoring system;

[0114] No material replenishment trigger check is performed;

[0115] No itaconic acid monomer is added to the system;

[0116] The polymerization process relies entirely on the initial feed during the reaction;

[0117] Tests were conducted on the solid-phase thickened bio-based polyamide resin:

[0118] The molecular weight and distribution were determined by gel permeation chromatography (GPC), with a number-average molecular weight of 28,500 g / mol and a molecular weight distribution index (K) of 1.95.

[0119] The bio-based carbon content, measured according to ASTM D6866-22 standard, is 62%.

[0120] The DES recovery rate, as calculated, is 90%.

[0121] Even if all the preferred conditions of the present invention are fully replicated, the lack of the core step of online monitoring and feeding results in the molecular weight distribution index deteriorating from 1.52 to 1.95.

[0122] Example 3

[0123] Please refer to Figure 6This embodiment provides a molecular weight control system for the above-described process, as follows:

[0124] The molecular weight control system is an integrated continuous operation platform that achieves precise control of the molecular weight of bio-based polyamide resin through the coordinated operation of three core units: a premixing tank, a twin-screw reactive extruder, and a solvent recovery device.

[0125] The premixing unit, the system includes a premixing vessel, which is a key piece of equipment for the preparation of deep eutectic solvent DES and the synthesis of homogeneous salt solutions;

[0126] The premixing vessel is equipped with a vacuum degassing device and a temperature control system. Specifically, a jacketed reactor can be used, and the temperature control system can achieve precise temperature control through circulating heat transfer oil in the jacket. The temperature control range is from room temperature to 100℃, with an accuracy of ±1℃.

[0127] The vacuum degassing device is connected to a vacuum pump, which can maintain the required absolute pressure in the premixing vessel during operation, such as 10 kPa, thereby effectively removing moisture and air from the system and ensuring the purity of DES and the stability of the homogeneous salt solution.

[0128] The premixing tank unit is mainly used to perform step S1, which is to mix bio-based monomers and DES in a total molar ratio of 1:1:2.5 and stir and dehydrate them for 45 minutes at 75°C and 10 kPa absolute pressure to form a homogeneous salt solution.

[0129] The twin-screw reactive extruder unit has a twin-screw reactive extruder as its core. Along the material conveying direction, the extruder is sequentially equipped with a feeding section, a microwave-heated reaction section, a molecular weight control section, and a devolatilization section, thereby realizing a continuous process of material conveying, reaction, monitoring, and devolatilization.

[0130] The feeding section, located at the extruder inlet, uses a metering pump to stably and continuously pump the homogeneous salt solution prepared in the premixing vessel into the extruder;

[0131] The microwave-heated reaction section is equipped with a microwave magnetron in the extruder barrel, which generates microwaves at a frequency of 2.45 GHz. The magnetron power is adjusted by the control system to achieve segmented power control. For example, the power density is 3.2 kW / kg from the start of the reaction to 30 minutes; the power density is adjusted to 2.6 kW / kg from 30 to 90 minutes; and the power density is maintained at 2.1 kW / kg after 90 minutes. This section provides energy for the polymerization reaction, enabling the material to undergo polycondensation at a temperature of 195°C and an absolute pressure of 1.5 kPa.

[0132] The molecular weight control section is the core of achieving precise molecular weight control, and it integrates an online near-infrared probe and a linked micro-feeding pump.

[0133] The online near-infrared probe is embedded in the extruder barrel via a flange sealing device, with its probe head directly contacting the molten polymer for real-time monitoring at 1710 cm⁻¹. -1 Changes in the peak area of ​​the characteristic carboxyl peak;

[0134] The near-infrared probe transmits the collected spectral signals to the central processing unit, such as a PLC or industrial computer, in real time. When the software algorithm determines that the area of ​​the carboxyl peak has dropped to a preset threshold of 25%-35% of the initial value, the processor will immediately send an instruction to the micro-feed pump.

[0135] Upon receiving an instruction, the micro-feed pump precisely injects a specific amount of itaconic acid monomer into the extruder reaction system, with the addition amount being 1.0% of the initial sebacic acid mass. This closed-loop feedback control system ensures the timeliness and accuracy of molecular weight control.

[0136] The devolatilization section, located at the end of the extruder, is equipped with at least one vacuum exhaust port. An absolute pressure of 1.5 kPa is maintained by an external vacuum system to effectively remove small molecule byproducts generated in the reaction, such as water vapor, thereby shifting the reaction equilibrium in the positive direction and purifying the polymer melt.

[0137] The system also includes a solvent recovery unit;

[0138] The device is connected to the outlet of the devolatilization section via a pipeline to collect the liquid complex formed by the recombination of melt material containing dissociated DES components extruded from the extruder during subsequent cooling.

[0139] Specifically, the solvent recovery device can be a receiving vessel, in which the melt that has completed the reaction from the devolatilization section of the extruder is introduced into a receiving vessel cooled to below 80°C. At this temperature, the choline chloride and 1,3-propanediol that have dissociated in the eutectic solvent will recombine into a liquid phase and separate from the solid polyamide resin. The receiving vessel serves as a simple liquid phase collection container, which facilitates the subsequent centralized processing and reuse of the recovered DES complex.

[0140] Specifically, the study reveals how the system deeply integrates the green solvent characteristics of DES, efficient microwave heating, and online near-infrared real-time monitoring technology with the reactive extrusion process through the orderly connection and synergy of units such as premixing, reactive extrusion, online monitoring and feeding, devolatilization and solvent recovery, ultimately achieving precise control of the molecular weight of bio-based polyamide and recycling of solvents.

[0141] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit the scope of protection of this application. Although this application has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this application without departing from the substance and scope of the technical solutions of this application.

Claims

1. A deep eutectic solvent based bio-based polyamide in-situ polymerization process characterized in that, Comprising the following steps: S1, mixing bio-based 2,5-furandimethanamine, bio-based sebacic acid and deep eutectic solvent in a total molar ratio of 1:1:2.5, stirring at 75℃ under an absolute pressure of 10kPa for 45 minutes to form a homogeneous salt solution; The deep eutectic solvent is composed of choline chloride, itaconic acid and 1,3-propanediol in a molar ratio of 1:1:1; S2, pumping the homogeneous salt solution obtained in step S1 into a twin-screw reaction extruder, heating to 195℃ under the condition of microwave frequency 2.45GHz and power density 3.2kW / kg of material, and carrying out polycondensation reaction under an absolute pressure of 1.5kPa; S3, when the condensation reaction is carried out for 75 minutes, the peak area of the characteristic peak of carboxyl at 1710 cm is monitored by the online near infrared spectrometer integrated in the reaction section of the extruder -1 When the peak area of the characteristic peak of carboxyl at 1710 cm is reduced to 25%-35% of the initial value, monomer itaconic acid is added to the system, and the amount of addition is 1.0% of the initial sebacic acid. S4, after a total reaction time of 120 minutes, extruding the melt and cooling to 80℃ to re-complex the dissociated choline chloride in the deep eutectic solvent with 1,3-propanediol into a liquid phase; collecting the recombined liquid phase complex; the product is cooled in a water bath, granulated, to obtain a bio-based polyamide resin.

2. The process according to claim 1, characterized in that, The microwave irradiation adopts segmented power control: From the start of the reaction to 30 minutes, the power density is 3.2kW / kg; From 30 to 90 minutes of reaction, the power density is adjusted to 2.6kW / kg; After 90 minutes of reaction, the power density is maintained at 2.1kW / kg until the end of the reaction.

3. The process of claim 1, wherein, The screw configuration of the twin-screw reaction extruder, from the feeding section to the devolatilization section, includes in order: Conveying element section, kneading block combination section, reverse threaded element section, and toothed disc element section located before the devolatilization section; The shear rate of the kneading block combination section is controlled at 180-220 s -1 The probe of the online near-infrared spectrometer is arranged at the end of the reverse thread element section.

4. The process of claim 1, wherein, After the water bath cooling and granulation in step S4, a solid phase tackifying step is further included: The obtained polyamide resin particles are treated at 170℃ under inert gas protection for 8 hours.

5. A bio-based polyamide resin prepared by the process of any one of claims 1-4, characterized in that, The number average molecular weight of the resin is 30000-32000 g / mol, the molecular weight distribution index .

6. A molecular weight control system for use in the process of any one of claims 1-4, characterized in that, Comprising: A premix kettle unit, the system includes a premix kettle provided with a vacuum degassing device and a temperature control system, for preparing the deep eutectic solvent and the homogeneous salt solution; A twin-screw reaction extruder, which is provided with a feeding section, a microwave heating reaction section, a molecular weight control section and a devolatilization section in order along the material conveying direction; The microwave heating reaction section is configured with a microwave magnetron; The molecular weight control section is integrated with an online near-infrared probe and a micro-feeding pump linked thereto; A solvent recovery device connected by pipeline to the outlet of the devolatilization section for collecting the liquid phase complex formed by the recombination of choline chloride and 1,3-propanediol.

7. The molecular weight regulation system of claim 6, wherein, The solvent recovery device is a receiving kettle.

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