Bio-based nylon 12 prepared by one-step method as well as preparation method and application of bio-based nylon 12

Abstract

The invention discloses bio-based nylon 12 prepared by a one-step method and a preparation method and application thereof, and belongs to the technical field of polyamide materials, the method comprises the following steps: (1) material preparation: mixing bio-based 12-amino dodecanoic acid, water and a reaction aid in a material preparation tank to form a suspension; (2) feeding: adding the turbid liquid into a polymerization kettle through nitrogen pressurization; and (3) polymerizing: sequentially executing the following operations through a control system: heating and boosting, constant-temperature and pressure maintaining, heating and pressure reducing, constant-temperature and normal-pressure, constant-temperature vacuum, nitrogen boosting, water-cooling, bracing and pelletizing to obtain the bio-based nylon 12. According to the invention, through comprehensive optimization of the process flow and precise control of key nodes and matching of a specific reaction auxiliary agent, the process for obtaining nylon 12 by polymerization with bio-based 12-amino dodecanoic acid as a monomer is finally realized through a one-step method, continuous production can be realized, precise control of polymer molecular weight distribution is also realized, the molecular weight distribution is narrow, and the production cost is low. The product viscosity is uniform.

Description

Technical Field

[0001] The present application relates to a bio-based nylon 12 prepared by a one-step method, a preparation method and an application thereof, belonging to the technical field of polyamide materials. Background Art

[0002] Long-chain nylon 12 has excellent properties such as low density, low water absorption, good dimensional stability of processed parts, good thermal stability, good toughness and flexibility, and also has advantages such as oil resistance, low temperature resistance, corrosion resistance and wear resistance. Nylon 12 prepared by traditional chemical industry is widely used in fields such as automobiles, chemical and petroleum pipelines, hydraulic transmission systems, and electronic, electrical, plastic alloys and aerospace and military equipment. At present, there are four foreign enterprises, Arkema, Swiss EMS, UBE, and Evonik, in large-scale production of nylon 12 in domestic manufacturers. In recent years, only one domestic enterprise, Wanhua Chemical, has broken the foreign monopoly and joined the production ranks.

[0003] At present, there are two process routes for synthesizing nylon 12: One is to prepare nylon 12 by ring-opening polymerization with laurolactam as the raw material, and the other is to polymerize nylon 12 with 12-aminododecanoic acid (lauric acid) as the monomer raw material. Laurolactam uses butadiene as the raw material to obtain cyclododecatriene as the intermediate, which is a chemical process route. The synthesis route is very long, up to 7 steps, and about 10% of the primary product has residual monomers to be extracted and refined, and the production process is long and the cost is high. The domestic enterprise Wanhua Chemical and the four foreign enterprises, Arkema, Swiss EMS, UBE, and Evonik, in large-scale production basically adopt this process route. Among them, Wanhua Chemical has a related patent CN106866956B - A multi-stage tandem polymerization method of poly(dodecanolactam) and its modified resin, which realizes production by using multi-stage reaction kettles. Although it can continuously produce, this process route is still relatively complex, the synthesis route is long, and the energy consumption and cost are large.

[0004] Another process route is to prepare nylon 12 with 12-aminododecanoic acid as the monomer raw material. The synthesis route is shorter than that of synthesizing laurolactam, the investment in equipment cost is low, and the comprehensive production cost is low. However, due to the high reactivity of 12-aminododecanoic acid, if the reaction process is not well controlled, problems such as explosive polymerization, depolymerization, or yellowing of the polymer will occur.

[0005] In Chinese Patent CN107312170B - A process for preparing nylon 12 using long-chain amino acids as monomers, 12-aminododecanoic acid is used as the monomer and prepared by a three-step method. Specifically, a pre-polymerization kettle, a polymerization kettle and a melt metering pump are used for segmented and stepwise polymerization, and finally a twin-screw extruder is used for viscosity increase to obtain nylon 12. Its main advantage is that high-viscosity and high-molecular-weight chips can be directly produced.

[0006] However, in actual applications, the following problems still exist in this technical solution: 1. This solution cannot be continuously produced in actual production. Its solution is a three-step method. After the production in the first reactor is completed, the temperature inside the reactor and in the jacket is still very high (about 240°C - 270°C). Raw materials, auxiliary materials, and normal temperature water cannot be added immediately, and it is very difficult to achieve continuous production in intermittent polymerization.

[0007] 2. In the examples of its specification, it is stated that the molecular weight distribution index (PDI) of the finally produced nylon 12 products is between 2.3 - 2.6. This indicates that the three-step method it adopts still fails to solve the problems of controlling the polymerization rate and the reaction process during the reaction. In the final system, the molecular weight distribution is wide. The wider the molecular weight distribution, the greater the difference in molecular weights in the polymer, and the distribution is uneven. That is, its normal distribution of molecular weights is still poor, and the product quality needs to be improved.

[0008] 3. The entire production cycle is long (about 8 - 12h), and there are many production equipment. The energy consumption required for heating and heat preservation is high, and the total production cost is high. Summary of the Invention

[0009] To solve the above problems, the present application provides a method for preparing bio-based nylon 12 by a one-step method, its preparation method and application. Through comprehensive optimization of the process flow and precise control of key nodes, and by matching specific reaction aids, finally, the process of polymerizing bio-based 12-aminododecanoic acid as a monomer to obtain nylon 12 is completed by a one-step method (i.e., in the same reaction kettle). It can not only be continuously produced with a short production cycle, but also achieve precise control of the molecular weight distribution of the polymer. The molecular weight distribution index of the prepared products is less than 2, the molecular weight distribution is narrow, the product viscosity is uniform, and the quality is stable. At the same time, for the bio-based nylon 12 finally prepared in the present application, the polymer system has a high yield, the residual amount of the remaining monomer is small and non-toxic, and it is green and environmentally friendly, and can be used in fields such as clothing, daily necessities, and medical packaging.

[0010] According to one aspect of the present application, a preparation method for preparing bio-based nylon 12 by a one-step method is provided, including the following steps: (1) Preparation of materials: Mix bio-based 12-aminododecanoic acid, water, and reaction aids in a preparation tank to form a suspension; (2) Feeding: Add the suspension to the polymerization kettle through nitrogen pressurization; (3) Polymerization: The following operations are sequentially performed through a control system: i. Heating and pressurizing: Start stirring, heat up to 175 - 185°C, and increase the pressure to 0.8 - 1.5 MPa; ii. Constant temperature and pressure holding: Keep the temperature not higher than 185°C, the pressure remains stable, gradually drain the water. After the water in the material is drained, the temperature will automatically rise. The temperature of the material is not higher than 220°C. When the temperature of the material rises to a certain temperature, gradually reduce the pressure in stages, but it is necessary to always maintain the pressure not less than 0.6 MPa; iii. Heating and pressure reduction: The material is gradually heated, and the pressure is reduced to atmospheric pressure. The temperature of the material is controlled at 230°C - 270°C; iv. Constant temperature and atmospheric pressure: Keep the temperature constant, and purge with nitrogen for 0.5 - 1 h for balance; v. Constant temperature and vacuum: Keep the temperature constant, and evacuate to 0.06 - 0.09 MPa; vi. Nitrogen pressurization: Discharge the polymerized melt by nitrogen pressurization, and obtain bio - based nylon 12 through water - cooling, strand - drawing and pelletizing; Among them, the reaction aids include a catalyst, an antioxidant and a molecular weight regulator, and the addition amounts are 0.005 - 0.04%, 0.01 - 0.5% and 0.02 - 0.5% of the total raw material mass respectively; the mass proportion of adipic acid in the molecular weight regulator is not less than 60%.

[0011] Optionally, in step (1), the mass ratio of bio - based 12 - aminododecanoic acid to water is 1:(1 - 2), and it is heated to 70 - 120°C and stirred and mixed evenly.

[0012] Specifically, the polymerization kettle of the present application is equipped with a special feeding tank, which can immediately press the mixed and temperature - suitable raw material suspension into the polymerization kettle in a waiting state by nitrogen pressure, so as to realize seamless intermittent polymerization continuous production. The control system used in step (3) is a DCS control system.

[0013] Optionally, in the constant - temperature and constant - pressure stage of step (3), the polymerization dehydration time is 2 - 3.5 h; the trigger temperature for step - by - step pressure reduction is 205 - 215°C, and the pressure reduction rate is 0.05 - 0.1 MPa / min. Preferably, the trigger temperature is 210°C.

[0014] Optionally, in the constant - temperature and atmospheric - pressure stage of step (3), the nitrogen purge flow rate is 0.5 - 1.5 L / min, and the initial flow rate is higher than the final flow rate.

[0015] Specifically, in the constant - temperature and atmospheric - pressure stage of step (3), the nitrogen purge includes three gradient stages in sequence: a. 0 - 20 min, flow rate 1.5 L / min; b. 20 - 40 min, flow rate 1.0 L / min; c. 40 - 60 min, flow rate 0.6 L / min.

[0016] Furthermore, in the process of researching the one - step method for preparing bio - based nylon 12 with 12 - aminododecanoic acid as a monomer, the inventors of the present application found that there are two core problems in the polymerization process of 12 - aminododecanoic acid: The first problem is that when the temperature rises to near the melting point, the polymerization reaction will occur rapidly. At this time, if the pressure and temperature control are improper, problems such as explosive polymerization, depolymerization, and coking and yellowing of the polymer will occur.

[0017] Therefore, in the second stage of polymerization, i.e., the isothermal and isobaric stage, the present application first precisely controls the polymerization dehydration temperature not to exceed 185°C, maintains the pressure stable and controls the drainage time, so that it is in a solid-liquid coexistence state at this stage, the lattice gap expands, enabling efficient diffusion of water molecules. At the same time, the pressure is controlled to maintain the existence of liquid water, avoiding volume expansion caused by premature vaporization and damaging the material structure. Meanwhile, due to the enthalpy change of the polycondensation reaction, heat is released during the process of water removal, and the material temperature will automatically rise, starting the melt polymerization. In order to further remove water and other impurities to increase the viscosity, and at the same time avoid yellowing, the present application stipulates that the pressure starts to be gradually reduced when the temperature reaches the trigger temperature, and the minimum pressure should be maintained above 0.6 MPa. At this time, the melt stability is maintained by high pressure, while the reverse polycondensation reaction is inhibited, enabling the material to polymerize stably and fully discharge water molecules. If the material temperature rises too high before the pressure is reduced in this stage, the product will coke and turn yellow; if the pressure is lower than 0.6 MPa, the molecular chains will depolymerize and the water cannot be fully discharged.

[0018] The second problem, which is also the most significant feature different from other nylons, is that due to its too fast polymerization rate, many small molecules do not have time to be discharged out of the polymer system. The slower the discharge becomes as the viscosity increases in the later stage of polymerization, ultimately resulting in uneven viscosity, too wide molecular weight distribution, and even inability to draw and pellet normally.

[0019] In response to this, the present application first blows an appropriate amount of nitrogen in the fourth stage of polymerization (isothermal and atmospheric pressure stage), and controls the initial flow rate of nitrogen to be higher than the final flow rate. The initial high flow rate makes the nitrogen form a turbulent flow on the melt surface, forming a vortex to peel off the boundary layer, accelerating the removal of free small molecules (water, oligomers, other organic substances, etc.). The intermediate transition flow continuously removes the substances remaining at the crystal boundary, and the later laminar flow maintains the stable state of the material.

[0020] Optionally, the molecular weight regulator at least includes adipic acid, and also includes acetic acid and / or benzoic acid.

[0021] Preferably, the molecular weight regulator includes adipic acid and acetic acid with a mass ratio of 3:1; or, the molecular weight regulator includes adipic acid and benzoic acid with a mass ratio of 7:3; or, the molecular weight regulator includes adipic acid, acetic acid and benzoic acid with mass ratios of 6:2:2 in sequence. Specifically, by using adipic acid and defining it as the main regulator, the carboxylic acid groups of adipic acid act as Bronsted acids, protonating the amino groups, reducing the nucleophilic activation energy of the amino groups. The protonated amino groups are more likely to attack the carbonyl oxygen of the carboxylic acid, forming amide bonds, which can assist in catalyzing and accelerating polycondensation in the early stage of the polymerization reaction, maintain stability during the mid-stage reaction, promote the improvement of monomer conversion rate, and achieve efficient chain termination and capping in the late stage of polymerization, effectively controlling the molecular weight distribution; defining its proportion can maintain linear control of the molecular weight while promoting the effective removal of water molecules. Additionally, if it is used in combination with acetic acid and benzoic acid, their synergistic effects can also inhibit the formation of oligomers to a certain extent and further optimize the molecular weight distribution.

[0022] Optionally, the catalyst is one or more of phosphoric acid, sodium phosphite, and sodium hypophosphite.

[0023] Optionally, the antioxidant is one or more of antioxidant 1010, antioxidant H10, and antioxidant 1098.

[0024] Optionally, in step (2), the suspension is pressed into the polymerization kettle by increasing the nitrogen pressure to 0.2 - 0.5 MPa.

[0025] Optionally, in step (3), during the heating and pressurizing stage, the stirring speed is 130 - 150 rpm and the time is 1 - 2 h; During the heating and depressurizing stage, the time is 1 - 1.5 h, and the pressure is gradually reduced to atmospheric pressure. The depressurization rate depends on the initial pressure and time of this stage; during the constant temperature and vacuum stage, the time is 30 - 60 min; during the nitrogen pressure increasing stage, the time is 10 - 15 min and the pressure is 0.2 - 0.5 MPa.

[0026] According to another aspect of the present application, there is also provided a bio-based nylon 12 prepared by the above preparation method. The molecular weight distribution index of the bio-based nylon 12 is 1.8 - 1.95, and the weight average molecular weight is 26000 - 30000.

[0027] According to still another aspect of the present application, there is also provided the application of the bio-based nylon 12 prepared by the above preparation method. The bio-based nylon 12 can be used for clothing, food packaging materials, and pharmaceutical packaging materials.

[0028] The beneficial effects of the present application include but are not limited to: 1. According to the one-step method for preparing bio-based nylon 12 of the present application, by adopting a feed tank to match the single-kettle six-stage full-process control, the entire polymerization process is integrated and completed in a single polymerization kettle, realizing one-step high-efficiency continuous production. The production cycle is compressed from 12 - 15 h to 6 - 8 h, significantly shortening the production cycle and having high production efficiency.

[0029] 2. The method for preparing bio-based nylon 12 by a one-step process according to the present application controls the temperature and pressure in the key polymerization stage (constant temperature and pressure stage). While achieving sufficient dehydration, it effectively controls the polymerization rate. Then, through gradient nitrogen purging, small molecule impurities are effectively removed. In combination with a specific molecular weight regulator, precise control of the molecular weight is achieved. The final product has a narrow molecular weight distribution (1.8 - 1.95), uniform viscosity, stable quality, and high yield.

[0030] 3. The method for preparing bio-based nylon 12 by a one-step process according to the present application uses bio-based raw material monomers and controls the temperature-pressure coordination in the constant temperature and pressure stage of the polymerization stage to improve the monomer conversion rate. At the same time, the combined use of gradient nitrogen purging and vacuum devolatilization can efficiently remove the remaining monomers. Finally, the amount of residual monomers in the product is small, it is green, environmentally friendly, and harmless, and can meet the applications in the fields of clothing, food, pharmaceutical packaging materials, etc., promoting the green upgrade of the industrial chain. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings required for use in the embodiments or the description of the prior art. Obviously, the following drawings are only some embodiments of the present application. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0032] Figure 1 It is the chromatogram of nylon 12 prepared by using Example 1 of the present application; Figure 2 It is the chromatogram of nylon 12 prepared by using Example 4 of the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0033] The present application will be described in detail below in conjunction with the embodiments, but the present application is not limited to these embodiments.

[0034] Unless otherwise defined, all professional and scientific terms used herein have the same meaning as those familiar to those skilled in the art. The reagents or raw materials used in the present invention can be obtained through conventional channels. Unless otherwise specified, the reagents or raw materials used in the present invention are used in the conventional manner in the art or in accordance with the product instructions. In addition, any methods and materials similar or equivalent to the described content can be applied to the method of the present invention. The preferred implementation methods and materials described in this patent are only for demonstration purposes.

[0035] Among them, the bio-based 12-aminododecanoic acid used in this application is a commercially available product and is derived from biological resources such as vegetable oils like castor oil. The polymerization kettle used in this application is a commercially available configuration with an external jacket + internal coil double heating system and is equipped with a reaction feed tank. In the first two steps (heating and pressurizing, and constant temperature and pressure maintaining processes) of the polymerization step in this application, the materials are polymerized in an environment equivalent to a nitrogen atmosphere. However, nitrogen, other gases, as well as moisture and other small molecule substances will gradually be discharged during the constant temperature and pressure maintaining process. The water used in the preparation method is high-purity water or demineralized water, and the normal pressure refers to the standard atmospheric pressure; the dosage of bio-based 12-aminododecanoic acid in the examples is 5 kg.

[0036] Example 1 of Bio-based Nylon 12-1# The preparation method of bio-based nylon 12-1# includes the following steps: (1) Preparation of materials: Mix bio-based 12-aminododecanoic acid, water, and reaction aids in the feed tank to form a suspension; (2) Feeding: Add the suspension into the polymerization kettle through nitrogen pressurization; (3) Polymerization: Sequentially perform the following operations through the control system: i. Heating and pressurizing: Start stirring, heat up to 180 °C, and increase the pressure to 1.2 MPa; ii. Constant temperature and pressure maintaining: Keep the temperature not higher than 185 °C, keep the pressure stable, gradually discharge the water. After the water in the materials is discharged, the temperature will automatically rise. The temperature of the materials is not higher than 220 °C. When the temperature of the materials rises to a certain temperature, start to reduce the pressure in stages, but always maintain the pressure not less than 0.6 MPa; iii. Heating and pressure reduction: Gradually heat up the materials, reduce the pressure to normal pressure, and control the temperature of the materials at 240 °C; iv. Constant temperature at normal pressure: Keep the temperature constant and purge with nitrogen for 1 h; v. Constant temperature under vacuum: Keep the temperature constant and evacuate to 0.06 MPa; vi. Nitrogen pressurization: Discharge the polymerized melt through nitrogen pressurization, and obtain bio-based nylon 12-1# by water-cooling, strand drawing, and pelletizing.

[0037] Among them, in step (1), the mass ratio of bio-based 12-aminododecanoic acid to water is 1:1, heat up to 80 °C, stir and mix evenly, and the stirring rate is 100 rpm; the reaction aids include a catalyst, an antioxidant, and a molecular weight regulator, and the addition amounts are 0.02%, 0.1%, and 0.2% of the total raw material mass respectively; the molecular weight regulator is adipic acid; the catalyst is phosphoric acid; the antioxidant is antioxidant 1010.

[0038] In step (2), the suspension is pressed into the polymerization kettle by nitrogen pressurization of 0.3 MPa.

[0039] In step (3), the stirring speed during the heating and pressurizing stage is 140 rpm and the time is 1.5 h; during the constant temperature and pressure maintaining stage, the polymerization and dehydration time is 2 h, the triggering temperature for stepwise pressure reduction is 210 °C, and the pressure reduction rate is 0.08 MPa / min; the time for the heating and pressure reduction stage is 1.2 h; during the constant temperature and normal pressure stage, the nitrogen purge flow rate in the first half of the time is 1.2 L / min, which is 0.5 L / min higher than the purge flow rate in the second half of the time. The time for the constant temperature and vacuum stage is 45 min; the time for the nitrogen pressurization stage is 12 min and the pressure is 0.3 MPa.

[0040] Example 2: Bio-based Nylon 12-2# The preparation method of bio-based nylon 12-2# comprises the following steps: (1) Material preparation: Mix bio-based 12-aminododecanoic acid, water and reaction aids in a preparation tank to form a suspension; (2) Feeding: Add the suspension into a polymerization kettle through nitrogen pressurization; (3) Polymerization: Sequentially perform the following operations through a control system: i. Heating and pressurizing: Start stirring, heat up to 175 °C, and increase the pressure to 0.8 MPa; ii. Constant temperature and pressure maintaining: Keep the temperature not higher than 185 °C, keep the pressure stable, gradually drain the water, the material temperature will rise automatically after the water is drained, the material temperature is not higher than 220 °C, when the material temperature rises to a certain temperature, start stepwise pressure reduction, but the pressure needs to be maintained not less than 0.6 MPa all the time; iii. Heating and pressure reduction: Gradually heat up the material, reduce the pressure to normal pressure, and control the material temperature at 230 °C; iv. Constant temperature and normal pressure: Keep the temperature constant and purge with nitrogen for 1 h; v. Constant temperature and vacuum: Keep the temperature constant and evacuate to 0.09 MPa; vi. Nitrogen pressurization: Discharge the polymerized melt through nitrogen pressurization, and obtain bio-based nylon 12-2# through water cooling, strand drawing and pelletizing.

[0041] Among them, in step (1), the mass ratio of bio-based 12-aminododecanoic acid to water is 1:2, heat up to 120 °C, stir and mix evenly, and the stirring rate is 100 rpm; the reaction aids include a catalyst, an antioxidant and a molecular weight regulator, and the addition amounts are 0.005%, 0.01% and 0.05% of the total raw material mass respectively; the molecular weight regulator includes adipic acid and acetic acid, and the mass ratio is 3:1; the catalyst is sodium phosphite; the antioxidant is antioxidant 1098.

[0042] In step (2), the suspension is pressed into the polymerization kettle by nitrogen pressurization of 0.5 MPa.

[0043] In step (3), the stirring speed during the heating and pressurizing stage is 130 rpm and the time is 2 h; during the constant temperature and pressure maintaining stage, the polymerization and dehydration time is 3 h, the triggering temperature for stepwise pressure reduction is 215°C, and the pressure reduction rate is 0.1 MPa / min; the time for the heating and pressure reduction stage is 1.5 h; during the constant temperature and normal pressure stage, the nitrogen purging flow rate in the first half of the time is 1.5 L / min, which is 0.5 L / min higher than the purging flow rate in the second half of the time. The time for the constant temperature and vacuum stage is 60 min; the time for the nitrogen pressurization stage is 10 min and the pressure is 0.5 MPa.

[0044] Example 3 Bio-based Nylon 12-3# The preparation method of Bio-based Nylon 12-3# comprises the following steps: (1) Material preparation: Mix bio-based 12-aminododecanoic acid, water and reaction aids in a preparation tank to form a suspension; (2) Feeding: Add the suspension into the polymerization kettle by nitrogen pressurization; (3) Polymerization: Sequentially perform the following operations through a control system: i. Heating and pressurizing: Start stirring, heat up to 185°C and increase the pressure to 1.5 MPa; ii. Constant temperature and pressure maintaining: Keep the temperature not higher than 185°C, keep the pressure stable, gradually drain the water, and the material temperature will rise automatically after the water is drained. The material temperature is not higher than 220°C. When the material temperature rises to a certain temperature, start stepwise pressure reduction, but always maintain the pressure not less than 0.6 MPa; iii. Heating and pressure reduction: Gradually heat up the material, reduce the pressure to normal pressure, and control the material temperature at 270°C; iv. Constant temperature and normal pressure: Keep the temperature constant and purge with nitrogen for 0.75 h; v. Constant temperature and vacuum: Keep the temperature constant and evacuate to 0.08 MPa; vi. Nitrogen pressurization: Discharge the polymerized melt by nitrogen pressurization, and obtain Bio-based Nylon 12-3# by water cooling, strand drawing and pelletizing.

[0045] Among them, in step (1), the mass ratio of bio-based 12-aminododecanoic acid to water is 1:1.5, heat up to 100°C, stir and mix evenly, and the stirring rate is 100 rpm; the reaction aids include a catalyst, an antioxidant and a molecular weight regulator, and the addition amounts are 0.04%, 0.5% and 0.5% of the total raw material mass respectively; the molecular weight regulator includes adipic acid and benzoic acid, and the mass ratio is 7:3; the catalyst is sodium hypophosphite; the antioxidant is antioxidant H10.

[0046] In step (2), the suspension is pressed into the polymerization kettle by nitrogen pressurization of 0.5 MPa.

[0047] In step (3), the stirring speed during the heating and pressurizing stage is 150 rpm and the time is 1 h; during the constant temperature and pressure maintaining stage, the polymerization and dehydration time is 2 h, the triggering temperature for stepwise pressure reduction is 205 °C, and the pressure reduction rate is 0.05 MPa / min; the time for the heating and pressure reduction stage is 1 h; during the constant temperature and normal pressure stage, the nitrogen purge flow rate in the first half of the time is 1.0 L / min, which is 0.5 L / min higher than the purge flow rate in the second half of the time. The time for the constant temperature and vacuum stage is 30 min; the time for the nitrogen pressure increase stage is 15 min and the pressure is 0.2 MPa.

[0048] Example 4 Bio-based Nylon 12-4# The preparation method of Bio-based Nylon 12-4# comprises the following steps: (1) Preparation of materials: Bio-based 12-aminododecanoic acid, water and a reaction aid are mixed in a preparation tank to form a suspension; (2) Feeding: The suspension is added to the polymerization kettle by nitrogen pressure increase; (3) Polymerization: The following operations are sequentially performed through a control system: i. Heating and pressurizing: Start stirring, heat to 180 °C and increase the pressure to 1.0 MPa; ii. Constant temperature and pressure maintaining: Keep the temperature not higher than 185 °C, keep the pressure stable, gradually discharge the water, the material temperature will rise automatically after the water is drained, the material temperature is not higher than 220 °C, when the material temperature rises to a certain temperature, start stepwise pressure reduction, but the pressure should always be maintained not less than 0.6 MPa; iii. Heating and pressure reduction: The material is gradually heated and the pressure is reduced to normal pressure, and the material temperature is controlled at 240 °C; iv. Constant temperature and normal pressure: Keep the temperature constant and purge with nitrogen for 0.8 h; v. Constant temperature and vacuum: Keep the temperature constant and evacuate to 0.06 MPa; vi. Nitrogen pressure increase: The polymerized melt is discharged by nitrogen pressure increase, water-cooled, strand-drawn and pelletized to obtain Bio-based Nylon 12-4#.

[0049] Among them, in step (1), the mass ratio of bio-based 12-aminododecanoic acid to water is 1:1.5, heat to 80 °C, stir and mix evenly, and the stirring rate is 100 rpm; the reaction aid includes a catalyst, an antioxidant and a molecular weight regulator, and the addition amounts are 0.01%, 0.2% and 0.5% of the total raw material mass respectively; the molecular weight regulator includes adipic acid, acetic acid and benzoic acid, and the mass ratio is 6:2:2 in sequence; the catalyst is phosphoric acid; the antioxidant is antioxidant H10.

[0050] In step (2), the suspension is pressed into the polymerization kettle by nitrogen pressure increase of 0.5 MPa.

[0051] In step (3), the stirring speed during the heating and pressurizing stage is 140 rpm and the time is 1.5 h; during the constant temperature and constant pressure stage, the polymerization and dehydration time is 2.5 h, the triggering temperature for stepwise pressure reduction is 210 °C, and the pressure reduction rate is 0.1 MPa / min; the heating and pressure reduction stage takes 1.5 h; during the constant temperature and normal pressure stage, nitrogen purging includes three gradient stages in sequence: a. 0 - 20 min, flow rate 1.5 L / min; b. 20 - 40 min, flow rate 1.0 L / min; c. 40 - 60 min, flow rate 0.6 L / min. The constant temperature and vacuum stage takes 45 min; the nitrogen pressurization stage takes 13 min and the pressure is 0.4 MPa.

[0052] Example 5 Bio - based Nylon 12 - 5# The preparation method of Bio - based Nylon 12 - 5# comprises the following steps: (1) Material preparation: Mix bio - based 12 - aminododecanoic acid, water, and a reaction aid in a preparation tank to form a suspension; (2) Feeding: Add the suspension into the polymerization kettle by nitrogen pressurization; (3) Polymerization: Sequentially perform the following operations through a control system: i. Heating and pressurizing: Start stirring, heat up to 180 °C, and increase the pressure to 1.3 MPa; ii. Constant temperature and constant pressure: Keep the temperature not higher than 185 °C, keep the pressure stable, gradually drain the water. After the water in the material is drained, the temperature will rise automatically. The material temperature is not higher than 220 °C. When the material temperature rises to a certain temperature, start stepwise pressure reduction, but always maintain the pressure not less than 0.6 MPa; iii. Heating and pressure reduction: Gradually heat the material, reduce the pressure to normal pressure, and control the material temperature at 250 °C; iv. Constant temperature and normal pressure: Keep the temperature constant and purge with nitrogen for 1 h; v. Constant temperature and vacuum: Keep the temperature constant and evacuate to 0.06 MPa; vi. Nitrogen pressurization: Discharge the polymerized melt by nitrogen pressurization, and obtain Bio - based Nylon 12 - 5# through water cooling, strand drawing, and pelletizing.

[0053] Among them, in step (1), the mass ratio of bio - based 12 - aminododecanoic acid to water is 1:1, heat up to 80 °C, stir and mix evenly, and the stirring rate is 100 rpm; the reaction aid includes a catalyst, an antioxidant, and a molecular weight regulator, and the addition amounts are 0.02%, 0.1%, and 0.3% of the total raw material mass respectively; the molecular weight regulator is adipic acid; the catalyst is phosphoric acid; the antioxidant is antioxidant 1010.

[0054] In step (2), the suspension is pressed into the polymerization kettle by nitrogen pressurization of 0.3 MPa.

[0055] In step (3), the stirring speed during the heating and pressure - increasing stage is 140 rpm and the time is 1.5 h; during the constant - temperature and constant - pressure stage, the polymerization and dehydration time is 2 h, the trigger temperature for step - by - step pressure reduction is 210 °C, and the pressure - reduction rate is 0.08 MPa / min; the time for the heating and pressure - reduction stage is 1.2 h; during the constant - temperature and normal - pressure stage, the nitrogen purging flow rate is constant at 0.8 L / min. The time for the constant - temperature and vacuum stage is 45 min; the time for the nitrogen pressure - increasing stage is 12 min and the pressure is 0.3 MPa.

[0056] Comparative Example 1: Comparative Bio - based Nylon 12 - 1# The difference between Comparative Example 1 and Example 1 is that in Comparative Example 1, during the constant - temperature and constant - pressure stage of step (3), when the material temperature reaches 240 °C, step - by - step pressure reduction starts.

[0057] Comparative Example 2: Comparative Bio - based Nylon 12 - 2# The difference between Comparative Example 2 and Example 1 is that in Comparative Example 2, during the constant - temperature and constant - pressure stage of step (3), the pressure finally drops to 0.4 MPa.

[0058] Comparative Example 3: Comparative Bio - based Nylon 12 - 3# The difference between Comparative Example 3 and Example 1 is that in Comparative Example 3, nitrogen purging is not used during the constant - temperature and normal - pressure stage of step (3).

[0059] Comparative Example 4: Comparative Bio - based Nylon 12 - 4# The difference between Comparative Example 4 and Example 1 is that in Comparative Example 4, the mass proportion of adipic acid in the molecular weight regulator is 20%, and the rest is acetic acid.

[0060] Experimental Example The bio - based nylon 12 1# - 5# prepared in Examples 1 - 5 and the comparative bio - based nylon 12 1# - 4# prepared in Comparative Examples 1 - 4 were tested for mechanical properties, molecular weight and its distribution, and yield, etc. The yield was obtained by weighing after vacuum drying. Table 1 shows the test items and methods, and Tables 2 and 3 show the experimental data.

[0061] Table 1 Experimental Test Items and Methods

[0062] Table 2 Experimental Data of Molecular Weight and Its Distribution, Viscosity and Yield

[0063] Table 3 Mechanical Property and Product State Data

[0064] As can be seen from the above list, the nylon 12 prepared by using the raw materials and methods defined in this application not only has a narrow molecular weight distribution (PDI is 1.86 - 1.95), low residual monomer content and high yield, but also has a weight average molecular weight of 26,000 - 30,000 and a PDI less than 2, indicating that it is a high-quality nylon 12 with a uniform molecular weight distribution. Moreover, it is non-toxic and environmentally friendly, ultimately enabling it to meet the requirements for high-quality nylon 12 in the fields of clothing, daily necessities or medical packaging, etc. In addition, the preparation method of this application can achieve one-step continuous production, with a short production cycle, high efficiency, simple equipment, low cost investment and significantly reduced energy consumption.

[0065] As described above, the above are only examples of this application. The protection scope of this application is not limited by these specific examples, but is determined by the claims of this application. For those skilled in the art, various changes and modifications can be made to this application. Any modification, equivalent replacement, improvement, etc. made within the technical idea and principle of this application shall be included within the protection scope of this application.

Claims

1. A preparation method for bio-based nylon 12 by a one-step method, characterized in that, It includes the following steps: (1) Preparation of materials: Mix bio-based 12-aminododecanoic acid, water and a reaction aid in a preparation tank to form a suspension; (2) Feeding: Add the suspension into a polymerization kettle through nitrogen pressurization; (3) Polymerization: Sequentially perform the following operations through a control system: i. Heating and pressurizing: Start stirring, heat up to 175 - 185 °C, and increase the pressure to 0.8 - 1.5 MPa; ii. Constant temperature and pressure maintenance: Keep the temperature not higher than 185 °C, keep the pressure stable, gradually drain the water. After the water in the material is drained, the temperature of the material will rise automatically. The temperature of the material is not higher than 220 °C. When the temperature of the material rises to a certain temperature, start to reduce the pressure in stages, but always maintain the pressure not less than 0.6 MPa; iii. Heating and pressure reduction: Gradually heat up the material, reduce the pressure to atmospheric pressure, and control the temperature of the material at 230 - 270 °C; iv. Constant temperature and atmospheric pressure: Keep the temperature unchanged, and purge with nitrogen for 0.5 - 1 h for balance; v. Constant temperature and vacuum: Keep the temperature unchanged, and evacuate to 0.06 - 0.09 MPa; vi. Nitrogen pressurization: Discharge the polymerized melt through nitrogen pressurization, and obtain bio-based nylon 12 by water cooling, strand pelletizing; Among them, the reaction aid includes a catalyst, an antioxidant and a molecular weight regulator, and the addition amounts are 0.005 - 0.04%, 0.01 - 0.5% and 0.02 - 0.5% of the total raw material mass respectively; the mass ratio of adipic acid in the molecular weight regulator is not less than 60%.

2. The preparation method according to claim 1, wherein, In the constant temperature and pressure maintenance stage of step (3), the polymerization dehydration time is 2 - 3.5 h, the triggering temperature for pressure reduction in stages is 205 - 215 °C, and the pressure reduction rate is 0.05 - 0.1 MPa / min.

3. The preparation method according to claim 1, wherein In the constant temperature and atmospheric pressure stage of step (3), the nitrogen purge flow rate is 0.5 - 1.5 L / min, and the initial flow rate is higher than the final flow rate.

4. The preparation method according to claim 1, characterized in that, The molecular weight regulator includes at least adipic acid, and also includes acetic acid and / or benzoic acid.

5. The preparation method according to claim 1, characterized in that, The catalyst is one or more of phosphoric acid, sodium phosphite and sodium hypophosphite.

6. The preparation method according to claim 1, characterized in that, The antioxidant is one or more of antioxidant 1010, antioxidant H10 and antioxidant 1098.

7. The preparation method according to claim 1, wherein, In step (1), the mass ratio of bio-based 12-aminododecanoic acid to water is 1:(1 - 2), heat up to 70 - 120 °C, and stir and mix evenly; In step (2), press the suspension into the polymerization kettle with nitrogen pressurization of 0.2 - 0.5 MPa.

8. The preparation method according to claim 1, characterized in that, In the heating and pressurizing stage of step (3), the stirring speed is 130 - 150 rpm, and the time is 1 - 2 h; The heating and pressure reduction stage takes 1 - 1.5 h; the constant temperature and vacuum stage takes 30 - 60 min; the nitrogen pressurization stage takes 10 - 15 min, and the pressure is 0.2 - 0.5 MPa.

9. A bio-based nylon 12 prepared by the preparation method according to any one of claims 1-8, characterized in that, The molecular weight distribution index of the bio-based nylon 12 is 1.8 - 1.95, and the weight average molecular weight is 26000 - 30000.

10. The application of the bio-based nylon 12 according to claim 9, characterized in that, The bio-based nylon 12 can be used for clothing, food packaging materials and pharmaceutical packaging materials.

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