Method for preparing high-molecular-weight bio-based high-temperature-resistant nylon 5t by means of salt solution polycondensation coupled with solid-phase polycondensation

Abstract

A method for preparing a high-molecular-weight bio-based high-temperature-resistant nylon 5T by means of salt solution polycondensation coupled with solid-phase polycondensation. The method comprises: concentrating a nylon 5T salt solution; solution pre-polycondensation: gradually reducing the pressure by means of a gradient pressure reduction method, whereby a prepolymer gradually precipitates out; solid-liquid separation: separating the prepolymer from water; crushing: crushing the prepolymer into particles; and solid-phase polycondensation: conveying the crushed prepolymer particles into a multi-stage continuous solid-phase polycondensation reactor, in which the viscosity of the prepolymer continuously increases in a hot carrier gas atmosphere, and then discharging the resulting material. By means of a method of solution pre-polymerization coupled with multi-stage solid-phase polycondensation under graded temperatures, the problems of side reactions and thermal degradation caused by traditional high-temperature melt polycondensation are solved, and the problem of polymer particle agglomeration during solid-phase polycondensation is solved; moreover, the solid-phase polycondensation time is greatly shortened, and the solid-phase polycondensation reaction efficiency is improved. The final product is discharged as a powder, and has a white color, a high molecular weight, and good melting temperature and decomposition temperature indexes.

Description

A method for preparing high molecular weight bio-based high temperature resistant nylon 5T by salt solution polycondensation coupled with solid phase polycondensation Technical Field

[0001] The present invention relates to the technical field of chemical production, and in particular to a method for preparing high-molecular-weight bio-based high-temperature-resistant nylon 5T through salt solution polycondensation coupled with solid-phase polycondensation. Background Art

[0002] With the rapid development of the automotive, electronics, aerospace, and military industries, the demands for heat resistance and strength in polymer materials are increasing, creating an urgent need to develop high-heat-resistant and high-strength polymer materials. Researchers have found that adding rigid aromatic compounds to the synthesis of polyamide can significantly improve the heat resistance and strength of conventional nylon. This type of high-temperature nylon addresses the shortcomings of conventional nylon in the high-temperature resistance field. As of 2020, global high-temperature nylon market production capacity was primarily held by developed countries such as Europe, the United States, and Japan. The high-temperature nylon products involved include nylon 4T, nylon 6T, and nylon 9T. The development of new high-temperature nylons will help break the long-standing foreign technology monopoly and achieve domestically independent intellectual property rights.

[0003] 1,5-Pentanediamine can be produced biologically: 1,5-Pentanediamine is obtained from the decarboxylation of lysine using lysine decarboxylase. Lysine can be obtained through microbial degradation of renewable sugars such as glucose, cellulose, and starch. Previously, bio-based pentamethylenediamine-based nylon 56 was commercially produced, but its high-end application, bio-based high-temperature resistant nylon 5T, had not yet achieved industrialization.

[0004] At present, most of the research on nylon 5T is based on its copolymerization modification, such as patents CN113999388B, CN113004514B, and CN110885442B, while there is little research on homopolymer nylon 5T. Compared with copolymer nylon 5T, homopolymer nylon 5T has simpler monomers, better melting temperature and thermal stability, and has important research significance. In addition, the solid-phase polycondensation method adopted in the above patents is mostly a one-stage solid-phase polycondensation, which easily causes product particles to agglomerate in the reactor, resulting in local excessive temperature, yellowing of the product, long residence time, low polycondensation efficiency and other problems. Therefore, in response to the above problems, the present invention provides a method for preparing high molecular weight bio-based high-temperature resistant nylon 5T by coupling salt solution polycondensation with solid-phase polycondensation.

[0005] Summary of the Invention

[0006] The object of the present invention is to provide a method for preparing high molecular weight bio-based high temperature resistant nylon 5T by salt solution polycondensation coupled with solid phase polycondensation, so as to shorten the solid phase polycondensation time and improve the reaction efficiency of the solid phase polycondensation.

[0007] In order to achieve the above object, the present invention provides the following technical solutions:

[0008] A method for preparing high molecular weight bio-based high temperature resistant nylon 5T by salt solution polycondensation coupled with solid phase polycondensation comprises the following steps:

[0009] (1) Concentration: The nylon 5T salt solution is filtered through activated carbon and then transported to a nylon 5T salt concentration kettle, where it is concentrated to a concentration of 80% to 95% by heating and evaporation;

[0010] (2) Solution pre-polycondensation: The concentrated salt solution obtained in step (1) is transported to a preheater and simultaneously added with a molecular chain terminator, an antioxidant and a defoaming agent for preheating, and continuously transported to a pre-polycondensation reactor, and the temperature and pressure are controlled to carry out a pre-polymerization reaction. Subsequently, a gradient pressure reduction method is used to gradually carry out the reaction while the pressure is gradually reduced to normal pressure. As the degree of polymerization of the product in the reactor increases, the low molecular weight prepolymer gradually precipitates from the solution;

[0011] (3) solid-liquid separation: the low molecular weight prepolymer precipitated in step (2) is transported to a solid-liquid separator, where the pressure is gradually reduced to normal pressure, and the low molecular weight prepolymer and liquid water are separated;

[0012] (4) Crushing: The low molecular weight prepolymer separated from water is conveyed to a crusher, where the low molecular weight prepolymer is crushed into low molecular weight prepolymer particles of uniform size;

[0013] (5) Solid-phase polycondensation: The low molecular weight prepolymer particles crushed in step (4) are transported to the first moving bed solid-phase polycondensation reactor of the multi-stage continuous solid-phase polycondensation reactor, and hot carrier gas is continuously introduced into the reactor. The low molecular weight prepolymer continues to increase in viscosity in the hot carrier gas atmosphere, and the degree of polymerization gradually increases; the product then enters the second moving bed solid-phase polycondensation reactor for further viscosity increase; and finally enters the rotary drum vacuum dryer for reduced pressure solid-phase polycondensation. The molecular weight of the product gradually stabilizes, and then the material is discharged to obtain high molecular weight bio-based high temperature resistant nylon 5T.

[0014] Preferably, in step (1), the nylon 5T salt solution is prepared using terephthalic acid and bio-based 1,5-pentanediamine as monomers and deionized water as solvent, and the initial molar ratio of terephthalic acid to bio-based 1,5-pentanediamine in salt formation is 1:1.00-1.20; the concentration of the nylon 5T salt solution is controlled at 20wt%-70wt%.

[0015] Further preferably, in step (1), the nylon 5T salt solution is prepared with terephthalic acid and bio-based 1,5-pentanediamine as monomers and deionized water as solvent, and the initial molar ratio of terephthalic acid and bio-based 1,5-pentanediamine to form a salt is 1:1.01-1.05; the concentration of the nylon 5T salt solution is controlled at 45wt%-55wt%.

[0016] Preferably, in step (1), the temperature of the concentrated salt evaporation tower in the concentration kettle is 155-165° C., and the pressure is 0.35-0.55 MPa.

[0017] Preferably, in step (2), the molecular chain terminator is selected from one or a combination of monoacids, monoamines, acid anhydrides, monoacyl halides and monohydric alcohols; the defoaming agent is a silicone oil emulsion; the antioxidant is selected from one or a combination of phosphoric acid, phosphorous acid, hypophosphorous acid and their salts or ester derivatives; the mass fraction of the antioxidant is 0.1wt% to 2wt%, more preferably, the mass fraction of the antioxidant is 0.15wt% to 0.5wt%.

[0018] Preferably, in the step (2), the temperature of the prepolymerization reaction is 240-260° C., the pressure is 2.0-4.0 MPa, the pressure is maintained for 1-3 hours, and then the system pressure is gradually reduced to normal pressure within 0.5-1 hour by a gradient pressure reduction method. The product precipitates after reaching the degree of polymerization to obtain a low molecular weight prepolymer with a degree of polymerization of 10-50.

[0019] Preferably, in step (2), the precondensation reactor is a horizontal tubular reactor or a vertical stirred reactor; the precondensation reactor has an exhaust port at the top for discharging water vapor to control the pressure of the reactor, a heating jacket is provided on the outside, and a liquid level gauge is provided on the inside to control the liquid level of the reactor.

[0020] Preferably, in step (3), the solid-liquid classifier is an inclined screen solid-liquid separator, which uses vibration force to move the solid-liquid mixture along the inclined surface, and the solid particles are separated through the screen, while the liquid flows out through the screen.

[0021] Preferably, in step (4), the particle size of the low molecular weight prepolymer after the low molecular weight prepolymer is crushed by a crusher is 10 to 500 meshes, and more preferably, the particle size of the low molecular weight prepolymer after the low molecular weight prepolymer is crushed by a crusher is 100 to 300 meshes.

[0022] Preferably, in step (5), the multi-stage continuous solid-phase polycondensation reactor consists of the first moving bed solid-phase polycondensation reactor, the second moving bed solid-phase polycondensation reactor and the rotary drum vacuum dryer; the low molecular weight prepolymer particles can continuously enter the multi-stage continuous solid-phase polycondensation reactor from top to bottom, and at the same time, hot carrier gas is continuously introduced into the first moving bed solid-phase polycondensation reactor and the second moving bed solid-phase polycondensation reactor from bottom to top.

[0023] Preferably, in step (5), the temperature in the first moving bed solid phase polycondensation reactor is 220-240°C; the temperature in the second moving bed solid phase polycondensation reactor is 260-280°C; the temperature in the rotary drum vacuum dryer is 130-160°C, and the absolute pressure is 50-2000 Pa, more preferably, the absolute pressure is 100-300 Pa.

[0024] Preferably, in step (5), the temperature of the hot carrier gas is 200-210°C; the hot carrier gas is a mixture of inert gas and superheated steam, the inert gas is selected from one of nitrogen, helium, carbon dioxide and supercritical carbon dioxide, and the ratio of the volume flow rate of the inert gas to the superheated steam in the hot carrier gas is 1:2-10:1; the total volume flow rate is 50-500 mL / min.

[0025] Further preferably, in step (5), the hot carrier gas is a mixture of an inert gas and superheated steam, the inert gas is selected from one of nitrogen, helium, carbon dioxide and supercritical carbon dioxide, and the ratio of the volume flow rate of the inert gas to the superheated steam in the hot carrier gas is 1:1 to 5:1; the total volume flow rate is 100 to 300 mL / min.

[0026] Preferably, in step (5), the residence time required for the low molecular weight prepolymer in the first moving bed solid phase polycondensation reactor is 1 to 2 hours, the residence time required in the second moving bed solid phase polycondensation reactor is 3 to 5 hours, and the residence time required in the rotary drum vacuum dryer is 1 to 1.5 hours.

[0027] Preferably, the reaction apparatus of the present invention is mainly composed of seven parts connected in series: a concentration kettle, a prepolymerization reactor, a solid-liquid separator, a crusher, a first moving bed solid phase polycondensation reactor, a second moving bed solid phase polycondensation reactor and a rotary drum vacuum dryer.

[0028] Preferably, the concentration kettle is a vertical stirred reactor with a solvent capacity of 60L, made of stainless steel, and fully mechanically sealed. The steam discharged from the concentrated salt solution can be used to produce hot water, saving a certain amount of energy consumption.

[0029] Preferably, the prepolymerization reactor is a vertical stirred reactor, which is preheated by a jacket and equipped with a radiation level gauge for controlling the liquid level.

[0030] Preferably, the solid-liquid separator is an inclined screen solid-liquid separator, which includes a body, a sieve plate, a transmission device, etc., can automatically clean the sieve plate to avoid clogging of the sieve holes, and separate the solid-liquid mixture through high-speed vibration.

[0031] The pulverizer preferably consists of a main unit, auxiliary units, and electronic control units, boasting a compact design and rational structure. Negative pressure conveying allows heat generated within the pulverizer chamber to be continuously dissipated during pulverization, making it suitable for pulverizing polymer materials. The production process is continuous, and the output particle size is adjustable.

[0032] Preferably, the first moving bed solid-phase polycondensation reactor and the second moving bed solid-phase polycondensation reactor are continuous moving bed reactors, including a cylindrical top and a conical bottom. The prepolymer particles enter from the top of the reactor and are discharged from the bottom after a certain residence time. Correspondingly, the hot mixed gas enters the reactor from the bottom of the reactor and is blown out from the top after sufficient mass transfer with the particles.

[0033] Preferably, the rotary drum vacuum dryer comprises a base, a support frame, a vacuum box, a vacuum cover and a rotating rod, and the surface of the base is connected to the support frame by welding.

[0034] Due to the application of the above technical solution, the present invention has significant advantages and beneficial effects compared with the prior art, which are specifically reflected in the following aspects:

[0035] 1. The present invention solves the problems of severe side reactions and thermal degradation caused by high-temperature melt polycondensation in traditional nylon preparation methods. The multi-stage solid-phase polycondensation temperature grading method can overcome the problem of local excessive temperature caused by polymer particle agglomeration during the solid-phase polycondensation process.

[0036] 2. The method of preparing high molecular weight bio-based high temperature resistant nylon 5T of the present invention greatly shortens the time of solid phase polycondensation and improves the reaction efficiency of solid phase polycondensation.

[0037] 3. The high molecular weight bio-based high temperature resistant nylon 5T final product prepared by the present invention is discharged in powder form, is white in color, has a high molecular weight, good melting temperature and decomposition temperature indicators, and has excellent comprehensive performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, a brief introduction is given below to the drawings required for use in the specific embodiments or the description of the prior art. Obviously, some of the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0039] FIG1 is a schematic diagram of a multi-stage continuous solid phase polycondensation reactor according to Example 1 of the present invention;

[0040] FIG2 is a process flow chart of Example 1 of the present invention;

[0041] FIG3 is a TG curve diagram of the final polymerization product of Example 20 of the present invention;

[0042] FIG4 is a DSC curve diagram of the final polymerization product of Example 20 of the present invention;

[0043] FIG5 is a physical picture of high molecular weight bio-based high temperature resistant nylon 5T prepared in Example 20 of the present invention;

[0044] FIG6 is a physical picture of high molecular weight bio-based high temperature resistant nylon 5T prepared in Comparative Example 1 of the present invention;

[0045] FIG7 is a physical picture of the high molecular weight bio-based high temperature resistant nylon 5T prepared in Comparative Example 2 of the present invention.

[0046] Among them, A: first moving bed solid phase polycondensation reactor; B: second moving bed solid phase polycondensation reactor; C: rotary drum vacuum dryer; 1-hot carrier gas; 2-hot carrier gas; 3-feed; 4-discharge. DETAILED DESCRIPTION

[0047] The technical solutions in the embodiments of the present invention will be described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0048] The product testing and characterization methods required by the embodiments of the present invention are as follows:

[0049] Relative viscosity test method: Refer to the test method for relative viscosity of nylon 6 chips in GB / T38138-2019. Using 50 ml of (96.0 ± 0.1)% concentrated sulfuric acid as the solvent, accurately weigh 0.5000 g of the dried polymer sample to prepare a 0.010 g / mL solution. The test is performed at (25.00 ± 0.02)°C. The capillary diameter of the Ubbelohde viscometer is 1.03 mm. The ratio of the residence time t of the sample solution through the viscometer to the residence time t0 of the pure solvent is the relative viscosity of the sample.

[0050] Molecular weight determination: Gel permeation chromatography (GPC) was used. The sample was dissolved one day in advance, using hexafluoroisopropanol (HFIP) as the solvent. Considering the polyelectrolyte effect of nylon materials, a small amount of sodium trifluoroacetate was added to the solvent to eliminate it. The standard curve was prepared using PMMA as the standard sample. The column oven temperature was set at 40°C, the mobile phase was HFIP, and the flow rate was 1 mL / min. -1 .

[0051] Test method for melting temperature and crystallization temperature: Differential scanning calorimetry (DSC) was used to test the melting point, and DiamondDSC (PerkinElmer) was used to analyze the isothermal and non-isothermal crystallization behavior of PA6 / 66 copolymer. The melting point and the melting enthalpy of high-purity indium metal were used to calibrate the temperature range and power response of the DSC analysis. All DSC analyses were performed under a nitrogen atmosphere. In order to analyze the crystallization and melting behavior, 5-10 mg of sample was heated to 380°C at a rate of 10°C / min and kept at this temperature for 10 minutes. Then, the sample was cooled to 20°C at a rate of 10°C / min. The crystallization exotherm was recorded and the corresponding crystallization temperature (T c Finally, the sample was heated to 380°C at a rate of 10°C / min, the melting curve was recorded and the corresponding melting point (T m ).

[0052] Determination of thermal decomposition temperature: Using a NETZSCH TGA209F3 thermogravimetric analyzer, place an appropriate amount of sample in a crucible and heat to 600°C at a rate of 10°C / min under a nitrogen atmosphere. Record the curve and measure the temperature corresponding to 5% thermal decomposition and the maximum thermal decomposition rate.

[0053] Example 1

[0054] 1 and 2 , this embodiment provides a method for preparing high molecular weight bio-based high temperature resistant nylon 5T by salt solution polycondensation coupled with solid phase polycondensation;

[0055] (1) Concentration: The nylon 5T salt solution is filtered through activated carbon and then transported to a nylon 5T salt concentration kettle, where it is concentrated to 80% of the concentrated salt solution by heating and evaporation;

[0056] (2) Solution pre-polycondensation: The concentrated salt solution obtained in step (1) is transported to a preheater and benzoic acid, sodium phosphite and silicone oil emulsion are added simultaneously for preheating, and continuously transported to a pre-polycondensation reactor, the reaction temperature is controlled to 240° C., the reaction pressure is controlled to 2.0 MPa, and the reaction is carried out for 1 hour. Subsequently, a gradient pressure reduction method is used to gradually proceed with the reaction, and the system pressure is gradually reduced to normal pressure within 1 hour. As the degree of polymerization of the product in the reactor increases, the low molecular weight prepolymer gradually precipitates from the solution;

[0057] (3) solid-liquid separation: the low molecular weight prepolymer precipitated in step (2) is transported to a solid-liquid separator, where the pressure is gradually reduced to normal pressure, and the low molecular weight prepolymer and liquid water are separated;

[0058] (4) Crushing: The low molecular weight prepolymer separated from water is conveyed to a crusher, where the low molecular weight prepolymer is crushed into low molecular weight prepolymer particles of 100 to 300 mesh;

[0059] (5) Solid-phase polycondensation: The low molecular weight prepolymer particles crushed in step (4) are transported as feed 3 to the first moving bed solid-phase polycondensation reactor A of the multi-stage continuous solid-phase polycondensation reactor, the reaction temperature is set to 220°C, the residence time is 1 hour, and hot carrier gas is continuously introduced into the reactor. The low molecular weight prepolymer continues to increase in viscosity in the hot carrier gas atmosphere, and the degree of polymerization gradually increases; the product then enters the second moving bed solid-phase polycondensation reactor B, the reaction temperature is set to 260°C, the residence time is 3 hours, and further viscosity increases; finally, it enters the rotary drum vacuum dryer C for reduced pressure solid-phase polycondensation, the reaction temperature is set to 150°C, the absolute pressure is 100 Pa, the residence time is 1 hour, the molecular weight of the product gradually stabilizes, and then the discharge 4 is obtained to obtain high molecular weight bio-based high temperature resistant nylon 5T. Hot carrier gas 1 enters the reactor from the bottom of the second moving bed solid phase polycondensation reactor, passes through the second moving bed solid phase polycondensation reactor and the first moving bed solid phase polycondensation reactor in sequence, and finally blows out hot carrier gas 2 from the top of the first moving bed solid phase polycondensation reactor; the temperature of the hot carrier gas is 200°C, and it is composed of a mixture of nitrogen and water vapor, with a volume flow rate ratio of 2:1 and a total volume flow rate of 150 mL / min.

[0060] Example 2-18

[0061] Based on Example 1, Examples 2-18 only adjusted the operating parameters of the salt solution polymerization reaction stage. The specific operating parameters of the salt solution polymerization stage in Examples 2-18 are shown in Table 1. The test analysis results of the high molecular weight bio-based high temperature resistant nylon 5T obtained in Examples 1-18 are shown in Table 2.

[0062] Examples 19-32

[0063] Based on Example 11, Examples 19-32 only adjusted the operating parameters of the nylon 5T solid phase polycondensation stage, among which Examples 19-21 only verified the influence of the first and second solid phase polycondensation reaction temperatures (see Figures 3, 4 and 5 for Example 20), Examples 22-23 only verified the influence of the prepolymer particle size, Examples 24-26 only verified the influence of the carrier gas flow rate, Examples 27-29 only verified the influence of the volume flow rate ratio of nitrogen to water vapor, and Examples 30-32 only verified the influence of the residence time; the specific operating parameters of the salt solution polymerization stage in Examples 19-32 are shown in Table 3, and the test analysis results of the obtained high molecular weight bio-based high temperature resistant nylon 5T are shown in Table 4.

[0064] Comparative Example 1

[0065] The only difference between this comparative example and Example 20 is that only the first moving bed solid-phase polycondensation reactor is used in the solid-phase polycondensation stage, the reaction temperature is 260°C, the residence time is 6 hours, and the other process parameters are exactly the same. The high molecular weight bio-based high-temperature resistant nylon 5T obtained is shown in Figure 6.

[0066] Comparative Example 2

[0067] The only difference between this comparative example and Example 20 is that only a rotary drum vacuum dryer is used in the solid phase polycondensation stage, the reaction temperature is 260°C, and the residence time is 6 hours. The other process parameters are exactly the same. The high molecular weight bio-based high temperature resistant nylon 5T obtained is shown in Figure 7.

[0068] The test and analysis results of the high molecular weight bio-based high temperature resistant nylon 5T obtained in Comparative Example 1 and Comparative Example 2 are shown in Table 5.

[0069] Table 1 is as follows:

[0070] Table 2 is shown below:

[0071] Table 3 is as follows:

[0072] Table 4 is shown below:

[0073] Table 5 is shown below:

[0074] It can be seen from Table 2 that increasing the concentration of nylon salt solution, raising the prepolymerization temperature, reaction pressure and extending the reaction time are all beneficial to increasing the molecular weight of the prepolymer.

[0075] As can be seen from Table 4, increasing the solid-phase polycondensation reaction temperature in the first and second moving beds, extending the solid-phase polycondensation residence time in the first and second moving beds, reducing the prepolymer particle size, increasing the carrier gas flow rate, and increasing the volume flow rate ratio of nitrogen in the carrier gas all contribute to increasing the molecular weight of the product. Examples 20, 27-29 demonstrate that mixing a certain proportion of water vapor (nitrogen:water vapor = 2:1) into the carrier gas can inhibit side reactions and product decomposition, thereby improving the thermal stability of the product. However, as the water vapor ratio continues to decrease, the thermal stability of the product decreases.

[0076] As can be seen from Table 4, Comparative Examples 1 and 2 both adopt a one-stage solid-phase polycondensation method, and the molecular weight of the products obtained is much lower than the product obtained by the multi-stage solid-phase polycondensation method in Example 20, and the melting temperature of the products obtained in Comparative Examples 1 and 2 is close to the initial decomposition temperature, and the thermal stability is poor, which is not conducive to subsequent melt processing.

[0077] By comparing Figures 6 and 7 with Figure 5, it can be found that the product obtained by the multi-stage solid-phase polycondensation method is lighter in color than the product of the one-stage solid-phase polycondensation, indicating that the multi-stage solid-phase polycondensation is beneficial to preventing product degradation and side reactions caused by local excessive temperature due to particle agglomeration.

[0078] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.

Claims

1. A method for preparing high molecular weight bio-based high temperature resistant nylon 5T by salt solution polycondensation coupled with solid phase polycondensation, characterized in that: The following steps are involved: (1) Concentration: The nylon 5T salt solution is filtered through activated carbon and then transported to a nylon 5T salt concentration kettle, where it is concentrated to a concentration of 80% to 95% by heating and evaporation; (2) Solution pre-polycondensation: The concentrated salt solution obtained in step (1) is transported to a preheater and simultaneously added with a molecular chain terminator, an antioxidant and a defoaming agent for preheating, and continuously transported to a pre-polycondensation reactor, and the temperature and pressure are controlled to carry out a pre-polymerization reaction. Subsequently, a gradient pressure reduction method is used to gradually carry out the reaction while the pressure is gradually reduced to normal pressure. As the degree of polymerization of the product in the reactor increases, the low molecular weight prepolymer gradually precipitates from the solution; (3) solid-liquid separation: the low molecular weight prepolymer precipitated in step (2) is transported to a solid-liquid separator, where the pressure is gradually reduced to normal pressure, and the low molecular weight prepolymer and liquid water are separated; (4) Crushing: The low molecular weight prepolymer separated from water is conveyed to a crusher, where the low molecular weight prepolymer is crushed into low molecular weight prepolymer particles of uniform size; (5) Solid-phase polycondensation: The low molecular weight prepolymer particles crushed in step (4) are transported to the first moving bed solid-phase polycondensation reactor of the multi-stage continuous solid-phase polycondensation reactor, and hot carrier gas is continuously introduced into the reactor. The low molecular weight prepolymer continues to increase in viscosity in the hot carrier gas atmosphere, and the degree of polymerization gradually increases; the product then enters the second moving bed solid-phase polycondensation reactor for further viscosity increase; and finally enters the rotary drum vacuum dryer for reduced pressure solid-phase polycondensation. The molecular weight of the product gradually stabilizes, and then the material is discharged to obtain high molecular weight bio-based high temperature resistant nylon 5T.

2. The method for preparing high molecular weight bio-based high temperature resistant nylon 5T by salt solution polycondensation coupled with solid phase polycondensation according to claim 1, characterized in that: In the step (1), the nylon 5T salt solution is prepared using terephthalic acid and bio-based 1,5-pentanediamine as monomers and deionized water as solvent, and the initial molar ratio of terephthalic acid to bio-based 1,5-pentanediamine in salt formation is 1:1.00-1.20; the concentration of the nylon 5T salt solution is controlled at 20wt%-70wt%.

3. The method for preparing high molecular weight bio-based high temperature resistant nylon 5T by salt solution polycondensation coupled with solid phase polycondensation according to claim 1, characterized in that: In the step (1), the temperature of the concentrated salt evaporation tower in the concentration kettle is 155-165° C., and the pressure is 0.35-0.55 MPa.

4. The method for preparing high molecular weight bio-based high temperature resistant nylon 5T by salt solution polycondensation coupled with solid phase polycondensation according to claim 1, characterized in that: In the step (2), the molecular chain terminator is selected from one or a combination of monoacids, monoamines, acid anhydrides, monoacyl halides and monoalcohols; the defoaming agent is a silicone oil emulsion; the antioxidant is selected from one or a combination of phosphoric acid, phosphorous acid, hypophosphorous acid and their salts or ester derivatives; the proportion of the antioxidant is 0.1wt% to 2wt%.

5. The method for preparing high molecular weight bio-based high temperature resistant nylon 5T by salt solution polycondensation coupled with solid phase polycondensation according to claim 1, characterized in that: In the step (2), the temperature of the prepolymerization reaction is 240-260° C., the pressure is 2.0-4.0 MPa, and the pressure is maintained for 1-3 hours. Subsequently, the system pressure is gradually reduced to normal pressure by a gradient pressure reduction method within 0.5-1 hour. The product precipitates after reaching the degree of polymerization to obtain a low molecular weight prepolymer with a degree of polymerization of 10-50.

6. The method for preparing high molecular weight bio-based high temperature resistant nylon 5T by salt solution polycondensation coupled with solid phase polycondensation according to claim 1, characterized in that: In the step (2), the pre-polycondensation reactor is selected from a horizontal tubular reactor and a vertical stirred reactor; the pre-polycondensation reactor has an exhaust port at the top, a heating jacket on the outside, and a liquid level gauge on the inside.

7. The method for preparing high molecular weight bio-based high temperature resistant nylon 5T by salt solution polycondensation coupled with solid phase polycondensation according to claim 1, characterized in that: In the step (3), the solid-liquid classifier is an inclined screen solid-liquid separator, which uses vibration force to move the solid-liquid mixture along the inclined surface, so that the solid particles are separated through the screen and the liquid flows out through the screen.

8. The method for preparing high molecular weight bio-based high temperature resistant nylon 5T by salt solution polycondensation coupled with solid phase polycondensation according to claim 1, characterized in that: In the step (4), the low molecular weight prepolymer is crushed by a crusher to obtain a particle size of 10 to 500 meshes.

9. The method for preparing high molecular weight bio-based high temperature resistant nylon 5T by salt solution polycondensation coupled with solid phase polycondensation according to claim 1, characterized in that: In the step (5), the multi-stage continuous solid-phase polycondensation reactor is composed of the first moving bed solid-phase polycondensation reactor, the second moving bed solid-phase polycondensation reactor and the rotary drum vacuum dryer; the low molecular weight prepolymer particles can continuously enter the multi-stage continuous solid-phase polycondensation reactor from top to bottom, and at the same time, hot carrier gas is continuously introduced into the first moving bed solid-phase polycondensation reactor and the second moving bed solid-phase polycondensation reactor from bottom to top.

10. The method for preparing high molecular weight bio-based high temperature resistant nylon 5T by salt solution polycondensation coupled with solid phase polycondensation according to claim 1, characterized in that: In the step (5), the temperature in the first moving bed solid phase polycondensation reactor is 220-240° C.; the temperature in the second moving bed solid phase polycondensation reactor is 260-280° C.; the temperature in the rotary drum vacuum dryer is 130-160° C., and the absolute pressure is 50-2000 Pa.

11. The method for preparing high molecular weight bio-based high temperature resistant nylon 5T by salt solution polycondensation coupled with solid phase polycondensation according to claim 1, characterized in that: In step (5), the temperature of the hot carrier gas is 200-210° C.; the hot carrier gas is a mixture of an inert gas and superheated steam, the inert gas is selected from one of nitrogen, helium, carbon dioxide and supercritical carbon dioxide, and the ratio of the volume flow rate of the inert gas to the superheated steam in the hot carrier gas is 1:2-10:1; the total volume flow rate is 50-500 mL / min.

12. The method for preparing high molecular weight bio-based high temperature resistant nylon 5T by salt solution polycondensation coupled with solid phase polycondensation according to claim 1, characterized in that: In the step (5), the residence time required for the low molecular weight prepolymer in the first moving bed solid phase polycondensation reactor is 1 to 2 hours, the residence time required in the second moving bed solid phase polycondensation reactor is 3 to 5 hours, and the residence time required in the rotary drum vacuum dryer is 1 to 1.5 hours.

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