Preparation method of nylon 46

Abstract

The invention relates to the technical field of high polymer materials, in particular to a preparation method of nylon 46, which comprises four steps of salifying, primary polymerization, pre-polymerization and solid-phase tackifying, in the salifying stage, 100 parts by weight of adipic acid and 800-1000 parts by weight of methanol are added into a salifying kettle, the temperature is raised to 40-60 DEG C, 55-60 parts by weight of 1, 4-butanediamine is added into the salifying kettle, and the mixture is heated to 40-60 DEG C; at the same time, maintaining the temperature at 40-60 DEG C to react for 2-3 hours, cooling to 20-30 DEG C, discharging the material in the salifying kettle, and filtering and drying in vacuum to obtain nylon 46 salt; in the initial polymerization stage, nylon 46 salt reacts with water at 180-210 DEG C, the water amount of a reaction system is controlled to maintain a liquid state, in the pre-polymerization stage, a continuous reaction mode is adopted to remove moisture, pre-polymer particles are obtained through bracing and pelletizing, and finally the high-viscosity nylon 46 polymer is obtained through solid-phase tackifying. The method can be used in the fields of machinery, automobiles, electronics, electrical appliances, aviation and aerospace industries and the like.

Description

Technical Field

[0001] The invention relates to the technical field of polymer materials, and in particular to a preparation method of nylon 46. Background Art

[0002] Polyamide, commonly known as nylon, is a type of polymer compound that characteristically contains amide groups in its main molecular chain. It is easy to form hydrogen bonds between its molecules and has the characteristics of high strength, high toughness, good wear resistance and easy processing.

[0003] Polybutylene adipamide (commonly known as nylon 46) is different from general aliphatic polyamides such as nylon 66 and nylon 6. Nylon 46 has high amide density and regular structure. It has the characteristics of high melting point, high crystallinity, high temperature resistance, high strength, etc. It has excellent comprehensive performance and has broad application prospects in machinery, automobiles, electronics, electrical appliances, aviation and aerospace industries. As a monomer of nylon 46, the industrial production process (chemical method) of butylene adipamide is only mastered by DSM of the Netherlands, so nylon 46 has always been a monopoly product of DSM. With the large-scale industrialization of domestic succinic acid bio-production, the production of butylene adipamide from succinic acid has become another feasible route, which provides strong conditions for the domestic development of nylon 46 and breaking the monopoly of DSM.

[0004] Due to the high melting point of nylon 46 (melting point is about 290℃), thermal degradation is prone to occur when reacting above the melting point. At the same time, the monomer 1,4-butanediamine is volatile and is prone to side reactions such as decomposition, oxidation, and cyclization at high temperatures. The traditional melt polymerization method cannot obtain high molecular weight nylon 46, and the color is poor and cannot meet the use requirements.

[0005] U.S. Patent No. 4408036 discloses a method for preparing white, high molecular weight nylon 46, which adopts a two-step synthesis method. In the first step, nylon 46 salt formed by 1,4-butanediamine and adipic acid reacts at 150°C-210°C to obtain a low molecular weight prepolymer, and in the second step, solid phase polycondensation is carried out at 225-275°C under a water vapor atmosphere. U.S. Patent No. 4460762 adds 0.5-15 mol% excess 1,4-butanediamine in the prepolymerization stage to make up for the loss of 1,4-butanediamine during the polymerization process to obtain high molecular weight nylon 46. Due to the volatility of 1,4-butanediamine and the side reactions that easily occur at high temperatures, the accuracy of the amount of 1,4-butanediamine added and the accuracy of the process temperature and pressure control will greatly affect the viscosity stability of the nylon 46 product, which places high demands on the industrial production of nylon 46.

[0006] U.S. Patent No. 4716214 discloses a method for continuously preparing high molecular weight nylon 46, wherein a nylon 46 salt solution is first prepolymerized at a pressure of 2-15 bar, and then the reaction is continued through one or two tubular reactors to obtain high molecular weight nylon 46. In order to keep the reaction materials in a liquid state during the prepolymerization process, the reaction materials contain a certain amount of water. When reacting in the tubular reactor, the water in the materials will evaporate to form steam, which causes the materials to flow in two phases in the tubular reactor, which has an adverse effect on the flow of the materials and has high requirements for the design and manufacture of the tubular reactor. The patent also does not specify how to remove the generated steam.

[0007] Chinese patent CN113321802A discloses a copolymer of synthetic nylon 46 / 66 and its preparation process, which adopts three steps of salt formation, prepolymerization and solid phase postpolymerization. The obtained powdery prepolymer is not easy to handle and is difficult to carry out industrial solid phase viscosity enhancement.

[0008] Chinese patent CN115819755B discloses a method for producing nylon 46, which includes steps of salt formation, pre-condensation and solid phase post-condensation. A two-stage solid phase polycondensation method is adopted, and a special solid phase polycondensation reactor is used to achieve uniform heating of the prepolymer and ensure the color of the product. Since the solid prepolymer obtained in the prepolymerization process needs to be crushed to obtain pellets, there is a problem of inconsistent particle size distribution, which may affect the consistency of product viscosity in the subsequent solid phase viscosity enhancement process.

[0009] Chinese patent CN102167815B discloses a method for preparing high molecular weight nylon 46 in supercritical carbon dioxide, which uses supercritical carbon dioxide as a solvent, and sequentially performs pre-polycondensation and post-solid phase polycondensation reactions to obtain high molecular weight nylon 46. In order to obtain high molecular weight nylon 46, it is necessary to perform the operation of filling and discharging carbon dioxide multiple times to discharge the water generated by the reaction, and the operation is relatively complicated. Summary of the invention

[0010] In view of the above technical problems and the shortcomings in the art, the present invention provides a method for preparing nylon 46. The method for preparing nylon 46 of the present invention has a short process and takes less time, and the high molecular weight nylon 46 produced can be used in the fields of machinery, automobiles, electronics, electrical appliances, aviation, aerospace industry, etc.

[0011] To achieve the above technical objectives, the technical solution adopted by the present invention is: a method for preparing nylon 46, comprising the following steps: (1) Salt formation: 100 parts by weight of adipic acid and 800-1000 parts of methanol are added to a salt forming kettle, the temperature is raised to 40-60°C, 55-60 parts of 1,4-butanediamine are added to the salt forming kettle, the temperature is maintained at 40-60°C for reaction for 2-3 hours, the temperature is lowered to 20-30°C, the material in the salt forming kettle is discharged, and nylon 46 salt is obtained by filtering and vacuum drying; (2) Preliminary polymerization: 100 parts of nylon 46 salt and 50-60 parts of deionized water are added to a preliminarily polymerizer by weight, nitrogen is introduced to discharge oxygen, stirring is started, the temperature is raised to 180-210°C, water vapor is discharged to maintain the pressure of the reactor at 0.8-1.8 MPa, the discharged water is condensed and collected, and the discharged water is weighed to calculate the remaining water in the reaction system. When the water in the reaction system is 8%-12% of the nylon 46 salt, the discharge of water vapor is stopped to obtain a nylon 46 preliminarily polymerized product; (3) Prepolymerization: The nylon 46 prepolymer obtained in step (2) is continuously passed through a heat exchanger to raise its temperature to 300-310°C, and then flows into a prepolymerizer. The prepolymer pressure is normal pressure and the temperature is 300-310°C. The material stays in the prepolymer for 5-10 minutes. The material is extruded into strips through a die head at the outlet of the prepolymerizer, and then cooled and pelletized to obtain a nylon 46 prepolymer. (4) Solid phase viscosity enhancement: The nylon 46 prepolymer obtained in step (3) is placed in a dryer, and nitrogen is continuously introduced to maintain the pressure of the dryer at 0.05-0.1 MPa. At the same time, the nitrogen is discharged to remove the moisture generated by the reaction. The temperature is raised to 220-250°C and dried for 10-15 hours to obtain a nylon 46 polymer.

[0012] Furthermore, the primary polymerization vessel in step (2) is a vertical reactor with a stirring device and a jacket, and the stirring blade is a three-blade swept type.

[0013] Furthermore, the drainage time in step (2) is 20-40 minutes.

[0014] Furthermore, the relative viscosity of the nylon 46 primary polymer in step (2) is 1.4-1.6.

[0015] Furthermore, the prepolymerizer in step (3) is a horizontal reactor with a spiral agitator, and the reactor is provided with 2-4 exhaust ports.

[0016] Furthermore, the relative viscosity of the nylon 46 prepolymer in step (3) is 1.8-2.4.

[0017] Furthermore, the dryer in step (4) is a drum dryer with a jacket.

[0018] Furthermore, the relative viscosity of the nylon 46 polymer in step (4) is 3.2-5.0.

[0019] Compared with the prior art, the technical solution of the embodiment of the present invention has the following beneficial effects: (1) In the initial polymerization stage, nylon 46 salt has a large solubility in water. During the heating process, a uniform solution can be quickly produced to avoid local overheating. The pressure generated by the evaporation of water vapor in the system is used to effectively reduce the volatilization of diaminobutane and maintain the stability of the molar ratio of diaminobutane to adipic acid. While discharging water to promote the amidation process, the amount of water in the reaction system is controlled to maintain the reaction system in a liquid state, which can facilitate subsequent reactions.

[0020] (2) In the prepolymerization stage, the reaction materials are rapidly raised to above the melting point of the materials by continuous reaction. A spiral reactor with an exhaust port is used to rapidly evaporate the water in the reaction materials, thereby further increasing the molecular weight. The obtained prepolymer can be stranded and pelletized to obtain prepolymer particles with uniform particle size, thereby avoiding the crushing of the solid prepolymer or the use of powder for solid phase viscosity enhancement, reducing the production steps, and improving the production efficiency and viscosity uniformity.

[0021] The preparation method of nylon 46 of the present invention has a short process and consumes little time, and the high molecular weight nylon 46 produced can be used in the fields of machinery, automobiles, electronics, electrical appliances, aviation, aerospace industry, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Schematic diagram of the preparation process of nylon 46 in an embodiment of the present invention. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0024] Example 1 like Figure 1 As shown, a method for preparing nylon 46 comprises the following steps: (1) Salt formation: 10 kg of adipic acid and 90 kg of methanol were added to a salt-forming kettle, stirring was started, the temperature was raised to 50°C, 5.9 kg of 1,4-butanediamine was added to the salt-forming kettle, and the reaction was carried out at 50°C for 2.5 hours, a white precipitate was precipitated, and the temperature was lowered to 25°C, the suspension in the salt-forming kettle was discharged and filtered to obtain crude nylon 46 salt, and the crude nylon 46 salt was dried at 80°C and 1 kPa vacuum for 5 hours to obtain nylon 46 salt; (2) Preliminary polymerization: 5 kg of nylon 46 salt obtained in step (1) and 2.6 kg of deionized water were added to a 10 L preliminarily polymerizer, nitrogen was introduced to remove oxygen, stirring was started, the temperature was raised to 190°C, the pressure was raised to 1.0 MPa, the exhaust valve was opened, the exhausted water vapor was cooled through a condenser, collected and weighed, the amount of condensed water collected was monitored, the exhaust speed was controlled by adjusting the exhaust valve opening and the heating amount, and the pressure was maintained at 1.0 MPa. After 25 minutes, the weight of the collected condensed water reached 2.1 kg, and the exhaust valve was closed; The primary polymerizer is a vertical reactor with stirring and jacket, and the stirring blade is a three-blade swept type; (3) Prepolymerization: Open the bottom valve of the prepolymerizer, start the melt pump of the prepolymerizer, set the melt pump flow rate to 10 kg / hr, and let the nylon 46 prepolymer in the prepolymerizer continuously pass through the heat exchanger with an outlet temperature of 300°C, and then flow into the 8L prepolymerizer. The stirring speed of the prepolymerizer is 45 RPM, the pressure of the prepolymerizer is normal pressure, and the temperature is 300°C. The residence time of the material in the prepolymerizer is 8 minutes. Open the prepolymerizer discharge valve and the discharge melt pump, set the flow rate to 9 kg / hr, and extrude the material into material strips through the die head. After cooling and pelletizing, nylon 46 prepolymer particles are obtained; The prepolymerizer is a horizontal reactor with a spiral agitator and three exhaust ports; (4) Solid phase viscosity enhancement: 5 kg of nylon 46 prepolymer particles were placed in a 20 L dryer, nitrogen was introduced to maintain the pressure of the dryer at 0.06 MPa, the temperature was raised to 230°C, nitrogen was discharged at the same time to remove the moisture generated by the reaction, and the nylon 46 polymer was obtained by drying for 12 hours. The dryer was a drum dryer with a jacket.

[0025] Example 2 like Figure 1 As shown, a method for preparing nylon 46 comprises the following steps: (1) Salt formation: 10 kg of adipic acid and 100 kg of methanol were added to a salt forming kettle, stirring was started, the temperature was raised to 50°C, 5.9 kg of 1,4-butanediamine was added to the salt forming kettle, the temperature was maintained at 50°C for reaction for 2.5 hours, a white precipitate was precipitated, the temperature was lowered to 25°C, the suspension in the salt forming kettle was discharged and filtered to obtain crude nylon 46 salt, the crude nylon 46 salt was dried at 80°C and 1 kPa vacuum for 5 hours to obtain nylon 46 salt; (2) Primary polymerization: 5 kg of nylon 46 salt and 2.8 kg of deionized water were added to a 10 L primary polymerization vessel, nitrogen was passed to remove oxygen, stirring was started, the temperature was heated to 205 ° C, the pressure was raised to 1.5 MPa, the exhaust valve was opened, the exhaust water vapor was cooled through the condenser, collected and weighed, the amount of condensed water collected was monitored, the exhaust speed was controlled by adjusting the exhaust valve opening and the heating amount, the reactor pressure was maintained at 1.5 MPa, and after 30 minutes, the weight of the collected condensed water reached 2.3 kg, and the exhaust valve was closed; The primary polymerizer is a vertical reactor with stirring and jacket, and the stirring blade is a three-blade swept type; (3) Prepolymerization: Open the bottom valve of the prepolymerizer, start the melt pump of the prepolymerizer, set the melt pump flow rate to 10 kg / hr, and let the nylon 46 prepolymer in the prepolymerizer pass through the heat exchanger continuously. The outlet temperature of the heat exchanger is 305°C, and then flow into the 8L prepolymerizer. The stirring speed of the prepolymerizer is 45 RPM, the pressure of the prepolymerizer is normal pressure, and the temperature is 305°C. The residence time of the material in the prepolymerizer is 8 minutes. Open the prepolymerizer discharge valve and the discharge melt pump, set the flow rate to 9 kg / hr, and extrude the material into material strips through the die head. After cooling and pelletizing, nylon 46 prepolymer particles are obtained; The prepolymerizer is a horizontal reactor with a spiral agitator and three exhaust ports; (4) Solid phase viscosity enhancement: 5 kg of nylon 46 prepolymer particles were placed in a 20 L dryer, nitrogen was introduced to maintain the pressure of the dryer at 0.06 MPa, the temperature was raised to 230°C, nitrogen was discharged at the same time to remove the moisture generated by the reaction, and the mixture was dried for 14 hours to obtain nylon 46 polymer. The dryer was a drum dryer with a jacket.

[0026] Comparative Example 1 A method for preparing nylon 46 comprises the following steps: (1) Salt formation: 10 kg of adipic acid and 100 kg of methanol were added to a salt forming kettle, stirring was started, the temperature was raised to 50°C, 5.9 kg of 1,4-butanediamine was added to the salt forming kettle, the temperature was maintained at 50°C for reaction for 2.5 hours, a white precipitate was precipitated, the temperature was lowered to 25°C, the suspension in the salt forming kettle was discharged and filtered to obtain crude nylon 46 salt, the crude nylon 46 salt was dried at 80°C and 1 kPa vacuum for 5 hours to obtain nylon 46 salt; (2) Prepolymerization: Add 5 kg of nylon 46 salt obtained in step (1) and 2.8 kg of deionized water into a 10 L prepolymerizer, pass nitrogen to remove oxygen, start stirring, heat to 205 ° C, and raise the pressure to 1.5 MPa. Open the exhaust valve of the reactor, cool the discharged water vapor through the condenser, collect and weigh it, monitor the amount of condensed water collected, adjust the exhaust valve opening to control the exhaust speed, adjust the intake valve opening and heating amount to maintain the pressure at 1.0 MPa, and after 35 minutes, the weight of the collected condensed water reaches 2.7 kg, and close the exhaust valve. The material solidifies in the prepolymerizer and cannot be discharged. Among them, the prepolymerizer is a vertical reactor with stirring and jacket, and the stirring paddle is a three-blade swept type.

[0027] Comparative Example 2 A method for preparing nylon 46 comprises the following steps: (1) Salt formation: 10 kg of adipic acid and 100 kg of methanol were added to a salt forming kettle, stirring was started, the temperature was raised to 50°C, 5.9 kg of 1,4-butanediamine was added to the salt forming kettle, the temperature was maintained at 50°C for reaction for 2.5 hours, a white precipitate was precipitated, the temperature was lowered to 25°C, the suspension in the salt forming kettle was discharged and filtered to obtain crude nylon 46 salt, the crude nylon 46 salt was dried at 80°C and 1 kPa vacuum for 5 hours to obtain nylon 46 salt; (2) Primary polymerization: 5 kg of nylon 46 salt and 2.8 kg of deionized water were added to a 10 L primary polymerization vessel, nitrogen was passed to remove oxygen, stirring was started, the temperature was heated to 205 ° C, the pressure was raised to 1.5 MPa, the exhaust valve was opened, the exhaust water vapor was cooled through the condenser, collected and weighed, the amount of condensed water collected was monitored, the exhaust speed was controlled by adjusting the exhaust valve opening and the heating amount, the reactor pressure was maintained at 1.5 MPa, and after 20 minutes, the weight of the collected condensed water reached 1.9 kg, and the exhaust valve was closed; The primary polymerizer is a vertical reactor with stirring and jacket, and the stirring blade is a three-blade swept type; (3) Prepolymerization: Open the bottom valve of the prepolymerizer, start the melt pump of the prepolymerizer, set the melt pump flow rate to 10 kg / hr, and let the nylon 46 prepolymer in the prepolymerizer pass through the heat exchanger continuously. The outlet temperature of the heat exchanger is 305°C, and then flow into the 8L prepolymerizer. The stirring speed of the prepolymerizer is 45 RPM, the pressure of the prepolymerizer is normal pressure, and the temperature is 305°C. The residence time of the material in the prepolymerizer is 8 minutes. Open the prepolymerizer discharge valve and the discharge melt pump, set the flow rate to 8.5 kg / hr, and extrude the material into material strips through the die head. The material has a low viscosity and cannot be pelletized normally. Put the material into water to cool it, and then crush it to obtain nylon 46 prepolymer particles. The prepolymerizer is a horizontal reactor with a spiral agitator and three exhaust ports; (4) Solid phase viscosity enhancement: 5 kg of nylon 46 prepolymer particles were placed in a 20 L dryer, nitrogen was introduced to maintain the pressure of the dryer at 0.06 MPa, the temperature was raised to 230°C, nitrogen was discharged at the same time to remove the moisture generated by the reaction, and the mixture was dried for 14 hours to obtain nylon 46 polymer. The dryer was a drum dryer with a jacket.

[0028] Comparative Example 3 A method for preparing nylon 46 comprises the following steps: (1) Salt formation: 10 kg of adipic acid and 100 kg of methanol were added to a salt forming kettle, stirring was started, the temperature was raised to 50°C, 5.9 kg of 1,4-butanediamine was added to the salt forming kettle, the temperature was maintained at 50°C for reaction for 2.5 hours, a white precipitate was precipitated, the temperature was lowered to 25°C, the suspension in the salt forming kettle was discharged and filtered to obtain crude nylon 46 salt, the crude nylon 46 salt was dried at 80°C and 1 kPa vacuum for 5 hours to obtain nylon 46 salt; (2) Primary polymerization: 5 kg of nylon 46 salt and 2.8 kg of deionized water were added to a 10 L primary polymerization vessel, nitrogen was passed to remove oxygen, stirring was started, the temperature was heated to 230 ° C, the pressure was raised to 2.7 MPa, the exhaust valve was opened, the exhaust water vapor was cooled through the condenser, collected and weighed, the amount of condensed water collected was monitored, the exhaust speed was controlled by adjusting the exhaust valve opening and the heating amount, the reactor pressure was maintained at 2.7 MPa, and after 35 minutes, the weight of the collected condensed water reached 2.3 kg, and the exhaust valve was closed; The primary polymerizer is a vertical reactor with stirring and jacket, and the stirring blade is a three-blade swept type; (3) Prepolymerization: Open the bottom valve of the prepolymerizer, start the melt pump of the prepolymerizer, set the melt pump flow rate to 10 kg / hr, and let the nylon 46 prepolymer in the prepolymerizer pass through the heat exchanger continuously. The outlet temperature of the heat exchanger is 305°C, and then flow into the 8L prepolymerizer. The stirring speed of the prepolymerizer is 45 RPM, the pressure of the prepolymerizer is normal pressure, and the temperature is 305°C. The residence time of the material in the prepolymerizer is 8 minutes. Open the prepolymerizer discharge valve and the discharge melt pump, set the flow rate to 9 kg / hr, and extrude the material into material strips through the die head. After cooling and pelletizing, nylon 46 prepolymer particles are obtained; The prepolymerizer is a horizontal reactor with a spiral agitator and three exhaust ports; (4) Solid phase viscosity enhancement: 5 kg of nylon 46 prepolymer particles were placed in a 20 L dryer, nitrogen was introduced to maintain the pressure of the dryer at 0.06 MPa, the temperature was raised to 230°C, nitrogen was discharged at the same time to remove the moisture generated by the reaction, and the mixture was dried for 14 hours to obtain nylon 46 polymer. The dryer was a drum dryer with a jacket.

[0029] The relevant performance parameters of the nylon 46 polymers obtained in Examples 1-2 and Comparative Examples 1-3 are shown in Table 1.

[0030] Table 1 Relevant performance parameters of nylon 46 polymer obtained in Examples 1-2 and Comparative Examples 1-3 The test methods for relative viscosity and b value in Table 1 are as follows: Relative viscosity: Weigh 1g of sample accurately, add it to 100mL of 96% sulfuric acid, and stir to dissolve at 20-30℃. After complete dissolution, place the solution in an Ubbelohde viscometer, place it in a constant temperature bath at 25℃ for 10 minutes, and measure the falling speed (t). In addition, measure the falling speed (t 0 ). According to the following formula, t and t 0 Calculate the relative viscosity, relative viscosity = t / t 0 .

[0031] b value: Take a certain amount of nylon 46 polymer particles and measure the b value of the particles using a CR-400 / 410 colorimeter.

[0032] From the relevant data comparison of the embodiment and the comparative example in Table 1, it can be seen that the comparative example 1 discharges too much water vapor in the prepolymerization stage, and the reaction system cannot maintain a liquid state. Although the initial polymer relative viscosity is higher than that of the embodiment, the material solidifies in the initial polymerizer and cannot react further. The comparative example 2 discharges less water vapor in the prepolymerization stage, and the initial polymer viscosity is on the low side, which affects the further reaction behind. The polymer viscosity obtained after prepolymerization and solid phase thickening is on the low side. The comparative example 3 increases the reaction temperature, the initial polymerization reaction temperature is too high, the prepolymer b value increases, and the color turns yellow. Although the relative viscosity of the prepolymer is not low and can be stranded and pelletized, the viscosity is not high after the solid phase thickening, indicating that the initial polymerization reaction temperature is too high to adversely affect the polymerization reaction, and the side reaction increases, which affects the improvement of the molecular weight. In the embodiment, the temperature and the amount of water discharged are controlled to be relatively low during the initial polymerization stage to carry out the initial polymerization reaction, maintain the system in a liquid state, obtain a suitable polymer viscosity, and rapidly remove the remaining water in the material during the prepolymerization stage. The relative viscosity of the prepolymer meets the requirements of strand pelletizing, and the obtained regular initial polymer particles avoid the breakage of block materials or the use of powder materials for solid phase viscosity enhancement. The entire production process can efficiently obtain a high-viscosity nylon 46 polymer.

[0033] Finally, it should be noted that the above specific implementation methods are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present invention, which should be included in the scope of the claims of the present invention.

Claims

1. A method for preparing nylon 46, characterized in that: The following steps are involved: (1) Salt formation: 100 parts by weight of adipic acid and 800-1000 parts of methanol are added to a salt forming kettle, the temperature is raised to 40-60°C, 55-60 parts of 1,4-butanediamine are added to the salt forming kettle, the temperature is maintained at 40-60°C for reaction for 2-3 hours, the temperature is lowered to 20-30°C, the material in the salt forming kettle is discharged, and nylon 46 salt is obtained by filtering and vacuum drying; (2) Preliminary polymerization: 100 parts of nylon 46 salt and 50-60 parts of deionized water are added to a preliminarily polymerizer by weight, nitrogen is introduced to discharge oxygen, stirring is started, the temperature is raised to 180-210°C, water vapor is discharged to maintain the pressure of the reactor at 0.8-1.8 MPa, the discharged water is condensed and collected, and the discharged water is weighed to calculate the remaining water in the reaction system. When the water in the reaction system is 8%-12% of the nylon 46 salt, the discharge of water vapor is stopped to obtain a nylon 46 preliminarily polymerized product; (3) Prepolymerization: The nylon 46 prepolymer obtained in step (2) is continuously passed through a heat exchanger to raise its temperature to 300-310°C, and then flows into a prepolymerizer. The prepolymer pressure is normal pressure and the temperature is 300-310°C. The material stays in the prepolymer for 5-10 minutes. The material is extruded into strips through a die head at the outlet of the prepolymerizer, and then cooled and pelletized to obtain a nylon 46 prepolymer. (4) Solid phase viscosity enhancement: The nylon 46 prepolymer obtained in step (3) is placed in a dryer, and nitrogen is continuously introduced to maintain the pressure of the dryer at 0.05-0.1 MPa. At the same time, the nitrogen is discharged to remove the moisture generated by the reaction. The temperature is raised to 220-250°C and dried for 10-15 hours to obtain a nylon 46 polymer.

2. The method for preparing nylon 46 according to claim 1, characterized in that: The primary polymerization vessel in step (2) is a vertical reactor with a stirring device and a jacket, and the stirring blade is a three-blade swept type.

3. The method for preparing nylon 46 according to claim 1, characterized in that: The drainage time in step (2) is 20-40 minutes.

4. The method for preparing nylon 46 according to claim 1, characterized in that: The relative viscosity of the nylon 46 primary polymer in step (2) is 1.4-1.

6.

5. The method for preparing nylon 46 according to claim 1, characterized in that: The prepolymerizer in step (3) is a horizontal reactor with a spiral agitator and 2-4 exhaust ports.

6. The method for preparing nylon 46 according to claim 1, characterized in that: The relative viscosity of the nylon 46 prepolymer in step (3) is 1.8-2.

4.

7. The method for preparing nylon 46 according to claim 1, characterized in that: The dryer in step (4) is a drum dryer with a jacket.

8. The method for preparing nylon 46 according to claim 1, characterized in that: The relative viscosity of the nylon 46 polymer in step (4) is 3.2-5.0.

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