Continuous polymerization preparation method and preparation system of polyamide

Abstract

The invention provides a continuous polymerization preparation method and a preparation system of polyamide, and belongs to the technical field of preparation of compounds. The continuous polymerization preparation method of the polyamide comprises the following steps: carrying out salt forming reaction on metered binary acid and diamine, and carrying out pH regulation to obtain a polyamide salt solution; evaporating and concentrating the polyamide salt solution to obtain a polyamide salt concentrated product; pre-polymerizing the polyamide concentrated product in the first reactor to obtain a polyamide prepolymer; performing condensation polymerization on the prepolymer of the polyamide in a second reactor to obtain a polycondensate of the polyamide; pelletizing the polycondensate of the polyamide to obtain wet slices of the polyamide; the wet slices of polyamide are sequentially dehydrated and dried to obtain polyamide slices, and the value range of the relative viscosity of the polyamide slices is 2.4-3.6. The continuous polymerization preparation system of polyamide can be used for realizing the method. The method has the characteristics of energy conservation, high efficiency and simple process flow.

Description

Technical Field

[0001] This invention relates to the field of compound preparation technology, and in particular to a method and system for the continuous polymerization preparation of polyamides. Background Technology

[0002] Polyamide, commonly known as nylon, is widely used in the automotive, textile, electronics, and machinery industries due to its excellent comprehensive properties, including good elasticity, high mechanical strength, good toughness, excellent wear resistance and self-lubrication, good oil resistance and chemical stability, and ease of processing and molding. However, current continuous polymerization methods for preparing polyamide involve high energy consumption and long process flows. Therefore, there is an urgent need to develop an energy-efficient and high-performance method for preparing polyamide materials. Summary of the Invention

[0003] In view of this, the present invention provides a continuous polymerization preparation method and system for polyamide, which effectively reduces the time and energy consumption of subsequent salt concentration processes and ensures the quality of polyamide salts; effectively reduces the energy consumption of processes such as high-pressure polymerization, is energy-saving and efficient, does not require high-pressure equipment, has strong operability and safety; the process is simple and time-saving, which can effectively improve production efficiency and is therefore more suitable for practical use.

[0004] To achieve the first objective mentioned above, the technical solution of the continuous polymerization preparation method for polyamide provided by the present invention is as follows:

[0005] The continuous polymerization preparation method for polyamide provided by this invention includes the following steps:

[0006] After a metered salt-forming reaction of a diacid and a diamine, and pH adjustment, a polyamide salt solution is obtained. The polyamide salt solution contains 75%-85% polyamide by mass, and its pH ranges from 7.8 to 9.0. The polyamide salt formation method involves obtaining a mixed suspension or solution of diacid / deoxygenated water under a nitrogen atmosphere with a purity greater than 99.999%. This suspension or solution is then added to the salt-forming reactor. Compared to polyamide salt solutions prepared by traditional processes, which have lower concentrations and require subsequent dehydration and concentration for polymerization, resulting in higher energy consumption, the polyamide salt solution prepared using the process provided by this invention has a higher concentration. Subsequent processes do not require extensive dehydration and concentration, effectively reducing process time and energy consumption. Furthermore, reducing salt concentration time effectively prevents polyamide oxidation during concentration, improving salt quality and consequently, polymer quality.

[0007] The polyamide salt solution is evaporated and concentrated to obtain a concentrated polyamide product, wherein the mass percentage of polyamide in the concentrated polyamide product ranges from 95% to 98%.

[0008] The concentrated product of the polyamide is prepolymerized in the first reactor to obtain a prepolymer of the polyamide.

[0009] The prepolymer of the polyamide undergoes a polycondensation reaction in the second reactor to obtain a polyamide condensate.

[0010] The polyamide condensate is pelletized to obtain wet polyamide chips;

[0011] The wet polyamide chips are sequentially dehydrated and dried to obtain polyamide chips, and the relative viscosity of the polyamide chips ranges from 2.4 to 3.6.

[0012] The continuous polymerization preparation method of polyamide provided by the present invention can be further implemented by the following technical measures.

[0013] Preferably, in the step of reacting the metered dicarboxylic acid and diamine to form a salt, and then adjusting the pH to obtain a polyamide salt solution,

[0014] The dicarboxylic acid is selected from one or more of sebacic acid, undecanoic acid, dodecanoic acid, tridecanoic acid, tetradecanoic acid, and octadecanoic acid;

[0015] The diamine is selected from one or more of pentanediamine and hexanediamine, or a mixture thereof.

[0016] Preferably, in the step of reacting the metered dicarboxylic acid and diamine to form a salt, and then adjusting the pH to obtain a polyamide salt solution,

[0017] The reactor temperature for the salt-forming reaction ranges from 75℃ to 90℃.

[0018] The duration of the salt formation reaction ranges from 0.5h to 3h.

[0019] Preferably, in the step of reacting the metered dicarboxylic acid and diamine to form a salt, and then adjusting the pH to obtain a polyamide salt solution,

[0020] The pH adjuster is selected from one or more of 2-methyl-pentanediamine, pentanediamine, hexamethylenediamine, and p-phenylenediamine.

[0021] Preferably, in the step of prepolymerizing the concentrated polyamide product to obtain the polyamide prepolymer, the polymerization reaction aid is selected from one or more of nucleating agents, molecular weight regulators, antioxidants, matting agents, and catalysts. In this case, by adding amines to adjust the pH of the salt solution, the stoichiometric ratio of diamine and diacid is effectively maintained during polymerization, preventing the loss of diamine due to salt decomposition in subsequent processes, which would lead to an imbalance in the polymer end-group ratio and affect the subsequent polymerization process. This helps to ensure the mechanical properties and thermal stability of the prepared polyamide material.

[0022] Preferably, in the step of prepolymerizing the concentrated polyamide product in the first reactor to obtain the polyamide prepolymer,

[0023] The temperature range of the first reactor is 140℃-170℃. In this case, by controlling the temperature of the first reaction, the reaction rate of polyamide salt forming oligomers can be effectively controlled, the decomposition of polyamide salt can be inhibited, thereby maintaining the fluidity of the oligomer / polyamide salt mixture and the stoichiometric balance of the terminal functional groups, ensuring the controllability of the solid-melt transition during prepolymerization, and preventing pipeline blockage caused by excessively rapid increase in melt viscosity.

[0024] The pressure of the first reactor ranges from 0.1 MPa to 0.2 MPa;

[0025] The residence time of the material in the first reactor ranges from 1h to 3h.

[0026] Preferably, in the step of obtaining the polyamide condensate by undergoing a polycondensation reaction in the second reactor, the prepolymer of the polyamide is subjected to a polycondensation reaction.

[0027] The temperature range of the second reactor is 230℃-260℃;

[0028] The pressure range of the second reactor is 0-0.05 MPa;

[0029] The residence time of the material in the second reactor ranges from 2h to 3h.

[0030] To achieve the second objective mentioned above, the technical solution for the continuous polymerization preparation system of polyamide provided by this invention is as follows:

[0031] The continuous polymerization preparation system for polyamide, which implements the continuous polymerization preparation method for polyamide provided by the present invention, includes:

[0032] Salt-forming vessel, used for the salt-forming reaction of the aforementioned dicarboxylic acid and diamine;

[0033] A salt storage tank for forming the polyamide salt solution, wherein the inlet of the salt storage tank is connected to the outlet of the salt-forming tank;

[0034] An auxiliary agent storage tank is used for storing auxiliary agents, wherein the outlet of the auxiliary agent storage tank is connected to the inlet of the salt storage tank;

[0035] An evaporator is used for evaporating and concentrating the polyamide salt solution to obtain a concentrated polyamide product;

[0036] The first reactor is used for prepolymerization of the concentrated product of the polyamide to obtain a prepolymer of the polyamide;

[0037] The second reactor is used for the polycondensation reaction of the prepolymer of the polyamide to obtain the polyamide condensate;

[0038] A pelletizer is used to pelletize the polyamide condensate to obtain wet polyamide chips;

[0039] A drying tower is used to sequentially dehydrate and dry the wet polyamide slices to obtain polyamide slices.

[0040] The continuous polymerization preparation system for polyamide provided by the present invention can be further implemented by the following technical measures.

[0041] Preferably, the continuous polymerization preparation system of the polyamide in the continuous polymerization preparation method further includes:

[0042] A mixer is provided and connected between the salt storage tank and the evaporator, wherein the outlet of the auxiliary agent storage tank is also connected to the inlet of the mixer. In this configuration, the polyamide salt solution can be thoroughly mixed using this mixer.

[0043] Preferably, the mixer is a static mixer. In this case, by using a static mixer, the polyamide salt solution can be mixed more thoroughly.

[0044] Preferably, the continuous polymerization preparation system of the polyamide further includes a first heat exchanger, which is disposed and connected between the salt storage tank and the evaporator. In this case, the polyamide salt solution can be heated to a set temperature by the first heat exchanger before entering the evaporator, thereby resulting in higher evaporation efficiency.

[0045] Preferably, the continuous polymerization preparation system of the polyamide further includes a second heat exchanger, disposed and connected between the first reactor and the second reactor. In this case, the obtained polyamide polymer can be heated to a set temperature before entering the second reactor, thereby further improving the preparation efficiency.

[0046] Preferably, the continuous polymerization preparation system of the polyamide further includes a stirring mechanism disposed within the first reactor for stirring the materials within the first reactor. In this case, the materials are mixed more thoroughly within the first reactor, and the reaction proceeds to a higher degree.

[0047] Preferably, the pelletizer is an underwater pelletizer. In this case, material loss or environmental pollution during the pelletizing process can be reduced to a much lower level.

[0048] Compared with the prior art, the advantages of the continuous polymerization preparation method and preparation system for polyamide provided by the present invention are as follows:

[0049] 1. This invention prepares a high-concentration polyamide salt solution by controlling the salt formation reaction process, effectively reducing the time and energy consumption of the subsequent salt concentration process and ensuring the quality of the polyamide salt.

[0050] 2. This invention employs a two-stage continuous atmospheric pressure polymerization process to obtain polyamide resin. Compared to traditional poly(diacid) diamide preparation processes, it can effectively reduce energy consumption in high-pressure polymerization and other processes, making it energy-saving and efficient. This process does not require high-pressure equipment, and it is highly operable and safe.

[0051] 3. The polyamide continuous polymerization system provided by the present invention has a simple process flow and short time consumption, which can effectively improve production efficiency. Attached Figure Description

[0052] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0053] Appendix Figure 1 This is a schematic diagram of the overall structure of the continuous polymerization preparation system for polyamide provided in an embodiment of the present invention. Detailed Implementation

[0054] In view of this, the present invention provides a continuous polymerization preparation method and system for polyamide, which effectively reduces the time and energy consumption of subsequent salt concentration processes and ensures the quality of polyamide salts; effectively reduces the energy consumption of processes such as high-pressure polymerization, is energy-saving and efficient, does not require high-pressure equipment, has strong operability and safety; the process is simple and time-saving, which can effectively improve production efficiency and is therefore more suitable for practical use.

[0055] To further illustrate the technical means and effects adopted by the present invention to achieve the intended purpose, the following, in conjunction with the accompanying drawings and preferred embodiments, details the specific implementation methods, structures, features, and effects of a continuous polymerization preparation method and system for polyamide according to the present invention. In the following description, different "embodiments" or "embodiments" do not necessarily refer to the same embodiment. Furthermore, specific features, structures, or characteristics in one or more embodiments can be combined in any suitable form.

[0056] In this article, the term "and / or" is merely a description of the relationship between related objects, indicating that there can be three relationships, such as A and / or B. Specifically, it can mean that A and B can be included at the same time, A can exist alone, or B can exist alone, and any of the above three situations can be met.

[0057] Example 1

[0058] In this embodiment, polyamide 510 is prepared using the following method:

[0059] a. Add 640 kg sebacic acid and 243 kg deoxygenated water to a salt-forming tank, start stirring, and heat to 75°C. Then, slowly add 330 kg pentanediamine to the salt-forming tank at a rate of 100 kg / h, continue the reaction at a constant temperature for 1.5 h, and then add pentanediamine to adjust the pH of the solution to 8.0, obtaining a clear and transparent 510 salt solution with a concentration of 80 wt%.

[0060] b. The polyamide salt solution is sent to a salt storage tank and then enters a falling film evaporator via a heat exchanger; the salt solution concentration is concentrated to 95 wt%.

[0061] c. The concentrated salt solution is sent to the first reactor at a temperature of 140°C, a residence time of 1.5 h, and a pressure of 0.1 MPa.

[0062] d. The material from the first reactor is transferred to the second reactor. The temperature of the second reactor is 230°C, the reaction pressure is atmospheric pressure, and the residence time is 2 hours.

[0063] e. The material from the second reactor is cooled, pelletized, extracted, and dried to obtain polyamide 510 with a relative viscosity of 2.36, terminal amino group of 80.2 mmol / kg, and terminal carboxyl group of 75.1 mmol / kg.

[0064] Example 2

[0065] In this embodiment, polyamide 610 is prepared using the following method:

[0066] a. Add 640 kg of sebacic acid and 206 kg of deoxygenated water to a salt-forming tank, start stirring, and heat to 75°C. Then, slowly add 368 kg of hexamethylenediamine to the salt-forming tank at a rate of 100 kg / h, continue the reaction at a constant temperature for 1.5 h, and then add hexamethylenediamine to adjust the pH of the solution to 8.5, obtaining a clear and transparent 610 salt solution with a concentration of 83 wt%.

[0067] b. The polyamide salt solution is sent to a salt storage tank and then enters a falling film evaporator via a heat exchanger; the salt solution concentration is concentrated to 95 wt%.

[0068] c. The concentrated salt solution is sent to the first reactor at a temperature of 145°C, a residence time of 1.2 h, and a pressure of 0.2 MPa.

[0069] d. The material from the first reactor is transferred to the second reactor. The temperature of the second reactor is 240℃, the reaction pressure is atmospheric pressure, and the residence time is 2.5h.

[0070] e. The material from the second reactor is cooled, pelletized, extracted, and dried to obtain polyamide 510 with a relative viscosity of 2.56, terminal amino group of 70.2 mmol / kg, and terminal carboxyl group of 68.1 mmol / kg.

[0071] Example 3

[0072] In this embodiment, polyamide 511 is prepared using the following method:

[0073] a. Add 685 kg of undecyl diacid and 178 kg of deoxygenated water to a salt-forming tank, start stirring, and heat to 80°C. Then, slowly add 323 kg of pentanediamine to the salt-forming tank at a rate of 100 kg / h, continue the reaction at a constant temperature for 1.5 h, and then add pentanediamine to adjust the pH of the solution to 8.2, obtaining a clear and transparent 511 salt solution with a concentration of 85 wt%.

[0074] b. The polyamide salt solution is sent to a salt storage tank and then enters a falling film evaporator via a heat exchanger; the salt solution concentration is concentrated to 98 wt%.

[0075] c. The concentrated salt solution is sent to the first reactor at a temperature of 150°C, a residence time of 1 hour, and a pressure of 0.15 MPa.

[0076] d. The material from the first reactor is transferred to the second reactor. The temperature of the second reactor is 253°C, the reaction pressure is atmospheric pressure, and the residence time is 2.5 hours.

[0077] e. The material from the second reactor is cooled, pelletized, extracted, and dried to obtain polyamide 510 with a relative viscosity of 2.46, terminal amino group of 83.2 mmol / kg, and terminal carboxyl group of 80.1 mmol / kg.

[0078] Example 4

[0079] In this embodiment, polyamide 512 is prepared using the following method:

[0080] a. Add 744 kg of dodecyl diic acid and 269 kg of deoxygenated water to a salt-forming tank, start stirring, and heat to 78°C. Then, slowly add 330 kg of pentanediamine to the salt-forming tank at a rate of 100 kg / h, continue the reaction at a constant temperature for 1.5 h, and then add 2-methyl-pentanediamine to adjust the pH of the solution to 8.0, obtaining a clear and transparent 512 salt solution with a concentration of 80 wt%.

[0081] b. The polyamide salt solution is sent to a salt storage tank and then enters a falling film evaporator via a heat exchanger; the salt solution concentration is concentrated to 98 wt%.

[0082] c. The concentrated salt solution is sent to the first reactor at a temperature of 170°C, a residence time of 1 hour, and a pressure of 0.1 MPa.

[0083] d. The material from the first reactor is transferred to the second reactor. The temperature of the second reactor is 250℃, the reaction pressure is 0.05 MPa, and the residence time is 3 hours.

[0084] e. The material from the second reactor is cooled, pelletized, extracted, and dried to obtain polyamide 510 with a relative viscosity of 2.86, terminal amino group of 60.8 mmol / kg, and terminal carboxyl group of 59.4 mmol / kg.

[0085] Example 5

[0086] In this embodiment, polyamide 612 is prepared using the following method:

[0087] a. Grind 599 kg of dodecyl diic acid and 100 kg of deoxygenated water, add them to a salt-forming tank, start stirring, and heat to 80°C. Then, slowly add 301 kg of hexamethylenediamine to the salt-forming tank at a rate of 100 kg / h, continue the reaction at a constant temperature for 2.5 h, and then add hexamethylenediamine to adjust the pH of the solution to 8.6, obtaining a clear and transparent 612 salt solution with a concentration of 90 wt%.

[0088] b. The polyamide salt solution is sent to a salt storage tank and then enters a falling film evaporator via a heat exchanger; the salt solution concentration is concentrated to 96 wt%.

[0089] c. The concentrated salt solution is sent to the first reactor at a temperature of 152°C, a residence time of 1.5 h, and a pressure of 0.15 MPa.

[0090] d. The material from the first reactor is transferred to the second reactor. The temperature of the second reactor is 250℃, the reaction pressure is 0.03MPa, and the residence time is 2h.

[0091] e. The material from the second reactor is cooled, pelletized, extracted, and dried to obtain polyamide 510 with a relative viscosity of 2.26, terminal amino group of 90.2 mmol / kg, and terminal carboxyl group of 85.1 mmol / kg.

[0092] Example 6

[0093] In this embodiment, polyamide 514 is prepared using the following method:

[0094] a. Add 833 kg of tetradecyl diacid and 273 kg of deoxygenated water to a salt-forming tank, start stirring, and heat to 86°C. Then, slowly add 330 kg of pentanediamine to the salt-forming tank at a rate of 100 kg / h, continue the reaction at a constant temperature for 1.5 h, and then add m-phenylenediamine to adjust the pH of the solution to 8.0, obtaining a clear and transparent 510 salt solution with a concentration of 81 wt%.

[0095] b. The polyamide salt solution is sent to a salt storage tank and then enters a falling film evaporator via a heat exchanger; the salt solution concentration is concentrated to 95 wt%.

[0096] c. The concentrated salt solution is sent to the first reactor at a temperature of 165°C, a residence time of 1 hour, and a pressure of 0.15 MPa.

[0097] d. The material from the first reactor is transferred to the second reactor. The temperature of the second reactor is 245℃, the reaction pressure is atmospheric pressure, and the residence time is 3h.

[0098] e. The material from the second reactor is cooled, pelletized, extracted, and dried to obtain polyamide 510 with a relative viscosity of 2.46, terminal amino group of 76.5 mmol / kg, and terminal carboxyl group of 72.9 mmol / kg.

[0099] Example 7

[0100] In this embodiment, polyamide 518 is prepared using the following method:

[0101] a. Add 1016 kg of octadecyl diacid and 337 kg of deoxygenated water to a salt-forming tank, start stirring, and heat to 90°C. Then, slowly add 330 kg of pentanediamine to the salt-forming tank at a rate of 100 kg / h, continue the reaction at a constant temperature for 1.5 h, and then add pentanediamine to adjust the pH of the solution to 8.0, obtaining a clear and transparent 510 salt solution with a concentration of 80 wt%.

[0102] b. The polyamide salt solution is sent to a salt storage tank and then enters a falling film evaporator via a heat exchanger; the salt solution concentration is concentrated to 98 wt%.

[0103] c. The concentrated salt solution is sent to the first reactor at a temperature of 165°C, a residence time of 1.5 h, and a pressure of 0.2 MPa.

[0104] d. The material from the first reactor is transferred to the second reactor. The temperature of the second reactor is 240℃, the reaction pressure is atmospheric pressure, and the residence time is 2h.

[0105] e. The material from the second reactor is cooled, pelletized, extracted, and dried to obtain polyamide 510 with a relative viscosity of 2.42, terminal amino group of 72.4 mmol / kg, and terminal carboxyl group of 68.5 mmol / kg.

[0106] Example 8

[0107] In this embodiment, polyamide 510 is prepared using the following method:

[0108] a. Add 640 kg sebacic acid and 243 kg deoxygenated water to a salt-forming tank, start stirring, and heat to 78°C. Then, slowly add 330 kg pentanediamine to the salt-forming tank at a rate of 100 kg / h, continue the reaction at a constant temperature for 1.5 h, and then add pentanediamine to adjust the pH of the solution to 8.0, obtaining a clear and transparent 510 salt solution with a concentration of 80 wt%.

[0109] b. The polyamide salt solution is sent to a salt storage tank and then enters a falling film evaporator via a heat exchanger; the salt solution concentration is concentrated to 95 wt%.

[0110] c. The concentrated salt solution is sent to the first reactor at a temperature of 140°C, a residence time of 1.5 h, and a pressure of 0.1 MPa.

[0111] d. The material from the first reactor is transferred to the second reactor. The temperature of the second reactor is 230°C, the reaction pressure is atmospheric pressure, and the residence time is 2 hours.

[0112] e. The material from the second reactor is cooled, pelletized, and extracted to obtain wet polyamide 510 chips;

[0113] f. The wet polyamide 510 chips were fed into a drying tower at 155°C for 36 hours. The polyamide 510 chips had a relative viscosity of 3.6, an amino group concentration of 45.6 mmol / kg, and a carboxyl group concentration of 43.5 mmol / kg.

[0114] Example 9

[0115] In this embodiment, polyamide 510 / 610 is prepared using the following method:

[0116] a. Add 640 kg of sebacic acid and 247 kg of deoxygenated water to a salt-forming tank, start stirring, and heat to 70°C. Then, slowly add 204 kg of pentanediamine and 143 kg of hexamethylenediamine to the salt-forming tank at a rate of 100 kg / h, and continue the reaction at a constant temperature for 1.5 h. Then, add pentanediamine to adjust the pH of the solution to 8.0, obtaining a clear and transparent 510 salt solution with a concentration of 80 wt%.

[0117] b. The polyamide salt solution is sent to a salt storage tank and then enters a falling film evaporator via a heat exchanger; the salt solution concentration is concentrated to 95 wt%.

[0118] c. The concentrated salt solution is sent to the first reactor at a temperature of 140°C, a residence time of 1.5 h, and a pressure of 0.1 MPa.

[0119] d. The material from the first reactor is transferred to the second reactor. The temperature of the second reactor is 230°C, the reaction pressure is atmospheric pressure, and the residence time is 2 hours.

[0120] e. The material from the second reactor is cooled, pelletized, extracted, and dried to obtain copolyamide 510 / 610 with a relative viscosity of 2.31, terminal amino group of 82.1 mmol / kg, and terminal carboxyl group of 77.4 mmol / kg.

[0121] Example 10

[0122] In this embodiment, polyamide 510 / 512 is prepared using the following method:

[0123] a. Add 438 kg sebacic acid, 216 kg dodecanoic acid, and 243 kg deoxygenated water to a salt-forming tank, start stirring, and heat to 82°C. Then, slowly add 330 kg pentanediamine to the salt-forming tank at a rate of 100 kg / h, continue the reaction at a constant temperature for 1.5 h, and then add pentanediamine to adjust the pH of the solution to 8.0, obtaining a clear and transparent 510 salt solution with a concentration of 80 wt%.

[0124] b. The polyamide salt solution is sent to a salt storage tank and then enters a falling film evaporator via a heat exchanger; the salt solution concentration is concentrated to 95 wt%.

[0125] c. The concentrated salt solution is sent to the first reactor at a temperature of 140°C, a residence time of 1.5 h, and a pressure of 0.1 MPa.

[0126] d. The material from the first reactor is transferred to the second reactor. The temperature of the second reactor is 230°C, the reaction pressure is atmospheric pressure, and the residence time is 2 hours.

[0127] e. The material from the second reactor is cooled, pelletized, extracted, and dried to obtain copolyamide 510 / 512 with a relative viscosity of 2.40, terminal amino group of 78.5 mmol / kg, and terminal carboxyl group of 72.6 mmol / kg.

[0128] Comparative Example 1

[0129] In this comparative example, polyamide 510 was prepared using the following method:

[0130] a. Add 640 kg sebacic acid, 330 kg pentanediamine, and 970 kg deoxygenated water to a salt-forming tank, start stirring, heat to 75°C, and continue the reaction at a constant temperature for 1.5 h. Then add pentanediamine to adjust the pH of the solution to 8.0, and obtain a clear and transparent 510 salt solution with a concentration of 50 wt%.

[0131] b. The polyamide salt solution is sent to a salt storage tank and then enters a falling film evaporator via a heat exchanger; the salt solution concentration is concentrated to 95 wt%.

[0132] The subsequent processes are the same as in Example 1;

[0133] The comparative example yielded polyamide 510 with a relative viscosity of 2.06, 40.2 mmol / kg of terminal amino groups, and 105.1 mmol / kg of terminal carboxyl groups.

[0134] Comparative Example 2

[0135] In this comparative example, polyamide 510 was prepared using the following method:

[0136] a. Add 640 kg sebacic acid and 243 kg deoxygenated water to a salt-forming tank, start stirring, and heat to 75°C. Then, slowly add 330 kg pentanediamine to the salt-forming tank at a rate of 100 kg / h, and continue the reaction at a constant temperature for 1.5 h. Then, add pentanediamine to adjust the pH of the solution to 8.0, and obtain a clear and transparent 510 salt solution with a concentration of 80 wt%.

[0137] b. The polyamide salt solution is sent to the salt storage tank, and then enters the first reactor through a heat exchanger at a temperature of 140°C, a residence time of 4.5 h, and a pressure of 0.1 MPa.

[0138] The subsequent steps are the same as in Example 1.

[0139] The comparative example yielded polyamide 510 with a relative viscosity of 1.96, 50.7 mmol / kg of terminal amino groups, and 125.7 mmol / kg of terminal carboxyl groups.

[0140] Comparative Example 3

[0141] In this comparative example, polyamide 510 was prepared using the following method:

[0142] a. Add 640 kg sebacic acid and 970 kg deoxygenated water to a salt-forming tank, start stirring, and heat to 75°C. Then, slowly add 330 kg pentanediamine to the salt-forming tank at a rate of 100 kg / h, and continue the reaction at a constant temperature for 1.5 h. Then, add pentanediamine to adjust the pH of the solution to 8.0, and obtain a clear and transparent 510 salt solution with a concentration of 50 wt%.

[0143] b. The polyamide salt solution is sent to the salt storage tank and then enters the first reactor via a heat exchanger;

[0144] c. The salt solution is sent to the first reactor at a temperature of 180°C, a residence time of 1 hour, and a pressure of 0.1 MPa.

[0145] d. The material from the first reactor is transferred to the second reactor. The temperature of the second reactor is 210℃, the reaction pressure is 1.7MPa, and the residence time is 1.5h.

[0146] e. The material in the second reactor is slowly depressurized and heated to 235°C, then sent to the third reactor, where the temperature is raised to 235°C. The reaction pressure is atmospheric pressure, and the reaction time is 1 hour.

[0147] e. The material from the third reactor is cooled, pelletized, extracted, and dried to obtain polyamide 510 with a relative viscosity of 2.56, terminal amino group of 65.8 mmol / kg, and terminal carboxyl group of 63.7 mmol / kg.

[0148] As can be seen from the above examples and comparative examples, Comparative Example 1 uses conventional processes to prepare a 50wt% polyamide salt solution, which is then sent to a falling film evaporator for concentration via a salt storage tank. This process requires a long concentration time, consumes a lot of energy, and the salt is prone to decomposition reaction, resulting in an imbalance in the molar ratio of amino and carboxyl groups, and a large difference in the end group ratio of the polymer product. Furthermore, the polyamide is prone to quality degradation when exposed to high temperatures for a long time, resulting in poor color of the polymer. Comparative Example 2, without concentration, directly used an 80wt% salt solution for prepolymerization. The increased water content led to higher system pressure, requiring continuous depressurization to maintain the pressure, resulting in the loss of some diamine and affecting the polymer's viscosity and end groups. Comparative Example 3 used a conventional high-pressure polymerization process to produce polyamide chips. However, its heating process was slow and required high pressure, further increasing the requirements for equipment and temperature control systems. Furthermore, the polyamide viscosity increased too rapidly during depressurization, making it difficult to control and guarantee polyamide quality. The examples using high-concentration salt formation, concentration, and micro-positive pressure polymerization processes solved these problems. The polyamide products prepared using this process have controllable viscosity and adjustable end groups.

[0149] The polyamide system provided by this invention has low equipment requirements and can be implemented on conventional polyamide equipment after necessary modifications. It is easy to carry out large-scale industrial production, with low energy consumption, high production efficiency, and stable product quality. It is an excellent raw material for engineering plastics, films, fibers, industrial filter felts and hot melt adhesives.

[0150] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0151] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for the continuous polymerization preparation of polyamide, characterized in that, Includes the following steps: After a metric reaction of dicarboxylic acid and diamine to form a salt, and pH adjustment, a polyamide salt solution is obtained. The polyamide salt solution contains 75%-85% by mass and has a pH range of 7.8-9.

0. The polyamide salt solution is evaporated and concentrated to obtain a concentrated polyamide product, wherein the mass percentage of polyamide in the concentrated polyamide product ranges from 95% to 98%. The concentrated product of the polyamide is prepolymerized in the first reactor to obtain a prepolymer of the polyamide. The prepolymer of the polyamide undergoes a polycondensation reaction in the second reactor to obtain a polyamide condensate. The polyamide condensate is pelletized to obtain wet polyamide chips; The wet polyamide chips are sequentially dehydrated and dried to obtain polyamide chips, and the relative viscosity of the polyamide chips ranges from 2.4 to 3.

6.

2. The continuous polymerization preparation method of polyamide according to claim 1, characterized in that, In the step of reacting metered diacids and diamines to form a salt, and then adjusting the pH to obtain a polyamide salt solution, The dicarboxylic acid is selected from one or more of sebacic acid, undecanoic acid, dodecanoic acid, tridecanoic acid, tetradecanoic acid, and octadecanoic acid; The diamine is selected from one or more of pentanediamine and hexanediamine, or a mixture thereof.

3. The continuous polymerization preparation method of polyamide according to claim 1, characterized in that, In the step of reacting metered diacids and diamines to form a salt, and then adjusting the pH to obtain a polyamide salt solution, The reactor temperature for the salt-forming reaction ranges from 75℃ to 90℃. The duration of the salt formation reaction ranges from 0.5h to 3h.

4. The continuous polymerization preparation method of polyamide according to claim 1, characterized in that, In the step of reacting metered diacids and diamines to form a salt, and then adjusting the pH to obtain a polyamide salt solution, The pH adjuster is selected from one or more of 2-methyl-pentanediamine, pentanediamine, hexamethylenediamine, and p-phenylenediamine.

5. The continuous polymerization preparation method of polyamide according to claim 1, characterized in that, In the step of prepolymerizing the concentrated polyamide product to obtain the polyamide prepolymer, the polymerization reaction aid is selected from one or more of the following: nucleating agent, molecular weight regulator, antioxidant, matting agent, and catalyst. Preferably, in the step of prepolymerizing the concentrated polyamide product in the first reactor to obtain the polyamide prepolymer, The temperature range of the first reactor is 140℃-170℃; The pressure of the first reactor ranges from 0.1 MPa to 0.2 MPa; The residence time of the material in the first reactor ranges from 1h to 3h; Preferably, in the step of obtaining the polyamide condensate by undergoing a polycondensation reaction in the second reactor, the prepolymer of the polyamide is subjected to a polycondensation reaction. The temperature range of the second reactor is 230℃-260℃; The pressure range of the second reactor is 0-0.05 MPa; The residence time of the material in the second reactor ranges from 2h to 3h.

6. A continuous polymerization preparation system for polyamide that implements the continuous polymerization preparation method for polyamide according to any one of claims 1-5, characterized in that, include: Salt-forming vessel, used for the salt-forming reaction of the aforementioned dicarboxylic acid and diamine; A salt storage tank for forming the polyamide salt solution, wherein the inlet of the salt storage tank is connected to the outlet of the salt-forming tank; An auxiliary agent storage tank is used for storing auxiliary agents, wherein the outlet of the auxiliary agent storage tank is connected to the inlet of the salt storage tank; An evaporator is used for evaporating and concentrating the polyamide salt solution to obtain a concentrated polyamide product; The first reactor is used for prepolymerization of the concentrated product of the polyamide to obtain a prepolymer of the polyamide; The second reactor is used for the polycondensation reaction of the prepolymer of the polyamide to obtain the polyamide condensate; A pelletizer is used to pelletize the polyamide condensate to obtain wet polyamide chips; A drying tower is used to sequentially dehydrate and dry the wet polyamide slices to obtain polyamide slices.

7. The continuous polymerization preparation system for polyamide according to claim 6, characterized in that, Also includes: A mixer is provided and connected between the salt storage tank and the evaporator, wherein the outlet of the auxiliary agent storage tank is also connected to the inlet of the mixer.

8. The continuous polymerization preparation system for polyamide according to claim 7, characterized in that, The mixer is a static mixer.

9. The continuous polymerization preparation system for polyamide according to claim 6, characterized in that, Also includes: A first heat exchanger is provided and connected between the salt storage tank and the evaporator.

10. The continuous polymerization preparation system for polyamide according to claim 6, characterized in that, Also includes: A second heat exchanger is disposed between the first reactor and the second reactor; Preferably, the continuous polymerization preparation system of the polyamide in the continuous polymerization preparation method further includes: A stirring mechanism is installed inside the first reactor and is used to stir the materials inside the first reactor; Preferably, the pelletizer is an underwater pelletizer.

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