Nylon 66 and anhydrous melt polymerization process thereof

Abstract

The invention provides nylon 66 and an anhydrous melt polymerization process thereof. The number-average molecular weight of the nylon 66 is 20000-33000 g / mol, the molecular weight distribution is 2-3.0, the melting point is 250-260 DEG C, the gel content is smaller than or equal to 0.3%, the black grain content is smaller than or equal to 10 pieces / kg, and the melt outflow volume is 70-100 g within 10 min at the temperature of 270 DEG C under the load of 2.16 kg. The process sequentially comprises a salifying stage, a pre-polymerization stage, a pre-polymerization stage and a post-polymerization stage, wherein rich amine and rich acid components with a specific molar ratio are fused respectively and then mixed to form a salt, and then pre-polymerization is carried out under the nitrogen atmosphere at the temperature of 225-230 DEG C and the pressure of 1.2-1.6 MPa; raising the temperature to 260-280 DEG C and reducing the pressure to normal pressure at 0.3-0.5 MPa / h to finish pre-polymerization; and finally, carrying out post-polymerization at-0.02 to-0.06 MPa to obtain the high-molecular-weight polymer. Anhydrous salt forming and melt polycondensation are achieved through an acid-rich / amine-rich system, the problems of diamine volatilization and temperature out-of-control in a traditional anhydrous melting system are solved, and the obtained product is balanced in end group, stable in performance, simple in process, low in energy consumption and suitable for industrial production.

Description

Technical Field

[0001] This invention relates to the field of nylon 66 preparation technology, specifically to a nylon 66 and its anhydrous melt polymerization process. Background Technology

[0002] Traditional aqueous solution polymerization of nylon 66 results in high energy consumption, high cost, and high emissions due to the need for heating and evaporation of large amounts of water. Furthermore, the presence of water inhibits polymerization equilibrium, induces side reactions such as hydrolysis and aminolysis, leading to difficulty in increasing molecular weight, imbalanced end-group ratios, and decreased product performance. It also causes problems such as high-pressure corrosion, cumbersome processes, and large-scale wastewater treatment. While solid-phase polycondensation can lower the temperature, reduce side reactions, and increase molecular weight, it suffers from slow reaction rates and low efficiency. Processes requiring precise control of trace amounts of moisture in the raw materials demand extremely high operational accuracy and exhibit poor stability. Anhydrous melt polymerization theoretically avoids the energy consumption and side reactions associated with water, but in practice, it is prone to problems such as diamine volatilization, stoichiometric imbalance, accelerated degradation, uncontrolled system viscosity, and insufficient heat transfer and mixing efficiency, making industrialization difficult. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this invention provides a nylon 66 and its anhydrous melt polymerization process.

[0004] This invention is achieved through the following technical solution: A type of nylon 66 has a number-average molecular weight of 20,000-33,000 g / mol, a molecular weight distribution of 2-3.0, a melting point of 250-260℃, a gel content of no more than 3 wt‰, and a black particle content of 0.3-1 mm in diameter of no more than 10 particles / kg. At a test temperature of 270℃ and a standard load of 2.16 kg, the mass of melt flowing from a standard die within 10 minutes is 70-100 g.

[0005] A process for anhydrous melt polymerization of nylon 66, characterized by comprising a salt-forming stage, a prepolymerization reaction, and a polycondensation reaction performed sequentially; S1 Salt Formation Stage: The acid-rich and amine-rich components are melted separately, and the acid-rich component is slowly added to the amine-rich component to obtain a polyamide solution; the molar ratio of hexamethylenediamine to adipic acid in the amine-rich component is 2:1 to 5:1, and the molar ratio of adipic acid to hexamethylenediamine in the acid-rich component is 2:1 to 5:1. S2 Prepolymerization Stage: The polyamide solution obtained in step S1 is heated to 225-230℃ under a nitrogen atmosphere and held for 60-150 min, with a reaction pressure of 1.2-1.6 MPa; S3 Prepolymerization Stage: After the prepolymerization reaction is completed, the temperature is raised to 260-280℃, the pressure is reduced to normal pressure and water is drained; S4 post-polymerization stage: The system is subjected to vacuum treatment to obtain high-quality nylon 66 products; Preferably, the molar ratio of hexamethylenediamine to adipic acid in the amine-rich component is 3:1, and the molar ratio of adipic acid to hexamethylenediamine in the acid-rich component is 2.5:1.

[0006] Preferably, in step S1, the salt formation stage, the rich acid and rich amine components are melted at 130-180℃ and 160-200℃ respectively. After ensuring complete melting, 1-5 wt% of sodium hypophosphite monohydrate and glacial acetic acid, which are the total mass of adipic acid and hexamethylenediamine, are added to the rich acid component as catalysts and end-capping agents. Then, the rich acid component is slowly added to the rich amine component, while maintaining the reaction vessel at 100-200 r / min. The feeding is stopped when the molar ratio is between 0.98 and 1.02.

[0007] Preferably, in step S3, the prepolymerization stage, the pressure is slowly reduced to atmospheric pressure at a rate of 0.3-0.5 MPa per hour, while the temperature is increased to 260-280°C at a rate of 30-50°C per hour, and the reaction is carried out for 1-3 hours, during which the temperature is kept constant.

[0008] Preferably, in the post-polymerization stage of step S4: the vacuum degree is -0.02 to -0.06 MPa, the reaction is stopped after 10-30 min, and nitrogen gas of 0.2-0.5 MPa is introduced for pressurized discharge. The beneficial effects of this invention are reflected in: (1) The present invention provides a process for preparing anhydrous melt polymerized nylon 66 by using acid-rich and amine-rich components to replace pure hexamethylenediamine adipic acid, thereby achieving anhydrous melt polymerization. (2) The preparation process of anhydrous melt polymerized nylon 66 of the present invention effectively solves the problem that the rapid temperature rise during the anhydrous melt polymerization process leads to the volatilization of a large amount of hexamethylenediamine, which causes the polymerization to fail, by releasing heat in advance by the acid-rich component and the amine-rich component during the salt formation stage. (3) The preparation process of anhydrous melt polymerized nylon 66 prepared by the present invention has a relatively balanced end group ratio and good sample stability; (4) The present invention provides a process for preparing anhydrous melt polymerized nylon 66. The process is simple, can be prepared on a large scale in existing polymerization equipment, has high production efficiency and low cost, and has great application prospects. Detailed Implementation

[0009] Numerous specific details are set forth in the following description to provide a full understanding of the invention. However, the invention can be practiced in many other ways different from those described herein, and similar modifications can be made by those skilled in the art without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0010] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0011] The present invention is described in detail below: A process for preparing anhydrous melt-polymerized nylon 66 according to the present invention includes a salt-forming stage, a prepolymerization stage, and a polycondensation stage performed sequentially. The salt-forming reaction refers to the contact between an anhydrous acid-rich component (molar ratio 2:1-5:1) and an amine-rich component (molar ratio 1:2-1:5). The acid-rich component is added to the amine-rich component at a uniform rate. The catalyst is sodium hypophosphite monohydrate, which is added to the acid-rich component at an amount of 1-5 wt% of the total mass of adipic acid and hexamethylenediamine. Glacial acetic acid is added to the acid-rich component as a capping agent at an amount of 1-5 wt% of the total mass of adipic acid and hexamethylenediamine. More preferably, when the ratio of adipic acid to hexamethylenediamine is 2.5:1, the melting temperature of the acid-rich component is the lowest, between 130-150°C. Simultaneously, when the ratio of hexamethylenediamine to adipic acid is 3:1, the melting temperature of the amine-rich component is also relatively low, between 160-180°C. The two materials can melt at low temperatures, which greatly reduces energy consumption. Furthermore, the contact does not release excessive heat, preventing excessively high temperatures and side reactions. The temperature of the system after mixing the two materials is between 190-210°C. Because adipic acid and hexamethylenediamine are mixed in advance in both the acid-rich and amine-rich components, the mixed material significantly inhibits the large-scale volatilization of hexamethylenediamine, greatly mitigating the drawbacks of anhydrous melt polymerization.

[0012] The prepolymerization stage involves mixing the two materials and raising the temperature to between 225-230℃. This prepolymerization stage lasts 60-150 minutes. The polycondensation reaction is divided into prepolymerization and postpolymerization, similar to traditional aqueous solution methods. The main purpose of prepolymerization is to fully remove moisture from the system. Since no water is added during the salt formation stage, the moisture removed in this stage is mainly water generated during the reaction. The postpolymerization stage primarily involves vacuuming the system to further remove moisture and significantly increase the degree of polymerization.

[0013] This method can yield high-quality Nylon 66 products with balanced end groups and a relative viscosity between 2.6 and 3.2.

[0014] As a preferred technical solution: The preparation method of anhydrous melt polymerized nylon 66 as described above includes the following specific steps: Step (1) Salt formation stage: Melt the rich acid and rich amine components separately. After ensuring complete melting, add the catalyst and end-capping agent to the rich acid component. Slowly add the rich acid component to the rich amine component to obtain a polyamide solution.

[0015] Step (2) Prepolymerization stage: The polyamide solution obtained in step (1) is gradually heated and maintained under a nitrogen atmosphere.

[0016] Step (3) Prepolymerization stage: After the prepolymerization reaction is completed, the temperature is increased and the water is gradually drained.

[0017] Step (4) Post-polymerization stage: Vacuum treatment is performed on the system to obtain high-quality nylon 66 products.

[0018] As described above, in the preparation method of anhydrous melt polymerized nylon 66, step (1) salt formation stage: the acid-rich and amine-rich components are melted at 130-150℃ and 160-180℃ respectively. After ensuring complete melting, 1-5wt% of sodium hypophosphite monohydrate and glacial acetic acid, which are the total mass of adipic acid and hexamethylenediamine, are added to the acid-rich component as catalysts and end-capping agents. Then, the acid-rich component is slowly added to the amine-rich component. During this period, the reaction vessel is kept at 100-200r / min, and the feeding is stopped when the molar ratio is between 0.98 and 1.02.

[0019] In the above-described method for preparing anhydrous melt-polymerized nylon 66, in the prepolymerization stage of step (2), the polyamide solution mixed in step (1) is subjected to a programmed temperature increase, with a reaction temperature of 225-230℃ and a reaction pressure of 1.2-1.6MPa. This state is maintained for 60-150 minutes, after which the prepolymerization ends and the next stage begins.

[0020] In the preparation method of anhydrous melt polymerized nylon 66 as described above, in the prepolymerization stage of step (3), the pressure is slowly reduced to atmospheric pressure at a rate of 0.3-0.5 MPa per hour, while the temperature is increased to 260-280°C at a rate of 30-50°C per hour, and the reaction is carried out for 1-3 hours, during which the temperature is kept constant.

[0021] In the preparation method of anhydrous melt polymerized nylon 66 as described above, the vacuum degree of the post-polymerization stage in step (4) is -0.02 to -0.06 MPa as mentioned above. After the reaction is completed after 10-30 min, nitrogen gas of 0.2-0.5 MPa is introduced for pressurized discharge.

[0022] This invention provides an anhydrous melt-polymerized nylon 66 prepared by the preparation method described above. The nylon 66 has a number-average molecular weight of 20,000-33,000 g / mol, a molecular weight distribution of 2-3.0, a melting point of 250-260℃, a gel content of no more than 3 wt‰, a black particle content of 0.3-1 mm in diameter of no more than 10 particles / kg, and a melt index (270℃, 2.16 kg) of 70-100 g / 10 min.

[0023] Invention principle: In the traditional aqueous solution polymerization process of nylon 66, the problems of high energy consumption of flash water, wastewater, water recycling, and environmental pollution have always been present. Anhydrous melt polymerization also suffers from excessive side reactions and problems such as the large-scale volatilization of hexamethylenediamine leading to end-group imbalance. This invention starts from overcoming the difficulties of anhydrous melt polymerization process by using acid-rich and amine-rich components to move the exothermic reaction forward, thereby reducing the occurrence of side reactions.

[0024] Specifically, this invention uses acid-rich and amine-rich components in the salt-forming stage without adding water as a solvent, effectively improving the situation where excessive volatilization of hexamethylenediamine and the generation of side reactions prevent the degree of polymerization from increasing. It also saves on the flash water distillation step and energy consumption. The analysis is as follows: The root cause is that when adipic acid and hexamethylenediamine are mixed in a non-stoichiometric ratio (e.g., the acid-amine molar ratio of the acid-rich component in this invention is 3:1), they form a eutectic mixture. The melting point of the eutectic mixture is lower than that of the single pure component because the lattice arrangement between molecules in the mixture is disrupted, reducing lattice energy and thus decreasing the energy required for melting. Simultaneously, excess adipic acid in the acid-rich component forms a physical or chemical combination with the generated nylon salt. While the nylon salt itself has a high melting point, excess adipic acid forms a eutectic with it, leading to a decrease in the overall melting point. The acid-rich component releases heat to some extent during melting, which is the previously mentioned pre-heating phenomenon, potentially generating low-molecular-weight polymers. These oligomers have low molecular weights (typically number-average molecular weight < 1000), weak intermolecular forces, and low melting points. When mixed with excess adipic acid and nylon salt, they further lower the overall melting point of the acid-rich component. The above characteristics allow the acid-rich component to melt at a relatively low temperature, facilitating subsequent reaction with the amine-rich component in the liquid phase to achieve the goal of efficient polyamide preparation. The amine-rich component usually melts at a moderate temperature. In this example, the amine-rich component is a 3:1 ratio of hexamethylenediamine to adipic acid, with a melting temperature between 160-180°C. Hexamethylenediamine itself has a melting point of about 40°C. In the amine-rich component, it forms a system with other components (such as nylon salts, low molecular weight amine-terminated polyamides, etc.). Under the temperature conditions required for the reaction, the system is in a liquid state. The interaction between hexamethylenediamine molecules and the interaction with other components make the volatilization of hexamethylenediamine require overcoming a large energy barrier, thus limiting the volatilization of hexamethylenediamine.

[0025] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the claims and specification of the present invention.

Claims

1. A type of nylon 66, characterized in that: Its number-average molecular weight is 20,000-33,000 g / mol, molecular weight distribution is 2-3.0, melting point is 250-260℃, gel content does not exceed 3wt‰, black particle content with diameter of 0.3-1mm does not exceed 10 particles / kg, and at a test temperature of 270℃, under a standard load of 2.16 kg, the mass of melt flowing from the standard die within 10 minutes is 70-100g.

2. A process for anhydrous melt polymerization of nylon 66, characterized in that: This includes the salt-forming stage, the prepolymerization reaction, and the condensation reaction, which occur sequentially. S1 Salt formation stage: The acid-rich and amine-rich components are melted separately, and the acid-rich component is slowly added to the amine-rich component to obtain a polyamide solution; The molar ratio of hexamethylenediamine to adipic acid in the amine-rich component is 2:1 to 5:1, and the molar ratio of adipic acid to hexamethylenediamine in the acid-rich component is 2:1 to 5:

1. S2 Prepolymerization Stage: The polyamide solution obtained in step S1 is heated to 225-230℃ under a nitrogen atmosphere and held for 60-150 min, with a reaction pressure of 1.2-1.6 MPa; S3 Prepolymerization Stage: After the prepolymerization reaction is completed, the temperature is raised to 260-280℃, the pressure is reduced to normal pressure and water is drained; S4 post-polymerization stage: The system is subjected to vacuum treatment to obtain high-quality nylon 66 products.

3. The anhydrous melt polymerization process for nylon 66 as described in claim 2, characterized in that: The molar ratio of hexamethylenediamine to adipic acid in the amine-rich component is 3:1, and the molar ratio of adipic acid to hexamethylenediamine in the acid-rich component is 2.5:

1.

4. The anhydrous melt polymerization process for nylon 66 as described in claim 2, characterized in that: Step S1 Salt formation stage: Melt the rich acid and rich amine components at 130-180℃ and 160-200℃ respectively. After ensuring complete melting, add 1-5 wt% of sodium hypophosphite monohydrate and glacial acetic acid as catalysts and end-capping agents to the rich acid component. Then, slowly add the rich acid component to the rich amine component, keeping the reaction vessel at 100-200 r / min during the process. Stop feeding when the molar ratio is between 0.98 and 1.

02.

5. The anhydrous melt polymerization process for nylon 66 as described in claim 2, characterized in that: Step S3 Prepolymerization stage: Slowly reduce the pressure to atmospheric pressure at a rate of 0.3-0.5 MPa per hour, while simultaneously increasing the temperature to 260-280°C at a rate of 30-50°C per hour, and react for 1-3 hours, maintaining a constant temperature during this period.

6. The anhydrous melt polymerization process for nylon 66 as described in claim 2, characterized in that: Post-polymerization stage in step S4: The vacuum degree is -0.02 to -0.06 MPa. The reaction is stopped after 10-30 minutes, and nitrogen gas at 0.2-0.5 MPa is introduced for pressurized discharge.