Polymerization method and system for producing chinlon 6 slices

Abstract

The invention relates to the technical field of polyester material production, and discloses a polymerization method and system for producing chinlon 6 slices, and the provided chinlon 6 slices have the advantages of higher relative viscosity, narrower molecular weight distribution, lower water content, and higher yield. According to the system used by the invention, a ZnO / Al2O3 composite variable active catalyst adding window is directly arranged at the bottom of the melting and mixing unit 1, so that the ZnO / Al2O3 composite variable active catalyst can be ensured to be more uniformly dispersed in the whole reaction system, the reaction conditions are optimized, the variable active catalyst is adopted, the pH is dynamically regulated and controlled, and the reaction efficiency is improved. The exposure degree of active sites of the catalyst can be accurately adjusted according to the requirements of different stages of a polymerization reaction, generation of cyclic dimers in the caprolactam hydrolysis ring-opening process is effectively inhibited in the pre-polymerization stage, the content of cyclic by-products is remarkably reduced to 3.5% or below, the monomer utilization rate is increased, increase of the molecular weight is promoted in the post-polymerization stage, and the yield of the catalyst is increased. And product quality.

Description

Technical Field

[0001] This invention belongs to the field of polyester material production technology, and particularly relates to a polymerization method and system for producing nylon 6 chips. Background Technology

[0002] In the traditional production process of nylon 6, a continuous or intermittent polymerization process using water as an initiator under high temperature and high pressure is commonly used. Although this process is mature and widely used, there are still many technical bottlenecks and limitations in actual operation, especially in terms of cyclic dimer control, energy consumption management, and production efficiency.

[0003] Traditional catalyst systems lack the ability to precisely control the reaction pathway. During the hydrolysis and ring-opening process, caprolactam is prone to intramolecular condensation, forming a cyclic structure that is difficult to participate in linear polymerization. This not only reduces the effective utilization rate of monomers but also affects the mechanical properties and thermal stability of the final product.

[0004] Existing catalysts are usually of a fixed activity type and cannot be dynamically adjusted according to the different needs of the polymerization stage. This makes it difficult to effectively suppress the formation of cyclic byproducts in the prepolymerization stage, and may affect the degree of polymerization in the later polymerization stage due to insufficient catalytic activity. Summary of the Invention

[0005] To address the technical problems mentioned in the background section of the prior art, which are typically of fixed activity types and cannot be dynamically adjusted according to the different needs of the polymerization stage, resulting in difficulty in effectively suppressing the formation of cyclic by-products in the prepolymerization stage and potentially affecting the degree of polymerization due to insufficient catalytic activity in the postpolymerization stage, this invention provides a polymerization system for producing nylon 6 chips. This system uses a variable-activity catalyst and dynamically controls the pH, enabling precise adjustment of the exposure degree of the catalyst's active sites according to the needs of different stages of the polymerization reaction. In the prepolymerization stage, it effectively suppresses the formation of cyclic dimers during the hydrolysis and ring-opening process of caprolactam, and in the postpolymerization stage, it promotes molecular weight growth and improves product quality.

[0006] The specific technical solution of this invention is as follows: A polymerization system for producing nylon 6 chips, comprising: The prepolymerization unit includes a melt mixing unit 1, a pH adjustment unit 1, and a prepolymerization reactor. The melt mixing unit 1 has a ZnO / Al2O3 composite variable active catalyst addition window at its bottom. The post-polymerization unit includes a post-polymerization reactor and a pH adjustment unit 2; The slicing and forming unit includes a cold casting strip unit, a pellet drying unit, and a melt mixing unit 2.

[0007] Furthermore, the specific operation method of the aggregation system includes the following steps: 1) Caprolactam, water, and ZnO / Al2O3 composite variable active catalyst are heated and melted under the protection of inert gas, mixed evenly, and then the pH is adjusted to carry out a prepolymerization reaction to obtain a prepolymerized melt. 2) After dehydrating the prepolymer melt obtained in step 1), adjust the pH and react at 270~280℃ for 1~2h, then raise the temperature to 285~295℃ and continue the reaction for 2~2.5h to obtain the postpolymer melt; 3) The post-polymerization melt obtained in step 2) is cold-cast into strips, granulated and dried, and then mixed and melted with a heat stabilizer to obtain nylon 6 chips.

[0008] This invention employs a variable-activity catalyst and dynamically controls pH, enabling precise adjustment of the exposure level of catalyst active sites according to the needs of different stages of the polymerization reaction. In the prepolymerization stage, it effectively inhibits the formation of cyclic dimers during the hydrolysis and ring-opening process of caprolactam, significantly reducing the content of cyclic byproducts to below 3.5%, thereby improving monomer utilization and product quality.

[0009] Further, in step 1), 99~99.5wt% caprolactam, 0.5~1.0wt% water and 0.01~0.05wt% variable active catalyst are heated and melted.

[0010] The variable active catalyst in step 1) is a ZnO / Al2O3 composite variable active catalyst.

[0011] Furthermore, the preparation method of the ZnO / Al2O3 composite variable active catalyst is as follows: γ-Al2O3 is soaked in 0.1~0.2mol / L nitric acid solution for 2~3h, and dried to obtain pretreated γ-Al2O3; the pretreated γ-Al2O3 is added to zinc nitrate solution, stirred evenly, dried, calcined at high temperature, and then reduced at high temperature in hydrogen atmosphere to obtain the ZnO / Al2O3 composite variable active catalyst.

[0012] Furthermore, pretreated γ-Al2O3 was added to the zinc nitrate solution at a ZnO:Al2O3 mass ratio of 1:(3.5~4.5).

[0013] Furthermore, the drying temperature is 80°C.

[0014] Furthermore, the high-temperature calcination conditions are calcination at 400~500℃ for 2~2.5h.

[0015] Furthermore, the conditions for high-temperature reduction are: reduction at 300~320℃ for 1~1.5h.

[0016] Furthermore, the pH of the prepolymerization in step 1) is 3-5.

[0017] Furthermore, the pH of the post-polymerization reaction in step 2) is 5-7.

[0018] Compared with the prior art, the beneficial effects of the present invention are: 1) This invention uses a composite variable activity catalyst to dynamically control pH, which can precisely adjust the exposure degree of catalyst active sites according to the needs of different stages of polymerization reaction. In the prepolymerization stage, it effectively inhibits the formation of cyclic dimers during the hydrolysis and ring-opening process of caprolactam, significantly reducing the content of cyclic by-products to below 3.5% and improving monomer utilization. In the postpolymerization stage, it promotes the increase of molecular weight and improves product quality.

[0019] 2) The system used in this invention directly sets the ZnO / Al2O3 composite variable active catalyst addition window from the bottom of the prepolymerization reactor, which can ensure that it is more uniformly dispersed in the entire reaction system, thereby optimizing the reaction conditions, significantly improving the rate of specific chemical reactions, and improving the production efficiency of the entire system.

[0020] 2) The nylon 6 chips provided by this invention have higher relative viscosity, narrower molecular weight distribution, and lower water content. These characteristics help improve the quality and processing performance of fiber or engineering plastic products, meet the demand of high-end markets for high-performance materials, and enhance the market competitiveness of products. Attached Figure Description

[0021] The present invention will be described by way of example and with reference to the accompanying drawings, wherein: Figure 1 This is a process flow diagram of the present invention.

[0022] The attached figures are labeled as follows: 1. Melting and mixing unit 1; 2. pH adjustment unit 1; 3. ZnO / Al2O3 composite variable active catalyst addition window; 4. Prepolymerization reactor; 5. pH adjustment unit 2; 6. Postpolymerization reactor; 7. Cold casting belt unit; 8. Pelletizing and drying unit 2; 9. Mixing and melting unit. Detailed Implementation

[0023] All features disclosed in this specification, or all steps in all disclosed methods or processes, may be combined in any way, except for mutually exclusive features and / or steps.

[0024] Example 1 A polymerization system for producing nylon 6 chips, such as Figure 1As shown, caprolactam and water are added to the melt mixing unit 1 (1) in proportion, and after the pH is adjusted by the pH adjustment unit 1 (2), they enter the prepolymerization reactor (4). ZnO / Al2O3 composite variable active catalyst is added to the bottom of the prepolymerization reactor through the ZnO / Al2O3 composite variable active catalyst addition window (4). After the prepolymerization reaction is completed, it enters the postpolymerization unit. After the pH is adjusted for the second time by the pH adjustment unit 2 (5), it enters the postpolymerization reactor (6) to undergo the postpolymerization reaction. After the reaction is completed, it enters the chip forming unit, and passes through the cold casting belt unit (7), the pellet drying unit (8), and the melt mixing unit 2 (9) in sequence to obtain nylon 6 chips. The specific operation steps are as follows: 1) Preparation of variable-activity catalysts γ-Al₂O₃ was soaked in 0.1 mol / L nitric acid solution for 3 h and dried to obtain pretreated γ-Al₂O₃. The pretreated γ-Al₂O₃ was added to zinc nitrate solution at a ZnO:Al₂O₃ mass ratio of 1:(3.5~4.5), stirred evenly, dried, calcined at 400℃ for 2 h, and then reduced in a hydrogen atmosphere at 300℃ for 1 h to obtain a ZnO / Al₂O₃ composite variable active catalyst.

[0025] 2) Prepolymerization reaction 99.0 wt% caprolactam, 1.0 wt% water, and 0.01 wt% of the variable active catalyst ZnO / Al2O3 composite variable active catalyst prepared in step 1) were heated and melted under the protection of inert nitrogen gas. After being mixed evenly, the pH was adjusted to 3 to carry out a prepolymerization reaction to obtain a prepolymerized melt. The formation of cyclic dimers was suppressed by controlling the pH value.

[0026] 3) Post-polymerization reaction After dehydrating the prepolymer melt obtained in step 2), the pH was adjusted to promote the increase of molecular weight. The reaction was carried out at 270℃ for 1 hour, and then the temperature was raised to 280℃ to continue the reaction for 2 hours to obtain the postpolymer melt.

[0027] 4) Preparation of nylon 6 chips The post-polymerization melt obtained in step 3) is cold-cast into strips, granulated, dried, and then mixed and melted with a heat stabilizer to obtain nylon 6 chips.

[0028] 5) Performance Testing The nylon 6 chips prepared in step 4) were subjected to relevant performance tests.

[0029] Comparative Example 1 The only difference between this comparative example and Example 1 is that γ-Al2O3 is used as the catalyst in this comparative example; all other processes are the same as in Example 1. Specifically, the operations are as follows: 1) Prepolymerization reaction 99.0 wt% caprolactam, 1.0 wt% water, and 0.01 wt% catalyst Al2O3 were heated and melted under the protection of inert nitrogen gas. After being mixed evenly, the pH was adjusted to 3 to carry out a prepolymerization reaction to obtain a prepolymerized melt. The formation of cyclic dimers was suppressed by controlling the pH value.

[0030] 2) Post-polymerization reaction After dehydrating the prepolymer melt obtained in step 1), the pH was adjusted to 6, and the reaction was carried out at 270℃ for 1 hour. The temperature was then raised to 280℃ and the reaction was continued for 2 hours to obtain the postpolymer melt.

[0031] 3) Preparation of nylon 6 chips The post-polymerization melt obtained in step 2) is cold-cast into strips, granulated, dried, and then mixed and melted with a heat stabilizer to obtain nylon 6 chips.

[0032] 4) Performance Testing The nylon 6 chips prepared in step 3) were subjected to relevant performance tests.

[0033] Comparative Example 2 The only difference between this comparative example and Example 1 is that ZnO is used as the catalyst in this comparative example; all other processes are the same as in Example 1. The specific operating steps are as follows: 1) Prepolymerization reaction 99.0 wt% caprolactam, 1.0 wt% water, and 0.01 wt% ZnO were heated and melted under the protection of inert nitrogen gas. After being mixed evenly, the pH was adjusted to 3 to carry out a prepolymerization reaction to obtain a prepolymerized melt. The formation of cyclic dimers was suppressed by controlling the pH value.

[0034] 2) Post-polymerization reaction After dehydrating the prepolymer melt obtained in step 1), the pH was adjusted to 6 to promote the increase of molecular weight. The reaction was carried out at 270℃ for 1 hour, and then the temperature was raised to 280℃ to continue the reaction for 2 hours to obtain the postpolymer melt.

[0035] 3) Preparation of nylon 6 chips The post-polymerization melt obtained in step 2) is cold-cast into strips, granulated, dried, and then mixed and melted with a heat stabilizer to obtain nylon 6 chips.

[0036] 4) Performance Testing The nylon 6 chips prepared in step 3) were subjected to relevant performance tests.

[0037] Comparative Example 3 The only difference between this comparative example and the embodiment is that this comparative example does not involve a composite reaction of ZnO and Al2O3. Instead, ZnO and Al2O3 are added as a catalyst at a ZnO:Al2O3 mass ratio of 1:(3.5~4.5). The rest of the process is the same as in Example 1. The specific steps are as follows: 1) Prepolymerization reaction 99.0 wt% caprolactam, 1.0 wt% water, and 0.01 wt% ZnO:Al2O3 catalyst in a mass ratio of 1:(3.5~4.5) = ZnO:Al2O3 were heated and melted under the protection of inert nitrogen gas. After being mixed evenly, the pH was adjusted to 3 to carry out a prepolymerization reaction to obtain a prepolymerized melt. The formation of cyclic dimers was suppressed by controlling the pH value.

[0038] 2) Post-polymerization reaction After dehydrating the prepolymer melt obtained in step 1), the pH was adjusted to 6 to promote the increase of molecular weight. The reaction was carried out at 270℃ for 1 hour, and then the temperature was raised to 280℃ to continue the reaction for 2 hours to obtain the postpolymer melt.

[0039] 3) Preparation of nylon 6 chips The post-polymerization melt obtained in step 2) is cold-cast into strips, granulated, dried, and then mixed and melted with a heat stabilizer to obtain nylon 6 chips.

[0040] 4) Performance Testing The nylon 6 chips prepared in step 3) were subjected to relevant performance tests.

[0041] Table 1. Effect of variable active catalyst on the properties of nylon 6 chips Catalyst type Cyclic dimer content Relative viscosity of polymer Number average molecular weight Mn Example 1 Variable active catalyst 3.2% 4.5 18000g / mol Comparative Example 1 <![CDATA[Al2O3]]> 5.8% 4.0 15000g / mol Comparative Example 2 ZnO 6.5% 3.8 14000g / mol Comparative Example 3 <![CDATA[ZnO、Al2O3]]> 5.2% 3.9 16000g / mol The data in Table 1 show that the ZnO / Al2O3 composite variable-activity catalyst used in this invention, through chemical composite reaction and dynamic regulation mechanism, is significantly superior to traditional single catalysts and physically mixed catalysts. According to this invention, the ZnO / Al2O3 composite variable-activity catalyst can significantly reduce the content of cyclic dimers, improve product performance, significantly reduce the molecular weight and viscosity of polymers, meet the requirements of high-performance materials, shorten the production cycle, and improve production efficiency.

[0042] The embodiments described above merely illustrate specific implementation methods of this application, and while the descriptions are detailed and specific, they should not be construed as limiting the scope of protection of this application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the technical solution of this application, and these modifications and improvements all fall within the scope of protection of this application.

Claims

1. A polymerization method for producing nylon 6, characterized in that, The specific operation method of the aggregation system includes the following steps: 1) Caprolactam, water, and ZnO / Al2O3 composite variable active catalyst are heated and melted under the protection of inert gas, mixed evenly, and then the pH is adjusted to carry out a prepolymerization reaction to obtain a prepolymerized melt. 2) After dehydrating the prepolymer melt obtained in step 1), adjust the pH and react at 270~280℃ for 1~2h, then raise the temperature to 285~295℃ and continue the reaction for 2~2.5h to obtain the postpolymer melt; 3) The post-polymerization melt obtained in step 2) is cold-cast into strips, granulated and dried, and then mixed and melted with a heat stabilizer to obtain nylon 6 chips.

2. The polymerization method for producing nylon 6 chips according to claim 1, characterized in that, In step 1), 99~99.5wt% caprolactam, 0.5~1.0wt% water and 0.01~0.05wt% variable active catalyst are heated and melted.

3. The polymerization method for producing nylon 6 chips according to claim 1, characterized in that, In step 1), the ZnO / Al2O3 composite variable active catalyst is prepared by soaking γ-Al2O3 in 0.1~0.2mol / L nitric acid solution for 2~3h, drying it to obtain pretreated γ-Al2O3; adding the pretreated γ-Al2O3 to zinc nitrate solution, stirring evenly, drying, calcining at high temperature, and then reducing it at high temperature in a hydrogen atmosphere to obtain the ZnO / Al2O3 composite variable active catalyst.

4. The polymerization method for producing nylon 6 chips according to claim 3, characterized in that, Pretreated γ-Al2O3 was added to a zinc nitrate solution at a ZnO:Al2O3 mass ratio of 1:(3.5~4.5).

5. The polymerization method for producing nylon 6 chips according to claim 3, characterized in that, The drying temperature is 80℃.

6. The polymerization method for producing nylon 6 chips according to claim 5, characterized in that, The conditions for high-temperature calcination are calcination at 400~500℃ for 2~2.5h.

7. A polymerization method for producing nylon 6 chips according to claim 3 or 6, characterized in that, The conditions for high-temperature reduction are: reduction at 300~320℃ for 1~1.5h.

8. The polymerization method for producing nylon 6 chips according to claim 1, characterized in that, The pH of the prepolymerization in step 1) is 3-5.

9. The polymerization method for producing nylon 6 chips according to claim 1, characterized in that, In step 2), the pH of the post-polymerization reaction is 5-7.

10. A system for a polymerization method for producing nylon 6 chips according to any one of claims 1 to 9, characterized in that, include: The prepolymerization unit includes a melt mixing unit 1, a pH adjustment unit 1, and a prepolymerization reactor. The bottom of the melt mixing unit 1 has a ZnO / Al2O3 composite variable active catalyst addition window. Post-polymerization unit; And slicing unit.

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