A continuous production apparatus and process for Nylon 66

Abstract

A continuous production apparatus for nylon 66 includes a concentration tank, a prepolymerization reactor, and a final polymerization reactor. The inlet of the concentration tank is connected to a nylon 66 salt solution device, and the outlet of the concentration tank supplies feed to the prepolymerization reactor via a reaction preheater. The outlet of the prepolymerization reactor supplies feed to the final polymerization reactor via a feeding pipeline and a flash evaporator. The feeding pipeline is connected to a titanium dioxide suspension device. This invention has a simple structure, is easy to operate, and can continuously produce high-quality full-matte / semi-matte nylon 66 materials.

Description

Technical Field

[0001] This invention relates to the chemical industry, and in particular to a continuous production apparatus and process for nylon 66. Background Technology

[0002] Polyamide 66, scientifically known as polyhexamethylene adipamide, commonly called nylon 66 (PA66), has the molecular formula H[HN(CH2)6NHOC(CH2)4CO]. n OH, with a molecular weight of 15,000-20,000, is a translucent or opaque milky-white crystalline polymer. It is resistant to corrosion from acids, alkalis, most inorganic salt solutions, halogenated hydrocarbons, hydrocarbons, esters, ketones, etc. It is insoluble in common solvents but readily soluble in polar solvents such as phenol and formic acid. It possesses excellent wear resistance, self-lubricating properties, and high mechanical strength. There are two polymerization processes for Nylon 66: batch polymerization and continuous polymerization. Both processes operate on the same principle, involving the polycondensation reaction of adipic acid and hexamethylenediamine. The main differences lie in the process flow and the application range of the product.

[0003] Nylon 66 is an important chemical raw material. Due to its advantages such as high strength, resistance to high temperatures and chemical resistance, high hardness, and wear resistance, it is widely used in industries such as rubber, tires, plastics, electronics, chemicals, and synthetic fibers. Compared to nylon 6, nylon 66 has a higher melting point and softening point, and better heat and low-temperature resistance, making it more suitable for manufacturing outdoor, sports, and cold-weather clothing. In addition, nylon 66 is widely used in military equipment due to its higher strength and better abrasion resistance.

[0004] Currently, the use of continuous polymerization with titanium dioxide as a matting agent to produce Nylon 66 civilian spinning chips in the chemical fiber industry has not been well applied. Therefore, in view of this situation, how to design a process for the continuous production of Nylon 66 civilian spinning chips with the addition of titanium dioxide as a matting agent, and fill the gap in current practical production applications, is an urgent problem to be solved by those skilled in the art. Summary of the Invention

[0005] One of the objectives of this invention is to address the shortcomings of existing technologies by providing a continuous nylon 66 production device that is simple in structure, easy to operate, and capable of continuously producing high-quality full-matte / semi-matte nylon 66 materials.

[0006] The second objective of this invention is to provide a process for the continuous synthesis of nylon 66 using the above-mentioned production equipment, which has a short process flow, simple process, continuous and stable production, and long equipment operation cycle.

[0007] One of the technical solutions to achieve the objective of this invention is: a continuous production device for nylon 66, comprising a concentration tank, a prepolymerization reactor, and a final polymerization reactor. The inlet of the concentration tank is connected to a nylon 66 salt solution device, and the outlet of the concentration tank supplies material to the prepolymerization reactor via a reaction preheater. The outlet of the prepolymerization reactor supplies material to the final polymerization reactor via a feeding pipeline and a flash evaporator. The feeding pipeline is connected to a titanium dioxide suspension device.

[0008] The nylon 66 salt solution device includes a crude salt reactor and a refined salt regulating tank.

[0009] The feed inlet of the crude salt reactor is connected to the hexamethylenediamine source and the adipic acid source. The top of the crude salt reactor is vented through the salt formation waste gas absorption tower and the liquid seal tank. The outlet of the crude salt reactor is connected to the first circulation pipeline for material return, and the first circulation pipeline also supplies material to the refined salt regulating tank. The top of the refined salt regulating tank is vented through the liquid seal tank. The outlet of the refined salt regulating tank is connected to the second circulation pipeline for material return, and the second circulation pipeline also discharges nylon 66 salt solution externally.

[0010] The feed inlet of the refined salt regulating tank is connected to the hexamethylenediamine source. A crude salt circulation pump and a crude salt circulation cooler are sequentially installed on the first circulation pipeline. The branch outlet on the first circulation pipeline is located between the crude salt circulation pump and the crude salt circulation cooler. The crude salt reactor supplies the refined salt regulating tank through the crude salt storage tank. A refined salt circulation pump and a refined salt circulation cooler are sequentially installed on the second circulation pipeline. The branch outlet on the second circulation pipeline is downstream of the refined salt circulation cooler. The refined salt regulating tank discharges nylon 66 salt solution to the outside through the refined salt storage tank.

[0011] The top of the refined salt regulating tank and the top of the refined salt storage tank are connected by a connecting pipe.

[0012] The titanium dioxide suspension device includes a solid-liquid mixer, a titanium dioxide pre-mixing tank, a titanium dioxide centrifuge, and a titanium dioxide suspension preparation tank. The feed inlet of the solid-liquid mixer is connected to a titanium dioxide powder source and a water source, respectively. The discharge outlet of the solid-liquid mixer supplies material to a titanium dioxide premixing tank. The discharge outlet of the titanium dioxide premixing tank supplies material to a titanium dioxide centrifuge. The liquid phase outlet of the titanium dioxide centrifuge supplies material to a titanium dioxide suspension preparation tank. The discharge outlet of the titanium dioxide suspension preparation tank discharges titanium dioxide suspension to the outside through a filter.

[0013] The outlet of the titanium dioxide pre-mixing tank is connected to a three-way valve. The second port of the three-way valve supplies material to the titanium dioxide centrifuge via the titanium dioxide pre-mixing intermediate tank, and the third port supplies material to the solid-liquid mixer. The bottom of the titanium dioxide pre-mixing tank is connected to a third circulation pipeline for material return, and the third circulation pipeline also supplies material to the titanium dioxide pre-mixing intermediate tank. A disperser is installed on the third circulation pipeline.

[0014] The solid phase outlet of the titanium dioxide centrifuge feeds a grinding mill via a centrifugal precipitate collection tank, and the outlet of the grinding mill feeds a titanium dioxide premixing tank.

[0015] The feed inlet of the concentration tank is connected to the concentration preheater, the intermediate salt tank, and the nylon 66 salt solution device via the concentration preheater. The top of the concentration tank provides heat to the concentration preheater. The reaction preheater includes a primary reaction preheater and a secondary reaction preheater connected in series. The prepolymerization reactor is a horizontal U-shaped tube reactor. The top of the prepolymerization reactor provides heat to the concentration tank via a reactor pressure reducing tower. The final polymerization reactor consists of an upper cylindrical section and a lower conical section connected together. An auger is installed in the lower conical section. The upper cylindrical section is connected to a negative pressure source via a polymerization tail gas scrubbing tower and a tower top condenser. The tube side of the flash evaporator is the process medium channel, and the inner diameter of the tube side gradually increases along the flow direction of the process medium.

[0016] The second technical solution to achieve the objective of this invention is: a process for continuously synthesizing nylon 66 using any of the above-mentioned production devices, comprising the following steps: 1) The concentration of the prepared nylon 66 salt solution was 55~62wt%, and the titanium dioxide particle size in the prepared titanium dioxide suspension was ≤1μm, with a concentration of 30~35wt%. 2) Nylon 66 salt solution was concentrated to 68-70 wt% at 0.03-0.04 MPa and 125-135℃, preheated to 210-220℃, and then fed into a prepolymerization reactor. The prepolymerization conditions were 1.8-2.0 MPa and 245-255℃ to obtain an oligomer aqueous solution. 3) After mixing the oligomer aqueous solution with the titanium dioxide suspension, the mixture is flash-evaporated. The flash-evaporation parameters are: heating to 280°C within 3 seconds and gradually dehydrating under reduced pressure to obtain a bubble-like polymer. 4) The foamed polymer enters the final polymerization reactor, and the final polymerization conditions are -0.06~-0.08MPa and 274~284℃ to obtain Nylon 66 melt.

[0017] Furthermore, the preparation method of the nylon 66 salt solution in step 1) is as follows: Based on adipic acid, hexamethylenediamine and water were added in proportion to generate a crude nylon 66 salt solution under an inert gas atmosphere, 1~2 kPaG, and 67~72℃. Hexamethylenediamine was added in a controlled proportion to generate a nylon 66 salt solution under 15~20 kPaG and 85~90℃. The preparation method of titanium dioxide suspension is as follows: Titanium dioxide powder and demineralized water are mixed in a solid-liquid mixture and then sent to a titanium dioxide premixing tank. After emulsification, shearing, and dispersion, the mixture is centrifuged. Titanium dioxide particles larger than 1 μm form a centrifugal precipitate, while the liquid phase containing titanium dioxide particles ≤ 1 μm is sent to a titanium dioxide suspension preparation tank and emulsified and sheared to obtain a titanium dioxide suspension.

[0018] The above technical solution has the following beneficial effects: 1. The continuous production apparatus for nylon 66 of the present invention includes a concentration tank, a prepolymerization reactor, and a final polymerization reactor. The concentration tank concentrates the nylon 66 salt solution, facilitating polymerization. The prepolymerization reactor dehydrates and prepolymerizes the nylon 66 salt solution, generating an aqueous solution of nylon 66 salt oligomers with a water content of approximately 10%. The final polymerization reactor further dehydrates the prepolymerized slurry, followed by addition polymerization and condensation polymerization to obtain a molten polymer. The inlet of the concentration tank is connected to the nylon 66 salt solution device. The prepared nylon 66 salt solution is fed to the concentration tank by gravity or pump. The outlet of the concentration tank supplies the prepolymerization reactor via a reaction preheater. The concentrated nylon 66 salt solution is first preheated in the reaction preheater before being sent to the prepolymerization reactor for prepolymerization, ensuring a gradual temperature rise of the nylon 66 salt and avoiding rapid temperature increases in the prepolymerization reactor that could generate byproducts, thereby improving the yield of the target product. The prepolymer reactor's outlet is fed to the final polymerization reactor via a feeding pipeline and a flash evaporator. The feeding pipeline is connected to a titanium dioxide suspension device. After initial mixing of the prepolymerized oligomer aqueous solution and the titanium dioxide suspension in the feeding pipeline, the mixture enters the flash evaporator. Through depressurization and dehydration vaporization, the titanium dioxide and materials are intensely and thoroughly mixed until the pressure approaches atmospheric pressure, resulting in a vapor-liquid mixture of titanium dioxide in a bubbly polymer. This polymer is then sent to the final polymerization reactor for further dehydration, polymerization, and condensation reactions under vacuum and high temperature conditions, generating a high-viscosity molten polymer with uniformly distributed titanium dioxide. This polymer can be extruded and pelletized to obtain fully matte / semi-matte nylon 66 products. Since the concentration tank, prepolymer reactor, and final polymerization reactor can all discharge continuously, continuous production of nylon 66 can also be achieved.

[0019] 2. The Nylon 66 salt solution device includes a crude salt reactor and a refined salt regulating tank. The inlet of the crude salt reactor is connected to a hexamethylenediamine source and an adipic acid source. The top of the crude salt reactor is vented through a salt formation waste gas absorption tower and a liquid seal tank. The outlet of the crude salt reactor is connected to a first circulation pipeline for material return. The first circulation pipeline also supplies material to the refined salt regulating tank. The raw materials hexamethylenediamine, adipic acid, and water generate a Nylon 66 crude salt solution in the crude salt reactor. Depending on the actual generation effect, partial or complete reflux is selected. The Nylon 66 crude salt solution is then sent to the refined salt regulating tank. The top of the refined salt regulating tank is emptied via a liquid-sealed tank. The outlet of the refined salt regulating tank is connected to a second circulation pipeline for material return, and the second circulation pipeline also diverts the discharge of nylon 66 salt solution. The inlet of the refined salt regulating tank is connected to a hexamethylenediamine source. Based on sampling data, the appropriate amount of hexamethylenediamine is added according to a ratio control, ensuring an excess of adipic acid in the crude salt reactor. This allows for operation at lower temperatures and pressures, reducing water evaporation, facilitating the feeding of adipic acid powder, and preventing blockage of the adipic acid feed pipe. A high-concentration salt solution (reaching over 60 wt%, whereas adding a standard ratio of adipic acid and hexamethylenediamine at once only yields a 50 wt% salt solution) is obtained under high temperature and high pressure in the refined salt regulating tank. This high-concentration salt solution is sent to the subsequent concentration process without the need for additional fresh steam, achieving energy saving and consumption reduction. The top of the refined salt regulating tank and the top of the refined salt storage tank are connected by a connecting pipe for smooth material discharge.

[0020] 3. The titanium dioxide suspension device includes a solid-liquid mixer, a titanium dioxide pre-mixing tank, a titanium dioxide centrifuge, and a titanium dioxide suspension preparation tank. The inlet of the solid-liquid mixer is connected to both a titanium dioxide powder source and a water source, mixing to obtain a mixture of titanium dioxide and water. The outlet of the solid-liquid mixer feeds the titanium dioxide pre-mixing tank, where it undergoes preliminary emulsification and shearing. The outlet of the titanium dioxide pre-mixing tank feeds the titanium dioxide centrifuge, and the liquid phase outlet of the titanium dioxide centrifuge feeds the titanium dioxide suspension preparation tank. By controlling the centrifuge parameters, titanium dioxide particles larger than 1 μm are separated as centrifugal precipitate, while titanium dioxide particles ≤ 1 μm are uniformly dispersed in the solution system. These particles are then emulsified and sheared again in a suspension preparation tank to obtain a stable 30-35 wt% high-concentration titanium dioxide suspension. The titanium dioxide suspension is discharged through a filter from the tank's outlet, ensuring stable quality and facilitating the subsequent preparation of the target nylon 66 product. A three-way valve is connected to the outlet of the titanium dioxide pre-mixing tank. The second port of this valve supplies material to the titanium dioxide centrifuge via the titanium dioxide pre-mixing intermediate tank, while the third port supplies material to the solid-liquid mixer. As needed, the mixture that has undergone preliminary emulsification and shearing can be partially or completely returned to the solid-liquid mixer for further mixing. The solid phase outlet of the titanium dioxide centrifuge feeds a grinding mill through a centrifugal sediment collection tank. The outlet of the grinding mill feeds a titanium dioxide pre-mixing tank. Titanium dioxide particles with a particle size greater than 1μm are ground and recycled for reuse, thereby improving the utilization rate of raw materials.

[0021] 4. The tube side of the flash evaporator is the process medium channel, and the inner diameter of the tube side gradually expands along the flow direction of the process medium. The oligomer aqueous solution mixed with titanium dioxide particles gradually depressurizes and dehydrates as it passes through the tube side (process medium channel) of the flash evaporator, gradually forming a bubble polymer. At the same time, the titanium dioxide and the material are vigorously and thoroughly mixed, which can greatly improve the mixing effect of titanium dioxide.

[0022] 5. The process of this invention: ① The salt formation adopts a two-step continuous salt formation process, which is more stable and energy-saving than the traditional intermittent salt formation process, and the salt solution quality is higher. Moreover, the salt concentration is high, with a concentration of ≥60wt%. The subsequent concentration process does not require the addition of fresh steam, and the process steam generated by the U-tube reactor can be used, which is more energy-saving and reduces consumption. ② The titanium dioxide suspension preparation process adopts a route of centrifugation followed by grinding. First, the titanium dioxide suspension with the required particle size (≤1μm) is separated by centrifugation, and the centrifugation residue with a particle size >1μm is then sent to grinding, which can greatly reduce the wasted work of the grinding machine and increase energy consumption. ③ The polycondensation reaction of nylon 66 is carried out in the molten state. Therefore, the initial reaction temperature should be controlled to be at least 10°C higher than the melting point of nylon 66 salt, generally around 210°C. Therefore, in this process, the salt needs to be preheated to 210°C before entering the prepolymerization reactor so that the reaction can proceed quickly after entering the U-shaped tube reactor. ④ The condensation polymerization of nylon 66 is a reaction accompanied by the removal of water and the formation of amide bonds, resulting in a linear polymer. As the polymer is formed, the melt viscosity of the reaction system increases. A key characteristic of this reaction is that the rate of water diffusion within the system determines the reaction rate. The flash evaporator used in this process utilizes biphenyl-biphenyl ether for efficient heating to 280℃ (approximately 15℃ higher than the polymer's melting point). Gradual pressure reduction is achieved by progressively increasing the diameter of the tubes within the flash evaporator until it approaches atmospheric pressure, causing the water in the material to vaporize and be removed, resulting in a bubbly polymer and significantly increasing the reaction rate. ⑤ The foamed polymer enters the final polymerization reactor, where moisture is further removed under reduced pressure, the polymer molecular weight increases further, and the viscosity increases; ⑥ Inject the matting agent titanium dioxide into the inlet pipe of the flash evaporator, so that the titanium dioxide suspension enters the flash evaporator together with the oligomer. As the diameter of the heat exchange tubes in the tube side of the flash evaporator is gradually increased to achieve gradual decompression and dehydration vaporization, the titanium dioxide and the polymer are mixed intensely and thoroughly, so that the titanium dioxide is uniformly dispersed in the polymer.

[0023] According to the applicant's experiments, the present invention can prepare fully matte nylon 66 chips for civilian use with a titanium dioxide content of 1.6% or semi-matte nylon 66 chips for civilian use with a titanium dioxide content of 0.3%, with a molecular weight range of 15,000 to 16,000.

[0024] The following description, in conjunction with the accompanying drawings and specific embodiments, provides further details. Attached Figure Description

[0025] Figure 1 This is a connection diagram of the present invention; Figure 2 This is a schematic diagram of the connection of the nylon 66 salt solution device of the present invention; Figure 3 This is a schematic diagram of the connection of the titanium dioxide suspension device of the present invention.

[0026] In the attached diagram, 1 is a concentration tank, 2 is a prepolymerization reactor, 3 is a final polymerization reactor, 31 is an upper cylindrical section, 32 is a lower conical section, 4 is a reaction preheater, 5 is a feeding pipeline, 6 is a flash evaporator, 7 is a feed pipeline, 8 is a concentration preheater, 9 is a reactor pressure reducing tower, 10 is an auger, 11 is a coarse salt reactor, 12 is a refined salt regulating tank, 13 is a salt formation waste gas absorption tower, 14 is a first circulation pipeline, 15 is a second circulation pipeline, 16 is a connecting pipe, 21 is a solid-liquid mixer, 22 is a titanium dioxide premixing tank, 23 is a titanium dioxide centrifuge, 24 is a titanium dioxide suspension preparation tank, 25 is a third circulation pipeline, and 26 is a grinder. Detailed Implementation

[0027] Example 1 See Figures 1 to 3The continuous production unit for nylon 66 includes a concentration tank 1, a prepolymerization reactor 2, and a final polymerization reactor 3. The inlet of the concentration tank 1 is connected to a nylon 66 salt solution device, and the outlet of the concentration tank 1 supplies feed to the prepolymerization reactor 2 via a reaction preheater 4. Specifically, the outer wall and interior of the concentration tank are equipped with heat exchange coils. The prepolymerization reactor 2 is a horizontal U-shaped tube reactor. The final polymerization reactor 3 consists of an upper cylindrical section 31 and a lower conical section 32 connected together. An auger 10 is installed in the lower conical section. Obviously, both the prepolymerization reactor and the final polymerization reactor are equipped with... It has a heat exchange jacket, and the top of the prepolymer reactor 2 provides heat to the concentration tank 1 through the reactor depressurization tower 9. The reactor depressurization tower absorbs small molecule materials in the gas phase through circulating spray. The upper cylindrical section of the final polymerization reactor is connected to a negative pressure source through a polymerization tail gas scrubbing tower and a tower top condenser. The feed inlet of the concentration tank 1 is connected to the nylon 66 salt solution device through the concentration preheater 8 and the salt solution intermediate tank. The top of the concentration tank 1 provides heat to the concentration preheater 8. The reaction preheater 4 includes a primary reaction preheater and a secondary reaction preheater connected in series. The prepolymer reactor 2 feeds the final polymerization reactor 3 through the feed pipe 5 and flash evaporator 6. The feed pipe 5 is equipped with a feed pipe 7 connected to the titanium dioxide suspension device. Specifically, the tube side of the flash evaporator 6 is the process medium channel, and the inner diameter of the tube side gradually increases along the flow direction of the process medium. The shell side of the flash evaporator is the heat exchange medium channel, using biphenyl-diphenyl ether vapor as the heat exchange medium. The number of feed pipes is usually set to at least two. In addition, a melt filter is usually installed at the outlet of the final polymerization reactor. The filtered melt is sent to the pelletizer, drying process, and grading process to obtain Nylon 66 product. In this embodiment, the nylon 66 salt solution device includes a crude salt reactor 11 and a refined salt regulating tank 12. Obviously, both the crude salt reactor and the refined salt regulating tank are equipped with heat exchange jackets and stirrers. The feed inlet of the crude salt reactor 11 is connected to the hexamethylenediamine source and the adipic acid source. The top of the crude salt reactor 11 is vented through the salt formation waste gas absorption tower 13 and the liquid seal tank. The discharge outlet of the crude salt reactor 11 is connected to the first circulation pipeline 14 for material return. The first circulation pipeline also supplies material to the refined salt regulating tank 12. A crude salt circulation pump and a crude salt circulation cooler are sequentially installed on the first circulation pipeline 14. The branch outlet on the first circulation pipeline is located between the crude salt circulation pump and the crude salt circulation cooler. The top of the refined salt regulating tank 12 is emptied via a liquid-sealed tank. The outlet of the refined salt regulating tank 12 is connected to the second circulation pipeline 15 for material return. The second circulation pipeline also has a branch line for discharging nylon 66 salt solution. A refined salt circulation pump and a refined salt circulation cooler are sequentially installed on the second circulation pipeline 15, with the branch line downstream of the refined salt circulation cooler. The inlet of the refined salt regulating tank 12 is connected to a hexamethylenediamine source. The crude salt reactor 11 feeds the refined salt regulating tank 12 through a crude salt storage tank. The refined salt regulating tank 12 discharges nylon 66 salt solution through the refined salt storage tank. Both the crude salt storage tank and the refined salt storage tank are equipped with heat exchange coils.The top of the refined salt regulating tank 12 and the top of the refined salt storage tank are connected by a connecting pipe 16. The titanium dioxide suspension device includes a solid-liquid mixer 21, a titanium dioxide pre-mixing tank 22, a titanium dioxide centrifuge 23, and a titanium dioxide suspension preparation tank 24. Obviously, both the titanium dioxide pre-mixing tank 22 and the titanium dioxide suspension preparation tank 24 are equipped with heat exchange coils and are equipped with emulsifiers. The feed inlet of the solid-liquid mixer 21 is connected to the titanium dioxide powder source and the water source respectively. The discharge outlet of the solid-liquid mixer supplies material to the titanium dioxide premixing tank 22. The discharge outlet of the titanium dioxide premixing tank 22 supplies material to the titanium dioxide centrifuge 23. Specifically, the discharge outlet of the titanium dioxide premixing tank 22 is connected to a three-way valve. The second port of the three-way valve supplies material to the titanium dioxide centrifuge 23 through the titanium dioxide premixing intermediate tank, and the third port supplies material to the solid-liquid mixer 21. The bottom of the titanium dioxide premixing tank 22 is connected to the third circulation pipeline 25 for material return. The third circulation pipeline diverts the material to the titanium dioxide premixing intermediate tank. A disperser is installed on the third circulation pipeline 25. The liquid phase outlet of the titanium dioxide centrifuge 23 supplies material to the titanium dioxide suspension preparation tank 24. The discharge port of the titanium dioxide suspension preparation tank 24 discharges the titanium dioxide suspension to the outside through a filter. In addition, the solid phase outlet of the titanium dioxide centrifuge 23 supplies material to a grinder 26 through a centrifugal sediment collection tank. The discharge port of the grinder 26 supplies material to the titanium dioxide premixing tank 22.

[0028] Example 2 A 30 wt% titanium dioxide suspension was prepared using the titanium dioxide suspension apparatus described in Example 1: 0.93t of solid titanium dioxide in ton bags is unpacked and fed into a solid-liquid mixer. Simultaneously, 2.17t of demineralized water is added to the titanium dioxide pre-mixing tank. The demineralized water flows into the solid-liquid mixer through the third port of a three-way valve to mix with the titanium dioxide powder. After mixing, the mixture is sent back to the titanium dioxide pre-mixing tank, thus forming a cycle. The mixture in the titanium dioxide pre-mixing tank is sheared and dispersed by a high-speed emulsifier at 2900 r / min, and then circulated after shearing by a disperser. After pre-mixing, 3.1t of titanium dioxide slurry is obtained and sent to the titanium dioxide pre-mixing intermediate tank. It is then sent to a titanium dioxide centrifuge for separation via a centrifuge feed pump. After centrifugation, 0.1t of titanium dioxide with a particle size greater than 1μm is separated as centrifugal precipitate and sent to a centrifugal precipitate collection tank. After being dispersed with water, it is sent to a grinder for grinding via a grinder feed pump and then returned to the titanium dioxide pre-mixing tank. 3 tons of titanium dioxide with a particle size ≤1μm were uniformly dispersed in a solution and sent to a titanium dioxide suspension preparation tank. After high-speed emulsification and shearing using a high-shear emulsifier at 2900 r / min, a stable 30wt% high-concentration titanium dioxide suspension was obtained. Then, the suspension was pressurized with nitrogen and temporarily stored in a titanium dioxide suspension storage tank. Two batches were prepared daily using this process.

[0029] Example 3 Nylon 66 salt solution was prepared using the apparatus described in Example 1: Adipic acid, after being weighed and metered, is quantitatively added to the crude salt reactor at a rate of 4078 kg / h. Using adipic acid as a baseline, hexamethylenediamine (2868 kg / h) and water (4893 kg / h) are added to the crude salt reactor through ratio adjustment. Under a nitrogen atmosphere, a slight positive pressure of 2 kPaG, and 72°C, the first step of salt formation produces a crude salt solution of 55% nylon 66. The crude salt solution is pumped out via a crude salt circulation pump at a rate of 35517 kg / h, cooled by a crude salt circulation cooler, and then circulated back to the crude salt reactor at a rate of 11839 kg / h. The solution is temporarily stored in a crude salt storage tank, then pumped to a refined salt conditioning tank via a crude salt transfer pump. 357 kg / h of hexamethylenediamine and a refined salt solution cooled by a refined salt circulation cooler are added under controlled ratio. After thorough mixing in a static mixer, the solution enters the refined salt conditioning tank, where a second salt formation process is carried out at 20 kPaG and 90°C to produce a 12196 kg / h nylon 66 salt solution with a concentration of approximately 60%. This solution is then temporarily stored in a refined salt storage tank via a refined salt circulation pump, and finally sent to the subsequent concentration process via the refined salt feed pump outlet.

[0030] Example 4 The continuous production of Nylon 66 products using the apparatus of Example 1 includes the following steps: The 12196 kg / h nylon 66 salt solution obtained in Example 3 was sent to a concentration tank and concentrated to 70 wt% under conditions of 0.03 MPa and 125°C. Part of the 1797 kg / h water vapor evaporated in the concentration tank was used as a heat source for the concentration preheater, while the excess steam was condensed by the concentration tank condenser and reused in the process water system. After concentration and preheating to 215°C, the solution entered a prepolymerization reactor. The prepolymerization conditions were 1.8 MPa and 245°C, producing an aqueous solution of 7908 kg / h of nylon 66 salt oligomers with a water content of approximately 10% and a molecular weight of approximately 5000. The process steam generated by the prepolymerization reactor enters the vacuum tower and is sprayed under reduced pressure. It then goes to the coil in the concentration tank as a heating source for salt solution concentration. The resulting oligomer aqueous solution is pumped to the flash evaporator and injected with a titanium dioxide suspension from Example 2 at a rate of 333.3 kg / h (for producing fully matte nylon 66 chips) or 62.5 kg / h (for producing semi-matte nylon 66 chips). This allows the titanium dioxide suspension to enter the flash evaporator along with the oligomers. An aqueous solution of nylon 66 salt oligomer containing titanium dioxide enters the tube side of a flash evaporator. The shell side of the flash evaporator is further heated with biphenyl-diphenyl ether vapor, rapidly heating the oligomer aqueous solution from 245°C to 280°C within 3 seconds. As the diameter of the heat exchange tubes in the tube side gradually increases, dehydration and vaporization are achieved through progressive decompression. Simultaneously, titanium dioxide is vigorously and thoroughly mixed with the material. Finally, the pressure is reduced to near atmospheric pressure, resulting in a vapor-liquid mixture of titanium dioxide in bubbly polymer. This polymer flows by gravity to the final polymerization reactor, where it undergoes further dehydration, addition polymerization, and condensation polymerization under a high-temperature vacuum of -0.08 MPaG and 284°C. The resulting polymer increases in molecular weight and is further mixed with titanium dioxide, producing a uniform, high-viscosity molten polymer with a molecular weight of approximately 17,000. The process steam generated during polymerization is sprayed and cooled in a polymerization tail gas scrubber, then cooled and sprayed again in the tail gas condenser before being discharged. Molten polymer is extruded through a bottom discharge screw in a polymerization reactor, then pumped to a melt filter for filtration, and finally sent to a pelletizer for pelletizing. The pellets are cut into chips of a certain size, which then flow into a centrifugal dryer for drying. After drying, the chips flow into a vibrating screen to screen out qualified products, and then into a color sorter to remove impurities. The final product is fully dull nylon 66 civilian spinning chips containing 1.6% titanium dioxide / semi-dull nylon 66 civilian spinning chips containing 0.3% titanium dioxide, with a molecular weight range of 15,000 to 16,000.

Claims

1. A continuous production apparatus for nylon 66, characterized in that: It includes a concentration tank (1), a prepolymerization reactor (2), and a final polymerization reactor (3). The inlet of the concentration tank (1) is connected to the nylon 66 salt solution device. The outlet of the concentration tank (1) supplies the prepolymer reactor (2) through the reaction preheater (4). The outlet of the prepolymer reactor (2) supplies the final polymerization reactor (3) through the feeding pipeline (5) and flash evaporator (6). The feeding pipeline (5) is equipped with a feeding pipeline (7) connected to the titanium dioxide suspension device.

2. The nylon 66 continuous production apparatus according to claim 1, characterized in that: The nylon 66 salt solution device includes a crude salt reactor (11) and a refined salt regulating tank (12). The feed inlet of the crude salt reactor (11) is connected to the hexamethylenediamine source and the adipic acid source. The top of the crude salt reactor (11) is emptied through the salt formation waste gas absorption tower (13) and the liquid seal tank. The outlet of the crude salt reactor (11) is connected to the first circulation pipeline (14) for material return. The first circulation pipeline also supplies material to the refined salt regulating tank (12). The top of the refined salt regulating tank (12) is emptied through the liquid seal tank. The outlet of the refined salt regulating tank (12) is connected to the second circulation pipeline (15) for material return. The second circulation pipeline also discharges nylon 66 salt solution to the outside.

3. The nylon 66 continuous production apparatus according to claim 2, characterized in that: The feed inlet of the refined salt regulating tank (12) is connected to the hexamethylenediamine source. A crude salt circulating pump and a crude salt circulating cooler are sequentially installed on the first circulation pipeline (14). The branch port on the first circulation pipeline is located between the crude salt circulating pump and the crude salt circulating cooler. The crude salt reactor (11) supplies the refined salt regulating tank (12) through the crude salt storage tank. A refined salt circulating pump and a refined salt circulating cooler are sequentially installed on the second circulation pipeline (15). The branch port on the second circulation pipeline is downstream of the refined salt circulating cooler. The refined salt regulating tank (12) discharges nylon 66 salt solution to the outside through the refined salt storage tank.

4. The nylon 66 continuous production apparatus according to claim 3, characterized in that: The top of the refined salt regulating tank (12) and the top of the refined salt storage tank are connected by a connecting pipe (16).

5. The continuous production apparatus for Nylon 66 according to claim 1, characterized in that: The titanium dioxide suspension device includes a solid-liquid mixer (21), a titanium dioxide premixing tank (22), a titanium dioxide centrifuge (23), and a titanium dioxide suspension preparation tank (24). The feed inlet of the solid-liquid mixer (21) is connected to the titanium dioxide powder source and the water source respectively. The discharge outlet of the solid-liquid mixer supplies the titanium dioxide premix tank (22). The discharge outlet of the titanium dioxide premix tank (22) supplies the titanium dioxide centrifuge (23). The liquid phase outlet of the titanium dioxide centrifuge (23) supplies the titanium dioxide suspension preparation tank (24). The discharge outlet of the titanium dioxide suspension preparation tank (24) discharges the titanium dioxide suspension to the outside through a filter.

6. The continuous production apparatus for Nylon 66 according to claim 5, characterized in that: The outlet of the titanium dioxide pre-mixing tank (22) is connected to a three-way valve. The second port of the three-way valve supplies material to the titanium dioxide centrifuge (23) through the titanium dioxide pre-mixing intermediate tank, and the third port supplies material to the solid-liquid mixer (21). The bottom of the titanium dioxide pre-mixing tank (22) is connected to the third circulation pipeline (25) for material return, and the third circulation pipeline diverts the material to the titanium dioxide pre-mixing intermediate tank. A disperser is installed on the third circulation pipeline (25).

7. The nylon 66 continuous production apparatus according to claim 5, characterized in that: The solid phase outlet of the titanium dioxide centrifuge (23) supplies material to a grinding mill (26) via a centrifugal precipitate collection tank, and the discharge port of the grinding mill (26) supplies material to a titanium dioxide premixing tank (22).

8. The continuous production apparatus for Nylon 66 according to claim 1, characterized in that: The feed inlet of the concentration tank (1) is connected to the concentration preheater (8), the intermediate salt tank and the nylon 66 salt solution device, and the top of the concentration tank (1) provides heat to the concentration preheater (8). The reaction preheater (4) includes a first-stage reaction preheater and a second-stage reaction preheater connected in series. The prepolymerization reactor (2) is a horizontal U-shaped tube reactor. The top of the prepolymerization reactor (2) provides heat to the concentration tank (1) through the reactor pressure reducing tower (9). The final polymerization reactor (3) is composed of an upper cylindrical section (31) and a lower conical section (32). An auger (10) is installed in the lower conical section. The upper cylindrical section is connected to the negative pressure source through the polymerization tail gas scrubbing tower and the tower top condenser. The tube side of the flash evaporator (6) is the process medium channel, and the inner diameter of the tube side gradually increases along the flow direction of the process medium.

9. A process for continuously synthesizing nylon 66 using any one of the production apparatuses of claims 1-8, characterized in that, Includes the following steps: 1) The concentration of the prepared nylon 66 salt solution was 55~62wt%, and the titanium dioxide particle size in the prepared titanium dioxide suspension was ≤1μm, with a concentration of 30~35wt%. 2) Nylon 66 salt solution was concentrated to 68-70 wt% at 0.03-0.04 MPa and 125-135℃, preheated to 210-220℃, and then fed into a prepolymerization reactor. The prepolymerization conditions were 1.8-2.0 MPa and 245-255℃ to obtain an oligomer aqueous solution. 3) After mixing the oligomer aqueous solution with the titanium dioxide suspension, the mixture is flash-evaporated. The flash-evaporation parameters are: heating to 280°C within 3 seconds and gradually dehydrating under reduced pressure to obtain a bubble-like polymer. 4) The foamed polymer enters the final polymerization reactor, and the final polymerization conditions are -0.06~-0.08MPa and 274~284℃ to obtain Nylon 66 melt.

10. The process according to claim 9, characterized in that, Step 1) The preparation method of nylon 66 salt solution is as follows: Based on adipic acid, hexamethylenediamine and water were added in proportion to generate a crude nylon 66 salt solution under an inert gas atmosphere, 1~2 kPaG, and 67~72℃. Hexamethylenediamine was added in a controlled proportion to generate a nylon 66 salt solution under 15~20 kPaG and 85~90℃. The preparation method of titanium dioxide suspension is as follows: Titanium dioxide powder and demineralized water are mixed in a solid-liquid mixture and then sent to a titanium dioxide premixing tank. After emulsification, shearing, and dispersion, the mixture is centrifuged. Titanium dioxide particles larger than 1 μm form a centrifugal precipitate, while the liquid phase containing titanium dioxide particles ≤ 1 μm is sent to a titanium dioxide suspension preparation tank and emulsified and sheared to obtain a titanium dioxide suspension.

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