A gas-liquid contact nylon 6 liquid phase viscosity increasing reaction device and method

Abstract

The application provides a gas-liquid contact nylon 6 liquid-phase tackifying reaction device and method, and the reaction device comprises a melt feeding unit, a liquid-phase tackifying reaction unit and a low-shear discharging online tackiness control unit which are connected in series, a carrier gas heating and distribution unit, a monomer recovery unit and a vacuum unit which are in communication with the liquid-phase tackifying reaction unit respectively; the liquid-phase tackifying reaction unit comprises a vertical tackifying reaction tower, a first low-shear gas-liquid contactor is arranged at the upper part of the vertical tackifying reaction tower, a second low-shear gas-liquid contactor is arranged at the middle part of the vertical tackifying reaction tower, and a third low-shear gas-liquid contactor is arranged at the lower part of the vertical tackifying reaction tower; an upper preheating zone jacket corresponding to the upper part, a middle tackifying reaction zone jacket corresponding to the middle part and a lower constant-temperature buffer zone jacket corresponding to the lower part are arranged on the outer wall of the vertical tackifying reaction tower, and the three jackets are independently temperature-controlled. The application solves the technical problems of long process flow, high energy consumption and uneven molecular weight distribution in the prior art.

Description

Technical Field

[0001] This invention belongs to the field of polymer post-processing technology, specifically relating to a gas-liquid contact nylon 6 liquid phase thickening reaction apparatus and method. Background Technology

[0002] Nylon 6, as an important engineering plastic, is widely used in the automotive, electronics, machinery, and marine engineering industries due to its high tensile strength, high elastic modulus, wear resistance, self-lubrication, and high temperature resistance. While nylon 6 is a raw material for manufacturing core marine equipment such as marine cages, large-scale deep-sea fishing nets, and towing ropes, its melt viscosity after hydrolytic ring-opening polymerization is typically only 2.2–2.6. The end groups retain a large amount of water, free caprolactam monomers, and cyclic dimer oligomers, making it unsuitable for high-viscosity applications such as high-strength spinning, blown films, and low-VOC modified plastics. Currently, the mainstream industrial approach relies on solid-phase thickening and liquid-phase thickening with devolatilizers to increase the molecular weight of nylon 6 and remove volatile small molecules. However, the solid-phase thickening route has inherent drawbacks: the entire process is lengthy, with a single thickening residence time of 40–60 hours; the accompanying extraction section generates a large amount of organic wastewater, and the combined energy consumption for drying and nitrogen circulation is extremely high; the melt needs to be cooled and pelletized first, making it impossible to directly connect to the polymerization unit for continuous production; the equipment occupies a large area, and the cost of single-line modification is high, making it difficult to adapt to the needs of short-process integrated production, failing to meet green production requirements, and failing to meet the directional requirements of high-performance nylon 6; the liquid-phase thickening with devolatilizers has a high shear rate (>200s). -1 This can easily cause mechanical breakage of molecular chains, resulting in a wide molecular weight distribution of the product, easy yellowing, and gel formation.

[0003] Therefore, there is an urgent need for a new method to thicken nylon 6, so as to solve the technical problems of low reaction efficiency, long process flow, high energy consumption and uneven molecular weight distribution in the existing hydrolysis ring-opening and solid-phase thickening technologies. Summary of the Invention

[0004] The purpose of this invention is to provide a gas-liquid contact nylon 6 liquid phase thickening device to solve the problems of long process flow, high energy consumption and uneven molecular weight distribution in the prior art.

[0005] Another objective of this invention is to provide a method for increasing the viscosity of nylon 6 in the liquid phase through gas-liquid contact.

[0006] To achieve the above objectives, the present invention provides a gas-liquid contact nylon 6 liquid phase thickening reaction device, comprising a melt feeding unit, a liquid phase thickening reaction unit and a low shear discharge online thickening control unit connected in series, a carrier gas heating and distribution unit, a monomer recovery unit and a vacuum unit respectively connected to the liquid phase thickening reaction unit;

[0007] The liquid-phase viscosity-enhancing reaction unit includes a vertical viscosity-enhancing reaction tower. The tower has a primary low-shear gas-liquid contactor at the top, a secondary low-shear gas-liquid contactor in the middle, and a tertiary low-shear gas-liquid contactor at the bottom. The outer wall of the tower has jackets corresponding to the upper preheating zone, the middle viscosity-enhancing reaction zone, and the lower isothermal buffer zone, each with independent temperature control. The primary low-shear gas-liquid contactor includes multiple vertically arranged guide vanes, with a first gas distributor at the bottom of each vane. The gap between adjacent guide vanes is 2-3 mm. The secondary low-shear gas-liquid contactor is a horizontally arranged structure of large and small discs, with multiple sets of these discs. The structure is vertically stacked, with the large disc on the upper layer and the small disc on the lower layer in each group of large and small disc structures. The large disc has multiple first openings on its edge, and the small disc has a second opening in its center. The material on the large disc flows towards the edge and falls into the small disc below through the first opening. The material in the small disc flows towards the center and flows into the next group of large discs through the second opening. A second gas distributor is located below the bottom group of large and small disc structures. The three-stage low-shear gas-liquid contactor is a horizontally arranged ridge structure. There are multiple groups of ridge structures, each group of ridge structures is vertically stacked, and each group of ridge structures has multiple ridge components. The ridge components in adjacent layers of ridge structures are staggered, and a third gas distributor is located below each ridge component.

[0008] The gas-liquid contact nylon 6 liquid phase viscosity-enhancing reaction device of the present invention has micro-guiding grooves on the surface of the guide plate.

[0009] The gas-liquid contact nylon 6 liquid phase thickening reaction device of the present invention includes a melt feeding unit comprising a single-shaft disc heater, a discharge screw conveyor, a filter, a buffer tank, a booster pump, an electric heater and a centrifugal feeder connected in series, wherein the centrifugal feeder is located at the top of the vertical thickening reaction tower.

[0010] The gas-liquid contact nylon 6 liquid phase viscosity-enhancing reaction device of the present invention includes a low-shear discharge online viscosity control unit located at the bottom of the vertical viscosity-enhancing reaction tower, comprising a discharge pump and an online viscometer.

[0011] The gas-liquid contact nylon 6 liquid phase thickening reaction device of the present invention includes a carrier gas heating and distribution unit which is sequentially equipped with a circulating fan and a heater. The heater is connected to a vertical thickening reaction tower for introducing carrier gas into the tower.

[0012] The gas-liquid contact nylon 6 liquid phase thickening reaction device of the present invention includes a monomer recovery unit comprising a tail gas scrubbing tower, a primary condenser, a secondary condenser, a monomer recovery tank and an external discharge pump connected in sequence, wherein the inlet of the tail gas scrubbing tower is connected to the tail gas outlet of the vertical thickening reaction tower.

[0013] The gas-liquid contact nylon 6 liquid phase viscosity-enhancing reaction device of the present invention includes a vacuum unit comprising a Venturi vacuum pump, a vacuum circulation storage tank, a condenser and a circulation pump connected in sequence. The outlet of the circulation pump is connected to the inlet of the Venturi vacuum pump, and the inlet of the Venturi vacuum pump is also connected to the monomer recovery unit. The vacuum circulation storage tank is also connected to a water ring vacuum pump.

[0014] To achieve the above objectives, the present invention also provides a gas-liquid contact method for liquid-phase thickening of nylon 6, using the reaction apparatus described above, comprising the following steps:

[0015] 1) Start the vacuum unit to maintain the pressure inside the vertical thickening reaction tower at -0.092 to -0.098 MPa;

[0016] 2) Start the carrier gas heating and distribution unit. After heating, the carrier gas is heated to 250-280℃ and then introduced into the vertical thickening reaction tower. The temperature of the thickening reaction zone is controlled at 260-275℃, and the carrier gas supply flow rate is 0.5-1.5 Nm³ / h·t melt.

[0017] 3) Start the melt feeding unit, heat the nylon 6 raw material to 225-250℃ to melt it, and then transport the melt to the vertical thickening reaction tower;

[0018] 4) Liquid phase thickening reaction: The molten nylon 6 material passes through a first-stage low-shear gas-liquid contactor, a second-stage low-shear gas-liquid contactor, and a third-stage low-shear gas-liquid contactor in a vertical thickening reaction tower from top to bottom, forming a uniform and continuous liquid film with a thickness of 0.1 to 0.4 mm; the heated carrier gas flows from bottom to top and contacts the uniform and continuous liquid film countercurrently, removing water and free caprolactam from the molten material, thus completing the thickening reaction;

[0019] 5) The molten material after thickening is discharged through a low-shear discharge line with the viscosity controlled in real time by an online viscosity control unit. If the viscosity meets the requirements, it is discharged; otherwise, it is recycled back to the vertical thickening reaction tower.

[0020] 6) The tail gas generated in the vertical thickening reaction tower is discharged into the monomer recovery unit.

[0021] The gas-liquid contact liquid phase thickening method for nylon 6 according to the present invention is wherein the carrier gas is high-purity nitrogen or carbon dioxide; and the nylon 6 raw material is one or more of virgin polymer melt, nylon 6 chip melt, and recycled nylon 6 melt.

[0022] Beneficial effects of this invention:

[0023] 1) Extremely low shear rate, inhibiting molecular chain degradation, with a stable melt shear rate of <50 s throughout the entire process. -1 Much lower than twin-screw extrusion (>200 s) -1Nylon 6 molecular chains have no mechanical breakage, the product has a narrow molecular weight distribution (PDI 1.7~2.0), no gelation or yellowing, and significantly improved tensile strength and impact toughness, making it suitable for high-end industrial yarns and blown nylon raw materials.

[0024] 2) The gas-liquid contact efficiency is greatly improved and the reaction time is greatly shortened. The vertical viscosity-enhancing reaction tower has a fully and efficiently contacting ultra-thin liquid film with multi-stage countercurrent distributed carrier gas, and the gas-liquid specific surface area is increased by 3 to 6 times. Under the same viscosity increase, the residence time is only 1 / 3 of that of the traditional vertical falling film reactor, which is more than 90% shorter than that of solid phase viscosity enhancement, and continuous production is possible.

[0025] 3) The system has low overall energy consumption and recyclable by-products. The elimination of screw-driven high-power shearing equipment reduces power consumption by more than 35%. The removed caprolactam is condensed, recycled, and reused, which greatly reduces raw material consumption, lowers production costs, and reduces organic waste gas emissions, making it green and environmentally friendly.

[0026] 4) The product has stable quality, wide process adaptability, no local hot spots, and no melt stagnation or degradation; it can be adapted to direct melting of virgin chips, waste recycled nylon 6, and online thickening of low-viscosity polymer melts; the viscosity adjustment range is wide, and one system can produce spinning grade, engineering plastic grade, and blow molding grade high-viscosity nylon 6.

[0027] 5) Wide range of applications. The high-viscosity nylon 6 prepared by this invention combines the advantages of ultra-high viscosity with stable molecular weight distribution, and can be widely used in multiple technical fields such as marine equipment, automotive interior parts, electronic and electrical components, and energy storage batteries, with broad market application prospects.

[0028] 6) Through optimized structural and process parameter design, it can stably adapt to the transformation of production lines with a capacity range of 0.2 to 300,000 tons / year. At the same time, it can be compatible with various different nylon 6 processing needs. The adaptable capacity range of this invention is large and the product coverage is comprehensive. It can meet the small-scale processing of small and medium-sized production lines, and can also be adapted to the batch production and modification of large industrial production lines. It has great industrial promotion value. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the gas-liquid contact nylon 6 liquid phase thickening reaction device of the present invention;

[0030] Figure 2 This is a schematic diagram of the vacuum unit of the present invention;

[0031] Figure 3 This is a schematic diagram of the structure of the first-stage low-shear gas-liquid contactor of the present invention:

[0032] Figure 4 This is a schematic diagram showing the flow direction of the molten material in the large and small disc structures of the present invention;

[0033] Figure 5 This is a schematic diagram of the large disk in the large and small disk structure of the present invention;

[0034] Figure 6 This is a schematic diagram of the small disk in the large and small disk structure of the present invention;

[0035] Figure 7 This is a schematic diagram of the structure of the three-stage low-shear gas-liquid contactor of the present invention.

[0036] In the attached figures, the following labels are used:

[0037] 1. Vertical viscosity-enhancing reaction tower; 2. Centrifugal feeder; 3. Distributor internals; 4. Primary low-shear gas-liquid contactor; 5. First gas distributor; 6. Secondary low-shear gas-liquid contactor; 7. Second gas distributor; 8. Tertiary low-shear gas-liquid contactor; 9. Third gas distributor; 10. Vertical viscosity-enhancing reaction tower shell jacket; 11. Discharge stirring scraper; 12. Gear booster discharge pump; 13. First switching valve; 14. Online viscometer; 15. Second switching valve; 16. Single-shaft... 17. Disc heater; 18. Twin-screw conveyor for discharge; 19. Precision filter; 20. Buffer tank; 21. Gear booster feed pump; 22. Electric heater; 23. Tail gas scrubber; 24. Primary condenser; 25. Secondary condenser; 26. Individual recovery tank; 27. External discharge pump; 28. Circulation pump; 29. ​​Circulation fan; 30. Finned tube heater; 31. Venturi vacuum pump; 32. Vacuum circulation storage tank; 33. Condenser; 34. Circulation pump; 35. Water ring vacuum pump. Detailed Implementation

[0038] The present invention will now be described in detail through embodiments. It should be noted that the following embodiments are only for further illustration of the present invention and should not be construed as limiting the scope of protection of the present invention. Those skilled in the art can make some non-essential improvements and adjustments to the present invention based on the above description.

[0039] like Figures 1 to 7 As shown, the gas-liquid contact nylon 6 liquid phase thickening reaction device of the present invention includes a melt feeding unit, a liquid phase thickening reaction unit and a low shear discharge online viscosity control unit connected in series, a carrier gas heating and distribution unit, a monomer recovery unit and a vacuum unit respectively connected to the liquid phase thickening reaction unit;

[0040] The liquid-phase viscosity-enhancing reaction unit includes a vertical viscosity-enhancing reaction tower 1. The vertical viscosity-enhancing reaction tower 1 is equipped with a primary low-shear gas-liquid contactor 4 at the top, a secondary low-shear gas-liquid contactor 6 in the middle, and a tertiary low-shear gas-liquid contactor 8 at the bottom. The outer wall of the vertical viscosity-enhancing reaction tower 1 is equipped with a vertical viscosity-enhancing reaction tower shell jacket 10. The vertical viscosity-enhancing reaction tower shell jacket 10 is a three-section jacket, namely the upper preheating zone jacket corresponding to the upper part, the middle viscosity-enhancing reaction zone jacket corresponding to the middle part, and the lower constant temperature buffer zone jacket corresponding to the lower part. The three sections of the jacket are independently temperature-controlled. The heating method of the three sections of the jacket is either heat transfer oil heating or resistance wire heating, and the temperature control accuracy is ±1℃.

[0041] like Figures 3 to 7 As shown, the primary low-shear gas-liquid contactor 4 includes multiple vertically arranged guide plates. A first gas distributor 5 is located at the bottom of each guide plate. The gap between two adjacent guide plates is 2-3 mm. In one specific embodiment, the guide plates have an inclined angle capable of holding liquid, such as a vertical wave shape or a vertical "W" shape. Micro-backflow grooves can also be provided on the surface of the guide plates to allow the material to form a thinner liquid film on the surface of the guide plates. The carrier gas flows upward through the first gas distributor 5, making countercurrent contact with the material passing through the primary low-shear gas-liquid contactor 4. The secondary low-shear gas-liquid contactor 6 is a horizontally arranged large and small disc structure, such as... Figure 4 As shown, there are multiple sets of large and small disk structures, which are vertically stacked and combined. In each set of large and small disk structures, the large disk is located on the upper layer and the small disk is located on the lower layer. The edge of the large disk has multiple first openings, such as... Figure 5 As shown, the small disk has a second opening at its center, such as... Figure 6 As shown, the material on the large disc flows towards the edge and falls into the smaller disc below through the first opening. The material in the smaller disc flows towards the center and flows into the next set of large discs through the second opening. A second gas distributor 7 is located below the bottom set of large and small discs. The carrier gas also flows upward through the second gas distributor 7, making countercurrent contact with the material that has passed through the secondary low-shear gas-liquid contactor 6. The tertiary low-shear gas-liquid contactor 8 is a horizontally arranged ridge structure, as shown... Figure 7As shown, the ridge structure comprises multiple sets, each set of which is vertically stacked and combined. Each set of ridge structures contains multiple ridge components, with the ridge components in adjacent layers arranged in a staggered manner. A third gas distributor 9 is provided below each ridge component. In a preferred embodiment, a discharge stirring scraper 11 is provided at the bottom of the vertical thickening reaction tower 1 to scrape the material at the bottom of the tower for easy discharge. In a preferred embodiment, a distributor internal component 3 is also provided between the centrifugal feeder 2 and the first-stage low-shear gas-liquid contactor 4 inside the vertical thickening reaction tower 1. This component is used to evenly distribute the material output from the centrifugal feeder 2 to the cross-section of the vertical thickening reaction tower 1, achieving uniform material distribution and providing a uniformly distributed feed to the first-stage low-shear gas-liquid contactor 4. This allows the material to spread and fall evenly along the cross-section of the tower, eliminating material deviation and backflow phenomena within the tower.

[0042] In the liquid-phase thickening process of nylon 6, the viscosity of the material gradually increases from top to bottom along the vertical thickening reaction tower 1, and the fluidity continuously deteriorates. Simultaneously, it is crucial to avoid high shear causing nylon 6 molecular chain breakage, material foaming, coking, and material blockage. The three-stage low-shear gas-liquid contactor is matched according to the material's viscosity evolution from low to medium to high from top to bottom. A primary low-shear gas-liquid contactor 4, a secondary low-shear gas-liquid contactor 6, and a tertiary low-shear gas-liquid contactor 8 are used respectively. Low-shear counter-current gas-liquid contact is employed throughout the process, with the carrier gas carrying away volatile small molecules upwards. The primary low-shear gas-liquid contactor 4 uses vertically arranged guide plates with a gap of 2-3 mm. The vertical arrangement relies on gravity to spread the melt downwards along the plate surface. The wavy, W-shaped inclined plate structure design forces the material to form a uniform, extremely thin liquid film on the guide plate surface, preventing the accumulation of a thick liquid flow. The narrow gap confines the material to the plate surface, suppressing liquid flow aggregation and droplet splashing. The thin liquid film greatly expands the gas-liquid mass transfer area, rapidly evaporating caprolactam and water into the gas phase under high load. The secondary low-shear gas-liquid contactor 6 uses vertically stacked large and small discs, with a large upper disc and a small lower disc. The large disc has openings at its edge, and the small disc has an opening at its center. A second gas distributor 7 is located below. After the first-stage devolatilization, the nylon 6 melt enters the medium viscosity range: its fluidity deteriorates, making it difficult to continuously spread into a thin liquid film on the vertical narrow plate; the melt easily adheres to the wall and flows along the plate in streams, causing a sharp drop in mass transfer efficiency. At this stage, it is necessary to continue removing residual caprolactam and low-molecular-weight oligomers. On the secondary low-shear gas-liquid contactor 6, the material falls onto the upper large disc and, affected by viscosity, slowly spreads towards the edge of the disc, dripping from the first opening at the edge to the lower small disc; the melt on the small disc converges towards the center and drips from the second opening at the center to the next large disc. The melt can spread and form a liquid film on the surface of each disc, no longer relying on the gravity stretching of the vertical plate for film formation, thus adapting to the flow characteristics of medium-viscosity melts. The disc surface is a horizontal film-spreading surface, requiring less melt flowability than the vertical guide plate. Multiple stages continuously renew the melt surface and the gas-liquid interface; each layer has new exposed surfaces, further diffusing and evaporating small molecules trapped inside the melt. The second gas distributor 7 introduces carrier gas from the bottom of this stage upwards, passing through the space between the discs, and making countercurrent contact with the melt that falls layer by layer and spreads on the disc surface; there are no agitating components throughout the process, relying solely on gravity flow to avoid shear degradation of nylon molecules. Therefore, the above-described two-stage low-shear gas-liquid contactor 6 can adapt to medium-viscosity nylon melts, overcoming the shortcomings of vertical guide plates in effectively forming films, while still maintaining extremely low shear to prevent molecular chain breakage. After passing through the secondary low-shear gas-liquid contactor 6, the melt viscosity is further increased and the melt flowability is further deteriorated; the tertiary low-shear gas-liquid contactor 8 is set as a vertical stacked ridge structure, with the ridge components between layers staggered, and a third gas distributor 9 is set under each ridge.High-viscosity melts are difficult to spread over a large area on a disc. The ridge has a sloping structure, and the high-viscosity melt flows downwards along the ridge slope, forming a thin liquid flow. The upper and lower ridges are staggered, so the material flowing down from the upper layer does not fall directly into the same position in the lower layer. The material is constantly dispersed and redistributed, continuously refreshing the free surface of the melt. The staggered structure also prevents the material from falling vertically directly and forming a column, preventing material accumulation and dead zones. Furthermore, the diffusion resistance of small molecules is high in the high-viscosity stage, requiring fresh carrier gas to be purged from the surface of the liquid film on each ridge. Therefore, the distributor supplies carrier gas to the liquid film surface of the ridge nearby, ensuring sufficient local gas-liquid contact, eliminating dead zones in the gas phase within the tower, and promptly removing trace small molecules that diffuse out. If a single-point bottom gas inlet is used, gas concentration enrichment is likely to occur in the upper part of the high-viscosity section, reducing the mass transfer driving force. High-viscosity nylon is prone to thermal degradation when subjected to strong shear, resulting in yellowing and a decrease in molecular weight. However, in the device of this invention, the entire ridge structure is not mechanically agitated, and the high-viscosity nylon flows along the slope solely by gravity, which can minimize the risk of molecular chain breakage caused by shear.

[0043] The gas-liquid contact nylon 6 liquid phase thickening reaction device of the present invention includes a melt feeding unit comprising a single-shaft disc heater 16, a discharge twin-screw conveyor 17, a precision filter 18, a buffer tank 19, a gear booster feed pump 20, an electric heater 21, and a centrifugal feeder 2 connected in series. The centrifugal feeder 2 is located at the top of the vertical thickening reaction tower 1. The discharge twin-screw conveyor 17 is installed at the outlet of the single-shaft disc heater 16. Depending on the arrangement, it can be installed horizontally or vertically. It is essential to ensure that there are no dead zones inside the single-shaft disc heater 16 and the discharge twin-screw conveyor 17. The outlet of the discharge twin-screw conveyor 17 is connected to the inlet of the gear booster feed pump 20. The outlet of the gear booster feed pump 20 is connected to the inlet of the electric heater 21. The outlet of the electric heater 21 is connected to the inlet of the centrifugal feeder 2. The centrifugal feeder 2 includes a high-speed centrifugal rotor and an annular guide plate, which is used to disperse the nylon 6 melt into a uniform and continuous liquid film with a thickness of 0.5 to 1 mm.

[0044] The gas-liquid contact nylon 6 liquid phase viscosity-enhancing reaction device of the present invention includes a low-shear discharge online viscosity control unit located at the bottom of the vertical viscosity-enhancing reaction tower 1, comprising a gear booster discharge pump 12 and an online viscometer 14. The gear booster discharge pump 12 discharges the material from the bottom of the vertical viscosity-enhancing reaction tower 1, and the online viscometer 14 monitors the material viscosity in real time. A circulation pipeline is provided between the gear booster discharge pump 12 and the vertical viscosity-enhancing reaction tower 1. If the product viscosity is unqualified, it is returned to the vertical viscosity-enhancing reaction tower 1 through the circulation pipeline. A first switching valve 13 is provided on the circulation pipeline. If the product viscosity is qualified, it is discharged through a second switching valve 15 on the discharge pipeline.

[0045] The gas-liquid contact nylon 6 liquid-phase thickening reaction device of the present invention includes a carrier gas heating and distribution unit sequentially equipped with a circulating fan 28 and a finned tube heater 29. The finned tube heater 29 is connected to the vertical thickening reaction tower 1 for introducing carrier gas into the tower. In a preferred embodiment, the finned tube heater 29 is connected in parallel with a first gas distributor 5, a second gas distributor 7, and a third gas distributor 9 for gas intake. The outlet of the circulating fan 28 is connected to the inlet of the finned tube heater 29. A portion of the carrier gas escaping from the vertical thickening reaction tower 1 is preferably circulated back into the circulating fan 28.

[0046] The gas-liquid contact nylon 6 liquid-phase thickening reaction device of the present invention includes a monomer recovery unit comprising a tail gas scrubbing tower 22, a primary condenser 23, a secondary condenser 24, a monomer recovery tank 25, and an external discharge pump 26 connected in sequence. The inlet of the tail gas scrubbing tower 22 is connected to the tail gas outlet of the vertical thickening reaction tower 1. The outlet of the tail gas scrubbing tower 22 is connected to the inlet of the primary condenser 23. The outlet of the primary condenser 23 is connected to the gas phase inlet of the secondary condenser 24. The outlet of the secondary condenser 24 is connected to the inlet of the monomer recovery tank 25. The non-condensable gas outlet of the monomer recovery tank 25 is connected to the inlet of the Venturi vacuum pump 30. The liquid phase outlet of the monomer recovery tank 25 is connected to the external discharge pump 26.

[0047] like Figure 2 As shown, the gas-liquid contact nylon 6 liquid-phase viscosity-enhancing reaction device of the present invention includes a vacuum unit comprising a Venturi vacuum pump 30, a vacuum circulation storage tank 31, a condenser 32, and a circulation pump 33 connected in sequence. The outlet of the circulation pump 33 is connected to the inlet of the Venturi vacuum pump 30, and the inlet of the Venturi vacuum pump 30 is also connected to the monomer recovery tank 25 in the monomer recovery unit. The vacuum circulation storage tank 31 is also connected to a water ring vacuum pump 34. The outlet of the Venturi vacuum pump 30 is connected to the inlet of the vacuum circulation storage tank 31, the outlet of the vacuum circulation storage tank 31 is connected to the inlet of the condenser 32, and the outlet of the condenser 32 is connected to the inlet of the circulation pump 33. The inlet of the water ring vacuum pump 34 is connected to the gas phase outlet of the vacuum circulation storage tank 31.

[0048] To achieve the above objectives, the present invention also provides a gas-liquid contact method for liquid-phase thickening of nylon 6, using the reaction apparatus described above, comprising the following steps:

[0049] 1) Start the vacuum unit to maintain the pressure inside the vertical thickening reaction tower at -0.092 to -0.098 MPa;

[0050] 2) Start the carrier gas heating and distribution unit. After heating, the carrier gas is heated to 250-280℃ and then introduced into the vertical thickening reaction tower. The temperature of the thickening reaction zone is controlled at 260-275℃, and the carrier gas supply flow rate is 0.5-1.5 Nm³ / h·t melt.

[0051] 3) Start the melt feeding unit, heat the nylon 6 raw material to 225-250℃ to melt it, and then transport the melt to the vertical thickening reaction tower;

[0052] 4) Liquid phase thickening reaction: The molten nylon 6 material passes through a first-stage low-shear gas-liquid contactor, a second-stage low-shear gas-liquid contactor, and a third-stage low-shear gas-liquid contactor in a vertical thickening reaction tower from top to bottom, forming a uniform and continuous liquid film with a thickness of 0.1 to 0.4 mm; the heated carrier gas flows from bottom to top and contacts the uniform and continuous liquid film countercurrently, removing water and free caprolactam from the molten material, thus completing the thickening reaction;

[0053] 5) The molten material after thickening is discharged through a low-shear discharge line with the viscosity controlled in real time by an online viscosity control unit. If the viscosity meets the requirements, it is discharged; otherwise, it is recycled back to the vertical thickening reaction tower.

[0054] 6) The tail gas generated in the vertical thickening reaction tower is discharged into the monomer recovery unit.

[0055] Specifically, the method includes the following steps:

[0056] Step (1): Add a certain amount of water to the vacuum circulation storage tank 31 through the pipeline to ensure that the vacuum unit can be used normally for circulation. Start the circulation pump 33 and the water ring vacuum pump 34 to maintain the pressure inside the vertical viscosity-enhancing reaction tower 1 at the design value. In a specific embodiment, the amount of water added to the vacuum circulation storage tank 31 is 60% to 80% of the tank volume, the water temperature is controlled at 50 to 60°C, the circulation rate of the circulation pump 33 is not less than 135 m³ / h, and the pressure head is not less than 8000 Pa; the pumping speed of the water ring vacuum pump 34 is 12 to 50 m³ / h, the inlet working pressure of the water ring vacuum pump 34 is maintained at 2000 to 8000 Pa absolute pressure, the working fluid temperature of the water ring vacuum pump 34 is controlled at 15 to 30°C, and a cavitation protection pipeline is configured.

[0057] Step (2): Turn on the circulating fan 28 of the carrier gas heating distribution unit. After ensuring that the outlet speed and flow rate of the circulating fan 28 meet the design values, turn on the heating switch of the finned tube heater 29. Most of the carrier gas is recycled and reused in the liquid phase viscosity-enhancing reaction unit, and a small portion of the carrier gas enters the monomer recovery unit. In one specific embodiment, the circulating fan 28 is a high-temperature circulating fan with a design temperature of 350°C and a design head of 5000Pa; the finned tube heater 29 has a design temperature of 350°C, a shell-side design head of 0.098MPa, and is heated by either electric heating or thermal oil heating.

[0058] Step (3): Reconfirm the temperature of the circulating carrier gas in step (2) and the pressure value at the top of the vertical viscosity-enhancing reaction tower 1 in step (1). After the design values ​​are met, the heated heat transfer oil enters the stirring blades and jacket of the single-shaft disc heater 16, and simultaneously enters the buffer tank 19, the upper preheating zone jacket, the middle viscosity-enhancing reaction zone jacket, and the lower constant temperature buffer zone jacket of the vertical viscosity-enhancing reaction tower 1. In a specific embodiment, the single-shaft disc heater 16 has a hollow shaft and hollow disc structure, and the heat transfer oil can enter the hollow disc through the hollow shaft to complete the heat exchange; the shell jacket of the single-shaft disc heater 16 is one of an integral jacket, a honeycomb jacket, or a Miller plate jacket; the design pressure of the single-shaft disc heater 16 is 0.8~1.2 MPa(g), and the design temperature is 250~300℃; the jacket design pressure is 0.8~1.02MPa(g), and the design temperature is 250~300℃.

[0059] The vertical thickening reaction tower 1 has a shell jacket consisting of an upper preheating zone jacket, a middle thickening reaction zone jacket, and a lower constant temperature buffer zone jacket. The jacket can be an integral jacket, a honeycomb jacket, or a Miller plate jacket. The shell design pressure is -0.1 MPa (g), and the design temperature is 250 to 300°C. The jacket design pressure is 0.8 to 1.02 MPa (g), and the design temperature is 250 to 300°C.

[0060] Step (4): The nylon 6 raw material is continuously heated to the single-shaft disc heater 16 through the feed pipeline. The heated molten material continuously passes through the discharge twin-screw conveyor 17, and after impurities are removed by the precision filter 18, it enters the buffer tank 19. After the liquid level meets the requirements, the gear booster feed pump 20 is turned on to pressurize the molten material and further heat it through the electric heater 21 before entering the centrifugal feeder 2. In one specific embodiment, the initial relative viscosity of the nylon 6 raw material is 2.2 to 2.6.

[0061] Step (5): After the thickening and heating process of the molten material in step (4), the material is spread out in a linear shape by the centrifugal feeder 2 located at the top of the vertical thickening reaction tower 1. Then, the material passes through the first-stage low-shear gas-liquid contactor 4, the second-stage low-shear gas-liquid contactor 6, and the third-stage low-shear gas-liquid contactor 8 from top to bottom. During the flow process of the nylon 6 melt, it spreads into a uniform and continuous liquid film with a thickness of 0.1-0.4 mm as it passes through the first-stage low-shear gas-liquid contactor 4, the second-stage low-shear gas-liquid contactor 6, and the third-stage low-shear gas-liquid contactor 8, and makes full contact with the inert carrier gas. The hot carrier gas entering from the bottom makes efficient gas-liquid contact with the uniform and continuous liquid film falling from the top, removes water and free caprolactam from the melt, promotes the condensation and chain extension of nylon 6 molecular chains, and completes the thickening reaction. The carrier gas is either high-purity nitrogen or carbon dioxide.

[0062] Step (6): Turn on the discharge stirring scraper 11 at the bottom of the vertical thickening reaction tower 1 and the outlet gear booster pump 12. The online viscometer 14 monitors the viscosity of nylon 6 at the bottom outlet of the vertical thickening reaction tower 1 in real time. Once the viscosity is within acceptable limits, open the second switch valve 15 to discharge the nylon 6; otherwise, open the first switch valve 13 to circulate the nylon 6 back to the vertical thickening reaction tower 1, completing the preparation of the nylon 6 thickening reaction process. The discharge stirring scraper 11 mainly prevents the molten nylon 6 from sticking to the wall. The gap between the stirring scraper and the inner wall of the cylinder is 1–3 mm, and the stirring speed is 2–5 r / min. In one specific embodiment, the relative viscosity of the discharged nylon 6 is controlled to be 3.0–4.2.

[0063] The gas-liquid contact liquid-phase thickening method for nylon 6 according to the present invention uses high-purity nitrogen or carbon dioxide as the carrier gas; the nylon 6 raw material is one or more of virgin polymer melt, nylon 6 chip melt, and recycled nylon 6 melt. In one specific embodiment, when the raw material is recycled nylon 6 melt, the residence time of the melt in the vertical thickening reaction tower 1 is controlled to be 30-60 min, and the carrier gas flow rate is 0.5-1.5 Nm³ / h·t melt.

[0064] The following methods were used to thicken nylon 6 primary chips (industrial conventional polymerization output) using the apparatus described in this invention, a conventional vertical falling film reactor (the mainstream equipment for liquid phase thickening), and an industrial intermittent solid-phase thickening (SSP) device for nylon 6 (a conventional high-viscosity product preparation process). When using the above three devices, the initial relative viscosity and target final viscosity of the molten nylon 6 were controlled to be the same. At the same time, the reaction temperature (245~255℃), system vacuum (-0.092MPa), high-purity nitrogen carrier gas flow rate (1.2Nm³ / h·t melt), purity (greater than 99.99%), and melt processing load (15Kg / h) were controlled to be completely consistent. The effective specific surface area of ​​gas and liquid, material residence time, and relative viscosity of nylon 6 were tested during the treatment process. Five parallel samples were set up for each test.

[0065] The testing method is as follows:

[0066] (1) Effective specific surface area of ​​gas and liquid: High-speed optical liquid film thickness scanning + inert gas pulse tracer method was used.

[0067] (2) Material residence time: The average residence time of the material under steady-state conditions was determined by the fluid residence time distribution (RTD) pulse tracer method.

[0068] (3) Relative viscosity of Nylon 6: The relative viscosity of the 98% concentrated sulfuric acid system was determined by Ubbelohde viscometer according to GB / T 12006.1 standard.

[0069] The data obtained from the above three sets of devices are as follows:

[0070]

[0071] The device of this invention completed five sets of parallel repeated tests. The gas-liquid specific surface area increase fluctuated by ±0.35 times, the material residence time fluctuated by ≤3 min, and the relative standard deviation (RSD) of viscosity detection was <2.7%. The test data showed excellent stability and repeatability with no significant deviation. Moreover, the core indicators in this study were all within the stable range under the standard nylon 6 viscosity-enhancing conditions, perfectly matching industrial production conditions. Slight thickening of the liquid film and a slight decrease in mass transfer efficiency during low-load operation are normal fluctuations under normal operating conditions and do not change the core technological advantages.

[0072] Traditional vertical falling film reactors for nylon 6 have large liquid film thickness and limited gas-liquid contact area, resulting in severe axial backmixing within the equipment. Residual caprolactam monomers and moisture easily accumulate at the melt interface, leading to a rapid decline in mass transfer driving force. This necessitates significantly extending the material residence time to complete the thickening reaction, resulting in extremely low efficiency. In solid-phase thickening processes for nylon 6, small molecule byproducts need to diffuse slowly within the solid chips, resulting in extremely low diffusion coefficients. A single batch reaction can take several hours to tens of hours, and production can only be intermittent, severely limiting capacity.

[0073] This invention's vertical thickening reaction tower, specifically designed for the melt characteristics of nylon 6, utilizes ultra-thin liquid film precision forming technology to shorten the diffusion distance of small molecules in the melt from millimeters to micrometers, significantly reducing mass transfer resistance. Combined with a multi-stage counter-current distributed nitrogen carrier gas structure, it progressively refreshes the gas phase environment at the gas-liquid interface, continuously and rapidly removing caprolactam and moisture, maintaining high mass transfer driving force, and breaking through the mass transfer bottleneck of traditional nylon 6 thickening processes. Simultaneously, the multi-stage structure effectively suppresses material backmixing, ensuring high melt reaction synchronization and good viscosity uniformity. While drastically compressing the reaction time, it avoids the thermal degradation defects caused by prolonged high temperatures, adapting to the continuous, high-quality, and high-efficiency thickening production requirements of nylon 6.

[0074] Of course, the present invention may have other various embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and modifications according to the present invention, but these corresponding changes and modifications should all fall within the protection scope of the claims of the present invention.

Claims

1. A gas-liquid contact nylon 6 liquid-phase viscosity-enhancing reaction device, characterized in that, It includes a melt feeding unit, a liquid phase thickening reaction unit and a low-shear discharge online viscosity control unit connected in series, a carrier gas heating and distribution unit, a monomer recovery unit and a vacuum unit respectively connected to the liquid phase thickening reaction unit; The liquid-phase viscosity-enhancing reaction unit includes a vertical viscosity-enhancing reaction tower. The tower has a primary low-shear gas-liquid contactor at the top, a secondary low-shear gas-liquid contactor in the middle, and a tertiary low-shear gas-liquid contactor at the bottom. The outer wall of the tower has jackets corresponding to the upper preheating zone, the middle viscosity-enhancing reaction zone, and the lower isothermal buffer zone, each with independent temperature control. The primary low-shear gas-liquid contactor includes multiple vertically arranged guide vanes, with a first gas distributor at the bottom of each vane. The gap between adjacent guide vanes is 2-3 mm. The secondary low-shear gas-liquid contactor is a horizontally arranged structure of large and small discs, with multiple sets of these discs. The structure is vertically stacked, with the large disc on the upper layer and the small disc on the lower layer in each group of large and small disc structures. The large disc has multiple first openings on its edge, and the small disc has a second opening in its center. The material on the large disc flows towards the edge and falls into the small disc below through the first opening. The material in the small disc flows towards the center and flows into the next group of large discs through the second opening. A second gas distributor is located below the bottom group of large and small disc structures. The three-stage low-shear gas-liquid contactor is a horizontally arranged ridge structure. There are multiple groups of ridge structures, each group of ridge structures is vertically stacked, and each group of ridge structures has multiple ridge components. The ridge components in adjacent layers of ridge structures are staggered, and a third gas distributor is located below each ridge component.

2. The gas-liquid contact nylon 6 liquid-phase viscosity-enhancing reaction apparatus according to claim 1, characterized in that, The surface of the guide plate is provided with micro-guide grooves.

3. The gas-liquid contact nylon 6 liquid-phase viscosity-enhancing reaction device according to claim 1, characterized in that, The melt feeding unit includes a single-shaft disc heater, a discharge screw conveyor, a filter, a buffer tank, a booster pump, an electric heater, and a centrifugal feeder connected in series. The centrifugal feeder is located at the top of the vertical thickening reaction tower.

4. The gas-liquid contact nylon 6 liquid-phase viscosity-enhancing reaction apparatus according to claim 1, characterized in that, The low-shear discharge online viscosity control unit is located at the bottom of the vertical viscosity-enhancing reaction tower and includes a discharge pump and an online viscometer.

5. The gas-liquid contact nylon 6 liquid-phase viscosity-enhancing reaction device according to claim 1, characterized in that, The carrier gas heating and distribution unit is equipped with a circulating fan and a heater in sequence. The heater is connected to the vertical viscosity-enhancing reaction tower for introducing carrier gas into the tower.

6. The gas-liquid contact nylon 6 liquid-phase viscosity-enhancing reaction apparatus according to claim 1, characterized in that, The monomer recovery unit includes a tail gas scrubbing tower, a primary condenser, a secondary condenser, a monomer recovery tank, and an external discharge pump connected in sequence. The inlet of the tail gas scrubbing tower is connected to the tail gas outlet of the vertical viscosity-enhancing reaction tower.

7. The gas-liquid contact nylon 6 liquid-phase viscosity-enhancing reaction apparatus according to claim 1, characterized in that, The vacuum unit includes a Venturi vacuum pump, a vacuum circulation storage tank, a condenser, and a circulation pump connected in sequence. The outlet of the circulation pump is connected to the inlet of the Venturi vacuum pump, and the inlet of the Venturi vacuum pump is also connected to the single-unit recovery unit. The vacuum circulation storage tank is also connected to a water ring vacuum pump.

8. A method for increasing the viscosity of nylon 6 in a gas-liquid contact phase, characterized in that, Using the reaction apparatus according to any one of claims 1 to 7, the steps include: 1) Start the vacuum unit to maintain the pressure inside the vertical thickening reaction tower at -0.092 to -0.098 MPa; 2) Start the carrier gas heating and distribution unit. After heating, the carrier gas is heated to 250-280℃ and then introduced into the vertical thickening reaction tower. The temperature of the thickening reaction zone is controlled at 260-275℃, and the carrier gas supply flow rate is 0.5-1.5 Nm³ / h·t melt. 3) Start the melt feeding unit, heat the nylon 6 raw material to 225-250℃ to melt it, and then transport the melt to the vertical thickening reaction tower; 4) Liquid phase thickening reaction: The molten nylon 6 material passes through a first-stage low-shear gas-liquid contactor, a second-stage low-shear gas-liquid contactor, and a third-stage low-shear gas-liquid contactor in a vertical thickening reaction tower, forming a uniform and continuous liquid film with a thickness of 0.1-0.4 mm; the heated carrier gas flows from bottom to top and contacts the uniform and continuous liquid film countercurrently, removing water and free caprolactam from the molten material, thus completing the thickening reaction; 5) The molten material after thickening is discharged through a low-shear discharge line with the viscosity controlled in real time by an online viscosity control unit. If the viscosity meets the requirements, it is discharged; otherwise, it is recycled back to the vertical thickening reaction tower. 6) The tail gas generated in the vertical thickening reaction tower is discharged into the monomer recovery unit.

9. The gas-liquid contact nylon 6 liquid phase thickening method according to claim 8, characterized in that, The carrier gas is high-purity nitrogen or carbon dioxide; the nylon 6 raw material is one or more of the following: virgin polymer melt, nylon 6 chip melt, and recycled nylon 6 melt.

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