A separation system for nylon extract liquid oligomers

Abstract

This application relates to the field of nylon 6 polymerization process technology, and provides a separation system for oligomers in nylon extract, including: a feed main pipe, crystallization devices, a temperature control system, a solid-liquid separation device, a fluidized bed, and an oligomer storage tank. At least two crystallization devices are provided, each connected in parallel and connected to the feed main pipe. The discharge end of each crystallization device is connected to the solid-liquid separation device. The temperature control system is connected to each crystallization device and regulates its temperature. The solid discharge port of the solid-liquid separation device is connected to the fluidized bed, and the fluidized bed is connected to the oligomer storage tank. Through the parallel arrangement of the crystallization devices, each crystallization device operates independently, providing time for cooling and crystallization to achieve continuous production.

Description

Technical Field

[0001] This application belongs to the field of nylon 6 polymerization process technology, and more specifically, relates to a separation system for oligomers of nylon extract. Background Technology

[0002] Large-scale polymerization production facilities in China generally employ hydrolytic ring-opening polymerization. After the reaction, the chip particles contain approximately 10% small molecules. These chips are extracted with water, and the extracted liquid containing small molecules is concentrated through triple-effect evaporation. The concentrate then enters a pyrolysis reactor, where it is pyrolyzed and then recycled back into the polymerization system. In existing production processes, the cyclic dimers in the oligomers are difficult to pyrolyze, leading to their enrichment within the production system. During the production of nylon-6, these oligomers crystallize and accumulate in equipment and pipelines, clogging pipes and severely affecting the processing performance of nylon-6 materials. Therefore, it is necessary to separate these oligomers from the production process or break down their molecular structure to form monomers for recycling.

[0003] Currently, there are three methods for treating oligomers in nylon 6 concentrate, both domestically and internationally:

[0004] One method is the high-pressure hydrolysis process of caprolactam concentrate. This process involves concentrating a 10% aqueous solution of caprolactam extractable to 85% through triple-effect evaporation, then pressurizing it with a diaphragm metering pump and sending it to a high-pressure hydrolysis reactor to open the rings of the cyclic oligomers. The resulting solution is then mixed with fresh caprolactam and fed into a prepolymerization reactor to produce nylon-6. The disadvantage of this process is that the ring-opening efficiency in the system is unknown, and the cyclic dimers are difficult to open and decompose into caprolactam, resulting in enrichment throughout the system.

[0005] The second method is the oligomer high-pressure pyrolysis + continuous distillation process. In this process, a 10% aqueous solution of caprolactam extract is concentrated to 70% via triple-effect evaporation. Then, in an oligomer separator, pure caprolactam and water are evaporated to a dehydration tower. The remaining high-boiling-point oligomers are pumped to an oligomer pyrolysis unit for catalytic pyrolysis. The pyrolysis product is caprolactam vapor, which is then recovered via a continuous distillation system. The pyrolysis residue is largely carbonized and treated as waste. The caprolactam recovered through continuous distillation is mixed with fresh caprolactam and fed into a prepolymer reactor to produce nylon-6. This method has drawbacks such as a long process flow, numerous pieces of equipment, complex operation, high energy consumption, and the inability to remove the catalyst from the subsequent catalytic pyrolysis. Therefore, polymerization plants generally do not use this process.

[0006] The third method is batch distillation. This process involves concentrating a 10% aqueous solution of caprolactam extract to 65-80% using triple-effect evaporation. The concentrate is then sent in batches to a distillation vessel, where water and caprolactam are distilled off separately and stored. The remaining caprolactam and oligomers at the bottom of the distillation vessel are discharged as waste. The distilled pure caprolactam is mixed with fresh caprolactam and fed into a prepolymer reactor to produce nylon-6. This method results in significant caprolactam waste and high consumption; this process has been phased out abroad.

[0007] Patent application CN210560194U discloses an oligomer separation system in the polymerization process of nylon-6, including a concentrate storage tank, a concentrate cooling tank, a concentrate discharge pump, a centrifuge, and a concentrate clearing tank. The concentrate discharge pump is located at the discharge pipe of the concentrate cooling tank, and the discharge pipe of the concentrate discharge pump is divided into two paths: one path is connected to the concentrate storage tank for circulation, and the other path is connected to the centrifuge for feeding. Since crystallization is usually an intermittent chemical operation, this patent designs it as a continuous operation unit. The concentrate cooling tank in this patent is continuously fed, resulting in insufficient cooling and crystallization time. Before crystals are formed, the liquid enters the centrifuge, making it impossible to effectively separate caprolactam and oligomers. The recycled liquid has a high oligomer content, which leads to oligomer enrichment when returned to the polymerization system. Utility Model Content

[0008] To address the shortcomings of the prior art, the purpose of this application is to provide a separation system for oligomers from nylon extract, which uses parallel crystallization devices, each of which operates independently, providing time for cooling and crystallization to achieve continuous production.

[0009] To achieve the above objectives, the technical solution adopted in this application is as follows: a separation system for oligomers in nylon extract is provided, comprising: a feed main pipe, a crystallization device, a temperature control system, a solid-liquid separation device, a fluidized bed, and an oligomer storage tank. At least two crystallization devices are provided, each crystallization device is connected in parallel and connected to the feed main pipe, the discharge end of each crystallization device is connected to the solid-liquid separation device, the temperature control system is connected to each crystallization device and regulates the temperature of the crystallization device, the solid discharge port of the solid-liquid separation device is connected to the fluidized bed, and the fluidized bed is connected to the oligomer storage tank.

[0010] In one embodiment, the separation system for nylon extract oligomers further includes a distillation column connected to the liquid phase outlet of the solid-liquid separation device.

[0011] In one embodiment, the separation system for nylon extract oligomers further includes a solvent supply device connected to each of the crystallization devices.

[0012] In one embodiment, the temperature control system includes: a heat exchange pipe, a chilled water supply device, a steam supply device, and a temperature sensor. The temperature sensor is disposed on the crystallization device. The chilled water supply device and the steam supply device are respectively connected to the heat exchange pipe, and the heat exchange pipe is connected to the crystallization device.

[0013] In one embodiment, a first mass flow meter is installed on the heat exchange pipeline. The chilled water supply device includes a chilled water supply source, a chilled water supply pipeline, a first delivery pump, and a first switching valve. One end of the chilled water supply pipeline is connected to the chilled water supply source, and the other end is connected to the heat exchange pipeline. The first delivery pump and the first switching valve are installed on the chilled water supply pipeline. The steam supply device includes a steam supply source, a steam supply pipeline, a second delivery pump, and a second switching valve. One end of the steam supply pipeline is connected to the steam supply source, and the other end is connected to the heat exchange pipeline. The second delivery pump and the second switching valve are installed on the steam supply pipeline.

[0014] In one embodiment, the solvent supply device includes a solvent storage tank, a solvent supply pipeline, a third delivery pump, and a second mass flow meter. One end of the solvent supply pipeline is connected to the solvent storage tank, and the other end is connected to each of the crystallization devices through a solvent branch pipe. The third delivery pump and the second mass flow meter are installed on the solvent supply pipeline.

[0015] In one embodiment, the distillation column is provided with a solvent reflux pipe, which is connected to the solvent supply pipe, and a fourth delivery pump is provided on the solvent reflux pipe.

[0016] In one embodiment, the feed main is equipped with a third mass flow meter and a fifth delivery pump. One end of the feed main is the feed end, and the other end is connected to each of the crystallization devices through a feed branch pipe. Each of the feed branch pipes is equipped with a third switch valve.

[0017] In one embodiment, a sixth delivery pump is provided on the connecting pipe between each crystallization device and the solid-liquid separation device, and a seventh delivery pump is provided on the connecting pipe between the solid-liquid separation device and the distillation column.

[0018] In one embodiment, the solid-liquid separation device is a centrifugal filter or a membrane separation device.

[0019] The beneficial effects of the separation system for nylon extract oligomers provided in this application are as follows: by setting up multiple crystallization devices in parallel, each crystallization device can work independently, so that at least one crystallization device can be used online at any time, while the remaining crystallization devices crystallize, effectively ensuring the crystallization time while enabling continuous production. The crystallized product enters the solid-liquid separation device for separation, the liquid phase is returned to the polymerization system, and the solid phase is dried by the fluidized bed and then temporarily stored in the oligomer storage tank.

[0020] By setting up multiple crystallization devices in parallel, extracts with concentrations of 20%-85% can be effectively crystallized, making it applicable to a wide range of applications. Since the crystallization time is effectively guaranteed, the content of oligomers in the solid phase separated by the solid-liquid separation device is ≥75%, and the content of oligomers in the liquid phase is ≤25%, thus improving the separation effect. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 A simplified connection structure diagram of the separation system for nylon extract oligomers provided in this application embodiment.

[0023] The following are the labeling elements in the figure:

[0024] 1. Feed main pipe; 11. Third mass flow meter; 12. Fifth transfer pump; 13. Feed branch pipe; 14. Third switch valve; 2. Crystallization unit; 3. Temperature control system; 31. Heat exchange pipeline; 311. First mass flow meter; 32. Chilled water supply device; 321. Chilled water supply source; 322. Chilled water supply pipeline; 323. First transfer pump; 324. First switch valve; 33. Steam supply device; 331. Steam supply source; 332. 1. Steam supply pipeline; 333. Second transfer pump; 334. Second switch valve; 4. Solid-liquid separation device; 5. Fluidized bed; 6. Oligomer storage tank; 7. Distillation column; 71. Solvent reflux pipe; 72. Fourth transfer pump; 8. Solvent supply device; 81. Solvent storage tank; 82. Solvent supply pipeline; 83. Third transfer pump; 84. Second mass flow meter; 85. Solvent branch pipe; 86. Fourth switch valve; 9. Sixth transfer pump; 10. Seventh transfer pump. Detailed Implementation

[0025] To make the technical problems, technical solutions, and beneficial effects to be solved by this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and are not intended to limit the scope of this application.

[0026] It should be noted that when a component is referred to as being "fixed to" or "set on" another component, it can be directly on or indirectly on that other component. When a component is referred to as being "connected to" another component, it can be directly connected to or indirectly connected to that other component.

[0027] It should be understood that the terms "length", "width", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0028] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0029] like Figure 1As shown, a separation system for oligomers from nylon extract provided in this application will now be described. This separation system for oligomers from nylon extract includes: a feed main 1, a crystallization device 2, a temperature control system 3, a solid-liquid separation device 4, a fluidized bed 5, an oligomer storage tank 6, a distillation column 7, and a solvent supply device 8. At least two crystallization devices 2 are provided, ranging from 2 to 10. The crystallization devices 2 are existing equipment, and may include an internal mechanical stirring structure to prevent oligomers from agglomerating within the crystallization device 2. Nitrogen gas is used as a protective gas within the crystallization device 2. In this embodiment, each crystallization device 2 is connected in parallel and connected to the feed manifold 1. The feed manifold 1 is connected to the extraction liquid source, such as to an existing triple-effect evaporation system. The outlet of each crystallization device 2 is connected to the solid-liquid separation device 4, which separates the crystallized oligomers from the liquid phase. The temperature control system 3 is connected to each crystallization device 2 and regulates the temperature of the crystallization device 2 to control the crystallization temperature of the oligomers. The solid outlet of the solid-liquid separation device 4 is connected to the fluidized bed 5, which dries the oligomers. The fluidized bed 5 is connected to the oligomer storage tank 6, which temporarily stores the dried oligomers. The distillation column 7 is connected to the liquid phase outlet of the solid-liquid separation device 4 and is also connected to the caprolactam polymerization system for recovering caprolactam. The solvent supply device 8 is connected to each crystallization device 2 to replenish the crystallization device 2 with solvent to achieve extraction crystallization. The solvent is a polar solvent, the purpose of which is to better precipitate the oligomers.

[0030] In this embodiment, by setting up multiple crystallization devices 2 in parallel, each crystallization device 2 can work independently, thus ensuring that at least one crystallization device 2 is used online at any given time, while the remaining crystallization devices 2 crystallize. This effectively ensures crystallization time while enabling continuous production. The crystallized product enters the solid-liquid separation device 4 for separation. The liquid phase is processed by the distillation tower 7 and then returned to the caprolactam polymerization system. The oligomer solid phase is dried by the fluidized bed 5 and then temporarily stored in the oligomer storage tank 6.

[0031] In this embodiment, by setting multiple crystallization devices 2 in parallel, extracts with a concentration of 20%-85% can be effectively crystallized, which has a wide range of applications. Since the crystallization time is effectively guaranteed, the content of oligomers in the solid phase separated by the solid-liquid separation device 4 is ≥75%, and the content of oligomers in the liquid phase is ≤25%, which improves the separation effect.

[0032] In this embodiment, the temperature control system 3 includes: a heat exchange pipe 31, a chilled water supply device 32, a steam supply device 33, and a temperature sensor. The temperature sensor is mounted on the crystallization apparatus 2. The outer side of the crystallization apparatus 2 is equipped with a jacket. The chilled water supply device 32 and the steam supply device 33 are respectively connected to the heat exchange pipe 31, and the heat exchange pipe 31 is connected to the jacket of the crystallization apparatus 2. The chilled water supply device 32 is used to provide chilled water for cooling the crystallization apparatus 2, the steam supply device 33 is used to provide steam for heating the crystallization apparatus 2, and the temperature sensor is used to monitor the temperature inside the crystallization apparatus 2. Specifically, the first mass flow meter 311 on the heat exchange pipe 31 is used to regulate the inflow rate of chilled water or steam. The chilled water supply device 32 includes a chilled water supply source 321, a chilled water supply pipe 322, a first transfer pump 323, and a first switching valve 324. One end of the chilled water supply pipe 322 is connected to the chilled water supply source 321, and the other end is connected to the heat exchange pipe 31. The first transfer pump 323 and the first switching valve 324 are installed on the chilled water supply pipe 322. The steam supply device 33 includes a steam supply source 331, a steam supply pipe 332, a second transfer pump 333, and a second switching valve 334. One end of the steam supply pipe 332 is connected to the steam supply source 331, and the other end is connected to the heat exchange pipe 31. The second transfer pump 333 and the second switching valve 334 are installed on the steam supply pipe 332. The chilled water supply source 321 and the steam supply source 331 can both be provided by existing chilled water and steam production equipment systems within the factory, or by equipment such as refrigerators or steam engines. When the temperature inside the crystallization device 2 is lower than the preset value, the first switch valve 324 closes, stopping the supply of chilled water; the second switch valve 334 opens, and steam enters the crystallization device 2 under the drive of the second transfer pump 333 to increase the temperature inside the crystallization device 2. Similarly, when the temperature inside the crystallization device 2 is higher than the preset value, the second switch valve 334 closes, stopping the supply of steam; the first switch valve 324 opens, and chilled water enters the crystallization device 2 under the drive of the first transfer pump 323 to decrease the temperature inside the crystallization device 2. The jacket of the crystallization device 2 is also connected to a return pipe, which is used to collect and return chilled water and steam.

[0033] In this embodiment, the solvent supply device 8 includes a solvent storage tank 81, a solvent supply pipeline 82, a third delivery pump 83, and a second mass flow meter 84. One end of the solvent supply pipeline 82 is connected to the solvent storage tank 81, and the other end is connected to each crystallization device 2 via a solvent branch pipe 85. The third delivery pump 83 and the second mass flow meter 84 are installed on the solvent supply pipeline 82, and each solvent branch pipe 85 is equipped with a fourth switch valve 86, so that solvent can be supplied to each crystallization device 2 individually. To improve solvent utilization, the distillation column 7 is equipped with a solvent reflux pipe 71, which is connected to the solvent supply pipeline 82. The solvent reflux pipe 71 is equipped with a fourth delivery pump 72, thereby realizing the recycling of solvent.

[0034] In this embodiment, the feed main pipe 1 is equipped with a third mass flow meter 11 and a fifth delivery pump 12 to control the feed flow rate of the extract. One end of the feed main pipe 1 is the feed end, which is used to connect to the triple-effect evaporation system or the extract storage tank, and the other end is connected to each crystallization device 2 through several feed branch pipes 13. Each feed branch pipe 13 is equipped with a third switching valve 14 to realize the individual or simultaneous operation of each crystallization device 2.

[0035] In this embodiment, a sixth transfer pump 9 is installed on the connecting pipe between each crystallization device 2 and the solid-liquid separation device 4, and a seventh transfer pump 10 is installed on the connecting pipe between the solid-liquid separation device 4 and the distillation column 7. In this embodiment, each transfer pump is used to provide power. In this embodiment, the solid-liquid separation device 4 is a centrifugal filter or a membrane separation device; of course, other solid-liquid separation equipment can also be used, as long as solid-liquid separation can be achieved.

[0036] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A separation system for oligomers in nylon extract, characterized in that, include: The system comprises a feed manifold (1), a crystallization device (2), a temperature control system (3), a solid-liquid separation device (4), a fluidized bed (5), and an oligomer storage tank (6). At least two crystallization devices (2) are provided, and each crystallization device (2) is connected in parallel and connected to the feed manifold (1). The discharge end of each crystallization device (2) is connected to the solid-liquid separation device (4). The temperature control system (3) is connected to each crystallization device (2) and regulates the temperature of the crystallization device (2). The solid discharge port of the solid-liquid separation device (4) is connected to the fluidized bed (5), and the fluidized bed (5) is connected to the oligomer storage tank (6).

2. The separation system for oligomers in nylon extract as described in claim 1, characterized in that: It also includes a distillation column (7), which is connected to the liquid phase outlet of the solid-liquid separation device (4).

3. The separation system for oligomers in nylon extract as described in claim 2, characterized in that: It also includes a solvent supply device (8) connected to each of the crystallization devices (2).

4. The separation system for oligomers in nylon extract as described in claim 3, characterized in that: The temperature control system (3) includes: a heat exchange pipe (31), a chilled water supply device (32), a steam supply device (33), and a temperature sensor. The temperature sensor is installed on the crystallization device (2). The chilled water supply device (32) and the steam supply device (33) are respectively connected to the heat exchange pipe (31), and the heat exchange pipe (31) is connected to the crystallization device (2).

5. The separation system for oligomers in nylon extract as described in claim 4, characterized in that: The heat exchange pipe (31) is equipped with a first mass flow meter (311). The chilled water supply device (32) includes a chilled water supply source (321), a chilled water supply pipe (322), a first delivery pump (323), and a first switching valve (324). One end of the chilled water supply pipe (322) is connected to the chilled water supply source (321), and the other end is connected to the heat exchange pipe (31). The first delivery pump (323) and the first switching valve (324) are installed on the chilled water supply pipe (322). The steam supply device (33) includes a steam supply source (331), a steam supply pipe (332), a second delivery pump (333), and a second switching valve (334). One end of the steam supply pipe (332) is connected to the steam supply source (331), and the other end is connected to the heat exchange pipe (31). The second delivery pump (333) and the second switching valve (334) are installed on the steam supply pipe (332).

6. The separation system for oligomers in nylon extract as described in claim 3, characterized in that: The solvent supply device (8) includes a solvent storage tank (81), a solvent supply pipeline (82), a third delivery pump (83), and a second mass flow meter (84). One end of the solvent supply pipeline (82) is connected to the solvent storage tank (81), and the other end is connected to each of the crystallization devices (2) through a solvent branch pipe (85). The third delivery pump (83) and the second mass flow meter (84) are installed on the solvent supply pipeline (82).

7. The separation system for oligomers in nylon extract as described in claim 6, characterized in that: The distillation column (7) is equipped with a solvent reflux pipe (71), which is connected to the solvent supply pipe (82). A fourth delivery pump (72) is provided on the solvent reflux pipe (71).

8. The separation system for oligomers of nylon extract as described in any one of claims 1-7, characterized in that: The feed main pipe (1) is equipped with a third mass flow meter (11) and a fifth delivery pump (12). One end of the feed main pipe (1) is the feed end, and the other end is connected to each of the crystallization devices (2) through the feed branch pipe (13). Each of the feed branch pipes (13) is equipped with a third switch valve (14).

9. The separation system for oligomers in nylon extract as described in claim 2, characterized in that: A sixth delivery pump (9) is provided on the connecting pipe between each crystallization device (2) and the solid-liquid separation device (4), and a seventh delivery pump (10) is provided on the connecting pipe between the solid-liquid separation device (4) and the distillation tower (7).

10. The separation system for nylon extract oligomers as described in claim 8, characterized in that: The solid-liquid separation device (4) is a centrifugal filter or a membrane separation device.

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