Ultra-pure UHMWPE (Ultra High Molecular Weight Polyethylene) production process based on wet circulating demagnetization

Abstract

The invention relates to an ultra-pure UHMWPE (Ultra High Molecular Weight Polyethylene) production process based on wet circulation demagnetization. Reaction raw materials enter a polymerization reaction unit through a circulation feeding system to be subjected to a polymerization reaction; the slurry subjected to the polymerization reaction enters a slurry treatment unit for treatment through overflow discharge; and a slurry demagnetizing unit is arranged in a pipeline through which the feed liquid flows to demagnetize the feed liquid and remove magnetic foreign matters. Compared with the prior art, the online magnetic separation device is arranged in the ethylene polymerization production process for circulating demagnetization, the concept of'process demagnetization 'is established, wet demagnetization is carried out on suspended metal particles in the polymerization stage, magnetic foreign matter entrained by slurry is greatly reduced, the purity of the product is improved, and production and preparation of a high-quality UHMWPE product are facilitated.

Description

Technical Field

[0001] The present invention relates to the technical field of ultra-high molecular weight polyethylene (UHMWPE) preparation, and particularly to an ultra-pure UHMWPE production process based on wet circulation demagnetization. Background Art

[0002] Ultra-high molecular weight polyethylene (UHMWPE) is obtained through a polymerization reaction, mostly by catalytic polymerization using Ziegler-Natta catalysts, metallocene catalysts, late transition metal catalysts, or chromium-based catalysts, etc. These catalysts all contain metal elements, and inevitably, non-combustible metal ash and the like remain in the obtained products. The key to preparing ultra-high purity polyethylene is to control the ash content, especially the magnetic impurity ash such as metal in the catalyst. A higher ash content means lower product purity and poor cleanliness, which will have an adverse impact on the performance of the prepared end products. For example, in the case of lithium battery separator materials, if the ash content in the raw materials is high, it is not conducive to the puncture strength of the battery separator. High-performance battery separator products have very high requirements for the cleanliness of high molecular weight polyethylene. In the medical field, such as medical filter materials and artificial joints, there are even higher requirements for the purity of polyethylene raw materials.

[0003] Most of the existing processes for purifying polyethylene are dry magnetic removal, that is, the polyethylene powder is demagnetized by a magnetic removal device during the homogenization and screening stage to remove magnetic metal impurities in the powder. For example, Patent CN117103510A discloses a powder purification system for producing high molecular weight polyethylene, which removes iron particles in the powder during the conveying process of the conveyor belt through a magnetic attraction mechanism, and the dust removal mechanism blows out the dust particles in the powder through air flow, but it is difficult for the processing equipment to meet the high purification standard. Some liquid-phase or wet magnetic removal technologies are disclosed in the prior art. For example, Patent CN 118231084 A discloses an efficient liquid-phase magnetic removal device and method, Patent CN 221934196 U discloses a slurry impurity removal device, Patent CN 118543443A discloses a liquid-phase magnetic removal device and method for lithium iron phosphate cathode battery materials, and Patent CN 221581390 U discloses a wet automatic magnetic removal and cleaning system for iron phosphate, etc. However, most of the existing wet magnetic removal devices are used for small-scale production, with single offline processing, and usually manual operation or mechanical opening of the iron remover for cleaning is selected, resulting in problems of low processing efficiency and poor system coherence. In addition, compared with the magnetic removal for battery materials, the medium characteristics are different when purifying polyethylene (flammable and explosive hydrocarbon solvents are used and the solid content is different), and it cannot be cleaned with pure water like lithium iron phosphate, which requires higher sealing and automation requirements. And due to the difficulty in controlling the fluidity of the slurry in the wet process, high solid content, and easy sedimentation, it is difficult for the prior art to realize the coordinated optimization of dynamic magnetic removal and reaction process. Therefore, the existing disclosed technical solutions are not suitable for the slurry-phase polyethylene process in large-scale continuous production in the petrochemical industry. Summary of the Invention

[0004] The purpose of the present invention is to solve the above problems and provide a super-pure UHMWPE production process based on wet-circulation magnetic removal. Compared with the traditional magnetic removal method for end products, the present invention sets an on-line magnetic separation device in the ethylene polymerization production system for circulating magnetic removal, establishing the concept of "process magnetic removal", which is suitable for the continuous production of high-end polyethylene with extremely strict requirements for the content of magnetic foreign matters.

[0005] The purpose of the present invention is achieved through the following technical solutions:

[0006] A super-pure UHMWPE production process based on wet-circulation magnetic removal,

[0007] The reaction raw materials enter the polymerization reaction unit through the circulating feeding system for polymerization reaction;

[0008] The slurry after polymerization reaction overflows and discharges into the slurry treatment unit for treatment;

[0009] In the pipeline through which the feed liquid flows, a slurry demagnetization unit is provided to demagnetize the feed liquid and remove magnetic foreign matters.

[0010] As a preferred technical solution of the present invention, the polymerization reaction unit includes a polymerization reactor with a jacket and a stirrer;

[0011] The slurry treatment unit includes a slurry dilution tank connected to the overflow port of the polymerization reactor through an overflow pipeline for separating the gas in the slurry. The downstream of the slurry dilution tank is connected to a flash tank for flashing out the non-condensable gas. The bottom of the flash tank is connected to the downstream process through a discharge pipeline with a slurry delivery pump;

[0012] The slurry demagnetization unit includes an in-line magnetic separation device provided on the circulating hexane pipeline and the discharge pipeline of the flash tank.

[0013] As a preferred technical solution of the present invention, the in-line magnetic separation device adopts a pipeline magnetic filter, and the pipeline magnetic filter includes 2 - 20 groups of magnetic separation modules arranged in parallel. The magnetic separation module includes:

[0014] A cylindrical magnetic filtration tank with a magnetic rod assembly inside, and a net material outlet and a cleaning liquid inlet are provided in communication with the magnetic filtration tank;

[0015] A four-way pipeline valve group is connected to the lower part of the magnetic filtration tank, and is respectively provided with a raw material inlet, a slag outlet and a return material outlet;

[0016] When the slurry is filtered and demagnetized, the path is: raw material inlet - magnetic filtration tank - net material outlet;

[0017] During backwashing, the path is: cleaning liquid inlet - magnetic filtration tank - slag outlet.

[0018] The slurry demagnetization unit performs circulating wet demagnetization. Through magnetic separation at key nodes (circulating solvent and discharge end), the cyclic accumulation of magnetic foreign matters (such as catalyst residual metals and equipment wear particles) is blocked, and the demagnetization and backwashing operations can be completed without stopping the machine, ensuring continuous and clean production.

[0019] As a preferred technical solution of the present invention, the magnetic rod assembly is composed of multiple magnetic rods, and the outer tube surface magnetism of the magnetic rod is not less than 9000 GS, and the temperature resistance is not lower than 150 °C;

[0020] The magnetic rods are installed on a fixed disk, and the fixed disk is hermetically connected to the shell of the magnetic filtration tank.

[0021] As a preferred technical solution of the present invention, the magnetic rod adopts a telescopic magnetic rod structure, and is configured with an electric telescopic rod or a cylinder drive mechanism;

[0022] And / or, a stirrer is provided in the magnetic filtration tank.

[0023] As a preferred technical solution of the present invention, the cleaning liquid inlet is connected to a high-pressure hexane pulse backwashing mechanism with a pressure of 0.5 - 0.8 MPa. The backwashing is used to completely strip the magnetic substances adhered to the magnetic rod.

[0024] As a preferred technical solution of the present invention, the polymerization reaction unit includes at least two polymerization reactors that can be switched between series and parallel operations. The polymerization reactors are connected to a circulating feed system, which includes an ethylene feed pipeline, a catalyst feed pipeline, and a circulating hexane pipeline. The polymerization reaction unit of the present invention includes at least two polymerization reactors that can be switched between series and parallel operations, and the reaction mode can be flexibly adjusted according to the requirements of the product molecular weight distribution (for example, series connection is used for multi-peak distribution control, and parallel connection is used for production capacity improvement) to adapt to the production of multiple grades.

[0025] As a preferred technical solution of the present invention, the polymerization reaction unit is also provided with a circulating cooling subsystem for removing reaction heat through the phase change of hexane, including:

[0026] A top condenser installed at the top of each polymerization reactor;

[0027] A hexane recovery tank connected to the top condenser;

[0028] A circulation loop composed of a circulating gas fan.

[0029] As a preferred technical solution of the present invention, the polymerization reaction unit adopts a low-pressure continuous polymerization process with an operating pressure of 0.25 - 0.7 MPaG and an operating temperature controlled at 60 - 90 °C.

[0030] As a preferred technical solution of the present invention, a gas phase balance pipeline is provided at the top of the slurry dilution tank to return the separated gas to the polymerization reactor;

[0031] And / or, a secondary cooling mechanism for recovering hexane is configured at the top of the flash tank, including a primary condenser and a secondary condenser;

[0032] And / or, a self-circulation loop with a slurry transfer pump is provided at the bottom of the polymerization reactor.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] In the process of producing ultra-high purity polymer, the present invention uses an online magnetic separation device to perform cyclic demagnetization, so that magnetic metal impurities are adsorbed under the action of magnetic field force, and metal particles in suspension can be effectively removed, and the entrained magnetic foreign matter (<50μg / kg) can be reduced or avoided as much as possible, greatly improving the purity of the product. In this process, an online magnetic separation device is respectively arranged in the circulating hexane pipeline and in the downstream transmission pipeline of the flash tank, and the magnetic metal impurities of the liquid flowing through are efficiently removed. The circulating hexane is continuously circulated in the entire production process, and the circulating hexane can be continuously demagnetized to ensure the purity of the circulating medium, and avoid the influence of the product purity due to the continuous accumulation of magnetic impurities in the circulation process.

[0035] The present invention provides two sets of polymerization reactors, which can be switched in series and parallel to produce bimodal / unimodal polyethylene. A reactor top cooler is provided on the top of the reactor to remove heat by gasifying low boiling point solvent hexane. At the same time, the reactor adopts a heat removal mechanism with a jacket to effectively solve the problem of heat removal of polyethylene reaction, and slurry circulation is performed at the bottom of the reactor to avoid slurry sedimentation, so that the polymerization process is carried out smoothly and orderly, which is conducive to the production of high-quality polyethylene products. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 A schematic diagram of a process of the production process of the present invention;

[0037] Figure 2 It is a structural schematic diagram of the pipeline magnetic separation module;

[0038] Figure 3 for Figure 2 Side view of

[0039] Figure 4 It is a schematic diagram of the structure of the magnetic rod assembly of the pipeline magnetic separation module;

[0040] Figure 5 It is a schematic diagram of the parallel structure of two groups of pipeline magnetic separation modules;

[0041] Figure 6 This is a schematic diagram of the parallel structure of four sets of pipeline magnetic separation modules. DETAILED DESCRIPTION

[0042] The present invention is described in detail below. All matters not described in detail in the present invention are technical solutions disclosed in the art.

[0043] A production process of ultra-pure UHMWPE based on wet cyclic demagnetization, specifically: reaction raw materials (including hexane solvent, ethylene, catalyst, hydrogen, etc.) enter the polymerization reaction unit through a circulating feeding system for polymerization reaction; the slurry after the polymerization reaction enters the slurry treatment unit for treatment through overflow discharge; a slurry demagnetization unit is set in the pipeline through which the slurry flows to demagnetize the slurry and remove magnetic foreign matter.

[0044] As a specific embodiment of the present invention, the polymerization reaction unit includes a polymerization reactor with a jacket and a stirrer; the slurry treatment unit includes a slurry dilution tank connected to the overflow port of the polymerization reactor through an overflow pipeline, which is used to separate the gas in the slurry. The downstream of the slurry dilution tank is connected to a flash tank for flashing out the non-condensable gas. The bottom of the flash tank is connected to the downstream process through a discharge pipeline with a slurry transfer pump; the slurry demagnetization unit includes an in-line magnetic separation device arranged on the circulating hexane pipeline and the discharge pipeline of the flash tank.

[0045] As a specific embodiment of the present invention, the in-line magnetic separation device adopts a pipeline magnetic filter. The pipeline magnetic filter includes 2-20 groups of magnetic separation modules arranged in parallel. The magnetic separation module includes: a cylindrical magnetic filtration tank with a magnetic rod assembly inside, and a clean material outlet and a cleaning liquid inlet are communicated with the magnetic filtration tank 1; a four-way pipeline valve group is connected to the lower part of the magnetic filtration tank, and is respectively provided with a raw material inlet, a slag outlet and a return outlet;

[0046] When filtering and demagnetizing the slurry, the path is: raw material inlet - magnetic filtration tank - clean material outlet; when backwashing, the path is: cleaning liquid inlet - magnetic filtration tank - slag outlet.

[0047] As a specific embodiment of the present invention, the magnetic rod assembly is composed of multiple magnetic rods. The outer surface magnetism of the magnetic rod is not less than 9000 GS, and the temperature resistance is not lower than 150 °C; the magnetic rods are installed on a fixed disk, and the fixed disk is hermetically connected to the shell of the magnetic filtration tank.

[0048] As a specific embodiment of the present invention, the magnetic rod adopts a telescopic magnetic rod structure, and is configured with an electric telescopic rod or a cylinder drive mechanism; a stirrer is arranged in the magnetic filtration tank.

[0049] As a specific embodiment of the present invention, the cleaning liquid inlet is communicated with a high-pressure hexane pulse backwashing mechanism, and the pressure is 0.5-0.8 MPa. The backwashing is used to strip the magnetic substances adhered to the magnetic rods clean.

[0050] As a specific embodiment of the present invention, the polymerization reaction unit includes at least two polymerization reactors that can be switched to operate in series or in parallel. The polymerization reactors are connected to a circulating feed system, and the circulating feed system includes an ethylene feed pipeline, a catalyst feed pipeline and a circulating hexane pipeline. The polymerization reaction unit of the present invention includes at least two polymerization reactors that can be switched to operate in series or in parallel, and the reaction mode can be flexibly adjusted according to the requirements of the product molecular weight distribution, such as series connection for multi-peak distribution control and parallel connection for production capacity improvement, to adapt to the production of multiple grades.

[0051] As a specific embodiment of the present invention, the polymerization reaction unit is further provided with a circulating cooling subsystem for removing reaction heat through the phase change of hexane, comprising: a top condenser disposed on the top of each polymerization reactor; a hexane recovery tank connected to the top condenser; and a circulating loop composed of a circulating gas blower.

[0052] As a specific embodiment of the present invention, the polymerization reaction unit adopts a low-pressure continuous polymerization process, with an operating pressure of 0.25 - 0.7 MPaG and an operating temperature controlled at 60 - 90 °C.

[0053] As a specific embodiment of the present invention, a gas-phase balance pipeline is provided at the top of the slurry dilution tank to return the separated gas to the polymerization reactor; a secondary cooling mechanism for recovering hexane is configured at the top of the flash tank, including a primary condenser and a secondary condenser. In addition, as a specific embodiment of the present invention, a self-circulation loop with a slurry transfer pump can also be provided at the bottom of the polymerization reactor.

[0054] A specific embodiment is given below in conjunction with the accompanying drawings.

[0055] Refer to Figure 1 , for the ultra-pure UHMWPE production process based on wet-circulation demagnetization, the reaction product leaves the stirred reactor by overflow, and hexane is used as a dispersant and a gasification heat-removing agent. This process is provided with two reactors, the first polymerization reactor R-201 and the second polymerization reactor R-221. This process can produce single-peak and double-peak resins through the series / parallel connection of the two reactors. When producing double-peak grade polyethylene, the reactors are operated in series; when producing single-peak grade polyethylene, the reactors are operated in parallel. Ethylene from outside the plant is purified and refined and then filtered through the ethylene filter tank S-201 and introduced into the reactor as raw material. Hydrogen from outside the plant is metered and then added into the circulating gas main pipelines of the first polymerization reactor R-201 and the second polymerization reactor R-221 respectively to enter the reactor. Hydrogen is used to control the molecular weight of the polymer.

[0056] The operating pressure of the first polymerization reactor R-201 is between 0.25 and 0.7 MPaG according to different grades, and the operating temperature is between 60 and 90 °C. The operating pressure of the second polymerization reactor R-221 is between 0.25 and 0.7 MPaG according to different grades, and the operating temperature is between 60 and 90 °C.

[0057] The polyethylene polymerization reaction is a strongly exothermic reaction. In this process, the heat removal from the two reactors is mainly carried out by the vaporization of hexane. The recycle gas composed of the hexane gas phase evaporated from the top of the first polymerization reactor R-201, unreacted ethylene, hydrogen, and inert gas components such as methane, ethane, nitrogen, etc. is cooled to 38 - 40 °C by the first top cooler E-201 and then enters the first hexane tank V-205 for liquid separation. A section of wire mesh demister is installed at the top of the first hexane tank V-205 to prevent liquid from being carried into the inlet of the first recycle gas blower B-201. The liquid phase of the first hexane tank V-205 is used as the recycled hexane and is circulated to the liquid phase inlet and the top washing port of the reaction kettle through the first condensate circulation pumps P-202A / B. The gas phase of the first hexane tank V-205 is pressurized by the first recycle gas blower B-201 and then returned to the first polymerization reactor R-201. Fresh ethylene and hydrogen are added to the outlet pipeline of the first recycle gas blower B-201. An on-line analyzer is installed before the addition of fresh raw materials to analyze the gas phase composition for controlling the reactor.

[0058] The second polymerization reactor R-221 operates in the same way as the first polymerization reactor R-201. The vaporized components at the top are cooled to 38 - 40 °C by the second top cooler E-221 and then enter the second hexane tank V-225 for liquid separation. A section of wire mesh demister is installed at the top of the second hexane tank V-225 to prevent liquid from being carried into the inlet of the second recycle gas blower B-221. The liquid phase of the second hexane tank V-225 is used as the recycled hexane and is circulated to the liquid phase inlet and the top washing port of the reaction kettle through the second condensate circulation pumps P-222A / B. The gas phase of the second hexane tank V-225 is pressurized by the second recycle gas blower B-221 and then returned to the second polymerization reactor R-221. Fresh ethylene and hydrogen are added to the outlet pipeline of the second recycle gas blower B-221.

[0059] The polymerized polyethylene slurry flows out from the overflow ports of the first polymerization reactor R-201 and the second polymerization reactor R-221, and the slurry content is as high as 35%. Since the medium flowing out from the overflow ports will entrain a large amount of gas due to the strong backmixing in the reaction kettle, the first slurry dilution tank V-202 and the second slurry dilution tank V-222 are respectively set up to separate the gas in the slurry and avoid the long-distance two-phase gas-liquid transportation. The separated gas is respectively returned to the tops of the first polymerization reactor R-201 and the second polymerization reactor R-221 through the gas phase balance pipeline.

[0060] The stable polyethylene slurry from the first slurry dilution tank V-202 and the second slurry dilution tank V-222 enters the first flash tank V-203 or the second flash tank V-223 respectively through the pressure difference to flash off the non-condensable gas. When producing tandem grades, the slurry after flashing in the first flash tank V-203 is transported to the second polymerization reactor R-221 through the first slurry transfer pump P-201A / B; when producing parallel grades, the material in the first slurry dilution tank V-202 is transported to the second flash tank V-223, and the slurry after flashing in V-223 is sent to the centrifugal unit PK-311 in the separation and drying process through the second slurry transfer pump P-221A / B for centrifugal separation, and then enters the subsequent drying unit.

[0061] The flash gas from the first flash tank V-203 or the second flash tank V-223 is respectively cooled by the first flash gas condenser E-202 or the second flash gas condenser E-222, and the condensed liquid then returns to the corresponding first flash tank V-203 or the second flash tank V-223 through the first flash gas liquid seal tank V-207 and the second flash gas liquid seal tank V-227 respectively. The non-condensable gas from the first flash gas condenser E-202 or the second flash gas condenser E-222 is cooled by the flash gas condenser E-223 at the second stage to recover hexane, and flows back to the second flash gas liquid seal tank V-227 by gravity difference and then enters the second flash tank V-223. The non-condensable gas from the flash gas condenser E-223 enters the next process for further treatment. The jacketed reactor is used for heat removal of the reaction kettle through the jacket water pump P-204 / P-224.

[0062] In this process, a first on-line magnetic separation device MS-100 is set in the circulating hexane pipeline, and a second on-line magnetic separation device MS-200 / third on-line magnetic separation device MS-300 is set in the downstream pipeline of the first flash tank V-203 / second flash tank V-223. Through the high-efficiency magnetic separation technology, the magnetic metal impurities in the flowing slurry are accurately removed. In the slurry state, for the polyethylene particle system that has not been completely solidified, the metal impurities entrained in the material are effectively removed, thereby significantly improving the purity of the product and preventing the metal impurities from being coated inside during the growth process of the polyethylene resin particles.

[0063] As a preferred specific implementation manner, the on-line magnetic separation device adopted in the present invention is specifically a pipeline magnetic filter, and the pipeline magnetic filter includes a pipeline magnetic separation module, and its structure is as Figure 2 、 Figure 3 shown. Preferably, multiple groups of pipeline magnetic separation modules are arranged in parallel, and there are 2 to 20 groups of pipeline magnetic separation modules, preferably 4 to 10 groups, and further preferably 4 to 8 groups, which are specifically designed according to the actual processing capacity.

[0064] Refer to Figure 2 、 Figure 3, The pipeline magnetic separation module is installed and fixed on the basic frame. The pipeline magnetic separation module includes a magnetic filtration tank 1, and a magnetic rod assembly is arranged inside the magnetic filtration tank 1 for adsorbing and removing magnetic metal particles from the flowing slurry. The pipeline magnetic separation module is provided with a raw material inlet 2, a purified material outlet 3, a cleaning liquid inlet 4 and a slag outlet 5 connected to the magnetic filtration tank 1. When the slurry is magnetically filtered, the slurry path is: raw material inlet - magnetic filtration tank - purified material outlet; during backwashing, the cleaning liquid path is: cleaning liquid inlet - magnetic filtration tank - slag outlet. The cleaning liquid is selected from hexane or mother liquor for flushing without introducing new impurities into the system.

[0065] As a preferred specific implementation manner, a return material outlet 6 is also connected to the magnetic filtration tank 1, which is used to discharge the remaining slurry before backwashing to avoid wasting materials or increasing costs.

[0066] As a preferred specific implementation manner, the lower part of the magnetic filtration tank 1 is connected to a four-way pipeline valve group. One port of the four-way pipeline valve group is connected to the magnetic filtration tank 1, and the other three are respectively connected to the raw material inlet 2, the slag outlet 5 and the return material outlet 6. The cleaning liquid inlet 4 and the purified material outlet 3 are directly connected to the magnetic filtration tank 1.

[0067] As a preferred specific implementation manner, the magnetic rod assembly is composed of multiple groups (for example, 3 to 20 magnetic rods) of magnetic rods 11, preferably 5 to 10 magnetic rods. In a specific embodiment, 7 magnetic rods 11 are used. The magnetic rods 11 form a concentric circle array, and the external surface magnetic of the magnetic rods 11 is not less than 9000 GS. The magnetic rod assembly is installed on a fixed disk 12, and the fixed disk 12 is hermetically connected to the shell of the magnetic filtration tank 1. Preferably, a stirrer 13 is arranged inside the pipeline magnetic separation module. The stirring shaft of the stirrer 13 is installed at the middle position of the fixed disk 12 and is driven by a motor 14 at the upper part. When the slurry is magnetically filtered, the stirrer 13 is turned on, which helps to avoid the settlement of polyethylene slurry. The stirrer 13 preferably adopts an inclined blade turbine, which is suitable for medium and low viscosity fluids, helps the slurry to be suspended, and helps the particles on the wall to accumulate inside the magnetic separation device, prolonging the service life of the magnetic rods.

[0068] As a preferred specific implementation manner, the magnetic rod 11 can be set as a telescopic type (for example, driven by an electric telescopic rod or a cylinder). After the magnetic rod 11 works for a period of time, during the cleaning process, by controlling the upward movement of the magnetic rod 11, the metal magnetic impurities adsorbed on the surface of the magnetic rod 11 can be removed.

[0069] During specific implementation, when producing polyethylene by large-scale continuous slurry method, the pipeline magnetic filter can adopt a pipeline magnetic filter composed of two groups of pipeline magnetic separation modules connected in parallel as shown in Figure 5 or adopt as shown in Figure 6The pipeline magnetic filter shown, which is composed of four groups of pipeline magnetic separation modules connected in parallel. The raw material inlet 2, cleaning liquid inlet 4, purified material outlet 3, recycled material outlet 6, slag material outlet 5, etc. of each pipeline magnetic separation module are all connected through a pipeline. Control solenoid valves are installed on the pipelines of each inlet and outlet, and are connected to the DCS control system. During operation, when half of the pipeline magnetic separation modules are used for magnetic filtration of the slurry, the other half is used to clean and "regenerate" the magnetic filtration tank (magnetic rod 11) with hexane solvent. Such repeated switching and continuous operation are carried out to achieve wet magnetic removal of the slurry, effectively remove the metal residues in the slurry, produce ultra-high purity polyethylene products, with a metal impurity removal rate of ≥99.8% and a product ash content of ≤50 ppm.

[0070] The above description of the embodiments is for the convenience of those of ordinary skill in the art to understand and use the invention. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative efforts. Therefore, the present invention is not limited to the above embodiments, and the improvements and modifications made by those skilled in the art without departing from the scope of the present invention according to the disclosure of the present invention should be within the protection scope of the present invention.

Claims

1. A process for producing ultra-pure UHMWPE based on wet cycle demagnetization, characterized in that: The reaction raw materials enter the polymerization reaction unit through the circulating feeding system to carry out polymerization reaction; The slurry after the polymerization reaction enters the slurry treatment unit for treatment through overflow discharge; A slurry demagnetization unit is arranged in the pipeline through which the slurry flows to demagnetize the slurry and remove magnetic foreign matter.

2. The ultra-pure UHMWPE production process based on wet cycle demagnetization according to claim 1, characterized in that: The polymerization reaction unit comprises a polymerization reactor with a jacket and stirring; The slurry processing unit comprises a slurry dilution tank connected to the overflow port of the polymerization reactor through an overflow pipe, which is used to separate the gas in the slurry. The downstream of the slurry dilution tank is connected to a flash tank, which is used to flash out non-condensable gas. The bottom of the flash tank is connected to the downstream process through a discharge pipeline with a slurry delivery pump. The slurry demagnetization unit comprises an online magnetic separation device arranged on a circulating hexane pipeline and a flash tank discharge pipeline.

3. The ultra-pure UHMWPE production process based on wet cycle demagnetization according to claim 2, characterized in that: The online magnetic separation device adopts a pipeline magnetic filter, and the pipeline magnetic filter includes 2-20 groups of magnetic separation modules arranged in parallel, and the magnetic separation module includes: A cylindrical magnetic filter tank (1) is provided with a magnetic rod assembly, and is connected to the magnetic filter tank (1) and is provided with a clean material outlet (3) and a cleaning liquid inlet (4); A four-way pipeline valve group is connected to the lower part of the magnetic filter tank (1) and is respectively provided with a raw material inlet (2), a slag outlet (5) and a return material outlet (6); When the slurry is filtered and demagnetized, the path is: raw material inlet (2) - magnetic filter tank (1) - clean material outlet (3); During backwashing, the path is: cleaning liquid inlet (4) - magnetic filter tank (1) - slag outlet (5).

4. The ultra-pure UHMWPE production process based on wet cycle demagnetization according to claim 3 is characterized in that: The magnetic bar assembly is composed of a plurality of magnetic bars (11), the outer tube surface magnetism of the magnetic bars (11) is not less than 9000 GS, and the temperature resistance is not less than 150°C. The magnetic rod is mounted on a fixed disk (12), and the fixed disk (12) is hermetically connected to the shell of the magnetic filter tank (1).

5. The ultra-pure UHMWPE production process based on wet cycle demagnetization according to claim 4, characterized in that: The magnetic rod adopts a telescopic magnetic rod structure and is equipped with an electric telescopic rod or a cylinder drive mechanism; And / or, a stirrer (13) is provided in the magnetic filtration tank (1).

6. The ultra-pure UHMWPE production process based on wet cycle demagnetization according to claim 4, characterized in that: The cleaning liquid inlet (4) is connected to a high-pressure hexane pulse recoil mechanism with a pressure of 0.5-0.8 MPa. The backwashing is used to remove the magnetic material adhered to the magnetic rod.

7. The ultra-pure UHMWPE production process based on wet cycle demagnetization according to claim 2, characterized in that: The polymerization reaction unit comprises at least two polymerization reactors which can be switched to operate in series or in parallel. The polymerization reactors are connected to a circulating feed system, and the circulating feed system comprises an ethylene feed pipeline, a catalyst feed pipeline and a circulating hexane pipeline.

8. The ultra-pure UHMWPE production process based on wet cycle demagnetization according to claim 7, characterized in that: The polymerization reaction unit is also provided with a circulating cooling subsystem for removing reaction heat through hexane phase change, comprising: A kettle top condenser arranged at the top of each polymerization reactor; A hexane recovery tank connected to the kettle top condenser; The circulation loop is composed of a circulating air fan.

9. The ultra-pure UHMWPE production process based on wet cycle demagnetization according to claim 7, characterized in that: The polymerization reaction unit adopts a low-pressure continuous polymerization process, the operating pressure is 0.25-0.7 MPaG, and the operating temperature is controlled at 60-90°C.

10. The ultra-pure UHMWPE production process based on wet cycle demagnetization according to claim 7, characterized in that: A gas phase balance pipeline is provided on the top of the slurry dilution tank to return the separated gas to the polymerization reactor; And / or, the top of the flash tank is provided with a secondary cooling mechanism for recovering hexane, including a primary condenser and a secondary condenser; And / or, a self-circulating loop with a slurry delivery pump is provided at the bottom of the polymerization reactor.

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