Ultrahigh-purity polyolefin polymerization production system

Abstract

The utility model relates to an ultra-pure polyolefin polymerization production system, which comprises a polymerization reaction unit, a slurry treatment unit and a slurry demagnetizing unit, the slurry demagnetizing unit comprises on-line magnetic separation devices arranged in a cyclohexane circulating pipeline and a flash tank discharge pipeline, and the on-line magnetic separation devices adopt pipeline magnetic filters. Compared with the prior art, in the ultra-pure polymer production process, a high-intensity magnetic field in the pipeline magnetic filter is used for conducting wet demagnetization on suspended metal particles in the polymerization stage, magnetic foreign matter carried by slurry is reduced, the purity of products is improved, and production and preparation of high-quality polyolefin products are facilitated.

Description

TECHNICAL FIELD

[0001] The utility model belongs to the technical field of ultrahigh purity polymer, concretely relates to a kind of ultrahigh purity polyolefin polymerization production system. BACKGROUND

[0002] High-end polyolefin is a new material category developed by the state, with high strategic value and large consumption. In the field of ultraclean high-purity polyolefin, the current production is low and cannot meet market demand. For example, in the case of ultrahigh molecular weight polyethylene, China's total demand for polyethylene in 2023 is 42.23 million tons, while domestic production capacity is 31.23 million tons, with imports of 11 million tons, of which 4 million tons have no production capacity in China, and most of them are ultrahigh-purity polyethylene. There is a serious gap in ultrahigh-purity polyethylene.

[0003] Polymer products such as ultrahigh molecular weight polyethylene (UHMWPE) are obtained through polymerization reactions, mostly through catalytic polymerization using Ziegler-Natta catalysts, metallocene catalysts, post-transition metal catalysts, or chromium-based catalysts. These catalysts contain metal elements, and the resulting products inevitably contain non-combustible metal ash. The key to preparing ultrahigh-purity polyethylene is to control the ash content, especially the magnetic impurity ash in the catalyst. Higher ash content means lower product purity and poor cleanliness, which can adversely affect the performance of the final product. For example, in lithium battery separator material, high ash content in raw materials is not conducive to the puncture strength of the battery separator. High-performance battery separator products have high requirements for the cleanliness of high molecular weight polyethylene. In the medical field, such as medical filters and artificial joints, there are higher requirements for the purity of polyolefin raw materials.

[0004] The existing device or process is mostly dry magnetic removal, that is, the magnetic metal impurities in the polyethylene powder are removed by a magnetic removal device in the homogenizing and screening stage, for example, patent CN117103510A discloses a powder purification system for high molecular weight polyethylene production, iron particles in the powder are removed during the conveying process by the magnetic attraction mechanism, and the dust particles in the powder are blown off by the airflow of the dust removal mechanism, but the treatment device is difficult to achieve high purification standards. The prior art discloses some liquid phase magnetic removal or wet magnetic removal technologies, such as patent CN118231084A discloses a high-efficiency liquid phase magnetic removal device and method, patent CN221934196U discloses a slurry impurity removal device, patent CN118543443A discloses a lithium iron phosphate positive electrode material liquid phase magnetic removal device and method, and patent CN221581390U discloses a phosphoric acid iron wet automatic magnetic removal cleaning system. However, the existing wet magnetic removal device is mostly used for small-scale production, and manual operation or mechanical opening of the iron remover is usually selected. In addition, compared with the magnetic removal of battery materials, the medium characteristics are different (flammable and explosive hydrocarbon solvents are used and the solid content is different) during the purification treatment of polyethylene, and pure water cannot be used for cleaning as in the lithium iron phosphate, which requires higher sealing and automation. Therefore, the existing disclosed technical solutions are not suitable for the slurry method polyethylene process of large-scale continuous production in the petrochemical industry. Practical new type content

[0005] The purpose of the present application is to provide an ultrahigh-purity polyolefin polymerization production system, which is suitable for the continuous production of high-end polyolefins with strict requirements on the content of magnetic foreign matter. The present application significantly reduces the content of magnetic foreign matter in polyolefin products through the synergistic innovation of modular polymerization reaction unit design, efficient slurry treatment process optimization and online circulation magnetic removal technology, while improving production efficiency and product consistency.

[0006] The purpose of the present application is achieved by the following technical solutions:

[0007] An ultrahigh-purity polyolefin polymerization production system, comprising:

[0008] A polymerization reaction unit, comprising at least two polymerization reactors that can be switched to operate in series or in parallel, the polymerization reactors being connected to a circulating feed system, the circulating feed system comprising an ethylene feed pipeline, a catalyst feed pipeline and a circulating hexane pipeline;

[0009] A slurry treatment unit, comprising a slurry dilution tank connected to the overflow port of the polymerization reactor through an overflow pipeline, a flash tank connected downstream of the slurry dilution tank, and a downstream process connected to the bottom of the flash tank through a discharge pipeline with a slurry conveying pump;

[0010] The slurry demagnetization unit includes an online magnetic separation device installed on the circulating hexane pipeline and the flash tank discharge pipeline.

[0011] This utility model's polymerization reaction unit includes at least two polymerization reactors that can be switched to operate in series or in parallel. The reaction mode can be flexibly adjusted according to the molecular weight distribution requirements of the product (e.g., series connection for multi-peak distribution control, parallel connection for capacity improvement), adapting to the production of multiple grades. The slurry demagnetization unit performs circulating wet demagnetization. Through magnetic separation at key nodes (circulating solvent and discharge end), it blocks the cyclic accumulation of magnetic foreign matter (such as catalyst residual metal and equipment wear particles). Demagnetization and backwashing operations can be completed without stopping the machine, ensuring continuous and clean production.

[0012] As a preferred technical solution, the polymerization reaction unit is further provided with a circulating cooling subsystem, comprising:

[0013] A top condenser is installed at the top of each polymerization reactor;

[0014] Hexane recovery tank connected to the top condenser of the reactor;

[0015] A circulating loop consisting of a circulating air fan;

[0016] The circulating cooling subsystem removes the heat of reaction through hexane phase change and utilizes the latent heat exchange of hexane vaporization-condensation to efficiently remove the heat of reaction and control the reaction temperature.

[0017] As a preferred technical solution, 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℃.

[0018] As a preferred technical solution, the top of the slurry dilution tank is equipped with a gas phase balance pipeline to return the separated gas to the polymerization reactor. The slurry concentration in the tank is ≤35wt%, preferably 20-30%.

[0019] As a preferred technical solution, the top of the flash tank is equipped with a secondary cooling mechanism for recovering hexane, including a primary condenser and a secondary condenser;

[0020] And / or, the bottom of the polymerization reactor is provided with a self-circulating loop with a slurry delivery pump.

[0021] As a preferred technical solution, the online magnetic separation device uses a pipeline magnetic filter.

[0022] As a preferred technical solution, the pipeline magnetic filter includes 2-20 sets of magnetic separation modules arranged in parallel, and the magnetic separation module includes:

[0023] A cylindrical magnetic filter tank, with a magnetic rod assembly inside, is connected to the magnetic filter tank and has a clean material outlet and a cleaning liquid inlet;

[0024] The four-way pipeline valve assembly is connected to the lower part of the magnetic filter tank and is respectively provided with a raw material inlet, a slag outlet and a return material outlet;

[0025] During slurry filtration and demagnetization, the path is: raw material inlet - magnetic filter tank - clean material outlet;

[0026] During backwashing, the path is: cleaning fluid inlet - magnetic filter tank - slag outlet.

[0027] While a single module is backwashing, other modules continue to run, achieving zero-downtime switching.

[0028] As a preferred technical solution, the magnetic rod assembly consists of multiple magnetic rods, the outer tube surface magnetic field of the magnetic rod is not less than 9000GS, the temperature resistance is not less than 150℃, and the capture efficiency for micron-sized (≤10μm) magnetic particles is ≥99.5%.

[0029] The magnetic rod is mounted on a fixed plate, and the fixed plate is in a closed connection with the shell of the magnetic filter tank.

[0030] As a preferred technical solution, the magnetic rod adopts a telescopic magnetic rod structure and is equipped with an electric telescopic rod or a cylinder drive mechanism; and / or, the magnetic filter tank is equipped with a stirrer. This utility model uses a telescopic magnetic rod in conjunction with a stirrer to prevent magnetic particles from caking and extend the cleaning cycle.

[0031] In the production of ultra-high purity polyolefins, the above-mentioned production system is used. The reaction raw materials undergo polymerization in the polymerization reaction unit, and the polymerized slurry overflows into the slurry treatment unit for processing. The slurry demagnetization unit in the system circulates and demagnetizes the flowing slurry to reduce magnetic foreign matter entrained in the slurry.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] This invention utilizes a strong magnetic field inside a demagnetizer in the production process of ultra-high purity polymers. Magnetic metallic impurities are adsorbed under the influence of the magnetic field, effectively removing crystalline metallic impurities and minimizing or eliminating entrained magnetic foreign matter (<50 μg / kg), thus significantly improving product purity. The system incorporates online magnetic separation devices in the circulating hexane pipeline and the downstream delivery pipeline of the flash tank. These devices efficiently remove magnetic metallic impurities from the flowing liquid. The circulating hexane continuously circulates throughout the production process, and the online magnetic separation devices continuously demagnetize the circulating hexane, ensuring the purity of the circulating medium and preventing the accumulation of magnetic impurities during circulation from affecting product purity.

[0034] Furthermore, this invention, by setting up two sets of polymerization reactors, allows for series-parallel switching to produce bimodal / unimodal grades of polyethylene. A reactor top cooler is installed at the top of the reactor, using the vaporization of the low-boiling-point solvent hexane for heat removal. Simultaneously, the reactor employs a jacketed heat removal mechanism, effectively solving the heat removal problem in the polyethylene reaction. Slurry circulation at the bottom of the reactor prevents slurry sedimentation, ensuring a stable and orderly polymerization process, which is beneficial for producing high-quality polyolefin products. Attached Figure Description

[0035] Figure 1 This is a flowchart illustrating the system of this utility model;

[0036] Figure 2 This is a schematic diagram of the pipeline magnetic separation module;

[0037] Figure 3 for Figure 2 Side view;

[0038] Figure 4 This is a schematic diagram of the magnetic rod assembly structure of the pipeline magnetic separation module;

[0039] Figure 5 This is a schematic diagram of two sets of parallel magnetic separation modules for pipelines;

[0040] Figure 6 This is a schematic diagram of the parallel structure of four sets of pipeline magnetic separation modules. Detailed Implementation

[0041] The present invention will now be described in detail. Any aspects not described in detail are technical solutions already disclosed in the field.

[0042] An ultra-high purity polyolefin polymerization production system includes a polymerization reaction unit, a slurry treatment unit, and a slurry demagnetization unit. 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, which includes an ethylene feed pipeline, a catalyst feed pipeline, and a circulating hexane pipeline. The slurry treatment unit includes a slurry dilution tank connected to the overflow port of the polymerization reactor via an overflow pipeline. A flash tank is connected downstream of the slurry dilution tank, and the bottom of the flash tank is connected to the downstream process via a discharge pipeline equipped with a slurry transfer pump. The slurry demagnetization unit includes an online magnetic separation device installed on the circulating hexane pipeline and the flash tank discharge pipeline.

[0043] The following is a specific implementation method.

[0044] Reference Figure 1The ultra-high purity polyolefin polymerization production system employs a low-pressure continuous polymerization process. The reaction products exit the reactor equipped with a stirrer via overflow. Hexane is used as a dispersant and a vaporization heat remover. The system consists of two reactors: a first polymerization reactor R-201 and a second polymerization reactor R-221. This system can produce both monophasic and biphasic resins through series / parallel connection of the two reactors. When producing biphasic polyethylene, the reactors operate in series; when producing monophasic polyethylene, the reactors operate in parallel. Ethylene from outside the system is purified and filtered through an ethylene filter tank S-201 before being fed into the reactors. Hydrogen from outside the system is metered and added to the circulating gas mains of both the first polymerization reactor R-201 and the second polymerization reactor R-221 before entering the reactors. The hydrogen is used to control the molecular weight of the polymer.

[0045] The operating pressure of the first polymerization reactor R-201 varies from 0.25 to 0.7 MPaG, and the operating temperature varies from 60 to 90°C, depending on the grade. The operating pressure of the second polymerization reactor R-221 also varies from 0.25 to 0.7 MPaG, and the operating temperature varies from 60 to 90°C, depending on the grade.

[0046] Polyethylene polymerization is a strongly exothermic reaction. In this system, heat removal from the two reactors is mainly achieved through hexane vaporization. The circulating gas, consisting of hexane vapor evaporated from the top of the first polymerization reactor R-201, unreacted ethylene, hydrogen, and inert gas components such as methane, ethane, and nitrogen, is cooled to 38–40°C by the first reactor top cooler E-201 before entering the first hexane tank V-205 for liquid separation. A wire mesh demister is installed at the top of the first hexane tank V-205 to prevent liquid carryover at the inlet of the first circulating gas blower B-201. The liquid phase from the first hexane tank V-205, as circulating hexane, is circulated to the reactor liquid phase inlet and top washing port by the first condensate circulation pump P-202A / B. The gas phase from the first hexane tank V-205 is pressurized by the first circulating gas blower B-201 and returned to the first polymerization reactor R-201. Fresh ethylene and hydrogen are added to the outlet gas line of the first circulating gas blower B-201. An online analyzer is installed to analyze the gas phase composition before fresh raw materials are added in order to control the reactor.

[0047] The second polymerization reactor R-221 operates in the same manner as the first polymerization reactor R-201. The vaporized components at the top are cooled to 38–40°C by the second reactor top cooler E-221 before entering the second hexane tank V-225 for liquid separation. A wire mesh demister is installed at the top of the second hexane tank V-225 to prevent liquid carryover at the inlet of the second circulating gas blower B-221. The liquid phase from the second hexane tank V-225 is circulated as circulating hexane through the second condensate circulation pumps P-222A / B to the reactor liquid phase inlet and the top washing port. The gaseous phase from the second hexane tank V-225 is pressurized by the second circulating gas blower B-221 and returned to the second polymerization reactor R-221. Fresh ethylene and hydrogen are added to the outlet gas line of the second circulating gas blower B-221.

[0048] Polyethylene slurry, containing up to 35% polyethylene, flows out of the overflow ports of the first polymerization reactor R-201 and the second polymerization reactor R-221. Because the overflowing medium carries a large amount of gas due to intense backmixing within the reactors, a first slurry dilution tank V-202 and a second slurry dilution tank V-222 are installed to separate the gas from the slurry, avoiding long-distance gas-liquid two-phase transport. The separated gas returns to the tops of the first polymerization reactor R-201 and the second polymerization reactor R-221 respectively through gas phase balance pipelines.

[0049] Stabilized polyethylene slurry from the first slurry dilution tank V-202 and the second slurry dilution tank V-222 is flashed through the first flash tank V-203 or the second flash tank V-223 via pressure differential to remove non-condensable gases. When producing series grades, the slurry after flashing in the first flash tank V-203 is transported to the second polymerization reactor R-221 by the first slurry transfer pump P-201A / B; when producing parallel grades, the material from 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 centrifuge unit PK-311 in the separation and drying process by the second slurry transfer pump P-221A / B for centrifugal separation, and then enters the subsequent drying unit.

[0050] The flash vapor from either flash tank V-203 or flash tank V-223, after being cooled by either flash condenser E-202 or flash condenser E-222, is returned to the corresponding flash tank V-203 or flash tank V-223 via flash liquid seal tanks V-207 and V-227, respectively. The non-condensable gas from flash condenser E-202 or flash condenser E-222 undergoes secondary cooling in flash condenser E-223 to recover hexane, and then flows back to flash liquid seal tank V-227 by gravity before entering flash tank V-223. The non-condensable gas from flash condenser E-223 proceeds to the next process for further treatment.

[0051] This system incorporates a first online magnetic separator MS-100 in the circulating hexane pipeline, and a second online magnetic separator MS-200 and a third online magnetic separator MS-300 in the downstream conveying pipelines of the first flash tank V-203 and the second flash tank V-223. Through efficient magnetic separation technology, it precisely removes magnetic metal impurities from the flowing slurry. In the slurry state, for suspended polyethylene particle systems, it effectively removes metal impurities entrained in the material, thereby significantly improving product purity and preventing metal impurities from being trapped inside the polyethylene resin particles during particle growth.

[0052] As a preferred embodiment, the online magnetic separation device used in this invention is specifically a pipeline magnetic filter, which includes a pipeline magnetic separation module, and its structure is as follows: Figure 2 , Figure 3 As shown, preferably, multiple sets of pipeline magnetic separation modules are connected in parallel. The pipeline magnetic separation modules are provided in 2 to 20 sets, preferably 4 to 10 sets, and more preferably 4 to 8 sets. The specific design is selected according to the actual processing volume.

[0053] Reference Figure 2 , Figure 3 The pipeline magnetic separation module is installed and fixed on the foundation frame. The module includes a magnetic filter tank 1, which contains a magnetic rod assembly for adsorbing and removing magnetic metal particles from the flowing slurry. The pipeline magnetic separation module has a raw material inlet 2, a clean material outlet 3, a cleaning liquid inlet 4, and a slag outlet 5, all connected to the magnetic filter tank 1. During magnetic filtration, the slurry path is: raw material inlet - magnetic filter tank - clean material outlet; during backwashing, the cleaning liquid path is: cleaning liquid inlet - magnetic filter tank - slag outlet. Hexane or mother liquor is used for backwashing to prevent the introduction of new impurities into the system.

[0054] As a preferred embodiment, a return outlet 6 is also provided in connection with the magnetic filter tank 1 to discharge the residual slurry before backwashing, so as to avoid wasting materials or increasing costs.

[0055] In a preferred embodiment, the lower part of the magnetic filter 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 filter 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 clean material outlet 3 are directly connected to the magnetic filter tank 1.

[0056] In a preferred embodiment, the magnetic rod assembly consists of multiple sets (e.g., 3 to 20) of magnetic rods 11, preferably 5 to 10 rods. In one specific embodiment, 7 magnetic rods 11 are used, arranged in a concentric array. The surface magnetic field of the outer tube of each magnetic rod 11 is not less than 9000 GS. The magnetic rod assembly is mounted on a fixed disk 12, which is sealed to the housing of the magnetic filter tank 1. Preferably, a stirrer 13 is installed inside the pipeline magnetic separation module. The stirring shaft of the stirrer 13 is installed in the middle of the fixed disk 12, and the upper part is driven by a motor 14. During slurry magnetic filtration, the stirrer 13 is turned on, which helps to prevent the polyethylene slurry from settling. The stirrer 13 is preferably an inclined blade turbine, suitable for medium to low viscosity fluids, which helps to suspend the slurry.

[0057] As a preferred embodiment, the magnetic rod 11 can be configured as telescopic (e.g., using an electric telescopic rod or a cylinder-driven component). After the magnetic rod 11 has been working for a period of time, during the cleaning process, by controlling the magnetic rod 11 to move upward, the metallic magnetic impurities adsorbed on the surface of the magnetic rod 11 can be removed.

[0058] In practical implementation, when producing polyethylene using a large-scale continuous slurry process, the pipeline magnetic filter can be used as follows: Figure 5 The pipeline magnetic filter shown is composed of two sets of pipeline magnetic separation modules connected in parallel, or uses, as shown in the example, a pipeline magnetic filter. Figure 6 The illustrated pipeline magnetic filter consists of four sets of parallel pipeline magnetic separation modules. Each pipeline magnetic separation module's raw material inlet 2, cleaning fluid inlet 4, clean material outlet 3, return material outlet 6, and slag outlet 5 are all connected via a single pipeline. Each inlet and outlet pipeline is equipped with a control solenoid valve connected to the DCS control system. During operation, half of the pipeline magnetic separation modules are used for slurry magnetic filtration, while the other half is used to clean and "regenerate" the magnetic filter tank (magnetic rod 11) using hexane solvent. This switching is repeated continuously to achieve wet demagnetization of the slurry, effectively removing metal residues and producing ultra-high purity polyethylene products with a metal impurity removal rate ≥99.5% and a product ash content ≤50ppm.

[0059] The above description of the embodiments is provided to enable those skilled in the art to understand and use the utility model. It will be apparent to those skilled in the art that various modifications can be easily made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present utility model is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present utility model without departing from its scope should be within the protection scope of the present utility model.

Claims

1. A production system for ultra-high purity polyolefin polymerization, characterized in that, include: 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, which includes an ethylene feed line, a catalyst feed line, and a circulating hexane line. The slurry treatment unit includes a slurry dilution tank connected to the overflow port of the polymerization reactor via an overflow pipe, a flash tank connected downstream of the slurry dilution tank, and the bottom of the flash tank connected to the downstream process via a discharge pipe with a slurry delivery pump. The slurry demagnetization unit includes an online magnetic separation device installed on the circulating hexane pipeline and the flash tank discharge pipeline.

2. The ultra-high purity polyolefin polymerization production system according to claim 1, characterized in that, The polymerization reaction unit is also equipped with a circulating cooling subsystem, which includes: A top condenser is installed at the top of each polymerization reactor; Hexane recovery tank connected to the top condenser of the reactor; A circulating loop consisting of a circulating air fan; The circulating cooling subsystem removes the heat of reaction through a hexane phase change.

3. The ultra-high purity polyolefin polymerization production system according to claim 1, characterized in that, 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℃.

4. The ultra-high purity polyolefin polymerization production system according to claim 1, characterized in that, The top of the slurry dilution tank is equipped with a gas phase balance pipeline to return the separated gas to the polymerization reactor.

5. The ultra-high purity polyolefin polymerization production system according to claim 1, characterized in that, The flash tank is equipped with a two-stage cooling mechanism at the top for hexane recovery, including a primary condenser and a secondary condenser.

6. The ultra-high purity polyolefin polymerization production system according to claim 1, characterized in that, The online magnetic separation device uses a pipeline magnetic filter.

7. The ultra-high purity polyolefin polymerization production system according to claim 6, characterized in that, The pipeline magnetic filter includes 2-20 sets of magnetic separation modules arranged in parallel, and the magnetic separation module comprises: A cylindrical magnetic filter tank (1) is provided with a magnetic rod assembly inside, and is connected to the magnetic filter tank (1) and has a clean material outlet (3) and a cleaning liquid inlet (4); The four-way pipeline valve group is connected to the lower part of the magnetic filter tank (1) and is respectively provided with raw material inlet (2), slag outlet (5) and 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 fluid inlet (4) - magnetic filter tank (1) - slag outlet (5).

8. The ultra-high purity polyolefin polymerization production system according to claim 7, characterized in that, The magnetic rod assembly consists of multiple magnetic rods (11), and the surface magnetic field of the outer tube of the magnetic rod (11) is not less than 9000GS; The magnetic rod is mounted on a fixed disk (12), and the fixed disk (12) is closedly connected to the shell of the magnetic filter tank (1).

9. The ultra-high purity polyolefin polymerization production system according to claim 8, 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.

10. The ultra-high purity polyolefin polymerization production system according to claim 8, characterized in that, The magnetic filter tank (1) is equipped with a stirrer (13).

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