High-pressure polymerization device for producing easily crosslinked polyethylene
By optimizing the reactor design and two-stage vacuum separation system of the high-pressure polymerization unit, the problem of incomplete separation of ethylene monomers was solved, enabling efficient production of high-quality easily cross-linked polyethylene, reducing energy consumption and production costs, and improving product purity and safety.
Patent Information
- Application Number
- CN202423146431.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2024-12-19
- Publication Date
- 2026-01-23
- Estimated Expiration
- 2034-12-19
AI Technical Summary
In the existing high-pressure polyethylene production process, incomplete separation of ethylene monomers leads to low product purity, consumes a large amount of crosslinking agent, increases production costs and safety risks, and traditional equipment is energy-intensive, complex to operate, and difficult to maintain.
Design a high-pressure polymerization apparatus including a tubular reactor and a two-stage pressure reduction and separation system. The reaction temperature is controlled by a heat exchange jacket, and ethylene monomer is removed by two-stage pressure reducing valves and separators to ensure that the polymerization reaction is carried out within a controllable temperature range. The product purity is improved by the two-stage pressure reduction and separation system.
This technology enables the efficient production of high-quality, easily cross-linked polyethylene, reduces energy consumption, simplifies the operation process, improves product purity and cross-linking performance, and reduces production costs and safety risks.
Smart Images
Figure CN223818623U_ABST
Abstract
Description
Technical Field
[0001] This utility model belongs to the field of high-pressure free radical polymerization for preparing polyolefins, specifically relating to a high-pressure polymerization apparatus for producing easily cross-linked polyethylene. Background Technology
[0002] High-density polyethylene (LDPE), also known as low-density polyethylene, has been widely used in various fields since its industrial production due to its unique physical and chemical properties. LDPE possesses excellent flexibility, extensibility, electrical insulation, transparency, and processability, making it a preferred material for industries such as food packaging, foamed sheets, multi-layer composite packaging, and wire and cable matrix materials. LDPE is produced by free radical polymerization of ethylene under high temperature (typically exceeding 100°C) and high pressure (generally exceeding 100 MPa). This polymerization method endows LDPE with a rich structure of long-chain, short-chain, and carbon-carbon double bonds, resulting in a rapid cross-linking speed.
[0003] However, despite the numerous application advantages brought by the branched structure and crosslinking properties of LDPE, a large amount of crosslinking agent is still required during the crosslinking modification process. These crosslinking agents introduce small molecule impurities during the reaction, leading to increased volatile organic compound (VOC) content and prolonged degassing time in LDPE products. Furthermore, the presence of small molecule impurities may negatively impact key performance indicators such as the electrical properties, mechanical properties, and thermal stability of crosslinked LDPE materials.
[0004] In the production of LDPE, the separation of ethylene monomers is a crucial step. However, most existing separation devices employ a single pressure reduction and separation step, which is insufficient to completely remove ethylene monomers from polyethylene. This not only results in low product purity, affecting subsequent processing and applications, but may also increase production costs and safety risks. Particularly in the production of high-density polyethylene, the residual amount of ethylene monomers has a significant impact on product quality and performance.
[0005] Furthermore, traditional high-pressure polyethylene (HPP) production facilities suffer from high energy consumption during the deheating and separation processes. This not only hinders energy conservation, emission reduction, and sustainable development but also increases production costs. Some existing facilities, in an effort to improve separation efficiency, employ complex structures and operating methods, leading to difficulties in operation and maintenance, further increasing production costs and safety risks.
[0006] To address the aforementioned issues, a novel high-pressure polyethylene (LDPE) production and separation device needs to be developed. This device should be able to optimize reaction conditions, improve the crosslinking performance of LDPE and product quality; simultaneously, it should possess efficient separation capabilities to ensure complete removal of ethylene monomers from polyethylene; furthermore, the device design should be simple and straightforward, facilitating operation and maintenance to reduce production costs and safety risks. Utility Model Content
[0007] This invention proposes a novel high-pressure polyethylene production and separation device, which aims to achieve efficient production and high-quality separation of LDPE by optimizing the design of the reactor and separator, and by precisely controlling the reaction and separation processes.
[0008] To achieve the above objectives, the technical solution of this utility model is as follows:
[0009] A high-pressure polymerization apparatus for producing easily cross-linkable polyethylene includes: a tubular reactor having at least one ethylene inlet and one initiator inlet, the tubular reactor having a built-in heat exchange jacket for heat removal, and its length-to-diameter ratio being set between 10,000 and 50,000.
[0010] The heat exchange jacket is used to effectively remove heat from the tubular reactor, ensuring that the polymerization reaction in the tubular reactor proceeds within a controllable temperature range. The tubular reactor has an aspect ratio of 10,000-50,000, a design that helps promote the full polymerization of ethylene monomers, increasing the molecular weight and crosslinking properties of LDPE.
[0011] Furthermore, the heat exchange jacket is equipped with a circulating medium channel. By adjusting the temperature and flow rate of the circulating medium, the reaction temperature inside the tubular reactor can be precisely controlled, preventing the material from being in a high-temperature range for a long time and ensuring the safety and stability of the reaction.
[0012] Furthermore, the ethylene inlet is connected to the ethylene supply source via an ethylene inlet pipeline, and the initiator inlet is connected to the initiator supply source via an initiator inlet pipeline. Both pipelines are equipped with flow controllers to ensure a stable supply and accurate metering of the reaction raw materials.
[0013] Furthermore, the outlet of the tubular reactor is connected to a pressure-reducing separation system, which includes a first pressure-reducing valve, a first separator, a second pressure-reducing valve, and a second separator connected in sequence. The first pressure-reducing valve is connected to the outlet of the tubular reactor. The first pressure-reducing valve is used to initially reduce the pressure of the mixture of polyethylene and unreacted ethylene monomers discharged from the reactor. The first separator is used to separate most of the ethylene monomers, leaving crude polyethylene containing a small amount of ethylene. The second pressure-reducing valve is used to further reduce the pressure of the crude polyethylene. The second separator is used to finally separate the remaining ethylene monomers to obtain high-purity polyethylene, and the pressure of the polyethylene is reduced to below 5 bar.
[0014] The pressure reduction and separation system reduces the pressure of polyethylene to below 5 bar through two-stage pressure reduction using a first pressure reducing valve and a second pressure reducing valve.
[0015] The first pressure reducing valve is used to initially reduce the pressure of the mixture of polyethylene and unreacted ethylene monomers discharged from the reactor, ensuring the smooth progress of subsequent separation processes.
[0016] The outlet of the first pressure reducing valve is connected to a first separator, which is equipped with a separation medium and / or a separation plate to separate most of the ethylene monomers, leaving crude polyethylene containing a small amount of ethylene.
[0017] A second pressure reducing valve is connected to the bottom outlet of the first separator. This valve further reduces the pressure of the crude polyethylene in preparation for it to enter the second separator for final ethylene separation.
[0018] The outlet of the second pressure reducing valve is connected to a second separator, which is equipped with a finer separation medium or separation technology to finally separate the remaining ethylene monomers and obtain high-purity polyethylene.
[0019] Furthermore, the outlet of the pressure-reducing separation system is connected to a polymer discharge pipeline.
[0020] Furthermore, the polymer discharge pipeline is equipped with a flow control valve and / or a pressure control valve to continuously and stably discharge the separated high-purity polyethylene from the device, facilitating subsequent collection and processing.
[0021] Furthermore, the tubular reactor also includes one or more temperature sensors configured to monitor the reaction temperature inside the tubular reactor in real time and feed the temperature data back to the control system to achieve closed-loop control of the reaction temperature.
[0022] Furthermore, the circulating medium channel is also connected to a heat exchanger, which is used to preheat or cool the circulating medium to further regulate and control the reaction temperature in the tubular reactor, improve thermal efficiency, and reduce energy consumption.
[0023] Furthermore, the pressure reduction and separation system also includes a pressure monitoring device, which is configured to monitor the pressure values of each component in the pressure reduction and separation system in real time and feed the pressure data back to the control system to ensure the stability and safety of the pressure reduction and separation process.
[0024] After being discharged from the tubular reactor, polyethylene and unreacted ethylene monomers undergo two stages of depressurization and separation. In the first separator, most of the ethylene is separated, leaving crude polyethylene mixed with a small amount of ethylene. The crude polyethylene then enters a second depressurization valve for further depressurization before entering the second separator for final ethylene separation. After these two stages of depressurization and separation, the pressure of the polyethylene is reduced to below 5 bar, ensuring the purity and stability of the product.
[0025] During the reaction process, this invention places particular emphasis on temperature control of the tubular reactor. Heat is removed from the tubular reactor via a heat exchange jacket, and the rate of heat removal is precisely controlled to prevent the material from being exposed to high temperatures for extended periods, thus ensuring the safety and stability of the reaction. Simultaneously, a two-stage depressurization and separation system effectively removes ethylene monomers from the polyethylene, improving the purity and crosslinking properties of the product.
[0026] In summary, the high-pressure polymerization apparatus for producing easily cross-linked polyethylene of this invention has advantages such as simple structure, convenient operation, high production efficiency, and high product purity. This apparatus is particularly suitable for preparing high-performance LDPE materials, and can meet the ever-growing market demand for easily cross-linked polyethylene materials. Attached Figure Description
[0027] Figure 1 This is a schematic diagram of a device according to an embodiment of the present invention. Detailed Implementation
[0028] The present invention will be further described and illustrated below with reference to specific embodiments. The technical features of each embodiment of the present invention can be combined accordingly, provided that there is no mutual conflict.
[0029] Product Characterization Methods
[0030] Melt index:
[0031] The melt flow rate (MFR) of low-density polyethylene was determined according to ISO 1133 at 190°C and a load of 2.16 kg. The melt flow rate is the amount of polymer, in grams, extruded within 10 minutes using a test apparatus standardized according to ISO 1133 at 190°C and a load of 2.16 kg.
[0032] Molecular weight:
[0033] Number-average molecular weight (Mn) and molecular weight distribution (PDI = Mw / Mn, where Mw is the weight-average molecular weight) were measured according to ISO 16014-4:2003 and ASTM D 6474-99. The number-average molecular weight and molecular weight distribution of low-density polyethylene were characterized using high-temperature gel permeation chromatography (HT-GPC, PL-GPC-220, UK). The polyethylene sample was dissolved in 1,2,4-trichlorobenzene at 160°C. After complete dissolution, the sample was filtered. 2 mL of the filtrate was characterized in the PL-GPC-220. The test temperature was 150°C, and the mobile phase of 1,2,4-trichlorobenzene flowed at a constant rate of 1 mL / min.
[0034] Branching degree (including long-chain branch LCB and short-chain branch SCB):
[0035] The branched content in the polymer product was measured using a nuclear magnetic resonance (NMR) spectrometer (Mercury Plus 300). 40 mg of sample was dissolved in 0.5 mL of deuterated o-dichlorobenzene, and the test temperature was 120 °C. Each sample was scanned 5000 times at an NMR resolution of 400 MHz to obtain a good NMR spectrum.
[0036] Double bond concentration:
[0037] The determination of the amount of terminal double bonds (CH2=CH2-CH2-) per 1000 carbon atoms was performed according to ASTM D3124-72. The extinction coefficient of the terminal double bonds was determined using the procedure described in Part 9 of ASTM-D 3124. Thin films with a thickness of approximately 0.1 mm were prepared at 125 °C and 15 MPa, and the actual thickness was measured. The testing instrument was a Nicolet iS50 infrared spectrometer equipped with a liquid nitrogen-cooled MCT detector. The number of scans was 32, and the resolution was 4 cm⁻¹. -1 KBr powder was used to collect background spectra.
[0038] From 980cm -1 Approximately 840cm -1 Draw a baseline at approximately 910cm. -1 Determine the peak height corresponding to the terminal ethylene group. Calculate the amount of terminal double bonds per 1000 carbon atoms using the following formula (ASTM D3124-72):
[0039] Terminal vinyl group / 1000 carbon atoms = (14 × A) / (13.13 × L × D), where A is absorbance (peak height), L is film thickness (mm), and D is material density (g / cm³). 3 ).
[0040] Gel content:
[0041] The polyethylene sample was placed in a rotary evaporator flask, and 1.6 wt% dicumyl peroxide (DCP) was added at 80°C, followed by hot-press crosslinking.
[0042] The gel content was determined using a solvent extraction technique based on ASTM D 2765-95. A known amount of cross-linked polyethylene sample was placed in a pre-weighed 120-mesh copper mesh. The intact copper mesh was then extracted in boiling xylene for 12 hours. The final gel product was removed and vacuum-dried at 80°C for 8 hours. The insoluble fraction was weighed and the gel content was calculated.
[0043] Example
[0044] Reference Figure 1 This utility model provides a high-pressure polymerization apparatus for producing easily cross-linked polyethylene, comprising:
[0045] (1) A tubular reactor 1 having at least one ethylene inlet and at least one initiator inlet;
[0046] (2) Ethylene feed line 2 connected to the ethylene feed inlet 11 of the tubular reactor;
[0047] (3) Initiator feed pipe 3 connected to the initiator inlet 12 of the tubular reactor;
[0048] (4) The first pressure reducing valve 4 is connected to the outlet 13 of the tubular reactor;
[0049] (5) The first separator 5 is connected to the outlet 41 of the first pressure reducing valve;
[0050] (6) A second pressure reducing valve 6 connected to the bottom outlet 51 of the first separator;
[0051] (7) The second separator 7 is connected to the outlet 61 of the second pressure reducing valve;
[0052] (8) Polymer discharge pipe 8 connected to the bottom outlet 71 of the second separator.
[0053] The tubular reactor has a heat exchange jacket, and the length-to-diameter ratio of the tubular reactor is 35000.
[0054] The steps for producing cross-linked polyethylene using the above-mentioned high-pressure polymerization apparatus include:
[0055] (1) Provide a tubular reactor with a jacket;
[0056] (2) Introduce the initiator into the tubular reactor;
[0057] (3) Ethylene is introduced into a tubular reactor, and polyethylene is prepared by contact reaction between ethylene and initiator under the conditions that the peak temperature in each reaction zone is 300℃-340℃ and the maximum reaction pressure Pmax is 200MPa-280MPa.
[0058] (4) Discharging polyethylene and unreacted ethylene from the reactor outlet: The mixture of polyethylene and unreacted ethylene is sequentially discharged from the outlet of the tubular reactor, enters a first pressure-reducing valve connected to the outlet of the tubular reactor, and then enters a first separator connected to the outlet of the first pressure-reducing valve; ethylene is separated from the top of the first separator, and crude polyethylene mixed with a small amount of ethylene is separated from the bottom; the crude polyethylene enters a second pressure-reducing valve connected to the bottom outlet of the first separator; then enters a second separator connected to the outlet of the second pressure-reducing valve; ethylene is separated from the top of the second separator, and polyethylene is separated from the bottom; finally, the polyethylene at the bottom of the second separator enters the polymer discharge pipeline connected to the bottom outlet of the second separator to obtain the finally separated polyethylene. The pressure of the polyethylene and unreacted ethylene monomers discharged from the outlet of the tubular reactor is reduced to below 5 bar after at least two stages of pressure reduction.
[0059] The parameters involved in the preparation process of each embodiment are detailed in Table 1, and the single-pass conversion rate of ethylene and the polyethylene yield in the tubular reactor are shown in Table 2. The characterization results of the polyethylene products prepared in each embodiment are shown in Table 3.
[0060] Table 1
[0061]
[0062] Table 2
[0063] Ethylene single-pass conversion rate Polyethylene production (t / h) Example 1 21％ 5.5 Example 2 27％ 24.0 Example 3 28％ 23.1 Example 4 25％ 20.5 Example 5 29％ 23.8
[0064] Table 3
[0065]
Claims
1. A high-pressure polymerization apparatus for producing easily cross-linked polyethylene, characterized in that, include: A tubular reactor having at least one ethylene inlet and one initiator inlet, the tubular reactor having a built-in heat exchange jacket for heat removal, and having an aspect ratio between 10,000 and 50,000.
2. The apparatus according to claim 1, characterized in that, The heat exchange jacket is equipped with a circulating medium channel. By adjusting the temperature and flow rate of the circulating medium, the reaction temperature inside the tubular reactor can be precisely controlled, preventing the material from being in a high-temperature range for a long time and ensuring the safety and stability of the reaction.
3. The apparatus according to claim 1, characterized in that, The ethylene inlet is connected to the ethylene supply source via an ethylene inlet pipeline, and the initiator inlet is connected to the initiator supply source via an initiator inlet pipeline. Both pipelines are equipped with flow controllers to ensure a stable supply and accurate metering of the reaction raw materials.
4. The apparatus according to claim 1, characterized in that, The outlet of the tubular reactor is connected to a pressure-reducing separation system, which includes a first pressure-reducing valve, a first separator, a second pressure-reducing valve, and a second separator connected in sequence. The first pressure-reducing valve is connected to the outlet of the tubular reactor. The first pressure-reducing valve is used to initially reduce the pressure of the mixture of polyethylene and unreacted ethylene monomer discharged from the reactor. The first separator is used to separate most of the ethylene monomer, leaving crude polyethylene containing a small amount of ethylene. The second pressure-reducing valve is used to further reduce the pressure of the crude polyethylene. The second separator is used to finally separate the remaining ethylene monomer to obtain high-purity polyethylene, and the pressure of the polyethylene is reduced to below 5 bar.
5. The apparatus according to claim 4, characterized in that, Both the first and second separators are equipped with separation media or separation plates to achieve effective separation of ethylene monomers and polyethylene. The separation media or separation plates in the second separator are finer to improve the purity of polyethylene.
6. The apparatus according to claim 4, characterized in that, The outlet of the pressure-reducing separation system is connected to a polymer discharge pipeline.
7. The apparatus according to claim 6, characterized in that, The polymer discharge pipeline is equipped with a flow control valve and / or a pressure control valve to continuously and stably discharge the separated high-purity polyethylene from the device, facilitating subsequent collection and processing.
8. The apparatus according to claim 1, characterized in that, The tubular reactor also includes one or more temperature sensors configured to monitor the reaction temperature inside the tubular reactor in real time and feed the temperature data back to the control system to achieve closed-loop control of the reaction temperature.
9. The apparatus according to claim 2, characterized in that, The circulating medium channel is also connected to a heat exchanger, which is used to preheat or cool the circulating medium to further regulate and control the reaction temperature in the tubular reactor, improve thermal efficiency and reduce energy consumption.
10. The apparatus according to claim 4, characterized in that, The pressure reduction and separation system also includes a pressure monitoring device, which is configured to monitor the pressure values of each component in the pressure reduction and separation system in real time and feed the pressure data back to the control system to ensure the stability and safety of the pressure reduction and separation process.