A continuous production apparatus, production method and application of ultra-high pressure polyethylene

Abstract

This invention provides a continuous production apparatus, method, and application for ultra-high pressure polyethylene (UHPE). The continuous production apparatus includes a first compression unit, a second compression unit, a reaction unit, a high-pressure separator, a high-pressure recirculation connection unit, a low-pressure separator, and a low-pressure recirculation connection unit connected by pipelines. The high-pressure recirculation connection unit includes coolers connected in series and capable of online cutting-out for cleaning cooling channels. The cooler to be cleaned is short-circuited via a three-way switching valve or a switching valve group, while the other coolers remain online. The technical solution provided by this invention has advantages such as fewer equipment requirements, high equipment utilization, low cost, long continuous operation time, and simple operation.

Description

Technical Field

[0001] This invention belongs to the field of ultra-high pressure polyethylene production technology, specifically relating to a continuous production apparatus, production method and application of ultra-high pressure polyethylene. Background Technology

[0002] Polyethylene is the most widely used polymer and can be produced through various methods. High-pressure polyethylene (HPPE) refers to a process that produces ethylene homopolymers and copolymers under high temperature and pressure conditions (150–350 MPa, 140–320 °C) using a free radical polymerization mechanism. The ethylene homopolymer product is LDPE, and the copolymers mainly include ethylene-vinyl acetate resin (EVA), and copolymers of ethylene with acrylic acid and its derivatives such as EAA / EMA / EEA / EBA.

[0003] The equipment for producing high-pressure polyethylene mainly includes a first compressor, a second compressor, a reactor, a separation system, and an extrusion granulation system. The monomers undergo polymerization in the reactor, with a single-pass conversion rate of 10%–50%. The reaction products include unreacted monomers and polymers. The unreacted monomers and polymers are then separated sequentially in a high-pressure separator and a low-pressure separator.

[0004] Chinese patent CN107750187A discloses a high-pressure polyethylene device with two or more parallel high-pressure circulating gas cooling channels. The coolers disclosed have low utilization rates, with more than half of them in standby mode, resulting in high equipment costs.

[0005] Chinese patent CN215277217U discloses an online descaling ethylene cooling system, employing a multi-stage cooler with a dewaxing separator connected in series after each stage. A backup set of coolers and separators is connected in parallel for online descaling. This patent involves a large number of devices, and only the final stage cooler enables online descaling; the earlier stages still require shutdown for descaling. Summary of the Invention

[0006] This invention provides a continuous production ultra-high pressure polyethylene (UHPE) apparatus, which has a high-pressure recirculation connection section connected in series and capable of being cut out online for cleaning and cooling. The reaction raw materials are ethylene, copolymers (optional), initiators (optional), modifiers (optional), etc., and the product is ethylene homopolymer or ethylene copolymer. The apparatus mainly includes, but is not limited to, a first compressor, a second compressor, a tubular reactor, a high-pressure separator, a high-pressure recirculation connection section, a low-pressure separator, and a low-pressure recirculation connection section.

[0007] One objective of this invention is to provide a continuous production apparatus for ultra-high pressure polyethylene, comprising a first compression unit, a second compression unit, a reaction unit, a high-pressure separator, a high-pressure recirculation connection, a low-pressure separator, and a low-pressure recirculation connection connected by pipelines. The high-pressure recirculation connection includes at least three coolers connected in series. Each cooler is provided with a parallel gas bypass connecting the material inlet and outlet, and a parallel refrigerant bypass connecting the refrigerant inlet and outlet. A three-way switching valve or a switching valve group is provided on the material inlet and refrigerant inlet pipelines of each cooler.

[0008] According to the present invention, in the ultra-high pressure polyethylene device:

[0009] The first compression unit includes at least one compressor. Preferably, an ethylene feedstock inlet is provided at the material inlet of the first compressor and / or on the pipeline between the compressors.

[0010] The second compression unit includes at least one compressor, and preferably, a comonomer raw material inlet is optionally provided at the material inlet of the second compression unit;

[0011] Optionally, an adjuster inlet is provided at either the compressor pipeline inlet of the first compression unit or the pipeline inlet of the second compression unit.

[0012] According to the present invention, in the ultra-high pressure polyethylene apparatus, the reaction unit includes at least one reactor, which is a tubular reactor or a batch reactor; preferably, the tubular reactor is a shell-and-tube reactor; the batch reactor is a high-pressure reactor with a built-in agitator; the reaction unit is optionally provided with at least one initiator inlet, and when a tubular reactor is used, 1 to 6 initiator inlets may be provided; the reaction unit is optionally provided with at least one comonomer raw material inlet.

[0013] According to the present invention, in the ultra-high pressure polyethylene device, the reaction products enter the high-pressure separator after being cooled and depressurized in the reaction cooler. The high-pressure separator is provided with a material inlet at the top or upper side, a gas outlet at the upper side or top, and a liquid outlet at the bottom. Preferably, the gas outlet is connected to the material inlet of the high-pressure recirculation connection, and the liquid outlet is connected to the material inlet of the low-pressure separator. The high-pressure separator is a two-phase separator used to separate supercritical small molecules such as ethylene from molten high-molecular polymers, and uses gravity sedimentation to remove polymer molten droplets.

[0014] According to the present invention, in the ultra-high pressure polyethylene device, the high-pressure recirculation connection provides a cooling channel for unreacted supercritical circulating gas from the high-pressure separator to return to the inlet of the second compressor. The cooler of the high-pressure recirculation connection needs to provide sufficient heat exchange area to cool the supercritical circulating gas to meet the suction temperature of the second compressor. The high-pressure circulating gas contains oligomers, which will form wax adhering to the wall surface after cooling. The cooler is a shell-and-tube cooler containing multiple heat exchange tubes, preferably a shell-and-tube cooler with an angle of 0 to 45° to the vertical. The cooler has two operating modes: cooling and dewaxing. Preferably, in cooling mode, the high-pressure circulating gas is cooled by a coolant, and the flow direction of the coolant is opposite to the gas flow direction in the pipeline; in dewaxing mode, the cooler is dewaxed by hot water or steam. The cooler is equipped with at least one dewaxing separator, and the bottom of the dewaxing separator is provided with a wax discharge outlet. The high-pressure recirculation connection needs to have a dewaxing separator separately or integrated with the cooler. The dewaxing separator can be installed in a commonly used manner. For example, in a shell-and-tube heat exchanger, an independent dewaxing separator can be installed for each of 1-2 heat exchange tubes. Alternatively, the length of the end heat exchange tube box of the shell-and-tube heat exchanger can be extended to 1-3 meters, and a heat jacket can be installed outside the tube box as a dewaxing separator. A wax discharge outlet can be provided at the bottom of the tube box to achieve an integrated cooling and wax discharge design. A three-way switching valve or switching valve group installed on the high-pressure recirculation connection pipeline can enable online disconnection of the cooler for dewaxing.

[0015] According to the present invention, in the ultra-high pressure polyethylene apparatus, a material inlet is provided at the top or upper side of the low-pressure separator, a gas outlet is provided at the upper side or top, and a liquid outlet is provided at the bottom; preferably, the gas outlet is connected to the material inlet of the low-pressure recirculation connection, and the liquid outlet is optionally connected to the extrusion granulation system. The low-pressure separator is a two-phase separator that uses cyclone separation or gravity sedimentation to remove unreacted small molecules such as ethylene from the molten polymer. The low-pressure recirculation connection includes at least one cooler and at least one separator. The material outlet of the cooler is connected to the top inlet of the separator via a pipeline, and a liquid discharge outlet is provided at the bottom of the separator. A gas outlet is also provided at the top of the separator, connected via a pipeline to the material inlet of the next cooler along the material flow direction. The gas outlet at the top of the last separator is connected via a pipeline to the feed pipeline of the first compression unit.

[0016] A second objective of this invention is to provide a method for producing ultra-high pressure polyethylene, implemented using the aforementioned continuous production apparatus for ultra-high pressure polyethylene. According to this invention, the method specifically includes:

[0017] (1) Ethylene is sequentially fed to the first compression unit and the second compression unit;

[0018] (2) An optional modifier is added between the first compression units, and an optional comonomer is added at the inlet of the second compression unit or at least one reactor inlet of the reaction unit;

[0019] (3) The compressed ethylene and optional comonomers are fed into the reactor, and an initiator is optional to carry out the polymerization reaction;

[0020] (4) The material obtained after the reaction is separated into gaseous small molecule compounds and molten polymer by a high-pressure separator. The gaseous small molecule compounds enter the high-pressure recirculation connection section for processing, and the molten polymer enters the low-pressure separator.

[0021] (5) The gas material after being processed by the high-pressure recirculation connection is circulated to the second compression unit, and the processed oligomer wax component is discharged for treatment.

[0022] (6) The molten polymer material obtained after separation by the low-pressure separator is extruded and granulated. The gaseous material obtained after separation enters the low-pressure recirculation connection section for processing. The gaseous component obtained after processing is recycled to the first compression unit, and the liquid component is discharged for processing.

[0023] (7) During continuous production, when the cooler in the high-pressure recirculation connection needs to be dewaxed, the cooler to be processed is short-circuited by adjusting the three-way switching valve or switching valve group, and hot water or steam is introduced into the cooler for heating and dewaxing.

[0024] This invention pressurizes ethylene to 200-350 MPa through a first compression unit and a second compression unit before introducing it into a high-pressure tubular or high-pressure autoclave reactor. The raw material, ethylene, is injected at the inlet or interstage of the first compression unit, while the comonomer (optional) is injected at the inlet of the second compression unit. A modifier (optional) is injected at the interstage of the first compression unit or at the inlet of the second compression unit. After the reaction products are separated by a high-pressure separator, unreacted raw materials are returned to the inlet of the second compression unit through a high-pressure recirculation connection. The operating pressure of the high-pressure separator and the high-pressure recirculation connection is 20-50 MPa. After the reaction products are separated by a low-pressure separator, unreacted raw materials are returned to the inlet of the first compression unit through a low-pressure recirculation connection. The operating pressure of the low-pressure separator and the low-pressure recirculation connection is 0.01-1 MPa.

[0025] According to the present invention, in the method for producing ultra-high pressure polyethylene:

[0026] The comonomer is selected from at least one of vinyl acetate and acrylate;

[0027] Based on a total weight of 100 wt% for the ethylene and comonomer, the amount of comonomer used is 0-50 wt%.

[0028] The modifier is not particularly limited and can be a commonly used modifier in the art and in the amount thereof. For example, the modifier is selected from at least one of olefins, alkanes, and aldehydes, preferably from at least one of propylene, 1-butene, propane, and butane. The modifier is used to adjust the molecular weight and melt index of the high-pressure polymerization product, and its amount can be adjusted according to this purpose.

[0029] The initiator is not particularly limited and can be any initiator commonly used in the art and in any amount. Preferably, the initiator can be any organic peroxide initiator commonly used in the art.

[0030] The material in the high-pressure recirculation connection has an oligomer content of less than 0.5 wt% and a comonomer content of 0-50 wt%.

[0031] According to the present invention, in the method for producing ultra-high pressure polyethylene, the inlet pressure of the first compression unit is 0-1 MPa, and the outlet pressure is 20-40 MPa; the inlet temperature of the first compression unit is 10-50°C, and the outlet temperature is 10-50°C; the inlet pressure of the second compression unit is 20-40 MPa, and the outlet pressure is 200-350 MPa; the inlet temperature of the second compression unit is 10-50°C, and the outlet temperature is 60-100°C. The second compression unit needs a sufficient pressure ratio to compress the process materials to the reaction pressure, but at the same time, to avoid self-aggregation and scaling of the materials in the flow channel, the discharge temperature of each stage of the compressor must be strictly controlled. Therefore, the inlet temperature of the second compression unit is crucial to the stable operation of the compressor.

[0032] According to the present invention, in the method for producing ultra-high pressure polyethylene, the reactor is a tubular or batch reactor. The batch reactor is a high-pressure reactor with a built-in agitator and a length of 5–20 m. The tubular reactor is a shell-and-tube type, with the inner tube containing the reactants and products, and the outer tube containing the cooling medium, and a total length of 1000–5000 m. The operating conditions of the reactor are: temperature 140–320°C and pressure 150–350 MPa. After being cooled and depressurized in a post-reaction cooler, the reaction products enter a high-pressure separator, the operating pressure of which is 20–50 MPa.

[0033] According to the present invention, in the production method of ultra-high pressure polyethylene, the operating pressure of the high pressure recirculation connection is 20-50 MPa, the gas inlet temperature is 150-250°C, and the gas outlet temperature is 30-50°C.

[0034] The pressure drop at the material inlet and material outlet of the high-pressure recirculation connection is less than 15 MPa, preferably less than 10 MPa, and more preferably less than 5 MPa.

[0035] The coolant used in the high-pressure recirculation connection and the low-pressure recirculation connection can be a coolant commonly used in the art, such as pressurized water or an equivalent coolant.

[0036] In the high-pressure recirculation connection section, the coolant inlet temperature is 10-40°C;

[0037] The operating pressure of the low-pressure separator is 0.01–1 MPa;

[0038] The operating pressure of the low-pressure recirculation connection is 0.01–1 MPa, the gas inlet temperature is 150–250°C, and the gas outlet temperature is 30–50°C.

[0039] The thermal dewaxing process can employ commonly used thermal dewaxing techniques in the field, such as hot water at a temperature of 150°C or above, or steam at a pressure of 1.0 MPa or above.

[0040] The third objective of this invention is to provide the above-mentioned continuous production apparatus or method for ultra-high pressure polyethylene, and its application in the production of ultra-high pressure polyethylene.

[0041] This invention relates to a high-pressure recirculation connection section for online cutting-out cleaning of cooling channels. It designs a series-connected, arbitrarily cut-out high-pressure circulating gas cooling channel. This cooling channel comprises at least three coolers connected in series. The coolers are shell-and-tube coolers containing multiple heat exchange tubes, preferably inclined shell-and-tube coolers with a separation space, at an angle of 0–45 degrees to the vertical plane, facilitating the flow of precipitated wax towards the downward wax discharge port. The coolers operate in two modes: cooling and dewaxing. In cooling mode, cooling water flows counter-currently through the series heat exchangers to cool the high-pressure circulating gas. The cooling water temperature is 10–45°C, preferably 25–40°C, and even more preferably 35–40°C. In dewaxing mode, hot water or steam is introduced to dewax the process side. Any single cooler can be cut out of the system for heat exchange tube dewaxing without affecting continuous operation. For heat exchangers requiring dewaxing, a three-way valve or switching valve assembly can be used for short-circuiting.

[0042] The manufacturing of high-pressure / ultra-high-pressure equipment in high-pressure polyethylene (HPLC) plants is demanding, time-consuming, and costly. Furthermore, because HPLC plants require reciprocating compressors to achieve ultra-high operating pressures, high-pressure / ultra-high-pressure piping is subject to numerous restrictions and difficulties, and must cope with various complex conditions such as vibration and pulsation in the high-pressure / ultra-high-pressure system. Existing technologies use at least two sets of cooling channels in parallel to cut out the cleaning channel, with at least one set of cooling channels in a dewaxing state, resulting in low equipment utilization. This invention proposes a method using only one set of cooling channels. By connecting at least three coolers in series and installing three-way switching valves or switching valve groups on the hot and cold sides of each cooler, the hot and cold sides of any cooler can be short-circuited, while the other coolers remain online. The HPLC production apparatus provided by this invention has a high-pressure recirculation connection section that connects in series and allows for online cutting out of the cleaning cooling channels, achieving the desired high-pressure circulating material cooling effect and enabling online dewaxing at the high-pressure recirculation connection section. The technical solution provided by this invention has advantages such as fewer equipment requirements, high equipment utilization, low cost, and simple operation. Moreover, the present invention reduces piping restrictions and lowers the difficulty of vibration and pulsation analysis due to the small number of devices and simplified process. Attached Figure Description

[0043] Figure 1 This is a continuous production process for ultra-high pressure polyethylene with a high-pressure recirculation connection that is connected in series and can be cut out online for cleaning and cooling channels; wherein, 1-first compression unit, 2-second compression unit, 3-reactor, 4-high pressure separator, 5-high pressure recirculation connection, 6-low pressure separator, 7-low pressure recirculation connection, E-1~E-4-coolers.

[0044] Figure 2 Taking four units connected in series as an example, the layout of a set of high-pressure recirculation connection shell-and-tube coolers is illustrated; wherein, E-1 to E-4 are coolers, and XV is a three-way valve.

[0045] Figure 3 For a system consisting of four shell-and-tube coolers connected in series, a heat exchange example of coolers E-1 to E-3 in the high-pressure recirculation connection is given, wherein cooler E-4 is cut off as a standby cooler bypass. Detailed Implementation

[0046] The present invention will now be described in detail with reference to specific embodiments. It should be noted that the following embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the content of the present invention are still within the scope of protection of the present invention.

[0047] The following description, in conjunction with the accompanying drawings, illustrates the continuous production apparatus and method for ultra-high pressure polyethylene provided by this invention.

[0048] like Figure 1 As shown, the continuous production unit for ultra-high pressure polyethylene includes a first compression unit 1, a second compression unit 2, a reaction unit 3, a high-pressure separator 4, a high-pressure recirculation connection 5, a low-pressure separator 6, and a low-pressure recirculation connection 7 connected by pipelines. The high-pressure recirculation connection 5 includes four coolers E-1, E-2, E-3, and E-4 connected in series (the coolers can also be three or more connected in series; the attached figure shows four connected in series as an example). Parallel gas pipelines connecting the inlet and outlet of the coolers (E-1, E-2, E-3, and E-4) are provided on the outside of the coolers. Three-way switching valves or switching valve groups are installed on the pipelines between the material inlet, material outlet, and cooling system of the high-pressure recirculation connection 5 (three-way switching valves or switching valve groups are commonly used components and are not marked in the figure).

[0049] like Figure 2 As shown, taking four coolers E-1, E-2, E-3, and E-4 connected in series as an example, this exemplifies the layout of a set of shell-and-tube coolers with a high-pressure recirculation connection. During normal operation, all four coolers can be operated in series, or any three can be selected for series operation. The three-way valves XV on both the process side and refrigerant side of the operating heat exchangers are located in the A→C flow channel. When a cooler is not in operation or requires online dewaxing, taking E1 dewaxing as an example, XV-011 and XV-012 are switched to the A→B flow channel, valve V13 is closed, and cooler E1 is disconnected from the system; valves V12 and V14 are opened to introduce hot water or steam, and the molten oligomer wax is discharged from valve V11.

[0050] like Figure 3The diagram illustrates a heat exchange example of a high-pressure recirculation connection section comprising four shell-and-tube coolers connected in series. One of the four coolers can be selected as a standby cooler, either operational or bypassed. This diagram uses the fourth cooler, E4, as an example of a standby cooler bypassed. The high-pressure recirculation gas and the cooling gas flow in opposite directions. Regarding the operation of the high-pressure recirculation gas stream, the high-pressure separator separates the gas into a high-pressure recirculation gas stream with a temperature of 200–250°C, which enters the first cooler E-1 at a flow rate of 60–120 t / h. The first cooler E-1 cools the gas stream to a temperature of 90–120°C, which then enters the second cooler E-2. The second cooler E-2 cools the gas stream to a temperature of 50–70°C, which then enters the third cooler E-3. The third cooler E-3 cools the gas stream to a temperature of 30–40°C, which then circulates to the second compression unit. Regarding the operation of the refrigerant, a refrigerant with a temperature of 15-35℃ is introduced into the third cooler E-3 at a flow rate of 75-155t / h. After passing through the third cooler E-3, the refrigerant with a temperature of 20-55℃ continues to enter the second cooler E-2. After passing through the second cooler E-2, the refrigerant with a temperature of 35-80℃ continues to enter the first cooler E-1. After passing through the first cooler E-1, the refrigerant temperature is 80-150℃.

[0051] Example 1:

[0052] like Figure 3 The example shown is a heat exchange example of a high-pressure recirculation connection of four shell-and-tube coolers connected in series. One of the four coolers connected in series can be selected as a standby cooler, which can be put into use or bypassed. In this example, the fourth cooler E4 is used as a standby cooler and bypassed.

[0053] The continuous production method for ultra-high pressure polyethylene in this embodiment includes the following steps:

[0054] (1) Ethylene is sequentially fed to the first compression unit 1 and the second compression unit 2;

[0055] (2) An optional modifier is added between the first compression units, and the comonomer vinyl acetate is added at the inlet of the second compression unit 2;

[0056] (3) After compression, ethylene and comonomer enter reactor 3 and initiate free radical polymerization under the action of organic peroxide initiator;

[0057] (4) The material obtained after the reaction is separated into gaseous small molecule compounds and molten polymer by high pressure separator 4. The gaseous small molecule compounds enter the high pressure recirculation connection section 5 for processing, and the molten polymer enters the low pressure separator 6.

[0058] (5) The gas material after being processed by the high-pressure recirculation connection part 5 is circulated to the second compression unit 2, and the processed oligomer wax component is discharged.

[0059] (6) The molten polymer material obtained after separation by the low-pressure separator 6 is extruded and granulated. The gaseous material obtained after separation enters the low-pressure recirculation connection section 7 for processing. The gaseous component obtained after processing is circulated to the first compression unit 1, and the liquid component is discharged for processing.

[0060] (7) During continuous production, when the coolers E-1 to E-3 in the high-pressure recirculation connection 5 need to be dewaxed, the coolers to be processed are short-circuited by adjusting the three-way switching valve or the switching valve group, and hot water or steam is introduced into the coolers for heating and dewaxing.

[0061] The raw material ethylene quantity is 30t / hr, the comonomer vinyl acetate quantity is 10t / hr, and the product ethylene-vinyl acetate copolymer quantity is 35t / hr.

[0062] The first compression unit has an inlet pressure of 0.1 MPa, an inlet temperature of 40℃, and an outlet pressure of 26 MPa.

[0063] The second compression unit has an inlet pressure of 24 MPa, an inlet temperature of 40℃, and an outlet pressure of 300 MPa.

[0064] The reactor is a tubular reactor with a length of 2500m, an operating pressure of 290MPa, and an operating temperature of 210℃.

[0065] The high-pressure separator operates at a pressure of 26 MPa and a temperature of 200–220°C.

[0066] The high-pressure recirculation connection operates at a pressure of 26 MPa, with an inlet temperature of 200–220°C, an outlet temperature of 40°C, and a pressure drop of 2 MPa.

[0067] The high-pressure recirculation connection uses four shell-and-tube heat exchangers connected in series. Each heat exchanger has a diameter of 600 mm, a tube length of 15 m, and a total of 450 tubes arranged at a 30° inclination. The cooling medium is 33°C water, which flows counter-currently through the heat exchangers. The mass ratio of the process medium (including ethylene, vinyl acetate, oligomers, modifiers, and light and heavy impurities) to the cooling water is 1:1.3.

[0068] The low-pressure separator operates at a pressure of 0.1 MPa and a temperature of 195°C.

[0069] The low-pressure recirculation connection operates at a pressure of 0.1 MPa, with an inlet temperature of 195°C and an outlet temperature of 40°C.

[0070] In continuous production, the high-pressure circulating gas and the refrigerant flow in opposite directions. Regarding the high-pressure circulating gas flow, the high-pressure separator separates the gas to a temperature of 200–220°C, which then enters the first cooler E1 at a flow rate of 90–120 t / h. The first cooler cools the gas to a temperature of 90–110°C, which then enters the second cooler E2. The second cooler cools the gas to a temperature of 50–70°C, which then enters the third cooler E3. The third cooler cools the gas to a temperature of 35–45°C, which then circulates to the second compression unit. Regarding the refrigerant, a refrigerant at a temperature of 30–35°C enters the third cooler E3 at a flow rate of 115–155 t / h. After passing through the third cooler, the refrigerant to a temperature of 37–45°C enters the second cooler E2. After passing through the second cooler, the refrigerant to a temperature of 55–70°C enters the first cooler E1, where the refrigerant temperature is 100–115°C. When a cooler is not in use or needs to be dewaxed online, taking E1 dewaxing as an example, switch XV-011 and XV-012 to the A→B flow channel, close valve V13, and disconnect cooler E1 from the system; open valves V12 and V14 to introduce hot water above 150℃ or steam above 1.0MPa, and the molten oligomer wax will be discharged from valve V11.

[0071] Example 2:

[0072] The continuous production method for ultra-high pressure polyethylene in this embodiment is the same as in Embodiment 1. Specifically, the raw material ethylene flow rate is 36 t / hr, with no comonomer, and the product ethylene homopolymer flow rate is 35 t / hr. The first compression unit 1 has an inlet pressure of 0.1 MPa, an inlet temperature of 40°C, and an outlet pressure of 30 MPa. The second compression unit 2 has an inlet pressure of 28 MPa, an inlet temperature of 40°C, and an outlet pressure of 310 MPa. Reactor 3 is a tubular reactor with a length of 2000 m, an operating pressure of 300 MPa, and an operating temperature of 300°C. The high-pressure separator 4 has an operating pressure of 30 MPa and an operating temperature of 230–250°C.

[0073] The high-pressure recirculation connection 5 operates at a pressure of 30 MPa, with an inlet temperature of 230–250°C and an outlet temperature of 40°C, and a pressure drop of 1 MPa.

[0074] The high-pressure recirculation connection section 5 employs four shell-and-tube heat exchangers connected in series. Each heat exchanger has a diameter of 580 mm, a tube length of 13 m, and a total of 410 tubes arranged at a 30° inclination. The cooling medium is 33°C water, which flows counter-currently through the heat exchangers in series, with a process medium to cooling water mass ratio of 1:1.2. The low-pressure separator operates at a pressure of 0.1 MPa and a temperature of 220°C.

[0075] The low-pressure recirculation connection operates at a pressure of 0.1 MPa, with an inlet temperature of 220℃ and an outlet temperature of 40℃. During continuous production, the high-pressure circulating gas and the cooling gas flow in opposite directions. Regarding the operation of the high-pressure circulating gas stream, the high-pressure separator 4 separates the gas into a high-pressure circulating gas stream with a temperature of 230–250℃, which then enters the first cooler E1 at a flow rate of 60–90 t / h. The first cooler E1 cools the gas stream to a temperature of 100–120℃, which then enters the second cooler E2. The second cooler E2 cools the gas stream to a temperature of 50–70℃, which then enters the third cooler E3. The third cooler E3 cools the gas stream to a temperature of 30–40℃, which then circulates to the second compression unit 2. Regarding the refrigerant operation, refrigerant with a temperature of 30-35℃ is introduced into the third cooler E3 at a flow rate of 75-110 t / h. After passing through the third cooler E3, the refrigerant with a temperature of 40-55℃ continues to enter the second cooler E2. After passing through the second cooler E2, the refrigerant with a temperature of 65-80℃ continues to enter the first cooler E1. After passing through the first cooler E1, the refrigerant temperature is 135-150℃. When a cooler is not in use or needs to be dewaxed online, taking E1 dewaxing as an example, XV-011 and XV-012 are switched to the A→B flow channel, valve V13 is closed, and cooler E1 is disconnected from the system; valves V12 and V14 are opened to introduce hot water above 150℃ or steam above 1.0MPa, and the molten oligomer wax is discharged from valve V11.

[0076] Table 1 shows the predicted yield, melt index, density, and power consumption for Examples 1 and 2.

[0077] Table 1

[0078]

[0079] Comparative Example 1

[0080] Using existing technology (e.g., patent CN 107750187A) and the same cooler conditions (e.g., the same number of coolers that need to work simultaneously as in Example 1, and the same heat exchange area and structural parameters of a single shell-and-tube cooler), taking the simultaneous operation of 3 coolers as an example.

[0081] As can be seen from Examples 1 and 2 above, the technical solution provided by the present invention only requires a 3+1 configuration (4 heat exchangers) to achieve continuous production of ultra-high pressure polyethylene and online dewaxing of the high-pressure recirculation connection. In contrast, the prior art requires a 1+2 / 2 configuration (5 heat exchangers) to achieve continuous polyethylene production. Furthermore, the first heat exchanger has no backup, and a shutdown is necessary if scaling becomes severe. The technical solution provided by the present invention achieves the same production efficiency with fewer devices, and the coolers in the high-pressure recirculation connection can serve as backups for each other, resulting in higher equipment utilization, longer continuous operation time, and lower investment costs. Simultaneously, the present invention, due to its fewer devices and simplified process, reduces piping limitations and lowers the difficulty of vibration and pulsation analysis.

Claims

1. A continuous production apparatus for ultra-high pressure polyethylene, comprising a first compression unit, a second compression unit, a reaction unit, a high-pressure separator, a high-pressure recirculation connection unit, a low-pressure separator, and a low-pressure recirculation connection unit connected by pipelines, wherein, The high-pressure recirculation connection includes at least three coolers connected in series. Each cooler has a parallel gas bypass connecting the material inlet and outlet, and a parallel refrigerant bypass connecting the refrigerant inlet and outlet. Each cooler has a three-way switching valve or switching valve assembly on its material and refrigerant inlet pipes. Unreacted raw materials from the high-pressure recirculation connection are returned to the inlet of the second compression unit. The high-pressure separator has a material inlet at its top or upper side, a gas outlet at its upper side or top, and a liquid outlet at its bottom. The low-pressure separator has a material inlet at its top or upper side, a gas outlet at its upper side or top, and a liquid outlet at its bottom. The cooler is a shell-and-tube cooler containing multiple heat exchange tubes. The cooler... At least one dewaxing separator is installed at the selected location, with a wax discharge outlet at the bottom of the dewaxing separator; the cooler has two operating modes: cooling and dewaxing. In cooling mode, a coolant is used to cool the high-pressure circulating gas, and the flow direction of the coolant is opposite to the gas flow direction in the pipeline; in dewaxing mode, hot water or steam is used to dewax the cooler; the low-pressure recirculation connection includes at least one cooler and at least one separator. The material outlet of the cooler is connected to the top inlet of the separator through a pipeline, and a liquid discharge outlet is provided at the bottom of the separator. A gas outlet pipeline is also provided at the top of the separator and connected to the material inlet of the next cooler along the material flow direction. The gas outlet at the top of the last separator is connected to the feed pipeline of the first compression unit through a pipeline.

2. The apparatus according to claim 1, characterized in that, The first compression unit includes at least one compressor; and / or, The second compression unit includes at least one compressor; and / or, Optionally, an adjuster inlet is provided at either the compressor pipeline inlet of the first compression unit or the pipeline inlet of the second compression unit.

3. The apparatus according to claim 2, characterized in that, The first compression unit is provided with an ethylene feedstock inlet at the material inlet of the first compressor and / or on the pipeline between the compressors; and / or, The material inlet of the second compression unit may optionally be provided with a copolymer monomer raw material inlet.

4. The apparatus according to claim 1, characterized in that, The reaction unit includes at least one reactor, which is a tubular reactor or a batch reactor; and / or, The reaction unit may optionally be provided with at least one initiator inlet; and / or, The reaction unit may optionally be provided with at least one comonomer feed inlet.

5. The apparatus according to claim 4, characterized in that, The tubular reactor is a shell-and-tube reactor; and / or, the batch reactor is a high-pressure reactor with a built-in agitator.

6. The apparatus according to claim 1, characterized in that, The gas outlet is connected to the material inlet of the high-pressure recirculation connection, and the liquid outlet is connected to the material inlet of the low-pressure separator; and / or, The gas outlet is connected to the material inlet of the low-pressure recirculation connection, and the liquid outlet is optionally connected to the extrusion granulation system.

7. The apparatus according to claim 1, characterized in that, The cooler is a shell-and-tube cooler with an angle of 0 to 45° to the vertical.

8. A method for producing ultra-high pressure polyethylene, implemented using the continuous production apparatus for ultra-high pressure polyethylene as described in any one of claims 1 to 7.

9. The production method according to claim 8, characterized in that, The method includes: (1) Ethylene is sequentially fed to the first compression unit and the second compression unit; (2) An optional modifier is added between the first compression units, and an optional comonomer is added at the inlet of the second compression unit or at least one reactor inlet of the reaction unit; (3) The compressed ethylene and optional comonomers are fed into the reactor, and an initiator is optionally added to carry out the polymerization reaction; (4) The material obtained after the reaction is separated into gaseous small molecule compounds and molten polymer by a high-pressure separator. The gaseous small molecule compounds enter the high-pressure recirculation connection section for processing, and the molten polymer enters the low-pressure separator. (5) The gas material after being processed by the high-pressure recirculation connection is circulated to the second compression unit, and the processed oligomer wax component is discharged externally. (6) The molten polymer material obtained after separation by the low-pressure separator is extruded and granulated. The gaseous material obtained after separation enters the low-pressure recirculation connection section for processing. The gaseous component obtained after processing is recycled to the first compression unit, and the liquid component is discharged for processing. (7) During continuous production, when the cooler in the high-pressure recirculation connection needs to be dewaxed, the cooler to be processed is short-circuited by adjusting the three-way switching valve or switching valve group, and hot water or steam is introduced into the cooler for heating and dewaxing.

10. The method according to claim 9, characterized in that, The comonomer is selected from at least one of vinyl acetate and acrylate; and / or, Based on a total weight of 100 wt% for the ethylene and comonomer, the amount of comonomer used is 0-50 wt%; and / or, The modifier is selected from at least one of olefins, alkanes, and aldehydes; and / or, The initiator is selected from at least one of organic peroxides; and / or, The material in the high-pressure recirculation connection has an oligomer content of less than 0.5 wt% and a comonomer content of 0~50 wt%.

11. The method according to claim 9, characterized in that, The inlet pressure of the first compression unit is 0~1MPa, and the outlet pressure is 20~40MPa; and / or, The inlet temperature of the first compression unit is 10~50℃, and the outlet temperature is 10~50℃; and / or, The inlet pressure of the second compression unit is 20~40MPa, and the outlet pressure is 200~350MPa; and / or, The inlet temperature of the second compression unit is 10~50℃, and the outlet temperature is 60~100℃; and / or, The operating conditions of the reactor are: temperature 140~320℃, pressure 150~350MPa; and / or, The high-pressure separator operates at a pressure of 20~50MPa; and / or, The operating pressure of the high-pressure recirculation connection is 20~50MPa, the gas inlet temperature is 150~250℃, and the gas outlet temperature is 30~50℃; and / or, The pressure drop at the material inlet and material outlet of the high-pressure recirculation connection is less than 15 MPa; and / or, In the high-pressure recirculation connection, the coolant inlet temperature is 10~40℃; and / or, The operating pressure of the low-pressure separator is 0.01~1MPa; and / or, The operating pressure of the low-pressure recirculation connection is 0.01~1MPa, the gas inlet temperature is 150~250℃, and the gas outlet temperature is 30~50℃; and / or, The thermal dewaxing process uses hot water at a temperature of 150°C or higher, or steam at a pressure of 1.0 MPa or higher.

12. The method according to claim 11, characterized in that, The pressure drop at the material inlet and material outlet of the high-pressure recirculation connection is less than 10 MPa.

13. The method according to claim 12, characterized in that, The pressure drop at the material inlet and material outlet of the high-pressure recirculation connection is less than 5 MPa.

14. The continuous production apparatus for ultra-high pressure polyethylene according to any one of claims 1 to 7 or the production method for ultra-high pressure polyethylene according to any one of claims 8 to 13, and its application in the production of ultra-high pressure polyethylene.

Images