A supercritical carbon dioxide multi-stage extraction and separation method and its application

Abstract

The present invention provides a supercritical carbon dioxide multi-stage extraction and separation method. The method includes charging, boosting pressure, extraction, depressurizing, and discharging using at least three extraction units and at least one separation column. Each extraction unit includes a multi-stage extraction device, and the extraction temperature and / or extraction pressure in each stage of the extraction device are different. When one extraction unit is performing extraction, at least one extraction unit is boosting pressure, and at the same time, at least one extraction unit is depressurizing and / or loading / unloading materials. The method of the present invention can achieve continuous extraction by multiple extraction devices, has a wide application range, high extraction efficiency, and is environmentally friendly.

Description

Technical Field

[0001] The present invention relates to the technical field of supercritical fluid extraction, and particularly relates to a supercritical carbon dioxide multi-stage extraction and separation method and its application in separating polymers. Background Art

[0002] Polyethylene wax is a polyethylene with a low relative molecular mass (usually between 1000 and 8000), and its density is usually 0.92 - 0.98 g / cm 3 , and it is widely used in fields such as plastic processing, plastic molding, road paint, waterborne coatings, plastic dyeing, printing ink, paraffin modification, etc. The production methods of polyethylene wax include ethylene polymerization method, polyethylene pyrolysis method, by-product method of high-density polyethylene (HDPE) plant, etc. With the increase in HDPE production capacity, the output of polyethylene wax (HDPE associated wax) produced by the by-product method is also increasing year by year. However, HDPE associated wax often has low purity, wide molecular weight distribution, wide melting range, and poor quality stability, and needs to be further purified and cut into products with different melting point ranges to improve quality and increase added value.

[0003] CN1597716A discloses a method: using an alkane, aromatic hydrocarbon or their mixture with C5 - C12 as a solvent and a monohydric alcohol with C2 - C4 as a precipitant, first dissolving, concentrating, precipitating, separating, and drying the HDPE associated wax at a lower temperature and a smaller solvent ratio to separate out a polyethylene wax product with a lower molecular weight level, gradually increasing the solvent ratio and temperature, and repeating the operations of dissolving, concentrating, precipitating, separating, and drying to correspondingly obtain polyethylene wax products with gradually increasing average molecular weight levels. However, this method has cumbersome operation steps, the used solvent has high toxicity, high solvent cost, and is difficult to industrialize.

[0004] CN102408609A discloses a method: using a solvent (xylene or n-heptane or a mixture of both) to selectively dissolve the low-melting-point components in the HDPE associated wax to obtain a liquid-solid mixed material, the solid substance obtained by filtration and separation is a high-melting-point polyethylene wax product, and the filtrate obtained is subjected to vacuum distillation to obtain a low-melting-point polyethylene wax product, and the solvent recovered by vacuum distillation can be reused. However, this method cannot obtain multi-stage polyethylene wax products, and solvent recovery, solvent removal, etc. will make the process flow longer.

[0005] CN102101923A discloses a method: by adding nucleating agents (mainly calcium stearate, zinc stearate, 1,3-dibenzylidene sorbitol or 2,4-dibenzylidene sorbitol or stearic acid), high melting point polyolefins (mainly polyethylene with a melting point of 140-180°C or polypropylene with a melting point of 155-165°C) to HDPE associated wax, performing high-temperature melting and then recrystallization, a polyethylene wax product with an increased melting point can be obtained. However, the nucleating agents, high melting point polyolefins, etc. used in this method are costly, and the purity and molecular weight distribution range of the obtained product are unknown.

[0006] Generally speaking, the existing cutting and separation methods for HDPE associated wax have problems such as high toxicity of the solvents used, poor separation effect, complex methods, high costs, and difficulties in industrialization. Since China's polyethylene production ranks among the top in the world, the amount of by-product HDPE associated wax obtained is considerable, and currently, the demand for high-quality polyethylene wax is large both in China and worldwide. Therefore, there is an urgent need to develop an environmentally friendly and efficient HDPE associated wax separation technology. Summary of the Invention

[0007] In view of the problems existing in the prior art, the present invention provides a method for continuous extraction and separation using supercritical carbon dioxide as the extraction medium and multiple extraction autoclaves. The method of the present invention uses multiple extraction units in combination, enabling the extraction process in each extraction unit to alternate with other processes such as loading / unloading, pressure boosting, and pressure reduction: when one extraction unit is in the extraction process, the other extraction units are in other processes such as loading / unloading, pressure boosting, and pressure reduction; when one extraction unit finishes extraction and starts other processes, another extraction unit then proceeds with extraction. In this way, the substances to be separated in the material can be continuously and uninterruptedly removed, making the entire extraction and separation process truly continuous, improving production efficiency, and saving costs. In addition, each extraction unit of the present invention includes a multi-stage extraction device, and by setting different extraction conditions for each stage of the extraction device, effective separation of different components can be achieved.

[0008] To achieve the above object, the present invention adopts the following technical solutions:

[0009] The first aspect of the present invention provides a supercritical carbon dioxide multi-stage extraction and separation method, the method comprising loading, pressure boosting, extraction, pressure reduction, and unloading using at least three extraction units and at least one separation tower, each extraction unit including a multi-stage extraction device and the extraction temperature and / or extraction pressure in each stage of the extraction device being different. When one extraction unit is extracting, at least one extraction unit is boosting pressure, and at the same time, at least one extraction unit is reducing pressure and / or loading / unloading.

[0010] Supercritical carbon dioxide has characteristics such as a gas-like diffusion coefficient, a liquid-like dissolution power, and a surface tension of zero. It can quickly penetrate into solid substances and has good solubility for many high-molecular-weight oligomers. In the present invention, by changing the extraction temperature and / or pressure in the extraction device, the solubility of supercritical carbon dioxide in high-molecular polymers with different molecular weights can be adjusted, thereby achieving effective separation of different polymer components.

[0011] In the present invention, "supercritical CO2" and "supercritical carbon dioxide" refer to carbon dioxide in a supercritical state. In the present invention, supercritical carbon dioxide is used as an extraction medium.

[0012] In the present invention, the number of the extraction units is preferably 3n, where n is a positive integer. For example, the number of the extraction units can be 3, 6, 9, or 12, and more preferably 3.

[0013] In some embodiments, the three extraction units include a first extraction unit, a second extraction unit, and a third extraction unit. The first extraction unit includes n-stage extraction devices A1 to A n , the second extraction unit includes n-stage extraction devices B1 to B n , and the third extraction unit includes n-stage extraction devices C1 to C n , where n is an integer greater than or equal to 2. In some embodiments, when the first extraction unit is extracting, the second extraction unit is boosting pressure, and at the same time, the second extraction unit is loading / unloading and / or reducing pressure. In some embodiments, when the second extraction unit is extracting, the third extraction unit is boosting pressure, and at the same time, the first extraction unit is reducing pressure and / or loading / unloading. In some embodiments, when the third extraction unit is extracting, the first extraction unit is boosting pressure, and at the same time, the second extraction unit is reducing pressure and / or loading / unloading.

[0014] It should be noted that the statement "the first extraction unit includes n-stage extraction devices A1 to A n " in the present invention means that the first extraction unit includes a first-stage extraction device A1, a second-stage extraction device A2, a third-stage extraction device A3... the nth-stage extraction device A n . The statement "the second extraction unit includes n-stage extraction devices B1 to B n " in the present invention means that the second extraction unit includes a first-stage extraction device B1, a second-stage extraction device B2, a third-stage extraction device B3... the nth-stage extraction device B n . The statement "the third extraction unit includes n-stage extraction devices C1 to C n " in the present invention means that the third extraction unit includes a first-stage extraction device C1, a second-stage extraction device C2, a third-stage extraction device C3... the nth-stage extraction device C nIt should be noted that the value of n in the first extraction unit, the second extraction unit, and the third extraction unit is the same, that is, the number of extraction devices in the three extraction units is the same. The extraction devices described in the present invention include, but are not limited to, extraction kettles, extraction towers, extractors, etc.

[0015] In some embodiments, the extraction device A in the first extraction unit n-1 has a higher extraction pressure than the extraction device A n For example, the extraction pressure in extraction device A1 is higher than that in extraction device A2, and the extraction pressure in extraction device A2 is higher than that in extraction device A3.

[0016] In some embodiments, the extraction device B in the second extraction unit n-1 has a higher extraction pressure than the extraction device B n For example, the extraction pressure in extraction device B1 is higher than that in extraction device B2, and the extraction pressure in extraction device B2 is higher than that in extraction device B3.

[0017] In some embodiments, the extraction device C in the third extraction unit n-1 has a higher extraction pressure than the extraction device C n For example, the extraction pressure in extraction device C1 is higher than that in extraction device C2, and the extraction pressure in extraction device C2 is higher than that in extraction device C3.

[0018] "Loading" as described in the present invention refers to loading materials into the extraction device, "unloading" refers to removing the raffinate phase from the extraction device, and "loading / unloading" refers to "loading" or "unloading". The materials described in the present invention include, but are not limited to, high molecular polymers with a wide molecular weight distribution, such as polyethylene wax, especially high-density polyethylene (HDPE) associated wax.

[0019] According to some embodiments of the present invention, the extraction of extraction devices A1 - A n and the pressure increase of extraction devices B1 - B n and the pressure decrease of extraction devices C1 - C n start simultaneously. For example, the extraction of extraction device A1, the pressure increase of extraction device B1, and the pressure decrease of extraction device C1 start simultaneously, or the extraction of extraction device A2, the pressure increase of extraction device B2, and the pressure decrease of extraction device C2 start simultaneously, or the extraction of extraction device A3, the pressure increase of extraction device B3, and the pressure decrease of extraction device C3 start simultaneously.

[0020] According to some embodiments of the present invention, the extraction of extraction devices B1 - B n and the pressure decrease of extraction devices A1 - A n and the extraction of extraction devices C1 - Cn The boosting starts simultaneously. For example, the extraction of extraction device B1 starts simultaneously with the pressure reduction of extraction device A1 and the boosting of extraction device C1, or the extraction of extraction device B2 starts simultaneously with the pressure reduction of extraction device A2 and the boosting of extraction device C2, or the extraction of extraction device B3 starts simultaneously with the pressure reduction of extraction device A3 and the boosting of extraction device C3.

[0021] According to some embodiments of the present invention, the extraction devices C1 to C n The extraction and extraction devices A1 to A n The boosting and extraction devices B1 to B n The pressure reduction starts simultaneously. For example, the extraction of extraction device C1 starts simultaneously with the boosting of extraction device A1 and the pressure reduction of extraction device B1, or the extraction of extraction device C2 starts simultaneously with the boosting of extraction device A2 and the pressure reduction of extraction device B2, or the extraction of extraction device C3 starts simultaneously with the boosting of extraction device A3 and the pressure reduction of extraction device B3.

[0022] According to some embodiments of the present invention, the extraction devices A1 to A n The extraction and extraction devices B1 to B n The boosting and extraction devices C1 to C n The charging ends simultaneously. For example, the extraction of extraction device A1 ends simultaneously with the boosting of extraction device B1 and the charging of extraction device C1, or the extraction of extraction device A2 ends simultaneously with the boosting of extraction device B2 and the charging of extraction device C2, or the extraction of extraction device A3 ends simultaneously with the boosting of extraction device B3 and the charging of extraction device C3.

[0023] According to some embodiments of the present invention, the extraction devices B1 to B n The extraction and extraction devices C1 to C n The boosting and extraction devices A1 to A n The charging ends simultaneously. For example, the extraction of extraction device B1 ends simultaneously with the boosting of extraction device C1 and the charging of extraction device A1, or the extraction of extraction device B2 ends simultaneously with the boosting of extraction device C2 and the charging of extraction device A2, or the extraction of extraction device B3 ends simultaneously with the boosting of extraction device C3 and the charging of extraction device A3.

[0024] According to some embodiments of the present invention, the extraction devices C1 to C n The extraction and extraction devices A1 to A n The boosting and extraction devices B1 to B n The charging ends simultaneously. For example, the extraction of extraction device C1 ends simultaneously with the boosting of extraction device A1 and the charging of extraction device B1, or the extraction of extraction device C2 ends simultaneously with the boosting of extraction device A2 and the charging of extraction device B2, or the extraction of extraction device C3 ends simultaneously with the boosting of extraction device A3 and the charging of extraction device B3.

[0025] According to some embodiments of the present invention, the pressure increase includes introducing a supercritical CO2 stream into the extraction device after charging is completed to increase the pressure of the extraction device to the extraction pressure.

[0026] According to some embodiments of the present invention, the pressure increase includes connecting the extraction device after charging is completed to the extraction device after extraction is completed, so that the pressure of the extraction device after charging is increased to the same as that of the extraction device after extraction. For example, the pressure increase of extraction device B1 in the present invention can be achieved in the following ways: after charging of extraction device B1 is completed, introducing a supercritical CO2 stream into extraction device B1 to increase the pressure of extraction device B1 to the extraction pressure; or first connecting extraction device B1 and extraction device C1 to reduce the pressure of extraction device C1, while increasing the pressure of extraction device B1 to the same as that of extraction device C1, and then introducing a supercritical CO2 stream into extraction device B1 to increase the pressure of extraction device B1 to the extraction pressure.

[0027] According to some embodiments of the present invention, the pressure reduction includes connecting the extraction device after extraction is completed to the extraction device after charging is completed, so that the pressure of the extraction device after extraction is reduced to the same as that of the extraction device after charging, and the step of further reducing the pressure of the extraction device after extraction to 0. For example, the pressure reduction of extraction device A1 in the present invention can be achieved in the following ways: after extraction of extraction device B1 is completed, first connecting extraction device A1 and extraction device C1 to reduce the pressure of extraction device A1, while increasing the pressure of extraction device C1 to the same as that of extraction device A1, and then venting extraction device A1 to further reduce the pressure to 0.

[0028] According to some embodiments of the present invention, when extracting with extraction devices A1 to A n During extraction, connect extraction device C n and extraction device B n to communicate, so that extraction device C n reduces pressure, and extraction device B n increases pressure to the same as that of extraction device C n For example, when extracting with extraction devices A1 to A2, connect extraction device C1 and extraction device B1 to reduce the pressure of extraction device C1, and increase the pressure of extraction device B1 to the same as that of extraction device C1. At the same time, connect extraction device C2 and extraction device B2 to reduce the pressure of extraction device C2, and increase the pressure of extraction device B2 to the same as that of extraction device C2.

[0029] According to some embodiments of the present invention, when extracting with extraction devices B1 to B n During extraction, connect extraction device A n and extraction device C n to communicate, so that extraction device A n reduces pressure, and extraction device C n increases pressure to the same as that of extraction device A nThe pressures are the same. For example, when the extraction device B 11 ~B2 is performing extraction, the extraction device A1 and the extraction device C1 are connected, so that the extraction device A1 reduces pressure, and the extraction device C1 increases pressure to the same pressure as the extraction device A1. At the same time, the extraction device A2 and the extraction device C2 are connected, so that the extraction device A2 reduces pressure, and the extraction device C2 increases pressure to the same pressure as the extraction device A2.

[0030] According to some embodiments of the present invention, when the extraction devices C1~C n are performing extraction, the extraction device B n and the extraction device A n are connected, so that the extraction device B n reduces pressure, and the extraction device A n increases pressure to the same pressure as the extraction device B n . For example, when the extraction devices C1~C2 are performing extraction, the extraction device B1 and the extraction device A1 are connected, so that the extraction device B1 reduces pressure, and the extraction device A1 increases pressure to the same pressure as the extraction device B1. At the same time, the extraction device B2 and the extraction device A2 are connected, so that the extraction device B2 reduces pressure, and the extraction device A2 increases pressure to the same pressure as the extraction device B2.

[0031] According to some embodiments of the present invention, the method includes the following steps:

[0032] (1) Load materials into the extraction device A1, and introduce supercritical CO2 into the extraction devices A1~A n , so that the extraction device A1 increases pressure to the extraction pressure P1, and the extraction device A n-1 increases pressure to the extraction pressure P n-1 , the extraction device A n increases pressure to the extraction pressure P n , where P n <P n-1 ≤P1; at the end of the pressure increase of the extraction device A1, the extraction device B1 starts to load materials, so that the pressure increase of the extraction device A1 and the loading of the extraction device B1 end at the same time;

[0033] (2) The extraction device A1 performs extraction, and at the same time, the extraction phase in the extraction device A n-1 enters the extraction device A n along with the supercritical CO2, the extraction device A n performs extraction, and supercritical CO2 is introduced into the extraction devices B1~B n , so that the extraction device B1 increases pressure to the extraction pressure P1, and the extraction device B n-1 increases pressure to the extraction pressure P n-1 , the extraction device B n increases pressure to the extraction pressure P n , in the extraction devices A1~A nAt the end of extraction and / or extraction apparatuses B1 - B n At the end of pressure increase, extraction apparatus C1 starts charging, and makes extraction apparatuses A1 - A n Extract, extraction apparatuses B1 - B n Pressure increase, charging of extraction apparatus C1 end simultaneously;

[0034] (3) Extraction apparatus B1 performs extraction, and meanwhile the extraction phase in extraction apparatus B n-1 enters extraction apparatus B with supercritical CO2 n , extraction apparatus B n performs extraction, connects extraction apparatuses A n and C n to make extraction apparatus A n reduce pressure, and meanwhile extraction apparatus C n increases pressure to the same pressure as extraction apparatus A n ;

[0035] (4) Supercritical CO2 is introduced into extraction apparatuses C1 - C n to make extraction apparatus C1 increase pressure to extraction pressure P1, extraction apparatus C n-1 increases pressure to extraction pressure P n-1 , extraction apparatus C n increases pressure to extraction pressure P n , and meanwhile extraction apparatuses A1 - A n continue to reduce pressure to 0, then discharge materials and reload materials into extraction apparatus A1, so that the charging of extraction apparatus A1, the extraction of extraction apparatuses B1 - B n and the pressure increase of extraction apparatuses C1 - C n end simultaneously;

[0036] (5) Extraction apparatus C1 performs extraction, and meanwhile the extraction phase in extraction apparatus C n-1 enters extraction apparatus C with supercritical CO2 n , extraction apparatus C n performs extraction, connects extraction apparatuses B n and A n to make extraction apparatus B n reduce pressure, and meanwhile extraction apparatus A n increases pressure to the same pressure as extraction apparatus B n ;

[0037] (6) Supercritical CO2 is introduced into extraction apparatuses A1 - A n to make extraction apparatus A1 increase pressure to extraction pressure P1, extraction apparatus A n-1 increases pressure to extraction pressure P n-1 , extraction apparatus A n increases pressure to extraction pressure P n , and meanwhile extraction apparatuses B1 - B nContinue to reduce the pressure to 0, then unload the material and reload it into the extraction device B1, so that the extraction devices A1 - A n Increase the pressure, load the extraction device B1, and the extraction devices C1 - C n The extraction ends simultaneously;

[0038] (7) The extraction device A1 performs extraction, and at the same time, the extraction phase in the extraction device A n-1 enters the extraction device A along with supercritical CO2, and the extraction device A n performs extraction. Connect the extraction devices B n and C n to make the extraction device C n reduce the pressure, and at the same time, the extraction device B n increases the pressure to the same pressure as the extraction device C n ; n The pressure is the same;

[0039] (8) Introduce supercritical CO2 into the extraction devices B1 - B n to increase the pressure of the extraction device B1 to the extraction pressure P1, and increase the pressure of the extraction device B n to the extraction pressure P n , and the extraction devices C1 - C n continue to reduce the pressure to 0, then unload the material and reload it into the extraction device C1, so that the extraction devices A1 - A n perform extraction, the extraction devices B1 - B n increase the pressure, and the loading of the extraction device C1 ends simultaneously;

[0040] (9) The same as step (3); and so on in a cycle.

[0041] In some embodiments, the material includes polyethylene wax.

[0042] According to some embodiments of the present invention, the flow rate of the supercritical CO2 is 250 L / h - 600 L / h, preferably 300 L / h - 400 L / h.

[0043] According to some embodiments of the present invention, the extraction pressure in the extraction device is 7.39 MPa - 45 MPa, such as 8 MPa, 10 MPa, 12 MPa, 15 MPa, 20 MPa, 25 MPa, 30 MPa, 35 MPa, 40 MPa or 45 MPa.

[0044] According to some embodiments of the present invention, the extraction temperature in the extraction device is 31.1 °C - 90 °C, such as 32 °C, 35 °C, 40 °C, 45 °C, 50 °C, 55 °C, 60 °C, 65 °C, 70 °C, 75 °C, 80 °C, 85 °C or 90 °C.

[0045] In a second aspect, the present invention provides the application of the method described in the first aspect in separating high molecular polymers.

[0046] According to some embodiments of the present invention, the polymer is polyethylene wax.

[0047] According to some embodiments of the present invention, the polymer is high-density polyethylene associated wax.

[0048] According to some embodiments of the present invention, the application includes loading a material containing polyethylene wax into the extraction device.

[0049] The beneficial effects of the present invention are as follows: (1) By using multiple extraction units in combination, the extraction process in one extraction unit and the processes such as loading / unloading, pressure boosting, and pressure reducing in other extraction units are carried out simultaneously, and the extraction steps are alternated in different extraction units, so that the extraction operation can be uninterrupted in the whole separation process, and the extraction efficiency is high; (2) By connecting two extraction devices in different extraction units, the pressure reduction in one extraction device is used for the pressure boosting of another extraction device, so that the full utilization of CO2 can be realized, and resources and costs can be saved. (3) Each extraction unit is provided with a multi-stage extraction device. By virtue of the solubility difference of supercritical CO2 under different conditions for polymers with different molecular weights (such as polyethylene wax), multi-stage extraction is carried out to effectively separate the components in different molecular weight ranges in the polymer. (4) The extraction and separation conditions are mild, the process is simple and easy to operate, the separation efficiency is high, and the obtained product has high purity. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 It is a process flow diagram of a six-kettle combined supercritical CO2 secondary extraction and separation according to an embodiment of the present invention. Among them, 1, 2, and 3 represent the compressor pressure boosting valves, 4, 5, 6, 7, 8, and 9 represent the equalizing valves between the extraction kettles, 10, 11, and 12 represent the connection valves between the extraction kettles and the separator, 13, 14, 15, 16, 17, and 18 represent the extraction kettle vent valves, 19, 20, and 21 represent the connection valves between the extraction kettles, 22, 23, 24, 25, 26, and 27 represent the connection valves between the extraction kettles and the CO2 recovery tank, 28 represents the CO2 recovery tank vent valve, and 29 represents the separator vent valve.

[0051] Figure 2It is a process flow diagram of a nine-kettle combined supercritical CO2 three-stage extraction and separation according to an embodiment of the present invention. Among them, 1, 2, and 3 represent the compressor boost valves, 4, 5, 6, 7, 8, 9, 10, 11, and 12 represent the equalizing valves between the extraction kettles, 13, 14, and 15 represent the connection valves between the extraction kettles and the separator, 16, 17, 18, 19, 20, 21, 22, 23, and 24 represent the extraction kettle vent valves, 25 represents the CO2 recovery tank vent valve, 26 represents the separator vent valve, 27, 28, 29, 30, 31, and 32 represent the connection valves between the extraction kettles, and 33, 34, 35, 36, 37, 38, 39, 40, and 41 represent the connection valves between the extraction kettles and the CO2 recovery tank. Detailed Embodiments

[0052] To make the objectives, technical solutions, and advantages of the present invention more clearly understood, the present invention will be further described in detail below in conjunction with embodiments and the accompanying drawings. These embodiments and the drawings are only used to explain the present invention and do not constitute any limitation to the present invention. The actual protection scope of the present invention is set forth in the claims.

[0053] It should be noted that in the present invention Figure 1 the "boost valve" refers to the valve connecting the compressor and the extraction device. Opening this valve allows the supercritical CO2 fluid introduced through the compressor to enter the extraction device, realizing the boosting of the extraction device. The "equalizing valve" refers to the valve connecting two extraction devices. Opening this valve allows one extraction device to depressurize and the other extraction device to pressurize, making the pressures of the two connected extraction devices the same, that is, realizing "equalizing pressure". The "vent valve" refers to a common valve that can vent pressurized gas or liquid in a non-working state. For example, after the extraction device finishes the extraction and / or equalizing pressure reduction operation, opening the vent valve connected to the extraction device can directly and completely vent the pressure in the extraction device. In the present invention, the above valves can all adopt conventional valves in the art and are not specifically limited here.

[0054] It should be noted that the "equalizing pressure" in the present invention means connecting two extraction kettles through an equalizing valve, using the pressure reduction of supercritical CO2 in one extraction kettle to boost the supercritical CO2 in the other extraction kettle, making the pressures of the two connected extraction kettles the same. For example, connecting extraction kettle A and extraction kettle C, allowing the supercritical CO2 flow in extraction kettle A to enter extraction kettle C, thereby realizing the pressure reduction of extraction kettle A and the pressure boost of extraction kettle C until the pressures in extraction kettle A and extraction kettle C are the same. At this time, the pressure reduction of extraction kettle A is called "equalizing pressure reduction", and the pressure boost of extraction kettle C is called "equalizing pressure boost".

[0055] The present invention provides a method for multi-stage extraction and separation of supercritical carbon dioxide. The method includes charging, boosting pressure, extraction, depressurizing, and discharging using at least three extraction units and at least one separation column. Each extraction unit includes a multi-stage extraction device, and the extraction temperature and / or extraction pressure in each stage of the extraction device are different. When one extraction unit is performing extraction, at least one extraction unit is boosting pressure, and at the same time, at least one extraction unit is depressurizing and / or loading / unloading materials.

[0056] In the present invention, the number of the at least three extraction units is preferably 3n, where n is a positive integer. For example, the number of the extraction units can be 3, 6, 9, or 12, and more preferably 3.

[0057] In the present invention, the multi-stage extraction device in the extraction unit is preferably a 2-6 stage extraction device, such as 2 stages, 3 stages, 4 stages, 5 stages, or 6 stages.

[0058] As a specific embodiment of the present invention, the method includes using three first-stage extraction kettles (high-pressure extraction kettles A, B, and C), three second-stage extraction kettles (medium-pressure extraction kettles A′, B′, and C′), one separator, and one CO2 recovery tank for loading / unloading materials, boosting pressure, extraction, and depressurizing. The process flow of the supercritical CO2 two-stage continuous extraction and separation using these six kettles in combination is as Figure 1 shown. During the extraction operation process, first-stage extraction kettle A and second-stage extraction kettle A′ are continuous, first-stage extraction kettle B and second-stage extraction kettle B′ are continuous, and first-stage extraction kettle C and second-stage extraction kettle C′ are continuous. The extraction and separation process is divided into 6 steps: 1 loading / unloading materials, 2 equalizing pressure and boosting pressure, 3 boosting pressure by a compressor, 4 extraction, 5 equalizing pressure and depressurizing, 6 depressurizing to 0. The step operations of each extraction kettle are shown in Table 1.

[0059] Table 1

[0060]

[0061]

[0062] When extraction kettles A and A′ are performing extraction, extraction kettles B and B′ are boosting pressure, and at the same time, extraction kettles C and C′ are loading materials and / or depressurizing; when extraction kettles B and B′ are performing extraction, extraction kettles C and C′ are boosting pressure, and at the same time, extraction kettles A and A′ are depressurizing and / or loading materials; when extraction kettles C and C′ are performing extraction, extraction kettles A and A′ are boosting pressure, and at the same time, extraction kettles B and B′ are depressurizing and / or loading materials.

[0063] Preferably, the operation of the supercritical CO2 continuous extraction and separation using the above six kettles in combination is as follows:

[0064] When the device is turned on for the first time, after loading the polyethylene wax material into the first-stage extraction kettle A (step 1), open the pressure boosting valve 1, connection valve 19, and connection valve 10, and use the compressor to compress the continuous supercritical CO2 stream to the operating pressure of extraction kettle A (step 3. Since kettle B has not started running at this time, equalization cannot be carried out yet) and introduce it into extraction kettle A. At this time, the second-stage extraction kettle A' is connected to the first-stage extraction kettle A, the second-stage extraction kettle A' is connected to the separator, and the pressure value of the second-stage extraction kettle A' is controlled to be at a certain specific pressure lower than that of the first-stage extraction kettle A, and the pressure value of the separation kettle is controlled to be at a certain specific pressure lower than that of the second-stage extraction kettle A'. At the end of the pressure boosting of the first-stage extraction kettle A, kettle B starts to be loaded (step 1), and the pressure boosting of kettle A and the loading of kettle B are completed simultaneously. Immediately afterwards, kettle A starts extraction. At this time, the polyethylene wax components that can be dissolved by high-pressure supercritical CO2 in the first-stage extraction kettle A are extracted into the second-stage extraction kettle A', and the polyethylene wax components with higher molecular weights are left in kettle A and finally flow out from the vent valve 13 of kettle A; among the polyethylene components entering the second-stage extraction kettle A', the components with relatively lower molecular weights that can be dissolved by medium-pressure supercritical CO2 are further extracted into the separator and continuously flow out from the separator. The polyethylene wax components left in the second-stage extraction kettle A' have a higher molecular weight than those flowing out of the separation kettle but lower than the molecular weight of the polyethylene wax components left in the first-stage extraction kettle A (step 4). At the same time, open the pressure boosting valve 2, and the compressor compresses the continuous supercritical CO2 stream to start the pressure boosting of the first-stage extraction kettle B (step 3). At the end of the extraction of kettles A and A' and the pressure boosting of kettles B and B', the first-stage extraction kettle C starts to be loaded (step 1). The extraction of kettles A and A' and the pressure boosting of kettles B and B' and the loading of kettle C end simultaneously. Immediately afterwards, kettles A and A' start to depressurize, and kettles B and B' start to extract (step 4. The extraction processes in kettles B and B' are the same as those in kettles A and A'), and kettles C and C' start to boost pressure. At this time, close the connection valves 19, 20, and 21 between the first-stage extraction kettle and the second-stage extraction kettle, and close the connection valves 10, 11, and 12 between the second-stage extraction kettle and the separator. By opening the equalization valves 5 between kettle A and kettle C and the equalization valves 8 between A' and C', depressurize kettles A and A' (step 5) while simultaneously boosting the pressure of kettles C and C' (step 2). When the pressures of kettles A and C and kettles A' and C' are the same, close the equalization valves 5 and 8, and the equalization depressurization of kettles A and A' and the equalization pressure boosting of kettles C and C' end synchronously. Open the connection valves 22 and 23 between the extraction kettles A and A' and the CO2 recovery tank to continue depressurizing kettles A and A' (step 6). At the same time, open the pressure boosting valve 3, and the compressor compresses the continuous supercritical CO2 stream to continue boosting the pressure of kettles C and C' to the extraction pressure (step 3). When the pressures of kettles A and A' and the CO2 recovery tank are the same, close the connection valve between them, open the vent valves 13 and 16 of kettles A and A', completely vent their pressures, and after depressurizing to 0, start unloading the extraction kettles A and A' and reload them (step 1).The charging of kettle A (step 1), the extraction in kettles B and B' (step 4), and the pressure increase in kettles C and C' (step 3) are completed synchronously. Immediately afterwards, the pressure equalizing valves 4 between kettle B and kettle A and the pressure equalizing valves 7 between kettle B' and kettle A' are opened, so that the pressure in kettles B and B' decreases (step 5), the pressure in kettles A and A' increases (step 2), and at the same time, the extraction starts in kettles C and C' (step 4, and the extraction process in kettles C and C' is the same as that in kettles A and A'). After the pressure equalization is completed, the pressure equalizing valves between A and B, A' and B' are closed, and the pressure in kettles B and B' continues to decrease (step 6), while the pressure in kettles A and A' starts to increase by the compressor (step 3). When the pressure in kettles B and B' decreases to 0, kettle B starts to discharge and charge (step 1). The pressure increase of kettles A and A' by the compressor (step 3), the charging of kettle B (step 1), and the extraction in kettles C and C' (step 4) are completed synchronously. At this time, kettles A and A' enter the extraction process (step 4), while kettles B and C, B' and C' achieve pressure equalization through the pressure equalizing valves 6 and 9. After the pressure equalization ends, the pressure in kettles B and B' continues to increase by compression (step 3), the pressure in kettles C and C' continues to decrease (step 6), and kettle C discharges and charges (step 1). The extraction in kettles A and A', the pressure increase in kettles B and B', and the charging of kettle C are completed synchronously, and then the extraction in kettles B and B' (step 4) and the pressure equalization between kettles A and C, A' and C' follow, and so on in a cycle. Finally, the relative molecular weight ranges of the polyethylene wax components separated from the primary extraction kettle, the secondary extraction kettle, and the separator are different.

[0065] As another specific embodiment of the present invention, the method includes using three primary extraction kettles (high-pressure extraction kettles A, B, and C), three secondary extraction kettles (medium-pressure extraction kettles A', B', and C'), three tertiary extraction kettles (low-pressure extraction kettles A'', B'', and C''), a separator, and a CO2 recovery tank for loading / unloading, pressure increase, extraction, and pressure decrease. The process flow of the supercritical CO2 three-stage continuous extraction and separation using nine kettles in combination is as Figure 2 shown. During the extraction operation process, primary extraction kettle A, secondary extraction kettle A', and tertiary extraction kettle A'' are continuous, primary extraction kettle B, secondary extraction kettle B', and tertiary extraction kettle B'' are continuous, and primary extraction kettle C, secondary extraction kettle C', and tertiary extraction kettle C'' are continuous. The extraction and separation process is the same as the supercritical CO2 two-stage continuous extraction and separation process using six kettles in combination described above, and it is also divided into 6 steps: 1 loading / unloading, 2 pressure equalization and pressure increase, 3 pressure increase by the compressor, 4 extraction, 5 pressure equalization and pressure decrease, 6 pressure decrease to 0. The step operations of each extraction kettle are shown in Table 2.

[0066] Table 2

[0067]

[0068] The difference between the supercritical CO2 three-stage continuous extraction and separation method using nine reactors and the above-mentioned supercritical CO2 two-stage continuous extraction and separation method using six reactors is that before the extraction starts, the pressure value of the third-stage extraction reactor A″ is controlled to be at a specific pressure lower than that of the second-stage extraction reactor A′, the pressure value of the second-stage extraction reactor A′ is controlled to be at a specific pressure lower than that of the first-stage extraction reactor A, and the pressure value of the separation reactor is controlled to be at a specific pressure lower than that of the third-stage extraction reactor A″. When the first-stage extraction reactor A starts extraction (step sequence 4), the polyethylene wax components that can be dissolved by high-pressure supercritical CO2 in the first-stage extraction reactor A are extracted into the second-stage extraction reactor A′, and the polyethylene wax components with higher molecular weights are left in reactor A. Then, the components in the polyethylene components of the second-stage extraction reactor A′ that can be dissolved by medium-pressure supercritical CO2 are extracted into the third-stage extraction reactor A″, and the polyethylene wax components with the second-highest molecular weights are left in reactor A′. Next, the components in the polyethylene components of the third-stage extraction reactor A″ that can be dissolved by low-pressure supercritical CO2 are extracted into the separator and continuously flow out from the separator. The polyethylene wax components left in the third-stage extraction reactor A″ have a higher relative molecular weight than those flowing out of the separator but lower than those in the second-stage extraction reactor A′. The polyethylene wax components left in the second-stage extraction reactor A′ have a lower relative molecular weight than those left in the first-stage extraction reactor A. Similarly, the extraction processes in the three extraction reactors (reactor B, reactor B′, and reactor B″) in the second extraction unit are the same as those in the three extraction reactors (reactor A, reactor A′, and reactor A″) in the first extraction unit; the extraction processes in the three extraction reactors (reactor C, reactor C′, and reactor C″) in the third extraction unit are also the same as those in the three extraction reactors (reactor A, reactor A′, and reactor A″) in the first extraction unit. Finally, the relative molecular weight ranges of the polyethylene wax components separated from the first-stage extraction reactor, the second-stage extraction reactor, the third-stage extraction reactor, and the separator are different from each other.

[0069] Example 1

[0070] This example provides a supercritical CO2 two-stage continuous extraction and separation method using six reactors, which includes using three first-stage extraction reactors (A, B, and C), three second-stage extraction reactors (A′, B′, and C′), a separator, and a CO2 recovery tank for loading / unloading, pressure boosting, extraction, and pressure reduction. The material used is high-density polyethylene associated wax, and the specific operations of extraction and separation are as follows:

[0071] Load 15 kg of materials into extraction kettle A. The high-pressure pump continuously feeds CO2 into extraction kettle A and starts to boost the pressure. Set the extraction conditions for extraction kettle A as: 30 MPa, 65 °C, 300 L / h. At this time, both ends of extraction kettle A′ are connected to the separator and extraction kettle A respectively, and extraction kettle A′ starts to boost the pressure. Set the extraction conditions for extraction kettle A′ as: 15 MPa, 65 °C, the temperature in the separator is 60 °C, and the pressure is 6 MPa. At the end stage of the pressure boost in kettle A and kettle A′, load 15 kg of materials into extraction kettle B. The pressure boost in kettle A and kettle A′ and the loading of materials in kettle B are completed simultaneously. When the extraction kettle and the separation kettle reach the set conditions, open the separator valve. Kettle A starts to extract. At this time, the components that can be dissolved by high-pressure supercritical CO2 in the first-stage extraction kettle A are extracted into the medium-pressure extraction kettle A′. The components with higher molecular weights are left in kettle A. Among the components that enter the medium-pressure extraction kettle A′, the components with relatively lower molecular weights that can be dissolved by medium-pressure supercritical CO2 are further extracted into the separator and continuously flow out from the separator. Liquid CO2 continuously flows out from the separator (this part of CO2 is purified by the recovery system and recycled). At the same time, kettles B and B′ are in the stage of compressor pressure boost (30 MPa, 65 °C, 300 L / h). At the end stage of the extraction in kettle A and kettle A′ and the pressure boost in kettle B and kettle B′, load 15 kg of materials into extraction kettle C. The extraction in kettle A and kettle A′, the pressure boost in kettle B and kettle B′, and the loading of materials in kettle C are completed simultaneously. Open the pressure equalizing valve between the extraction kettle A that has completed extraction and extraction kettle C to reduce the pressure of kettle A and simultaneously boost the pressure of kettle C. At the same time, connect extraction kettle B to the separator, and kettles B and B′ extract. When the pressures of kettles A and C are the same (about 15 MPa), close the pressure equalizing valve between A and C, open the connection valve between extraction kettle A and the CO2 recovery tank (the temperature of the recovery tank is room temperature, and the pressure is about MPa. This CO2 is purified and recycled), so that kettle A continues to reduce the pressure. At the same time, kettle C continues to be boosted by the high-pressure pump (30 MPa, 65 °C, 300 L / h). When the pressures of kettle A, kettle A′ and the CO2 recovery tank are the same, close the connection valves between them, open the vent valves of kettle A and kettle A′, and completely vent and reduce the pressure to 0, then start unloading and reload materials into kettle A. The loading of materials into kettle A, the extraction in kettles B and B′ (3 hours), and the pressure boost in kettle C are completed synchronously. Open the pressure equalizing valves between kettle B and kettle A to reduce the pressure of kettle B and boost the pressure of kettle A. Open the pressure equalizing valves between kettle B′ and kettle A′ to reduce the pressure of kettle B′ and boost the pressure of kettle A′. At the same time, kettles C and C′ extract. After the pressure equalization is completed, close the pressure equalizing valves between A and B and between A′ and B′. Kettles B and B′ continue to reduce the pressure, and kettles A and A′ start to be boosted by the compressor. When the pressures of kettles B and B′ are reduced to 0, start unloading and loading materials. The compressor pressure boost in kettles A and A′, the loading of materials in kettles B and B′, and the extraction in kettles C and C′ (3 hours) are completed synchronously. Kettles A and A′ enter the extraction process again, while kettles B and C achieve pressure equalization through the pressure equalizing valve, and kettles B′ and C′ achieve pressure equalization through the pressure equalizing valve. After the pressure equalization is completed, kettles B and B′ continue to be compressed and boosted, and kettles C and C′ continue to reduce the pressure, unload and reload materials.The extraction in kettle A and A' (3 hours), the pressure increase in kettle B and B', and the charging in kettle C are completed synchronously. Immediately afterwards, it enters the extraction in kettle B and B' again, the pressure equalization in kettle A and kettle C, and the pressure equalization in kettle A' and kettle C' again, and so on in a cycle.

[0072] Sampling and analysis are carried out. Gel permeation chromatography is used to detect the molecular weight range of the products separated by each extraction kettle, and the molecular weight of the products is determined by comparing with the molecular weight standard (polystyrene): the molecular weight of the components flowing out after extraction and separation in the first-stage extraction kettles A, B, and C is about 1500 or more, the molecular weight of the components flowing out after extraction and separation in the second-stage extraction kettles A', B', and C' is about 1000 - 1500, and the molecular weight of the components flowing out in the separator is about 1000 or less.

[0073] Example 2

[0074] This example provides a method for supercritical CO2 three-stage continuous extraction and separation using nine kettles in combination. The material used is high-density polyethylene associated wax, and the extraction process is as Figure 2 shown.

[0075] Among them, the mass of the materials loaded in the first-stage extraction kettles A, B, and C is 15 kg, the carbon dioxide flow rate is 300 L / h, and the extraction conditions are: 40 MPa, 65 °C, 300 L / h; the extraction conditions in the second-stage extraction kettles A', B', and C' are: 30 MPa, 65 °C; the extraction conditions in the third-stage extraction kettles A'', B'', and C'' are: 20 MPa, 65 °C.

[0076] Sampling and analysis are carried out. Gel permeation chromatography is used to detect the molecular weight range of the products separated by each extraction kettle, and the molecular weight of the products is determined by comparing with the molecular weight standard (polystyrene): the molecular weight of the components flowing out after extraction and separation in the first-stage extraction kettles A, B, and C is about 2200 or more, the molecular weight range of the components flowing out after extraction and separation in the second-stage extraction kettles A', B', and C' is about 1500 - 2200, the molecular weight of the components flowing out after extraction and separation in the third-stage extraction kettles A'', B'', and C'' is about 1200 - 1500, and the molecular weight of the components flowing out in the separator is about 1200 or less.

[0077] The technical solution of the present invention is not limited to the limitations of the above specific embodiments. Any technical deformation made according to the technical solution of the present invention falls within the protection scope of the present invention.

Claims

1. A supercritical carbon dioxide multi-stage extraction and separation method, the method comprising charging, boosting pressure, extraction, reducing pressure and discharging by using at least three extraction units and at least one separation column, each extraction unit comprising a multi-stage extraction device and the extraction temperature and / or extraction pressure in each stage of the extraction device being different. When one of the extraction units is performing extraction, at least one extraction unit is boosting pressure, and at the same time at least one extraction unit is reducing pressure and / or loading / unloading.

2. The method according to claim 1, characterized in that The three extraction units include a first extraction unit, a second extraction unit, and a third extraction unit. The first extraction unit includes n-stage extraction devices A1 to A n , the second extraction unit includes n-stage extraction devices B1 to B n , and the third extraction unit includes n-stage extraction devices C1 to C n . wherein, n is an integer greater than or equal to 2; When the first extraction unit is extracting, the second extraction unit is boosting pressure, and at the same time the third extraction unit is loading / unloading materials and / or reducing pressure; when the second extraction unit is extracting, the third extraction unit is boosting pressure, and at the same time the first extraction unit is reducing pressure and / or loading / unloading materials; when the third extraction unit is extracting, the first extraction unit is boosting pressure, and at the same time the second extraction unit is reducing pressure and / or loading / unloading materials.

3. The method according to claim 2, characterized in that The extraction device A in the first extraction unit n-1 has a higher extraction pressure than that of the extraction device A n ; and / or the extraction device B in the second extraction unit n-1 has a higher extraction pressure than that of the extraction device B n ; and / or the extraction device C in the third extraction unit n-1 has a higher extraction pressure than that of the extraction device C n in it.

4. The method according to claim 2, characterized in that The extraction device A1 - A n Extraction and extraction device B1 - B n Boost pressure and extraction device C1 - C n The pressure reduction starts simultaneously; and / or The extraction device B1 - B n Extraction and extraction device A1 - A n Step - down and extraction device C1 - C n The step - up starts simultaneously; and / or The extraction device C1 - C n Extraction and extraction device A1 - A n Boost pressure and extraction device B1 - B n The pressure reduction starts simultaneously; and / or The extraction device A1 to A n Extraction and extraction device B1 to B n Pressure boosting and extraction device C1 to C n The charging ends simultaneously; and / or The extraction devices B1 - B n Extraction and extraction devices C1 - C n Pressure boosting and extraction devices A1 - A n The charging ends simultaneously; and / or The extraction device C1 - C n Extraction and extraction device A1 - A n Boost pressure and extraction device B1 - B n The charging ends simultaneously.

5. The method according to any one of claims 1 to 4, characterized in that The pressure boosting includes introducing supercritical CO2 flow into the extraction device that has finished loading to boost the pressure of the extraction device to the extraction pressure, and / or connecting the extraction device that has finished loading with the extraction device that has finished extraction to boost the pressure of the extraction device that has finished loading to the same pressure as the extraction device that has finished extraction.

6. The method according to any one of claims 1 to 4, characterized in that The pressure reduction includes connecting the extraction device that has finished extraction with the extraction device that has finished loading to reduce the pressure of the extraction device that has finished extraction to the same pressure as the extraction device that has finished loading, and the step of continuously reducing the pressure of the extraction device that has finished extraction to 0.

7. The method according to claim 2, characterized in that When the extraction devices A1 to A n are extracting, connect the extraction device C n and the extraction device B n to make the extraction device C n reduce pressure, and raise the pressure of the extraction device B n to the same pressure as that of the extraction device C n ; and / or when the extraction device B1 - B n is extracting, connect the extraction device A n and the extraction device C n so that the extraction device A n reduces pressure, and the extraction device C n increases pressure to the same as that of the extraction device A n pressure; and / or when the extraction devices C1 to C n are extracting, connect the extraction device B n and the extraction device A n so that the extraction device B n is depressurized and the extraction device A n is pressurized to the same pressure as the extraction device B n for extraction.

8. The method according to claim 2, characterized in that The method includes the following steps: (1) Load materials into the extraction device A1, and introduce supercritical CO2 into the extraction devices A1 to A n to increase the pressure of the extraction device A1 to the extraction pressure P1. The extraction device A n-1 is pressurized to the extraction pressure P n-1 , and the extraction device A n is pressurized to the extraction pressure P n , where P n < P n-1 ≤ P1; at the end of the pressure increase of the extraction device A1, the extraction device B1 starts to load materials, so that the pressure increase of the extraction device A1 and the loading of the extraction device B1 end simultaneously; (2) The extraction device A1 performs extraction, and at the same time, the extraction phase in the extraction device A n-1 enters the extraction device A along with supercritical CO2 n , and the extraction device A n performs extraction. Supercritical CO2 is introduced into the extraction devices B1 - B n to increase the pressure of the extraction device B1 to the extraction pressure P1, and the extraction device B n-1 is pressurized to the extraction pressure P n-1 , and the extraction device B n is pressurized to the extraction pressure P n . At the end of the extraction in the extraction devices A1 - A n and / or at the end of the pressurization in the extraction devices B1 - B n , the extraction device C1 starts to be loaded, and the extraction in the extraction devices A1 - A n , the pressurization in the extraction devices B1 - B n and the loading of the extraction device C1 end simultaneously; (3) The extraction device B1 performs extraction, and at the same time, the extraction phase in the extraction device B n-1 enters the extraction device B along with supercritical CO2 n , and the extraction device B n performs extraction, connects the extraction devices A n and C n to make the extraction device A n reduce pressure, and at the same time, the extraction device C n increases pressure to the same as that of the extraction device A n ; (4) Feed supercritical CO2 into extraction apparatuses C1 to C n to increase the pressure of extraction apparatus C1 to the extraction pressure P1, and increase the pressure of extraction apparatus C n-1 to the extraction pressure P n-1 , and increase the pressure of extraction apparatus C n to the extraction pressure P n , and at the same time, continue to reduce the pressure of extraction apparatuses A1 to A to 0, then unload the materials and refill extraction apparatus A1. Then, the loading of extraction apparatus A1, the extraction of extraction apparatuses B1 to B n , and the pressure increase of extraction apparatuses C1 to C n are ended simultaneously; n ​ (5) The extraction device C1 performs extraction, and at the same time, the extraction phase in the extraction device C n-1 enters the extraction device C along with supercritical CO2 n , and the extraction device C n performs extraction. Connect the extraction devices B n and A n to make the extraction device B n reduce pressure, and at the same time, the extraction device A n increases pressure to the same pressure as the extraction device B n ; (6) Feed supercritical CO2 into extraction apparatuses A1 to A n to increase the pressure of extraction apparatus A1 to the extraction pressure P1. Increase the pressure of extraction apparatus A n-1 to the extraction pressure P n-1 , and increase the pressure of extraction apparatus A n to the extraction pressure P n . At the same time, continue to reduce the pressure of extraction apparatuses B1 to B to 0, then unload the materials and refill extraction apparatus B1. Then increase the pressure of extraction apparatuses A1 to A n , refill extraction apparatus B1, and extract extraction apparatuses C1 to C n simultaneously until the extraction ends; n ​ (7) The extraction device A1 performs extraction, and at the same time, the extraction phase in the extraction device A n-1 enters the extraction device A along with supercritical CO2 n , and the extraction device A n performs extraction, connects the extraction devices B n and C n , reduces the pressure of the extraction device C n , and at the same time, increases the pressure of the extraction device B n to the same pressure as that of the extraction device C n ; (8) Feed supercritical CO2 into extraction apparatuses B1 to B n to raise the pressure of extraction apparatus B1 to the extraction pressure P1, and raise the pressure of extraction apparatus B n to the extraction pressure P n , and for extraction apparatuses C1 to C n continue to reduce the pressure to 0, then unload the materials and reload the materials into extraction apparatus C1, and end the extraction of extraction apparatuses A1 to A n , the pressure increase of extraction apparatuses B1 to B n , and the loading of extraction apparatus C1 at the same time.

9. The method according to claim 8, characterized in that The material includes polyethylene wax.

10. The method according to any one of claims 1 to 4, characterized in that, The flow rate of the supercritical CO2 is 250 L / h to 600 L / h; and / or the extraction pressure in the extraction device is 7.39 MPa to 45 MPa, and the extraction temperature in the extraction device is 31.1 °C to 90 °C.

11. The method according to claim 10, characterized in that, The flow rate of the supercritical CO2 is 300 L / h to 400 L / h.

12. Use of the method according to any one of claims 1 to 11 in separating high molecular polymers.

13. The use according to claim 12, characterized in that, The high molecular polymer is polyethylene wax.

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