Solvent and extraction agent separation method in ultra-high molecular weight polyethylene dissolving and forming

Abstract

The invention discloses a method for separating and purifying a mixture of a solvent and an extracting agent in the dissolving and forming process of ultra-high molecular weight polyethylene, which comprises the following steps of: primarily separating the mixture of the solvent and the extracting agent in a solvent-extracting agent mixture crude separation device to respectively obtain a colored crude solvent and the extracting agent; the separated colored crude solvent enters a decolorizing device for decolorizing and impurity removal to obtain a decolorized crude solvent; the decolorized crude solvent enters a solvent-extractant mixture fine separation device to further separate the extractant in the solvent, and the obtained qualified solvent and the qualified extractant are respectively reused for a production line; impurities adsorbed in the decolorizing agent in the decolorizing device are eluted out through the regenerant to regenerate the decolorizing agent, the regenerant and the impurities in the eluted mixture are separated through the regenerant separation device, and the obtained regenerant is used for recycling the decolorizing agent. The method has the advantages of low generation amount of hazardous wastes, low solvent loss, and high and stable purity of the extracted solvent.

Description

Technical Field

[0001] The present invention relates to the field of separation, purification, refinement and reuse of a mixture of solvent and extractant used in the production of diaphragms and fiber products using ultra-high molecular weight polyethylene as raw material, and in particular to a method for separating the mixture of solvent and extractant and decolorizing and removing impurities from the solvent. Background Art

[0002] Ultra-high molecular weight polyethylene (UHMWPE) refers to linear polyolefins with an average relative molecular weight greater than 1.5 million. It is a thermoplastic engineering plastic with exceptionally outstanding comprehensive properties. Compared to other polymers, UHMWPE exhibits a low coefficient of friction, excellent wear resistance, and superior resistance to chemical corrosion, impact, pressure, stress cracking, low temperatures, and light. It also exhibits anti-scaling, high toughness, high modulus, safety and hygiene, vibration and noise reduction, and is non-toxic and pollution-free. Precisely because of its exceptional mechanical, physical, and chemical properties, UHMWPE has a wide range of applications, including machinery, chemicals, transportation, military, textiles, mining, agriculture, packaging, and papermaking. Currently, UHMWPE products primarily exist in the form of sheets, profiles, films, pipes, and fibers. However, the melt viscosity of ultra-high molecular weight polyethylene (UHMWPE) increases dramatically with increasing molecular weight. During processing, the melt viscosity is very high (108 Pa∙s), resulting in a low coefficient of friction, prone to slippage during extrusion and stretching, and difficult to feed. The critical shear rate is low, the melt is prone to fracture, the molding temperature range is narrow, and it is susceptible to oxidative degradation. Conventional methods for molding UHMWPE into products are extremely difficult. A commonly used method involves dissolving high-molecular-weight polyethylene at high temperatures using hydrocarbon solvents such as naphthalene and paraffin oil to form a semi-dilute solution. This solution is then extruded and cast, then cooled at a constant rate. During the cooling process, due to polymer crystallization and a decrease in the solvent's solubility, a solid-liquid phase separation occurs, forming a blend. The blend is then stretched and formed. The solvent is then extracted from the molded polyethylene article using a low-boiling-point, volatile extractant. The extractant adhering to the polyethylene article is then heated and volatilized, resulting in a final polymer product. Products produced using this method include high-strength and high-modulus polyethylene fibers and high-molecular-weight diaphragms.

[0003] Low-boiling-point, volatile extractants generally use organic substances such as dichloromethane, tetrachloroethylene, n-hexane, and No. 120 solvent oil. The content of highly volatile extractants in the extraction tank is generally greater than that of high-boiling-point solvents, with the extractant content exceeding 80% and the high-boiling-point solvent content less than 20%. This mixture needs to be separated and purified to separate the extractant from the solvent to obtain an extractant with a purity exceeding 99.9% and a high-purity solvent, with the extractant content in the solvent being less than 0.1%. The separated extractant and solvent are then reused in production. The extractant adhering to high-strength and high-modulus polyethylene fibers and high-molecular-weight diaphragm products is heated in a drying oven to evaporate and then recovered using a gas purification and recovery device.

[0004] During the production of ultra-high molecular weight polyethylene (UHMWPE) products, a small amount of hydrocarbon solvents such as naphthalene and paraffin white oil can oxidize and denature during the heating process to dissolve the polyethylene. This can lead to darker solvent color, increased viscosity, and increased impurities, ultimately resulting in substandard product. In existing solvent and extractant mixture separation and purification processes, the recovered solvent is colored. This requires the addition of approximately 5% white clay to adsorb and purify the oxidative impurities in the solvent. Only after obtaining a clear solvent can it be reused. The added white clay is separated from the solvent by filtration. The separated white clay contains over 50% white oil and is disposed of as hazardous waste by specialized companies. Because the white clay is disposable, the daily generation of hazardous white clay waste presents a significant challenge for the industry, and the solvent contained in the waste clay is also wasted. Existing solvent and extractant separation and purification processes operate independently from the solvent decolorization process, which is intermittent. This chemical separation process is not only energy-intensive but also leads to unstable quality of the recovered solvent product, resulting in rework and other negative consequences.

[0005] Chinese invention patent publication number CN 110591752 A discloses a method and apparatus for recovering and purifying a dichloromethane-white oil mixture, relating to the field of lithium battery separators. The method for recovering and purifying a dichloromethane-white oil mixture involves feeding the dichloromethane-white oil mixture into a double-effect evaporator, separating the mixture in a first-effect evaporator to obtain first-effect dichloromethane vapor and a first-effect concentrated liquid, and then separating the mixture in a second-effect evaporator to obtain second-effect dichloromethane vapor and a second-effect concentrated liquid. The first-effect dichloromethane vapor serves as a heat source and enters the second-effect evaporator to heat the dichloromethane-white oil mixture fed into the second-effect evaporator. The first-effect dichloromethane vapor is condensed and discharged from the second-effect evaporator. The first-effect concentrated liquid and the second-effect concentrated liquid are then distilled to obtain residual dichloromethane and crude white oil. The crude white oil is then subjected to gas stripping to obtain white oil. The apparatus for recovering and purifying the dichloromethane-white oil mixture comprises a double-effect evaporator, a distillation tower, and a gas stripping system. The device for recovering and purifying a dichloromethane-white oil mixture provided by this application has high stability, low process operating temperature, and low energy consumption. While this patent allows for the separation of the dichloromethane extractant and the white oil solvent, the separated white oil still requires decolorization and impurity removal before it can be reused in production.

[0006] The Chinese invention patent with publication number CN 113981570 A discloses a method for recovering white oil in the production process of ultra-high molecular weight polyethylene fibers, which belongs to the field related to the production of ultra-high molecular weight polyethylene fibers and includes the following process steps: S1, filtration, specifically using a multi-porous material as a filler to adsorb and remove solid impurities in the white oil to obtain filtered white oil; S2, decolorization, specifically using a decolorizer as a filler to adsorb and decolorize the filtered white oil obtained in step S1 to obtain recycled white oil. The white oil recovery method in this application adopts a two-step decolorization process of first filtering for preliminary decolorization and then further adsorption decolorization, and the multi-porous material and the decolorizer are both in the form of fillers, which improves the overall decolorization efficiency. This method uses substances that do not exist in the production process, such as nitric acid and octadecyltrimethylammonium chloride, during the decolorization process. The introduction of these substances may remain in the white oil and affect the polyethylene fiber product.

[0007] The Chinese invention patent with publication number CN 117586802 A discloses a white oil decolorization system and a white oil decolorization method, including a white oil raw material tank, a white oil delivery pump, an adsorption tank, an intermediate reboiler, a condenser, an activation device, a solvent buffer tank and a solvent delivery pump. The white oil raw material tank is connected to the white oil delivery pump, the white oil delivery pump is connected to the adsorption tank, the adsorption tank is connected to the intermediate reboiler, the intermediate reboiler is connected to the condenser, the condenser is connected to the activation device, the activation device is connected to the solvent buffer tank, and the solvent buffer tank is connected to the solvent delivery pump. After the method uses the solvent to regenerate the adsorbent, nitrogen is needed to blow off the solvent in the adsorbent until no solvent remains. During the implementation process, the energy consumption is relatively high. Summary of the Invention

[0008] To address the above issues, the present invention provides a method for separating, purifying, and decolorizing the solvent-extractant mixture involved in the production of diaphragms and fiber products using ultra-high molecular weight polyethylene as raw material. The decolorized solvent and purified extractant are then reused in the production line, allowing the separation, purification, and decolorization of the solvent-extractant mixture to be completed automatically and continuously. This method addresses the current industry issues of high levels of hazardous waste, high solvent loss, and unstable purity during the separation, purification, and decolorization of solvent and extractant mixtures.

[0009] To achieve the above objectives, the present invention relates to a method for separating, purifying, and decolorizing a solvent-extractant mixture, comprising a solvent-extractant mixture coarse separation device, a decolorization device, a solvent-extractant mixture fine separation device, and a regeneration agent separation device. The solvent-extractant mixture is initially separated in the solvent-extractant mixture coarse separation device to obtain a colored crude solvent and an extractant, respectively. The separated colored crude solvent enters the decolorization device for decolorization and impurity removal, resulting in a decolorized crude solvent. The decolorized crude solvent enters the solvent-extractant mixture fine separation device for further separation of the extractant from the solvent, and the obtained qualified solvent and qualified extractant are respectively returned to the production line. After the decolorization device decolorizes the colored crude solvent for a certain period of time, the decolorizer gradually loses its decolorization performance and the decolorization effect deteriorates. The regeneration agent is then used to elute the impurities adsorbed in the decolorizer to achieve regeneration of the decolorizer. The eluted mixture contains impurities such as regeneration agent, white oil, and pigment. The regeneration agent and impurities are separated in the regeneration agent separation device, and the obtained regeneration agent is recycled to regenerate the decolorizer.

[0010] The solvent-extractant mixture separation device mainly utilizes the property that the boiling point of the extractant is lower than that of the solvent to separate the extractant from the solvent by heating, including but not limited to: one or more combinations of distillation separation, distillation separation, falling film evaporation separation, and gas stripping separation.

[0011] The decolorizing agent in the solvent decolorizing device includes but is not limited to: bleaching clay, decolorizing silica gel, activated carbon, activated carbon fiber, molecular sieve, resin, or a mixture thereof.

[0012] The regeneration agent includes but is not limited to one or more organic solvents such as dichloromethane, tetrachloroethylene, carbon tetrachloride, ethanol, ethyl acetate, and n-hexane.

[0013] As a preferred solution, after the decolorizing agent is eluted and regenerated by the regeneration agent, the regeneration agent remaining in the decolorizing agent enters the solvent-extraction agent mixture fine separation device together with the crude white oil in the next decolorizing process.

[0014] As a preferred solution, the regenerant carrying impurities is sent to a regenerant separation device to separate the impurities from the regenerant, and the regenerant after separation is reused for regeneration of the decolorant.

[0015] As a preferred embodiment, the regeneration agent and the extractant of the polymer solvent are the same substance. If substance A is used as the extractant of the polymer solvent in the production process, substance A is used as the regeneration agent of the decolorizing agent.

[0016] As a preferred embodiment, the temperature for separation of the solvent-extractant mixture is 40° C.-200° C. and the pressure is 100 Pa-0.2 MPa.

[0017] As a preferred solution, the decolorization temperature is 40°C-120°C and the pressure is 100Pa-0.12MPa.

[0018] As a preferred solution, the regeneration agent separation temperature is 40-200°C and the pressure is 100Pa-0.1MPa.

[0019] As a preferred solution, the regeneration agent and impurities are separated by using one or more of the technical means such as distillation, membrane separation, and electrostatic adsorption.

[0020] The method for separating and recycling the solvent and the extractant of the present invention comprises the following steps: 1. A solvent-extractant mixture containing 70% to 98% extractant is separated through a crude solvent-extractant mixture separation device to obtain an extractant with a purity greater than 99.5% and a colored crude solvent with an extractant content less than 20%. The crude solvent-extractant mixture separation device utilizes a distillation device, a rectification device, or a falling film evaporation device. The operating temperature of the separation device is 40-120°C and the operating pressure is 100 Pa to 0.12 MPa.

[0021] 2. The colored crude solvent with extractant content less than 20% is directly sent to the decolorization device to remove color and impurities to obtain decolorized crude solvent. The decolorized crude solvent is sent to the solvent-extractant mixture fine separation device for further separation to obtain an extractant with a purity higher than 99.5% and a solvent with an extractant content less than 1%. The decolorization device uses a fixed bed adsorption device with an operating temperature of 40-120℃ and an operating pressure of 100Pa-0.12MPa. The volumetric space velocity GHSV of the colored crude solvent in the fixed bed adsorption device is 0.2m 3 / h / m 3 -5m 3 / h / m 3 The colored crude solvent leaves the solvent-extractant mixture crude separation device and directly enters the decolorization device to complete the solvent decolorization. The platinum-cobalt color number of the decolorized crude solvent obtained is less than 150.

[0022] 3. After the decolorization unit in step 2 has been decolorized for a certain period of time, the decolorant adsorption becomes saturated and the unit switches to a regeneration state. The parallel standby decolorization unit also enters the decolorization state. Multiple decolorization units can be connected in parallel, and valves can be used to switch between the decolorization and regeneration states of the units to achieve a continuous decolorization process.

[0023] 4. Introduce an extractant as a regeneration agent to elute impurities such as pigments adsorbed by the decolorizer in the decolorizer, thereby regenerating the decolorizer in step 3. The regenerated decolorizer is repeatedly used in the decolorization process.

[0024] 5. The regenerant elution mixture from step 4 enters a regenerant separation device to remove regenerant, pigment, and other impurities. The resulting regenerant can be reused to regenerate the decolorant in the decolorization device. The regenerant separation device can be a distillation device, a rectification device, or a falling film evaporation device. The operating temperature of the separation device is 120-200°C and the operating pressure is 100 Pa-0.1 MPa.

[0025] The beneficial effects of the present invention are as follows: the method for separating and purifying the solvent and extractant mixture involved in the dissolution and molding process of ultra-high molecular weight polyethylene is as follows: in the process of separating and purifying the solvent and the extractant, a solvent decolorization device is embedded between a solvent-extractant mixture coarse separation device and a solvent-extractant mixture fine separation device, and the solvent-extractant mixture fine separation device is used to separate the extractant in the decolorized crude solvent to obtain qualified solvent and extractant, thereby realizing the automatic operation of the solvent separation and decolorization refining process and significantly reducing the operating energy consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 is a schematic diagram of the present invention; Figure 2 This is a schematic diagram of Example 1; Figure 3 This is a schematic diagram of Example 2; Figure 4 This is a schematic diagram of Example 3; like Figure 1 As shown, the colored solvent-extractant mixture produced on the ultra-high molecular weight polyethylene product production line is conveyed to a solvent-extractant mixture coarse separation device for separation to obtain an extractant and a colored crude solvent, the extractant is conveyed to an extractant tank, the colored crude solvent is directly conveyed to a decolorization device A for online decolorization to obtain a decolorized crude solvent, the decolorized crude solvent is conveyed to a solvent-extractant mixture fine separation device to obtain an extractant and a solvent, the extractant is conveyed to an extractant tank, the solvent is conveyed to a solvent tank, and the materials in the extractant tank and the solvent tank are respectively reused.

[0027] After the decolorizer reaches saturation, the regeneration process begins. The regenerant is transported to decolorizer B to remove impurities such as pigments adsorbed by the decolorizer, achieving regeneration of decolorizer B. The regenerant-eluted mixture enters the regenerant separation unit for separation into the regenerant and impurities such as pigments. The regenerant enters the regenerant tank for recycling. The extractant from the polymer solvent is transported to the regenerant tank to serve as the regenerant for the decolorizer.

[0028] The above process separates and purifies the solvent and extractant mixture used in the dissolution and molding of ultra-high molecular weight polyethylene (UHMWPE). In the crude solvent-extractant mixture separation unit, over 90% of the extractant is separated at temperatures below 120°C. This reduces the amount of colored crude solvent entering the decolorization unit by 90%, thereby reducing the equipment investment for the decolorization unit by 90%. The colored crude solvent enters the decolorization unit for decolorization, eliminating the need for cooling and energy loss. The hot colored crude solvent also washes away any residual regenerant from the regeneration process. The decolorized crude solvent then enters the fine solvent-extractant mixture separation unit, where it is separated at temperatures below 200°C into the solvent and extractant tanks for reuse. No additional equipment or process is required to remove residual regenerant from the decolorization unit after regeneration. DETAILED DESCRIPTION

[0029] For a better understanding of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and specific examples. Example 1

[0030] On the ultra-high molecular weight polyethylene diaphragm product production line, white oil is used as a solvent to dissolve polyethylene at 100°C. After cooling, stretching and other processes, the ultra-high molecular weight polyethylene diaphragm is obtained. Then, dichloromethane is used as an extractant to extract the white oil remaining in the ultra-high molecular weight polyethylene diaphragm. The white oil in the production process will slowly oxidize and discolor under high temperature conditions, resulting in a 20 t / h white oil-dichloromethane mixture containing colored impurities. Its platinum cobalt color number is 500 and it cannot be used anymore.

[0031] like Figure 2 , a 20 ton / h white oil-dichloromethane mixture with a white oil content of 5% and a dichloromethane content of 95% is fed into the falling film evaporator 1 of the crude separation device. The operating temperature of the falling film evaporator 1 is 100°C and the pressure is 0.1 MPa. 99.7% dichloromethane and colored crude white oil are separated. The separated dichloromethane enters the extractant tank 6 for reuse through valve 8, and the colored crude white oil directly enters the fixed bed adsorption device 2A filled with decolorizing silica gel through valve 9. The operating temperature of the fixed bed adsorption device 2A is 40-120°C and the operating pressure is 0.1 MPa. The colored crude white oil is discharged at a volume space velocity GHSV=2m 3 / h / m 3 After passing through the fixed bed adsorption device 2A, it enters the stripping tower 3 of the solvent-extractant mixture fine separation device through valve 11. The operating temperature of the stripping tower is 80°C and the operating pressure is 0.1 MPa. The stripping tower 3 separates dichloromethane and white oil. The dichloromethane is condensed and enters the extractant tank 6 for reuse through valve 14. The qualified white oil has a platinum-cobalt color number of 14 and enters the solvent tank 7 for reuse through valve 13.

[0032] After the decolorizing silica gel in the fixed bed adsorption device 2A is saturated with adsorption, close valves 9 and 11, open valves 10 and 12, switch to the fixed bed adsorption device 2B to decolorize and remove impurities from the colored crude solvent, and the fixed bed adsorption device 2A enters the regeneration state.

[0033] The extractant dichloromethane from the production line is replenished to regeneration agent tank 5 through valve 24 as the regeneration agent for fixed-bed adsorption unit 2A. The dichloromethane in regeneration agent tank 5 enters fixed-bed adsorption unit 2A through valves 16 and 18. The dichloromethane removes impurities such as pigments adsorbed on the decolorizing silica gel in fixed-bed adsorption unit 2A and flows through valve 20 into regeneration agent intermediate tank 15. After regeneration of fixed-bed adsorption unit 2A is complete, it can directly enter the next decolorization process. After fixed-bed adsorption unit 2B reaches saturation, it is regenerated according to the regeneration process for fixed-bed adsorption unit 2A. The decolorization and regeneration processes of fixed-bed adsorption units 2A and 2B are performed alternately, achieving continuous decolorization and purification of the colored crude white oil.

[0034] The regenerant elution mixture in the regenerant intermediate tank 15 enters the regenerant separation device falling film evaporator 4 through valve 25. The operating temperature of the falling film evaporator 4 is 100°C and the operating pressure is 1 kPa. 99.96% of the recovered dichloromethane enters the regenerant tank 5 through valve 21, and impurities such as pigments are discharged through valve 22. Example 2

[0035] On the ultra-high molecular weight polyethylene fiber production line, white oil is used as a solvent to dissolve polyethylene at 100°C. Ultra-high molecular weight polyethylene fibers are obtained through cooling, stretching and other processes. Then, dichloromethane is used as an extractant to extract the white oil remaining in the ultra-high molecular weight polyethylene fibers. The white oil in the production process will slowly oxidize and discolor under high temperature conditions, resulting in a 20 t / h white oil-dichloromethane mixture containing colored impurities. Its platinum-cobalt color number is greater than 500 and it cannot be used anymore.

[0036] like Figure 3, a white oil-dichloromethane mixture with a white oil content of 15% and a dichloromethane content of 85% is fed into a crude separation device distillation tower 1. The operating temperature of the distillation tower 1 is 41°C and the pressure is 0.1MPa. The white oil content in the separated dichloromethane is less than 0.01ppm, and the dichloromethane content in the colored crude white oil exceeds 75%. The separated dichloromethane enters the extractant tank 6 for reuse through valve 8, and the colored crude white oil enters the solvent-extractant mixture crude separation device distillation tower 23 through valve 9. The operating temperature of the distillation tower 23 is 87°C and the operating pressure is 0.2 MPa. The white oil content in the separated dichloromethane is less than 2 ppm, and the dichloromethane content in the colored crude white oil is less than 15%. The separated dichloromethane enters the extractant tank 6 for reuse through valve 24, and the colored white oil directly enters the fixed bed adsorption device 2B filled with bleaching clay through valve 10. The operating temperature of the fixed bed adsorption device 2B is 40-87°C and the operating pressure is 100 Pa. The colored crude white oil is extracted at a volume space velocity GHSV = 0.2 m 3 / h / m 3 After passing through the fixed bed adsorption device 2B, it enters the solvent-extractant mixture separation device distillation tower 3 through valve 12. The operating temperature of the distillation tower 3 is 200°C and the operating pressure is 5kPa. The distillation tower 3 separates dichloromethane and white oil. The dichloromethane is condensed and enters the extractant tank 6 for reuse through valve 14. The qualified white oil has a platinum-cobalt color number of 13 and enters the solvent tank 7 for reuse through valve 27.

[0037] After the decolorizing silica gel in the fixed bed adsorption device 2B is saturated with adsorption, close valve 10 and valve 12, open valve 13 and valve 11, switch to the fixed bed adsorption device 2A to decolorize and remove impurities from the colored crude solvent, and the fixed bed adsorption device 2B enters the regeneration state.

[0038] The extractant dichloromethane from the production line is added to regeneration agent tank 5 through valve 25 to serve as the regeneration agent for fixed-bed adsorption unit 2B. The dichloromethane in regeneration agent tank 5 enters fixed-bed adsorption unit 2B through valves 16 and 17. The dichloromethane elutes impurities such as pigments adsorbed on the decolorizing silica gel in fixed-bed adsorption unit 2B and flows through valve 19 into regeneration agent intermediate tank 15. After regeneration of fixed-bed adsorption unit 2B is complete, it can directly enter the next decolorization process. After fixed-bed adsorption unit 2A reaches saturation, regeneration is completed according to the regeneration process for fixed-bed adsorption unit 2B. The decolorization and regeneration processes of fixed-bed adsorption units 2A and 2B alternate, achieving continuous decolorization and purification of the colored crude solvent.

[0039] The regeneration agent elution mixture in the regeneration agent intermediate tank 15 enters the regeneration agent separation device distillation tower 4 through valve 26. The operating temperature of the distillation tower 4 is 200°C and the operating pressure is 0.1 MPa. 99% of the recovered dichloromethane enters the regeneration agent tank 5 through valve 21. Example 3

[0040] On the ultra-high molecular weight polyethylene fiber production line, white oil is used as a solvent to dissolve polyethylene at 100°C. Ultra-high molecular weight polyethylene fibers are obtained through cooling, stretching and other processes. Then, tetrachloroethylene is used as an extraction agent to extract the white oil remaining in the ultra-high molecular weight polyethylene fibers. The white oil in the production process will slowly oxidize and discolor under high temperature conditions, resulting in a 20 t / h white oil-tetrachloroethylene mixture containing colored impurities. Its platinum-cobalt color number is greater than 500 and it cannot be used anymore.

[0041] like Figure 4 , a 20 t / h white oil-dichloromethane mixture with a white oil content of 15% and a tetrachloroethylene content of 85% is fed into the falling film evaporator 1 of the crude separation device. The operating temperature of the falling film evaporator 1 is 125°C and the pressure is 0.1 MPa. The white oil content in the separated tetrachloroethylene is less than 6 ppm, and the tetrachloroethylene content in the colored crude white oil is 80%. The separated tetrachloroethylene enters the extractant tank 6 for reuse through valve 8, and the colored crude white oil enters the solvent-extractant mixture crude separation device distillation tower 23 through valve 9. The distillation tower The operating temperature of 23 is 200°C, the operating pressure is 0.08 MPa, the white oil content in the separated tetrachloroethylene is less than 10 ppm, and the tetrachloroethylene content in the colored crude white oil is less than 7.2%. The separated tetrachloroethylene enters the extractant tank 6 for reuse through valve 24, and the colored white oil directly enters the fixed bed adsorption device 2B filled with decolorizing activated carbon through valve 10. The operating temperature of the fixed bed adsorption device 2B is 40-200°C, the operating pressure is 100 Pa, and the colored crude white oil is decolorized at a volume space velocity GHSV = 5m 3 / h / m 3 After passing through the fixed bed adsorption device 2B, the product enters the distillation tower 3 of the solvent-extractant mixture separation device through valve 12. The operating temperature of the distillation tower 3 is 100°C and the operating pressure is 0.01 MPa. The distillation tower 3 separates tetrachloroethylene and white oil. The tetrachloroethylene is condensed and enters the extractant tank 6 for reuse through valve 14. The white oil enters the stripping tower 31 of the solvent-extractant mixture separation device through valve 28. Trace tetrachloroethylene in the white oil is removed by nitrogen stripping. The operating temperature of the stripping tower is 150°C and the pressure is 0.03 MPa. The non-condensable gas at the top of the stripping tower 31 is sent to the subsequent treatment facility through valve 29. The platinum-cobalt color number of the qualified white oil at the bottom of the stripping tower 31 is 7, and it enters the solvent recovery tank 7 through valve 27 for reuse.

[0042] After the decolorizing silica gel in the fixed bed adsorption device 2B is saturated with adsorption, close valve 10 and valve 12, open valve 13 and valve 11, switch to the fixed bed adsorption device 2A to decolorize and remove impurities from the colored crude solvent, and the fixed bed adsorption device 2B enters the regeneration state.

[0043] The extractant tetrachloroethylene (TCE) from the production line is added to regeneration agent tank 5 through valve 25 to serve as the regeneration agent for fixed-bed adsorption unit 2B. The TCE in regeneration agent tank 5 enters fixed-bed adsorption unit 2B through valves 16 and 17. The TCE elutes impurities such as pigments adsorbed on the decolorizing silica gel in fixed-bed adsorption unit 2B and flows through valve 19 into regeneration agent intermediate tank 15. The eluted mixture in regeneration agent intermediate tank 15 circulates through valves 32 and 17 to fixed-bed adsorption unit 2B until regeneration of fixed-bed adsorption unit 2B is complete. After regeneration of fixed-bed adsorption unit 2B is complete, the next decolorization process can proceed directly. After saturation of fixed-bed adsorption unit 2A, regeneration is completed by following the regeneration process for fixed-bed adsorption unit 2B. The decolorization and regeneration processes of fixed-bed adsorption units 2A and 2B alternate, achieving continuous decolorization and purification of the colored crude solvent.

[0044] The regeneration agent elution mixture in the regeneration agent intermediate tank 15 enters the regeneration agent separation device distillation tower 4 through valve 26. The operating temperature of the distillation tower 4 is 200°C and the operating pressure is 0.001MPa. 99% of the recovered tetrachloroethylene enters the regeneration agent tank 5 through valve 21.

[0045] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

Claims

1. A method for separating a solvent and an extractant during the dissolution and molding of ultra-high molecular weight polyethylene, characterized by: The following steps are involved: The solvent-extractant mixture is preliminarily separated in a solvent-extractant mixture coarse separation device to obtain a colored crude solvent and an extractant, respectively. The separated colored crude solvent enters a decolorization device for decolorization and impurity removal to obtain a decolorized crude solvent; the decolorized crude solvent enters a solvent-extractant mixture fine separation device to further separate the extractant from the solvent, and the obtained qualified solvent and qualified extractant are respectively reused in the production line; a regeneration agent is used to elute the impurities adsorbed in the decolorant in the decolorization device to achieve regeneration of the decolorant, and the eluted mixture contains the regeneration agent, white oil, and pigment impurities. The regeneration agent and the impurities are separated in a regeneration agent separation device, and the obtained regeneration agent is recycled to regenerate the decolorant; the regeneration agent is the same substance as the extractant used in the dissolution and molding process of ultra-high molecular weight polyethylene.

2. The method for separating the solvent and the extractant during dissolution and molding of ultra-high molecular weight polyethylene according to claim 1, characterized in that: The method is realized by a solvent-extractant mixture coarse separation device, a decolorization device, a solvent-extractant mixture fine separation device and a regeneration agent separation device connected by pipelines.

3. The method for separating the solvent and the extractant during dissolution and molding of ultra-high molecular weight polyethylene according to claim 1, characterized in that: The decolorization device uses a fixed bed adsorption device, and the decolorizing agent in the fixed bed adsorption device includes one or more mixtures of bleaching clay, decoloring silica gel, activated carbon, activated carbon fiber, molecular sieve, and resin; the decolorization operating temperature is: 40℃~200℃, the operating pressure is: 100Pa~0.12MPa, and the volume space velocity GHSV of the colored crude solvent in the decolorization device is 0.2m 3 / h / m 3 -5m 3 / h / m 3 .

4. The method for separating the solvent and the extractant during dissolution and molding of ultra-high molecular weight polyethylene according to claim 3, characterized in that: The number of the fixed bed adsorption devices is ≥2 and they are connected in parallel, one fixed bed adsorption device is in a decolorization state and the other fixed bed adsorption devices are in a regeneration or waiting state.

5. The method for separating the solvent and the extractant during dissolution and molding of ultra-high molecular weight polyethylene according to claim 1, characterized in that: The regeneration agent separation device uses a distillation tower, a rectification tower or a falling film evaporator. The operating temperature of the separation equipment is 60-200°C and the operating pressure is 100Pa-0.1MPa.

6. The method for separating the solvent and the extractant during dissolution and molding of ultra-high molecular weight polyethylene according to claim 1, characterized in that: The solvent-extractant mixture coarse separation device comprises a series combination of one or more devices selected from the group consisting of a rectification tower, a distillation tower, and a falling film evaporator. The operating temperature of the solvent-extractant mixture coarse separation device is 40-200°C and the operating pressure is 100 Pa-0.12 MPa. The operating temperature of the solvent-extractant mixture fine separation device is 80-200°C and the operating pressure is 1000 Pa-0.1 MPa.

7. The method for separating the solvent and the extractant during dissolution and molding of ultra-high molecular weight polyethylene according to claim 1, characterized in that: The solvent-extractant mixture separation device comprises a series combination of one or more devices selected from the group consisting of a rectification tower, a distillation tower, a falling film evaporator, and a gas stripping separation device.

8. The method for separating the solvent and the extractant during dissolution and molding of ultra-high molecular weight polyethylene according to claim 1 or 3, characterized in that: The regeneration agent of the decolorant in the fixed bed adsorption equipment is one or a mixture of organic solvents such as dichloromethane, tetrachloroethylene, carbon tetrachloride, ethanol, ethyl acetate, and n-hexane.

9. The method for separating the solvent and the extractant during dissolution and molding of ultra-high molecular weight polyethylene according to claim 1, characterized in that: The separation and purification method is achieved by the following device, which includes a falling film evaporator (1), wherein the light phase outlet at the top of the falling film evaporator (1) is connected to the inlet of the extractant tank (6), the heavy phase outlet at the bottom of the falling film evaporator (1) is connected to the inlet of the distillation tower (23) of the solvent-extractant mixture coarse separation device, the top outlet of the distillation tower (23) of the solvent-extractant mixture coarse separation device is connected to the inlet of the extractant tank (6), the bottom outlet of the distillation tower (23) of the extractant mixture coarse separation device is connected to the inlet of the fixed bed adsorption devices (2A) and (2B) connected in parallel, and the outlets of the fixed bed adsorption devices (2A) and (2B) are connected. The fixed bed adsorption devices (2A) and (2B) are further connected to the inlet of the distillation tower (3) of the solvent-extractant mixture separation device, the top outlet of the distillation tower (3) of the solvent-extractant mixture separation device is connected to the inlet of the extractant tank (6), the bottom outlet of the distillation tower (3) of the solvent-extractant mixture separation device is connected to the inlet of the gas stripping tower (31), and the bottom outlet of the gas stripping tower (31) is connected to the inlet of the solvent recovery tank (7); the fixed bed adsorption devices (2A) and (2B) are also connected to the regeneration agent intermediate tank (15), the outlet of the regeneration agent intermediate tank (15) is connected to the inlet of the distillation tower (4), and the top outlet of the distillation tower (4) is connected to the inlet of the regeneration agent tank (5).

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