Washing system for obtaining ultra-clean polypropylene

Abstract

The utility model discloses a washing system for obtaining ultra-clean polypropylene. The washing system comprises a washing unit, a separating unit, a drying unit, a solution recycling unit, a filtering unit and a gas-liquid separating unit. The washing system disclosed by the utility model not only can obtain ultra-clean polypropylene, but also can realize environment-friendly, low-consumption and stable long-period operation.

Description

Technical Field

[0001] This utility model belongs to the field of polypropylene technology and relates to a washing system for ultra-clean polypropylene. Background Technology

[0002] Polypropylene has the advantages of low relative density, good chemical resistance and water resistance, as well as good mechanical strength and electrical insulation. It can be used in films, pipes, sheets, various molded products, wires and cables, etc., and has a wide range of applications in agriculture, packaging, electronics, electrical, automotive, machinery and daily necessities.

[0003] High-performance polyolefin materials include metallocene polyolefin elastomers, high-rigidity and high-impact copolymers, and a variety of modified resin materials. The main indicators affecting polyolefin quality are isotacticity and impurities (such as residual catalysts, co-catalysts, oligomers, salts, and reaction products), with impurities primarily represented by ash content. The main reasons for excessive ash content in polyolefin materials are: high impurity content in raw materials leading to poorer reaction conditions; and the presence of residual metal ions from the main catalyst and TEAL in the polyolefin resin. Excessive ash content in polyolefin materials significantly impacts extrusion processing, especially film formation, resulting in the following effects: 1) Polypropylene films are prone to breakage, making them unsuitable for electrical-grade products; 2) Filters in granulation units are prone to clogging.

[0004] In existing processes, the polypropylene powder obtained from the reaction usually contains impurities, such as metals in the catalyst and co-catalyst, and byproducts generated during the reaction (such as low molecular weight polymers with molecular weights of several hundred to several thousand). Before using polypropylene to prepare capacitor films, the metals and byproducts in the impurities must be removed; otherwise, it may cause short circuits in electrical-grade products or even fires.

[0005] In existing technologies, polypropylene powder and detergent are typically reacted countercurrently in a washing tower to remove ash. For example, patent CN 114014960 B uses saturated alkanes such as n-hexane as the washing solution and performs the washing operation at atmospheric pressure; while Chinese patent CN 114011103 B uses isobutylene-1 as the washing solvent and operates under supercritical conditions. The polypropylene powder and washing solvent react countercurrently in a full-tank washing container, and their separation is achieved through density difference: alkanes, with their lower density, flow upwards from the bottom of the washing container, reaching the top and exiting; polypropylene powder, with its higher density, enters from the top, flows by gravity to the bottom, and then exits. However, this flow pattern results in a high slurry concentration at the bottom of the washing container, which can potentially clog the bottom outlet during continuous industrial operations, affecting the long-term operation of the equipment.

[0006] In patent CN 117619286 A, both the washing and separation processes are completed in a rotary filter press. The washing solution and the polyolefin material from the polymerization reaction enter the filter press together, where washing and solid-liquid separation are achieved under nitrogen pressure and protection. However, the filter press in this patent is easily clogged by low molecular weight substances and polyolefin powder in the polymer, requiring regular cleaning, which is done using water. Since the main catalyst and co-catalyst in polyolefin processes are highly sensitive to water, this inevitably leads to increased costs and shortened operating cycles for the material refining system, making it unsuitable for continuous polyolefin processes.

[0007] Patent CN 220425355 U describes a washing effect achieved by arranging two screws vertically. The vertically arranged screw mixes and conveys the polyolefin powder and washing solution, while the horizontally arranged screw heats, conveys, and washes the mixture. However, in this patent, the vertical screw tends to trap low-molecular-weight polymers when conveying the slurry, leading to reduced screw rotation and necessitating timely shutdown for inspection and maintenance as the start-up time increases. In the horizontally arranged screw configuration, the slurry flow rate is lower, and solid particles tend to accumulate on the vessel walls, shortening the start-up cycle. Summary of the Invention

[0008] This utility model provides a washing system for obtaining ultra-clean polypropylene, the washing system comprising:

[0009] The unit includes a washing unit, a separation unit, a drying unit, a solution recovery unit, a filtration unit, and a gas-liquid separation unit; among which,

[0010] The washing unit includes a washing container, a slurry circulation pump, and a slurry heater; the separation unit includes a centrifugal separation module; the solution recovery unit includes a washing evaporation tower; the drying unit includes a drying device; the filtration unit includes a filter; and the gas-liquid separation unit includes a gas-liquid separation tank.

[0011] The top and bottom of the washing container form a loop, and the slurry circulation pump and slurry heater are installed on the loop. The loop is connected to the feed inlet of the centrifugal separation module.

[0012] The solid discharge port of the centrifugal separation module is connected to the feed port of the drying device, and the liquid discharge port of the centrifugal separation module is connected to the feed port of the washing evaporation tower.

[0013] The top of the washing evaporation tower is connected to the washing container;

[0014] The top of the drying device is connected to the filter to form a loop, and the bottom of the drying device is provided with a gas inlet, which is connected to the gas outlet of the gas-liquid separator.

[0015] The gas inlet of the gas-liquid separator is connected to the gas outlet of the filter, and the liquid outlet of the gas-liquid separator is connected to the washing container.

[0016] According to an embodiment of this invention, the washing unit further includes a stirrer. Preferably, the stirrer is disposed inside the washing container for solid-liquid mixing. The stirrer of this invention can be any stirrer known in the art, as long as it can provide high shear force. The materials are thoroughly mixed in the stirrer under high shear force, thereby allowing impurities such as oligomers and ash to fully dissolve into the solvent.

[0017] According to an embodiment of this utility model, the feed inlet of the centrifugal separation module is connected to the slurry circulation pump.

[0018] According to an embodiment of this utility model, a solid discharge port is further provided at the bottom of the drying device. Preferably, the bottom of the drying device is connected to a solid material pipeline, and the material dried by the drying device is transported to the next process via the solid material pipeline.

[0019] According to an embodiment of this utility model, the gas inlet of the drying device is connected to a gas supply pipeline. Preferably, a heater is also provided on the gas supply pipeline for heating the gas in the gas supply pipeline.

[0020] According to an embodiment of the present invention, the solution recovery unit further includes a cooler connected to the top of the washing evaporation tower for cooling the pure washing solution (preferably a vaporized washing solution) at the top of the washing evaporation tower.

[0021] According to an embodiment of this utility model, a vapor phase outlet is provided at the top of the washing evaporation tower, and the vapor phase outlet is connected to a cooler.

[0022] According to an embodiment of the present invention, the solution recovery unit further includes a bottom heat exchanger, which is connected to the bottom of the washing evaporation tower.

[0023] According to an embodiment of this utility model, the liquid outlet at the bottom of the gas-liquid separator is connected to the circulating washing solvent inlet of the washing container via a washing liquid pipeline.

[0024] According to an embodiment of this utility model, a heat exchanger is also provided at the gas inlet of the gas-liquid separator to reduce the temperature of the gas entering the gas-liquid separator, thereby achieving gas-liquid separation.

[0025] According to an embodiment of this utility model, the liquid outlet and gas inlet of the gas-liquid separator are respectively connected to a heat exchanger. Preferably, after the liquid flows out of the liquid outlet of the gas-liquid separator, it is further heated by the heat exchanger, and preferably exchanges heat with the gas entering the gas-liquid separator.

[0026] According to an embodiment of this utility model, the liquid outlet of the gas-liquid separator is further provided with a liquid circulation pump for pressurizing the liquid in the gas-liquid separator.

[0027] According to an embodiment of this utility model, the gas outlet of the gas-liquid separator is connected to a gas supply pipeline.

[0028] According to an embodiment of the present invention, a compressor is further provided on the gas outlet of the gas-liquid separator for pressurizing the gas separated by the gas-liquid separator.

[0029] Beneficial effects

[0030] The washing system of this invention not only produces ultra-clean polypropylene, but also achieves environmentally friendly, low-consumption, and stable long-term operation.

[0031] 1. The washing system of this utility model adopts a sequential feeding method of polypropylene and washing solution into the washing container for washing, and simultaneously realizes material circulation (e.g., washing solvent circulation, nitrogen circulation) and heat circulation in the washing system.

[0032] 2. After the polypropylene powder containing impurities such as metals and oligomers obtained by polymerization is washed by the washing system of this utility model, the metals and oligomers carried by the polypropylene powder can be effectively reduced. For example, the isotacticity of the washed polypropylene powder is ≥98%, and the ash content is ≤20ppm and the oligomer content is <0.5%. Attached Figure Description

[0033] Figure 1 Flowchart of a washing system for polyolefin powder;

[0034] The components include: 1. Polypropylene powder; 2. Washing solution; 3. Agitator; 4. Slurry circulation pump; 5. Slurry heater; 6. Washing container; 7. Pipeline for conveying unheated slurry; 8. Centrifugal separation module; 9. Liquid material conveying pipeline; 10. Washing evaporation tower; 11. Cooler; 12. Drying device; 13. Filter; 14. Gas-liquid separator; 15. Compressor; 16. Liquid circulation pump; 17. Waste liquid collection tank; 18. Heater; 19. Pipeline for conveying fine polypropylene powder; 20. Gas pipeline; 21. Heat exchanger; 22. Washing liquid pipeline; 23. Tower bottom heat exchanger; 24. Solid material pipeline; 25. Gas supply pipeline. Detailed Implementation

[0035] The technical solution of this utility model will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are only illustrative and explanatory of this utility model, and should not be construed as limiting the scope of protection of this utility model. All technologies implemented based on the above content of this utility model are covered within the scope of protection intended by this utility model.

[0036] Unless otherwise stated, the raw materials and reagents used in the following examples are commercially available products or can be prepared by known methods.

[0037] Example 1 uses the following Figure 1 The washing system shown obtains ultra-clean polypropylene, the washing system comprising:

[0038] A washing system for obtaining ultra-clean polypropylene, the washing system comprising:

[0039] The unit includes a washing unit, a separation unit, a drying unit, a solution recovery unit, a filtration unit, and a gas-liquid separation unit; among which,

[0040] The washing unit includes a washing container 6, a slurry circulation pump 4, and a slurry heater 5; the separation unit includes a centrifugal separation module 8; the solution recovery unit includes a washing evaporation tower 10; the drying unit includes a drying device 12; the filtration unit includes a filter 13; and the gas-liquid separation unit includes a gas-liquid separation tank 14.

[0041] The top and bottom of the washing container 6 form a loop, and the slurry circulation pump 4 and the slurry heater 5 are installed on the loop. The loop is connected to the feed inlet of the centrifugal separation module 8.

[0042] The solid discharge port of the centrifugal separation module 8 is connected to the feed port of the drying device 12, and the liquid discharge port of the centrifugal separation module 8 is connected to the feed port of the washing evaporation tower 10.

[0043] The top of the washing evaporation tower 10 is connected to the washing container 6;

[0044] The top of the drying device 12 is connected to the filter 13 to form a loop, and a gas inlet is provided at the bottom of the drying device 12. The gas inlet of the drying device 12 is connected to the gas outlet of the gas-liquid separator 14.

[0045] The gas inlet of the gas-liquid separator 14 is connected to the gas outlet of the filter 13, and the liquid outlet of the gas-liquid separator 14 is connected to the washing container 6.

[0046] In one specific embodiment, the washing unit further includes an agitator 3. Preferably, the agitator 3 is disposed inside the washing container 6. The agitator of this invention can be any agitator known in the art, as long as it can provide high shear force. The materials are thoroughly mixed in the agitator under high shear force, thereby allowing impurities such as oligomers and ash to fully dissolve into the solvent.

[0047] In one specific embodiment, the feed inlet of the centrifugal separation module 8 is connected to the slurry circulation pump 4.

[0048] In one specific embodiment, the bottom of the drying device 12 is also provided with a solid discharge port. Preferably, the bottom of the drying device 12 is connected to a solid material pipeline, and the material dried by the drying device 12 is transported to the next process through the solid material pipeline.

[0049] In one specific embodiment, the gas inlet of the drying device 12 is connected to the gas supply pipe 25. Preferably, a heater 18 is also provided on the gas supply pipe 25 for heating the gas in the gas supply pipe 25.

[0050] In one specific embodiment, the solution recovery unit further includes a cooler 11 connected to the top of the washing evaporation tower 10 for cooling the pure washing solution (preferably a vaporized washing solution) at the top of the washing evaporation tower 10.

[0051] In one specific embodiment, the top of the washing evaporation tower 10 is provided with a vapor phase outlet, which is connected to the cooler 11.

[0052] In one specific embodiment, the solution recovery unit further includes a bottom heat exchanger 23, which is connected to the bottom of the washing evaporation tower 10.

[0053] In one specific embodiment, the liquid outlet at the bottom of the gas-liquid separator 14 is connected to the circulating washing solvent inlet of the washing container 6 via a washing liquid pipeline.

[0054] In one specific embodiment, the gas inlet of the gas-liquid separator 14 is also provided with a heat exchanger 21 to reduce the temperature of the gas entering the gas-liquid separator 14, thereby achieving gas-liquid separation.

[0055] In one specific embodiment, the liquid outlet and gas inlet of the gas-liquid separator 14 are respectively connected to the heat exchanger 21. Preferably, after the liquid flows out of the liquid outlet of the gas-liquid separator 14, it is further heated by the heat exchanger 21, and preferably exchanges heat with the gas entering the gas-liquid separator 14.

[0056] In one specific embodiment, the liquid outlet of the gas-liquid separator 14 is also provided with a liquid circulation pump 16 for pressurizing the liquid in the gas-liquid separator 14.

[0057] In one specific embodiment, the gas outlet of the gas-liquid separator 14 is connected to the gas supply pipeline 25.

[0058] In one specific embodiment, a compressor 15 is also provided on the gas outlet of the gas-liquid separator 14 for pressurizing the gas separated by the gas-liquid separator 14.

[0059] In the production process of polypropylene, the polymerized product obtained after polymerization includes at least polypropylene powder and impurities (such as metallic substances, oligomers, propylene, etc.). To remove these impurities, methods such as... Figure 1 The ultra-clean polypropylene is washed using the washing system shown, specifically:

[0060] The polymer product 1 containing impurities and the washing solution 2 are simultaneously added to the washing container 6 in a co-current manner, with a material ratio of 1:3. The materials are thoroughly mixed and washed in the washing container 6 by a stirrer 3. After a certain washing time (preferably 1-5 hours, for example, 3 hours), the resulting slurry is discharged from the slurry outlet at the bottom of the washing container 6 and then fed into the centrifugal separation module 8 by a slurry circulation pump 4 for centrifugal drying. Preferably, the temperature in the washing container 6 is 80-100°C (for example, 85°C).

[0061] To maintain the washing temperature in the washing container, a slurry heater 5 is installed at the outlet of the slurry circulation pump 4. The slurry flow from the slurry circulation pump 4 is divided into two parts. One part of the slurry material is heated to 60-90°C by the slurry heater 5 at the outlet of the slurry circulation pump 4 and then circulated into the washing container 6. The other part of the slurry material enters the centrifugal separation module 8 through the pipeline 7 for centrifugal drying.

[0062] After passing through centrifugal separation module 8, the slurry material is separated into solid material and liquid material. The solid material includes a small amount of washing solution and polypropylene; the liquid material includes impurities and washing solution.

[0063] Liquid material enters the washing evaporator 10 through pipe 9, and a clean washing solution is obtained at the top of the washing evaporator 10. The clean washing solution at the top of the washing evaporator 10 is cooled by cooler 11 and then recycled to washing container 6 for reuse; the material at the bottom of the washing evaporator 10 is cooled by recycling heat exchanger 23 and then discharged into waste liquid collection tank 17, awaiting further processing. Preferably, the temperature in the washing evaporator is 100-160°C, for example, 130°C.

[0064] The solid material enters the drying unit 12 for drying. In the drying unit 12, heated nitrogen gas is typically used for drying to completely separate the washing solution and impurities from the liquid material. After drying in the drying unit 12, the resulting solid powder is a polypropylene powder that is almost free of washing solvent, which enters the downstream extrusion granulation system via the solid material pipeline 24. Preferably, the temperature in the drying unit is above 100°C, for example, 105°C.

[0065] Nitrogen gas, heated by heater 18, enters the drying device 12 from the bottom, agitating and heating the solid material. This mixture, along with the vaporized washing solution, forms a gaseous mixture that exits from the top of the drying device 12, thus achieving separation. Preferably, the temperature of the heated nitrogen gas is above 100°C, for example, 110°C. Preferably, the temperature of the gaseous mixture is above 80°C, for example, 85°C. Preferably, the nitrogen entering the drying device 12 is primarily supplied through a nitrogen pipeline, and also includes circulating nitrogen.

[0066] The mixed gas exiting from the top of the drying device 12 enters the filter 13, filtering out any small amounts of solid powder (such as fine polypropylene powder entrained in nitrogen). The filtered solid powder returns to the drying device 12 by gravity through pipe 19. Because the filtered mixed gas carries a large amount of heat, to fully utilize this heat, it is first used as a cold source to cool the heat exchanger 23 at the bottom of the heating tower, and then as a heat source to exchange heat with the heat exchanger 21, providing heat to the devices in the washing system, preferably the washing evaporation tower 10 and the washing container 6. Preferably, the heating tower bottom heat exchanger 23 provides heat to the washing evaporation tower 10. Preferably, the heat exchanger 21 provides heat to the circulating washing solution.

[0067] After heat exchange, the mixed gas enters the gas-liquid separator 14, where it is separated into a gas phase and a liquid phase. The gas phase is nitrogen, and the liquid phase is a washing solution. The gas phase in the gas-liquid separator 14 is used as circulating nitrogen. After being pressurized by the gas compressor 15, it enters the gas supply pipeline 25, and is then heated by the heater 18 before returning to the drying device, thus realizing the recycling of nitrogen. The liquid phase in the gas-liquid separator 14 is used as circulating washing solution. The washing solution is sent to the washing container 6 by the liquid circulation pump 16 for recycling of the washing solution.

[0068] Preferably, after the circulating washing solution is pressurized by the liquid circulation pump 16, it can also exchange heat with the mixed gas through the heat exchanger 21, and then return to the washing container 6 through the circulating washing solution pipeline 22.

[0069] Example 2

[0070] use Figure 1 The washing system shown involves adding 75 kg / h of polypropylene powder (containing 0.75 kg / h of oligomers and 63 ppm of metals) and 225 kg / h of washing solution co-currently into the washing container. The washing temperature is set at 80°C, the drying unit at 105°C, the washing evaporator at 160°C, the heated nitrogen at 110°C, and the mixed gas at 85°C. The washing process lasts for 3 hours. The mass ratio of polypropylene powder to washing solution is 1:3. The washing solution includes alkanes and alcohols, with a volume ratio of alkanes to alcohols of 3:1.

[0071] The solid material after leaving the washing container was dried by a drying device to obtain ultra-clean polypropylene powder. Sampling and analysis yielded the following results:

[0072] through Figure 1 The washing system shown indicates that after washing, the polypropylene contains 17 ppm of metals and 11 ppm of oligomers. This fully meets the national standards for premium-grade products.

[0073] Compared with existing washing processes, the adopted Figure 1 The washing system shown processes polypropylene powder, saving over 50% in energy and approximately one-third of the washing solvent.

[0074] The exemplary embodiments of this utility model have been described above. However, the scope of protection of this application is not limited to the above embodiments. Any modifications, equivalent substitutions, improvements, etc., made by those skilled in the art within the spirit and principles of this utility model should be included within the scope of protection of this utility model.

Claims

1. A washing system for obtaining ultra-clean polypropylene, characterized in that, The washing system includes: The unit includes a washing unit, a separation unit, a drying unit, a solution recovery unit, a filtration unit, and a gas-liquid separation unit; among which, The washing unit includes a washing container, a slurry circulation pump, and a slurry heater; the separation unit includes a centrifugal separation module; the solution recovery unit includes a washing evaporation tower; the drying unit includes a drying device; the filtration unit includes a filter; and the gas-liquid separation unit includes a gas-liquid separation tank. The top and bottom of the washing container form a loop, and the slurry circulation pump and slurry heater are installed on the loop. The loop is connected to the feed inlet of the centrifugal separation module. The solid discharge port of the centrifugal separation module is connected to the feed port of the drying device, and the liquid discharge port of the centrifugal separation module is connected to the feed port of the washing evaporation tower. The top of the washing evaporation tower is connected to the washing container; The top of the drying device is connected to the filter to form a loop, and the bottom of the drying device is provided with a gas inlet, which is connected to the gas outlet of the gas-liquid separator. The gas inlet of the gas-liquid separator is connected to the gas outlet of the filter, and the liquid outlet of the gas-liquid separator is connected to the washing container.

2. The washing system according to claim 1, characterized in that, The washing unit also includes an agitator.

3. The washing system according to claim 1, characterized in that, The feed inlet of the centrifugal separation module is connected to the slurry circulation pump.

4. The washing system according to claim 1, characterized in that, The bottom of the drying device is also provided with a solid discharge port; The gas inlet of the drying device is connected to the gas supply pipeline.

5. The washing system according to claim 1, characterized in that, The solution recovery unit also includes a cooler connected to the top of the washing evaporation tower for cooling the pure washing solution at the top of the washing evaporation tower.

6. The washing system according to claim 1 or 5, characterized in that, The top of the washing evaporation tower is provided with a vapor phase outlet, which is connected to a cooler.

7. The washing system according to claim 1, characterized in that, The solution recovery unit also includes a bottom heat exchanger, which is connected to the bottom of the washing evaporation tower.

8. The washing system according to claim 1, characterized in that, The liquid outlet at the bottom of the gas-liquid separator is connected to the circulating washing solvent inlet of the washing container via a washing liquid pipeline. The gas inlet of the gas-liquid separator is also equipped with a heat exchanger to reduce the temperature of the gas entering the gas-liquid separator, thereby achieving gas-liquid separation.

9. The washing system according to claim 1, characterized in that, The liquid outlet and gas inlet of the gas-liquid separator are respectively connected to a heat exchanger; The liquid outlet of the gas-liquid separator is also equipped with a liquid circulation pump for pressurizing the liquid in the gas-liquid separator.

10. The washing system according to claim 1, characterized in that, The gas outlet of the gas-liquid separator is connected to a gas supply pipeline; The gas-liquid separator is also equipped with a compressor at its gas outlet, which is used to pressurize the gas separated by the gas-liquid separator.

Images