A method and system for removing impurities from low-value waste plastics

Abstract

This application discloses a method and system for removing impurities from low-value waste plastics, relating to the field of plastics processing. The method includes mixing raw materials with heated solvent oil, dehydrating and melting to form a molten mixture; then entering a deimpurification zone where auxiliary deimpurification gas is introduced to carry out the deimpurification reaction; the gas generated by the deimpurification reaction is discharged through an exhaust unit; after the deimpurification reaction, the material enters a homogenization zone for mixing and reaction; after completion, part of the deimpurified product is output, and the other part is mixed with the raw material through a circulation channel and continues the deimpurification reaction. This application employs a pre-deimpurification process, with the entire deimpurification process at a temperature of less than or equal to 350℃, achieving a sulfur, chlorine, and other halogen content of less than 100ppm after deimpurification, thereby avoiding the generation of difficult-to-treat chlorides during the deimpurification process; furthermore, the pre-deimpuration process allows for the neglect of sulfur, chlorine, and other impurities' corrosion of the equipment during the subsequent deep pyrolysis of the waste plastics, greatly improving the efficiency of obtaining pure, high-value products.

Description

Technical Field

[0001] This application relates to the technical field of plastic processing, specifically to a method and system for removing impurities from low-value waste plastics. Background Technology

[0002] Low-value plastics refer to waste plastics with low added value and high recycling costs. They are mainly composed of polyolefins mixed with small amounts of PVC and high molecular weight polymers such as aromatics, esters, and adhesives. Examples include mixed waste plastics from municipal solid waste, waste plastics from paper mills, and mixtures from multiple recycling processes. Since low-value plastics lack physical recycling value, they are typically processed through pyrolysis. This process converts low-value waste plastics into oil, gas, or other chemicals. However, low-value waste plastics often contain impurities such as halogens and sulfur. These impurities significantly impact the catalytic materials, equipment, and final product performance used in the pyrolysis process, including poisoning and deactivation of catalytic materials, damage to critical equipment, and high impurity content in related products. Therefore, effectively addressing the impact of impurities is one of the key issues facing the industrial recycling of waste plastics.

[0003] Currently, there are two main methods for removing impurity elements. The first method involves removing them before pyrolysis, i.e., setting a low-temperature impurity removal reaction section (300℃) before the high-temperature pyrolysis section (350℃). This impurity removal process cannot achieve a long reaction time, so the impurity removal rate is not high, and the removed impurity elements can easily undergo secondary reactions immediately, forming impurity molecules that are even more difficult to remove. An existing Chinese patent CN114437776A discloses a method and system for preparing pyrolysis feedstock from waste plastic oil and / or waste tire oil. It is a dechlorination and impurity removal process for oil products generated after the pyrolysis of waste plastics. The pyrolyzed oil has low viscosity and good fluidity, making it easier to process from the perspective of heat and mass transfer. However, when chlorinated waste plastics are converted into plastic oil, they need to undergo pyrolysis temperatures of 350-400℃ or even higher. During this process, many small-molecule polysubstituted chlorinated / halogenated hydrocarbons, as well as monosubstituted and polysubstituted chlorobenzenes, are formed. The boiling points and polarities of these small-molecule organochlorides are similar to those of the pyrolysis oil, making it difficult to separate them from the pyrolysis oil by physical means. Even though high-temperature hydrogenation can remove chlorides, this process requires additional energy consumption and involves high temperature and high pressure. Furthermore, halogens can easily poison the catalyst during the removal process. Therefore, removing chlorides from plastic pyrolysis oil is a significant challenge.

[0004] The second method involves removal after pyrolysis. This means that impurity elements are not intentionally removed before pyrolysis; purification is then sought after obtaining the initial pyrolysis products. Halogen, sulfur, and nitrogen impurities readily react with hydrocarbons at high temperatures, forming molecules that are more difficult to remove, such as polycyclic aromatic hydrocarbons, thiols, thioethers, and heterocyclic hydrocarbons. Simultaneously, the presence of excessive sulfur and chlorine elements during the pyrolysis process poses a challenge to the corrosion resistance of the entire system. Furthermore, the high impurity content of the primary pyrolysis products makes it difficult to introduce them into the catalyst system, thus limiting the conversion of pyrolysis products into higher-value products. Summary of the Invention

[0005] To address at least one of the problems mentioned in the background art, this application provides a method and system for removing impurities from low-value waste plastics. This method can completely remove halogens, sulfur, and nitrogen impurities from low-value waste plastics before pyrolysis, achieving a final concentration of less than 100 ppm for sulfur, chlorine, and halogens. This avoids the generation of difficult-to-treat chlorides during the impurity removal process, thereby simplifying the subsequent pyrolysis process and significantly improving the efficiency of obtaining pure pyrolytic hydrocarbons.

[0006] The specific technical solutions provided in this application are as follows:

[0007] Firstly, a method for removing impurities from low-value waste plastics is provided, the method comprising the following steps:

[0008] S1: The raw material is mixed with heated solvent oil, and then dehydrated and melted to form a molten mixture;

[0009] S2: The molten mixture enters the impurity removal zone after filtration, and auxiliary impurity removal gas is introduced into the impurity removal zone to mix with the molten mixture and carry out the impurity removal reaction;

[0010] S3: The gas generated by the impurity removal reaction is discharged through the exhaust unit. After the impurity removal reaction, the material enters the homogenization zone to be mixed evenly and react.

[0011] S4: After the reaction is completed, a depurified product is obtained. A portion of the depurified product is output according to the preset output conditions. The remaining depurified product is mixed with the original material through the circulation channel, and steps S1 to S3 are continued.

[0012] In one specific embodiment, the ratio of solvent oil to raw material in step S1 is 2-10:1 kgh. -1 / kgh -1 The ratio of the auxiliary depurifying gas to the raw material is 0.01–0.2:1 kgh. -1 / kgh -1 .

[0013] In one specific embodiment, the ratio of solvent oil to raw material in step S1 is 4-6:1 kgh. -1 / kgh -1 .

[0014] In one specific embodiment, the temperature of the heated solvent oil is 150–230°C, and the temperature of the impurity removal reaction is 260–350°C.

[0015] In one specific embodiment, the temperature of the deimpurification reaction is 280–320°C.

[0016] In one specific embodiment, the solvent oil in step S1 includes at least one or more of the following: heavy oil in the 350-500°C distillation range, heavy diesel oil in the 280-350°C distillation range, reduced-steam wax oil, and molten paraffin.

[0017] In one specific embodiment, the auxiliary depurification gas in step S2 is a combination gas of hydrogen and one or more of oxygen, ozone, nitrogen, carbon dioxide and argon, wherein the molar percentage of hydrogen is greater than or equal to 10%.

[0018] Secondly, a low-value waste plastic impurity removal system is provided, the system comprising an impurity removal unit, an auxiliary impurity removal unit, and a recycling unit;

[0019] The impurity removal unit is used to dehydrate and remove impurities from the raw materials. The impurity removal unit includes a reactor, a dehydration zone, an impurity removal zone and a material homogenization zone disposed in the reactor. The dehydration zone, the impurity removal zone and the material homogenization zone are arranged sequentially from top to bottom along the reactor.

[0020] The auxiliary impurity removal unit includes at least one air inlet disposed on the reactor, the air inlet being used to introduce auxiliary impurity removal gas into the impurity removal zone;

[0021] The circulation unit includes a circulation pipe connected to the bottom of the reactor. The other end of the circulation pipe is connected to a first branch pipe and a second branch pipe. The first branch pipe leads into the reactor, and the second branch pipe is used for discharging material. The first branch pipe is also connected to a solvent oil input pipe for introducing solvent oil into the reactor.

[0022] In one specific embodiment, a circulation pump, a heat exchanger, and several control valves are also installed in the middle of the circulation pipeline. The circulation pipeline is used to heat the impurity removal product liquid to a preset temperature and output it to the first branch pipe or the second branch pipe.

[0023] In one specific embodiment, a discharge control valve is also connected to the second branch pipe, and a liquid level sensor is connected to the reactor. The discharge control valve is electrically connected to the liquid level sensor to control the output of the depurified liquid.

[0024] In one specific embodiment, a screen is installed between the dehydration zone and the impurity removal zone, the screen being used to filter the molten mixture.

[0025] In one specific embodiment, the system further includes:

[0026] The feeding unit includes at least one feed inlet, which is located on the side wall near the upper end of the reactor and is used to input raw materials.

[0027] The exhaust unit is used to discharge the gas generated in the impurity removal reaction. The exhaust unit includes at least one exhaust port opened at the upper end of the reactor. The exhaust port is also connected to an exhaust valve and an exhaust pipe. The end of the exhaust pipe away from the reactor is connected to an external vacuum system.

[0028] The embodiments of this application have the following beneficial effects:

[0029] 1. The pre-purification process provided in this application embodiment can mix the solvent oil in the raw material using the purification method described in this application before deep pyrolysis, and then successively dehydrate and melt it. An auxiliary purification gas is then introduced to carry out the purification reaction. After purification is completed, the gas generated after the purification reaction is discharged through an exhaust unit, and part of the purified product is output from the reactor, while the other part is recycled back to the purification system to mix with other raw materials and continue the purification reaction. This pre-purification process ensures that the temperature of the entire purification process is less than or equal to 350°C, achieving sulfur, chlorine, and halogen content of less than 100 ppm after purification, thereby avoiding the generation of difficult-to-treat chlorides during the purification process. Furthermore, the waste plastic treated by pre-purification can ignore the corrosion of equipment by impurities such as sulfur and chlorine during the next deep pyrolysis step, greatly improving the efficiency of obtaining pure, high-value products. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 A schematic diagram illustrating the steps of the method for removing impurities from low-value waste plastics according to this application is shown.

[0032] Figure 2 A schematic diagram of a low-value waste plastic impurity removal system according to this application is shown;

[0033] In the diagram, 1. Reactor; 2. Dehydration zone; 3. Impurity removal zone; 4. Equalization zone; 5. Screen; 6. Feed inlet; 7. Air inlet; 8. Air inlet pipe; 9. Air inlet valve; 10. Brown gas generator; 11. Aeration plate; 12. Exhaust port; 13. Exhaust valve; 14. Exhaust pipe; 15. Circulation pipe; 16. First control valve; 17. First branch pipe; 18. Second branch pipe; 19. Second control valve; 20. Discharge control valve; 21. Solvent oil input pipe; 22. Oil inlet control valve; 23. Circulation pump; 24. Heat exchanger; 25. Liquid level sensor. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0035] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein in the specification of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0036] Example 1

[0037] A method for removing impurities from low-value waste plastics, such as Figure 1 As shown, the method includes the following steps:

[0038] Step S1: The raw material is mixed with heated solvent oil, and then dehydrated and melted to form a molten mixture.

[0039] In one specific embodiment, the raw material is low-value waste plastic. Because low-value waste plastic is complex and contains many impurities, direct pyrolysis will result in pyrolysis products containing large amounts of halogenated aromatic hydrocarbons, halogenated hydrocarbons, thiols, and heterocyclic compounds. These pyrolysis products are dark in color, have a strong odor, poor combustion performance, and very low utilization value. Therefore, low-value waste plastic needs to be pretreated before pyrolysis to remove halogen, sulfur, and nitrogen impurities.

[0040] Low-value waste plastics (raw material) and solvent oil are added to the reactor according to a pre-set dosage. The solvent oil is heated before being added. The material enters the impurity removal system through the reactor's inlet, while the hot solvent oil also flows into the system. The raw material and the heated solvent oil exchange heat, causing the moisture in the low-value waste plastics to rapidly vaporize and be discharged as water vapor. After dehydration in the dehydration zone, the temperature of the raw material continues to rise to 150-230℃. The plastic components soften and melt, spontaneously mixing with the circulating solvent oil to form a molten mixture. This molten mixture passes through a screen plate, filtering out large mechanical impurities. Even if some plastic does not melt in time, it will be trapped on the screen plate. For example, large inorganic impurities such as iron blocks and stones will be intercepted by the screen. These impurities will continue to absorb heat and heat up until they melt and pass through the screen plate.

[0041] In one specific embodiment, the screen is also equipped with a scraper. When the material trapped on the screen accumulates to a certain extent, the scraper removes the trapped material, thereby preventing the screen from becoming clogged.

[0042] The solvent oil includes at least one or more of the following: high-temperature heat transfer oil, heavy oil in the 350-500℃ distillation range, heavy diesel oil in the 280-350℃ distillation range, reduced-steam wax oil, and molten paraffin.

[0043] In one specific embodiment, the ratio of solvent oil to raw material in step S1 is 2–10:1 kgh⁻¹ / kgh⁻¹; preferably, the ratio is 4–6:1 kgh⁻¹. -1 / kgh -1 The temperature of the heated solvent oil is 150–230°C.

[0044] Step S2: After filtration, the molten mixture enters the impurity removal zone, and an auxiliary impurity removal gas is introduced into the impurity removal zone to mix with the molten mixture and carry out the impurity removal reaction.

[0045] After being filtered through a sieve, the molten mixture continues to exchange heat with the solvent oil, causing the temperature of the molten mixture to continue to rise. At the same time, the temperature reaches the decomposition temperature of impurity elements such as chlorine and sulfur, thus causing a deimpurification reaction. With the help of an auxiliary deimpurification gas, impurity elements such as chlorine and sulfur undergo a deimpurification reaction, producing gases such as hydrogen chloride and hydrogen sulfide, which are discharged from the reactor in gaseous form.

[0046] To further improve the reaction efficiency between the molten mixture and the auxiliary depurifying gas, the auxiliary depurifying gas introduced into the depurifying zone is a preheated depurifying gas, which is preheated to a temperature of 200–250°C. Simultaneously, the heated auxiliary depurifying gas forms microbubbles in the depurifying zone through the aeration plate, allowing the depurifying gas to escape in the form of microbubbles. This increases the contact area between the gas and the substance, thereby ensuring that the auxiliary depurifying gas fully contacts the impurity components in the molten mixture and assists in its complete depurification.

[0047] In one specific embodiment, the ratio of the auxiliary depurifying gas to the original material is 0.01–0.2:1 kgh. -1 / kgh -1 The temperature for the depurification reaction is 260–350°C; preferably, the temperature for the depurification reaction is 280–320°C.

[0048] The auxiliary depurification gas in step S2 is a combination of hydrogen and one or more of oxygen, ozone, nitrogen, carbon dioxide and argon, wherein the molar percentage of hydrogen is greater than or equal to 10%.

[0049] Step S3: The gas generated by the impurity removal reaction is discharged through the exhaust unit. After the impurity removal reaction, the material enters the homogenization zone to be mixed evenly and react.

[0050] Halogens and impurities such as sulfur and nitrogen in organic matter from low-value waste plastics undergo a purification reaction at 280-320℃ using an auxiliary purification gas. This process removes the impurities from the solution and discharges them into the exhaust unit. The exhaust unit is connected to a vacuum system to ensure the entire purification system operates under vacuum.

[0051] Meanwhile, the material after the impurity removal reaction enters the homogenization zone of the reactor and is further mixed with the auxiliary impurity removal gas and reacted.

[0052] In one specific embodiment, the molten mixture and auxiliary depurifying gas, after passing through a depurifying zone to remove impurities such as chlorine, sulfur, and halogens, enter a homogenization zone. This homogenization zone is equipped with a turbulence channel, which further and thoroughly mixes the molten mixture and auxiliary depurifying gas, resulting in a more complete depurification reaction. The molten mixture and auxiliary depurifying gas undergo dehydration and depurification before flowing out through a circulation channel connected to the bottom of the reactor. A circulation pump and heat exchanger are installed in the middle of this channel. When the temperature of the reacted solution decreases, it is further heated by the circulation pump and heat exchanger until the temperature of the thoroughly mixed reaction solution reaches the temperature required for the circulating solvent oil inlet.

[0053] Step S4: After the reaction is completed, a depurified product is obtained. A portion of the depurified product is output according to the preset output conditions. The remaining depurified product is mixed with the original material through the circulation channel, and steps S1 to S3 are continued.

[0054] In one specific embodiment, after a reaction time, a depurified product is obtained. The depurified product flows out from the circulation channel at the bottom of the reactor. Specifically, the current liquid level in the reactor is detected by a level gauge and controlled by the control valve at the outlet to ensure that the liquid level in the reactor is maintained at the initial liquid level. That is, the output depurified product is the solution volume corresponding to the difference between the current liquid level and the initial liquid level. Another part of the depurified product enters the reactor along the first branch pipe of the circulation channel and mixes with the original material to continue the depurification reaction.

[0055] In one specific embodiment, low-value waste plastics undergo a purification process to remove moisture, chlorine, sulfur, and other halogen impurities. The purified waste plastics are then mixed with a solvent to form a fluid mixture, primarily composed of hydrocarbons of various carbon and hydrogen elements. This mixture is then fed into a deeper pyrolysis process, where it is broken down into smaller hydrocarbon molecules, such as pyrolysis gas and pyrolysis oil. Because impurities have been removed in the initial stage, the resulting pyrolysis products, such as pyrolysis gas and pyrolysis oil, are cleaner.

[0056] This application employs a mixed gas as an auxiliary depurification gas to react with low-value waste plastics in solution, thereby improving the removal rate of halogens, sulfur, and nitrogen. This allows for the simultaneous removal of halogens, sulfur, and nitrogen. The auxiliary gas serves both as a reaction participant and a protective gas, preventing the removed halogens and sulfur from reacting again with certain molecules in the waste plastic to form halogenated or thiolated hydrocarbons. Furthermore, the entire depurification reaction process is a dynamic, cyclical system, ensuring sufficient reaction time for more thorough depurification. The vacuum system creates a negative pressure environment during the depurification reaction, enabling the dehydration and depurification of low-value waste plastics with lower energy consumption.

[0057] Example 2

[0058] Corresponding to the above embodiments, this application provides a low-value waste plastic impurity removal system, such as... Figure 2 As shown, the system includes a de-impurity unit, an auxiliary de-impurity unit, a circulation unit, a feeding unit, and an exhaust unit.

[0059] The impurity removal unit is used to dehydrate and remove impurities from the raw materials. The impurity removal unit includes a reactor 1, a dehydration zone 2, an impurity removal zone 3 and a material homogenization zone 4 disposed in the reactor 1. The dehydration zone 2, the impurity removal zone 3 and the material homogenization zone 4 are arranged sequentially from top to bottom along the reactor 1.

[0060] In one specific embodiment, a screen 5 is installed between the dehydration zone 2 and the impurity removal zone 3. The screen 5 is used to filter larger mechanical impurities in the molten mixture. Specifically, a scraper is also installed on the screen 5. When the material trapped on the screen 5 accumulates to a certain extent, the scraper removes the trapped material, thereby preventing the screen 5 from becoming clogged. A turbulence channel is provided in the homogenization zone 4. Under the action of the turbulence channel, the molten mixture and the auxiliary impurity removal gas are further and more thoroughly mixed, thereby carrying out a more complete impurity removal reaction.

[0061] Specifically, low-value waste plastics (raw material) and solvent oil are added to reactor 1 according to a pre-set dosage. The solvent oil is heated solvent oil. The material enters the impurity removal system through the feed inlet 6 of reactor 1, while the hot solvent oil also flows into reactor 1. The raw material and the heated solvent oil exchange heat, and the moisture in the low-value waste plastics rapidly vaporizes and is discharged as water vapor. After dehydration in dehydration zone 2, the temperature of the raw material continues to rise to 150-230℃, causing the plastic components to soften and melt spontaneously, mixing with the circulating solvent oil to form a molten mixture. The molten mixture flows downward along reactor 1, passing through screen 5 to filter impurities, and then enters impurity removal zone 3.

[0062] The auxiliary impurity removal unit includes an air inlet 7 installed on the reactor 1. An air inlet pipe 8 is connected to the outside of the air inlet 7. An air inlet valve 9 is also installed on the air inlet pipe 8. A Brown gas generator device 10 is connected to the end of the air inlet pipe 8 away from the reactor 1. The air inlet 7 is used to introduce auxiliary impurity removal gas into the impurity removal zone 3.

[0063] Furthermore, an aeration plate 11 is installed inside the reactor 1. The aeration plate 11 is positioned between the impurity removal zone 3 and the material equalization zone 4. The air inlet 7 is connected to one end of the aeration plate 11 to introduce auxiliary impurity removal gas into the aeration plate 11. The auxiliary impurity removal gas forms microbubbles in the impurity removal zone 3 through the aeration plate 11, allowing the gas to escape in the form of microbubbles. This increases the contact area between the gas and the material, thereby ensuring that the auxiliary impurity removal gas fully contacts the impurity components in the molten mixture, assisting in its complete removal.

[0064] In one specific embodiment, an exhaust unit is used to discharge the gases generated during the impurity removal reaction. The exhaust unit includes an exhaust port 12 located at the upper end of the reactor 1. The exhaust port 12 is also connected to an exhaust valve 13 and an exhaust pipe 14. The end of the exhaust pipe 14 furthest from the reactor 1 is connected to an external vacuum system. As the temperature of the molten mixture continues to rise, it reaches the decomposition temperature of impurity elements such as chlorine and sulfur, thereby causing a impurity removal reaction. During the impurity removal reaction, impurity elements such as chlorine and sulfur react with the introduced auxiliary impurity removal gas to generate gases such as hydrogen chloride and hydrogen sulfide, which are discharged from the reactor 1 in gaseous form.

[0065] The circulation unit includes a circulation pipe 15 connected to the bottom of the reactor 1. Several control valves are installed on the circulation pipe 15. One end of the circulation pipe 15 is connected to the bottom of the reactor 1, and a first control valve 16 is installed on the pipe of the circulation pipe 15 near the bottom of the reactor 1. The other end of the circulation pipe 15 is connected to a first branch pipe 17 and a second branch pipe 18. The first branch pipe 17 leads into the reactor 1, and a second control valve 19 is installed on the pipe of the first branch pipe 17 near the reactor 1. The second branch pipe 18 is used for discharging material, and a discharge control valve 20 is installed on the pipe of the second branch pipe 18 near the discharge port. A solvent oil inlet pipe 21 is also connected to the first branch pipe 17 for introducing solvent oil into the reactor 1, and an oil inlet control valve 22 is installed on the first branch pipe 17.

[0066] Furthermore, a circulation pump 23 and a heat exchanger 24 are installed in the middle of the circulation pipe 15. A third control valve and a fourth control valve are respectively installed on the inlet and outlet pipes of the heat exchanger 24. The circulation pipe 15 is used to heat the impurity removal product liquid to a preset temperature and output it to the first branch pipe 17 or the second branch pipe 18. It flows out through the circulation channel connected to the bottom of the reactor 1. The circulation pump 23 and the heat exchanger 24 are also installed in the middle of the circulation channel. When the temperature of the solution after the reaction drops, it continues to be heated under the action of the circulation pump 23 and the heat exchanger 24, so that the temperature of the fully mixed reaction liquid rises to the temperature required for the circulating solvent oil inlet.

[0067] A discharge control valve 20 is installed on the second branch pipe 18, and a liquid level sensor 25 is connected to the reactor 1. The discharge control valve 20 is electrically connected to the liquid level sensor 25 to control the output of the depurified product. After a period of reaction, the depurified product is obtained and flows out from the circulation channel at the bottom of the reactor 1. Specifically, the liquid level in the reactor 1 is detected by a liquid level gauge and controlled by the control valve at the discharge port to ensure that the liquid level in the reactor 1 is maintained at the initial liquid level. That is, the output depurified product is the solution volume corresponding to the difference between the current liquid level and the initial liquid level. Another part of the depurified product enters the reactor 1 along the first branch pipe 17 of the circulation channel and mixes with the original material to continue the depurification reaction.

[0068] In one specific embodiment, the first branch pipe 17 extends into the reactor 1 for spraying solvent oil into the reactor 1.

[0069] Through the above steps, the low-value waste plastics first undergo dehydration, then melt, and are uniformly mixed with the solvent. Subsequently, under the action of auxiliary depurifying gas, a gas-liquid reaction occurs. Simultaneously, the gas, existing in the form of microbubbles through the aeration plate 11, greatly enhances the contact between the gas and the solute, ensuring sufficient contact between the auxiliary gas and the reactants, thus achieving a complete reaction. At the same time, the entire system is under negative pressure, allowing the removed impurities from the low-value waste plastics to quickly separate from the raw materials. Furthermore, the presence of excess auxiliary gas prevents secondary reactions.

[0070] Specifically, according to the steps in Examples 1 and 2, different reaction conditions were used to remove impurities from the raw materials of low-value waste plastics, and the impurity elements in the product liquid after the reaction were detected. Based on the reaction steps and results, Examples 3 to 5 were obtained.

[0071] Example 3: A method for removing impurities from low-value waste plastics, comprising the following steps:

[0072] Step S1: The raw materials are mixed with solvent oil and heated, and then dehydrated and melted to form a molten mixture.

[0073] In one specific embodiment, the raw material is low-value waste plastic. Since low-value waste plastic is complex and contains many impurities, the pyrolysis products obtained by direct pyrolysis will contain a large amount of halogenated aromatic hydrocarbons, halogenated hydrocarbons, thiols, and heterocyclic compounds.

[0074] In step S1, the ratio of solvent oil to raw material is 4:1 kgh. -1 / kgh -1 The temperature of the heated solvent oil is 180℃, and the solvent oil is a high-temperature heat transfer oil.

[0075] Low-value waste plastics (raw materials) and solvent oil are added to the reactor according to a pre-set dosage. The solvent oil is heated solvent oil. The material enters the impurity removal system through the reactor inlet, and the hot solvent oil also flows into the impurity removal system. The two materials pass through the dehydration zone for dehydration in sequence, and then continue to be heated to form a molten mixture.

[0076] Step S2: After filtration, the molten mixture enters the impurity removal zone, and an auxiliary impurity removal gas is introduced into the impurity removal zone to mix with the molten mixture and carry out the impurity removal reaction.

[0077] The auxiliary depurification gas is a mixture of hydrogen, ozone, and nitrogen, with a hydrogen content of 15%, an ozone content of 5%, and a nitrogen content of 80%. The auxiliary depurification gas introduced into the depurification zone by the auxiliary depurification system is a preheated depurification gas, which is preheated to a temperature of 230°C. At the same time, the heated auxiliary depurification gas forms microbubbles of auxiliary gas in the depurification zone through the aeration plate, which allows the depurification gas to be released in the form of microbubbles, increasing the contact area between the gas and the substance.

[0078] In one specific embodiment, the ratio of the auxiliary depurifying gas to the original material is 0.1:1 kgh. -1 / kgh -1 The temperature during the deimpurification reaction is 320°C.

[0079] Step S3: The gas generated by the impurity removal reaction is discharged through the exhaust unit. After the impurity removal reaction, the material enters the homogenization zone to be mixed evenly and react.

[0080] Halogens and impurities such as sulfur and nitrogen in organic matter from low-value waste plastics are released as gaseous elements from the solution after the impurity removal reaction and discharged into the exhaust unit. Simultaneously, the material after the impurity removal reaction enters the homogenization zone of the reactor for further mixing and reaction with the auxiliary impurity removal gas.

[0081] Step S4: After the reaction is completed, a depurified product is obtained. A portion of the depurified product is output according to the preset output conditions. The remaining depurified product is mixed with the original material through the circulation channel, and steps S1 to S3 are continued.

[0082] In one specific embodiment, after a reaction time, a depurified product is obtained. The depurified product flows out from the circulation channel at the bottom of the reactor. Specifically, the current liquid level in the reactor is detected by a level gauge and controlled by the control valve at the outlet to ensure that the liquid level in the reactor is maintained at the initial liquid level. That is, the output depurified product is the solution volume corresponding to the difference between the current liquid level and the initial liquid level. Another part of the depurified product enters the reactor along the first branch pipe of the circulation channel and mixes with the original material to continue the depurification reaction.

[0083] The purification step in this embodiment, wherein the main components and impurity content of the original material and the main components and impurity content of the purified original material are as follows:

[0084] Table 1. Component detection results before and after impurity removal in Example 3

[0085]

[0086] By adopting the method in Example 3, the content of chlorine and sulfur in the product after impurity removal is 85ppm and 55ppm, respectively, both of which are less than 100ppm. The entire impurity removal reaction process is a dynamic circulation system, which ensures the reaction time of the material and makes the impurity removal more thorough. The impurity removal reaction is carried out in a negative pressure environment by setting up a vacuum system, which can achieve dehydration and impurity removal of low-value waste plastics with low energy consumption.

[0087] Example 4

[0088] A method for removing impurities from low-value waste plastics includes the following steps:

[0089] Step S1: The raw materials are mixed with solvent oil and heated, and then dehydrated and melted to form a molten mixture.

[0090] In one specific embodiment, the raw material is low-value waste plastic. Since low-value waste plastic is complex and contains many impurities, the pyrolysis products obtained by direct pyrolysis will contain a large amount of halogenated aromatic hydrocarbons, halogenated hydrocarbons, thiols, and heterocyclic compounds.

[0091] In step S1, the ratio of solvent oil to raw material is 4:1 kgh. -1 / kgh -1 The temperature of the heated solvent oil is 180℃, and the solvent oil is a high-temperature heat transfer oil. Low-value waste plastics (raw materials) and solvent oil are added to the reactor according to a pre-set dosage. The solvent oil is heated before being added. The materials enter the impurity removal system through the reactor inlet, and the hot solvent oil also flows into the impurity removal system. Both materials pass through the dehydration zone for dehydration, and then are heated to form a molten mixture.

[0092] Step S2: After filtration, the molten mixture enters the impurity removal zone, and an auxiliary impurity removal gas is introduced into the impurity removal zone to mix with the molten mixture and carry out the impurity removal reaction.

[0093] The auxiliary depurifying gas is a mixture of hydrogen, ozone, and nitrogen, with a hydrogen content of 15%, an ozone content of 5%, and a nitrogen content of 80%. The auxiliary depurifying gas introduced into the depurifying zone is preheated to 230°C. Simultaneously, the heated auxiliary depurifying gas forms microbubbles in the depurifying zone through an aeration plate, allowing the depurifying gas to escape in the form of microbubbles, thus increasing the contact area between the gas and the substance.

[0094] In one specific embodiment, the ratio of the auxiliary depurifying gas to the original material is 0.1:1 kgh. -1 / kgh -1 The temperature during the deimpurification reaction is 320°C.

[0095] Step S3: The gas generated by the impurity removal reaction is discharged through the exhaust unit. After the impurity removal reaction, the material enters the homogenization zone to be mixed evenly and react.

[0096] Halogens and impurities such as sulfur and nitrogen in organic matter from low-value waste plastics are released as gaseous elements from the solution after the impurity removal reaction and discharged into the exhaust unit. Simultaneously, the material after the impurity removal reaction enters the homogenization zone of the reactor for further mixing and reaction with the auxiliary impurity removal gas.

[0097] Step S4: After the reaction is completed, a depurified product is obtained. A portion of the depurified product is output according to the preset output conditions. The remaining depurified product is mixed with the original material through the circulation channel, and steps S1 to S3 are continued.

[0098] In one specific embodiment, after a reaction time, a depurified product is obtained. The depurified product flows out from the circulation channel at the bottom of the reactor. Specifically, the current liquid level in the reactor is detected by a level gauge and controlled by the control valve at the outlet to ensure that the liquid level in the reactor is maintained at the initial liquid level. That is, the output depurified product is the solution volume corresponding to the difference between the current liquid level and the initial liquid level. Another part of the depurified product enters the reactor along the first branch pipe of the circulation channel and mixes with the original material to continue the depurification reaction.

[0099] The purification step in this embodiment, wherein the main components and impurity content of the original material and the main components and impurity content of the purified original material are as follows:

[0100] Table 2. Component detection results before and after impurity removal in Example 4.

[0101]

[0102] By adopting the method in Example 4, the content of chlorine and sulfur in the product after impurity removal is 89ppm and 47ppm, respectively, both of which are less than 100ppm. The entire impurity removal reaction process is a dynamic circulation system, which ensures the reaction time of the material and makes the impurity removal more thorough. The impurity removal reaction is carried out in a negative pressure environment by setting up a vacuum system, which can achieve dehydration and impurity removal of low-value waste plastics with low energy consumption.

[0103] The conditions in Example 4 were changed, namely, the proportion of hydrogen in the auxiliary depurification gas was increased, the amount of auxiliary depurification gas compared with the original material was increased, and the amount of solvent oil was increased. Comparative Examples 1 to 4 corresponding to Example 4 were set up as shown in Table 3, and the element content of impurities before and after depurification under different conditions was detected. The detection results are shown in Table 4.

[0104] Table 3 shows the reaction conditions for Comparative Examples 1–4.

[0105]

[0106] Table 4 shows the test results before and after impurity removal in Comparative Examples 1–4.

[0107]

[0108] The comparison of the impurity removal conditions and the test results after impurity removal in Examples 1-4 shows that when the halogen impurity content in the initial raw material is high, increasing the hydrogen content in the auxiliary impurity removal gas, increasing the amount of auxiliary impurity removal gas, and increasing the amount of solvent oil can improve the impurity removal efficiency. Specifically, when the proportion of hydrogen is above 50%, the effect of removing impurities from the raw material is better. At the same time, increasing the amount of solvent oil makes the heat exchange between the solvent oil and the material more rapid and reduces the viscosity of the system, thereby further promoting the removal of mechanical impurities. Under the above reaction conditions, the chlorine and sulfur impurity content after impurity removal is less than 100 ppm. The entire impurity removal process can achieve dehydration and impurity removal of low-value waste plastics with low energy consumption.

[0109] Example 5

[0110] A method for removing impurities from low-value waste plastics, the method comprising the following steps:

[0111] Step S1: The raw materials are mixed with solvent oil and heated, and then dehydrated and melted to form a molten mixture.

[0112] In one specific embodiment, the raw material is low-value waste plastic. Since low-value waste plastic is complex and contains many impurities, the pyrolysis products obtained by direct pyrolysis will contain a large amount of halogenated aromatic hydrocarbons, halogenated hydrocarbons, thiols, and heterocyclic compounds.

[0113] In step S1, the ratio of solvent oil to raw material is 5:1 kgh. -1 / kgh -1 The temperature of the heated solvent oil is 200℃, and the solvent oil is heavy oil in the 350-500℃ distillation range.

[0114] Low-value waste plastics (raw materials) and solvent oil are added to the reactor according to a pre-set dosage. The solvent oil is heated solvent oil. The material enters the impurity removal system through the reactor inlet, and the hot solvent oil also flows into the impurity removal system. The two materials pass through the dehydration zone for dehydration in sequence, and then continue to be heated to form a molten mixture.

[0115] Step S2: After filtration, the molten mixture enters the impurity removal zone, and an auxiliary impurity removal gas is introduced into the impurity removal zone to mix with the molten mixture and carry out the impurity removal reaction.

[0116] The auxiliary depurification gases are hydrogen and nitrogen, with a hydrogen content of 12% and a nitrogen content of 88%. The auxiliary depurification gas introduced into the depurification zone is preheated to a temperature of 200℃. Simultaneously, the heated auxiliary depurification gas forms microbubbles in the depurification zone through the aeration plate, allowing the depurification gas to escape in the form of microbubbles, thus increasing the contact area between the gas and the substance.

[0117] In one specific embodiment, the ratio of the auxiliary depurifying gas to the original material is 0.12:1 kgh. -1 / kgh -1 The temperature during the deimpurification reaction is 300℃.

[0118] Step S3: The gas generated by the impurity removal reaction is discharged through the exhaust unit. After the impurity removal reaction, the material enters the homogenization zone to be mixed evenly and react.

[0119] Halogens and impurities such as sulfur and nitrogen in organic matter from low-value waste plastics are released as gaseous elements from the solution after the impurity removal reaction and discharged into the exhaust unit. Simultaneously, the material after the impurity removal reaction enters the homogenization zone of the reactor for further mixing and reaction with the auxiliary impurity removal gas.

[0120] Step S4: After the reaction is completed, a depurified product is obtained. A portion of the depurified product is output according to the preset output conditions. The remaining depurified product is mixed with the original material through the circulation channel, and steps S1 to S3 are continued.

[0121] In one specific embodiment, after a reaction time, a depurified product is obtained. The depurified product flows out from the circulation channel at the bottom of the reactor. Specifically, the current liquid level in the reactor is detected by a level gauge and controlled by the control valve at the outlet to ensure that the liquid level in the reactor is maintained at the initial liquid level. That is, the output depurified product is the solution volume corresponding to the difference between the current liquid level and the initial liquid level. Another part of the depurified product enters the reactor along the first branch pipe of the circulation channel and mixes with the original material to continue the depurification reaction.

[0122] The purification step in this embodiment, wherein the main components and impurity content of the original material and the main components and impurity content of the purified original material are shown in Table 5 below:

[0123] Table 5. Component detection results before and after impurity removal in Example 5

[0124]

[0125] By employing the method described in Example 5, the chlorine content in the purified product was 130 ppm, and the sulfur content was 3200 ppm. This indicates that the chlorine removal effect was good, while the sulfur removal effect was poor, with the sulfur content in the residue remaining high. This suggests that when the sulfur content is high, the purification conditions need further adjustment.

[0126] The conditions in Example 5 were changed, namely, the amount of oxidizing gas was reduced, the proportion of hydrogen in the auxiliary impurity removal gas was increased, and an oil agent with better high-temperature stability was selected to obtain the products obtained by different impurity removal processes. Comparative Examples 5 to 8 corresponding to Example 5 were set up as shown in Table 6, and the element content of impurities before and after impurity removal under different impurity removal conditions was detected. The detection results are shown in Table 7.

[0127] Table 6 shows the reaction conditions for Comparative Examples 5–8.

[0128]

[0129] Table 7 shows the test results before and after impurity removal in Comparative Examples 5-8.

[0130]

[0131] The results of the impurity removal conditions and post-removal tests in Examples 5-8 show that when the initial feedstock has a high sulfur impurity content, the proportion of hydrogen in the auxiliary removal gas can be increased, the amount of oxidizing gas can be reduced, and a solvent oil with better high-temperature stability can be selected for the reaction. The solvent oils in the comparative examples, ranked from least to most stable, are vacuum wax oil, heavy oil in the 350-500℃ distillation range, and heavy diesel oil in the 280-350℃ distillation range. The post-removal test results in Examples 6 and 7 show that replacing the solvent oil with heavy diesel oil helps remove difficult-to-remove impurities. Simultaneously, removing ozone from the auxiliary removal gas and increasing hydrogen in the auxiliary removal gas promotes dechlorination and desulfurization. Furthermore, selecting a more stable solvent oil avoids secondary reactions between the solvent oil and sulfur, preventing the formation of substances that are difficult to remove, thus improving desulfurization efficiency. The entire impurity removal system process and the choice of solvent oil are closely related to the impurities in the feedstock. Considering economic, safety, and other factors, these parameters can be adjusted for each different material to achieve the best impurity removal effect before pyrolysis.

[0132] Although preferred embodiments have been described in this application, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of the embodiments of this application.

[0133] Obviously, those skilled in the art can make various modifications and variations to this application without departing from the spirit and scope of this application. Therefore, if such modifications and variations fall within the scope of the claims of this application and their equivalents, this application also intends to include such modifications and variations.

Claims

1. A method for removing impurities from low-value waste plastics, characterized in that, The method includes the following steps: S1: The raw material is mixed with heated solvent oil, and then dehydrated and melted to form a molten mixture; the raw material and the heated solvent oil exchange heat, the water in the raw material vaporizes and is converted into water vapor and discharged; after the raw material is dehydrated, the temperature rises to 150~230℃, and the plastic component in the raw material softens and melts and mixes with the solvent oil to form a molten mixture; S2: After filtration, the molten mixture enters the impurity removal zone, where an auxiliary impurity removal gas is introduced to mix with the molten mixture and carry out the impurity removal reaction. The auxiliary impurity removal gas is preheated at a temperature of 200-250°C, forming microbubbles in the impurity removal zone. The auxiliary impurity removal gas is a combination of hydrogen and one or more of oxygen, ozone, nitrogen, carbon dioxide, and argon, wherein the molar percentage of hydrogen is greater than or equal to 10%. S3: The gas generated by the impurity removal reaction is discharged through the exhaust unit. After the impurity removal reaction, the material enters the homogenization zone to be mixed evenly and react. S4: After the reaction is completed, a depurified product is obtained. A portion of the depurified product is output according to the preset output conditions. The remaining depurified product is mixed with the original material through the circulation channel, and steps S1 to S3 are continued.

2. The method for removing impurities from low-value waste plastics according to claim 1, characterized in that, In step S1, the ratio of solvent oil to raw material is 2~10:1 kgh. -1 / kgh -1 The ratio of the auxiliary depurifying gas to the raw material is 0.01~0.2:1 kgh. -1 / kgh -1 .

3. The method for removing impurities from low-value waste plastics according to claim 2, characterized in that, The temperature of the heated solvent oil is 150~230℃, and the temperature of the impurity removal reaction is 260~350℃.

4. The method for removing impurities from low-value waste plastics according to claim 3, characterized in that, The solvent oil in step S1 includes at least one or more of the following: heavy oil in the 350-500℃ distillation range, heavy diesel oil in the 280-350℃ distillation range, vacuum wax oil, and molten paraffin.

5. A low-value waste plastic impurity removal system for use in the method according to any one of claims 1 to 4, characterized in that, The system includes a de-impurification unit, an auxiliary de-impurification unit, and a circulation unit; The impurity removal unit is used to dehydrate and remove impurities from the raw materials. The impurity removal unit includes a reactor, a dehydration zone, an impurity removal zone and a material homogenization zone disposed in the reactor. The dehydration zone, the impurity removal zone and the material homogenization zone are arranged sequentially from top to bottom along the reactor. The auxiliary impurity removal unit includes at least one air inlet disposed on the reactor, the air inlet being used to introduce auxiliary impurity removal gas into the impurity removal zone; The circulation unit includes a circulation pipe connected to the bottom of the reactor. The other end of the circulation pipe is connected to a first branch pipe and a second branch pipe. The first branch pipe leads into the reactor, and the second branch pipe is used for discharging material. The first branch pipe is also connected to a solvent oil input pipe for introducing solvent oil into the reactor.

6. The low-value waste plastic impurity removal system according to claim 5, characterized in that, The circulation pipeline is also equipped with a circulation pump, a heat exchanger and several control valves in the middle. The circulation pipeline is used to heat the impurity removal product liquid to a preset temperature and output it to the first branch pipe or the second branch pipe.

7. The low-value waste plastic impurity removal system according to claim 6, characterized in that, The second branch pipe is also connected to a discharge control valve, and the reactor is connected to a liquid level sensor. The discharge control valve is electrically connected to the liquid level sensor to control the output of the depurified liquid.

8. The low-value waste plastic impurity removal system according to claim 7, characterized in that, A screen is installed between the dehydration zone and the impurity removal zone, and the screen is used to filter the molten mixture.

9. The low-value waste plastic impurity removal system according to any one of claims 6 to 8, characterized in that, The system also includes: The feeding unit includes at least one feed inlet, which is located on the side wall near the upper end of the reactor and is used to input raw materials. An exhaust unit is provided for discharging the gases generated during the impurity removal reaction. The exhaust unit includes at least one exhaust port located at the top of the reactor. The exhaust port is also connected to an exhaust valve and an exhaust pipe. The end of the exhaust pipe away from the reactor is connected to an external vacuum system.

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