Separation cleaning device and separation cleaning method for pet microplastic powder

Abstract

The present application relates to the technical field of PET micro-plastic recycling, and particularly relates to a separation and cleaning device and method for PET micro-plastic powder. The device comprises a circular cleaning device shell, a middle stirring mechanism, an ultrasonic wave aeration mixing device, a high-low position sealing mechanism arranged along the circumference of the side wall and a peripheral water channel, a bottom opening and closing mechanism, and a bottom and inclined screw conveying mechanism. A composite flow field is formed by the lower end stirring and tilting mechanism, so that the PET micro-plastic powder is fully mixed and suspended with the solvent containing dioctyl phthalate, and then the ultrasonic wave and aeration are used to strengthen the density stratification. The water surface stirring mechanism concentrates the floating impurities to the high position sealing mechanism for discharge, and the bottom opening and closing mechanism and the screw conveying mechanism realize the continuous discharge and conveying of the cleaned PET material. The present application significantly improves the purity of PET recycling, reduces the consumption of water and chemicals, and has the advantages of high structural integration and high automation degree.

Description

Technical Field

[0001] This invention relates to the field of PET microplastic recycling technology, and in particular to a separation and cleaning device and method for PET microplastic powder. Background Technology

[0002] Microplastics typically refer to plastic particles or fragments with a diameter of less than 5 mm. They are generated in large quantities during plastic production, fiber processing, and bottle chip recycling, with polyester (PET) microplastic powder and granules being the most common. Due to their small particle size and large specific surface area, microplastics readily adsorb organic pollutants and heavy metals in the environment, accumulating in water, soil, and organisms, posing a potential threat to ecological safety and human health. On the other hand, chemical fiber companies and recycled plastic companies generate large amounts of PET microplastic powder containing silt, paper scraps, labels, and blends of various resins during the crushing, washing, and recycling of waste fibers, bottle chips, and scraps. If impurities such as PE, PP, PS, and PVC cannot be efficiently separated and surface adhering substances cannot be thoroughly cleaned, it will not only affect the quality of recycled polyester and the stability of downstream spinning and granulation, but also increase wastewater treatment load and operating costs. Therefore, developing efficient impurity removal, washing, and sorting equipment suitable for PET microplastic powder is of great significance.

[0003] Currently, various devices and processes have been proposed for the separation and recycling of microplastics or polyester microparticles. Chinese patent CN115157485A discloses a microplastic particle impurity removal and separation device. This device uses first and second spiral accelerating coils and connected to first and second conical cylinders to create a spiral vortex flow field within the conical cylinders, causing microplastic particles containing impurities such as mud, sand, and labels to flow through. Floating impurities like labels are discharged from the top using water flow and density differences, while settled mud is discharged from the bottom of the second conical cylinder, resulting in relatively pure micro-polyester plastic particles. This method utilizes multi-stage vortex and gravity stratification principles to "separately separate" microplastics, suitable for processing granular microplastics containing mud and labels. However, the device structure is relatively complex, with a long flow path, limiting its adaptability to finer, easily agglomerated powdery microplastics. Furthermore, it primarily focuses on removing mud and paper impurities, and its ability to finely separate PET from plastics such as PE / PP / PS / PVC in multi-resin blends remains insufficient.

[0004] Chinese patent CN115230018A proposes a method and system for recycling polyester microplastic particles. The system comprises a friction cleaner, a microplastic particle impurity removal and analysis device, a heating tank, a washing and rinsing tank, a microparticle material sorting machine, and a microparticle color sorting mechanism. The process first involves pre-cleaning and dispersing the microparticles using the friction cleaner. Then, the microplastic particle impurity removal and analysis device removes mud, sand, and suspended label matter. Next, the particles undergo further washing in the heating tank and washing and rinsing tank to remove the cleaning solution. Finally, the microparticle material sorting machine and color sorting machine separate particles of different materials and colored particles, achieving tiered purification and recycling of polyester microplastics. This system combines multiple units, including mechanical friction cleaning, vortex analysis, heating and washing, rinsing, dry material sorting, and color sorting, resulting in good overall recycling performance. It is suitable for granular or short-fiber polyester microplastics. However, this scheme still mainly relies on multiple devices connected in series, with the cleaning and separation processes being completed in multiple linear devices. The liquid utilization rate is relatively low, and the ability to quickly disperse and repeatedly clean powder-grade microplastic agglomerates is limited. It has not been specifically designed for the integrated process of "strong shear mixing - ultrasonic aeration enhancement - multi-stage stratified discharge - bottom centralized discharge" of high-concentration powder slurry in a single container.

[0005] Chinese patent CN120399283A further discloses a method and equipment for recycling and removing impurities from polyester microplastics. Its key feature is the use of irradiation technology to treat polyester microplastics. Electron beam irradiation alters the structure or properties of impurity plastics such as polyvinyl chloride (PVC), and combined with gravity separation, PVC impurities are efficiently removed from the mixed microplastics. The patent emphasizes precise control of radiation dose and processing time to balance impurity removal efficiency with polyester matrix properties. While this technology has certain advantages in removing specific impurities such as PVC, it requires a dedicated irradiation device, resulting in high equipment investment and energy consumption. Furthermore, it still requires density separation or flotation / sinking separation units to complete subsequent phase separation. This presents a significant barrier to entry for general chemical fiber plants or recycled plastic washing lines, and it does not solve the problems of agglomeration, unstable floating and sinking, and multiple rounds of washing required for powder-grade microplastics during wet washing.

[0006] In summary, while existing equipment for removing impurities and recovering microplastics, especially PET microplastic powder, has made beneficial explorations in vortex washing, multi-machine combination processes, and irradiation / flotation, there is still room for improvement in the following aspects: First, simultaneously achieving strong shear mixing, enhanced ultrasonic aeration, and a controllable rotating flow field within a single circular tank to accommodate the rapid dispersion and density stratification of fine powders and agglomerated particles; second, constructing multi-stage, selectable discharge ports on the sidewalls and bottom of the same tank, and coordinating with an external flow channel to achieve graded and directional discharge of upper flotation impurities, bottom residual liquid / heavy impurities, and washed PET material; third, completing a continuous process of washing, separation, slag discharge, and material discharge through integrated connection with bottom spiral conveyors and inclined spiral conveyors, while facilitating closed-loop circulation and intelligent control of the cleaning solution and reagents. Based on the above requirements, it is necessary to provide a separation and cleaning device and corresponding method with a more integrated structure, stronger flow field controllability, and the ability to achieve multi-round circulating washing and multi-level graded discharge of PET microplastic powder within a single piece of equipment, to overcome the shortcomings of existing technologies. Summary of the Invention

[0007] The technical objective of this invention is to provide a separation and cleaning device and its supporting method specifically for PET microplastic powder. This device achieves efficient dispersion and enhanced density separation and cleaning of powdered PET and its constituent PE, PP, PS, PVC, and other impurities within a single circular tank. Through a central agitator, an ultrasonic aeration mixing structure, and an integrated design of closed drainage and bottom discharge, it solves the problems of easy agglomeration of powdered microplastics, insufficient stratification, the need for multiple devices connected in series, and low water and agent utilization rates in existing technologies. This improves the purity of PET recycling, reduces water and agent consumption, and achieves continuous and automated cleaning and conveying processes.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] A separation and cleaning apparatus for PET microplastic powder, the apparatus comprising:

[0010] The outer shell of the cleaning device is a circular frame groove with an opening at the top, its side walls are arranged circumferentially, and a bottom discharge port is provided at the bottom.

[0011] The intermediate agitation mechanism is vertically positioned at the center of the cleaning device housing. The intermediate agitation mechanism includes a rotating shaft, a stirring mechanism, a water surface agitation mechanism, and a motor. The stirring mechanism is used to stir the material underwater, forming a composite flow field with axial and radial components during the stirring process, which promotes the mixing of the material and the water solvent and the dispersing of agglomerated materials. The water surface agitation mechanism is used to agitate floating objects near the water surface.

[0012] An ultrasonic aeration mixing device is arranged near the central actuation mechanism. Its lower end can extend below the liquid surface inside the cleaning device housing. The ultrasonic aeration mixing device introduces fine bubbles in the rotating flow field and applies ultrasonic vibration to enhance particle dispersion and floating / sinking according to density difference.

[0013] The sealing mechanism assembly is arranged circumferentially along the outer shell of the cleaning device and includes several openable sealing mechanisms, with the water outlet of the sealing mechanism located on the side wall of the outer shell of the cleaning device.

[0014] An outer water trough is arranged around the outer shell of the cleaning device. The outlet of each closed mechanism is connected to the outer water trough. The outer water trough has a water trough outlet that guides the discharged liquid to the impurity removal and slag discharge device.

[0015] A bottom opening and closing mechanism is provided at the bottom discharge port to realize bottom discharge of material.

[0016] Preferably, the upper end of the ultrasonic aeration mixing device is connected to the first cylinder via a bracket. The first cylinder is fixed above the water surface and is used to drive the ultrasonic aeration mixing device to move up and down between the underwater working position and the standby position above the water surface.

[0017] And / or, the ultrasonic aeration mixing device includes an ultrasonic transducer and an aeration pipeline connected to an external air source. Multiple micropores are opened on the wall of the aeration pipeline along the circumferential and axial directions to form a uniform cluster of microbubbles. The ultrasonic transducer is arranged along the aeration pipeline or coaxially with it, so that the bubbles break and vibrate in the ultrasonic field, thereby enhancing the density separation effect between PET and other plastic impurities in PET microplastics.

[0018] Preferably, the sealing mechanism includes several high-level sealing mechanisms and several low-level sealing mechanisms. The outlet of the high-level sealing mechanism is located on the upper part of the side wall of the cleaning device housing, and the outlet of the low-level sealing mechanism is located on the lower part of the side wall of the cleaning device housing. Each sealing mechanism includes an outlet communicating with the cleaning device housing and a gate for opening or closing the outlet. The gate is connected to a second cylinder located above the water surface through a connecting rod and a hinge to realize the opening and closing of the sealing mechanism.

[0019] Preferably, the high-position sealing mechanism and the low-position sealing mechanism are linked by the same second cylinder and connecting rod. The control system can selectively drive some or all of the high-position sealing mechanisms to open, or drive the low-position sealing mechanism to open, so as to achieve graded discharge of floating impurities on the water surface and secondary floating impurities respectively.

[0020] Preferably, the device also includes a bottom spiral conveying mechanism arranged below the bottom opening and closing mechanism for receiving materials falling from the bottom opening and closing mechanism and conveying them horizontally.

[0021] And / or, an inclined screw conveyor mechanism, the feed end of which is connected to the discharge end of the bottom screw conveyor mechanism, for lifting the material conveyed by the bottom screw conveyor mechanism along the inclined direction to the next process.

[0022] Preferably, the stirring mechanism includes multiple stirring blades arranged radially inclined, with each stirring blade staggered relative to the vertical axis and inclined relative to the axis of rotation.

[0023] And / or, the water surface agitation mechanism includes a plurality of arc-shaped paddles connected to a rotating shaft. Each arc-shaped paddle has a gap between its outer edge and the inner wall of the cleaning device housing, and is set at a predetermined arc and angle relative to the radial direction, so as to orient microplastic impurities floating on the water surface toward the peripheral area near the high-position closed mechanism when rotating.

[0024] Preferably, the bottom opening and closing mechanism includes a double door composed of two door panels. The double door is hinged to the bottom edge of the cleaning device housing via a bottom hinge and connected to a third cylinder located above the water surface via multiple force transmission rods, so as to realize the synchronous opening and closing of the double door under the drive of the third cylinder.

[0025] And / or, the double doors of the bottom opening and closing mechanism are arranged along the arc-shaped contour of the circular bottom outlet when closed. After the two doors are closed, they form an approximately integral arc-shaped sealing surface with the bottom outlet to reduce interference with the material flow field during the stirring process.

[0026] Preferably, the device also includes the control system, which includes a PLC controller and a human-machine interface. The PLC controller is connected to the liquid level sensor, temperature sensor and reagent metering unit. By setting process parameters such as ultrasonic working time, aeration rate, high-level drainage rate, low-level drainage rate and number of cycles, adaptive cleaning of PET materials with different levels of contamination can be achieved.

[0027] Furthermore, the present invention also provides a method for cleaning and separating PET microplastic powder, which utilizes the aforementioned separation and cleaning device and includes the following steps:

[0028] S1, microplastic powder containing PET and PE, PS, PP or PVC is added into the outer shell of the cleaning device through the feed port. Under the control of the adjustable flow rate water supply system, water is quantitatively supplied into the outer shell of the cleaning device, and dioctyl terephthalate agent is added at the same time, so that water and dioctyl terephthalate form a solvent system of the target concentration in the tank.

[0029] S2, control the motor to drive the stirring mechanism to run at the first speed, and stir the added microplastic powder and solvent system at low speed in both forward and reverse directions, so that the powder is fully wetted and evenly dispersed in the circular frame tank;

[0030] S3, adjust the water flow rate and motor speed to the second speed, so that the stirring mechanism forms a controllable rotating flow field inside the cleaning device shell, and control the rotation speed of microplastics and water flow to be in a range that is conducive to density separation;

[0031] S4. Start the ultrasonic aeration mixing device, so that its lower end extends below the liquid surface, and apply the combined action of ultrasound and aeration to the solvent system in the rotating flow field. This causes the agglomeration between PET microplastics and other plastic impurities to be broken up, and PET tends to sink according to the density difference, while PE / PS / PP / PVC impurities tend to float upward.

[0032] S5, after ultrasonic aeration, controls the water surface agitation mechanism to move the microplastic impurities floating on the liquid surface toward the periphery of the high-level closed mechanism, and opens part or all of the high-level closed mechanism under the control of the control system, so that the upper solvent carrying the flotation impurities is discharged into the outer water tank through the closed mechanism assembly, and then introduced into the impurity removal and slag discharge device from the outlet of the water tank for solid-liquid separation.

[0033] Preferably, the mass concentration of dioctyl terephthalate in step S1 is 3.5-4%; and / or, the ultrasonic power of the ultrasonic aeration mixing device in step S4 is 500-800W, and the aeration intensity is 3.0-5.0m. 3 / (m 2 .h).

[0034] This invention integrates a central agitator, a liftable ultrasonic aeration mixing device, a high-low level tiered sealing mechanism assembly, an outer water tank, a bottom opening and closing mechanism, and a spiral conveying mechanism within a single circular cleaning device housing. This creates an integrated reaction-separation space that combines strong shear mixing, enhanced ultrasonic aeration, density stratification, and multi-stage discharge. The stirring mechanism forms a composite flow field with axial and radial components underwater, rapidly dispersing and wetting agglomerated PET microplastic powder, ensuring that PET and impurities such as PE / PP / PS / PVC are fully exposed at the solvent interface. The ultrasonic aeration mixing device introduces fine bubbles into the rotating flow field and applies ultrasonic oscillation, further enhancing particle dispersion and density separation. The poor floating / sinking behavior significantly improves the rate and selectivity of density separation; the surface agitation mechanism directs the floated light impurities to the vicinity of the high-level sealing mechanism, and the high-level drainage achieves fine discharge that "only removes the upper layer of impurity-laden solvent without disturbing the lower layer of PET". The outlet of the low-level sealing mechanism is located below the high-level sealing mechanism and is used for secondary discharge to remove the secondary upper layer solution carrying PE, PP, PS or PVC light impurity microplastics; after cleaning is completed, the bottom opening and closing mechanism opens with a double-leaf door structure driven by the water cylinder. In conjunction with the bottom spiral conveying mechanism and the inclined spiral conveying mechanism, the highly purified PET microplastic powder can be smoothly and centrally transported to the next process. Through the aforementioned synergistic effect, this invention not only significantly improves the separation purity and cleaning efficiency of PET microplastics and other resin powders, and reduces entrainment and material loss, but also realizes the continuous and automated process of cleaning, grading and slag removal, solvent reuse and material conveying. It can effectively reduce the water consumption and reagent consumption per unit product, reduce the number of equipment and the footprint, and overall demonstrates a superior comprehensive technical effect compared to existing multi-machine series systems and traditional static density separation equipment. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the structure of the present invention.

[0036] Figure 2 for Figure 1 A top-view structural diagram.

[0037] Figure 3 This is a schematic diagram of the structure of the cleaning device housing, the intermediate actuation mechanism, the ultrasonic aeration mixing device 3, the sealing mechanism assembly 4, and the outer water tank 5.

[0038] Figure 4 This is a schematic diagram of the bottom opening and closing mechanism.

[0039] Figure 5 This is a schematic diagram of the closed structure of the bottom opening and closing mechanism.

[0040] Figure 6 This is a schematic diagram of the opening structure of the bottom opening and closing mechanism. Detailed Implementation

[0041] The structure and method of the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. Those skilled in the art should understand that the following embodiments are for illustrative purposes only and are not intended to limit the scope of protection of the present invention; any equivalent substitutions or modifications to the structural form, dimensional proportions, process parameters, etc., without departing from the concept of the present invention, shall fall within the scope of protection of the present invention.

[0042] In this specification, unless otherwise expressly defined, the orientations or positional relationships such as "up," "down," "left," "right," "inner," and "outer" are based on the illustrated state or the normal installation and use state of the equipment, and are only used to facilitate the description of the present invention, and are not an absolute limitation of the present invention.

[0043] I. Overall Structure of the Device

[0044] like Figure 1 , Figure 2 As shown, the present invention provides a separation and cleaning device for PET microplastic powder, comprising:

[0045] Cleaning device housing 1;

[0046] Intermediate actuation mechanism 2;

[0047] Ultrasonic aeration mixing device 3;

[0048] Enclosed mechanism assembly 4 and peripheral water channel 5;

[0049] Bottom opening and closing mechanism 6, bottom spiral conveying mechanism 7, and inclined spiral conveying mechanism 8;

[0050] Control system 9.

[0051] The device is preferably arranged in a vertical structure. The outer shell 1 of the cleaning device is fixed on a foundation platform or supporting steel structure. The central actuating mechanism 2 is vertically set at the center of the outer shell 1, with a drive motor 24 connected above it and extending into the tank below to stir the material. The ultrasonic aeration mixing device 3 is arranged near the central actuating mechanism 2 and is raised and lowered by the first cylinder 31. The sealing mechanism assembly 4 is arranged around the outer shell 1 of the cleaning device and is connected to the outer water tank 5. The bottom of the tank is provided with a bottom opening and closing mechanism 6, which is connected in sequence to a bottom spiral conveying mechanism 7 and an inclined spiral conveying mechanism 8 to transport the cleaned PET microplastic powder to the next process. All the above-mentioned actuators are electrically connected to the control system 9 to realize automated control.

[0052] II. Structure and Connection Relationships of Each Component

[0053] 1. Cleaning device housing 1

[0054] like Figure 1 , Figure 2 As shown, the cleaning device housing 1 is an overall circular frame groove with an open top, preferably made of stainless steel or carbon steel lined with corrosion-resistant material to adapt to working environments containing dioctyl terephthalate solvent. The cleaning device housing 1 includes:

[0055] The circular sidewalls 12 are continuously arranged along the circumference to form an annular space;

[0056] Bottom end cap or flat bottom plate, with a bottom discharge port 11 set in the center of the bottom;

[0057] The upper end can be equipped with a reinforcing ring and a support beam for mounting the bearing seat of the intermediate actuation mechanism 2 and the support components of the first cylinder 31, the second cylinder 44, and the third cylinder 62.

[0058] Several interfaces are reserved circumferentially on the upper and lower parts of the side wall 12 for arranging the water outlets of the high-level sealing mechanism 41 and the low-level sealing mechanism 42, as well as process interfaces such as raw material inlet, reagent addition inlet, and water replenishment inlet.

[0059] To improve the uniformity of the flow field, in this embodiment, the bottom plate of the tank can be designed to be slightly inclined towards the bottom discharge port 11, so that the settled particles naturally converge to the area of ​​the bottom opening and closing mechanism 6, reducing dead corner accumulation.

[0060] 2. Intermediate toggle mechanism 2

[0061] like Figure 1 , Figure 3 As shown, the intermediate actuation mechanism 2 is vertically arranged at the center of the cleaning device housing 1, and mainly includes:

[0062] A pivot 21 that runs through the upper support frame and the space inside the groove;

[0063] A stirring mechanism 22 is arranged below the liquid surface;

[0064] A water surface agitation mechanism 23 is arranged near the liquid surface;

[0065] Motor 24 is installed above the tank.

[0066] The rotating shaft 21 is supported by two bearings, an upper bearing mounted on a support beam above the tank, and a lower bearing that can be fixed to an intermediate support frame or a reinforced structure at the bottom of the tank to ensure the rotational stability of the shaft. The motor 24 is connected to the rotating shaft 21 via a coupling, preferably a variable frequency motor, to enable switching between different speed modes and to achieve alternating forward and reverse rotation under the control of the control system 9.

[0067] Stirring mechanism 22:

[0068] The mechanism, installed near the bottom of the tank on the rotating shaft 21, includes several radially inclined stirring blades. These blades have both radial and axial components relative to the shaft 21 and are staggered in the vertical direction, creating a composite flow field by simultaneously generating axial circulating flow, radial flow, and circumferential rotating flow within the tank during rotation. This allows for thorough mixing of the added PET microplastic powder and solvent, breaking up agglomerated powder and suspending it uniformly. Furthermore, switching between forward and reverse rotation breaks the flow field "memory" caused by a single rotation direction, which helps to weaken vortex cores and dead zones.

[0069] Water surface actuation mechanism 23:

[0070] The mechanism, positioned near the intended working liquid level, consists of several arc-shaped paddles fixedly connected to the rotating shaft 21. Each arc-shaped paddle has a certain curvature and angle relative to the radial direction, with a small gap between its outer edge and the inner wall of the cleaning device housing 1. When the rotating shaft 21 rotates at a set speed, the arc-shaped paddles generate a gentle propulsive effect in the liquid surface area, pushing the lightweight microplastic impurities that have floated to the surface circumferentially and concentrating them in the surrounding area, bringing them closer to the peripheral area where the high-level sealing mechanism 41 is located, thus creating conditions for subsequent discharge through the high-level sealing mechanism 41.

[0071] In practical design, the number and size of the stirring blades and arc-shaped vanes can be adjusted according to the tank diameter and throughput. For example, 6 to 10 stirring blades and 4 to 8 arc-shaped vanes can be set. The specific number and angle can be obtained through flow field simulation and experimental optimization.

[0072] 3. Ultrasonic aeration mixing device

[0073] like Figure 1 , Figure 3 As shown, the ultrasonic aeration mixing device 3 is arranged near the intermediate actuation mechanism 2, preferably installed in the central area on one side of the rotating shaft 21. Its structure includes: an upper support frame connected to the first cylinder 31; and an ultrasonic-aeration combination component that can be raised and lowered in the vertical direction, including an ultrasonic transducer and an aeration pipeline.

[0074] The first cylinder 31 is fixed on the frame above the outer shell 1 of the cleaning device. Its telescopic end is connected to the support frame of the ultrasonic aeration mixing device 3. Under the command of the control system 9, the combined component can be lowered from the standby position above the water surface to the working position at a predetermined depth below the liquid surface, or raised in the opposite direction to the standby position.

[0075] The ultrasonic aeration mixing device 3 has an aeration pipeline connected to an external air source. The aeration pipeline has a large number of micropores along its length and circumference to generate a uniform and dense group of bubbles. The ultrasonic transducer is arranged along the aeration pipeline or coaxially with it. When the ultrasonic waves are working, the bubbles oscillate and break in the ultrasonic field, and the rotating flow field works together to enhance the dispersion and density stratification of the material.

[0076] With its adjustable height, ultrasonic and aeration effects are activated only at the required stages and depths, avoiding adverse effects on the flow field and particle structure caused by prolonged operation, while also reducing energy consumption and equipment wear.

[0077] 4. Enclosed mechanism assembly 4 and peripheral water channel 5

[0078] like Figure 2 , Figure 3 As shown, the closure mechanism assembly 4 is arranged circumferentially along the side wall 12 of the cleaning device housing 1, and includes multiple openable closure mechanisms. Preferably, the closure mechanisms are divided into two types: a high-position closure mechanism 41 and a low-position closure mechanism 42.

[0079] High-level sealing mechanism 41: Its outlet is located in the upper part of the side wall 12 of the outer shell 1 of the cleaning device, near or slightly below the working liquid surface, and is used to discharge the upper solvent carrying floating microplastic impurities.

[0080] Low-level sealing mechanism 42: The outlet of the low-level sealing mechanism is located at the lower part of the high-level sealing mechanism and is used for secondary discharge of the secondary upper layer solution carrying light impurities such as PE, PP, PS or PVC microplastics.

[0081] Each enclosure includes a water outlet communicating with the outer casing 1 of the cleaning device, and a gate 43 for controlling the opening and closing of the water outlet. The gate 43 is hinged to a side wall opening, and the other end of the gate is connected to the telescopic end of a second cylinder 44 via a connecting rod. The second cylinder 44 is installed above the water surface, and through the force transmission of the connecting rod and hinge, it can drive the gate 43 to open or close under the control of the control system 9, thereby realizing the opening and closing control of water outlets at different heights.

[0082] The outlet of the closed mechanism is connected to the outer water tank 5 via a short pipe or guide pipe. The outer water tank 5 surrounds the outer shell 1 of the cleaning device, and its cross-section can be designed as a "U"-shaped or "trapezoidal" trough with a slight slope at the bottom. It has one or more water tank outlets 51 to guide the liquid discharged from the closed mechanism to the impurity removal and slag discharge device. The impurity removal and slag discharge device can take the form of a sedimentation tank, a filter unit, or a scum collection mechanism to separate the microplastic impurities contained therein. The aqueous phase is treated and then returned to the cleaning system as makeup water or solvent for reuse.

[0083] By combining the high-level sealing mechanism 41 and the low-level sealing mechanism 42 and unifying the outer water tank 5, the present invention can achieve the discharge of upper flotation impurities and secondary upper solution in the same tank, and send all discharged liquids to the impurity removal and slag discharge unit, which facilitates the centralized treatment and reuse of water and reagents.

[0084] 5. Bottom opening and closing mechanism; 6. Bottom screw conveyor mechanism; 7. Inclined screw conveyor mechanism; 8.

[0085] like Figure 1 , Figure 4 As shown, the bottom opening and closing mechanism 6 is located at the bottom discharge port 11 and is used to control the discharge of PET microplastic material after cleaning.

[0086] In a preferred embodiment, such as Figures 4-6 As shown, the bottom opening and closing mechanism 6 includes: a double-leaf door 61 composed of two door panels, the two door panels being arranged along the arc-shaped contour of the bottom discharge port 11, forming an integral arc-shaped sealing surface that basically matches the bottom discharge port 11 in the closed state; a bottom hinge 64 connecting the two door panels to the bottom edge of the tank, allowing the double-leaf door 61 to rotate around the hinge to open or close; and a third cylinder 62 located on the outside or above the tank, connected to the double-leaf door 61 via multiple force-transmitting connecting rods 63. When the third cylinder 62 extends or retracts under the control of the control system 9, the force-transmitting connecting rods 63 drive the double-leaf door 61 to open or close synchronously, thereby achieving bottom discharge control driven above the water surface, avoiding the sealing and maintenance problems caused by arranging the driving components underwater. In the closed state, the double-leaf door forms a continuous and smooth inner surface, which is beneficial for maintaining the flow field required for stirring and stratification, and will not significantly interfere with the energy distribution of the stirring at the lower end.

[0087] Below the bottom opening and closing mechanism 6, a bottom spiral conveying mechanism 7 and an inclined spiral conveying mechanism 8 are arranged in sequence. The bottom spiral conveying mechanism 7 is preferably arranged horizontally and is used to receive PET microplastic powder slurry or wet granules falling from the bottom opening and closing mechanism 6 and convey them to one side in a horizontal direction. The inlet end of the inclined spiral conveying mechanism 8 is connected to the outlet end of the bottom spiral conveying mechanism 7 and is arranged upward at a certain angle to lift the material to the inlet position of the next process, so as to achieve seamless connection between the device and the subsequent process.

[0088] 6. Control System 9

[0089] The control system 9 can be a combination of a PLC controller and a human-machine interface (HMI). The PLC is connected to the motor 24, each cylinder, ultrasonic power supply, air source solenoid valve, as well as signal / actuator elements such as liquid level sensor, temperature sensor, flow meter, and reagent metering unit.

[0090] Through the human-machine interface, operators can set or call different process formula parameters, such as: ultrasonic working time and power; aeration intensity; stirring forward and reverse rotation cycle and speed, first speed and second speed; emission cycle and emission duration of high-level sealing mechanism 41; emission cycle of low-level sealing mechanism 42; number of cycle cleaning, etc.

[0091] The PLC automatically determines the cleaning status based on information such as liquid level and temperature fed back by sensors, and controls the start, stop and sequence of each actuator to realize the automated operation of the entire cleaning, separation, slag discharge and material discharge process.

[0092] III. Method Implementation Process

[0093] The following combination Figure 5 The process flow shown illustrates the method for cleaning and separating PET microplastic powder using the apparatus of the present invention.

[0094] In a typical embodiment, the material to be treated is a mixture of microplastic powders containing PET and various plastics such as PE, PS, PP, or PVC. The powder particle size can range from tens to hundreds of micrometers. The mass fraction of PET in the material is approximately 80% to 95%, with the remainder consisting of impurities such as PE / PP / PS / PVC, as well as small amounts of paper dust, inorganic particles, etc. The cleaning solvent system is a mixture of water and dioctyl terephthalate, with the preferred mass concentration of dioctyl terephthalate being 3.5% to 4%.

[0095] Step S1: Feeding and Initial Wetting

[0096] A mixture containing PET microplastic powder is quantitatively fed into the outer shell 1 of the cleaning device via an upstream conveying device. The inlet can be located on the upper side wall 12 or the top opening of the tank. Simultaneously, water is quantitatively supplied into the outer shell 1 of the cleaning device under the control of an adjustable flow rate water supply system, and a predetermined amount of dioctyl terephthalate is added into the tank through a reagent metering unit, so that water and dioctyl terephthalate form a solvent system of the target concentration in the tank.

[0097] The control system 9 starts the motor 24, driving the stirring mechanism 22 to run at a relatively low initial speed. In this stage, a lower speed and a longer forward and reverse rotation cycle are preferred, so that the microplastic powder is gradually and fully wetted by water and solvent under a gentler shearing action, disintegrates and agglomerates, and is evenly dispersed in the tank, avoiding the powder from directly depositing to the bottom or forming floating clumps on the liquid surface.

[0098] Step S2: Forming a controllable rotating flow field

[0099] When the liquid level in the tank reaches the preset height and the material is basically wetted and dispersed, the control system 9 increases the speed of the motor 24 to the second speed, so that the stirring mechanism 22 forms a stronger rotating flow field in the tank. Since the stirring blades are inclined radially and misaligned vertically, a composite flow with axial and radial components is formed in the tank, which can maintain the suspension of the material and promote the relative movement of particles of different densities in the flow field.

[0100] At this point, depending on the material properties and load conditions, a certain interval between forward and reverse rotation can be set, such as briefly stopping after rotating forward for several minutes and then reversing for several minutes, in order to break the stable vortex structure formed by a single rotation direction and enhance the overall mixing capacity of the flow field.

[0101] Step S3: Ultrasonic aeration to enhance stratification

[0102] After the rotating flow field is formed and stabilized for a period of time, the control system 9 starts the first cylinder 31 to lower the ultrasonic aeration mixing device 3 from the standby position above the water surface to the working position at a predetermined depth below the liquid surface. The depth can be set according to the height of the tank and the flow field distribution, and is generally set in the middle and lower part of the liquid depth.

[0103] Subsequently, the ultrasonic power supply and air source are turned on. The aeration pipeline releases a large number of tiny bubbles into the tank through micropores. The ultrasonic transducer emits ultrasonic waves into the liquid. In the ultrasonic field, the microbubbles continuously oscillate, break up, and interact with the particles, loosening the bond between PET microplastics and other plastic impurities, and further breaking up the aggregates. At the same time, the bubbles form complexes with low-density plastic particles, which facilitates their floating, while the denser PET particles tend to sink. Under the combined effect of the rotating flow field, ultrasonic vibration, and bubble buoyancy, a lower layer dominated by PET and an upper layer dominated by impurities such as PE / PP / PS / PVC gradually form in the tank, achieving density separation.

[0104] The ultrasonic power and aeration intensity can be set according to the equipment scale and treatment capacity. For example, the ultrasonic power can be 500-800W, and the aeration intensity can be 3.0-5.0 m. 3 / (m 2 The ultrasonic treatment time can be 5–20 minutes. The control system can automatically adjust this parameter based on online detection results or empirical formulas.

[0105] Step S4: Water surface stirring and high-level discharge

[0106] After the ultrasonic aeration stage is completed, the control system 9 turns off the ultrasonic waves and shuts off the air source. The first cylinder 31 can either keep the ultrasonic aeration mixing device 3 in the underwater position or raise it to the standby position above the water surface to avoid interfering with the subsequent water surface flow field.

[0107] Subsequently, the control system 9 activates the water surface agitation mechanism 23, driving the rotating shaft 21 to move the liquid and floating microplastic impurities in the water surface area in a circumferential motion at a moderate speed. Due to the arc-shaped agitator having a certain curvature and tilt angle, the floating objects on the water surface are gradually pushed to the surrounding area under the action of the agitator and concentrated in the peripheral area near the high-position closed mechanism 41.

[0108] Once the visible floating impurities on the water surface have been largely pushed to the periphery, the control system 9 sends a command to open part or all of the high-level sealing mechanism 41. Driven by the second cylinder 44, the gate 43 of the corresponding high-level sealing mechanism 41 opens, and the solvent carrying the floating impurities in the upper layer of the tank flows into the outer water tank 5 through the outlet, and then is introduced into the impurity removal and slag discharge device through the outlet 51 of the water tank. In this device, light microplastic impurities are collected or filtered, and the water phase can be reused in this cleaning device or discharged after treatment.

[0109] In this way, the microplastic impurities in the upper layer of the tank can be discharged in a concentrated manner, while the lower layer of materials, mainly PET, remains largely undisturbed, and the liquid level in the tank decreases slightly.

[0110] Step S5: Discharge of the secondary supernatant solution

[0111] After the high-level sealing mechanism 41 is closed, the control system 9 can, according to process requirements, continue to operate the forward and reverse stirring tilting mechanism and the ultrasonic aeration mixing device to continue separating PET from plastic impurities, and under the control of the control system, partially or fully open the low-level sealing mechanism to discharge the remaining plastic impurities.

[0112] Step S6: Discharge and conveying of cleaned PET material

[0113] When online or offline detection confirms that the impurity content in the material has dropped below the preset threshold, the control system 9 stops the discharge of the ultrasonic aeration mixing device 3 and the sealing mechanism assembly 4, and at the same time adjusts the stirring speed so that the stirring mechanism 22 runs at a suitable speed to maintain the material in the tank in a uniform flow state.

[0114] At this time, the control system 9 issues a command to activate the third cylinder 62 to open the double-leaf door 61 of the bottom opening and closing mechanism 6. The cleaned PET microplastic powder falls into the bottom screw conveyor mechanism 7 through the bottom outlet 11 under the action of the stirring flow field and gravity. After the bottom screw conveyor mechanism 7 is started, it conveys the material horizontally to one end outlet, and then is lifted by the inclined screw conveyor mechanism 8 to the next process, such as melt extrusion, granulation or further drying process.

[0115] After the material discharge is completed, the bottom double-leaf door 61 closes, and the bottom screw conveyor mechanism 7 and the inclined screw conveyor mechanism 8 can continue to operate for a period of time as needed to clear the pipeline, and then be shut down to prepare for the next batch of material processing.

[0116] IV. Implementation Results

[0117] In the above embodiments, the present invention integrates a central actuating mechanism 2, a liftable ultrasonic aeration mixing device 3, a high-position sealing mechanism 41 and a low-position sealing mechanism 42, an outer water tank 5, a bottom opening and closing mechanism 6, a bottom spiral conveying mechanism 7, and an inclined spiral conveying mechanism 8 within a single circular tank, thereby achieving multi-round cyclic cleaning and separation of powdered PET microplastics, and has the following technical effects:

[0118] 1. The composite flow field formed by the stirring mechanism 22 can effectively break up powder agglomerates and improve the contact efficiency between materials and solvents;

[0119] 2. Through the synergistic effect of ultrasound and aeration in a rotating flow field, the stratification between PET and various plastic impurities of different densities is more complete, the floating and sinking behavior is clearer, and the separation efficiency is significantly improved.

[0120] 3. The water surface agitation mechanism 23 directs the floating impurities to the periphery and discharges the solvent carrying the impurities from the upper layer through the high-level sealing mechanism 41, achieving precise control of "only removing the upper layer impurities without disturbing the lower layer PET".

[0121] 4. The presence of the low-level sealing mechanism 42 is used for secondary discharge of the secondary upper layer solution carrying light impurities such as PE, PP, PS or PVC microplastics.

[0122] 5. The bottom opening and closing mechanism 6, the bottom screw conveyor mechanism 7, and the inclined screw conveyor mechanism 8 enable the centralized and continuous discharge and conveying of PET materials after cleaning, thereby improving the automation level of the entire cleaning, separation, and conveying system.

[0123] Those skilled in the art can make the following improvements or modifications to the present invention according to actual needs, for example: changing the diameter and height of the tank to adapt to different processing capacities; adjusting the number, size and installation angle of the stirring blades and arc-shaped deflectors to optimize the flow field; using multiple sets of ultrasonic aeration mixing devices 3 distributed at different radial positions to further enhance the stratification effect in the large-diameter tank; adjusting the solvent type and concentration, as well as ultrasonic and aeration parameters, according to different microplastic systems.

[0124] Experimental Example

[0125] I. Experimental Objective

[0126] By comparing the cleaning and separation effects of the present invention's separation and cleaning device with a control device (without ultrasonic aeration, high and low level graded discharge, etc.), the comprehensive technical advantages of the present invention in terms of: PET purity improvement, impurity removal rate, cleaning time and number of cycles, water consumption per unit product, solvent consumption, energy consumption index, etc. are verified.

[0127] II. Experimental Materials and Evaluation Indicators

[0128] 1. Test materials

[0129] Original mixed microplastic powder:

[0130] PET: Approximately 85wt%

[0131] Impurities in plastics such as PE / PP / PS / PVC: Approximately 10wt%

[0132] Paper dust / inorganic particles, etc.: Approximately 5 wt%

[0133] Particle size: 50–500 μm, in powder form, with obvious agglomeration.

[0134] 2. Cleaning system

[0135] Solvent: tap water and dioctyl terephthalate (DOTE), mass ratio 3.5–4.0%.

[0136] Feed rate: 100kg of mixed microplastic powder per batch.

[0137] 3. Evaluation Indicators

[0138] PET mass fraction (wt%) in the product after cleaning;

[0139] Total residual impurities in plastics (wt%) and removal rate (%);

[0140] Total cleaning time per batch (min);

[0141] Water consumption per unit of PET product (m³) 3 / t), DOTE consumption (kg / t);

[0142] Electricity consumption per unit of PET product (kWh / t).

[0143] III. Experimental Example 1 (using the device of the present invention)

[0144] 1. Equipment: Configure a circular cleaning device according to the above structure.

[0145] 2. Process parameters:

[0146] DOTE concentration: 3.8 wt%

[0147] Initial stirring speed: 50 rpm (10 min for initial wetting stage)

[0148] Second stirring speed: 120 rpm (10 min to form a rotating flow field)

[0149] Ultrasonic power: 600W, aeration intensity: 4.0 m 3 / (m2 .h), Action time: 10min / cycle

[0150] High-level discharge per cycle: 15–20% of the tank's volume; Low-level discharge: 10% of the tank's volume discharged every 2 cycles.

[0151] Number of cycles: 3.

[0152] 3. Test Procedure:

[0153] 1) Add 100 kg of raw microplastic powder and the corresponding water + DOTE solvent, and perform S1 wetting and dispersion and S2 rotating flow field;

[0154] 2) Start the ultrasonic aeration mixing device 3 and perform enhanced stratification for 10 minutes;

[0155] 3) Start the water surface agitation mechanism 23 and start the high-level sealing mechanism 41 to discharge the upper layer of impurity solvent, which is then sent to the impurity discharge device for treatment via the outer water tank 5;

[0156] 4) The low-level sealing mechanism 42 can be opened as needed for secondary discharge to discharge the secondary upper layer solution carrying light impurities such as PE, PP, PS or PVC microplastics.

[0157] 5) After the cleaning process is completed, open the bottom opening and closing mechanism 6, the bottom spiral conveying mechanism 7, and the inclined spiral conveying mechanism 8 to discharge the cleaned PET microplastic powder sample, dry it, weigh it, and perform component analysis.

[0158] IV. Comparative Example 1 (Ultrasonic aeration removed)

[0159] Under the premise that other structures and parameters are basically the same, only the ultrasonic aeration mixing device 3 is turned off, that is, no ultrasonication and aeration are performed, and the same stirring, number of cycles, and high and low level drainage strategies are still implemented.

[0160] Difference: Layering is achieved solely through mechanical stirring and density difference, without ultrasonic / aeration enhancement.

[0161] V. Comparative Example 2 (Traditional Single Overflow Discharge)

[0162] Select a circular cleaning tank of the same volume and configure it with: a simple paddle agitator (without tilting blades or a central water surface stirring mechanism); no ultrasonic aeration mixing device, only aeration heads or no aeration at all; a single overflow weir is set on the upper edge of the tank to discharge the upper layer of water, and a row of mud outlets is set on the bottom of the tank to discharge residual liquid.

[0163] It lacks a high / low level grading sidewall sealing mechanism and an outer annular flow channel.

[0164] Under the same DOTE concentration, feed rate and total cleaning time, three rounds of cleaning were carried out according to the existing process (continuous stirring, top overflow, bottom timed sludge discharge) to obtain comparative samples.

[0165] VI. Tests and Results

[0166] The following analyses were performed on the cleaned samples of Experimental Example 1, Comparative Example 1, and Comparative Example 2:

[0167] 1) Ash and volatile matter tests to estimate the content of inorganic and organic impurities;

[0168] 2) The residual mass fractions of PET and PE / PP / PS / PVC were determined by density gradient separation or thermogravimetric analysis (TGA);

[0169] 3) Calculate the total water consumption, DOTE consumption, and energy consumption recorded by the electricity meter for each batch.

[0170] The test results are shown in Table 1:

[0171] Table 1

[0172]

[0173] VII. Technical Effects

[0174] As shown in Table 1, compared with Comparative Example 1 (which did not use an ultrasonic aeration mixing device), the mass fraction of the PET product in Experimental Example 1 increased from 93.0 wt% to 97.5 wt%, and the residual plastic impurities decreased from 5.0 wt% to 1.8 wt%, resulting in an increase in impurity removal rate of approximately 32 percentage points. This demonstrates that the present invention, through the combined action of the stirring mechanism and the liftable ultrasonic aeration mixing device, significantly enhances the dispersion and density-based stratification process of microplastic powder. Furthermore, compared with Comparative Example 2, which uses a traditional single overflow discharge structure, under the same cleaning time conditions, the present invention not only achieves higher PET purity and impurity removal rate, but also reduces the water consumption per unit product from 6.0 m³. 3 / t reduced to 4.0m 3 / t, DOTE consumption decreased from 25kg / t to 18kg / t, which fully demonstrates that the high and low level closed mechanism combined with the graded discharge design of the outer water tank is conducive to the directional discharge of floating impurities and bottom residual liquid and the efficient reuse of cleaning liquid in a single tank, thus showing a comprehensive technical effect that is superior to the existing technology.

[0175] The foregoing description of embodiments of the present invention, through which those skilled in the art are able to implement or use the present invention, will be readily apparent to those skilled in the art. Various modifications to these embodiments will be readily apparent to those skilled in the art. The general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novelty disclosed herein.

Claims

1. A separation and cleaning device for PET microplastic powder, characterized in that, include: The outer shell (1) of the cleaning device is a circular frame groove with an opening at the top, its side wall (12) is arranged circumferentially, and the bottom is provided with a bottom discharge port (11). The intermediate agitation mechanism (2) is vertically arranged at the center of the outer shell (1) of the cleaning device. The intermediate agitation mechanism (2) includes a rotating shaft (21), a stirring mechanism (22), a water surface agitation mechanism (23), and a motor (24). The stirring mechanism (22) is used to stir the material underwater and form a composite flow field with axial and radial components during the stirring process, which promotes the mixing of the material and the water solvent and the dispersing of agglomerated materials. The water surface agitation mechanism (23) is used to agitate floating objects near the water surface. An ultrasonic aeration mixing device (3) is arranged near the intermediate actuation mechanism (2), and its lower end can extend into the liquid surface inside the cleaning device housing (1). The ultrasonic aeration mixing device introduces fine bubbles in the rotating flow field and applies ultrasonic oscillation to enhance particle dispersion and floating / sinking according to density difference. The closing mechanism assembly (4) is arranged circumferentially along the outer shell (1) of the cleaning device and includes several openable closing mechanisms. The water outlet of the closing mechanism is located on the side wall (12) of the outer shell (1) of the cleaning device. An outer water tank (5) is arranged around the outer shell (1) of the cleaning device. The outlet of each closed mechanism is connected to the outer water tank (5). The outer water tank (5) has a water tank outlet (51) that guides the discharged liquid to the impurity removal and slag discharge device. The bottom opening and closing mechanism (6) is located at the bottom discharge port (11) and is used to realize the discharge of material from the bottom of the tank.

2. The separation and cleaning device according to claim 1, characterized in that, The upper end of the ultrasonic aeration mixing device (3) is connected to the first cylinder (31) via a bracket. The first cylinder (31) is fixed above the water surface and is used to drive the ultrasonic aeration mixing device (3) to move up and down between the underwater working position and the standby position above the water surface. And / or, the ultrasonic aeration mixing device (3) includes an ultrasonic transducer and an aeration pipeline connected to an external air source. Multiple micropores are opened on the wall of the aeration pipeline along the circumferential and axial directions to form a uniform microbubble cluster. The ultrasonic transducer is arranged along the aeration pipeline or coaxially with it, so that the bubbles break and vibrate in the ultrasonic field, thereby enhancing the density separation effect between PET and other plastic impurities in PET microplastics.

3. The separation and cleaning device according to claim 1, characterized in that, The closing mechanism includes several high-level closing mechanisms (41) and several low-level closing mechanisms (42). The outlet of the high-level closing mechanism (41) is located on the upper part of the side wall (12) of the cleaning device housing (1), and the outlet of the low-level closing mechanism (42) is located on the lower part of the high-level closing mechanism (41). Each closing mechanism includes an outlet that communicates with the cleaning device housing (1) and a gate (43) for opening or closing the outlet. The gate (43) is connected to a second cylinder (44) located above the water surface through a connecting rod and a hinge to realize the opening and closing of the closing mechanism.

4. The separation and cleaning device according to claim 3, characterized in that, The high-level sealing mechanism (41) and the low-level sealing mechanism (42) are linked by the same second cylinder (44) and connecting rod. The control system (9) can selectively drive some or all of the high-level sealing mechanism (41) to open, or drive the low-level sealing mechanism (42) to open, so as to realize the graded discharge of floating impurities on the water surface and secondary floating impurities respectively.

5. The separation and cleaning device according to claim 1, characterized in that, The device also includes a bottom spiral conveying mechanism (7), which is arranged below the bottom opening and closing mechanism (6) for receiving materials falling from the bottom opening and closing mechanism (6) and conveying them in the horizontal direction; And / or, the inclined screw conveyor (8), whose feed end is connected to the discharge end of the bottom screw conveyor (7), is used to lift the material conveyed by the bottom screw conveyor (7) along the inclined direction to the next process.

6. The separation and cleaning device according to claim 1, characterized in that, The stirring mechanism (22) includes multiple stirring blades arranged radially inclined, each stirring blade being staggered relative to the vertical axis (21); And / or, the water surface agitation mechanism (23) includes a plurality of arc-shaped paddles connected to the rotating shaft (21), with a gap between the outer edge of each arc-shaped paddle and the inner wall of the cleaning device housing (1), and set at a predetermined arc and angle relative to the radial direction, so as to orient the microplastic impurities floating on the water surface toward the peripheral area near the high-position sealing mechanism (41) when rotating.

7. The separation and cleaning device according to claim 1, characterized in that, The bottom opening and closing mechanism (6) includes a double door (61) consisting of two door panels. The double door (61) is hinged to the bottom edge of the cleaning device housing (1) via a bottom hinge (64) and connected to a third cylinder (62) located above the water surface via multiple force transmission rods (63) for synchronous opening and closing of the double door (61) under the drive of the third cylinder (62). And / or, the double doors (61) of the bottom opening and closing mechanism (6) are arranged along the arc contour of the circular bottom outlet (11) in the closed state. After the two doors (61) are closed, they form an approximately integral arc-shaped sealing surface with the bottom outlet (11) to reduce the interference to the material flow field during the stirring process.

8. The separation and cleaning device according to claim 4, characterized in that, The device also includes the control system (9), which includes a PLC controller and a human-machine interface. The PLC controller is connected to the liquid level sensor, temperature sensor and reagent metering unit. By setting process parameters such as ultrasonic working time, aeration volume, high-level drainage volume, low-level drainage volume and number of cycles, adaptive cleaning of PET materials with different levels of contamination can be achieved.

9. A method for cleaning and separating PET microplastic powder, characterized in that, The separation and cleaning process, using the separation and cleaning apparatus as described in any one of claims 1-8, includes the following steps: S1, microplastic powder containing PET and PE, PS, PP or PVC is added into the shell (1) of the cleaning device through the feed port. Under the control of the adjustable flow rate water supply system, water is quantitatively supplied into the shell (1) of the cleaning device, and dioctyl terephthalate agent is added at the same time, so that water and dioctyl terephthalate form a solvent system of the target concentration in the tank. S2, control the motor (24) to drive the stirring mechanism (22) to run at the first speed, and stir the added microplastic powder and solvent system at low speed in both directions, so that the powder is fully wetted and evenly dispersed in the circular frame groove; S3, adjust the water flow rate and the speed of the motor (24) to the second speed, so that the stirring mechanism (22) forms a controllable rotating flow field in the outer shell (1) of the cleaning device, and control the rotation speed of the microplastics and water flow to be in a range that is conducive to density separation; S4, start the ultrasonic aeration mixing device (3) so that its lower end extends below the liquid surface and applies a combined ultrasonic and aeration effect to the solvent system in the rotating flow field, causing the agglomeration between PET microplastics and other plastic impurities to be broken, and causing PET to sink downwards and PE / PS / PP / PVC impurities to float upwards according to the density difference. S5. After ultrasonic aeration, the water surface agitation mechanism (23) is controlled to move the microplastic impurities floating on the liquid surface to the periphery of the high-level sealing mechanism (41). Under the control of the control system (9), part or all of the high-level sealing mechanism (41) is opened, so that the upper solvent carrying the flotation impurities is discharged into the outer water tank (5) through the sealing mechanism assembly (4), and then introduced into the impurity removal and slag discharge device through the water tank outlet (51) for solid-liquid separation.

10. The method according to claim 9, characterized in that, In step S1, the mass concentration of dioctyl terephthalate is 3.5-4%; and / or, in step S4, the ultrasonic aeration mixing device (3) has an ultrasonic power of 500-800W and an aeration intensity of 3.0-5.0m. 3 / (m 2 .h).

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