Method for separating foamed particles from polyolefin flakes

Abstract

The present invention relates to a process for separating foamed particles from polyolefin flakes, comprising the steps of: a. Providing a first aqueous mixture comprising foamed particles and polyolefin flakes wherein the first aqueous mixture has less than 5%, preferably less than 2%, of organic solvent, wherein the first aqueous mixture contains air bubbles to have a density in the range of 600-850 kg / m3, and wherein the first aqueous mixture comprises a surfactant in the range of 0.05-2 wt%, where the wt% is relative to the total weight of the first aqueous mixture; b. Introducing the first aqueous mixture into a tank (10) comprising a feed port (11), a first compartment (18), a second compartment (28), a conveying element (13), a discharge port (15) and a transfer port (25), in which the first aqueous mixture is in motion, keeping the polyolefin flakes suspended in the first aqueous mixture, and allowing the formation of a top layer (17) having floating foamed particles and a bottom layer (12) containing a second aqueous mixture of suspended polyolefin flakes; c. Discharging a layer (17) of floating foamed particles through the discharge opening (15) of the first compartment (18) using the conveying element (13); d. Transferring the second aqueous mixture to the second compartment (28) and releasing air to obtain a third aqueous mixture comprising suspended polyolefin flakes having a density of between 900 and 1050 kg / m3; and e. Discharging a third aqueous mixture through the transfer opening (25), the third aqueous mixture comprising less than 0.1% by volume of foamed particles.

Description

Technical Field

[0001] This invention relates to a method for separating foamed particles from polyolefin sheets in a plastic recycling facility, and to a device for separating foamed particles from polyolefin sheets. Existing technology

[0002] The prevalence of plastic packaging and the importance of environmental policies have highlighted the growing importance of recycling plastic materials. The recycling of paper, textiles, glass, and metals is already on a large scale, whether through individual collection or by sorting recycled materials. The recycling and reuse of plastic waste is also increasing.

[0003] Plastic recycling is the process of reprocessing plastic waste into new products. If implemented properly, this can reduce reliance on landfills, conserve resources, and protect the environment from plastic pollution. Almost all plastics are non-biodegradable, thus accumulating in the environment and causing harm. Substitution of virgin polymer components is considered the only way to solve the global plastic waste problem, prevent the depletion of natural resources, and promote a circular economy.

[0004] Recycling is done by remelting used plastics and reforming them into new items (mechanical recycling) or by converting waste plastics into their starting chemicals (raw material recycling), which can then be further processed into new plastics.

[0005] Plastic waste consists of various types of polymers used in products such as packaging. Polyolefins account for nearly 50% of all plastic waste, and more than 90% of the waste is made from remeltable, heat-softening polymers.

[0006] Polypropylene (PP), polyethylene (PE), polyethylene terephthalate (also known as polyester (PET) and high-density polyethylene (HDPE)) have the highest recycling rates, while polystyrene (PS) and polyurethane (PU) are typically recycled very little.

[0007] Expanded polystyrene (EPS), expanded polypropylene (fPP), expanded polyethylene (fPE), expanded polyurethane (fPU), and expanded cross-linked polyethylene (fXLPE) are widely found in municipal waste. For over 50 years, it has been the material of choice due to its versatility, performance, and cost-effectiveness. Expanded polystyrene (EPS) is a thermoplastic foam product (98% air-based) that is lightweight, strong, and durable, with shock-absorbing and insulating properties. EPS is found in many everyday items, such as refrigerated produce containers (e.g., for fish), bicycle helmets, and insulation materials. EPS foam is highly resistant to normal biodegradation processes, occupies significant space in landfills and waste storage facilities, and can pose disposal challenges. A solution to this problem could be increasing the recycling of foamed plastic materials; however, unfortunately, recycling remains very difficult to date because available equipment cannot automatically and completely separate foamed plastic materials from polyolefin materials.

[0008] Foamed particles contaminate recycling equipment by accumulating in it, damaging the equipment, and / or causing it to stop operating. Furthermore, when foamed particles are not completely separated from the polyolefin sheet material, the mechanical properties of the recycled polyolefin material will be negatively affected, for example, making manufactured products more brittle.

[0009] Although plastics typically contain only 0.1% foamed material, the low density of the foamed particles can cause them to accumulate in the equipment during certain recycling steps. In some cases, this can reach over 60% by volume, limiting the amount of water / polyolefin dispersion that can be used in this method. Under these conditions, equipment (e.g., pumps) may stop operating unless the accumulated foamed particles are effectively removed. To date, the accumulated foamed particles in the equipment have been manually removed every few days.

[0010] The purpose of this invention is to minimize the accumulation of foamed particles in plastic recycling equipment and to separate the foamed particles from polyolefin flakes, thereby achieving an efficient, simple and easy recycling process.

[0011] CN104441324 describes a separation apparatus including a stirring device for separating expanded polystyrene (EPS) from a plastic film. The method uses a mixed solvent consisting of water and alcohol to separate polymer particles.

[0012] There is a need for an economically viable device and method that can continuously separate foamed particles from polyolefin sheets, achieving high separation efficiency in a cost-effective and reliable manner.

[0013] Through extensive research, the inventors solved the aforementioned problems and developed new equipment and methods for the continuous separation of foamed particles from polyolefin flakes for use in plastic recycling systems. Summary of the Invention

[0014] This invention relates to a method for separating foamed particles from polyolefin sheets, the method comprising the following steps:

[0015] a) Provide a first aqueous mixture comprising foamed particles and polyolefin flakes, wherein the first aqueous mixture has less than 5% organic solvent, and wherein the first aqueous mixture contains air bubbles to have a concentration of 600-850 kg / m³. 3 The density is within the range of 0.05-2% by weight, and the first aqueous mixture contains surfactant in the range of 0.05-2% by weight, where the percentage by weight is relative to the total weight of the first aqueous mixture.

[0016] b) A first aqueous mixture is introduced into a tank 10, which includes an inlet 11, a first compartment 18, a second compartment 28, a conveying element 13, an outlet 15, and a transfer port 25, wherein the first aqueous mixture is in motion, keeping the polyolefin sheets suspended in the first aqueous mixture; and

[0017] Allows the formation of a top layer of floating foamed particles and a bottom layer of a second aqueous mixture containing suspended polyolefin flakes;

[0018] c) The floating foamed particles are discharged through the outlet 15 of the first compartment 18 by using the conveying element 13, and the second aqueous mixture is transferred to the second compartment 28.

[0019] d) Release air from the second aqueous mixture to obtain a density of 900-1050 kg / m³ 3 A third aqueous mixture comprising suspended polyolefin flakes; and

[0020] e) Discharge the third aqueous mixture through transfer port 25, wherein the third aqueous mixture contains less than 0.1% by volume of foaming particles.

[0021] General recycling process and problems to be solved

[0022] The recycling process begins with the collection and sorting of waste. Waste can be sorted according to polymer type and color to obtain materials suitable for recycling. This initial sorting can be carried out, for example, using near-infrared light. Subsequently, plastic materials containing polyethylene (PE) and / or polypropylene (PP) are typically crushed into flakes / granules, which are preferably washed in a cold wash followed by an alkaline hot wash to provide clean polymer flakes. PE and PP flakes may also contain small amounts of foamed particles, such as EPS, which have a lower density compared to PP and / or PE flakes.

[0023] Expanded polystyrene (EPS) particles present in recycled PE or PP will negatively impact the properties of the recycled polyolefin materials, such as making manufactured products more brittle. Furthermore, EPS particles contaminate recycling equipment by accumulating in it, damaging the equipment, and / or causing it to stop operating.

[0024] To enable large-scale continuous recycling production, the above problems need to be solved.

[0025] Surprisingly, the inventors of this invention have discovered that the method and apparatus of this invention can effectively separate foamed granules from polyolefin flakes. The method and apparatus of this invention are simple and can be advantageously used for continuous, large-scale plastic recycling. Attached Figure Description

[0026] Figure 1 An apparatus is shown, comprising: a tank 10, an inlet 11, a conveying element 13, an outlet 15 (not shown), a transfer port 25, a pump 26, a first baffle 14, a first compartment 18, a second compartment 28, a first aqueous mixture (with a layer of floating foamed particles) 17, a second aqueous mixture 12, and a third aqueous mixture 22.

[0027] Figure 2 An apparatus is shown, comprising: a tank 10, an inlet 11, a conveying element 13, an outlet 15 (not shown), a transfer port 25, a pump 26, a first baffle 14, a second baffle 24, a first compartment 18, a second compartment 28 divided into sub-compartments 28A and 28B by the second baffle 24, a first aqueous mixture (a layer of floating foamed particles) 17, a second aqueous mixture 12, a third aqueous mixture 22A, and a third aqueous mixture 22B.

[0028] Figure 3 It shows that according to Figure 1 The front view of the equipment shows a tank 10, an inlet 11, a screw 13 for discharging a layer 17 of foamed particles, an outlet 15, a container 16 for the discharged foamed particles 17, and a transfer port 25 leading to a pump 26 for discharging a third aqueous mixture. Detailed Implementation

[0029] This invention relates to a method for separating foamed particles from polyolefin sheets, the method comprising the following steps:

[0030] a) Provide a first aqueous mixture comprising foamed particles and polyolefin flakes, wherein the first aqueous mixture has less than 5% organic solvent, and wherein the first aqueous mixture contains air bubbles to have a concentration of 600-850 kg / m³. 3 The density is within the range of 0.05-2% by weight, and the first aqueous mixture contains surfactant in the range of 0.05-2% by weight, where the percentage by weight is relative to the total weight of the first aqueous mixture.

[0031] b) A first aqueous mixture is introduced into a tank 10, which includes an inlet 11, a first compartment 18, a second compartment 28, a conveying element 13, an outlet 15, and a transfer port 25, wherein the first aqueous mixture is in motion, keeping the polyolefin sheets suspended in the first aqueous mixture; and

[0032] Allows the formation of a top layer of floating foamed particles and a bottom layer of a second aqueous mixture containing suspended polyolefin flakes;

[0033] c) Using the conveying element 13, the floating foamed particles are discharged through the outlet 15 of the first compartment 18, and the second aqueous mixture is transferred to the second compartment 28;

[0034] d) Release air from the second aqueous mixture to obtain a density of 900-1050 kg / m³ 3 A third aqueous mixture comprising suspended polyolefin flakes; and

[0035] e) Discharge the third aqueous mixture through transfer port 25, wherein the third aqueous mixture contains less than 0.1% by volume of foaming particles.

[0036] The method of the present invention begins with providing a first aqueous mixture comprising foamed particles and polyolefin sheets.

[0037] Foamed materials are obtained from various plastics such as polypropylene (PP), polystyrene (PS), polyethylene (PE), and polyurethane (PU) using methods known in the art. Foamed materials with various densities can be obtained and are typically used in plastic products, either alone or in combination with non-foamed materials.

[0038] The term "foamed particles" in this invention refers to small fragments of foamed material obtained when the foamed material is pulverized. These small fragments may be, for example, particles having a maximum cross-section of 1 cm to 10 cm, preferably 1 cm to 5 cm.

[0039] The foamed particles of the present invention are selected from the following: expanded polystyrene (EPS) particles, expanded polypropylene (fPP) particles, expanded polyethylene (fPE) particles, expanded polyurethane (fPU) particles, and expanded cross-linked polyethylene (fXLPE) particles or mixtures thereof.

[0040] The foamed particles of the present invention can have a content of less than 500 g / m³. 3 Preferably below 400 g / m 3 More preferably, below 300 g / m 3 The packing density.

[0041] As is known to those skilled in the art, polyolefins are polymers generally derived from a small group of simple olefins (chain olefins) and are widely used. Many polyolefins with different properties, such as thermoplastic polyolefins or polyolefin elastomers, are known in the art. In a commercial sense, the most important polyolefins are polyethylene (PE) and polypropylene (PP), which are commonly used in many materials. Polyethylene (PE) is commonly used in commodity packaging films, blow molding (e.g., liquid containers, bleach bottles), injection molding (e.g., toys, screw caps), extrusion coating (e.g., coatings on milk cartons), pipes for distributing water and gas, and insulation for wires and cables (e.g., telephone cables). Polypropylene is commonly used in injection molding, fibers, and films.

[0042] The term "polyolefin flakes" in this invention refers to small fragments of polyolefin material obtained when plastic material is crushed.

[0043] The polyolefin sheets of the present invention are selected from the following: polypropylene (PP) sheets, such as homopolymer PP sheets, copolymer PP sheets, stereoblock PP sheets, and propylene-butane copolymer sheets; polyethylene (PE) sheets, such as low-density polyethylene (LDPE) sheets, linear low-density polyethylene (LLDPE) sheets, very low-density polyethylene (VLDPE) sheets, ultra-low-density polyethylene (ULDPE) sheets, medium-density polyethylene (MDPE) sheets, and polymethylpentene (PMP) sheets; or mixtures thereof.

[0044] Preferably, the polyolefin sheet of the present invention is selected from polypropylene (PP) sheet and polyethylene (PE) sheet or a mixture thereof.

[0045] The first aqueous mixture used in this invention contains less than 5%, preferably less than 2%, of an organic solvent. The term "organic solvent" in this invention refers to a carbon-based substance capable of dispersing the foamed particles and polyolefin sheets of this invention. Examples of organic solvents that may be present are alcohols, such as methanol, ethanol, and propanol. Preferably, no organic solvent is added to the method of this invention; however, some organic solvents may be present as part of the contaminants from plastics obtained from waste streams.

[0046] The amount of foaming particles in the first aqueous mixture is typically in the range of 0.5-2% by volume (relative to the volume of the first aqueous mixture).

[0047] Advantageously, the method of the present invention allows for the effective separation of foamed particles from polyolefin flakes without the need for the addition of organic solvents, thereby improving safety, environmental impact and avoiding the problems of recycling and disposing of organic solvents; the process is simple, scalable, and energy efficient, and can be applied to any type of recycling plant.

[0048] The first aqueous mixture used in this invention has a concentration of 600-850 kg / m³. 3 Preferred weight: 650-800 kg / m³ 3 More preferably 670-750 kg / m 3 The density is within a certain range. The specific density of the first aqueous mixture is achieved by the presence of air bubbles in the first aqueous mixture. When the density of the first aqueous mixture of the present invention is less than 600 kg / m³... 3 or higher than 850 kg / m 3 At this time, the foamed particles may not be able to separate effectively from the polyolefin sheets.

[0049] Air bubbles can be incorporated using various methods. For example, air can be incorporated by cleaning the flakes in a friction washer (e.g.) or by adding water containing air bubbles from a separate system. The presence of surfactants is important for stabilizing the bubbles.

[0050] The first aqueous mixture contains 0.05-2% by weight, preferably 0.2-1% by weight, of a surfactant, where the percentage by weight is relative to the total weight of the first aqueous mixture. Too little surfactant may not produce a stable bubble suspension, resulting in an excessively high density of the first aqueous mixture, while too much surfactant may cause the first aqueous mixture to foam or produce an overly stable suspension, which may prevent the second aqueous mixture from releasing the entrained air. As known to those skilled in the art, a surfactant is a compound that reduces the surface tension or interfacial tension between two liquids, between a liquid and a gas, or between a liquid and a solid. Surfactants can be used as emulsifiers, wetting agents, detergents, foaming agents, or dispersants.

[0051] Any surfactant known to those skilled in the art can be used in this invention. Surfactants include primary amine salts with carboxyl groups, hydrophilic groups (such as hydroxyl and amino groups), sodium alkyl naphthalene sulfonate, long-chain fatty alcohols, polyoxyethylene ethers, polycarboxylates, etc. In the recycling of household waste, a variety of different surfactants are present, for example, from shampoo bottles. Additional surfactants can be added to the method of this invention if desired.

[0052] Preferably, a nonionic surfactant containing an ethylene oxide group may be added to the suspension in an amount of 0.01-0.5% by weight relative to the first aqueous mixture.

[0053] The first aqueous mixture used in this invention may contain a defoamer. As known to those skilled in the art, a defoamer is a chemical additive that reduces and inhibits the formation of foam in the form of bubbles in industrial process liquids. The term "defoamer" according to this invention is interchangeable with the term "antifoaming agent." Therefore, the term "defoamer" in this invention refers to an additive that can eliminate existing foam or prevent further foam formation. Well-known defoamers are insoluble oils, certain alcohols, polydimethylsiloxane (PDMS) and other organosilicones, stearates, and glycols. Preferably, the defoamer used in this invention is polydimethylsiloxane (PDMS). The defoamer can be used in the range of 0-0.5% by weight, preferably 0.1-0.4% by weight, where the weight percentage is relative to the total weight of the first aqueous mixture. The defoamer can be used to balance air release from the second aqueous mixture and prevent excessive foaming in the system.

[0054] The first aqueous mixture of the present invention is introduced into the first compartment of the can 10. The can 10 designed for use in the present invention can have any shape, particularly one capable of producing a residence time sufficient to separate the foamed particles from the first aqueous mixture and the residual air from the second aqueous mixture. Essentially, the can 10 has at least two compartments, namely a first compartment 18 and a second compartment 28, which are in fluid communication with each other. The residence time in the first compartment 18 is preferably between 20 and 40 seconds. The residence time in the second compartment 28 is preferably between 1 and 2 minutes. Various embodiments of the can 10 are feasible, in which preferred residence times can be achieved. In a preferred embodiment of the can 10, the second compartment 28 is partitioned, resulting in a can 10 configuration in which, in addition to the first compartment 18, there are a first sub-compartment 28A and a second sub-compartment 28B of the second compartment 28. For this purpose, a baffle 24 is provided at an appropriate position in the second compartment 28 of the tank 10, which extends from the bottom of the tank 10 in a generally upward direction.

[0055] The dwell time in the first sub-compartment 28A of the second compartment 28 is preferably in the range of 20 seconds to 50 seconds, while the dwell time in the second sub-compartment 28B of the second compartment is preferably in the range of 30 seconds to 1.5 minutes.

[0056] Preferably, all aqueous mixtures in tank 10 are in motion, ensuring that the polyolefin sheets are adequately suspended. Preferably, no settling of the polyolefin sheets occurs in tank 10. In other words, substantially all (at least 98%, preferably at least 99%, more preferably at least 99.9%) of the polymer sheets are adequately suspended in the different aqueous mixtures.

[0057] Preferably, the tank 10 used in this invention is designed to be unpressurized to facilitate maintaining a low density in the first aqueous mixture containing bubbles, while keeping the polyolefin flakes suspended in the first aqueous mixture and allowing the foamed particles to float to the top surface of the first aqueous mixture. The foamed particles on the top surface of the first aqueous mixture preferably form a layer 17 containing the floating foamed particles. After the foamed particles form layer 17, a second aqueous mixture 12 containing polyolefin flakes is formed, in which the amount of foamed particles is reduced. The amount of foamed particles in the second aqueous mixture is preferably less than 0.1% by volume relative to the volume of the second aqueous mixture. The density of the second aqueous mixture is preferably between 600 and 850 kg / m³. 3 Within the range of [specific range]. The second aqueous mixture is transferred to the second compartment 28 to release the entrained air from the mixture and form a third aqueous mixture with a higher density, which has little or no entrained air. Preferably, the density of the third aqueous mixture is in the range of 900-1050 g / l.

[0058] The trapped air can be released through the outlet 15 located in the tank 10 as shown in the figure.

[0059] The conveying element 13 designed for use in this invention is positioned such that it can discharge the layer 17 containing foamed particles through the outlet 15 during operation. The conveying element 13 is used to remove the floating foamed particle layer 17 through the outlet and can be implemented in any suitable manner within the framework of this invention. Examples of conveying elements 13 designed for use in this invention are, for example, conveying screws, rivets, conveying blades, conveying paddles, scrapers, skimmers, and pumps. A screw is a preferred choice for the conveying element 13 designed for use in this invention.

[0060] The transfer port 25, designed for use in this invention, is preferably located near or at the bottom of the tank 10 in the second compartment 28, and preferably in the first sub-compartment 28B of the second compartment 28. Preferably, the third aqueous mixture is actively drawn from the second compartment 28 or from the second sub-compartment 28B of the second compartment 28 when the second compartment 28 is separated, using a pump 26.

[0061] In this embodiment of the invention, the tank 10 includes a first baffle 14 vertically disposed from the top of the tank 10, which divides the tank 10 into a first compartment 18 and a second compartment 28. The term "baffle" in this invention is intended to cover any type of barrier that has the function of at least partially blocking and guiding the flow of an aqueous mixture, wherein a plate is a practical example of such a barrier.

[0062] Different designs of the first baffle 14 and different positions of the first baffle 14 within the tank 10 can be considered. Preferably, the first baffle 14 has a simple design and is mounted from the top of the tank 10, wherein the lower edge of the first baffle 14 is generally straight. Preferably, the first baffle 14 has a dimension in a generally downward direction. In an embodiment, the first baffle 14 is permeable to air released from the aqueous mixture in the second compartment 28, whereby air can travel from the second compartment 28 to the first compartment 18 and exit the tank 10. The first compartment 18 includes an inlet 11, a conveying element 13, and an outlet 15, and the second compartment 28 includes a transfer port 25.

[0063] The aforementioned design of tank 10 provides the possibility of controlling the presence of air bubbles in tank 10. Indeed, a large number of air bubbles are present in the first compartment 18, thus providing a first aqueous mixture with a low density, and the foamed particles 17 can float to the top, while the polyolefin flakes are dispersed in the aqueous mixture. After passing through the baffle, the third aqueous mixture is allowed to have a longer residence time compared to the first compartment 18, allowing air to escape from the second aqueous mixture and increase the density of the mixture.

[0064] The first baffle 14 of the present invention can extend in a generally downward direction to at least 50% of the total height of the tank 10, preferably to 50% to 70% of the total height of the tank 10. The first baffle 14 can be arranged to move vertically up and down in the tank 10, such that the length of the baffle 14 extending from the top of the tank 10 can be varied, thereby controlling the residence time of the aqueous mixture in the first compartment 18 and the second compartment 28.

[0065] With the second compartment 28 separated, the tank 10 designed for use in this invention may further include a second baffle 24. Different designs of the second baffle 24 and different positions of the second baffle 24 within the tank 10 are conceivable. Preferably, the second baffle 24 has a simple design and is mounted from the bottom of the tank 10, wherein the upper edge of the second baffle 24 is generally straight. The third aqueous mixture is divided by the second baffle 24 into a third aqueous mixture 22A in the first sub-compartment 28A of the second compartment 28 and a third aqueous mixture 22B in the second sub-compartment 28B of the second compartment 28.

[0066] The above design provides further control over the bubble distribution in the third aqueous mixture 22A located in the first sub-compartment 28A of the second compartment 28 and the third aqueous mixture 22B located in the second sub-compartment 28B of the second compartment 28, allowing for continuous and constant flow of the aqueous mixture and discharge of the third aqueous mixture 22B through the transfer port 25, and avoiding equipment failure caused by bubbles at the transfer port. The control of bubbles allows the third aqueous mixture 22A in the first sub-compartment 28A of the second compartment 28 to have a bubble distribution of 850-900 kg / m³. 3 The density is within the range, and the third aqueous mixture 22B in the second sub-compartment 28B of the second compartment 28 can have a density of 900-1050 kg / m³. 3 The density is within the range. Therefore, the air bubbles in the third aqueous mixture 22B are reduced to the point that the third aqueous mixture 22B essentially contains no air bubbles.

[0067] The second baffle 24 of the present invention can be further movably arranged in the tank 10, particularly arranged to move horizontally toward and away from the first baffle 14. The second baffle 24 can extend upward to at least 50% of the total height of the tank 10, preferably 50% to 70% of the total height of the tank 10. In embodiments, the second baffle 24 can overlap the first baffle 14 vertically by 10% to 40%, preferably 20% to 30%. The second baffle 24 can be arranged to move vertically up and down in the tank 10, such that the length of the baffle 24 extending from the bottom of the tank 10 can be varied, thereby controlling the residence time of the aqueous mixture in the sub-compartments 28A, 28B of the second compartment 28.

[0068] The present invention also relates to an apparatus for separating foamed particles from polyolefin sheets, the apparatus comprising:

[0069] Tank 10, inlet 11, conveying element 13, outlet 15, transfer port 25, first baffle 14 and second baffle 24,

[0070] The first baffle 14 is installed from the top of the tank 10, and is permeable to air at the top, defining the first compartment and the second compartment 28.

[0071] The second baffle 24 is installed from the bottom of the tank 10, dividing the second compartment 28 into sub-compartment 28A and sub-compartment 28B.

[0072] The first compartment 18 includes an inlet 11, a conveying element 13, and an outlet 15.

[0073] Sub-compartment 28B includes a transfer port 25 located at the bottom of tank 10.

[0074] The equipment contains a first aqueous mixture in use in the first compartment 18, the first aqueous mixture comprising foamed particles and polyolefin flakes, wherein the first aqueous mixture in the first compartment 18 has a concentration of 600-850 kg / m³. 3 Density within the range,

[0075] The first aqueous mixture is in motion, keeping the polyolefin flakes suspended within it, and allowing the formation of a top layer with floating foamed particles 17 and a bottom layer with a second aqueous mixture 12 containing the suspended polyolefin flakes.

[0076] The conveying element 13 discharges the layer containing the floating foamed particles 17 through the outlet 15 of the tank 10.

[0077] The second aqueous mixture 12 is transferred to the second compartment 28, where the trapped air is released, forming a third aqueous mixture 22 in motion, which suspends the polyolefin sheet.

[0078] In a preferred embodiment, the third aqueous mixture 22 formed in sub-compartment 28A has a density of 600 to 900 kg / m³. 3 The density of the third aqueous mixture 22A and the sub-compartment 28B is between 900 and 1100 kg / m³. 3 The third aqueous mixture 22B,

[0079] The third aqueous mixture 22B in the second compartment 28B contains less than 1% by volume of foaming particles 17.

[0080] Pump 26 transfers the third aqueous mixture 22B in sub-compartment 28B to the outside of tank 10 via transfer port 25.

[0081] The device described above can be used alone or as part of a waste plastic recycling system.

Claims

1. A method for separating foamed particles from polyolefin sheets, comprising the following steps: a. Providing a first aqueous mixture comprising foamed particles and polyolefin flakes, wherein the first aqueous mixture has less than 5%, preferably less than 2%, of an organic solvent, wherein the first aqueous mixture contains air bubbles having a concentration of 600-850 kg / m³. 3 The density is within the range, and the first aqueous mixture contains a surfactant in the range of 0.05-2% by weight, wherein the percentage by weight is relative to the total weight of the first aqueous mixture; b. The first aqueous mixture is introduced into a tank (10), the tank (10) including an inlet (11), a first compartment (18), a second compartment (28), a conveying element (13), an outlet (15) and a transfer port (25), wherein the first aqueous mixture is in motion, so that the polyolefin flakes remain suspended in the first aqueous mixture, and allows the formation of a top layer (17) with floating foamed particles and a bottom layer (12) containing the suspended polyolefin flakes. c. The layer (17) of floating foamed particles is discharged through the outlet (15) of the first compartment (18) by using the conveying element (13); d. Transfer the second aqueous mixture to the second compartment (28) and release air to obtain a density of 900-1050 kg / m³. 3 A third aqueous mixture containing suspended polyolefin flakes; and e. Discharge the third aqueous mixture through the transfer port (25), wherein the third aqueous mixture contains less than 0.1% by volume of foaming particles.

2. The method according to claim 1, wherein the foamed particles are expanded polystyrene (EPS) particles, and the polyolefin sheet is a polyethylene (PE) sheet and / or a polypropylene (PP) sheet.

3. The method according to claim 1 or 2, wherein the foamed particles have a content of less than 500 g / m³. 3 Preferably below 400g / m 3 More preferably, below 300 g / m 3 The packing density.

4. The method according to any one of the preceding claims, wherein the amount of foaming particles in the first aqueous mixture is in the range of 0.5-2% by volume.

5. The method according to any one of the preceding claims, wherein the density of the first aqueous mixture is 650-800 kg / m³. 3 More preferably 670-750 kg / m 3 The range.

6. The method according to any one of the preceding claims, wherein the first aqueous mixture contains a surfactant in the range of 0.2-1% by weight.

7. The method according to any one of the preceding claims, wherein a nonionic surfactant comprising an ethylene oxide group is present in the first aqueous mixture in an amount of 0.01-0.5% by weight relative to the first aqueous mixture.

8. The method according to any one of the preceding claims, wherein a defoamer is used, preferably said defoamer is polydimethylsiloxane (PDMS), and said defoamer is used in the range of 0.1-0.4% by weight, said weight percentage being relative to the total weight of the first aqueous mixture.

9. The method according to any one of the preceding claims, wherein the dwell time in the first compartment 18 is in the range of 20 to 40 seconds, and the dwell time in the second compartment 28 is in the range of 1 to 2 minutes.

10. The method according to any one of the preceding claims, wherein the second compartment (28) is divided into a first sub-compartment (28A) and a second sub-compartment (28B) by placing a baffle in the second compartment (28) from the bottom of the tank (10) upward.

11. The method according to any one of the preceding claims, wherein the dwell time in the first sub-compartment (28A) is in the range of 30 seconds to 50 seconds, and the dwell time in the second sub-compartment (28B) is in the range of 40 seconds to 1.5 minutes.

12. The method of any of the preceding claims, wherein, The conveying element (13) designed for use is a screw.

13. An apparatus for separating foamed particles from a polyolefin sheet, the apparatus comprising: Tank 10, inlet 11, conveying element 13, outlet, transfer port 25, first baffle 14, and second baffle 24. The first baffle 14 is mounted from the top of the tank 10 and is permeable to air at the top, defining a first compartment and a second compartment 28. The second baffle 24 is installed from the bottom of the tank 10, dividing the second compartment 28 into a first sub-compartment 28A and a second sub-compartment 28B. The first compartment 18 includes the feed inlet 11, the conveying element 13, and the discharge outlet 15. The second sub-compartment 28B includes the transfer port 25 located at the bottom of the tank 10. In use, the device contains a first aqueous mixture in the first compartment 18, the first aqueous mixture comprising foamed particles and polyolefin flakes, wherein the first aqueous mixture has less than 5%, preferably less than 2%, of organic solvent, and wherein the first aqueous mixture contains bubbles having a concentration of 600-850 kg / m³. 3 The density is within the range, and the first aqueous mixture contains a surfactant in the range of 0.05-2% by weight, wherein the percentage by weight is relative to the total weight of the first aqueous mixture; The first aqueous mixture is in motion, keeping the polyolefin flakes suspended within it, and allowing the formation of a top layer with floating foamed particles 17 and a bottom layer with a second aqueous mixture 12 containing the suspended polyolefin flakes. The conveying element 13 is configured to discharge a layer having floating foamed particles 17 through the outlet 15 of the trough 10. The second aqueous mixture 12 is transferred to the second compartment 28, where the trapped air is released, forming a third aqueous mixture 22 in motion, thereby suspending the polyolefin sheet. Pump 26 transfers the third aqueous mixture 22B from the second sub-compartment 28B to the outside of the tank 10 via the transfer port 25.

14. The device according to claim 14, wherein, in use, the density of the third aqueous mixture 22 formed in the first sub-compartment 28A is 600-900 kg / m³. 3 The density of the third aqueous mixture 22A and the second sub-compartment 28B is 900-1100 kg / m³. 3 The third aqueous mixture 22B, The third aqueous mixture 22B in the second sub-compartment 28B contains less than 1% by volume of foaming particles 17.

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