Hydrothermal upgrading and separation of mixed plastics

Abstract

A process for separating at least one light fraction comprising low-density plastic having a density less than that of water from plastic waste using superheated water. The method is also based on effective phase separation between the different plastics and at least partial melting of the low-density plastics.

Description

Technical Field

[0001] The present invention belongs to the field of processing and recycling plastic waste. In particular, the present invention relates to a method for recovering at least a light fraction comprising low-density plastics from plastic waste. Background Art

[0002] Plastic waste is widely acknowledged to have a negative impact on the environment. As a result, people are constantly seeking ways to recycle plastics in an attempt to achieve a circular economy (i.e. a closed-loop system in which renewable resources are used and used materials lose as little of their value as possible).

[0003] Typically, the recycling process starts after a plastic product is deemed unacceptable during the production phase and can be mechanically recycled, or after it has reached the end of its useful life and is considered waste. The waste is collected and sorted. Sorting typically involves first mechanical sorting by material type (e.g. plastic, paper) and then sorting the separated plastic streams by polymer type, for example using infrared spectroscopy. This results in the creation of several single streams and mixed plastic waste streams. Ideally, a single stream consists essentially of one type of polymer or a plurality of polymers of similar types. However, single streams are usually not of sufficiently high purity or quality for use with or interchangeable with virgin materials.

[0004] Therefore, separation of plastic waste into high purity single streams remains difficult and can be further complicated by material shape or composition (e.g., presence of fillers, additives, copolymers, etc.). For example, discarded foils, cups and some bottles are more difficult to separate by these existing methods, leaving a stream that does not optimally allow direct mechanical or chemical recycling. Therefore, this stream is often applied to low-grade applications or incineration. In addition, recycling methods such as mechanical recycling, chemical recycling and depolymerization are often hampered by contamination, especially dirt and organic matter still present in the stream.

[0005] There are several publications describing methods for separating polymers from plastic waste mixtures for higher-level recycling.

[0006] A first example is provided in WO02 / 074845. In this article, a method for treating mixed plastic waste is described. The method comprises mixing the plastic waste with water to obtain a slurry. The slurry is maintained at an elevated temperature under autogenous pressure to melt at least 80wt% of the plastics together. After cooling, the melted mixed plastic solidifies and forms purified mixed plastic particles. However, the separation between the plastics is not optimal, and it still delivers a large amount of low-grade plastic streams, which is associated with lower value energy applications (e.g., as an ore reducing agent in a blast furnace or as a secondary fuel in a smelter).

[0007] Flotation techniques can also be used, as described in US4132633. In this paper, air bubbles are introduced which selectively adhere to polypropylene and / or polyethylene to allow these plastics to float. Another example is described in US5248041. However, for odd-shaped plastic fragments, flotation techniques are generally not good enough because the contaminants are easily captured.

[0008] Another method is described in US9469049. In this article, a method for separating materials from mixed plastic waste is described. Multiple separation steps are used to separate impurities and separate the plastic waste into several streams. At least one of the separation steps includes sink-or-float separation. Disadvantageously, this method requires multiple processing steps. Summary of the invention

[0009] The object of the present invention is to provide an improved method for recovering plastics from plastic waste which overcomes at least some of the above disadvantages. In particular, the method according to the invention can be used to provide individual plastic streams for further processing to achieve higher levels of recycling. The inventors surprisingly found that this can be achieved by mixing plastic waste and superheated water and allowing phase separation of the different layers to occur. It was found that in this way, at least a light plastic fraction can be recovered from plastic waste. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 Experimental results of light plastic fraction recovered from plastic waste at different temperatures according to DKR310 are shown. DETAILED DESCRIPTION

[0011] Therefore, in a first aspect, the present invention relates to a method for recovering a light plastic fraction (e.g., polyolefins) from plastic waste. The light plastic fraction comprises low-density plastics having a relative humidity of less than 1 g / cm at 20°C. 3 Therefore, it has a density less than that of water. The method comprises the following steps:

[0012] - providing plastic waste and superheated water in a container at a temperature of 120° C. to 240° C. to obtain a superheated aqueous plastic mixture;

[0013] - stirring the superheated aqueous plastic mixture to cause phase separation to obtain a light plastic fraction above the aqueous fraction and a heavy plastic fraction below the aqueous fraction, wherein the heavy plastic fraction comprises high-density plastics having a density greater than 1 g / cm at 20°C 3 The density of (i.e. the relative density is greater than 1);

[0014] - Separating the light plastic fraction from the heavy plastic and aqueous fractions to obtain a recycled light plastic fraction.

[0015] In a specific embodiment, the method comprises feeding plastic waste into a water-containing container to obtain an aqueous plastic mixture, and heating the mixture to a temperature of 120° C. to 270° C. to obtain a superheated aqueous plastic mixture. Heat may be provided to the water before, during and / or after the feeding of the plastic waste and during stirring of the aqueous mixture. Preferably, the water is heated before feeding the plastic waste, as this requires less energy. However, it will be appreciated that during stirring, the temperature of the aqueous plastic mixture must remain high enough to keep the water superheated.

[0016] It has been found that the present process does not require the addition of a base. Therefore, the superheated water and / or the superheated aqueous plastic mixture is preferably substantially free of added alkaline components.

[0017] The method comprises stirring the aqueous plastic mixture so that phase separation occurs before and during melting to obtain a light plastic fraction above the aqueous fraction and a heavy plastic fraction below the aqueous fraction. The fractions are separated based on their relative density, since the light plastic fraction contains a density of less than 1 g / cm at 20°C. 3 The low-density plastics (i.e., less than the density of water) are included, while the heavy plastics fraction contains plastics with a density greater than 1 g / cm at 20 °C. 3 It is understood that due to the high content of low-density plastics in the light plastic fraction, the fraction as a whole also has a density of less than 1 g / cm at 20°C. 3 Similarly, it is understood that the heavy plastic fraction as a whole has a density greater than 1 g / cm at 20°C. 3 After phase separation occurs, the light plastic portion is separated from the heavy plastic and aqueous fractions to obtain a recycled light plastic fraction.

[0018] The plastic waste to be hydrothermally upgraded is usually a mechanically separated stream from a mainstream of industrial and / or domestic crude plastic waste. For example, typical plastic waste that can be used in the process of the present invention is plastic waste according to the DKR-310 and / or DKR-350 standards. The DKR standards were established by the German "Deutsche Gesellschaft für Kreislaufwirtschaft und RohstoffembH (DKR)".

[0019] Plastic waste according to DKR-310 includes foils consisting of at least 92 wt% of one specific polymer type. According to this standard, the surface area of ​​the foil should be larger than DIN A4, such as plastic bag and wrapping foil. Plastic waste according to DKR-350 contains packaging materials with at least 90 wt% of typical packaging plastics.

[0020] According to the present invention, although large plastic waste fragments may be fed into the container, preferably the plastic waste comprises, preferably consists essentially of, fragments having a maximum size of at most 150 mm, preferably at most 100 mm, more preferably at most 50 mm, most preferably at most 20 mm. Therefore, a DKR-310, DKR-350 or other type of plastic waste stream containing large fragments is preferably first subjected to a pre-treatment step, such as shredding or grinding. It has been found that the purity of the light plastic fraction increases as the average size of the plastic waste decreases. Therefore, taking into account the maximum size of the plastic waste fragments, preferably the plastic waste has an average size of at most 150 mm, preferably at most 100 mm, more preferably at most 50 mm, preferably at most 20 mm.

[0021] It is further preferred that the plastic waste comprises polyolefins, as these generally have a carbon content of less than 1 g / cm2 at 20°C. 3 In particular, preferably the plastic waste comprises at least 50 wt%, preferably at least 60 wt%, more preferably at least 65 wt%, most preferably at least 70 wt% of polyolefins based on the total weight of the plastic waste.

[0022] The most common examples of polyolefins are polyethylene (PE) and polypropylene (PP). Therefore, preferably the light plastic comprises a polyolefin, preferably polypropylene (PP) and / or polyethylene (PE). In fact, the light plastic preferably contains at least 50 wt%, preferably at least 60 wt%, more preferably at least 65 wt%, most preferably at least 70 wt% of PP and / or PE based on the total weight of the plastic waste.

[0023] Heavy plastics commonly found in plastic waste are polyethylene terephthalate (PET), polycarbonate (PC), polyamide (PA) and / or polyvinyl chloride (PVC). These polymers have a density greater than 1 g / cm at 20 °C. 3 Therefore, the heavy plastic of the present invention preferably contains these polymers alone or in any combination.

[0024] There is no particular limitation on the type of container that can be used in the present invention, and any container that can adapt to the conditions of the method according to the present invention will suffice.

[0025] The term superheated aqueous plastic mixture means in this context that the aqueous plastic mixture is in a superheated state. In the present invention, the water is superheated to a temperature of 120° C. to 270° C. Superheat is a term used to indicate that a liquid (herein water) is heated to a temperature above its boiling point at atmospheric pressure. The liquid is prevented from boiling at the superheat pressure by increasing the pressure. In the process according to the invention, the pressure may be autogenous.

[0026] By providing heat and stirring the superheated aqueous plastic mixture, at least a portion of the low-density plastic can be melted to obtain at least partially melted plastic. Once the low-density plastic melts, the low-density plastic tends to shrink into particles of a particle-like or ball-like shape. Without wishing to be bound by theory, it is believed that the shape is caused by a combination of the stirring of the aqueous plastic mixture to force a portion to be immersed in water (surface tension) and the shape memory of the plastic material. Shape memory refers to the tendency of plastic to at least partially restore the original shape of the plastic material. In addition, stirring can provide shear forces on the plastic, which helps to form a particle-like or ball-like material of smaller size. Therefore, the at least partially melted low-density plastic preferably comprises a particle-like material. The inventive method can also include cooling the molten plastic to solidify it, so that the light plastic fraction comprises a particle-like material containing the low-density plastic.

[0027] The average particle size of the granular material is generally at most 10 mm, preferably at most 5 mm.

[0028] Advantageously, the granular material has a relatively dense packing, which enables efficient transportation. In addition, reuse is generally simplified because the shape of the material approximates the shape properties of the granular pure material. In addition, the shape allows for higher purity because fewer contaminants can be trapped by the low-density plastic. Another advantage includes the ease of drying the granular material.

[0029] The inventors have found that the temperature to which the superheated aqueous plastic mixture is heated may have an effect on the results of the method. If the water is superheated to a relatively high temperature, more low-density plastics melt, generally resulting in higher purification and better separation. Therefore, the viscosity of the aqueous plastic mixture can decrease with increasing temperature, and in addition, higher temperatures generally result in the production of smaller granular or ball-like materials that melt low-density plastics. Although the term viscosity is generally used to describe the properties of a continuous mixture of a fluid or a fluid and a solid, it is understood that in this article, viscosity refers to the aqueous plastic mixture as a whole. Therefore, lower viscosities generally allow for lower density mixtures. However, the temperature is preferably not more than 270°C, more preferably not more than 250°C, because the plastic may degrade at such high temperatures. In addition, compounds transferred to the aqueous fraction may be formed, which may be unfavorable for its further processing (such as digestion) (see below). Typically, the temperature of the superheated aqueous plastic mixture is 120°C to 240°C, preferably 180°C to 240°C, more preferably 190°C to 230°C, and most preferably 200°C to 220°C. This temperature range may provide an optimal balance between viscosity, amount, purity of fractions of low-density and / or high-density polymers recovered from plastic waste, size of melted low-density plastic, energy consumption, degradation of plastics and formation of toxic compounds.

[0030] Agitation can be achieved by any means known to the skilled person. Examples include agitation with any type of mechanical agitator by using a nozzle (jet) or (fast) recirculation. Nozzles and recirculation may be preferred because this minimizes the entanglement of plastics in the agitation device. Agitation is also considered to allow organic and / or inorganic dirt that sticks to low-density and / or high-density plastics to be physically separated from the plastics. It is generally found that increasing the agitation intensity allows the formation of cleaner and smaller particle-like or ball-like materials. Without wishing to be bound by theory, it is believed that due to the shear force applied to the plastics, the size decreases with the increase of agitation intensity. It is understood that another factor that affects the final size of the particles is the initial particle size of the plastic waste provided in the container. Therefore, based on the desired particle size, the initial particle size and the agitation intensity can be changed. However, it should be noted that the agitation should be careful not to be too strong so that the phase separation of the fractions no longer occurs, or it should not be too small to effectively clean and separate the fractions.

[0031] Typically, phase separation occurs after stirring and superheating for at least 5 minutes, such as approximately 30 minutes. However, the optimal residence time depends, inter alia, on the composition of the plastic waste, the temperature and the intensity of stirring.

[0032] As mentioned above, at least three fractions are formed, i.e., light plastic fraction, aqueous fraction and heavy plastic fraction. In addition to relative density, these fractions can also be distinguished according to their relative plastic content. Compared with the other two fractions, the light plastic fraction is richest in low-density plastics, while compared with the other two fractions, the heavy plastic fraction is richest in high-density plastics. Compared with the light plastic fraction, the aqueous fraction in the low-density plastic is poor, while compared with the heavy plastic fraction, the aqueous fraction in the high-density plastic is poor. The light plastic fraction comprises low-density plastic, which is at least partially melted or shrunk due to superheated water. Due to the relative density of the fraction, the fraction is formed as the top layer. By any suitable technology known to the technician, the light plastic fraction can be easily recovered after phase separation. These technologies can include, for example, hydrocyclones, filtration and / or screening. The light plastic fraction can be recovered while the at least partially melted low-density plastic is still in its molten state, or when the at least partially melted low-density plastic solidifies, such as by cooling solidification, the fraction can be recovered. It will be appreciated that it is also possible that some of the partially melted low density plastic remains in its molten state while others have solidified.

[0033] The present invention makes the light plastic fraction have very high purity, which allows the fraction to be recycled. That is, it is found that the content of the light plastic fraction recovered can be at least 95wt% of the total dry weight of the light plastic fraction, usually even at least 99wt% of low-density plastics, for example, PE and / or PP. Dry weight refers to the total weight of the fraction after the recovery and drying of the fraction. Typically, after separation and allowing some aqueous fractions (mainly water) to drip, the water content is 30-40 wt% based on the total weight of the light plastic fraction. This can be further thermally dried, in which case the water content is generally less than 1 wt%. Therefore, it is understood that some water is left after drying, but this is generally negligible. Advantageously, the method of the present invention can cause the light plastic fraction to contain a significantly reduced amount of heteroatoms, for example, oxygen, chlorine, nitrogen and / or sulfur. Therefore, the separated light plastic fraction can be appropriately further processed, such as dissolution / solvolysis, pyrolysis and / or naphtha cracking for mechanical recycling. In a particularly preferred embodiment, the recycled light plastic fraction contains less than 0.050 wt%, preferably less than 0.010 wt% of chlorine, and / or less than 0.100 wt% of sulfur, and / or less than 0.100 wt% of nitrogen, and / or less than 3.0 wt% of oxygen, based on the total dry weight of the recycled light plastic fraction.

[0034] In a preferred embodiment, the recycled light plastic fraction has a higher heating value (HHV) of 42 MJ / kg or more, preferably 43 MJ / kg or more.

[0035] The aqueous fraction is formed as an intermediate layer. The aqueous fraction generally contains biogenic materials. Biogenic materials generally contain organic materials produced by the physiological activities of organisms, such as plants and / or animals. Some biogenic materials can be dissolved, but can also be suspended in the aqueous fraction (e.g., cellulose). Biogenic materials can, for example, include wood, food waste and / or cellulose fibers from paper and cardboard. Cellulose fibers can be suspended. In addition, the aqueous fraction can contain water-soluble components, such as salts and / or sugars. The aqueous fraction can contain chlorides (e.g., hydrogen chloride or chloride salts). In fact, advantageously, if the temperature is expanded to 250° C., the method of the present invention can also be suitable for the dechlorination of chlorine-containing plastics (especially PVC). It can be further understood that in the case of some biodegradable polymers in the plastic mixture, they are generally depolymerized into monomers under the conditions of the present invention and dissolved in the aqueous fraction. The monomers can be recovered to allow further processing.

[0036] The aqueous fraction may be recovered by any suitable means, for example by using a hydrocyclone, filtering and screening or a combination thereof. Thus, the method may further comprise recovering the aqueous fraction from the aqueous plastic mixture. After recovery, the aqueous fraction may be further processed, such as digested, as known according to the TORWASH® process described in, for example, inter alia, WO2013 / 162355 (incorporated herein in its entirety).

[0037] The heavy plastic fraction contains high-density plastics. These plastics generally have a higher melting point than low-density plastics. However, it is understood that some high-density plastics can melt under the conditions of the method of the present invention. Similarly, once melted, high-density plastics can form granular materials. This shape is advantageous because it generally does not allow too much air or other light materials to be captured. Limited by the fact that no air or other light materials are included, this makes high-density plastics actually sink, rather than floating undesirably due to artificial low density. In addition, other pollutants that are insoluble in the aqueous fraction may be present in the original plastic waste. Such pollutants may include inorganic materials, such as sand, metals, glass, additives and / or pigments. Due to its density being generally greater than 1 g / cm 3 , these pollutants usually sink below the aqueous fraction and are usually part of the heavy plastic fraction. Therefore, the heavy plastic fraction may further include a non-plastic insoluble fraction, which includes sand, metal, glass, additives and / or pigments. The heavy plastic fraction can also be recovered by any suitable tool (such as a screw). Therefore, the method can further include recovering the heavy plastic fraction from the aqueous plastic mixture. In addition, the method can also include separating high-density plastics from the non-plastic insoluble fraction. The separation of high-density plastics from sand, metal, and glass can be achieved by separation based on density / size differences. Separation from metals can be accomplished by, for example, magnetic separation or eddy current separation.

[0038] There is no specific order for recycling the fractions. However, it is understood that the aqueous fraction cannot be recycled first, because recycling the light plastic fraction will be unnecessarily complicated. Typically, high-value products are contained in the light plastic fraction. Therefore, this fraction is usually recycled first, leaving a two-layer system of aqueous fractions above the heavy plastic fraction. Then, these fractions can be recycled separately. It is understood that a small amount of aqueous fraction can be separated from the light plastic fraction. However, after separating the light plastic fraction, most (such as substantially all) of the aqueous fraction is usually left behind, such as staying above the heavy plastic fraction.

[0039] The ease of recovery is at least partially determined by the cleanliness of the phase separation of the fractions. In turn, the phase separation is at least partially determined by the intensity of stirring (see above). In addition to the intensity of stirring, the liquid-to-solid ratio (L / S) also determines the ease of phase separation, purity and recovery. Appropriate L / S ratio and stirring result in a well-dispersed superheated water-soluble plastic mixture. In this article, the liquid-to-solid ratio refers to the weight ratio of water to plastic waste. More liquid provides more space for the fractions to be physically separated. For example, more liquid allows the top light plastic fraction to be located away from the bottom heavy plastic fraction (i.e., the aqueous fraction has a larger volume). In addition, more liquid results in a less viscous aqueous plastic mixture, thereby allowing more relative movement of plastics to each other. In addition, the higher the L / S ratio, the more impurities can be contained in the aqueous fraction. Therefore, the optimal L / S ratio depends on the composition of the plastic waste. Generally, if there is more biogenic material, a larger L / S ratio is preferred in the container. Typically, the L / S ratio is at least 10:1, preferably at least 15:1, more preferably at least 20:1, most preferably the ratio is from 20:1 to 40:1.

[0040] In an embodiment of the present invention, the aqueous plastic mixture may contain reagents, such as surfactants and / or pH modifiers or regulators (e.g., buffers), to help remove ink or other additives from the polymer material. These reagents can be added in any step of the method before and during superheating, such as added to the water before or after mixing the water with the plastic material, or added to the plastic waste before the mixing. Suitable surfactants can be cationic, anionic, nonionic or zwitterionic. Preferably, the surfactant is a low-foam or non-foaming surfactant. Therefore, nonionic surfactants are preferred. In addition, preferably, reagents such as surfactants are biodegradable so that they can be digested when the aqueous fraction is digested.

[0041] The process can be carried out batchwise, but a continuous process is preferred.The vessel used in the process can be selected appropriately.

[0042] For purposes of clarity and concise description, features are described herein as being part of the same or separate embodiments, however, it is to be understood that the scope of the invention may include embodiments having a combination of all or some of the described features.

[0043] The invention is illustrated by the following non-limiting examples.

[0044] Example 1 - DKR310 plastic waste treated at different temperatures

[0045] According to DKR310, water and plastic waste were supplied to the container at an L / S ratio of 20. The experiments were conducted at a stirring rate of 600 rpm and a residence time of 30 minutes. The water was superheated to a temperature ranging from 200 to 240°C. The corresponding composition of the DKR310 waste is provided in Table 1. Before the plastic waste was fed into the container, it was chopped to obtain a maximum size of 20 mm.

[0046] Table 1

[0047] Values ​​expressed on a dry basis

[0048]

[0049] The polyolefin content of the provided waste was estimated to be 70 wt % based on the total weight of the plastic waste.

[0050] The light fraction was recovered, dried and analyzed. The experimental conditions and results are shown in Table 2. The results are also shown in Figure 1 The experiments were performed with a smaller scale multiclave system (6x) with an individual internal volume of 100 ml.

[0051] Table 2

[0052] *Weight ratio; **Fraction from plastic waste dry matter input

[0053]

[0054] It was found that the temperature increase has a beneficial effect on the bulk density and the amount of the separated light plastic fraction containing mainly polyolefins. It was also found that the temperature increase has a beneficial effect in increasing the C content while reducing the heteroatom level. The chemical composition of the light fraction is similar to that of commercial polyolefins (including fillers and additives used in the plastic production process).

[0055] Example 2 - DKR310 waste of different input sizes

[0056] According to DKR310, water and plastic waste were provided in a 20 L autoclave vessel at an L / S ratio of 20. The experiments were conducted at a temperature of 220°C, with a stirring speed of 600 rpm and a residence time of 30 min. The corresponding composition of the DKR310 waste was the same as in Example 1 and is provided in Table 1. The plastic waste was shredded to obtain a maximum size of 20 mm for one experiment and a maximum size of 100 mm for one experiment.

[0057] The polyolefin content of the provided waste was estimated to be 70 wt % based on the total weight of the plastic waste.

[0058] Recover, dry and analyze the light fraction. Experimental conditions and results are shown in Table 3. The increase of input particle size has a slight effect on the bulk density of the polyolefin recovered, and this density decreases. The difference of N and S content can be attributed to the inhomogeneous nature of the input waste. The detection of N in the polyolefin recovered can be attributed to the existence of some polyamides, which is proven to exist with a concentration lower than 1wt%.

[0059] Table 3

[0060] *Weight ratio; **Fraction from plastic waste dry matter input

[0061]

[0062] Example 3—DKR310 and DKR350 Plastic Waste

[0063] According to DKR310 and DKR350, water and plastic waste were supplied to the container. The L / S ratio was set to 20, the stirring speed was 600 rpm, the temperature was 220 °C, and the residence time was 30 min. The corresponding compositions of the DKR310 and DKR350 wastes are provided in Table 4. The plastic waste was shredded to a maximum of 100 mm.

[0064] The polyolefin content of the provided waste was estimated to be 70 wt % based on the total weight of the plastic waste.

[0065] Table 4

[0066] Values ​​expressed on a dry basis

[0067]

[0068] The light fraction was recovered, dried and analyzed. The experimental conditions and results are shown in Table 5. By using plastic waste from different sources (DKR310 and DKR350), the method was demonstrated to be robust and effective for the separation of polyolefins.

[0069] Table 5

[0070] *Weight ratio; **Fraction from plastic waste dry matter input

[0071]

[0072] Example 4 - Aqueous Fraction Digestion

[0073] Aqueous fractions were obtained and digested for Tests 1, 2, 4 and 6. The results are provided in Table 6.

[0074] Table 6

[0075]

[0076] Comparative Example - Purity of polyolefin light layer treated under the conditions of WO 02 / 074845

[0077] According to DKR310, water and plastic waste were supplied to a 2L autoclave vessel at a L / S ratio of 4. The experiment was conducted at a temperature of 250°C, with a stirring speed of 900 rpm and a residence time of 120 min, in order to simulate the conditions used when using DKR-310 in WO 02 / 074845. The light fraction was recovered, dried and analyzed. Table 7 provides the experimental conditions and results.

[0078] Table 7

[0079] * Weight Ratio

[0080]

[0081] The results show that the recovered light fraction, based on relatively low HHV, H and C values ​​and relatively high ash and heteroatoms (i.e. N, S, O and Cl), is still present in the mixed plastic material, which contains significantly higher polyamide and PVC fractions, despite the use of more severe washing conditions (i.e. higher temperature and residence time) when compared to the process of the present invention.

Claims

1. A method for recovering a light plastic fraction from plastic waste, wherein the light plastic fraction comprises low-density plastics and has a carbon content of less than 1 g / cm at 20°C. 3 The method comprises: - providing the plastic waste and superheated water in a container at a temperature of 120°C to 270°C to obtain a superheated aqueous plastic mixture; - stirring the superheated aqueous plastic mixture so that phase separation occurs to obtain the light plastic fraction above the aqueous fraction and a heavy plastic fraction below the aqueous fraction, wherein the heavy plastic fraction contains high-density plastic and has a molecular weight greater than 1 g / cm at 20°C. 3 density; - separating the light plastic fraction from the heavy plastic fraction and the aqueous fraction to obtain a recycled light plastic fraction.

2. The method according to the preceding claim, wherein the low-density plastic comprises a polyolefin, preferably polypropylene (PP) and / or polyethylene (PE).

3. The method according to any one of the preceding claims, wherein the high-density plastic comprises polyethylene terephthalate (PET), polycarbonate (PC), polyamide (PA) and / or polyvinyl chloride (PVC).

4. The method according to any one of the preceding claims, further comprising separating the heavy plastic fraction from the aqueous fraction.

5. A method according to any one of the preceding claims, wherein the aqueous fraction comprises biogenic material, preferably biogenic organic matter and / or suspended cellulose fibres.

6. A method according to any one of the preceding claims, wherein the recycled light plastic fraction contains less than 0.050 wt%, preferably less than 0.01 wt% chlorine and / or less than 0.100 wt% sulphur, and / or less than 0.100 wt% nitrogen and / or less than 3.0 wt% oxygen, based on the total dry weight of the recycled light plastic fraction.

7. The method according to any one of the preceding claims, wherein the recycled light plastic fraction comprises PE and / or PP in an amount greater than 95 wt%, preferably greater than 99 wt%, based on the total dry weight of the recycled light plastic fraction.

8. A method according to any one of the preceding claims, comprising melting at least part of the low-density plastic by contacting the plastic waste with superheated water and / or by stirring the superheated aqueous plastic mixture to obtain at least partly molten plastic, and then cooling the molten plastic so that the recovered light plastic fraction contains granular material containing the low-density plastic.

9. A method according to any one of the preceding claims, wherein the heavy plastic fraction also contains inorganic materials, preferably sand, metals, additives, pigments and / or glass; and wherein the method preferably also comprises separating the heavy plastic fraction from the inorganic materials such as sand, metals, additives, pigments and / or glass.

10. The method according to any one of the preceding claims, wherein the plastic waste comprises at least 55 wt%, preferably at least 60 wt%, more preferably at least 65 wt%, most preferably at least 70 wt% of polyolefins based on the total weight of the plastic waste.

11. The method according to any one of the preceding claims, wherein the plastic waste is according to the DKR-310 and / or according to the DKR-350 standard.

12. The method according to any one of the preceding claims, wherein the weight ratio of water to the plastic waste in the container (L / S ratio) is at least 10:1, preferably at least 15:1, more preferably at least 20:

1.

13. The method according to any one of the preceding claims, wherein the plastic waste comprises fragments having a maximum dimension of at most 150 mm, preferably at most 100 mm, more preferably at most 50 mm, most preferably at most 20 mm.

14. The method according to any one of the preceding claims, wherein the plastic waste and superheated water are provided and / or stirred in the container at a temperature of 180 to 240°C, preferably 190 to 230°C, most preferably 200 to 220°C.

15. The process according to any one of the preceding claims, wherein the process is continuous.

Images