Hydrothermal upgrading and separation of mixed plastics

Abstract

A method for separating at least a light fraction containing low-density plastics having a density lower than that of water from plastic waste using a superheating process in water. The method is further based on efficient phase separation between various plastics and at least a partial melting process of the low-density plastics.

Description

Technical Field

[0001] The present invention is in the field of processing and recycling of plastic waste. Specifically, the present invention relates to a method for recovering at least a light fraction containing low-density plastic from plastic waste.

Background Art

[0002] It is widely recognized that plastic waste has an adverse impact on the environment. Therefore, methods for recycling plastics have been continuously demanded since the attempt to achieve a circular economy (i.e., a closed-loop system in which renewable sources are used and the materials used do not lose their value as much as possible).

[0003] Usually, the recycling process starts after the plastic product is rejected during the manufacturing phase or after it reaches the end of its life and is considered waste. The waste is collected and sorted. Sorting usually includes a step of mechanically sorting first by the type of material (e.g., plastic, paper), and then a step of sorting the separate plastic streams by the type of polymer using, for example, infrared spectroscopy. This results in several single streams and mixed plastic waste streams. It is ideal for a single stream to substantially contain one type of polymer or multiple similar types of polymers. However, single streams usually do not reach a purity or quality high enough to be a material replaceable with the materials used or virgin materials.

[0004] Therefore, separating plastic waste into high-purity single streams remains a challenge and can be further complicated by the shape or composition of the material (e.g., the presence of fillers, additives, copolymers, etc.). For example, waste foils, cups, and some bottles are more difficult to separate by these existing methods, leaving streams that are not optimal for direct mechanical recycling or chemical recycling. Therefore, this stream is usually applied to low-grade uses or incinerated. In addition, recycling methods such as mechanical recycling, chemical recycling, and depolymerization are often still inhibited by contamination present in the stream, i.e., by mud and organic matter.

[0005] There are several disclosures that describe methods for separating polymers from plastic waste mixtures for high-grade recycling.

[0006] A first example is presented in International Patent Application No. 02 / 074845. The specification describes a method for treating mixed plastic-containing waste. The method includes a step of mixing plastic waste and water to obtain a slurry. This slurry is held at a high temperature and autogenous pressure that dissolves at least 80% by weight of the plastics in each other. After cooling, the molten mixed plastics solidify to form purified mixed plastic particles. However, the separation between the plastics is not optimal and still produces a large amount of low-grade plastic stream, and the method is associated with low-value energy uses (e.g., for use as an ore reducing agent in a blast furnace or as a second fuel in a furnace).

[0007] For example, the flotation method described in U.S. Patent No. 4,132,633 can also be used. The specification enables these plastics to float by introducing bubbles that selectively adhere to polypropylene and / or polyethylene. Another example is described in U.S. Patent No. 5,248,041. However, the flotation method is often not sufficient because contaminants are easily trapped in plastic pieces with odd shapes.

[0008] Another method is described in U.S. Patent No. 9,469,049. The specification describes a method for separating materials from mixed plastic waste. Impurities are separated and the plastic waste is separated into several streams using multiple separation steps. At least one separation step includes sink-or-float separation. Unfortunately, this method requires many processing steps.

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Summary of the Invention

Means for Solving the Problems

[0010] An object of the present invention is to provide an improved method for recovering plastics from plastic waste that overcomes at least some of the above-mentioned drawbacks. In particular, the method according to the present invention can be used to provide individual plastic streams for further processing to achieve high-grade recycling. The inventors of the present invention have surprisingly found that this can be achieved by mixing plastic waste and superheated water to cause phase separation of various layers. For the above reasons, it has been found that at least the light plastic fraction can be recovered from the plastic waste.

Brief Description of the Drawings

[0011]

Figure 1

DETAILED DESCRIPTION OF THE INVENTION

[0012] Thus, in the first aspect, the present invention relates to a method for recovering a light plastic fraction (e.g., polyolefin) from plastic waste. The light plastic fraction includes low-density plastics having a density of less than 1 g / cm 3 at 20 °C. Therefore, it has a lower density than water. The method includes - supplying plastic waste and superheated water into a container at a temperature between 120 °C and 240 °C to obtain a superheated plastic aqueous mixture; - stirring the superheated plastic aqueous mixture to cause phase separation to obtain a light plastic fraction at the top of the aqueous fraction and a heavy plastic fraction below the aqueous fraction, wherein the heavy plastic fraction includes high-density plastics and has a density of more than 1 g / cm 3 at 20 °C (i.e., a relative density of more than 1); - separating the light plastic fraction from the heavy plastic fraction and the aqueous fraction to obtain a recovered light plastic fraction and includes.

[0013] In a specific embodiment, the method includes supplying plastic waste into a container containing water to obtain a plastic aqueous mixture, and heating the mixture to a temperature between 120 °C and 270 °C to obtain a superheated plastic aqueous mixture. The step of heating the water may be performed before, during, and / or after the step of supplying the plastic waste, and during the stirring of the aqueous mixture. Preferably, the water is heated before supplying the plastic waste because it requires less energy. However, it can be understood that during stirring, the temperature of the plastic aqueous mixture must be maintained high enough to keep the water in a superheated state.

[0014] The process of the present invention has also been found not to require the addition of an alkali. Therefore, the superheated water and / or the superheated plastic aqueous mixture preferably contains substantially no added alkali component.

[0015] The above method includes a step of stirring the plastic aqueous mixture before and during the melting step to cause phase separation in order to obtain a light plastic fraction on top of the aqueous fraction and a heavy plastic fraction below the aqueous fraction. The light plastic fraction contains low-density plastics with a density at 20 °C of less than 1 g / cm 3 (i.e., lower than the density of water), and the heavy plastic fraction contains high-density plastics with a density at 20 °C of more than 1 g / cm 3 3, so the above fractions are separated based on their relative densities. Also, since the content of low-density plastics in this fraction is high, it can also be understood that the light plastic fraction as a whole has a density at 20 °C of less than 1 g / cm 3 . Similarly, it can also be understood that the heavy plastic fraction as a whole has a density at 20 °C of more than 1 g / cm 3 . After phase separation occurs, the light plastic fraction is separated from the heavy plastic fraction and the aqueous fraction, and a recovered light plastic fraction is obtained.

[0016] The plastic waste to be hydrothermally upgraded is usually a mechanically separated stream derived from the main streams of industrial and / or household raw material plastic waste. For example, common plastic waste that can be used in the method of the present invention is plastic waste conforming to the DKR-310 and / or DKR-350 standards. The DKR standard was established by the "Deutsche Gesellschaft fur Kreislaufwirtschaft und Rohstoffe mbH (DKR)" in Germany.

[0017] Plastic waste compliant with the DKR-310 standard contains a foil consisting of at least 92% by mass of one specific polymer type. According to the above standard, the foil should have a surface area larger than DIN A4, such as plastic bags or packaging foils. Plastic waste compliant with the DKR-350 standard contains a packaging material that includes at least 90% by mass of common packaging plastics.

[0018] According to the present invention, plastic waste with large pieces can be supplied to a container, but the plastic waste preferably contains pieces with a maximum dimension of at most 150 mm, preferably at most 100 mm, more preferably at most 50 mm, and most preferably at most 20 mm, and preferably consists essentially of these. Therefore, plastic waste streams of DKR-310, DKR-350 or other types containing large pieces are preferably first subjected to a pretreatment step such as shredding or pulverization. When the average size of the plastic waste decreases, it has been found that the purity of the light plastic fraction increases. Thus, considering the maximum dimension of the plastic waste pieces, the average size of the plastic waste is preferably at most 150 mm, preferably at most 100 mm, more preferably at most 50 mm, and preferably at most 20 mm.

[0019] Furthermore, since these usually have a density at 20 °C of less than 1 g / cm 3 it is preferable to contain polyolefin. Specifically, the plastic waste preferably contains at least 50% by mass, preferably at least 60% by mass, more preferably at least 65% by mass, and most preferably at least 70% by mass of polyolefin based on the total mass thereof.

[0020] The most common examples of polyolefins are polyethylene (PE) and polypropylene (PP). Thus, the lightweight plastic preferably contains polyolefin, preferably polypropylene (PP) and / or polyethylene (PE). In practice, the lightweight plastic preferably contains at least 50% by mass, preferably at least 60% by mass, more preferably at least 65% by mass, and most preferably at least 70% by mass of PP and / or PE based on the total mass of the plastic waste.

[0021] Heavy plastics that are usually present in plastic waste are polyethylene terephthalate (PET), polycarbonate (PC), polyamide (PA) and / or polyvinyl chloride (PVC). The density of these polymers at 20 °C is greater than 1 g / cm 3 ³. Thus, the heavy plastics of the present invention preferably contain these polymers individually or any combination thereof.

[0022] The type of container that can be used in the present invention is not particularly limited, and any container that can adapt to the conditions of the method according to the present invention may be sufficient.

[0023] The term "superheated plastic aqueous mixture" in this specification means that the plastic aqueous mixture is in a superheated state. In the present invention, water is superheated to a temperature between 120 °C and 270 °C. Superheating is a term used to indicate that a liquid, in this case water, is heated to a temperature higher than its boiling point at atmospheric pressure. The boiling of the liquid at the pressure during superheating is suppressed by the increase in pressure. The pressure in the method according to the present invention may be self-generated.

[0024] By subjecting the heated plastic aqueous mixture to a heating step and a stirring step, at least a part of the low-density plastic can be melted to obtain at least partially melted plastic. When the low-density plastic melts, it tends to shrink into granular or spherical particles. This shape is thought to be caused by a combination with the step of stirring the plastic aqueous mixture and partially immersing it in water (surface tension) and the shape memory of the plastic material, although not bound by theory. Shape memory refers to the tendency of the plastic to return at least partially to the original shape of the plastic material. In addition, stirring can apply a shearing force to the plastic that contributes to the formation of relatively small-sized granular or spherical material. Thus, the at least partially melted low-density plastic preferably contains granular material. The method of the present invention may further include a step of cooling and solidifying the melted plastic so that the lightweight plastic fraction contains granular material containing the low-density plastic.

[0025] The average particle diameter of the granular material is usually at most 10 mm, preferably at most 5 mm.

[0026] Advantageously, the granular material enables efficient transportation due to its relatively high bulk density. In addition, since the shape of the material approximates the shape characteristics of the granulated virgin material, recycling is usually facilitated. Furthermore, the above shape can reduce the contaminants trapped by the low-density plastic, enabling an increase in purity. Another advantage includes the ease of drying of the granular material.

[0027] The inventors of the present invention have found that the temperature at which the heated plastic aqueous mixture is heated can affect the results of the above method. If the water is superheated to a relatively high temperature, the less dense plastic melts, usually resulting in higher cleanliness and better separation. The viscosity of the plastic aqueous mixture may decrease with increasing temperature. In addition, a higher temperature usually makes the melted low-density plastic into smaller granular or spherical materials. While the term "viscosity" is usually used to represent the properties of a fluid or a continuous mixture of a fluid and a solid, it is understood herein that the viscosity relates to the entire plastic aqueous mixture. Thus, a low viscosity usually allows for a less dense mixture. However, the above temperature preferably does not exceed 270, more preferably 250 °C, because there is a risk of plastic degradation at such high temperatures. Furthermore, compounds that may be disadvantageous for further processing such as digestion (see below) and that migrate into the aqueous fraction may also be formed. Generally, the temperature at which the heated plastic aqueous mixture is heated is between 120 °C and 240 °C, preferably between 180 °C and 240 °C, more preferably between 190 °C and 230 °C, and most preferably between 200 °C and 220 °C. This temperature range can provide an optimal balance between viscosity, the quality of the recycled low- and / or high-density polymers from plastic waste, the purity of the fractions, the size of the melted low-density plastic, energy consumption, plastic degradation, and the formation of toxic compounds.

[0028] Stirring can be achieved by any method known to those skilled in the art. Examples include stirring using any type of mechanical stirrer by means of jets or (high-speed) recirculation. Jets and recirculation may be preferred in order to minimize entanglement of plastics in the stirring method. The above stirring is also thought to enable the physical separation of organic and / or inorganic sludge adhering to low-density plastics and / or high-density plastics from the plastics. Generally, it can be seen that an increase in the stirring intensity enables the formation of cleaner, smaller granular or spherical materials. Without wishing to be bound by theory, it is thought that the size decreases with an increase in the stirring intensity due to the shear force applied to the plastics. It can be understood that another factor affecting the final size of the fine particles is the initial particle size of the plastic waste fed into the container. Depending on the desired size of the fine particles, the initial particle size and the stirring intensity can be changed accordingly. However, it should be noted that the stirring should not be too strong so that no further phase separation of the fractions occurs, or the stirring should not be too weak for the efficient cleaning and separation of the fractions.

[0029] Normally, phase separation occurs after at least 5 minutes, for example approximately 30 minutes, of stirring and overheating. However, the optimal residence time depends on, that is, the composition, temperature and stirring intensity of the plastic waste.

[0030] As described above, at least three fractions are formed, namely a light plastic fraction, an aqueous fraction and a heavy plastic fraction. In addition to the relative density, the fractions can be further distinguished by their relative plastic content. The light plastic fraction contains the most low-density plastic compared to the other two fractions, while the heavy plastic fraction contains the most high-density plastic compared to the other two fractions. The aqueous fraction contains less low-density plastic than the light plastic fraction and less high-density plastic than the heavy plastic fraction. The light plastic fraction contains low-density plastic that has been at least partially melted or shrunk as a result of the superheated water. This fraction forms the top layer due to the relative density of the fraction. The light plastic fraction can be easily recovered after phase separation by any suitable method known to those skilled in the art. The methods described above may include, for example, hydrocyclones, filtration and / or sieving. The light plastic fraction can be recovered while at least partially melted low-density plastics remain in their molten state, or the fraction can be recovered, for example, when at least partially melted low-density plastics solidify upon cooling. It can also be understood that some of the at least partially melted low-density plastics can remain in their molten state while others solidify.

[0031] The present invention enables a very high purity of the light plastic fraction and allows this fraction to be recycled. That is, it has been found that the content of the recovered light plastic fraction can be at least 95% by mass, usually even at least 99% by mass of low-density plastics such as PE and / or PP, based on the total dry mass of the light plastic fraction. "Dry mass" refers to the total mass of the fraction after the recovery process and the drying process of the fraction. Usually, after some aqueous fraction (mainly water) is separated and dripped off, the water content is between 30 and 40% by mass based on the total mass of the light plastic fraction. This can be further subjected to thermal drying, in which case the water content is usually less than 1% by mass. Thus, it can be understood that although some water remains after drying, this can usually be ignored. Advantageously, the method of the present invention can result in a light plastic fraction with a significantly reduced content of heteroatoms such as oxygen, chlorine, nitrogen and / or sulfur. Thus, the separated light plastic fraction can be suitably subjected to further processing such as mechanical recycling, pyrolysis and / or decomposition / solvolysis for naphtha cracking. In a particularly preferred embodiment, the recovered light plastic fraction contains less than 0.050% by mass, preferably less than 0.010% by mass of chloride, and / or less than 0.100% by mass of sulfur, and / or less than 0.100% by mass of nitrogen, and / or 3.0% by mass of oxygen, based on the total dry mass of the recovered light plastic fraction.

[0032] In a preferred embodiment, the higher heating value (HHV) of the recovered light plastic fraction is 42 MJ / kg or more, preferably 43 MJ / kg or more.

[0033] The aqueous fraction is formed as an intermediate layer. The aqueous fraction usually contains bio-derived materials. Bio-derived materials usually include organic materials produced by the physiological activities of organisms such as plants and / or animals. Some of the bio-derived materials can be dissolved, but can also be suspended in the aqueous fraction (for example, cellulose). The above bio-derived materials can include, for example, wood, food waste, and / or cellulose fibers from paper and cardboard. The above cellulose fibers can be suspended. Further, the aqueous fraction may contain water-soluble constituents such as salts and / or saccharides. The aqueous fraction may contain chlorides (for example, hydrogen chloride or chloride salts). In practice, advantageously, the method of the present invention may also be suitable for the dechlorination of chlorine-containing plastics (that is, PVC) when the temperature is extended to 250°C. Further, when some biodegradable polymers are present in the plastic mixture, it can be understood that they usually depolymerize into monomers under the conditions of the present invention and dissolve in the aqueous fraction. The above monomers can be recovered for further processing.

[0034] The aqueous fraction can be recovered by any suitable method, such as a hydrocyclone, a filtration step and a sieving step, or a combination thereof. Therefore, the above method may further include a step of recovering the aqueous fraction from the plastic aqueous mixture. After recovery, the aqueous fraction can be subjected to further treatment such as digestion, which is known to follow, for example, the TORWASH® method described in International Patent Application No. 2013 / 162355, which is incorporated herein in its entirety.

[0035] The heavy plastic fraction includes high-density plastics. These plastics usually have a higher melting point than low-density plastics. However, it can be understood that some high-density plastics can melt under the conditions of the method of the present invention. Similarly, high-density plastics can form granular materials immediately after melting. This shape is usually advantageous because it does not trap much air or other light materials. The limited inclusion or non-inclusion of air or other light materials ensures the sinking of high-density plastics instead of unwanted floating due to artificial low density. Furthermore, other contaminants may be present in the original plastic waste that is insoluble in the aqueous fraction. Such contaminants may include inorganic materials such as sand, metal, glass, additives and / or pigments. Since their density is usually greater than 1 g / cm 3 sup, these contaminants often sink below the aqueous fraction and are usually part of some heavy plastic fraction. Thus, the heavy plastic fraction may further include a non-plastic insoluble fraction containing sand, metal, glass, additives and / or pigments. The heavy plastic fraction can also be recovered by any suitable means, such as by a screw. Thus, the above method may further include a step of recovering the heavy plastic fraction from the plastic aqueous mixture. In addition, the above method may also include the separation of the high-density plastic fraction from the non-plastic insoluble fraction. The separation of high-density plastics from sand, metal, glass can be achieved by separation based on density / size differences. The separation from metal can be carried out, for example, by magnetic or eddy current separation.

[0036] There is no specific order for collecting the fractions. However, it can be understood that the aqueous fraction cannot be collected first because the process of collecting the light plastic fraction would be unnecessarily complicated in that case. Usually, the more valuable products are contained in the light plastic fraction. Therefore, often this fraction is collected first, leaving a two-layer system of the aqueous fraction on top of the heavy plastic fraction. These fractions can then be collected respectively. It can be understood that a small amount of the aqueous fraction can be separated together with the light plastic fraction. However, most, for example substantially all, of the aqueous fraction usually remains after separating the light plastic fraction, for example remaining on top of the heavy plastic fraction.

[0037] The ease of collection is at least partially determined by the cleanliness of the phase separation of the fractions. The phase separation is at least partially determined by the stirring intensity (see below). In addition to the stirring intensity, the ratio of liquid to solid (L / S) in the liquid also determines the phase separation, purity and ease of collection. Appropriate L / S ratio and stirring result in a well-dispersed and heated plastic-aqueous mixture. The ratio of liquid to solid in this specification refers to the mass ratio of water to plastic waste. When there is more liquid, more space is provided for the fractions to physically separate. For example, when there is more liquid, it is possible to move the position of the top light plastic fraction far from the bottom heavy plastic fraction (i.e., the volume of the aqueous fraction is larger). Furthermore, when there is more liquid, the viscosity of the plastic-aqueous mixture becomes lower, making the relative movement of the plastics more possible. 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 more bio-derived materials are present, it is preferable to have a larger L / S ratio in the container. Usually, the L / S ratio is at least 10:1, preferably at least 15:1, more preferably at least 20:1, and most preferably the ratio is between 20:1 and 40:1.

[0038] In an embodiment of the present invention, the plastic aqueous mixture may contain a surfactant for assisting in ink removal and / or a chemical agent such as a pH corrector or regulator (e.g., buffer agent), or other additives from polymer materials. These chemical agents can be added to water, for example, before or after the step of mixing water with the plastic material in any stage of the process before and during the superheating process, or added to the plastic waste before this mixing step. Suitable surfactants may be cationic, anionic, nonionic or zwitterionic. Preferably, the surfactant is a low-foaming surfactant or a non-foaming surfactant. Therefore, nonionic surfactants are preferred. Furthermore, it is preferable that the chemical agents such as surfactants are biodegradable so that they can be digested when the aqueous fraction is subjected to digestion.

[0039] The above method can be carried out batchwise, but a continuous method is preferred. The container for the above method can be appropriately selected.

[0040] For the purpose of clear and concise description, in this specification, features are described as part of the same or separate embodiments, but it can be understood that the scope of the present invention may include embodiments having all or part of the combinations of the described features.

[0041] The present invention can be illustrated by the following non-limiting examples.

Example

[0042] DKR310 plastic waste treated at various temperatures Water and plastic waste were supplied into the container according to DKR310 with an L / S ratio of 20. The experiment was carried out at a stirring speed of 600 rpm and a residence time of 30 minutes. Water was superheated to a temperature in the range of 200 to 240 °C. The respective compositions of the DKR310 waste are shown in Table 1. Before being supplied into the container, the plastic waste was shredded so that the maximum size became 20 mm.

[0043]

Table 1

[0044] The polyolefin content of the supplied waste was estimated to be 70% by mass based on the total mass of the plastic waste.

[0045] The light fraction was recycled, dried, and analyzed. The experimental conditions and results are shown in Table 2. The above results are also illustrated in Figure 1 under a wider range of temperature conditions in the same manner. Experiments were carried out using a small-scale multi-cavity system (6x) with an individual internal volume of 100 mL.

[0046]

Table 2

[0047] It has been found that the temperature increase has a beneficial effect on the bulk density and quality of the separated light plastic fraction, mainly those containing polyolefins. The above temperature increase has also been found to have a beneficial effect of increasing the C content while decreasing the level of heteroatoms. The chemical composition of the light fraction is similar to that of commercially available polyolefins (including fillers and additives used in the plastic manufacturing process).

Examples

[0048] DKR310 waste with various input sizes Water and plastic waste were supplied into a 20 L autoclave vessel according to DKR310 with an L / S ratio of 20. Experiments were carried out with a stirring speed of 600 rpm and a residence time of 30 minutes at a temperature of 220 °C. The composition of each of the DKR310 waste is the same as that in Example 1 and is shown in Table 1. The plastic waste was shredded so that sizes of up to 20 mm were obtained in one experiment and up to 100 mm in one experiment.

[0049] The polyolefin content of the supplied waste was estimated to be 70% by mass based on the total mass of the plastic waste.

[0050] The light fraction was recycled, dried, and analyzed. The experimental conditions and results are shown in Table 3. The increase in the input particle size slightly affected the bulk density of the recycled polyolefin, which decreased. The difference in the N and S contents may be due to the heterogeneous nature of the input waste. The detection of N in the recycled polyolefin may be due to the presence of some polyamide, but it was demonstrated to be present at a concentration of less than 1% by mass.

[0051] [Table 3]

Examples

[0052] DKR310 plastic waste vs. DKR350 plastic waste According to DKR310 and DKR350, water and plastic waste were supplied into the container. The L / S ratio was set to 20, the stirring speed was set to 600 rpm, the temperature was set to 220 °C, and the residence time was set to 30 minutes. The respective compositions of the DKR310 waste and the DKR350 waste are shown in Table 4. The plastic waste was shredded to a maximum of 100 mm.

[0053] The polyolefin content of the supplied waste was estimated to be 70% by mass based on the total mass of the plastic waste.

[0054]

Table 4

[0055] The light fraction was recycled, dried, and analyzed. The experimental conditions and results are shown in Table 5. The above method was demonstrated to be robust and efficient for separating polyolefins by using various sources of plastic waste (DKR310 and DKR350).

[0056]

Table 5

Examples

[0057] Digestion of the aqueous fraction The aqueous fractions of Tests 1, 2, 4 and 6 were obtained and subjected to digestion. The results are shown in Table 6.

[0058]

Table 6

[0059] Comparative Examples Purity of the light layer of polyolefin processed under the conditions of International Patent Application No. 02 / 074845 Water and plastic waste were fed into a 2 L autoclave vessel according to DKR310 at an L / S ratio of 4. Intending to simulate the conditions used in International Patent Application No. 02 / 074845 with DKR-310, experiments were carried out at a stirring speed of 900 rpm and a residence time of 120 minutes at a temperature of 250 °C. The light fraction was recycled, dried and analyzed. The experimental conditions and results are shown in Table 7.

[0060]

Table 7

[0061] The results show that, based on relatively low HHV values, H values and C values, and relatively high ash content, and heteroatoms (i.e., N, S, O and Cl), even when using more severe washing conditions (i.e., higher temperature and residence time) compared to the method of the present invention, the recycled light fraction still contains a mixed plastic material containing a significantly large amount of polyamide and PVC fractions.

Claims

1. A method for recovering a light plastic fraction from plastic waste, wherein The light plastic fraction includes low-density plastics and has a density at 20 °C of less than 1 g / cm 3 and is less than the method comprises - a step of supplying plastic waste and superheated water into a container at a temperature between 120°C and 270°C to obtain a superheated plastic aqueous mixture; - A step of stirring the heated plastic aqueous mixture to cause phase separation to obtain a light plastic fraction at the top of the aqueous fraction and a heavy plastic fraction below the aqueous fraction, wherein the heavy plastic fraction contains high-density plastic and has a density at 20 °C of 1 g / cm 3 or more, and - a step of separating the light plastic fraction from the heavy plastic fraction and the aqueous fraction to obtain a recovered light plastic fraction A method comprising the above steps.

2. The method according to claim 1, wherein the low-density plastic comprises polyolefin, preferably polypropylene (PP) and / or polyethylene (PE).

3. The method according to claim 1 or 2, 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 claims 1 to 3, further comprising a step of separating the heavy plastic fraction from the aqueous fraction.

5. The method according to any one of claims 1 to 4, wherein the aqueous fraction comprises a bio-derived material, preferably a bio-derived organic substance and / or suspended cellulose fibers.

6. The method according to any one of claims 1 to 5, wherein the recovered light plastic fraction contains less than 0.050% by mass, preferably less than 0.01% by mass, of chloride, and / or less than 0.100% by mass of sulfur, and / or less than 0.100% by mass of nitrogen and / or less than 3.0% by mass of oxygen based on its total dry mass.

7. The method according to any one of claims 1 to 6, wherein the recovered light plastic fraction contains PE and / or PP in an amount of more than 95% by mass, preferably more than 99% by mass, based on the total dry mass of the recovered light plastic fraction.

8. Following the step of melting at least a part of the low-density plastic by bringing the plastic waste into contact with the superheated water and / or by stirring the superheated plastic aqueous mixture to obtain at least partially molten plastic, a step of cooling the molten plastic so that the recovered light plastic fraction contains a granular material containing the low-density plastic A method comprising the above steps.

9. The heavy plastic fraction further comprises inorganic materials, preferably sand, metal, additives, pigments and / or glass, and preferably further comprises a step of separating the heavy plastic fraction from inorganic materials such as sand, metal, additives, pigments and / or glass, the method according to any one of claims 1 to 8.

10. The plastic waste contains at least 55% by mass, preferably at least 60% by mass, more preferably at least 65% by mass, and most preferably at least 70% by mass of polyolefin based on the total of its mass, the method according to any one of claims 1 to 9.

11. The plastic waste complies with the DKR-310 standard and / or complies with the DKR-350 standard, the method according to any one of claims 1 to 10.

12. The mass ratio of water in the container to the plastic waste (L / S ratio) is at least 10:1, preferably at least 15:1, more preferably at least 20:1, the method according to any one of claims 1 to 11.

13. The plastic waste includes pieces with a maximum dimension of at most 150 mm, preferably at most 100 mm, more preferably at most 50 mm, and most preferably at most 20 mm, the method according to any one of claims 1 to 12.

14. The plastic waste and the superheated water are supplied into the container and / or stirred therein at a temperature between 180°C and 240°C, preferably between 190°C and 230°C, and most preferably between 200°C and 220°C, the method according to any one of claims 1 to 13.

15. The method according to any one of claims 1 to 14 is continuous.

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