Cleaning of waste plastic

Abstract

Methods of cleaning waste plastic using an extraction system and extraction systems for cleaning waste plastic are disclosed. The extraction system (100) may comprise an extractor vessel (102) for contacting waste plastic with a supercritical carbon dioxide (scCO2) stream and a recycle loop fluidly connecting a scCO2 stream outlet (108) and scCO2 stream inlet (106) of the extractor vessel (102). The extractor vessel (102) and recycle loop may together form a circulation pathway for CO2.

Description

[0001] Cleaning of waste plastic

[0002] Field of the Invention

[0003] The present invention concerns methods of cleaning waste plastic, in particular thin film plastic. The invention also concerns extraction systems for use in the cleaning methods.

[0004] Background of the Invention

[0005] Recycling of waste plastic is necessary to reduce the amount of plastic that goes to landfill and to conserve valuable resources. Recycling of plastic is an important part of the circular economy, where materials are reused and repurposed, ultimately leading to a reduction in greenhouse gas emissions.

[0006] Plastic materials are not inert and migration of contaminants from the plastic to products in contact with the plastic occurs. It is particularly important to consider this issue when the plastic is used in food contact or pharmaceutical applications. For plastics in contact with food stuffs or pharmaceuticals, there are strict regulations for the migration of substances out of the plastic. Regulations, such as EU Commission Regulation No. 10 / 2011, define migration limits of additives and non-intentionally added substances that may migrate from food-contact plastics to food substances, expressed in mg of contaminant per kg of food.

[0007] Waste plastics may be contaminated by migration of substances into the polymer during the life cycle or first use of the plastic. If not removed at the recycle stage, such contaminants may be released by the recycled plastic. Therefore, rigorous decontamination of waste plastics to remove contaminants is required. It is particularly important to remove low molecular weight, volatile contaminants as these contaminants are the most likely to migrate from the plastic to contaminate a product in contact with the plastic.

[0008] It is especially challenging to recycle plastic films, such as high density polyethylene (HDPE), linear low density polyethylene (LLDPE), low density polyethylene (LDPE) and polypropylene (PP) films, and enormous amounts of plastic film end up in landfill or combusted each year. According to WRAP UK, approximately 400 ktpa of polyolefin films (HDPE, LLDPE and PP) are placed on the market in the UK and only about 4% of films are recycled. The UK Plastics Pact target of 30% recycled content by 2025 would require an additional 120kt of waste films diverted from landfill and energy plants. Diversion of 120 kt of waste per year is estimated to provide 120 kt of CO2 savings per year based on a saving of 1 tonne of carbon per tonne of polyethylene recycled, as well as water and treatment savings of 360 ktpa.

[0009] Present industrial decontamination processes typically comprise washing of plastic with aqueous and organic solvent washing e.g. with chlorinated solvents, and may be followed by thermal desorption of contamination molecules. Such processes are energy intensive and have a significant environmental impact. For example, chlorinated solvents are often used, waste streams need to be cleaned (e.g. aqueous streams are contaminated and require bio-chemical treatments), and the processes typically include energy intensive drying steps.

[0010] Supercritical CO2, herein abbreviated to ‘scCCh’, is a non-toxic, nonflammable, non-corrosive solvent that has liquid like density, gas like viscosities, negligible surface tension and diffusion properties between those of gases and liquids leading to improvement of mass transfer and better extraction properties in terms of efficiency and speed. The solubility of contaminants in scCCh can also be tuned, for example by simple phase change of CO2 to release dissolved contaminants.

[0011] Lab-scale and modelled processes for removing contaminants from plastics have been reported. For example, Chalamet et al. modelled processes of extracting contaminants from polypropylene pellets using scCCh at a temperature of 50-90 °C and a pressure of from 100 bar and no greater than 300 bar (Chemical Engineering Research and Design, Volume 117, January 2017, Pages 95-109). Similar processes are reported in J. of Supercritical Fluids, Volume 98, 2015, pages 25-32. In such processes, large quantities of CO2 are required resulting in S / F ratios (i.e. total amount of SCCO2 contacted with the plastic) typically in excess of 47.

[0012] US 7,745,566 discloses methods of purifying polymers in which a supercritical fluid, such as scCCh, is contacted with an emulsion formed of a solution of polymer dissolved in organic solvent and aqueous solution. The supercritical fluid extracts the organic solvent from the polymer solution, precipitating polymer in the aqueous phase. Such methods involve complicated pre-decontamination processing stages to dissolve the polymer in solvent and to form an emulsion of the polymer solution and aqueous solution. Chlorinated solvents are generally used in such processes.

[0013] The present invention seeks to mitigate the above-mentioned problems. Alternatively or additionally, the present invention seeks to provide an improved method of cleaning waste plastic, and to provide extraction systems for performing the same.

[0014] Summary of the Invention

[0015] The present invention provides, according to a first aspect, a method of cleaning waste plastic using an extraction system, the extraction system comprising: an extractor vessel for receiving waste plastic, and, a recycle loop comprising at least one pressure regulator, at least one separator and at least one compressor, wherein the extractor vessel and recycle loop together form a circulation pathway for CO2; the method optionally comprising: i) feeding the waste plastic into the extractor vessel; ii) contacting a supercritical carbon dioxide, scCCh, stream with the waste plastic within the extractor vessel to withdraw an extractant from the waste plastic into the scCCh stream; iii) passing at least a portion of the scCCh stream comprising the extractant to the recycle loop and depressurising said portion of the scCCh stream via the pressure regulator of the recycle loop to form a depressurised CO2 stream; iv) passing the depressurised CO2 stream through the at least one separator of the recycle loop to separate extractant from the depressurised CO2 stream; v) re-pressurising at least a portion of the CO2 stream that has been passed through the at least one separator of the recycle loop in the at least one compressor of the recycle loop and returning to the extractor vessel as at least a portion of the scCCh stream; vi) optionally repeating steps (ii) to (vi) to form a cleaned plastic; and vii) discharging the cleaned plastic from the extractor vessel; optionally, wherein the method optionally further comprises: adding a co-solvent to the circulation pathway for CO2; and / or, removing at least a portion of the co-solvent from the circulation pathway in the at least one separator of the recycle loop and / or in an additional separator of the recycle loop.

[0016] The method of cleaning waste plastic according to the first aspect of the invention has been found by the present inventors to provide a particularly effective method of extracting substances from waste plastic, particularly in extracting volatile substances from the waste plastic. Substances removed from the polymer may be referred to collectively as an ‘extractant’. Extractants are substances present in the waste plastic other than the polymer or mixtures of polymers from which the plastic material is formed. Extractants include additives, non-intentionally added substances and substances that migrate into the plastic waste during the lifecycle of the plastic. It will be understood that additive means a substance which is intentionally added to plastics to achieve a physical or chemical effect during processing of the plastic or in the final material or article and is intended to be present in the final material or articles. It will also be understood that non-intentionally added substance means an impurity in the substances used or a reaction intermediate formed during the production process or a decomposition or reaction product. Extractants also include contaminants such as oils, fats, flavourings and fragrances.

[0017] In the method of the present invention, extractants are removed from the waste plastic by extraction into the scCCh stream. The scCCh stream is provided in direct contact with the waste plastic in the extractor vessel. It will be understood that the waste plastic is in the form of a solid. The scCCh penetrates the waste plastic material and extracts the extractants from the material. The scCCh stream then exits the extractor vessel as a contaminated scCCh stream comprising extractant and is passed to the recycle loop to be depressurised. It will be understood that ‘depressurisation’ refers to a step in which a pressure of a stream is reduced, and may or may not result in a phase change (for example from super-critical to liquid, or liquid to gas). It will therefore be understood that a ‘depressurised’ stream may, for example, nevertheless have a pressure above ambient pressure, and thus may or may not be further depressurised. At least a portion of the extractant is then removed from the depressurised CO2 stream in at least one separator. Because the pressure of the CO2 is changed (particularly when the state is changed, e.g. from supercritical CO2 to liquid CO2), the solubility of the extractant within the CO2 is reduced and the extractant, or at least a portion of the extractant, can be removed by the one or more separators. Optionally, the at least one separator is a phase separator, such as a gas / liquid phase separator. It will be understood that a phase separator allows for separation of components that split into separate phases in the separator, and that any suitable phase separator may be used. Optionally, the method comprises operating the at least one separator to separate a gaseous CO2 stream from a liquid extractant stream, for example a liquid extractant and co-solvent stream. Preferably, the separator comprises a vaporising section to convert the depressurised CO2 stream to the gas phase (preferably from the liquid phase). The present inventors have surprisingly found that residual extractant may remain within the CO2 stream even after the CO2 stream is passed through the one or more separators. Although the residual extractant may remain in the CO2 in only small concentration e.g. less than 10 ppm, the CO2 is returned to the extractor vessel and thus the residual extractant is brought back into contact with the plastic. This residual extractant therefore hinders cleaning of plastic waste. This may not be an issue in some applications; however, plastics which are to be reused or repurposed in food contact or pharmaceutical applications are required to have a extractant content below very low thresholds to meet migration limits. The present inventors have discovered that adding a co-solvent to the circulation pathway such that the scCCh contacted with the waste plastic in the extractor vessel is a mixture of CO2 and co-solvent, increases the extraction efficiency by removing or reducing the amount of residual extractants present in the CO2 recycled to the extractor vessel.

[0018] The co-solvent is soluble in scCCh. Optionally, the co-solvent is a polar solvent. Optionally, the co-solvent is an apolar solvent. The co-solvent may be provided as a mixture of polar and apolar solvents. Whilst not wishing to be bound by theory, it is believed that when the depressurised CO2 and co-solvent mixture is passed through the separator and allowed to form a mixture of gaseous CO2 and liquid co-solvent, a partition coefficient is formed and extractants of the waste plastic, particularly volatile extractants, are more soluble in the co-solvent than in the gaseous CO2 . Thus, extractants are extracted into the co-solvent, which itself is removed from the circulation pathway in the at least one separator of the recycle loop used to remove extractant from the CO2 stream and / or in an additional separator of the recycle loop. It will be understood that system may comprise multiple separators, i.e. at least two separators or at least three separators. It may be that each separator is operated at different conditions (e.g. temperature and pressure). It may be the at least one separator removes a portion of the extractants, such as high molecular weight extractants, but does not remove co-solvent. It may be that an additional separator extracts co-solvent and at least a portion of the low molecular weight extractants.

[0019] The present invention further provides, according to a second aspect, a extraction system for performing the method of the first aspect of the invention. The extraction system according to the second aspect of the invention comprises: an extractor vessel for contacting waste plastic with a scCCh stream, the extractor vessel preferably comprising a waste plastic inlet, cleaned plastic outlet, scCCh stream inlet and scCCh stream outlet; and, a recycle loop fluidly connecting the scCCh stream outlet and scCCh stream inlet so that the extractor vessel and recycle loop together form a circulation pathway for CO2;wherein the recycle loop comprises at least one pressure regulator, at least one separator and at least one compressor, wherein the at least one pressure regulator is upstream of the at least one separator and the at least one separator is upstream of the at least one compressor. It will be understood that reference to ‘upstream’ is in reference to the flow of CO2, i.e. from a scCCh stream outlet to a scCCh stream inlet of the extractor vessel.

[0020] Optionally, the extraction system comprises a co-solvent supply system in fluid communication with the circulation pathway for CO2. Optionally, the co-solvent supply system comprises at least one solvent pump.

[0021] Optionally, the recycle loop comprises at least one of an activated carbon filter and / or a cold trap. Preferably, the activated carbon filter and / or cold trap are downstream of the separator and upstream of the compressor. Preferably, the activated carbon filter is downstream of the cold trap. The cold trap and / or activated carbon filter have been found to remove extractants, particularly volatile extractants from the depressurised CO2 stream.

[0022] The present invention further provides, according to a third aspect, a method of cleaning waste plastic using an extraction system, the extraction system comprising: an extractor vessel for receiving waste plastic, and, a recycle loop comprising a pressure regulator, at least one separator and at least one compressor, wherein the extractor vessel and recycle loop together form a circulation pathway for CO2; the method comprising: i) feeding the waste plastic into the extractor vessel; ii) contacting a scCCh stream with the waste plastic within the extractor vessel to extract an extractant from the waste plastic into the scCCh stream; iii) passing at least a portion of the scCCh stream comprising the extractant to the recycle loop and depressurising said portion of the scCCh stream via the pressure regulator of the recycle loop to form a depressurised CO2 stream; iv) passing the depressurised CO2 stream through the at least one separator of the recycle loop; v) re-pressurising at least a portion of the CO2 stream that has been passed through the at least one separator of the recycle loop in the at least one compressor of the recycle loop and returning to the extractor vessel as at least a portion of the scCCh stream; vi) repeating steps (ii) to (vi) to form a cleaned plastic; and vii) discharging the cleaned plastic from the extractor vessel; wherein the recycle loop further comprises at least one of an activated carbon filter and / or a cold trap, and the method further comprises passing the depressurised CO2 stream through the at least one of the activated carbon filter and the cold trap to remove extractant. It will be understood that by passing the depressurised CO2 stream through the activated carbon filter and / or cold trap, extractants, particularly volatile extractants, may be removed from the depressurised CO2 stream.

[0023] The present invention further provides, according to a fourth aspect, a method of cleaning waste plastic comprising: contacting a scCCh stream with the waste plastic in an extractor vessel to extract an extractant from the waste plastic into the scCCh stream; the SCCO2 stream has a pressure of greater than 300 bar and a temperature in the range of about 31 °C to about 120 °C. Optionally, the S / F ratio is in a range of about 10 to about 45, the S / F ratio being defined as:

[0024] S / F = (mass flow rate of SCCO2, kg / hr * extraction time, hr) / (mass of waste plastic, kg), wherein the mass flow rate of SCCO2 is the mass flow rate of the SCCO2 stream passed through the extractor vessel, the extraction time is the time over which the SCCO2 stream is contacted with the waste plastic and the mass of waste plastic is the total mass of waste plastic loaded into the extractor vessel. Advantageously, the waste plastic is a thin film having a thickness in the range of about 10 to about 200 pm.

[0025] The present inventors have discovered that a scCCh stream having a pressure greater than 300 bar provides unexpected benefits in extraction of substances (extractants) from waste plastic. While not wishing to be bound by theory, it is believed that the polarity of the scCCh stream at such pressures is advantageous for extracting extractants. The present inventors have discovered that by operating the method at an S / F ratio in the range of about 10 to about 45, excellent extraction can be achieved while reducing or minimising the total amount of CO2 used in the method. It is believed that a S / F ratio of less than 10 may not adequately clean waste plastic, at least not for reuse or repurposing in food contact or pharmaceutical applications. Although a S / F ratio of more than 45 may result in sufficient extraction, it is believed that no further rate of extraction is achieved and a high S / F results in CO2 waste and thus loses in efficiency and cost.

[0026] It will of course be appreciated that features described in relation to one aspect of the present invention may be incorporated into other aspects of the present invention. For example, any features described in relation to the method of the first aspect of the invention may be incorporated into the method of the third or fourth aspect of the invention and vice versa. It will in particular be understood that any method conditions such as pressure and temperature described in relation to the first aspect of the invention, may be incorporated into the third or fourth aspect of the invention and vice versa. Additionally, any features of the waste plastic described in relation to the first aspect of the invention, including the composition of the waste plastic or pre-processing or post-processing stages may be incorporated into the third or fourth aspect of the invention. It will also be understood that the extraction system of the second aspect of the invention may be used to perform the firth, third or fourth aspect of the invention.

[0027] Description of the Drawings

[0028] Embodiments of the present invention will now be described by way of example only with reference to the accompanying schematic drawings of which: Figure l is a schematic diagram of an extraction system for cleaning waste plastic according to the present invention;

[0029] Figure 2 is a flow diagram of the steps of a method of cleaning waste plastic according to the present invention;

[0030] Figure 3 is a flow diagram of the steps of a method of cleaning waste plastic according to the present invention;

[0031] Figures 4A and 4B are graphical representations of the extraction relationship of various surrogates with changing pressure. The x axis is the pressure (bar) of the extraction process and the y axis is the residual contamination index, as measured by gas chromatography. The greater the residual contamination index, the higher the amount of surrogate in the sample after extraction;

[0032] Figures 5A and 5B are graphical representations of the extraction relationship of various surrogates with changing temperature. The x axis is the temperature (°C) of the extraction process, and the y axis is the residual contamination index, as measured by gas chromatography. The greater the residual contamination index, the higher the amount of surrogate in the sample after extraction;

[0033] Figures 6A and 6B are graphical representations of the decontamination relationship of various surrogates with changing S / F ratio. The x axis is the S / F ratio of the extraction process, and the y axis is the residual contamination index, as measured by gas chromatography. The greater the residual contamination index, the higher the amount of surrogate in the sample after extraction. Detailed Description

[0034] Waste plastic

[0035] According to the present invention, the waste plastic to be cleaned is preferably a post-consumer plastic. That is, the plastic is not virgin plastic and has been used in a consumer application prior to being cleaned. Optionally, the waste plastic is post-consumer plastic that has been in contact with foodstuff, for example the waste plastic is food packaging waste. Such post-consumer plastic may be obtained from municipal waste, material recovery facility, plastic recovery facility, food packaging business operators, front-of-store return or deposit return schemes.

[0036] Optionally, the waste plastic comprises polyolefin. Optionally, the waste plastic comprises low density polyethylene (LDPE), linear low density polyethylene (LLDPE), high density polyethylene (HDPE), polypropylene (PP), polystyrene, polyethylene terephthalate (PET), polyamide, nylon, ethylene-vinyl alcohol (EVOH), polyvinyl chloride (PVC) or mixtures thereof. Most preferably, the waste plastic comprises low density polyethylene (LDPE), linear low density polyethylene (LLDPE), high density polyethylene (HDPE), polypropylene (PP).

[0037] Optionally, the waste plastic comprises melt pellet i.e. a plastic pellet that has been formed by heat treatment or extrusion.

[0038] Optionally, the waste plastic comprises plastic film, such as at least 75% by weight plastic film. Optionally, the waste plastic consists substantially entirely (e.g. at least 95% by weight), or entirely, of plastic film. Preferably, the plastic film comprises a thin film having a thickness in the range of about 10 to about 200 pm, most preferably a thickness in the range of about 20 to 40 pm. It will be understood that thin films, or films in general, may be a laminated (e.g. thermally laminated) film such that the film comprises more than one layer of film. When the thin film is a (thermally) laminated film, reference to the thickness of the film refers to the total thickness (including all laminated layers).

[0039] Optionally, the waste plastic may comprise a plastic film such as thin film, wherein the plastic film is in the form of flake. It will be understood that flake is shredded fragments of plastic film, especially thin film. Optionally, the flake has an average surface area of from about 50 mm2to about 100 mm2per fragment of flake.

[0040] Flake is a thin material with a low bulk density. To increase the bulk density, and thus the amount of film that can be loaded into the extractor vessel, the flake may be processed into a pelleted flake. Optionally, and as described herein, methods according to the present invention comprise a pre-processing stage including the step of increasing the bulk density of the flake by processing the flake in a pelleting mill and / or agglomerator to form pelleted flake. Optionally, the bulk density of the pelleted flake is in the range of about 100 to about 350 kg / m3, preferably in the range of about 200 to about 300 kg / m3. It will be understood that the pelleted flake contains independently identifiable layers of thin film and provides a convenient compressed form of thin film. Preferably, the pelletized flake has not undergone a melt treatment to melt the layers of thin film together, e.g. into a substantially homogenous pellet. This is in contrast to melt pellets which have undergone heat treatment or extrusion to form a dense, homogeneous solid pellet.

[0041] It will be understood that the scCCh stream is contacted directly with the waste plastic within the extractor vessel when the waste plastic is a solid form. The waste plastic remains in solid state throughout the extraction method steps (i) to (vi). The waste plastic is not heated above its melting point (which would provide a melt), nor is the waste plastic dissolved in solution prior to or during the contacting stage with the scCCh stream.

[0042] Extractant

[0043] Methods according to the present invention remove an extractant from waste plastic. Extractants are substances present in the waste plastic other than the polymer or mixtures of polymers from which the plastic material is formed. It will be understood that the extractant may comprise a single substance or a mixture of substances. The method of the present invention is widely applicable to a range of substances found in plastics. Extractants include additives, non-intentionally added substances and substances that migrate into the plastic waste during the lifecycle of the plastic. For example, the extractant may comprise compounds derived from foodstuffs, such as fats, oils fragrances and flavourings such as limonene. The extractant may comprise one or more compounds which have been absorbed or adsorbed by the waste plastic during first use or over the lifetime of the waste plastic. The extractant may be defined as a compound or mixture of compounds that are foodsafe, not food-safe, or are only food-safe below defined concentrations. It may be that the extractant comprises a polymer additive, such as an antioxidant, UV stabiliser, plasticiser or unreacted monomer, or non-intentionally added substance.

[0044] Optionally, the extractant comprises at least one volatile compound having a molecular weight in the range of about 50 to about 800 g / mol. Optionally, the extractant comprises at least one volatile compound having a boiling point in the range of about 50 °C to about 350 °C. Optionally, the extractant comprises at least one volatile compound having a molecular weight in the range of about 50 to about 180 g / mol, preferably in the range of about 80 to about 120 g / mol, and / or a boiling point in the range of about 50 °C to about 150 °C. Optionally, the extractant comprises at least one non-volatile compound having a molecular weight in the range of about 200 g / mol to about 400 g / mol, and / or a boiling point in the range of about 200 °C to about 350 °C.

[0045] Optionally, the extraction process described herein removes at least 95 wt% of the extractants from the waste plastic, preferably at least 98 wt%, most preferably at least 99 wt% of the extractants from the waste plastic. Such extraction efficiencies are required to meet food grade standards. Preferably, the cleaned plastic discharged from the extractor vessel has an extractants content of no more than 1,000 ppm, preferably no more than 500 ppm.

[0046] Extraction system

[0047] The extraction system for performing the method of the invention comprises an extractor vessel into which the waste plastic is fed and within which the scCCh stream is contacted with the waste plastic to extract the extractant. The extractor vessel optionally comprises one or more of: a waste plastic inlet for receiving waste plastic, a cleaned plastic outlet for discharging cleaned plastic, a scCCh stream inlet for receiving the scCCh stream, and a scCCh stream outlet for discharging the scCCh stream as a contaminated scCCh stream (i.e. a scCCh stream comprising extractant). It will be understood that the waste plastic inlet and cleaned plastic outlet may be the same. For example, waste plastic may be loaded into the extractor vessel via an inlet which also serves as the outlet from which the cleaned plastic can be discharged. Alternatively, the waste plastic inlet and cleaned plastic outlet may be different. For example, the waste plastic may be loaded into the extractor vessel via an inlet at the top of the vessel and the cleaned plastic may be discharged from the extractor vessel via an outlet at the bottom of the vessel.

[0048] Optionally, the extraction system comprises a basket into which the waste plastic is loaded. The basket, if present, may be inserted into the extractor vessel via a waste plastic inlet and removed from the extractor vessel via a cleaned plastic outlet, preferably wherein the waste plastic inlet and cleaned plastic outlet are the same. The basket therefore provides a particularly convenient means for loading and unloading waste plastic into the extractor vessel.

[0049] Optionally, the plastic is removed from the vessel via air conveying, for example wherein an air stream is passed through the vessel to convey plastic through the outlet.

[0050] The extractor vessel is rated to withstand pressures of at least 300 bar and preferably at least 550 bar. Suitable extractor vessels are known to the skilled person. Optionally, the extractor vessel has a volume of at least 80 L, preferably at least 1000 L, such as up to 20,000 L. Optionally, the extractor vessel is loaded with waste plastic in a packing density in the range of about 100 to about 300 kg / m3, preferably in the range of about 150 to about 250 kg / m3. Optionally the extractor vessel has an aspect ratio of from about 3 : 1 to about 10: 1, the aspect ratio being the ratio of average internal length to average internal diameter. Optionally, the extractor vessel has a substantially constant internal diameter along its internal length, and / or the extractor vessel includes a substantially cylindrical cavity along at least a portion of its internal length.

[0051] Waste plastic is loaded into the extractor vessel and the extractor vessel is then pressurised with scCO2. Optionally, the extractor vessel is pressurised to a pressure of greater than 300 bar, such as at least 350 bar. Preferably, the extraction method is operated as a batch process in which waste plastic is loaded into the extractor vessel in a batch for cleaning. Optionally, when the method is a batch process, the SCCO2 stream is passed continuously through the extractor vessel during each batch processing cycle.

[0052] The extraction system of the present invention comprises a recycle loop, e.g. fluidly connecting a SCCO2 stream outlet and a SCCO2 stream inlet of the extractor vessel. Thus, the extractor vessel and recycle loop together form a circulation pathway for CO2. The recycle loop allows the CO2 stream to be continuously recycled to the extractor vessel. Whilst the recycle loop allows for circulation of CO2 in the system, it will be understood that the circulation pathway for CO2 is optionally not a closed loop, and that, for example, additional CO2 can be added to the circulation loop during the method, for example to compensate for losses in CO2 during the separation of extractants from the CO2 stream.

[0053] The recycle loop comprises at least one pressure regulator, at least one separator and at least one compressor. The at least one pressure regulator is upstream of the at least one separator. The at least one separator is upstream of the at least one compressor. The scCCh stream that has been in contact with the waste plastic in the extractor vessel (the contaminated scCCh stream) exits the extractor vessel via the SCCO2 stream outlet and enters the recycle loop. The scCCh stream is then passed through the pressure regulator of the recycle loop to form a depressurised stream. The depressurised stream is then passed through at least one separator to remove extractant and form a cleaned CO2 stream. At least a portion of the cleaned CO2 stream is passed to the compressor of the recycle loop to increase the pressure of the CO2 stream, e.g. to a critical pressure, such as a pressure of between about 330 bar and about 500 bar. The re-pressurised CO2 stream is then returned to the extractor vessel as at least a portion of the scCCh stream. The scCCh stream is continuously recycled until it is deemed that sufficient extraction of the plastic has occurred and the cleaned plastic is then discharged from the extractor vessel.

[0054] It will be understood that the state of the CO2 stream changes within the circulation pathway. For example, the scCCh stream is in the supercritical state within the extractor vessel and immediately after discharge into the recycle loop. The scCCh stream passed through the at least one pressure regulator is lowered in pressure. Preferably, the pressure of the stream is lowered to a pressure below the critical point of CO2, for example a pressure of between 45 bar and 60 bar so that the CO2 is no longer in the supercritical state. For example, the CO2 may be in the liquid state after passing through the at least one pressure regulator. A further phase change may be initiated to facilitate phase separation in the at least one separator and / or the additional separator, for example transitioning CO2 to the gas phase for separation from liquid phase extractant. Preferably, the at least one separator and / or the additional separator comprises a vaporising section to convert the depressurised CO2 stream to the gas phase within the separator. It will be understood that at least a portion of the extractant phase separates from the gaseous CO2 and can therefore be separated from the CO2 in the separator. If co-solvent is present, the co-solvent may for example also phase separate from the gaseous CO2 thereby allowing removal via the separator.

[0055] Optionally, the recycle loop comprises one or more temperature controllers for adjusting temperature of the CO2 stream. For example, the recycle loop optionally comprises a temperature controller (e.g. a cooler) upstream of the compressor (e.g. between the separator and the compressor, such as immediately upstream of the compressor), for example to adjust (e.g. reduce) the CO2 stream temperature to a temperature near the critical temperature (about 31 °C) prior to compression of the CO2 stream to transition the CO2 into the critical phase. Additionally or alternatively, the recycle loop optionally comprises a temperature controller (e.g. a heater) downstream of the compressor (e.g. between the compressor and the extraction vessel, such as immediately upstream of the extraction vessel), for example to adjust (e.g. increase) the CO2 stream temperature to a temperature of at least 45 °C. Optionally, the one or more temperature controllers utilise water as a coolant / heating fluid, for example wherein the temperature controllers comprise a cool and / or warm water jacket. Optionally, the recycle loop comprises a CO2 condenser, for example for converting gaseous CO2 to liquid CO2, optionally wherein the condenser is located upstream of the compressor, for example between the separator and the compressor. Optionally, the recycle loop comprises a CO2 holding tank, for example to provide additional CO2 holding capacity in the extraction system, optionally wherein the holding tank is positioned between a condenser and the compressor, such as between a condenser and a cooler. Optionally, when the recycle loop comprises a first separator and a second separator, the recycle loop further comprises a CO2 evaporator between the first separator and the second separator. Optionally, the extractor system comprises a warm water system, for example for providing warm heating water to a CO2 heater, the at least one separator, and / or a CO2 evaporator. Additionally or alternatively, the extractor system comprises a cold water system, for example for providing cold cooling water to a CO2 cooler, and / or a CO2 condenser.

[0056] It will be understood that the pressure regulator is operable to reduce pressure of the CO2 stream, for example to provide controlled reduction in pressure in order to provide a phase change of the CO2 from supercritical to liquid. Optionally, the pressure regulator is a pressure let-down valve. Optionally, the pressure let-down valve is a back-pressure valve. Optionally, the recycle loop comprises additional pressure regulators (e.g. pressure let-down valves) such that the pressure of the CO2 can be reduced in cascade.

[0057] Optionally, the extraction system comprises a co-solvent supply system in fluid communication with the circulation pathway for CO2. Optionally, the co-solvent supply system comprises at least one co-solvent pump. According to methods of the present invention, co-solvent may be added to the circulation pathway for CO2 by means of one of more co-solvent pumps. It will be understood that by adding cosolvent to the circulation pathway for CO2 it is meant that the co-solvent is added directly to the CO2 stream (i.e. mixed with the CO2 stream), thus forming a co-solvent and CO2 mixture. Thus, in methods of the present invention where co-solvent is added to the circulation pathway, the scCCh stream passed through the extractor vessel comprises a mixture of scCCh stream and co-solvent.

[0058] Optionally, the co-solvent is dosed into the circulation loop by at least one cosolvent pump of the co-solvent supply system. Optionally, the at least one co-solvent pump is a controlled dosing pump configured to deliver co-solvent to the circulation pathway at a rate sufficient to maintain the concentration of co-solvent in the SCCO2 stream entering the extractor vessel in the range of about 1 % to about 15 % (w / w) of co-solvent in scCCh, wherein the co-solvent concentration is expressed as the amount of co-solvent by weight based on the weight of the scCCh stream. Optionally, the cosolvent is dosed into the circulation loop at a mass flow rate in the range of about 25 to 60 kg / h, such as in the range of about 35 to about 45 kg / h. Optionally, the cosolvent pump is located upstream of the at least one compressor and downstream of the extractor vessel.

[0059] When co-solvent is introduced into the circulation pathway such that the SCCO2 stream comprises a mixture of SCCO2 and co-solvent, the co-solvent is removed from the circulation pathway by the at least one separator of the recycle loop or an additional separator of the recycle loop. It will be understood that within the separator, the depressurised CO2 and co-solvent phase separate and the extractant is withdrawn into the co-solvent phase. Preferably, the at least one separator and / or additional separator is a phase separator, such as a gas / liquid phase separator, for example configured to separate a gaseous CO2 stream from a liquid extractant stream. Optionally, the at least one separator and / or additional separator comprises a vaporising section to convert the depressurised CO2 stream to the gas phase, to encourage phase separation of the depressurised CO2 and co-solvent / extractant. Optionally, the at least one separator of the recycle loop and / or an additional separator of the recycle loop each comprise a CO2 outlet (an outlet for CO2 that has been separated from the co-solvent and extractant) and a co-solvent and extractant mixture outlet (an outlet for the co-solvent and extractant mixture that has been separated from the CO2). Optionally, the extraction system further comprises a co-solvent recovery loop fluidly connecting the co-solvent and extractant mixture outlet, with the circulation pathway for CO2. Optionally, the co-solvent recovery loop comprises at least one distillation column for removing extractant from the co-solvent and optionally the at least one co-solvent supply system, and the method preferably further comprises returning at least a portion of the co-solvent discharged from the co-solvent and extractant mixture outlet via the at least one distillation column of the co-solvent recovery loop to remove extractant from the co-solvent.

[0060] Optionally, the recycle loop comprises at least one of an activated carbon filter and a cold trap. Optionally, methods of the present invention may provide passing the depressurised CO2 stream through the activated carbon filter and / or the cold trap to remove extractants. It will be understood that the activated carbon filter and / or cold trap may be provided instead of a co-solvent supply system or in addition to the cosolvent supply system. Thus, extractants, particularly volatile extractants, may be removed from the depressurised CO2 stream by at least one of an activated carbon filter, a cold trap, or by providing the scCCh stream as a mixture of depressurised CO2 and co-solvent.

[0061] Optionally, the output of the extraction system is at least 1 tonne, preferably at least 100 tonnes, preferably at least 1000 tonnes per year, such as 10,000 tonnes per year of cleaned plastic. scCOz stream conditions

[0062] It will be understood that reference to the conditions of the scCCh stream, such as temperature, pressure or composition, refers to the scCCh stream at the point of entry into the extractor vessel, unless otherwise stated.

[0063] In order for CO2 to be in the supercritical state, the CO2 must have a pressure of at least 73.8 bar and a temperature of at least 31 °C. Optionally, the SCCO2 stream has a pressure of at least 300 bar. Optionally, the SCCO2 stream has a pressure of no greater than about 500 bar. Preferably, the scCCh stream has a pressure in the range of about 330 bar to about 460 bar. Optionally, the scCO2 stream has a temperature in the range of about 31 °C to about 120 °C, preferably in the range of about 35 °C to about 70 °C. The pressure and temperature of the SCCO2 stream are selected so that the SCCO2 stream is in the supercritical state. The temperature or pressure of the SCCO2 stream may be adjusted within the stated ranges to alter the properties, such as the solvent properties, of the SCCO2 stream.

[0064] Optionally, the method of the present invention is operated so that the S / F ratio is in the range of about 10 to about 45. Optionally, the S / F ratio is from about 10 to about 30. The S / F ratio may be defined as the ratio of mass of SCCO2 used in the extraction method per batch of waste plastic to the mass of waste plastic per batch. The S / F ratio may be conveniently expressed as S / F = (mass flow rate of SCCO2, kg / hr * extraction time, hr) / (mass of waste plastic, kg). The mass flow rate of SCCO2 is the mass flow rate of the scCCh stream passed through the extractor vessel per hour, the extraction time is the time over which the scCCh stream is contacted with the waste plastic and the mass of waste plastic is the total mass of waste plastic loaded into the extractor vessel per batch. S / F ratio is particularly useful in expressing the quantity of CO2 required in the method per batch when different batch sizes and / or vessel sizes may be used. It will be understood that any of the CO2 mass flow rate, contact time and mass of waste plastic may be adjusted to provide a S / F ratio in the desired range. The S / F ratio does not include CO2 used during pressurizing, drying and depressurising steps. For example, when the mass of waste plastic processed is about 11 kg, an appropriate S / F ratio may be achieved by providing a scCCh stream having a mass flow rate in the range of about 400 kg / hour to about 500 kg / hr, and an extraction time in the range of about 15 minutes and about 1 hour. The extraction time will be understood to be the total amount of time the scCCh stream is contacted with the batch of waste plastic to remove the extractant and does not include time to pressurize or depressurize the extractor vessel nor time taken to dry the cleaned plastic. Optionally, the flow velocity (cm / min) of the SCCO2 stream through the extractor vessel is from about 1 to about 12 cm / min.

[0065] Co-solvent

[0066] Optionally, the SCCO2 stream that is passed through the extractor vessel is provided as a mixture of SCCO2 and co-solvent. The co-solvent is soluble in SCCO2. Advantageously, the extractant has a higher solubility in the co-solvent than gaseous CO2. Optionally, the co-solvent is polar. Optionally, the co-solvent is apolar. Optionally the co-solvent is provided as a mixture of polar and apolar solvents. Optionally, the co-solvent is a solvent selected from water, Ci-6 alcohol, C3-10 ester, heterocyclic solvent, aromatic solvent, C4-20 hydrocarbon solvent or mixtures thereof. Optionally, the co-solvent is selected from ethanol, propan-2-ol, ethylacetate, ethylmethylketone, acetone, THF, and hexane, or mixtures thereof. Most preferably, the co-solvent is ethanol, propan-2-ol, ethylacetate or ethylmethyl ketone. It is preferred that the co-solvent is a volatile solvent that can be easily removed from the cleaned plastic. Optionally, the solvent is food-grade. Using a food-grade solvent means that not all of the solvent needs to be removed post-extraction and residual solvent may remain on the cleaned plastic discharged from the process. Food-grade solvents may include or consist of the solvents listed in Annex I of EU Directive 2009 / 32 / EC.

[0067] Optionally, the co-solvent is a minor component of the SCCO2 stream entering the extractor vessel such that when co-solvent is present, greater than 50 % (w / w) of the SCCO2 stream is CO2, wherein the co-solvent concentration is expressed as the amount of co-solvent by weight based on the weight of the SCCO2 stream. Optionally, the SCCO2 stream entering the extractor vessel comprises the co-solvent in an amount of from about 1 % to about 15 % (w / w) of co-solvent in SCCO2. Preferably, in an amount from about 5 % to about 12 % (w / w) of co-solvent in SCCO2. It will be understood that reference to the conditions of the scCCh stream, such as temperature, pressure or composition, refers to the scCCh stream at the point of entry into the extractor vessel, unless otherwise stated. An appropriate amount of co-solvent may be chosen depending on the extractants to be removed and / or the nature of the cosolvent. For example, a co-solvent that has limited solubility in scCCh, such as water, may be provided in an amount of less than 5 % (w / w) of the scCCh stream, whereas a co-solvent that has good solubility in scCCh, such as propan-2-ol, may be present in an amount of greater than 5% (w / w) of the scCCh stream.

[0068] Optionally, when a co-solvent is present the extraction method may further comprise a step of extracting or removing the co-solvent from the cleaned plastic (a ‘drying period’) prior to the plastic being discharged from the extractor vessel. Thus, the extraction method may further comprise a step of drying the cleaned plastic to remove co-solvent prior to the plastic being discharged from the extractor vessel, wherein the step of drying the cleaned plastic comprises stopping addition of cosolvent to the circulation pathway for CO2 and flushing the extractor vessel with CO2. The CO2 used to flush the extractor may be in the supercritical state. Optionally, the drying CO2 ratio is at least 10, wherein the drying CO2 ratio is the mass of CO2 used to flush the extractor vessel during the drying period divided by the mass of cosolvent used in the process. Optionally, the drying period may be at least 15 minutes, most preferably at least 30 minutes. It will be understood that the drying period begins at the point in time when addition of co-solvent to the circulation pathway for CO2 is stopped and the drying period ends at the point when flushing of the extractor vessel with CO2 ends. The co-solvent used in the drying process may be any co-solvent disclosed herein.

[0069] Pre-extractor processing of plastic

[0070] The waste plastic may be sorted into homogeneous feed streams prior to being cleaned in a method according to the present invention. For example, the waste plastic may be hand sorted or sorted automatically by plastic type. Preferably, the waste plastic is fed into the extractor vessel as a uniform waste plastic feed comprising at least 90 wt% of a single polymer type, preferably at least 95 wt% of a single polymer type. By polymer type is meant polymer class and can include homopolymers or copolymers. Providing the waste plastic by type means that the plastic that is cleaned can be directly processed after the extraction process e.g. by extrusion, and sent to consumer applications without post-extraction sorting.

[0071] When the waste plastic to be cleaned is a plastic film, the plastic film may be shredded or agglomerated to form flake. The method of the present invention described herein, may therefore optionally comprise a pre-processing stage prior to the waste plastic being fed into the extractor vessel, wherein the pre-processing stage comprises shredding the plastic film into flake. Alternatively, the waste plastic may be delivered to site in the form of flake. Optionally, the extraction system comprises a shredder upstream of the extractor vessel (e.g. upstream of a waste plastic inlet of the extractor vessel). The shredder converts plastic films, especially thin films, into flake.

[0072] Optionally, the flake may be processed in a further pre-processing stage prior to the waste plastic being fed into the extractor vessel to increase the bulk density of the flake. The further pre-processing stage may comprise compressing layers of flake to form a pelleted flake. For example, the pre-processing stage may comprise processing the flake in a pelleting mill and / or agglomerator to form a pelleted flake. Optionally, the extraction system comprises a pelleting mill and / or agglomerator upstream of the extractor vessel (e.g. upstream of a waste plastic inlet of the extractor vessel), and preferably between the shredder and the extractor vessel. It will be understood that pelletizing the flake does not comprise applying a heat treatment, nor melting the layers of film.

[0073] Optionally, the waste plastic is washed prior to being fed into the extractor vessel to remove macro-contaminants such as greases and fats from the surface of the waste plastic. The waste plastic may be washed using an aqueous sodium hydroxide solution (e.g. 1% (w / v) sodium hydroxide in water solution), detergents and optionally antifoaming agents. Optionally, the waste plastic is washed at a temperature of at least about 45 °C. Optionally, the waste plastic is washed for a residence time of at least 10 minutes. Optionally, washing processes is followed by a rinsing stage in which residual washing solution is rinsed off the waste plastic. For example, the rinsing stage may comprise rinsing the waste plastic with water. After washing and, if used, rinsing stages, the waste plastic is optionally dried with air.

[0074] When the waste plastic is film, the waste plastic may be washed prior to processing the film to flake, but most preferably, the film is washed after the film has been processed into flake. Advantageously, when the waste plastic film is processed into flake, the pre-processing stage may further comprise separating any flake of differing density to the bulk, for example by using sink-float tanks and / or hydrocyclones.

[0075] Post-extractor processing of plastic

[0076] Optionally, the cleaned plastic discharged from the extraction vessel is extruded into either pellets or directly into packaging. Therefore, extraction systems according to the present invention may optionally comprise an extruder for extruding cleaned plastic downstream of the cleaned plastic outlet of the extractor vessel. Optionally, the extruder comprises a melt degassing section to remove residual cosolvent of the cleaned plastic either prior to or during extrusion. Optionally, the extruder comprises a fine filtration step, for example a filter with a pore size of between about 80 pm and about 150 pm. It will be understood that methods according to the present invention may comprise after step (vii), extruding the cleaned plastic and subjecting the extruded plastic to vacuum degassing in a vacuum degassing section of the extruder.

[0077] Exemplary methods and systems

[0078] An exemplary extraction system will now be described with reference to Figure 1. The extraction system 100 comprises an extractor vessel 102 which receives waste plastic to be cleaned. The waste plastic is in the form of a solid and preferably the waste plastic comprises plastic film. Optionally, a basket 104 is provided into which plastic to be cleaned is loaded. The basket 104 loaded with plastic is lowered into extractor vessel 102 and thus contains the plastic during the extraction method. After the extraction method is complete, the plastic is removed from the extractor vessel 102 by lifting the basket 104 from the extractor vessel 102. Thus, the basket 104 provides a convenient means for loading and unloading plastic into the extractor vessel. However, it will be understood that other means for loading and unloading plastic into the extractor vessel 102 may be provided, such as a hopper for discharging waste plastic into an inlet at the top of the extractor vessel 102 and an outlet at the bottom of the extractor vessel 102 for discharging cleaned plastic. A further alternative is to transfer plastic by air conveying. The extractor vessel 102 is rated to withstand the conditions of the scCCh stream of the present method. Thus, the extractor vessel 102 is rated to withstand high pressures, for example of up to about 550 bar. Suitable extractor vessels are known to the skilled person and, for example, are available from NATEX Prozesstennologie GmbH. Suitably, the extractor vessel has a volume of at least 80 L, most preferably at least 1000 L such as up to 20,000 L.

[0079] The extractor vessel 102 receives a scCCh stream via scCCh stream inlet 106 and scCCh is discharged via contaminated scCCh stream outlet 108. During the method of the invention, scCCh is continuously passed through the extractor vessel 102. The scCCh is passed in direct contact with solid plastic within the extractor vessel. Extractants within the waste plastic are extracted into the scCCh stream and the scCCh exits via the contaminated scCCh stream outlet 108 as a contaminated scCCh stream (i.e. a scCCh stream comprising extractant). Thus, it will be understood that the scCCh stream leaving the extractor vessel contains dissolved extractants withdrawn from the plastic waste.

[0080] As shown in Figure 1, the scCCh stream inlet 106 and contaminated scCCh stream outlet 108 are fluidly connected by a recycle loop (solid arrows of Fig. 1). Thus, together the extractor vessel and recycle loop form a circulation pathway for CO2. It will be understood that the phase state of the CO2 is varied at different stages of the circulation pathway for CO2 as described herein by altering the temperature and / or pressure of the CO2 stream.

[0081] The recycle loop comprises a CO2 tank 110, precooler 112, compressor 114 and preheater 116. CO2 is stored in the CO2 tank 110 in the gas phase and is passed from the CO2 tank 110 to the precooler 112 to adjust the temperature of the CO2 to a temperature near the critical temperature (about 31 °C) before the CO2 is passed to the compressor 114. The compressor 114 increases the pressure of the CO2 to a pressure at or above the critical pressure. For example, the CO2 may be compressed to a pressure in excess of 300 bar, such as up to about 460 bar. It may be that more than one compressor is present, for example a cascade of compressors may be present to sequentially increase the pressure of the CO2. The temperature of the scCCh stream is increased in the preheater 116 to a desired temperature, such as at least 45 °C. The SCCO2 stream is then fed to the extractor vessel 102 via the scCCh inlet 106.

[0082] The recycle loop further comprises a first pressure regulator in the form of a pressure let-down valve 118, a first separator 120 in the form of a gas / liquid phase separator, evaporator 122, a second separator 124 in the form of a gas / liquid phase separator, a second pressure regulator in the form of a pressure let-down valve 128 and condenser 128. After exiting the extractor vessel 102, the scCCh stream is depressurised via pressure let-down valve 118 so that the CO2 is no longer in the supercritical state, thereby transitioning to the liquid state. For example, the CO2 stream is depressurised to a pressure of about 50 bar and cooled or allowed to cool to a temperature of about 40 °C. The CO2 is then passed to a first separator 120 to extract at least a portion of extractants extracted from the waste plastic. In the first separator, the CO2 is evaporated to form a gaseous CO2 phase and a liquid extractant phase, allowing separation of the extractant from the CO2 stream. The CO2 is optionally further depressurised at the second pressure let-down valve 126, forming a lower pressure gaseous CO2 stream. In the second separator 124, further liquid extractant phase separates from CO2 stream, allowing removal of additional extractants in the second separator 124. The first separator 120 and second separator 124 may be operated at the same or different conditions as desired to extract extractants from the CO2. For example, the separators may operate at the same or different pressures, and the same or different temperatures. Further heaters, coolers or pressure let-down valves may be present. Activated carbon filter 127 and / or cold trap 129 may be added to the CO2 recirculation loop to further assist in the clean-up of the CO2.

[0083] CO2 is continuously passed through the recycle loop throughout the method. However, some losses of CO2 are expected, for example during the separation of extractant. The extraction system 100 further comprises a CO2 make-up tank 130 for storing additional CO2 and supplying additional CO2 to the CO2 tank 110, as required.

[0084] Cold water for providing cooling to the precooler 112 and condenser 128 is provided by cold water system 132 including cold water pump 134. Hot water for providing heating to the first separator 122 and evaporator 124 is provided by hot water system 136, including hot water pump 138.

[0085] A co-solvent pump 140 of a solvent supply system (not shown) is optionally provided to supply co-solvent or mixtures of co-solvents to the circulation loop for CO2. It will be understood that the co-solvent is mixed with the CO2 within the circulation loop. As shown in Fig. 1 the co-solvent pump 140 is preferably provided so that co-solvent enters the CO2 circulation loop between the precooler 112 and CO2 pump 114. In that way, the co-solvent and CO2 are both pressurised by CO2 pump 114. However, the co-solvent pump 140 may be provided at an alternative location such that the co-solvent may be mixed with the CO2 at any point in the CO2 circulation loop.

[0086] When the scCCh stream comprises a mixture of CO2 and co-solvent, at least a portion of the co-solvent may be removed in the first separator 120 and / or second separator 124, and / or an additional separator (not shown). Because the extractant has a higher affinity to the co-solvent than the CO2 stream, the removal of co-solvent on the separator(s) also removes extractant from the depressurised CO2 stream. The system 100 may further comprise a co-solvent recovery loop (not shown) connecting to an outlet of the separator that extracts the co-solvent from the CO2 stream. The cosolvent recovery loop comprises at least one distillation column for purifying the co- solvent by removing extractant. The co-solvent recovery loop is fluidly connected to the circulation pathway for CO2 so that recovered solvent can be returned to the circulation pathway for CO2 via the at least one distillation column.

[0087] A method 200 of the present invention will now be described with reference to Fig. 2. The method 200, comprises feeding 201 waste plastic into an extractor vessel. SCCO2 is then contacted 202 with the waste plastic within the extractor vessel by passing a scCCh stream through the extractor vessel. Extractant of the waste plastic is extracted into the scCCh stream. At least a portion of the scCCh stream that has been contacted with the waste plastic is discharged from the extractor vessel as a contaminated scCCh stream and passed 205 to a recycle loop. The contaminated SCCO2 stream comprising extractant is depressurised 207 via a let-down valve of the recycle loop to form a depressurised CO2 stream. The solubility of the extractant is decreased in the depressurised CO2 stream. The depressurised CO2 stream is passed through at least one separator of the recycle loop to separate 209 extractant from the depressurised CO2 stream. The depressurised CO2 stream that has been passed through the at least one separator of the recycle loop is then repressurised 211 in at least one compressor of the recycle loop. The repressurised CO2 stream is returned 212 to the extractor vessel as at least a portion of the scCCh stream. The CO2 is continuously cycled during the method through the extractor vessel and recycle loop. The cleaned plastic is then discharged 213 from the extractor vessel.

[0088] The method further comprises adding a co-solvent 215 to the circulation pathway formed by the extractor vessel and recycle loop. The co-solvent and CO2 are mixed within the circulation pathway. Thus, the scCCh stream passed through the extractor vessel is a combination of scCCh and co-solvent. Step 209 also comprises removing at least a portion of the co-solvent from the circulation pathway in the at least one separate of the recycle loop for removing extractant and / or in an additional separator of the recycle loop. Optionally, the portion of co-solvent removed from the circulation pathway is distilled to remove extractants and is returned 214 to the circulation pathway. Optionally, the recycle loop comprises an activated carbon filter and / or cold trap to remove extractant.

[0089] A further method of the invention will now be described with reference to Fig. 3. The method comprises contacting 303 a SCCO2 stream with waste plastic in an extractor vessel. The SCCO2 stream has a pressure of more than 300 bar and preferably less than about 500 bar. The scCCh stream has a temperature of from about 31 °C to about 120 °C. The scCCh stream is contacted with the waste plastic to remove extractant and form 313 as a cleaned plastic.

[0090] Examples

[0091] Surrogate testing involved intentionally introducing chemical substances to virgin plastics and was used to evaluate the extraction performance of the method. The chemical surrogates chosen mimic the chemical properties of potential extractants in waste plastic and were as follows: phenylcyclohexane (bp 238 °C, Mw 160.26); benzophenone (bp 305.4 °C, Mw 182.22); hexyl salicylate (bp 290 °C, Mw 222.28) and isopropyl myristate (bp 315 °C, Mw 270.45), toluene (bp 110 °C, Mw 92.14); chlorobenzene (bp 132 °C, Mw 112.56).

[0092] Surrogates were prepared by submerging virgin plastic film in a surrogate solution at elevated temperature for several days, removing the plastic film from the surrogate solution and rinsing the film with solvent, and drying the plastic film to remove solvent. The virgin plastic film was in the form of flake i.e. shredded thin film material.

[0093] An exemplary procedure for preparing surrogates will now be described. A batch of 4 kg cut virgin LDPE in the form of flake was submerged in a 1% (w / v) surrogate solution. The solution was prepared by dissolving 50 g of each surrogate in 5 L of propan-2-ol (Medicalcomer24 99.9%). The surrogates selected were toluene (Sigma-Aldrich 179418), chlorobenzene (Sigma- Aldrich 284513), phenylcyclohexane (Sigma-Aldrich C104809), benzophenone (Sigma-Aldrich B9300), hexyl salicylate (Sigma- Aldrich 84280) and isopropyl myristate (Sigma-Aldrich W355690). The container containing both the surrogate solution and film was closed and rotated to coat all the film with solution. A heating jacket was wrapped around the container with the thermostat set to produce an internal temperature of 38 - 45 °C. The container was rotated daily and the heating jacket was removed after 5 days. The residual solution was drained from the film, then rinsed with 5 L of propan-2-ol, three times. The film was pressed to remove most of the surface propan-2-ol and allowed to drip dry for 30 minutes, then thoroughly mixed and sampled in airtight containers. Extraction process

[0094] An exemplary extraction process will now be described. Packets of surrogate films were placed in zipped nylon net bags within an extractor vessel supplied by NATEX Prozesstennologie GmbH Each packet was weighed before and after the test to determine to total mass of surrogate before and after the supercritical extraction period. For the extraction testing, packets of surrogate film were placed in the top, middle and bottom of the vessel, with the makeup material consisting of uncontaminated plastic film (i.e. virgin plastic comprising negligible surrogates).

[0095] After charging the extractor vessel, the extractor was vented with CO2 to remove air and to pressurise the extractor vessel to the desired pressure. A heat exchanger was used to regulate the temperature of the CO2 stream. The scCCh stream was then passed through the extraction vessel at the desired flow rate, temperature, pressure and time. Co-solvent, if used, was mixed with the scCCh stream upstream of the extractor vessel.

[0096] The SCCO2 stream discharged from the extractor vessel was passed through two separators arranged in series to remove extracted surrogate. Extracted surrogates were removed from the CO2 stream in the separators by means of pressure reduction and vaporisation of the CO2. This caused phase separation of the gaseous CO2 and extracted surrogate, and when present, phase separation of the gaseous CO2 and cosolvent. The extracted surrogate and, if used, co-solvent were discharged from the separators as a first stream, and the cleaned CO2 was discharged as a second stream. The cleaned CO2 stream was recycled to the extractor vessel via a compressor and pre-heater to control the pressure and temperature of the CO2 stream re-entering the extractor vessel.

[0097] At the end of the cycle, the packets of surrogate material and makeup material was discharged from the extractor vessel and the surrogate content of the material analysed. When co-solvent was used in the process, a ‘drying period’ was performed prior to discharging the surrogate and makeup material. During the drying period, no further co-solvent was added to the CO2 stream and the CO2 stream was continued to passed through the surrogate and makeup material for the desired drying period. e analysis

[0098] Surrogate samples prior to treatment and portions of treated film (including surrogate treated film and makeup treated film) were analysed to determine the concentration of surrogate in the material. Samples for analysis were collected and contained in heat sealed foil bags. Samples obtained from the extraction process were taken from the top, middle and bottom packets and from the surrounding makeup flake. The surrogate samples were stored in PTFE capped vials. The concentration of surrogate was determined by performing an exhaustive extraction of 1 g film in 10 mL tetrahydrofuran, at 50 °C for 3-5 days, with quantification by GC-MS. An example procedure for GC-MS analysis comprised placing a 1,000 pL aliquot of the extract into a 2 mL GC vial followed by a 100 pL aliquot of an internal standard. All extracts with the exception of the surrogate samples before challenge tests used a low concentration internal standard (LR IS), whereas the surrogate samples used a high concentration internal standard (HR IS). An internal standard was prepared by diluting 0.1 g glyceryl trioctanoate (Sigma-Aldrich T9126) in 100 mL propan-2-ol (Romil SpS H625). This solution is referred to as HR IS and used as an internal standard for the high concentration calibration (HR Cal) and samples surrogate film before challenge testing. A lower concentration internal standard was prepared by diluting 1 mL of the HR IS in 100 mL propan-2-ol. This solution is referred to as LR IS and used as an internal standard for the low concentration calibration (LR Cal) and all samples following challenge testing and makeup film samples. Calibration curves were prepared from surrogate samples of known concentration. A stock calibration solution was prepared by dissolving 0.1 g toluene (Sigma- Aldrich 179418), chlorobenzene (Sigma-Aldrich 319996), phenylcyclohexane (Sigma- Aldrich C104809), benzophenone (Sigma-Aldrich B9300), hexyl salicylate (Sigma-Aldrich 84280) and isopropyl myristate (Sigma-Aldrich W355690) together in 100 mL propan-2-ol. This solution was used to prepare high range calibration standards for the GC-MS. A lower concentration calibration solution was prepared by diluting 1 mL of the HR Cal in 100 mL propan-2-ol. This solution was used to prepare low range calibration standards for the GC-MS. A series of 6 calibration standards were prepared directly into 2 mL GC vials, where 1,000 pL of matrix matched tetrahydrofuran was added to the vial, followed by 100 pL internal standard. Varying amount of the calibration stock was added to each vial consisting of 0, 20, 50, 100, 150 and 200 pL additions. The vial was capped and mixed thoroughly. This was performed for both high and low concentration solutions.

[0099] Extraction is calculated as the [(amount surrogate start)-(amount of surrogate end) / amount of surrogate start] * 100. Surrogates, particularly phenyl cyclohexane, were found to migrate into makeup material during the process. Therefore, a mass balance approach was used to determine the total amount of surrogate present in the system (surrogate packets and makeup material) before and after extraction to calculate the extraction efficiency.

[0100] Example 1 - Extraction on small scale

[0101] A LDPE film was artificially contaminated with the surrogates phenyl cyclohexane (bp 238 °C, Mw 160.26); benzophenone (bp 305.4 °C, Mw 182.22); hexyl salicylate (bp 290 °C, Mw 222.28) and isopropyl myristate (bp 315 °C, Mw 270.45). The artificially contaminated LDPE film was loaded into a 250 mL extractor vessel and the surrogates extracted by scCCh. The conditions of the scCCh stream passed through the extractor vessel were as follows:

[0102] Mass of plastic (g): 31.5

[0103] Pressure (bar): 276 or 350

[0104] Temperature (°C): 40, 50, 70

[0105] Extraction time (minutes): 30

[0106] Flow rate (g / min): 20

[0107] S / F ratio: 19

[0108] Flow velocity: 2.1 cm / min

[0109] Table 1 - % removal of surrogate Table 1 shows the % extraction of the surrogate film after the extraction process at various scCCh conditions. A comparison of run 1 and run 4, shows that an increase in pressure from 276 bar to 350 bar generally increased surrogate extraction, especially for isopropyl myristate. Excellent extraction was maintained when the temperature was reduced to 40 °C at a pressure of 350 bar (run 3 vs run 4).

[0110] Example 2 - Extraction on large scale

[0111] The conditions of run 4 of Example 1 were repeated with in an 80 L extractor vessel fitted with a 72 L basket and under the following exemplary reaction parameters:

[0112] Mass of plastic (kg): 11.1-11.7

[0113] Pressure (bar): 350, 460

[0114] Temperature (°C): 40, 50

[0115] Extraction time (minutes): 23, 30, 55, 58

[0116] Flow rate (kg / hour): 164, 167, 324, 408

[0117] S / F ratio: 13.8, 13.9

[0118] Flow velocity: 4.87, 4.67, 9.23, 11.9 cm / min

[0119] Approximately 500 g packets of surrogate shredded film (flake) were placed into a zipped nylon net bags. Packets of surrogate plastic were placed at the top, middle and bottom of the extractor vessel and surrounded by uncontaminated (makeup) film (shredded virgin LDPE film (run 1) or shredded post-industrial LDPE film (runs 2, 3, 4). The reaction parameters for each run are summarised in Table 2. The flow rate of scCCh was varied across the runs. Because the mass of LDPE was constant, the extraction time was also varied to maintain a constant S / F ratio across each run. Only run 2 comprised a mixture of co-solvent (propan-2-ol) and SCCO2. Total cycle time includes time to pressurize and depressurize the system. With propan2-ol, time was needed for drying, which is why the total cycle time is similar to test 1. Prior to the extraction, the contaminated film was sampled to determine the starting concentration by analysing 10 samples of contaminated film replicates. After the extraction procedure, samples were taken of both the contaminated film and the makeup film to determine the residual contamination and quantify any cross contamination to the makeup flake. Quantification was done in triplicate for each of the top, middle and bottom variants of both contaminated film and makeup film. A portion of the makeup film from each test was extruded into pellets, where the residual concentration was determined. The sample selected for extrusion was the middle portion of the makeup material. The makeup material was found to comprise surrogate after the extraction process because of migration between the surrogate samples and makeup material.

[0120] Extrusion was carried out with a twin-screw extruder set to a temperature of 200 °C at the vacuum section. The material used for extrusion was derived from the mid-section of the makeup material stored in the heat seal foil bags from each challenge test. The vacuum port was fitted to a vacuum pump with a vacuum pressure of approximately 0.5 bar. The residence time at the vacuum port was calculated to be 2 - 3 seconds. For run 2 material, two variants of pellet were produced, with and without the extruder vacuum on to assess the effect of the extruder vacuum on the surrogate removal. Residual surrogate phenylcyclohexane after extraction was reduced by 75% following extrusion with vacuum degassing. Table 2 - reaction parameters for each run of Example 2 As shown in Table 3 run 2 with co-solvent present provided a better extraction performance for volatile surrogates, chlorobenzene and phenyl cyclohexane than runs 1, 3 and 4 which were performed without co-solvent.

[0121] Table 3 - extraction performance without vacuum extrusion

[0122] Table 4 shows extraction with each run with and without vacuum extrusion of the film. The percentage extraction was calculated using a mass balance approach due to transfer of surrogates from the artificially contaminated material to the makeup material during the process. The extraction efficiencies for each run were found to be between 97% and 100%.

[0123] Table 4 - surrogate concentration, mg / kg

[0124] Although extraction rates appear high, it is important that either the input contamination or output contamination levels of post-consumer wastes are considered alongside any extraction efficiencies. The FDA evaluates based on how much residual surrogate is remaining after extraction rather than the proportion removed. Similarly, EFSA applies a extraction rate to an input contamination rate to calculate a residual contamination rate for its assessments. Table 4 shows the surrogate concentration of the surrogate sample (prior to extraction) and the samples for runs 1-4, with or without extrusion of the cleaned plastic. All 4 of the tests have adequate extraction performance for benzophenone, hexyl salicylate and isopropyl myristate, based on a target residual below 1 mg / kg. The residual concentration of phenylcyclohexane was reduced to below 1 mg / kg by vacuum extrusion.

[0125] The Estimated Dietary Intake (EDI) of each surrogate was calculated for run 2 as shown in Table 5, based on the maximum migration of 100 pm film. The residual surrogate contamination after the supercritical CO2 process was so low that when assuming complete migration from a 100 pm film to food, the EDI of 1.5 pg / person / day would not be exceeded. This means that the resulting material would be suitable for all conditions of use and food types at 100% recycled content.

[0126] Table 5 - migration of surrogates

[0127] Example 3 - Effect of extraction conditions on extraction of surrogates

[0128] The effect of the extraction conditions pressure, temperature and SF ratio on extraction the surrogates toluene, chlorobenzene, phenylcyclohexane, benzophenone, hexyl salicylate and isopropyl myristate was investigated. An extraction process was performed on samples of plastic film impregnated with the surrogates. One of pressure, temperature and S / F ratio were varied, while all other conditions remained constant. Residual contamination index was determined by GC analysis and is related to the signal output of the GC. The greater the residual contamination index, the greater than amount of surrogate present in the samples after extraction; a lower residual contamination index indicates better extraction performance.

[0129] Pressure

[0130] Figure 4 shows the effect of pressure (bar) (x axis) on residual contamination index (y axis). The extraction process was performed at a temperature of 50 °C, a flow velocity of 0.73 cm / min and a S / F ratio of 3.75.

[0131] It was found that the extraction efficiency of the low molecular weight, volatile surrogates toluene and chlorobenzene, decreased with increased pressure. The extraction efficiency of the semi-volatile surrogates increased with increased pressure.

[0132] Temperature

[0133] Figure 5 shows the effect of temperature (°C) (x axis) on residual contamination index (y axis). The extraction process was performed at a pressure of 350 bar, a flow velocity of 0.73 cm / min and a S / F ratio of 3.75.

[0134] It was found that extraction efficiency of all surrogates has an inverse relationship with temperature; greater extraction efficiency was observed at lower temperatures.

[0135] S / F ratio

[0136] Figure 6 shows the effect of temperature S / F ratio (x axis) on residual contamination index (y axis). The S / F ratio is the total CO2 mass contacted with the polymer over the total mass of polymer. The extraction process was performed at a pressure of 350 bar, a flow velocity of 1.41 cm / min and a temperature of 40°C. The extraction time was varied to change the S / F ratio. An extraction time of 10 minutes gave an S / F ratio of 5, an extraction time of 30 minutes gave an S / F ratio of 15 and an extraction time of 45 minutes gave an S / F ratio of 22.5.

[0137] The effect of increased SF ratio was observed increase the efficiency of extraction for the higher molecular weight surrogates. Increasing the S / F ratio above 22.5 was found to have diminishing returns on extraction efficiency.

[0138] Where in the foregoing description, integers or elements are mentioned which have known, obvious or foreseeable equivalents, then such equivalents are herein incorporated as if individually set forth. Reference should be made to the claims for determining the true scope of the present invention, which should be construed so as to encompass any such equivalents. It will also be appreciated by the reader that integers or features of the invention that are described as preferable, advantageous, convenient or the like are optional and do not limit the scope of the independent claims. Moreover, it is to be understood that such optional integers or features, whilst of possible benefit in some embodiments of the invention, may not be desirable, and may therefore be absent, in other embodiments.

Claims

Claims1. A method of cleaning waste plastic using an extraction system, the extraction system comprising: an extractor vessel for receiving waste plastic, and, a recycle loop comprising a pressure regulator, at least one separator and at least one compressor, wherein the extractor vessel and recycle loop together form a circulation pathway for CO2; the method comprising: i) feeding the waste plastic into the extractor vessel; ii) contacting a supercritical carbon dioxide, scCCh, stream with the waste plastic within the extractor vessel to withdraw an extractant from the waste plastic into the scCCh stream; iii) passing at least a portion of the scCCh stream comprising the extractant to the recycle loop and depressurising said portion of the scCCh stream via the pressure regulator of the recycle loop to form a depressurised CO2 stream; iv) passing the depressurised CO2 stream through the at least one separator of the recycle loop to separate extractant from the depressurised CO2 stream; v) re-pressurising at least a portion of the CO2 stream that has been passed through the at least one separator of the recycle loop in the at least one compressor of the recycle loop and returning to the extractor vessel as at least a portion of the scCCh stream; vi) repeating steps (ii) to (vi) to form a cleaned plastic; and vii) discharging the cleaned plastic from the extractor vessel; wherein the method further comprises: adding a co-solvent to the circulation pathway for CO2; and, removing at least a portion of the co-solvent from the circulation pathway in the at least one separator of the recycle loop and / or in an additional separator of the recycle loop.

2. The method of claim 1, wherein the co-solvent is a solvent selected from water, Ci-6 alcohol solvent, C3-10 ester solvent, heterocyclic solvent, aromatic solvent,C4-20 hydrocarbon solvent or mixtures thereof, preferably wherein the co-solvent is selected from ethanol, propan-2-ol, ethylacetate, ethylmethylketone, acetone, THF, and hexane, or mixtures thereof.

3. The method of claim 1 or claim 2, wherein the co-solvent is food-grade.

4. The method of any preceding claim, wherein the scCCh stream entering the extractor vessel comprises the co-solvent in an amount in the range of about 1 % to about 15 % (w / w) of co-solvent in scCCh, preferably in an amount in the range of about 5 % to about 12 % (w / w) of co-solvent in scCCh.

5. The method of any preceding claim, wherein the at least one separator of the recycle loop and / or additional separator of the recycle loop comprises a CO2 outlet and a co-solvent and extractant mixture outlet, and the extraction system further comprises a co-solvent recovery loop fluidly connecting the co-solvent and extractant mixture outlet with the circulation pathway for CO2, wherein the co-solvent recovery loop comprises at least one distillation column for removing extractant from the co-solvent, and the method further comprises returning at least a portion of the co-solvent discharged from the co-solvent and extractant mixture outlet to the circulation pathway for CO2 via the at least one distillation column of the co-solvent recovery loop to remove extractant from the cosolvent.

6. The method of any preceding claim, wherein the waste plastic is postconsumer plastic that has been in contact with foodstuff.

7. The method of any preceding claim, wherein the extractant comprises at least one volatile compound having a molecular weight in an amount in the range of about 50 to about 180 g / mol, preferably in an amount in the range of about 80 to about 120 g / mol and / or a boiling point in the range of about 50 °C to about 150 °C.

8. The method of any preceding claim, wherein the waste plastic comprises low density polyethylene (LDPE), linear low density polyethylene (LLDPE), high densitypolyethylene (HDPE), polypropylene (PP), polystyrene, polyethylene terephthalate (PET), polyamide, nylon, ethylene-vinyl alcohol (EVOH), polyvinyl chloride (PVC) or mixtures thereof.

9. The method of any preceding claim, wherein the waste plastic comprises plastic film, preferably the plastic film is a thin film having a thickness in a range of about 10 to 200 pm.

10. The method of claim 9, wherein the plastic film is in the form of flake, wherein the flake has an average surface area of from about 50 mm2to about 100 mm2per fragment of flake.

11. The method of claim 10, wherein the flake is in the form of pelleted flake, wherein the bulk density of the pelleted flake is in the range of about 100 to about 350 kg / m3, preferably in the range of about 200 to about 300 kg / m3.

12. The method of any preceding claim, wherein the extractor vessel has a volume of at least 80 L, preferably at least 1000 L such as up to 20,000 L.

13. The method of any preceding claim, wherein the extractor vessel is loaded with waste plastic at a packing density in a range of about 100 to about 300 kg / m3, preferably in a range of about 150 to about 250 kg / m3.

14. The method of any preceding claim, wherein the method further comprises a step of drying the cleaned plastic to remove co-solvent prior to the plastic being discharged from the extractor vessel, wherein the step of drying the cleaned plastic comprises stopping addition of co-solvent to the circulation pathway for CO2 so that the extractor vessel is flushed with scCCh.

15. The method of any preceding claim, wherein the method further comprises after step (vii), extruding the cleaned plastic in an extruder and subjecting the extruded plastic to vacuum degassing in a vacuum degassing section of the extruder.

16. The method of any preceding claim, wherein the recycle loop comprises at least one of an activated carbon filter and a cold trap, and the method further comprises passing the depressurised CO2 stream through the activated carbon filter and / or the cold trap to remove further extractants.

17. An extraction system for performing the method of any one of claims 1 to 16, the extraction system comprising: an extractor vessel for contacting waste plastic with a scCCh stream, the extractor vessel comprising a scCCh stream inlet and a scCCh stream outlet; and, a recycle loop fluidly connecting the scCCh stream outlet and scCCh stream inlet so that the extractor vessel and recycle loop together form a circulation pathway for CO2; wherein the recycle loop comprises at least one pressure regulator, at least one separator and at least one compressor, wherein the at least one pressure regulator is upstream of the at least one separator and the at least one separator is upstream of the at least one compressor; wherein the extraction system comprises at least one co-solvent supply system in fluid communication with the circulation pathway for CO2.

18. The extraction system of claim 17, wherein the co-solvent supply system comprises at least one co-solvent pump, optionally wherein the co-solvent pump is a controlled dosing pump configured to deliver co-solvent to the circulation pathway at a rate sufficient to maintain the concentration of co-solvent in the scCCh stream entering the extraction vessel in the range of about 1 % to about 15 % (w / w) of cosolvent in SCCO2.

19. The extraction system of claim 17 or claim 18, wherein the at least one separator of the recycle loop and / or an additional separator of the recycle loop comprises a CO2 outlet and a co-solvent and extractant mixture outlet, and the extraction system further comprises a co-solvent recovery loop fluidly connecting the co-solvent and extractant mixture outlet with the circulation pathway for CO2, and,wherein the co-solvent recovery loop comprises at least one distillation column for purifying co-solvent and optionally the co-solvent supply system.

20. The extraction system of any one of claims 17 to 19, wherein the system further comprises at least one of a pelleting mill and / or an agglomerator upstream of the extractor vessel.

21. The extraction system of any one of claims 17 to 20, wherein the system further comprises at least one extruder downstream of the cleaned plastic outlet, wherein the at least one extruder comprises a vacuum degassing section for degassing feed material prior to or during extrusion.

22. The extraction system of any one of claim 17 to 21, wherein the recycle loop comprises at least one of an activated carbon filter and a cold trap for removing further extractants.

23. A method of cleaning waste plastic using an extraction system, the extraction system comprising: an extractor vessel for receiving waste plastic, and, a recycle loop comprising a pressure regulator, at least one separator and at least one compressor, wherein the extractor vessel and recycle loop together form a circulation pathway for CO2; the method comprising: i) feeding the waste plastic into the extractor vessel; ii) contacting a scCCh stream with the waste plastic within the extractor vessel to extract an extractant from the waste plastic into the scCCh stream; iii) passing at least a portion of the scCCh stream comprising the extractant to the recycle loop and depressurising said portion of the scCCh stream via the pressure regulator of the recycle loop to form a depressurised CO2 stream;iv) passing the depressurised CO2 stream through the at least one separator of the recycle loop to separate extractant from the depressurised CO2 stream; v) re-pressurising at least a portion of the CO2 stream that has been passed through the at least one separator of the recycle loop in the at least one compressor of the recycle loop and returning to the extractor vessel as at least a portion of the scCCh stream; vi) repeating steps (ii) to (vi) to form a cleaned plastic; and vii) discharging the cleaned plastic from the extractor vessel; wherein the recycle loop further comprises at least one of an activated carbon filter and / or a cold trap, and the method further comprises passing the depressurised CO2 stream through the activated carbon filter and / or the cold trap, if present, to remove further extractant from the depressurised CO2 stream.

24. The method of claim 23, wherein the method is according to any one of claims 1 to 16.

25. An extraction system for performing the method of claim 23 or claim 24, the extraction system comprising: an extractor vessel for contacting waste plastic with a scCCh stream, the extractor vessel comprising a scCCh stream inlet and a scCCh stream outlet; and, a recycle loop fluidly connecting the scCCh stream outlet and scCCh stream inlet so that the extractor vessel and recycle loop together form a circulation pathway for CO2; wherein the recycle loop comprises at least one pressure regulator, at least one separator and at least one compressor, wherein the at least one pressure regulator is upstream of the at least one separator and the at least one separator is upstream of the at least one compressor; and, wherein the recycle loop further comprises at least one of an activated carbon filter and / or a cold trap for removing further extractant.

26. The extraction system of claim 25, wherein the extraction system is an extraction system according to any one of claims 17 to 21.

27. A method of cleaning waste plastic, comprising: contacting a scCCh stream with the waste plastic in an extractor vessel to extract an extractant from the waste plastic into the scCCh stream; the SCCO2 stream having a pressure of greater than 300 bar and a temperature in the range of about 31 °C to about 120 °C.

28. The method of claim 27, wherein the waste plastic comprises thin film having a thickness in the range of about 10 to about 200 pm.

29. The method of claim 27 or claim 28, wherein the method is performed at an S / F ratio in the range of about 10 to about 45, optionally in the range of about 10 to about 30, the S / F ratio being defined as:S / F = (mass flow rate of scCCh, kg / hr * extraction time, hr) / (mass of waste plastic, kg).

30. The method of any one of claims 27 to 29, wherein the thin film is in the form of pelleted flake, wherein the bulk density of the pelleted flake is in the range from about 100 to about 350 kg / m3.

31. The method of any one of claims 27 to 30, wherein the scCCh stream has a temperature in the range of about 35 °C to about 70 °C.

32. The method of any one of claims 27 to 31, wherein the scCCh stream has a pressure of no more than 500 bar, such as in the range of about 330 bar to about 460 bar.

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