Mechanical recycling methods for polyolefins

Abstract

A polyolefin mechanical recycling process in which a specific combination of processing steps, in a given sequence, results in a high purity recycled polyolefin grade having a balanced set of mechanical and optical properties that are superior to those typically found in similar recycled polyolefin grades, and a polyolefin mechanical recycling apparatus for carrying out said polyolefin mechanical recycling process.

Description

[Technical Field]

[0001] The present invention relates to a polyolefin mechanical recycling process in which a specific combination of processing steps, in a given sequence, results in a high purity recycled polyolefin grade having a balance of mechanical and optical properties superior to those typically found in similar recycled polyolefin grades, and to a polyolefin mechanical recycling apparatus for carrying out the polyolefin mechanical recycling process. [Background technology]

[0002] Over the past decade, there has been increased attention to the environmental sustainability of plastics and their current usage. This has led to the creation of new legislation regarding the disposal, recovery, and recycling of polyolefins. Furthermore, many countries are making efforts to increase the proportion of plastic material that is recycled instead of being sent to landfills.

[0003] In Europe, plastic waste accounts for approximately 27 million tonnes of waste annually. In 2016, of this, 7.4 million tonnes were disposed of in landfills, 11.27 million tonnes were burned (to produce energy), and approximately 8.5 million tonnes were recycled. Polypropylene-based materials are particularly problematic due to the widespread use of these materials in packaging. Considering that the amount of waste collected is enormous compared to the amount recycled back into the stream (only around 30%), there is still great potential for intelligent reuse of plastic waste streams and mechanical recycling of plastic waste.

[0004] Take the automotive industry as an example. In Europe, the EU End-of-Life Vehicle (ELV) Directive stipulates that 85% / 95% of materials from vehicles must be recyclable or recoverable. Current recycling rates for automotive parts fall far short of this target. On average, a vehicle is composed of 9% plastic by weight, but of this 9% by weight, only 3% by weight is currently recycled. Therefore, there are still demands to be met if the automotive industry's plastic recycling targets are to be achieved. The present invention focuses specifically on mechanically recycled waste streams, rather than "energy recycling," in which polyolefins are burned for energy. However, due to cost reasons, poor mechanical properties, and poor processability, waste streams containing crosslinked polyolefins are often used for energy recovery (e.g., incineration in district heating plants or heat generation in the cement industry) and are rarely recycled into new products.

[0005] One of the major trends in the polyolefin field is the use of recycled materials from various sources. Durable goods streams, such as those derived from waste electrical equipment (WEE) or end-of-life vehicles (ELV), contain a variety of plastics. These materials can be processed to recover acrylonitrile butadiene styrene (ABS), high-impact polystyrene (HIPS), polypropylene (PP), and polyethylene (PE) plastics. Separation can be achieved using density separation in water, followed by further separation based on fluorescence, near-infrared absorption, or Raman fluorescence. However, obtaining pure recycled polypropylene or pure recycled polyethylene is generally very difficult. Commercially available recycled polypropylene is typically a mixture of both polypropylene (PP) and polyethylene (PE), and this is especially true for post-consumer waste streams. Commercially available recyclable materials from post-consumer waste sources typically contain a mixture of PP and PE, with trace components of <50% by weight.

[0006] The better the quality, i.e., the purer, the more expensive the material. Furthermore, recycled polyolefin materials are often cross-contaminated with non-polyolefin materials such as polyethylene terephthalate, polyamide, polystyrene, or non-polymeric substances such as wood, paper, glass, or aluminum.

[0007] Additionally, materials containing a high percentage of recycled polypropylene typically have properties much worse than virgin materials unless the amount of recycled polyolefin added to the final formulation is extremely low. For example, such materials often have poor odor and taste, low stiffness, low impact strength, and poor mechanical properties (e.g., brittleness) that do not meet customer demands. Summary of the Invention [Means for solving the problem]

[0008] The present invention is based on the observation that a specific combination of processing steps, in a given sequence, results in high purity recycled polyolefin grades with a good balance of mechanical and optical properties that are superior to those typically found in similar recycled polyolefin grades. Furthermore, the specific combination of steps means that the quality of the high purity recycled polyolefin grades is less dependent on the quality of the raw materials, which is known to vary widely depending on the source of the raw materials.

[0009] Thus, in a first aspect, the present invention provides a method for preparing a composition comprising, in a given order: a) providing a precursor mixed plastic recycling stream (A); Step b) sieving the precursor mixed plastic recycle stream (A) to create a sieved mixed plastic recycle stream (B) containing only articles with a longest dimension in the range of 30 to 400 mm; step c) of sorting the sieved mixed plastic recycle stream (B) with one or more optical sorters to produce a single-color sorted polyolefin recycle stream (C), wherein the sieved mixed plastic recycle stream (B) is sorted at least by color, and optionally by polyolefin type and / or article form; Step d) of reducing the size of the monochromatically separated polyolefin recycle stream (C) pieces to form a flake polyolefin recycle stream (D); Step e) of washing the flaked polyolefin recycle stream (D) with a first aqueous wash liquid (W1) without input of thermal energy to produce a first suspended polyolefin recycle stream (E); step f) removing at least a portion of said first aqueous wash liquid (W1), preferably substantially all of said first aqueous wash liquid (W1), from said first suspended polyolefin recycle stream (E) to obtain a first washed polyolefin recycle stream (F); g) washing the first washed polyolefin recycle stream (F) with a second aqueous wash liquid (W2) to produce a second suspended polyolefin recycle stream (G), wherein sufficient heat energy is introduced into the second suspended polyolefin recycle stream (G) to achieve a washing temperature in the range of 65-95°C; step h) removing said second aqueous wash liquid (W2) and any material not floating on the surface of said second aqueous wash liquid from said second suspended polyolefin recycle stream (G) to obtain a second washed polyolefin recycle stream (H); i) drying the second washed polyolefin recycle stream (H) to obtain a dried polyolefin recycle stream (I); step j) optionally separating the dried polyolefin recycle stream (I) into a light fraction and a heavy fraction polyolefin recycle stream (J); step k) further filtering the heavy fraction polyolefin recycle stream (J), or the dried polyolefin recycle stream (I) in the absence of step j), with one or more optical sorters that separate the one or more target polyolefins by removing any flakes containing materials other than the one or more target polyolefins, to obtain a purified polyolefin recycle stream (K); step l) of melt extruding and preferably pelletizing said optionally purified polyolefin recycle stream (K) to form an extruded, preferably pelletized recycled polyolefin product (L), wherein preferably an additive (Ad) is added in the molten state; Optionally, step m) of aerating said recycled polyolefin product (L) or said purified polyolefin recycle stream (K) in the absence of step l) to remove volatile organic compounds, thereby producing an aerated recycled polyolefin product (M), which is either an aerated extruded, preferably pelletized, recycled polyolefin product (M1) or an aerated recycled polyolefin flake (M2); wherein the purified polyolefin recycle stream (K) is first aerated to form the aerated recycled polyolefin flakes (M2) and then extruded, preferably by reversing the order of steps l) and m) so that the additive (Ad) is added in the molten state to form an extruded, preferably pelletized, aerated recycled polyolefin product (M3).

[0010] In yet another aspect, the present invention relates to an apparatus for mechanically recycling polyolefins for carrying out the method for mechanically recycling polyolefins according to any one of the preceding claims. DETAILED DESCRIPTION OF THE INVENTION

[0011] definition Post-consumer waste refers to objects that have completed at least their first use cycle (or life cycle), i.e., have already fulfilled their initial purpose, while post-industrial waste refers to manufacturing scrap that usually never reaches the consumer.

[0012] A recycle stream may include both articles to be recycled and fragments (such as flakes) of articles to be recycled. In the context of the present invention, the contents of a recycle stream are referred to as pieces, whether they are whole articles, fragments thereof, or flakes thereof. In some embodiments, the pieces may be flakes, while in other embodiments, the pieces may be larger objects that can be converted to flakes at a later stage.

[0013] In the context of this invention, a mixed plastics recycle stream may be any stream suitable for recycling in which polyolefins are present and the stream does not contain only a single polyolefin product, as is the case, for example, in certain post-industrial waste recycle streams where a single polyolefin-grade manufacturing waste product or a single polyolefin-containing article may be the only product present in the stream. Generally speaking, all polyolefin-containing post-consumer waste recycle streams will be mixed plastics recycle streams, as will many polyolefin-containing post-industrial waste recycle streams.

[0014] The term "article form" as used herein refers to the shape and form of the articles present in the polyolefin recycling stream. Such articles may be present in the form of films, bags, and pouches, among others, which are considered flexible articles, or in the form of molded articles such as food containers, skin care product containers, and plastic bottles, among others, which are considered rigid articles. Commercially available optical sorters, such as Tomra Autosort, RTT Steinert Unisort, and Redwave Pellenc, can separate so-called rigid articles from so-called flexible articles by utilizing aerodynamic properties (i.e., a gas stream is usually applied to the stream, and rigid articles fall in a different arc than flexible articles), and can convert the stream containing such articles into so-called rigid and flexible streams.

[0015] According to the present invention, a color-sorted polyolefin stream (C) is obtained as an intermediate product as a result of the sorting method in which polyolefin-containing articles are sorted at least by their color. Those skilled in the art will recognize that a significant amount of polyolefin-containing articles in any given mixed-color recycle stream will be transparent, i.e., colorless. For purposes of the present invention, any transparent, i.e., colorless, polyolefin-containing articles are considered a separate color classification, resulting in a color-sorted polyolefin stream (C) whose "color" is colorless (i.e., transparent). In some embodiments, this colorless polyolefin recycle stream is subjected to subsequent steps in the method to obtain a colorless recycled product; or, in other embodiments, the colorless polyolefin recycle stream is mixed with a non-colorless, colorless recycle stream (e.g., a white polyolefin recycle stream), and the combined stream is considered a non-colorless, colorless recycle stream (i.e., a mixture of the colorless and white streams is then considered a white stream). While not wishing to be bound by theory, it is believed that the addition of colorless polyolefins to a non-colorless polyolefin recycle stream does not significantly affect the final color of the recycled product.

[0016] According to the present invention, it is important that a monochromatically sorted recycle stream is subjected to subsequent processing steps d) to m). In the context of the present invention, the term "monochromatic" should be interpreted as meaning substantially the same color; i.e., a polyolefin stream containing various shades of red would be classified as a monochromatic stream, while a polyolefin stream containing red and yellow pieces would not. The accuracy of monochromatic selection depends on the technology used for color sorting and is therefore limited by available technology. Since the impression of color on the human eye cannot be strictly defined by wavelength, the CIELAB color scale is the most appropriate descriptor, given that the same color can be obtained with a single wavelength of light or a combination of different wavelengths. Particularly preferably, the same color means ΔE<50, preferably ΔE<40, more preferably ΔE<30, and most preferably ΔE<10. ΔE is defined by the following formula:

number

[0017] Furthermore, those skilled in the art will recognize that state-of-the-art sorting methods, including automated sorting machines of the type discussed below, do not provide perfect sorting, which means that any phrases such as "the stream contains only a single color" or "the stream contains only a single polyolefin type" are to be interpreted broadly; a stream so described will contain substantially only the color or polyolefin type described, but will not be 100% pure due to technical limitations of the sorting step.

[0018] However, those skilled in the art will recognize that sorting by optical sorters, i.e., automatic sorters of the type discussed below, will result in a much more accurate sorting than so-called "rough sorting," in which articles are separated by simple visual inspection and assigned to color fractions corresponding to their predominant color, the result of such "rough sorting" would not constitute a monochromatic polyolefin stream within the meaning of the present invention.

[0019] Those skilled in the art will recognize that while pH values ​​greater than 14.0 and less than 0.0 are theoretically possible, it is very difficult to measure such pH values ​​using a conventional pH probe. Thus, in the context of the present invention, an aqueous solution having an effective pH greater than 14.0 will be considered to have a pH of 14.0, and an aqueous solution having an effective pH less than 0.0 will be considered to have a pH of 0.0.

[0020] In the context of the present invention, the term "washing" is used to refer to the addition of a solvent, usually water, used to remove foreign matter or residual liquid from the surface of the polyolefin. This can be accomplished in a very short time, less than 5 minutes, often less than 1 minute, in contrast to a "washing" step, which usually requires longer time and agitation to remove foreign matter from the surface of the polyolefin and potentially extract volatile organic compounds from the polyolefin.

[0021] Where the term "comprising" is used in the present specification and claims, it does not exclude other, unspecified elements of primary or secondary functional importance. For the purposes of the present invention, the term "consisting of" is considered to be a preferred embodiment of the term "comprising". Hereinafter, if a group is defined to include at least a certain number of elements, this is also understood to disclose a group that preferably consists only of these elements.

[0022] Where an indefinite or definite article is used when referring to a singular noun e.g. "a", "an" or "the", this also includes the plural of that noun, unless something else is stated.

[0023] The present invention comprises, in a given order: a) providing a precursor mixed plastic recycling stream (A); Step b) sieving the precursor mixed plastic recycle stream (A) to create a sieved mixed plastic recycle stream (B) containing only articles with a longest dimension in the range of 30-400 mm; step c) of sorting the sieved mixed plastic recycle stream (B) with one or more optical sorters to produce a single-color sorted polyolefin recycle stream (C), wherein the sieved mixed plastic recycle stream (B) is sorted at least by color, and optionally also by polyolefin type and / or article form; Step d) reducing the size of the pieces of the monochromatically sorted polyolefin recycle stream (C) to form a flake polyolefin recycle stream (D); Step e) of washing the flake polyolefin recycle stream (D) with a first aqueous wash liquid (W1) without input of thermal energy to produce a first suspension polyolefin recycle stream (E); step f) removing at least a portion of the first aqueous wash liquid (W1), preferably substantially all of the first aqueous wash liquid (W1), from the first suspended polyolefin recycle stream (E) to obtain a first washed polyolefin recycle stream (F); g) washing the first washed polyolefin recycle stream (F) with a second aqueous wash liquid (W2) to produce a second suspended polyolefin recycle stream (G), wherein sufficient heat energy is introduced into the second suspended polyolefin recycle stream (G) such that the temperature during washing is in the range of 65-95°C; step h) removing the second aqueous wash liquid (W2) and any material that does not float on the surface of the second aqueous wash liquid from the second suspended polyolefin recycle stream (G) to obtain a second washed polyolefin recycle stream (H); i) drying the second washed polyolefin recycle stream (H) to obtain a dried polyolefin recycle stream (I); step j) optionally separating the dried polyolefin recycle stream (I) into a light fraction and a heavy fraction polyolefin recycle stream (J); step k) further separating the heavy fraction polyolefin recycle stream (J), or the dried polyolefin recycle stream (I) in the absence of step j), with one or more optical sorters that separate the one or more target polyolefins by removing any flakes containing materials other than the one or more target polyolefins, to obtain a purified polyolefin recycle stream (K); step l) of melt extruding and preferably pelletizing the optionally purified polyolefin recycle stream (K) to form an extruded, preferably pelletized, recycled polyolefin product (L), wherein preferably an additive (Ad) is added in the molten state; Optionally, step m) of aerating (aeration) the recycled polyolefin product (L) or the purified polyolefin recycle stream (K) in the absence of step l) to remove volatile organic compounds, thereby producing an aerated recycled polyolefin product (M), which is either an aerated extruded, preferably pelletized, recycled polyolefin product (M1) or an aerated recycled polyolefin flake (M2); wherein the purified polyolefin recycle stream (K) is first aerated to form aerated recycled polyolefin flakes (M2) which are then extruded, preferably by reversing the order of steps l) and m) so that the additive (Ad) is added in the molten state to form an extruded, preferably pelletized, aerated recycled polyolefin product (M3).

[0024] Alternatively, the mechanical recycling method for polyolefins may comprise, in a given order: a) providing a precursor mixed plastic recycling stream (A); Step b) sieving the precursor mixed plastic recycle stream (A) to create a sieved mixed plastic recycle stream (B) containing only articles with a longest dimension in the range of 30-400 mm; step c) of sorting the sieved mixed plastic recycle stream (B) with one or more optical sorters to produce a single-color sorted polyolefin recycle stream (C), wherein the sieved mixed plastic recycle stream (B) is sorted at least by color, and optionally also by polyolefin type and / or article form; Step d) reducing the size of the pieces of the monochromatically sorted polyolefin recycle stream (C) to form a flake polyolefin recycle stream (D); Step e) of washing the flake polyolefin recycle stream (D) with a first aqueous wash liquid (W1) without input of thermal energy to produce a first suspension polyolefin recycle stream (E); step f) removing the first aqueous wash liquid (W1) from the first suspended polyolefin recycle stream (E) to obtain a first washed polyolefin recycle stream (F); g) washing the first washed polyolefin recycle stream (F) with a second aqueous wash liquid (W2) to produce a second suspended polyolefin recycle stream (G), wherein sufficient heat energy is input into the system to raise the temperature during washing to a range of 65-95°C; step h) removing the second aqueous wash liquid (W2) and any material that does not float on the surface of the second aqueous wash liquid from the second suspended polyolefin recycle stream (G) to obtain a second washed polyolefin recycle stream (H); i) drying the second washed polyolefin recycle stream (H) to obtain a dried polyolefin recycle stream (I); step j) optionally separating the dried polyolefin recycle stream (I) into a light fraction and a heavy fraction polyolefin recycle stream (J); step k) further separating the heavy fraction polyolefin recycle stream (J) or the dried polyolefin recycle stream (I) in the absence of step j) through one or more optical sorters that remove any flakes containing material other than the polyolefin of interest to obtain a purified polyolefin recycle stream (K); step l) of melt extruding and preferably pelletizing the optionally purified polyolefin recycle stream (K) to form an extruded, preferably pelletized, recycled polyolefin product (L), wherein preferably an additive (Ad) is added in the molten state; Optionally, step m) of aerating the recycled polyolefin product (L) or the purified polyolefin recycle stream (K) in the absence of step l) to remove volatile organic compounds to produce an aerated recycled polyolefin product (M), which is either an aerated extruded, preferably pelletized, recycled polyolefin product (M1) or an aerated recycled polyolefin flake (M2); wherein the purified polyolefin recycle stream (K) is first aerated to form aerated recycled polyolefin flake (M2) and then extruded, preferably by reversing the order of steps l) and m) so that the additive (Ad) is added in the molten state to form an extruded, preferably pelletized, aerated recycled polyolefin product (M3).

[0025] In one embodiment, steps i) and subsequent steps are, in the given order: i) drying the second washed polyolefin recycle stream (H) to obtain a dried polyolefin recycle stream (I); k) further sorting the dried polyolefin recycle stream (I) with one or more optical sorters that separate the one or more target polyolefins by removing any flakes containing materials other than the one or more target polyolefins to obtain a purified polyolefin recycle stream (K); Includes.

[0026] In another embodiment, steps i) and subsequent steps are, in the given order: i) drying the second washed polyolefin recycle stream (H) to obtain a dried polyolefin recycle stream (I); j) separating the dried polyolefin recycle stream (I) into a light fraction and a heavy fraction polyolefin recycle stream (J); k) further separating the heavy fraction polyolefin recycle stream (J) with one or more optical sorters that separate the one or more target polyolefins by removing any flakes containing materials other than the one or more target polyolefins to obtain a purified polyolefin recycle stream (K); Includes.

[0027] In yet another embodiment, steps i) and subsequent steps are, in the given order: j) drying the second washed polyolefin recycle stream (H) to obtain a dried polyolefin recycle stream (I); k) further sorting the dried polyolefin recycle stream (I) with one or more optical sorters that separate the one or more target polyolefins by removing any flakes containing materials other than the one or more target polyolefins to obtain a purified polyolefin recycle stream (K); step l) of melt extruding and preferably pelletizing the purified polyolefin recycle stream (K) to form an extruded, preferably pelletized, recycled polyolefin product (L), wherein preferably an additive (Ad) is added in the molten state; Includes.

[0028] In yet another embodiment, steps i) and subsequent steps are, in the given order: i) drying the second washed polyolefin recycle stream (H) to obtain a dried polyolefin recycle stream (I); j) separating the dried polyolefin recycle stream (I) into a light fraction and a heavy fraction polyolefin recycle stream (J); k) further separating the heavy fraction polyolefin recycle stream (J) with one or more optical sorters that separate the one or more target polyolefins by removing any flakes containing materials other than the one or more target polyolefins to obtain a purified polyolefin recycle stream (K); step l) of melt extruding and preferably pelletizing the purified polyolefin recycle stream (K) to form an extruded, preferably pelletized, recycled polyolefin product (L), wherein preferably an additive (Ad) is added in the molten state; Includes.

[0029] In yet another embodiment, steps i) and subsequent steps are, in the given order: i) drying the second washed polyolefin recycle stream (H) to obtain a dried polyolefin recycle stream (I); k) further sorting the dried polyolefin recycle stream (I) with one or more optical sorters that separate the one or more target polyolefins by removing any flakes containing materials other than the one or more target polyolefins to obtain a purified polyolefin recycle stream (K); a step m) of aerating the purified polyolefin recycle stream (K) to remove volatile organic compounds, thereby producing aerated recycled polyolefin flakes (M2); Includes.

[0030] In another embodiment, steps i) and subsequent steps are, in the given order: i) drying the second washed polyolefin recycle stream (H) to obtain a dried polyolefin recycle stream (I); j) separating the dried polyolefin recycle stream (I) into a light fraction and a heavy fraction polyolefin recycle stream (J); k) further separating the heavy fraction polyolefin recycle stream (J) with one or more optical sorters that separate the one or more target polyolefins by removing any flakes containing materials other than the one or more target polyolefins to obtain a purified polyolefin recycle stream (K); a step m) of aerating the purified polyolefin recycle stream (K) to remove volatile organic compounds, thereby producing aerated recycled polyolefin flakes (M2); Includes.

[0031] In yet another embodiment, steps i) and subsequent steps are, in the given order: i) drying the second washed polyolefin recycle stream (H) to obtain a dried polyolefin recycle stream (I); k) further sorting the dried polyolefin recycle stream (I) with one or more optical sorters that separate the one or more target polyolefins by removing any flakes containing materials other than the one or more target polyolefins to obtain a purified polyolefin recycle stream (K); step l) of melt extruding and preferably pelletizing the purified polyolefin recycle stream (K) to form an extruded, preferably pelletized, recycled polyolefin product (L), wherein an additive (Ad) is preferably added in the molten state; a step m) of aerating the recycled polyolefin product (L) to remove volatile organic compounds, thereby producing an aerated, extruded, preferably pelletized, recycled polyolefin product (M1); Includes.

[0032] In yet another embodiment, steps i) and subsequent steps are, in the given order: i) drying the second washed polyolefin recycle stream (H) to obtain a dried polyolefin recycle stream (I); j) separating the dried polyolefin recycle stream (I) into a light fraction and a heavy fraction polyolefin recycle stream (J); k) further separating the heavy fraction polyolefin recycle stream (J) with one or more optical sorters that separate the one or more target polyolefins by removing any flakes containing materials other than the one or more target polyolefins to obtain a purified polyolefin recycle stream (K); step l) of melt extruding and preferably pelletizing the purified polyolefin recycle stream (K) to form an extruded, preferably pelletized, recycled polyolefin product (L), wherein an additive (Ad) is preferably added in the molten state; a step m) of aerating the recycled polyolefin product (L) to remove volatile organic compounds, thereby producing an aerated, extruded, preferably pelletized, recycled polyolefin product (M1); Includes.

[0033] In yet another embodiment, steps i) and subsequent steps are, in the given order: i) drying the second washed polyolefin recycle stream (H) to obtain a dried polyolefin recycle stream (I); k) further sorting the dried polyolefin recycle stream (I) with one or more optical sorters that separate the one or more target polyolefins by removing any flakes containing materials other than the one or more target polyolefins to obtain a purified polyolefin recycle stream (K); a step m) of aerating the purified polyolefin recycle stream (K) to remove volatile organic compounds, thereby producing aerated recycled polyolefin flakes (M2); step l) of melt-extruding and preferably pelletizing the aerated recycled polyolefin flakes (M2) to form an extruded, preferably pelletized, aerated recycled polyolefin product (M3), wherein preferably an additive (Ad) is added in the molten state; Includes.

[0034] In a final embodiment, steps i) and subsequent steps are performed in the given order: i) drying the second washed polyolefin recycle stream (H) to obtain a dried polyolefin recycle stream (I); j) separating the dried polyolefin recycle stream (I) into a light fraction and a heavy fraction polyolefin recycle stream (J); k) further separating the heavy fraction polyolefin recycle stream (J) with one or more optical sorters that separate the one or more target polyolefins by removing any flakes containing materials other than the one or more target polyolefins to obtain a purified polyolefin recycle stream (K); a step m) of aerating the purified polyolefin recycle stream (K) to remove volatile organic compounds, thereby producing aerated recycled polyolefin flakes (M2); step l) of melt-extruding and preferably pelletizing the aerated recycled polyolefin flakes (M2) to form an extruded, preferably pelletized, aerated recycled polyolefin product (M3), wherein preferably an additive (Ad) is added in the molten state; Includes.

[0035] Without wishing to be bound by theory, it is believed that performing step m) before step l) is advantageous because the improved surface area to volume ratio of the polyolefin flakes means that more volatile organic compounds can be removed, whereas performing step l) before step m) is advantageous because extrusion may generate new volatile organic compounds via decomposition of the polyolefin or contaminants (e.g., PVC or PET) or may migrate volatile organic compounds not in close proximity to the surface of the flakes to the surface of the extruded product, increasing odor. Which embodiment is preferred will vary from process to process and will need to be optimized accordingly.

[0036] Step a) involves providing a precursor mixed plastics recycle stream (A).

[0037] This precursor mixed plastics recycle stream (A) may be derived from post-consumer waste, post-industrial waste, or a combination thereof.

[0038] Preferably, the precursor mixed plastics recycle stream (A) is derived from post-consumer waste.

[0039] As one skilled in the art will appreciate, providing such a precursor mixed plastics recycle stream may involve collecting suitable polyolefin-containing materials from post-consumer sources (e.g., curbside recycling bins) or post-industrial sources, or pre-collected mixed plastics recycle streams may be purchased from any number of commercial recycling companies.

[0040] The form of the precursor mixed plastic recycling stream (A) is not critical, but it is desired that the items present in the precursor mixed plastic recycling stream (A) do not stick together in steps b) to m). A common form in which commercially available mixed plastic recycling streams are obtained is in the form of bales. If the precursor mixed plastic recycling stream (A) is provided in the form of bales, the bales must be broken up before the precursor mixed plastic recycling stream (A) undergoes sieving in step b). Depending on the method used to package the bales, it may be necessary to remove any wire used to tie the bales together (de-wiring the bales) and / or empty the bales from containers such as plastic bags or packaging materials (opening the bags / bales).

[0041] Additionally, it may be necessary to store the intermediate product (i.e., intermediate recycle stream) of the polyolefin mechanical recycling process (such as the monochromated polyolefin recycle stream (C)), in which case this intermediate product may be formed into bales. Any bales thus formed should be disassembled, preferably using one of the appropriate methods listed above, before the intermediate product undergoes the next step in the process.

[0042] Those skilled in the art will understand that within the scope of the present invention are methods that not only involve performing the essential steps of the present polyolefin mechanical recycling method in the given order, but also involve removing the intermediate product in a bale or other form for a period of time and reintroducing the stored intermediate product into the polyolefin mechanical recycling method at the location from which it was removed.

[0043] Step b) involves sieving the precursor mixed plastic recycle stream (A) to create a sieved mixed plastic recycle stream (B) containing only articles with a longest dimension in the range of 30-400 mm.

[0044] Those skilled in the art will recognize multiple ways in which the sieving in step b) can be achieved, and therefore, this sieving step is not particularly limited. Preferably, however, the sieving in step b) is achieved by using a sieve with a sieve diameter of 30 mm and a sieve with a sieve diameter of 400 mm to separate the precursor mixed recycle stream into three streams: a small item stream having a longest dimension of less than 30 mm, an oversized item stream having a longest dimension of more than 400 mm, and a sieved mixed plastic recycle stream (B). The small item stream and the oversized item stream may be discarded or transferred for use in other mechanical polyolefin recycling methods.

[0045] Step c) involves sorting the sieved mixed plastic recycle stream (B) with one or more optical sorters to produce a single color sorted polyolefin recycle stream (C), where the sieved mixed plastic recycle stream (B) is sorted at least by color, and optionally also by polyolefin type and / or article form.

[0046] The articles separated from the monochromatically sorted polyolefin recycle stream (C) may be discarded or transferred to a further iteration of step c) directed to another monochromatically sorted polyolefin recycle stream.

[0047] In the process of the present invention, it is essential that the recycle stream entering from step d) onwards is a monochromatically separated polyolefin recycle stream (C).

[0048] In the broadest sense, any optical sorter can be used to achieve the sorting of step c). In the context of the present invention, the term "optical sorter" refers to a sorting unit that uses any form of electromagnetic radiation (visible or invisible) to distinguish pieces of the sieved mixed plastic recycling stream (B).

[0049] Preferably, the optical sorter in step c) sorts by a method selected from the group consisting of a camera system (operating in the visible range of the electromagnetic spectrum), visible reflectance spectroscopy, near-infrared spectroscopy, mid-infrared spectroscopy, high-speed laser spectroscopy, Raman spectroscopy, and Fourier transform infrared (FT-IR) spectroscopy.

[0050] Suitable methods for sorting recycling streams by color include camera systems (operating in the visible range of the electromagnetic spectrum) and visible reflectance spectroscopy.

[0051] Suitable methods for sorting recycle streams by polyolefin type include near-infrared spectroscopy, mid-infrared spectroscopy, high-speed laser spectroscopy, Raman spectroscopy, and Fourier transform infrared (FT-IR) spectroscopy, with near-infrared spectroscopy being particularly preferred.

[0052] Suitable methods for sorting recycling streams by type of item include camera systems (operating in the visible range of the electromagnetic spectrum).

[0053] Preferably, the sorting in step c) is by color and polyolefin type, meaning that the mono-color sorted polyolefin recycle stream (C) is mono-colored and all articles contain a single polyolefin.

[0054] In some embodiments, a single sensor type (e.g., a near-infrared sensor or a camera system operating in the visible range of the electromagnetic spectrum) can be used to distinguish between multiple characteristics (e.g., color and polyolefin type, or color and article morphology). Additionally, many near-infrared sensor units may include a visible reflectance unit or be configured to measure both the near-infrared and visible regions of the electromagnetic spectrum, meaning that a single sensor unit may use multiple detection methods.

[0055] To achieve the sorting in step c), multiple detection methods and / or multiple sensors can be used.

[0056] More preferably, the sorting in step c) is carried out by color, type of polyolefin, and type of article, which means that the monochromatically sorted polyolefin recycle stream (C) is monochromatic, all articles contain a single polyolefin, and the stream contains only rigid or flexible articles.

[0057] Although the process of the present invention is suitable for isolating any desired polyolefin from a mixed polyolefin recycle stream, isolation of polyethylene or polypropylene is particularly desirable because these are likely to be the major polyolefin components of any mixed polyolefin recycle stream, and the isolated polyethylene or isolated polypropylene can be fed into a pure recycled polyolefin stream or extruded and pelletized to obtain pellets of the desired polyolefin, i.e., polyethylene or polypropylene.

[0058] Particularly preferably, the monochromatically separated polyolefin recycle stream (C) is either a monochromatically separated polyethylene recycle stream or a monochromatically separated polypropylene recycle stream.

[0059] The sorting in step c) can be achieved through a simple sorting algorithm where the optical sensor is programmed to evaluate which pieces should be selected or rejected based on a simple binary decision, or more complex AI-based systems can be used to achieve more accurate sorting, especially when sorting by item morphology.

[0060] Without wishing to be bound by theory, the inventors believe that providing a color-sorted polyolefin recycle stream in step c) is essential to obtaining a recycled product with improved properties. As expected, not only is the recycled product color-sorted, but the presence of the crucial sorting step c) prior to any of the processing steps d)–m) also allows for a purer recycled product. For example, color sorting in step c) may select only white polyolefin pieces, while all other colors, including colorless pieces, are removed in this stage. Transparent pieces are often made from PET plastic bottles. Therefore, it is expected that the combined transparent pieces will have a higher PET content than pieces of other colors, such as white pieces. PET is prone to decomposition, for example, during the high-temperature washing in step g), producing acetaldehyde, among other small organic molecules. These small organic molecules ultimately have a negative impact on the odor of the recycled product. Reducing the PET content through color sorting in this stage can reduce this problem.

[0061] Furthermore, different packaging in different countries or regions may have different typical colors, making it more likely that, for example, green pieces contain certain non-polyolefins or undesired polyolefins. The benefits of color sorting in step c) vary depending on which country or region the precursor mixed plastics recycling stream comes from.

[0062] Although non-polyolefins and undesired polyolefin flakes can be removed in step k), any sorting method has limited efficiency, which means that the purer the flakes fed into such a method, the purer the product from such a method. Considering the difficulty in obtaining a pure product from prior art methods, even seemingly small improvements in the purity of the recycled product can be very valuable commercially.

[0063] Furthermore, removing such flakes after washing steps e) and g) does not avoid the problem of cross-contamination between flakes during steps d) to j).

[0064] Furthermore, the presence of the sorting step c) prior to the mechanical recycling steps d)-m) means that the polyolefin mechanical recycling method of the present invention allows operators to obtain a high quality recycled product, regardless of the quality of the raw material, which is well known to vary greatly in terms of polyolefin content and foreign matter contamination and is highly dependent on the source of the raw material (i.e., the source of the precursor mixed plastics recycle stream (A)).

[0065] Step d) involves reducing the size of the pieces of the monochromatically sorted polyolefin recycle stream (C) to form a flake polyolefin recycle stream (D).

[0066] The size reduction in step d) may be carried out by any method known to those skilled in the art. One suitable method comprises grinding the monochromatically sorted polyolefin recycle stream (C). Another method comprises shredding the monochromatically sorted polyolefin recycle stream (C). Particularly preferably, the size reduction in step d) is a shredding step.

[0067] The shredding in step d) may be a wet shredding process or a dry shredding process. Preferably, the shredding in step d) is a wet shredding process in which the sorted polyolefin recycle stream (C) is first contacted with an aqueous solution (W0) to provide a sorted suspended polyolefin recycle stream which is then shredded.

[0068] In other words, the shredding in step d) is preferably a wet shredding process in which the sorted polyolefin recycle stream (C) is first contacted with an aqueous solution (W0) and the resulting suspension is shredded.

[0069] The aqueous solution (W0) is not particularly limited, but the pH of the aqueous solution (W0) is preferably in the range of 8.0 to 14.0, more preferably in the range of 10.0 to 14.0, and most preferably in the range of 12.0 to 14.0.

[0070] More preferably, the aqueous solution (W0) is at least a part of the recycled aqueous cleaning liquid removed in step h).

[0071] In other words, the aqueous solution (W0) is preferably the recycled aqueous washing liquid previously used in step h).

[0072] If the shredding in step d) is a wet shredding process, the resulting flaked polyolefin recycle stream (D) is preferably mechanically dried before step e) begins. Suitable forms of mechanical drying include centrifugal drying and dewatering presses (filters or screw presses), both of which are capable of separating liquids from solids.

[0073] Recycling the aqueous wash solution used in step h) improves the economics of the process, as only one aqueous wash solution needs to be prepared for use throughout the process. Furthermore, the aqueous wash solution used in step h) is an alkaline solution in nature, which aids in the removal of contaminants in either step d) or step e). It is important to use the cleanest wash solution (i.e., the wash solution with the least contaminants) in the final wash step so that the resulting washed polyolefin stream is as clean as possible. Finally, using a single aqueous wash solution multiple times simplifies waste stream treatment, avoiding the need to treat multiple different waste streams containing different chemicals.

[0074] Step e) involves washing the flaked polyolefin recycle stream (D) with a first aqueous wash liquid (W1) without input of thermal energy to produce a first suspended polyolefin recycle stream (E).

[0075] Those skilled in the art will recognize that cleaning steps known in the art may be heated to achieve high temperature cleaning or may be carried out at ambient conditions to achieve low temperature cleaning, and in the present method, step e) represents such low temperature cleaning.

[0076] Those skilled in the art will also recognize that depending on the selection of the first aqueous cleaning liquid (W1), the temperature in step d) may or may not actually correspond to ambient conditions, since the first aqueous cleaning liquid (W1) may be hotter than ambient conditions, for example, due to its use in a previous high-temperature cleaning. Even if the temperature of the first aqueous cleaning liquid (W1) is higher than ambient conditions, it is expected to be significantly lower than the temperature normally required for high-temperature cleaning. It is important for the definition of step e) that no additional thermal energy is consumed to increase the temperature of the first aqueous cleaning liquid (W1) during the cleaning of step e).

[0077] However, the temperature of the first aqueous washing liquid (W1) in step e) is preferably below 70°C, more preferably below 65°C, most preferably below 60°C.

[0078] The selection of the first aqueous washing liquid (W1) is not particularly limited, but the pH of the first aqueous washing liquid (W1) is preferably in the range of 8.0 to 14.0, more preferably in the range of 10.0 to 14.0, and most preferably in the range of 12.0 to 14.0.

[0079] The first aqueous cleaning liquid (W1) may contain the detergent in an amount ranging from 0.1% to 1.0% by weight, based on the total weight of the first aqueous cleaning liquid (W1).

[0080] The detergent may be a commercially available detergent mixture or may be composed in any manner known to those skilled in the art. Suitable detergents include TUBIWASH SKP, TUBIWASH GFN, TUBIWASH EYE, and TUBIWASH TOP available from CHT, KRONES colclean AD 1004, KRONES colclean AD 1002, and KRONES colclean AD 1008 available from KIC KRONES, and P3-stabilon WT and P3 stabilon AL available from ECOLAB Ltd.

[0081] More preferably, the first aqueous washing liquid (W1) is at least a part of the recycled aqueous washing liquid removed in step h).

[0082] In other words, the first aqueous washing liquid (W1) is preferably the recycled aqueous washing liquid previously used in step h).

[0083] The advantages of reusing the recycled aqueous cleaning solution from step h) as the first aqueous cleaning solution are similar to those described above for the aqueous solution (W0).

[0084] The washing in step e) is a cleaning step as opposed to a rinsing step as defined herein and therefore typically lasts for 5 minutes or more, for example 5 minutes to 4 hours.

[0085] The washing in step e) preferably lasts for 5 minutes to 2 hours, more preferably for 5 minutes to 1 hour, most preferably for 5 minutes to 30 minutes.

[0086] More preferably, the combination of the first aqueous wash solution (W1) and the flake polyolefin recycle stream (D) in step g) is agitated by mechanical mixing, ultrasonic treatment, mechanical grinding, or a pump around loop, and preferably the combination of the first aqueous wash solution (W1) and the flake polyolefin recycle stream (D) in step g) is agitated by ultrasonic treatment, which exposes the flakes in the recycle stream to fresh washing solution and prevents the process from being hindered by the accumulation of contaminants in the immediate vicinity of the flakes.

[0087] Those skilled in the art will recognize that the individual methods provided above can be combined to improve agitation, for example, by combining mechanical mixing with sonication.

[0088] Step f) involves removing at least a portion of the first aqueous wash liquid (W1), preferably substantially all of the first aqueous wash liquid (W1), from the first suspended polyolefin recycle stream (E) to obtain a first washed polyolefin recycle stream (F).

[0089] In other words, step f) involves removing the first aqueous wash liquid (W1) from the first suspended polyolefin recycle stream (E) to obtain a first washed polyolefin recycle stream (F).

[0090] Those skilled in the art will appreciate that although small amounts of foreign matter suspended or dissolved in the first suspended polyolefin recycle stream (E) are removed in the first aqueous wash liquid (W1), step f) does not involve targeted removal of foreign matter, for example by the use of so-called sink-float separation, in this case (density 1.00 g / cm 3 It will be appreciated that any foreign matter that does not float to the surface of the solution (considering that less than 1000g of polyolefin is expected to float) will be removed by the solution.

[0091] After removing at least a portion of the first aqueous wash liquid (W1), the first washed polyolefin recycle stream (F) may be optionally rinsed with water to remove any traces of the first aqueous wash liquid (W1) remaining on the surfaces of the flakes of the first washed polyolefin recycle stream.

[0092] Regardless of whether it is washed or not, the first washed polyolefin recycle stream (F) may be dried prior to step g), however, it is preferred not to dry the first washed polyolefin recycle stream (F) prior to step g), as this contributes to a decrease in process efficiency in terms of energy efficiency and step efficiency and does not contribute significantly to the benefits of the present invention.

[0093] Step g) involves washing the first washed polyolefin recycle stream (F) with a second aqueous wash liquid (W2) to produce a second suspended polyolefin recycle stream (G), wherein sufficient heat energy is introduced into the second suspended polyolefin recycle stream (G) such that the temperature during washing is in the range of 65-95°C.

[0094] In other words, step g) involves washing the first washed polyolefin recycle stream (F) with a second aqueous wash liquid (W2) to produce a second suspended polyolefin recycle stream (G), wherein sufficient heat energy is input into the system to raise the temperature during washing to a range of 65-95°C.

[0095] As previously mentioned, those skilled in the art will recognize that cleaning steps known in the art may be heated to achieve high temperature cleaning or may be performed at ambient conditions to achieve low temperature cleaning. The cleaning step g) is a high temperature cleaning, in contrast to the cleaning step e), in which thermal energy is introduced to achieve a temperature of 65-95°C during cleaning.

[0096] The temperature in step g) is in the range of 65 to 95°C, more preferably in the range of 70 to 95°C, and most preferably in the range of 75 to 95°C.

[0097] Preferably, the second aqueous washing liquid (W2) is an alkaline aqueous washing liquid.

[0098] Preferably, the pH of the alkaline aqueous cleaning liquid is in the range of 9.0 to 14.0, more preferably in the range of 11.0 to 14.0, and most preferably in the range of 12.0 to 14.0.

[0099] Preferably, the alkaline aqueous wash liquid is an aqueous solution of a base selected from the group consisting of calcium hydroxide, potassium hydroxide, magnesium hydroxide, lithium hydroxide, sodium bicarbonate, sodium hydroxide and mixtures thereof. Most preferably, the second aqueous wash liquid (W2) is an aqueous solution of sodium hydroxide.

[0100] The amount of base in the alkaline aqueous solution is preferably in the range of 0.05 to 10% by weight, more preferably in the range of 0.10 to 7% by weight, and most preferably in the range of 0.50 to 5% by weight, based on the total weight of the alkaline aqueous solution.

[0101] In a particularly preferred embodiment, the second aqueous cleaning liquid (W2) is a sodium hydroxide solution having a sodium hydroxide concentration in the range of 0.50 to 5.0 wt. % relative to the total weight of the second aqueous cleaning liquid (W2).

[0102] The second aqueous cleaning liquid (W2) may contain the detergent in an amount ranging from 0.1% to 1.0% by weight, based on the total weight of the second aqueous cleaning liquid (W2).

[0103] The detergent may be a commercially available detergent mixture or may be composed in any manner known to those skilled in the art. Suitable detergents include TUBIWASH SKP, TUBIWASH GFN, TUBIWASH EYE, and TUBIWASH TOP available from CHT, KRONES colclean AD 1004, KRONES colclean AD 1002, and KRONES colclean AD 1008 available from KIC KRONES, and P3-stabilon WT and P3 stabilon AL available from ECOLAB Ltd.

[0104] The washing in step g) is a cleaning step as opposed to a rinsing step as defined herein and therefore typically lasts for 5 minutes or more, for example 5 minutes to 4 hours.

[0105] The washing in step g) preferably lasts from 5 minutes to 2 hours, more preferably from 5 minutes to 1 hour, most preferably from 10 minutes to 45 minutes.

[0106] More preferably, the combination of the second aqueous wash liquid (W2) and the first washed polyolefin recycle stream (F) in step g) is agitated by mechanical mixing, sonication, mechanical grinding, or a pump-around loop, and preferably the combination of the second aqueous wash liquid (W2) and the first washed polyolefin recycle stream (F) in step g) is agitated by sonication. This agitation exposes the flakes in the recycle stream to fresh washing solution, thereby preventing the process from being hindered by the accumulation of contaminants in the immediate vicinity of the flakes.

[0107] Those skilled in the art will recognize that the individual methods provided above can be combined to improve agitation, for example, by combining mechanical mixing with sonication.

[0108] Step h) involves removing the second aqueous wash liquid (W2) and any material that does not float on the surface of the second aqueous wash liquid from the second suspended polyolefin recycle stream (G) to obtain a second washed polyolefin recycle stream (H).

[0109] In contrast to step f), in which only small amounts of foreign matter suspended or dissolved in the cleaning liquid are removed, step h) involves a so-called sink-float separation, which removes all material that does not float on the surface of the cleaning liquid. Those skilled in the art will recognize that this is equivalent to a concentration of 1.00 g / cm 3 It will be appreciated that this is effective in removing any foreign matter having a density greater than 1.

[0110] Without wishing to be bound by theory, it is believed that including a float-sink separation step immediately after the high-temperature washing in step g) is very beneficial in removing as many foreign materials as possible. Subsequent steps in the method, such as aeration (step m) or drying (step i), can cause foreign materials removed from the polyolefin flakes to reattach to the polyolefin flakes. This can lead to contamination of the final recycled product or a reduction in yield if these polyolefin flakes are removed in subsequent steps, such as separation in step j) or sorting in step k). Therefore, it is important that this step be performed immediately after step g).

[0111] Particularly preferably, the aqueous washing liquid removed in step h) is recycled for use as the first aqueous washing liquid (W1) and, if present, as the aqueous solution (W0), as described above.

[0112] If the aqueous washing liquid removed in step h) is recycled as described above, preferably the foreign matter removed by the sink-float separation is filtered off before it is used as the first aqueous washing liquid (W1) and / or the aqueous solution (W0).

[0113] After the second aqueous wash liquid (W2) has been removed, the second washed polyolefin recycle stream (H) may optionally be rinsed with water to remove any traces of the second aqueous wash liquid (W2) remaining on the surfaces of the flakes of the second washed polyolefin recycle stream.

[0114] Step i) involves drying the second washed polyolefin recycle stream (H) to obtain a dried polyolefin recycle stream (I).

[0115] The drying in step i) can be achieved by thermal drying or by a combination of mechanical and thermal drying. Suitable forms of mechanical drying include centrifugal drying and dewatering presses (filters or screw presses), both of which are capable of separating liquids from solids.

[0116] Step j) involves separating the dried polyolefin recycle stream (I), if present, into a light fraction and a heavy fraction polyolefin recycle stream (J).

[0117] The light fraction typically contains labels and other non-polyolefin materials, while polyolefin flakes are sorted into the heavy fraction polyolefin recycle stream (J).

[0118] The separation in step j) can be carried out by any known dry state density separation technique known in the art, suitable techniques include air classification, air sieving, zigzag cascade or air separation.

[0119] As will be understood by those skilled in the art, separation into light and heavy fractions by such methods is influenced not only by the density of the flakes, but more importantly by the aerodynamic properties of the flakes (typically influenced by the surface area to weight ratio). Thus, flat labels are separated from the bulkier polyolefin flakes. The terms "light fraction" and "heavy fraction" are commonly used in the art and do not strictly refer to a classification by density. The meaning of these terms in the present invention is consistent with the terms commonly understood in the art.

[0120] Between steps j) and k), there may be an additional step of removing any pieces (so-called chips) whose longest dimension is less than 2 mm. Any method known to those skilled in the art may be used, for example using a screen or sieve.

[0121] Step k) involves further sorting the heavy fraction polyolefin recycle stream (J), or the dried polyolefin recycle stream (I) in the absence of step j), with one or more optical sorters that separate the one or more target polyolefins by removing any flakes containing materials other than the one or more target polyolefins to obtain a purified polyolefin recycle stream (K).

[0122] In step k), at least a first optical sorter is used to remove flakes containing one or more target non-polyolefin materials, the selection criteria for this optical sorter being such that if any material other than one or more target non-polyolefin materials is present in a given flake, this flake will be separated from the stream to obtain a purified polyolefin recycle stream.

[0123] If one or more optical sorters separate two or more polyolefins of interest, the resulting purified polyolefin recycle stream (K) may be a purified mixed polyolefin recycle stream, but preferably these polyolefins of interest are separated into individual purified polyolefin recycle streams (K), each containing only a single polyolefin of interest.

[0124] Multiple optical sorters with the same sorting criteria may be arranged in series to improve the purity of the purified polyolefin recycle stream (K). Alternatively or additionally, multiple optical sorters may be arranged in series to sort according to different criteria, such as color and / or article morphology, but preferably each of the one or more optical sorters of step k) sorts by polyolefin type as described above.

[0125] Any material removed by one or more optical sorters from the heavy fraction polyolefin recycle stream (J), or the dried polyolefin recycle stream (I) in the absence of step j), may be discarded or returned to an earlier step in the mechanical recycling process, either directly or after further sorting by an optical sorter to extract waste flakes containing one or more target polyolefins.

[0126] Step l) involves melt extruding and preferably pelletizing the purified polyolefin recycle stream (K), if present, to form an extruded, preferably pelletized, recycled polyolefin product (L), to which additives (Ad) are preferably added in the molten state.

[0127] The extrusion of the recycled polyolefin product (L) in step l) is preferably carried out using an extruder, more preferably a twin-screw extruder.

[0128] In particular, it is preferred to use conventional compounding or mixing equipment, such as a Banbury mixer, a two-roll rubber mill, a Basco kneader, or a twin-screw extruder. More preferably, the mixing is completed in a co-rotating twin-screw extruder. The recycled polyolefin product (L) recovered from the extruder is usually in the form of pellets, but if step m) is not present in the mechanical recycling method, the recycled polyolefin product (L) may also be in the form of an extrudate such as a pipe. Preferably, the recycled polyolefin product (L) is in the form of pellets.

[0129] The optional additives (Ad) added in step l) are selected from additives known in the art, and are preferably selected from the group consisting of antioxidants, stabilizers, fillers, colorants, nucleating agents, antistatic agents, and mixtures thereof.

[0130] Such additives are generally commercially available and are described, for example, in "Plastic Additives Handbook" by Hans Zweifel, 5th edition, pp. 871-873, 2001.

[0131] Step m) involves aerating the recycled polyolefin product (L), if present, or the purified polyolefin recycle stream (K), if step l) is not present, to remove volatile organic compounds, thereby producing an aerated recycled polyolefin product (M), which is either an aerated extruded, preferably pelletized, recycled polyolefin product (M1) or an aerated recycled polyolefin flake (M2).

[0132] The aeration of step m) may be achieved by the use of air, an inert gas, or steam, among others.

[0133] Preferably, the aeration of step m) is achieved by contacting the recycled polyolefin product (L), or the purified polyolefin recycle stream (K) in the absence of step l), with a gas that is at least 60% by volume of N gas.

[0134] The temperature at which the aeration in step m) is carried out may be selected depending on the attributes of the polyolefins present in the recycled polyolefin product (L) or the purified polyolefin recycle stream (K).

[0135] Suitable ranges for typical polyolefins are as follows: In the case of HDPE, the temperature is preferably in the range of 50 to 130°C, more preferably in the range of 90 to 122°C, and most preferably in the range of 100 to 115°C. In the case of LDPE, the temperature is preferably in the range of 50 to 155°C, more preferably in the range of 75 to 105°C. In the case of polypropylene, the temperature is preferably in the range of 50 to 155°C, more preferably in the range of 100 to 150°C.

[0136] It may also be beneficial to carry out the aeration in step m) at reduced pressure, for example below 500 mbar, more preferably below 200 mbar, most preferably below 100 mbar.

[0137] The aeration in step m) minimizes the content of volatile organic compounds in the aerated recycled polyolefin product (M) and avoids the unpleasant odors typically associated with similar recycled polyolefin mixtures. These volatile organic compounds typically result from contamination of the polyolefin during first-time consumer use, e.g., through contact with food, skin care products, and other toiletries, or simply from the breakdown of the polyolefin into volatile oligomeric chains during processing steps.

[0138] Device In another aspect, the present invention relates to a polyolefin mechanical recycling apparatus for carrying out the polyolefin mechanical recycling method as described above.

[0139] All preferred embodiments and alternatives of the above-mentioned mechanical polyolefin recycling methods apply mutatis mutandis to the mechanical polyolefin recycling apparatus of the present invention.

Claims

1. In the given order, a) providing a precursor mixed plastics recycle stream (A); b) sieving the precursor mixed plastics recycle stream (A) to create a sieved mixed plastics recycle stream (B) containing only articles with a longest dimension in the range of 30 to 400 mm; step c) sorting the sieved mixed plastic recycle stream (B) with one or more optical sorters to produce a single-color sorted polyolefin recycle stream (C), wherein the sieved mixed plastic recycle stream (B) is sorted by at least color; step d) shredding the monochromatically separated polyolefin recycle stream (C) to form a flake polyolefin recycle stream (D); Step e) of washing the flaked polyolefin recycle stream (D) with a first aqueous wash liquid (W1) without input of thermal energy to produce a first suspended polyolefin recycle stream (E); f) removing at least a portion of said first aqueous wash liquid (W1) from said first suspended polyolefin recycle stream (E) to obtain a first washed polyolefin recycle stream (F); g) washing said first washed polyolefin recycle stream (F) with a second aqueous wash liquid (W2) to produce a second suspended polyolefin recycle stream (G), wherein sufficient thermal energy is introduced into said second suspended polyolefin recycle stream (G) such that the temperature during washing is in the range of 65-95°C; h) removing said second aqueous wash liquid (W2) and any material not floating on the surface of said second aqueous wash liquid from said second suspended polyolefin recycle stream (G) to obtain a second washed polyolefin recycle stream (H); i) drying the second washed polyolefin recycle stream (H) to obtain a dried polyolefin recycle stream (I); and j) separating the dried polyolefin recycle stream (I) into a light fraction and a heavy fraction polyolefin recycle stream (J), and further sorting the heavy fraction polyolefin recycle stream (J) in one or more optical sorters to select for one or more target polyolefins and remove any flakes containing materials other than the one or more target polyolefins to obtain a purified polyolefin recycle stream (K); or step k), further sorting said dried polyolefin recycle stream (I) with one or more optical sorters that separate out the one or more target polyolefins and remove any flakes containing materials other than said one or more target polyolefins to obtain a purified polyolefin recycle stream (K); A method for mechanically recycling polyolefins comprising:

2. A method for mechanically recycling polyolefins as described in claim 1, wherein the sorting in step c) further comprises sorting by type of polyolefin and / or by form of article.

3. 2. The method for mechanically recycling polyolefins according to claim 1, wherein the optical sorter in step c) performs sorting by a method selected from the group consisting of a camera system (operating in the visible range of the electromagnetic spectrum), visible reflectance spectroscopy, near-infrared spectroscopy, mid-infrared spectroscopy, high-speed laser spectroscopy, Raman spectroscopy, and Fourier transform infrared (FT-IR) spectroscopy.

4. 2. The method for mechanically recycling polyolefins according to claim 1, wherein the shredding in step d) is a wet shredding process in which the single-color sorted polyolefin recycle stream (C) is first contacted with an aqueous solution (W0) to provide a sorted suspended polyolefin recycle stream, which is then shredded.

5. 2. The method for mechanically recycling polyolefins according to claim 1, wherein the second aqueous washing liquid (W2) is an alkaline aqueous washing liquid.

6. The mechanical recycling method for polyolefins described in Claim 5, wherein the alkaline aqueous cleaning solution is an aqueous solution of a base selected from the group consisting of calcium hydroxide, potassium hydroxide, magnesium hydroxide, lithium hydroxide, sodium bicarbonate, sodium hydroxide, or mixtures thereof.

7. 6. The method for mechanically recycling polyolefins according to claim 5, wherein the pH of the alkaline aqueous wash solution ranges from 9.0 to 14.

0.

8. 6. The method for mechanically recycling polyolefins according to claim 5, wherein the amount of base in the alkaline aqueous washing solution is in the range of 0.05 to 10 wt. %, based on the total weight of the alkaline aqueous washing solution.

9. 5. A method for mechanically recycling polyolefins according to claim 4, wherein the aqueous washing liquid (W2) removed in step h) is recycled for use as the first aqueous washing liquid (W1) and / or, if present, as the aqueous solution (W0).

10. 5. The method for mechanically recycling polyolefins according to claim 4, wherein the first aqueous wash liquid (W1) and / or the aqueous solution (W0), if present, has a pH in the range of 8.0 to 14.

0.

11. 10. The method of claim 1, wherein the precursor mixed plastics recycle stream (A) is derived from post-consumer waste, post-industrial waste, or a combination thereof.

12. The method described in claim 1, wherein the single-color sorted polyolefin recycle stream (C) is either a single-color sorted polyethylene recycle stream or a single-color sorted polypropylene recycle stream.

13. A mechanical polyolefin recycling apparatus for carrying out the mechanical polyolefin recycling method of claim 1.

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