Mechanical recycling of 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 high purity recycled polyolefin grades having a balance of mechanical and optical properties superior to those typically found in similar recycled polyolefin grades, and a polyolefin mechanical recycling apparatus for carrying out the polyolefin mechanical recycling process. [Background technology]

[0002] Over the past decade, there has been an increased focus on the environmental sustainability of plastics and their current usage. This has led to 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 waste landfills.

[0003] In Europe, plastic waste represents around 27 million tonnes of waste annually. Of this, in 2016, 7.4 million tonnes were disposed of in landfills, 11.27 million tonnes were burned (for energy production) and around 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 huge compared to the amount recycled back into the stream (only around 30%), there is still great potential for the intelligent reuse of plastic waste streams and for the 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 of automotive parts are significantly below 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. Thus, there are still demands to be met if the recycling targets for plastics in the automotive industry are to be achieved. The present invention focuses specifically on mechanically recycled waste streams, rather than "energy recycling", where polyolefins are burned and used for energy. However, due to cost reasons, poor mechanical properties, and poor processing properties, 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 main 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 done using density separation in water, followed by further separation based on fluorescence, near-infrared absorption, or Raman fluorescence. However, it is generally very difficult to obtain pure recycled polypropylene or pure recycled polyethylene. Generally, commercially available recycled amounts of polypropylene are 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 are generally found to contain a mixture of PP and PE, with trace components of <50 wt%.

[0006] The better the quality, i.e., the purer, recycled polyolefin is, the more expensive the material is. 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] Also, materials that are rich in recycled polypropylene, e.g., polypropylene-rich materials, typically have much worse properties than virgin materials unless the final formulation contains extremely low amounts of recycled polyolefins, e.g., such materials often have poor odor and taste, poor stiffness, poor 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 that have 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 are 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 method for preparing a composition comprising, in a given order: a) providing a precursor mixed plastics recycling stream (A); 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 plastics recycle stream (B) with one or more optical sorters to produce one or more single-color sorted polyolefin recycle streams (C) and a mixed-color sorted polyolefin recycle stream (CM), wherein the sieved mixed plastics recycle stream (B) is sorted at least by color, and optionally by polyolefin type and / or article form, and each of the one or more single-color sorted polyolefin recycle streams (C) and the mixed-color sorted polyolefin recycle stream (CM) is separately subjected to step d) or later; d) reducing the size of the pieces of the selected polyolefin recycle stream (C or CM) to form a flake polyolefin recycle stream (D); e) washing said 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); 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 thermal 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; 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 said second washed polyolefin recycle stream (H) to obtain a dried polyolefin recycle stream (I); 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 material 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, a step m) of aerating said recycled polyolefin product (L) or, in the absence of step l), said purified polyolefin recycle stream (K) 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 said purified polyolefin recycle stream (K) is first aerated to form said aerated recycled polyolefin flakes (M2) and then extruded, preferably by interchanging the order of steps l) and m) such that said 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 a polyolefin mechanical recycling apparatus for carrying out the polyolefin mechanical recycling method according to any one of the preceding claims.

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

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

[0013] In the context of this invention, a mixed plastic 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 piece present in the stream. Generally speaking, all polyolefin-containing post-consumer waste recycle streams will be mixed plastic 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 article 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, plastic bottles, among others, which are considered rigid articles. Commercially available optical sorters, such as Tomra Autosort, RTT Steinert Unisort, Redwave Pellenc, etc., can separate so-called rigid articles from so-called flexible articles by utilizing aerodynamic properties (i.e., a stream of gas is usually applied to the stream, and articles that are rigid articles fall in a different arc than flexible articles), and convert the stream containing such articles into so-called rigid streams and flexible streams.

[0015] According to the present invention, the sorting method for sorting polyolefin-containing articles at least according to their color results in one or more monochromatic sorted polyolefin streams (C) as intermediate products. Those skilled in the art will recognize that a significant amount of polyolefin-containing articles in any given mixed-color recycle stream are transparent, i.e., colorless. For the purposes of the present invention, any transparent, i.e., colorless, polyolefin-containing articles are considered as a separate color classification, resulting in a monochromatic sorted polyolefin stream (C) whose "color" is colorless (i.e., transparent). In some embodiments, this colorless polyolefin recycle stream is passed through a subsequent step of the method to obtain a colorless recycle product, or in other embodiments, the colorless polyolefin recycle stream is mixed with a non-colorless monochromatic recycle stream (e.g., a white polyolefin recycle stream), and the mixed stream is considered a non-colorless monochromatic recycle stream (i.e., a mixture of a colorless stream and a white stream is then considered a white stream). Without wishing to be bound by theory, it is believed that the addition of colorless polyolefins to non-colorless polyolefin recycle streams does not significantly affect the final color of the recycled product.

[0016] According to the present invention, it is important that both the one or more monochromatically sorted recycle streams (C) and the mixed-color sorted polyolefin recycle streams (CM) are subjected to the 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 red pieces of various shades would be classified as a monochromatic stream, while a polyolefin stream containing red and yellow pieces would not be classified as a monochromatic stream. The accuracy of the monochromatic selection depends on the technology used for color sorting and is therefore limited by the available technology. Since the impression of color on the human eye cannot be strictly defined by wavelength, the definition on the CIELAB color scale is the most appropriate descriptor, considering that the same color may be obtained by a single wavelength of light or by a combination of different wavelengths. Particularly preferably, the same color means ΔE<50, preferably ΔE<40, more preferably ΔE<30, most preferably. ΔE is defined by the following formula:

number

[0017] Moreover, those skilled in the art will recognize that prior 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 and that a stream so described contains substantially only the color or polyolefin type described, but is not 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, results 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] Similarly, a mixed color sorted polyolefin recycle stream (CM) obtained via such a sorting process will necessarily be deficient in one or more colors and, therefore, is not equivalent to a mixed color polyolefin recycle stream that has not been subjected to one or more sorting steps.

[0020] 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 conventional pH probes. Thus, in the context of the present invention, an aqueous solution having an effective pH greater than 14.0 is considered to have a pH of 14.0, and an aqueous solution having an effective pH less than 0.0 is considered to have a pH of 0.0.

[0021] In the context of the present invention, the term "washing" is used to indicate the addition of a solvent, usually water, used to remove foreign matter or residual liquid from the polyolefin surface. 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 adherent foreign matter from the polyolefin surface and potentially extract volatile organic compounds from the polyolefin.

[0022] When 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, when 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.

[0023] Where an indefinite or definite article is used when referring to a singular noun e.g. "a", "an" or "the", the plural of that noun is also included unless specifically stated otherwise. [Brief description of the drawings]

[0024] [Figure 1] A preferred configuration of the optical sorter of step c). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] The present invention comprises, in a given order: a) providing a precursor mixed plastics recycling stream (A); 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; c) sorting the sieved mixed plastics recycle stream (B) with one or more optical sorters to produce one or more single-color sorted polyolefin recycle streams (C) and a mixed-color sorted polyolefin recycle stream (CM), wherein the sieved mixed plastics recycle stream (B) is sorted at least by color, and optionally by polyolefin type and / or article form, and each of the one or more single-color sorted polyolefin recycle streams (C) and the mixed-color sorted polyolefin recycle stream (CM) is separately subjected to step d) or later; d) reducing the size of the pieces of the selected polyolefin recycle stream (C or CM) to form a flake polyolefin recycle stream (D); e) 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); 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 thermal 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; h) removing the second aqueous wash liquid (W2) and any material that is not suspended 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); 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 separators that separate the one or more target polyolefins by removing any flakes that contain material 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, a step m) of aerating (venting) 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 an aerated recycled polyolefin flake (M2) and then extruded, preferably with the order of steps l) and m) reversed so that the additive (Ad) is added in the molten state to form an extruded, preferably pelletized, aerated recycled polyolefin product (M3).

[0026] 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 separating the dried polyolefin recycle stream (I) with one or more optical separators that separate the one or more target polyolefins by removing any flakes that contain material other than the one or more target polyolefins to obtain a purified polyolefin recycle stream (K); Includes.

[0027] 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 separators that separate the one or more target polyolefins by removing any flakes that contain material other than the one or more target polyolefins to obtain a purified polyolefin recycle stream (K); Includes.

[0028] 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 separating the dried polyolefin recycle stream (I) with one or more optical separators that separate the one or more target polyolefins by removing any flakes that contain material 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); 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 separators that separate the one or more target polyolefins by removing any flakes that contain material 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.

[0030] 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 separating the dried polyolefin recycle stream (I) with one or more optical separators that separate the one or more target polyolefins by removing any flakes that contain material other than the one or more target polyolefins to obtain a purified polyolefin recycle stream (K); aerating the purified polyolefin recycle stream (K) to remove volatile organic compounds, thereby producing an aerated recycled polyolefin flake (M2); Includes.

[0031] 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 separators that separate the one or more target polyolefins by removing any flakes that contain material other than the one or more target polyolefins to obtain a purified polyolefin recycle stream (K); aerating the purified polyolefin recycle stream (K) to remove volatile organic compounds, thereby producing an aerated recycled polyolefin flake (M2); 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); k) further separating the dried polyolefin recycle stream (I) with one or more optical separators that separate the one or more target polyolefins by removing any flakes that contain material 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; m) 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); 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 separators that separate the one or more target polyolefins by removing any flakes that contain material 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; m) aerating the recycled polyolefin product (L) to remove volatile organic compounds, thereby producing an aerated extruded, preferably pelletized, recycled polyolefin product (M1); Includes.

[0034] 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 separating the dried polyolefin recycle stream (I) with one or more optical separators that separate the one or more target polyolefins by removing any flakes that contain material other than the one or more target polyolefins to obtain a purified polyolefin recycle stream (K); m) aerating the purified polyolefin recycle stream (K) to remove volatile organic compounds, thereby producing an aerated recycled polyolefin flake (M2); step l) of melt extruding and preferably pelletizing the aerated recycled polyolefin flake (M2) to form an extruded, preferably pelletized, aerated recycled polyolefin product (M3), preferably in which an additive (Ad) is added in the molten state; Includes.

[0035] In a final embodiment, steps i) and onwards are carried out 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 separators that separate the one or more target polyolefins by removing any flakes that contain material other than the one or more target polyolefins to obtain a purified polyolefin recycle stream (K); m) aerating the purified polyolefin recycle stream (K) to remove volatile organic compounds, thereby producing an aerated recycled polyolefin flake (M2); step l) of melt extruding and preferably pelletizing the aerated recycled polyolefin flake (M2) to form an extruded, preferably pelletized, aerated recycled polyolefin product (M3), preferably in which an additive (Ad) is added in the molten state; Includes.

[0036] 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, but 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 migrate volatile organic compounds that are 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 method to method and will need to be optimized accordingly.

[0037] Step a) involves providing a precursor mixed plastics recycling stream (A).

[0038] This precursor mixed plastics recycle stream (A) may be derived from post-consumer waste, post-industrial waste, or a combination thereof.

[0039] Preferably, the precursor mixed plastics recycle stream (A) is derived from post-consumer waste.

[0040] As one skilled in the art will appreciate, providing such a precursor mixed plastics recycle stream may involve collection of 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.

[0041] The form of the precursor mixed plastics recycling stream (A) is not important, but it is required that the items present in the precursor mixed plastics recycling stream (A) do not stick together in steps b) to m). A common form in which commercially available mixed plastics recycling streams are obtained is in the form of bales. If the precursor mixed plastics recycling stream (A) is provided in the form of bales, the bales must be broken up before the precursor mixed plastics recycling stream (A) undergoes screening in step b). Depending on the method used to package the bales, it may also be necessary to remove any wires used to tie the bales (de-wiring the bales) and / or empty the bales from containers such as plastic bags or packaging materials (opening the bags / bales).

[0042] Furthermore, it may be necessary to store the intermediate product (i.e., intermediate recycle stream) of the polyolefin mechanical recycling process (such as at least one of the one or more single color sorted polyolefin recycle streams (C) or the mixed color sorted polyolefin recycle stream (CM)), in which case this intermediate product may be formed into a bale. Any bales thus formed must be broken up, preferably using one of the suitable methods listed above, before the intermediate product undergoes the next step of the process. Similarly, the intermediate product (i.e., intermediate recycle stream) may be stored, for example in a suitable container, without being formed into a bale, in which case the intermediate product may be reintroduced into the next step of the process without the need for breaking up or the like.

[0043] Those skilled in the art will appreciate that those methods which not only involve performing the requisite steps of the present polyolefin mechanical recycling process in the given order, but also 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 process at the location from which it was removed, are within the scope of the present invention.

[0044] Step b) involves sieving the precursor mixed plastics recycle stream (A) to create a sieved mixed plastics recycle stream (B) containing only articles whose longest dimension is in the range of 30-400 mm.

[0045] Those skilled in the art are aware of multiple ways that the sieving of step b) can be achieved, and therefore this sieving step is not particularly limited. However, preferably, the sieving of 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 divide the precursor mixed recycle stream into three streams, namely a small item stream with a longest dimension of less than 30 mm, an oversized item stream with a longest dimension of more than 400 mm, and a sieved mixed plastic recycle stream (B). The small item stream and the oversized stream can be discarded or transferred for use in other mechanical polyolefin recycling methods.

[0046] Step c) involves sorting the sieved mixed plastics recycle stream (B) with one or more optical sorters to produce one or more single color sorted polyolefin recycle streams (C) and mixed color sorted polyolefin recycle streams (CM), where the sieved mixed plastics recycle stream (B) is sorted at least by color, and optionally also by polyolefin type and / or article form.

[0047] 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 differentiate pieces of the sieved mixed plastics recycling stream (B).

[0048] Preferably, 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, fast laser spectroscopy, Raman spectroscopy, and Fourier transform infrared (FT-IR) spectroscopy.

[0049] Suitable methods for sorting recycling streams by color include camera systems (operating in the visible range of the electromagnetic spectrum) and visible reflectance spectroscopy.

[0050] Suitable methods for separating recycle streams by type of polyolefin include near infrared spectroscopy, mid-infrared spectroscopy, fast laser spectroscopy, Raman spectroscopy, and Fourier transform infrared (FT-IR) spectroscopy, with near infrared spectroscopy being particularly preferred.

[0051] Suitable methods for sorting recycling streams by item type include camera systems (operating in the visible range of the electromagnetic spectrum).

[0052] Preferably, the sorting in step c) is by color and polyolefin type, meaning that each of the one or more monochromatically sorted polyolefin recycle streams (C) is monochromatic and every article contains a single polyolefin.

[0053] 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.

[0054] To achieve the sorting in step c), multiple detection methods and / or multiple sensors may be used.

[0055] More preferably, the sorting in step c) is by color, polyolefin type, and article form, meaning that each of the one or more monochromatically sorted polyolefin recycle streams (C) is monochromatic, all articles contain a single polyolefin, and each stream contains only rigid or flexible articles.

[0056] 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 since 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 to a pure recycled polyolefin stream or extruded and pelletized to obtain pellets of the desired polyolefin, i.e., polyethylene or polypropylene.

[0057] Particularly preferably, the monochromatically separated polyolefin recycle stream (C) is either a monochromatically separated polyethylene recycle stream or a monochromatically separated polypropylene recycle stream.

[0058] In one embodiment, the mixed color sorted polyolefin recycle stream (CM) obtained in step c) is then subjected to a sorting step, which sorts according to the type of polyolefin, for example selecting only polyethylene fractions or selecting only polypropylene fractions.

[0059] In one preferred embodiment, the sorting in step c) comprises sorting the filtered mixed plastics recycle stream (B) into at least a first single-color sorted polyolefin recycle stream (C1) containing a first target polyolefin (PO1), a second single-color sorted polyolefin recycle stream (C2) containing a second target polyolefin (PO2), and a mixed-color sorted polyolefin recycle stream (CM), the first target polyolefin (PO1) and the second polyolefin (PO2) differing in at least one characteristic selected from color, polyolefin type, and article morphology, and the first single-color sorted polyolefin recycle stream (C1), the second single-color sorted polyolefin recycle stream (C2), and the mixed-color sorted polyolefin recycle stream (CM) are individually subjected to step d) onwards.

[0060] By targeting multiple polyolefins, fewer mixed plastic recycle streams are sorted into high purity, single color sorted polyolefin recycle streams, but the mixed color sorted polyolefin recycle streams are also ultimately purer. Additionally, fewer iterations of the sorting process are required per target polyolefin, improving process efficiency.

[0061] If the mono-color sorted polyolefin recycle stream (C) is a non-color sorted polyolefin recycle stream, this non-color sorted polyolefin recycle stream may be subjected to step d) onwards after being combined with a different mono-color sorted polyolefin recycle stream, for example a non-color sorted polyolefin recycle stream.

[0062] In one particular embodiment, a white sorted polyolefin recycle stream and a colorless sorted polyolefin recycle stream are obtained from step c), while a mixed color polyolefin recycle stream (CM) contains all other colors.

[0063] In a particularly preferred embodiment, the selection in step c) comprises: c1) using a first optical sorter to separate the filtered polyolefin recycle stream (B) to obtain a fraction (C4) containing the two target polyolefins (PO1 and PO2) and a mixed color recycle stream (C5); c2) using a second optical sorter to separate the fraction (C4) containing the two target polyolefins to obtain a first target fraction (C6) containing the first target polyolefin (PO1) and a second target fraction (C7) containing the second target polyolefin (PO2); c3) further purifying the first target fraction (C6) and the second target fraction (C7) using a third optical sorter to remove any articles not containing the first target polyolefin (PO1) from the first target fraction (C6) and any articles not containing the second target polyolefin (PO2) from the second target fraction (C7), thereby obtaining a first mono-color sorted polyolefin recycle stream (C1) and a second mono-color sorted polyolefin recycle stream (C2) and a further mixed-color recycle stream (C8), wherein the first mono-color sorted polyolefin recycle stream (C1) and the second mono-color sorted polyolefin recycle stream (C2) are individually subjected to step d) onwards; c4) feeding the mixed color recycle stream (C5) and the further mixed color recycle stream (C8) to a fourth optical sorter to remove any articles containing the first target polyolefin (PO1) or the second target polyolefin (PO2) to produce a reclaimed fraction (C9) and a mixed color polyolefin recycle stream (C3); step c5) of feeding the regenerated fraction (C9) back to the first optical sorter during step c1); wherein the mixed color polyolefin recycle stream (C3) is either subjected to step d) onwards as a mixed color sorted polyolefin recycle stream (CM) or subjected to a further repetition of step c), whereby the mixed color polyolefin recycle stream (C3) is separated into a further first single color sorted polyolefin recycle stream (C1), a further second single color sorted polyolefin recycle stream (C2) and a further mixed color polyolefin recycle stream (C3).

[0064] This embodiment may be better understood with reference to FIG.

[0065] The labels in FIG. 1 correspond to those of the embodiments described above, with all solid arrows indicating recycle streams on their way to one of one or more single color sorted polyolefin recycle streams (C), and dashed streams representing streams on their way to a mixed color sorted polyolefin recycle stream (CM).

[0066] It is preferred that the first target polyolefin (PO1) and the second target polyolefin (PO2) are the same color but contain different polyolefin types, or that the first target polyolefin (PO1) and the second target polyolefin (PO2) contain the same polyolefin type but are different colors.

[0067] In one particularly preferred embodiment, the first target polyolefin (PO1) is a polypropylene having a first desired color and the second target polyolefin (PO2) is a polypropylene having a second desired color different from the first desired color, or the first target polyolefin (PO1) is a polyethylene having a first desired color and the second target polyolefin (PO2) is a polyethylene having a second desired color different from the first desired color.

[0068] It is particularly preferred that the first target polyolefin (PO1) and the second target polyolefin (PO2) are of the same color but contain different polyolefin types.

[0069] In another particularly preferred embodiment, the first target polyolefin (PO1) is a polypropylene having a desired color and the second target polyolefin (PO2) is a polyethylene having the same desired color as the first target polyolefin (PO1).

[0070] Alternatively, the first target polyolefin (PO1) and the second target polyolefin (PO2) are the same color and contain the same polyolefin type, but are in different article form, i.e., if the first target polyolefin (PO1) is a rigid white polyethylene recycle stream, the second target polyolefin (PO2) is a flexible white polyethylene recycle stream.

[0071] In a particularly preferred embodiment, the sorting in step c) comprises first sorting the sieved mixed plastics recycle stream (B) by polyolefin type in one or more optical sorters to produce a mixed color single polyolefin recycle stream (CS), which is then sorted by color to produce one or more single color sorted polyolefin recycle streams (C) and mixed color sorted polyolefin recycle streams (CM), each single color sorted polyolefin recycle stream (C) and mixed color sorted polyolefin recycle stream (CM) containing the same polyolefins, preferably selected from polyethylene and polypropylene.

[0072] By first sorting for polyolefin type and then sorting by color, it is ensured that the resulting mixed-color sorted polyolefin recycle stream (CM) contains substantially only one type of polyolefin, which avoids the need for further sorting steps at subsequent stages, such as the subsequent sorting steps described above.

[0073] Each of the preferred embodiments described above and below can be combined mutatis mutandis with this embodiment in which the polyolefin type sorting step precedes the color sorting step.

[0074] For example, step c) may involve first sorting the sieved mixed plastics recycle stream (B) by polyolefin type with one or more optical sorters to produce a mixed color single polyolefin recycle stream (CS), which is then sorted via steps c1) to c5) above, wherein the first target polyolefin (PO1), the second target polyolefin (PO2) and the mixed color polyolefin recycle stream (C3) are of the same polyolefin type, preferably selected from polyethylene and polypropylene.

[0075] It is particularly preferred that the mixed color sorted polyolefin recycle stream (CM) is a single polyolefin type, more preferably selected from polyethylene and polypropylene. This may be achieved by an embodiment of step c) including an initial polyolefin sorting step prior to the color sorting steps, or by sorting the mixed color sorted polyolefin recycle stream (CM) after completion of all color sorting steps. Preferably, this is achieved by an embodiment of step c) including an initial polyolefin sorting step prior to the color sorting steps.

[0076] The sorting in step c) can be achieved through a simple sorting algorithm where the optical sensor is programmed to assess which pieces should be selected or rejected based on simple binary decisions, or more complex AI-based systems can be used to achieve more accurate sorting, especially when sorting by item morphology.

[0077] Without wishing to be bound by theory, the inventors believe that the provision of a monochromatically sorted polyolefin recycle stream in step c) is essential to obtain a recycled product with improved properties. As expected, not only is an improvement in the color of the recycled product achieved, but the presence of the important sorting step c) prior to any of the processing steps d)-m) allows a purer recycled product to be obtained. For example, in the sorting by color in step c), only the white polyolefin pieces may be selected, all other colors, including colorless pieces, are removed at this stage. The transparent pieces often come from plastic bottles, which are often made of PET. Thus, it is expected that the combined transparent pieces will have a higher PET content than the other colors, e.g., white pieces. PET is prone to decomposition, for example, during the high temperature washing in step g), producing acetaldehyde, among other small organic molecules. Such small organic molecules have a negative impact on the odor of the resulting recycled product. Reducing the PET content by color sorting at this stage can reduce this problem.

[0078] Furthermore, in different countries or regions, different packages may have different typical colors, making it more likely that, for example, a green piece contains some non-polyolefins or undesirable polyolefins. The benefits of color sorting in step c) vary depending on which country or region the precursor mixed plastics recycling stream is sourced from.

[0079] In addition, certain colored polymers contain certain pigments / dyes which may individually result in contamination of the recycled polyolefin product if they contain metallic pigments or are susceptible to decomposition during extrusion and thus form malodorous compounds or catalyze the degradation of the polyolefin during extrusion, etc. Removal of colored polymers known to contain these pigments / dyes would avoid these problems and result in improved quality of the recycled product.

[0080] The removal of certain problematic single color polyolefin recycle streams from a mixed color sorted polyolefin recycle stream (CM) can help produce a high quality product having a gray / black color (for the same reasons given above for single color recycle products). In this regard, the removal of certain colors can improve the purity of the final gray / black recycle product in terms of polyolefin content, not just in terms of color.

[0081] Non-polyolefins and undesired polyolefin flakes can be removed in step k), but any sorting method has limited efficiency, which means that the purer the flakes fed to such a method, the purer the product of such a method. Considering the difficulty in obtaining a pure product with the prior art methods, even seemingly small improvements in the purity of the recycled product can be commercially very valuable.

[0082] Furthermore, removing such flakes after washing steps e) and g) does not avoid the problem of cross-contamination between the flakes during steps d) to j).

[0083] Furthermore, the presence of the sorting step c) prior to the mechanical recycling steps d)-m) means that the polyolefin mechanical recycling method according to the invention allows the operator to obtain a high quality recycled product, regardless of the quality of the feedstock, which is well known to be highly variable in terms of polyolefin content and foreign matter contamination, and highly dependent on the source of the feedstock (i.e. the source of the precursor mixed plastics recycle stream (A)).

[0084] Step d) involves reducing the size of pieces of the monochromatically sorted polyolefin recycle stream (C or CM) to form a flake polyolefin recycle stream (D).

[0085] The size reduction in step d) may be carried out by any method known to the person skilled in the art. One suitable method comprises a step of grinding the sorted polyolefin recycle stream (C or CM). Another method comprises a step of shredding the sorted polyolefin recycle stream (C or CM). Particularly preferably, the size reduction in step d) is a shredding step.

[0086] 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 or CM) is first contacted with an aqueous solution (W0) to provide a sorted suspended polyolefin recycle stream which is then shredded.

[0087] The selection of 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.

[0088] More preferably, the aqueous solution (W0) is at least a part of the recycled aqueous washing liquid removed in step h).

[0089] If the shredding in step d) is a wet shredding process, the flaked polyolefin recycle stream (D) obtained therefrom 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.

[0090] 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 last wash step so that the resulting washed polyolefin stream is as clean as possible. Finally, the multiple use of a single aqueous wash solution simplifies the treatment of waste streams, avoiding the need to treat multiple different waste streams containing different chemicals.

[0091] 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).

[0092] 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. In the present method, step e) represents such a low temperature cleaning.

[0093] A person 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).

[0094] 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.

[0095] The selection of the first aqueous cleaning liquid (W1) is not particularly limited, but the pH of the first aqueous cleaning 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.

[0096] 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).

[0097] 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, P3 stabilon AL available from ECOLAB Ltd.

[0098] More preferably, the first aqueous washing liquid (W1) is at least a part of the recycled aqueous washing liquid removed in step h).

[0099] The advantages of reusing the recycled aqueous cleaning solution from step h) as the first aqueous cleaning solution are similar to those discussed above for the aqueous solution (W0).

[0100] The wash in step e) is a cleaning step as opposed to a rinsing step as defined herein and therefore typically lasts for more than 5 minutes, for example from 5 minutes to 4 hours.

[0101] 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.

[0102] 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, ultrasonication, mechanical grinding, or 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 ultrasonication. This agitation exposes the flakes in the recycle stream to fresh washing solution, so that the process is not hindered by the accumulation of contaminants in the immediate vicinity of the flakes.

[0103] One of skill in the art will recognize that agitation can be improved by combining multiple individual methods provided above, for example, by combining mechanical mixing with sonication.

[0104] 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).

[0105] The skilled person 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, e.g. by use of so-called sink-float separation, in this case with 0.1% or more of the foreign matter (with a density of 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 1000 g of polyolefin is expected to float) will be removed with the solution.

[0106] 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.

[0107] The first washed polyolefin recycle stream (F), whether washed or not, 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), since this contributes to a decrease in the process efficiency in terms of energy efficiency and step efficiency, but does not contribute significantly to the effectiveness of the present invention.

[0108] 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 thermal 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.

[0109] As previously mentioned, one of skill in the art will recognize that cleaning steps known in the art may be heated to achieve a high temperature cleaning, or may be performed at ambient conditions to achieve a low temperature cleaning. The cleaning of step g) is a high temperature cleaning, in contrast to the cleaning of step e), in which thermal energy is introduced such that the temperature during cleaning is between 65-95°C.

[0110] 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.

[0111] Preferably, the second aqueous washing liquid (W2) is an alkaline aqueous washing liquid.

[0112] 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.

[0113] 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.

[0114] The amount of the 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.

[0115] 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% by weight, based on the total weight of the second aqueous cleaning liquid (W2).

[0116] The second aqueous cleaning liquid (W2) may also contain a 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).

[0117] 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, P3 stabilon AL available from ECOLAB Ltd.

[0118] The wash in step g) is a cleaning step as opposed to a rinsing step as defined herein and therefore typically lasts for more than 5 minutes, for example from 5 minutes to 4 hours.

[0119] The washing in step g) preferably lasts for 5 minutes to 2 hours, more preferably for 5 minutes to 1 hour, most preferably for 10 minutes to 45 minutes.

[0120] 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, ultrasonication, mechanical grinding or a pump-around loop, preferably the combination of the second aqueous wash liquid (W2) and the first washed polyolefin recycle stream (F) in step g) is agitated by ultrasonication, which agitates 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.

[0121] One of skill in the art will recognize that agitation can be improved by combining multiple individual methods provided above, for example, by combining mechanical mixing with sonication.

[0122] 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).

[0123] 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 any material that does not float on the surface of the cleaning liquid. 3 It will be appreciated that the effect of this is to remove any foreign matter having a density greater than 100 nm.

[0124] Without wishing to be bound by theory, it is believed that the inclusion of a float-sink separation step immediately after the high-temperature washing in step g) is very beneficial in order to remove as many foreign bodies as possible. Subsequent steps in the method, such as aeration (step m) or drying (step i), may cause foreign bodies removed from the polyolefin flakes to reattach to the polyolefin flakes. This may result in contamination of the final recycled product or a reduced yield if these polyolefin flakes are removed in a subsequent step, such as separation in step j) or sorting in step k). It is therefore important that this step is carried out immediately after step g).

[0125] 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.

[0126] If the aqueous washing liquid removed in step h) is recycled as described above, preferably the foreign matter removed in the sink-float separation is filtered out of the solution before it is used as the first aqueous washing liquid (W1) and / or the aqueous solution (W0).

[0127] After removal of the second aqueous wash liquid (W2), the second washed polyolefin recycle stream (H) may be optionally 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.

[0128] Step i) involves drying the second washed polyolefin recycle stream (H) to obtain a dried polyolefin recycle stream (I).

[0129] 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.

[0130] Step j), if present, involves separating the dried polyolefin recycle stream (I) into a light fraction and a heavy fraction polyolefin recycle stream (J).

[0131] The light fraction typically contains labels and other non-polyolefin materials, while polyolefin flakes are sorted into the heavy fraction polyolefin recycle stream (J).

[0132] 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.

[0133] As will be understood by those skilled in the art, the separation into light and heavy fractions by such methods is not only influenced 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.

[0134] 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 the skilled person may be used, for example using a screen or sieve.

[0135] Step k) involves further screening 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 material other than the one or more target polyolefins to obtain a purified polyolefin recycle stream (K).

[0136] In step k), at least a first optical sorter is used to remove flakes containing materials other than the one or more target polyolefins, the selection criteria for this optical sorter being that if any materials other than the one or more target polyolefins are present in a given flake, this flake is separated from the stream to obtain a purified polyolefin recycle stream.

[0137] If the one or more optical sorters separate two or more target polyolefins, the resulting purified polyolefin recycle stream (K) may be a purified mixed polyolefin recycle stream, but preferably these target polyolefins are separated into individual purified polyolefin recycle streams (K), each containing only a single target polyolefin.

[0138] 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.

[0139] Any material removed by the 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 may be returned to an earlier step in the mechanical recycling process, either directly or after further sorting by an optical sorter to extract waste flakes comprising one or more target polyolefins.

[0140] 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), wherein additives (Ad) are preferably added in the molten state.

[0141] The extrusion of the recycled polyolefin product (L) in step l) is preferably carried out using an extruder, more preferably a single screw extruder.

[0142] In particular, it is preferred to use conventional compounding or mixing equipment, such as a single screw extruder, a conical co-rotating twin screw extruder, or multiple extruders arranged in series (either single screw, twin screw, or a combination thereof). 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.

[0143] The optional additives (Ad) added in step l) are selected from additives known in the art, preferably selected from the group consisting of antioxidants, stabilizers, fillers, colorants, nucleating agents, antistatic agents, and mixtures thereof.

[0144] Such additives are generally commercially available and are described, for example, in "Plastic Additives Handbook" by Hans Zweifel, 5th Edition, pages 871-873, 2001.

[0145] 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 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).

[0146] The aeration in step m) may be achieved by the use of air, an inert gas, or steam, among others.

[0147] 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 N2 gas.

[0148] 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).

[0149] 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, and 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, and more preferably in the range of 100 to 150°C.

[0150] 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.

[0151] 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, which typically result from contamination of the polyolefin during first consumer use, e.g., through contact with food, skin care products, other toiletries, or simply from the breakdown of the polyolefin into volatile oligomeric chains during processing steps.

[0152] 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.

[0153] All preferred embodiments and alternatives of the polyolefin mechanical recycling process described above apply mutatis mutandis to the polyolefin mechanical 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 30-400 mm; Step c) of sorting the sieved mixed plastics recycle stream (B) with one or more optical sorters to produce one or more single-color sorted polyolefin recycle streams (C) and a mixed-color sorted polyolefin recycle stream (CM), wherein the sieved mixed plastics recycle stream (B) is sorted at least by color, and optionally by type of polyolefin and / or by article form, and each of the one or more single-color sorted polyolefin recycle streams (C) and the mixed-color sorted polyolefin recycle stream (CM) is separately subjected to step d) or later; d) shredding the screened polyolefin recycle stream (C or CM) to form a flake polyolefin recycle stream (D); e) washing said 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); 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 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 said second washed polyolefin recycle stream (H) to obtain a dried polyolefin recycle stream (I); j) optionally separating the dried polyolefin recycle stream (I) into a light fraction and a heavy fraction polyolefin recycle stream (J); step k) further screening 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 screeners that screen the one or more target polyolefins by removing any flakes containing material 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, a step m) of aerating said recycled polyolefin product (L) or, in the absence of step l), said purified polyolefin recycle stream (K) 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 said purified polyolefin recycle stream (K) is first aerated to form an aerated recycled polyolefin flake (M2) and then extruded, preferably by interchanging the order of steps l) and m) such that the additive (Ad) is added in the molten state to form an extruded, preferably pelletized, aerated recycled polyolefin product (M3).

2. 2. The method of claim 1, wherein 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, fast laser spectroscopy, Raman spectroscopy, and Fourier transform infrared (FT-IR) spectroscopy.

3. 3. The mechanical recycling method of polyolefins according to claim 1 or 2, wherein 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.

4. 4. The process for mechanical recycling of polyolefins according to any one of claims 1 to 3, wherein the second aqueous wash liquid (W2) is an alkaline aqueous wash liquid, preferably 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, preferably sodium hydroxide.

5. The method for mechanically recycling polyolefins according to claim 4, wherein the pH of said aqueous alkaline solution is in the range of 9.0 to 14.0, preferably in the range of 12.0 to 14.

0.

6. 6. The method for mechanically recycling polyolefins according to claim 4 or 5, wherein the amount of the base in the aqueous alkaline solution is in the range of 0.05 to 10 wt.%, more preferably in the range of 0.10 to 7.0 wt.%, most preferably in the range of 0.50 to 5.0 wt.%, based on the total weight of the aqueous alkaline solution.

7. 7. Process for mechanically recycling polyolefins according to any one of claims 1 to 6, wherein at least a portion of 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).

8. Process for mechanical recycling of polyolefins according to any one of the preceding claims, wherein the first aqueous wash liquid (W1) and / or, if present, the aqueous solution (W0) have a pH in the range of 8.0 to 14.0, preferably in the range of 12.0 to 14.

0.

9. 9. The method according to any one of claims 1 to 8, wherein the precursor mixed plastics recycle stream (A) is derived from post-consumer waste, post-industrial waste, or a combination thereof, preferably from post-consumer waste.

10. 10. The method according to any one of claims 1 to 9, wherein one of the one or more mono-color sorted polyolefin recycle streams (C1) is either a mono-color sorted polyethylene recycle stream or a mono-color sorted polypropylene recycle stream.

11. 11. The method according to any one of claims 1 to 10, wherein the sorting in step c) comprises sorting the filtered mixed plastics recycle stream (B) into at least a first mono-color sorted polyolefin recycle stream (C1) containing a first target polyolefin (PO1), a second mono-color sorted polyolefin recycle stream (C2) containing a second target polyolefin (PO2), and a mixed-color sorted polyolefin recycle stream (CM), wherein the first target polyolefin (PO1) and the second polyolefin (PO2) differ in at least one property selected from color, polyolefin type, and article morphology, and wherein the first mono-color sorted polyolefin recycle stream (C1), the second mono-color sorted polyolefin recycle stream (C2), and the mixed-color sorted polyolefin recycle stream (CM) are individually subjected to step d) onwards.

12. The screening in step c) comprises: c1) using a first optical sorter to separate the filtered polyolefin recycle stream (B) to obtain a fraction (C4) containing the two target polyolefins (PO1 and PO2) and a mixed color recycle stream (C5); c2) using a second optical sorter to separate the fraction (C4) containing two target polyolefins to obtain a first target fraction (C6) containing the first target polyolefin (PO1) and a second target fraction (C7) containing the second target polyolefin (PO2); c3) further purifying the first target fraction (C6) and the second target fraction (C7) using a third optical sorter to remove any products not containing the first target polyolefin (PO1) from the first target fraction (C6) and any products not containing the second target polyolefin (PO2) from the second target fraction (C7), thereby obtaining a first mono-color sorted polyolefin recycle stream (C1) and a second mono-color sorted polyolefin recycle stream (C2) and a further mixed-color recycle stream (C8), wherein the first mono-color sorted polyolefin recycle stream (C1) and the second mono-color sorted polyolefin recycle stream (C2) are individually subjected to step d) onwards; c4) feeding the mixed color recycle stream (C5) and the further mixed color recycle stream (C8) to a fourth optical sorter to remove any articles containing said first target polyolefin (PO1) or said second target polyolefin (PO2) thereby producing a regenerated fraction (C9) and a mixed color polyolefin recycle stream (C3); c5) feeding the regenerated fraction (C9) back into the first optical sorter during step c1); 12. The method for mechanically recycling polyolefins according to claim 11, wherein the mixed color polyolefin recycle stream (C3) is subjected to step d) onwards as the mixed color sorted polyolefin recycle stream (CM) or subjected to a further repetition of step c), whereby the mixed color polyolefin recycle stream (C3) is separated into a further first mono-color sorted polyolefin recycle stream (C1), a further second mono-color sorted polyolefin recycle stream (C2) and a further mixed color polyolefin recycle stream (C3).

13. 13. A method for mechanically recycling polyolefins according to claim 11 or 12, wherein the first target polyolefin (PO1) and the second target polyolefin (PO2) are of the same colour but contain different polyolefin types, or the first target polyolefin (PO1) and the second target polyolefin (PO2) contain the same polyolefin type but are of different colours.

14. 14. The method for mechanically recycling polyolefins according to claim 13, wherein the first target polyolefin (PO1) is a polypropylene having a first desired color and the second target polyolefin (PO2) is a polypropylene having a second desired color different from the first desired color, or the first target polyolefin (PO1) is a polyethylene having a first desired color and the second target polyolefin (PO2) is a polyethylene having a second desired color different from the first desired color.

15. 15. The method for mechanically recycling polyolefins according to any one of claims 1 to 14, wherein the sorting in step c) comprises first sorting the sieved mixed plastics recycle stream (B) by polyolefin type to produce a mixed color single polyolefin recycle stream (CS), which is then sorted by color to produce one or more single color sorted polyolefin recycle streams (C) and a mixed color sorted polyolefin recycle stream (CM), each single color sorted polyolefin recycle stream (C) and the mixed color sorted polyolefin recycle stream (CM) containing the same polyolefins, preferably selected from polyethylene and polypropylene.

16. A polyolefin mechanical recycling device for carrying out the polyolefin mechanical recycling method according to any one of claims 1 to 15.

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