METHOD FOR THE PRODUCTION OF POLYOLEFIN RECYCLATES

Description

[0001] The present invention relates to an improved process for producing polyolefin recyclates and in particular HDPE and PP recyclates. Background of the invention

[0002] Polyolefins are robust, flexible plastics that have numerous applications due to their ease of processing and chemical resistance. With a share of around 45%, they represent the largest single group of consumer plastics in Europe.

[0003] By far the largest application for polyolefin plastics is packaging. The ubiquity of plastic packaging repeatedly places it at the center of environmental policy debates. If a suitable infrastructure for collection, sorting, and recycling is lacking, plastic packaging can become a problem, as the debate about marine pollution clearly demonstrates. The EU Packaging Directive and the corresponding national legislation have initiated the development of such infrastructures across Europe over the past 25 years, to varying degrees and extents. In Germany, these are the yellow bag / yellow bin collection systems and the associated concepts and facilities for sorting and recycling.The long-term sustainability of these infrastructures and their expansion to other countries depends crucially on the industrial demand for recycled plastics, which will improve the higher the quality of the recyclates offered.

[0004] With PET packaging, this is already possible today in a so-called closed-loop process, whereby packaging plastics are used to produce packaging again in the next usage cycle. With polyolefins, the problem is that polyolefins from standard recycling processes are processed in mixed colors, which are also found in the recycled material. The end products produced in this way therefore exhibit different shades of gray, depending on the composition of the starting material. Since the recycling processes available to date also leave residual contaminants on the polyolefin plastics, the processed products develop odors typical of recycled materials, which preclude applications close to the end user. This means that today, polyolefin plastics are predominantly used for "open-loop" applications that are far removed from the end user, i.e.The recyclates are not reused for packaging, but rather processed into durable plastic products, for example in the construction sector.

[0005] For the reuse of polyolefin plastics, foreign substances that are absorbed in small quantities during the primary use of the polyolefins are particularly problematic. For example, a polyethylene shampoo container can absorb non-polar ingredients such as perfumes from the shampoo, which cannot be removed by simply washing with water. If such a polyolefin recyclate is exposed to high thermal stress, as is the case, for example, during extrusion processes, these migrating substances decompose, which is a major source of the odor nuisances typical of recyclates.

[0006] Another problem, especially with polyolefin packaging materials, is that, unlike PET beverage packaging, for example, they do not come from a relatively uniform color source. This results in products with varying shades of gray, as mentioned above, when using the sorting methods currently in use.

[0007] An exception to this are special collection systems for uniform packaging, e.g., milk bottles, which, like other beverage packaging, are collected separately in supermarkets, for example, in Great Britain. However, the vast majority of polyolefin packaging, which often contains not only differently colored polyolefin packaging but also a significant proportion of other plastics and foreign substances such as metals, wood, or paper, is simply sorted by material type (e.g., "PE") and, as explained above, is usually granulated after shredding and washing with cold water and used in non-end-consumer applications at a revenue level that is usually significantly below the price of virgin material. A prior art process for producing polyolefin recyclate is known, for example, from WO2012 / 117250A1.

[0008] The long-term trend of rising raw material prices and the perceived pressure in the consumer goods industry to adapt to increasing demand for sustainably produced products have triggered a need for processes that can process polyolefin packaging waste, particularly from private households, for reuse in packaging for end consumers. To this end, the process should yield a recycled product that is as pure as possible and can be re-extruded without generating by-products with an unpleasant odor. Furthermore, the process should be as straightforward as possible, even with large throughput volumes, and cost-effectively, in order to obtain a market-competitive product. The present invention addresses this need. Summary of the invention

[0009] In general, the present invention discloses processes for producing polyolefin recyclates from mixed-color polyolefin-containing residues. In particular, the disclosed process can separate polyolefins from contaminants that have been incorporated into the polyolefins as a result of migration processes. However, the process can also separate contaminants that adhere to the surface of the polyolefins or that are present in a mixture with the polyolefins.

[0010] In particular, the present invention relates to a process for producing a polyolefin suitable for the production of consumer products according to claim 1.

[0011] Where it is stated above that steps (ii) and (iii) can also be carried out in reverse order, this is to be understood as meaning that, in this case, the water treatment (i), in which no thermal energy is supplied, is followed by flake sorting of the polyolefin residue fraction obtained from the water treatment to obtain one or more colour-pure polyolefin residue fractions, which is followed by treatment of the residue fraction by washing with an alkaline medium at a temperature of at least 60°C. The treatment described in (iv) then follows this washing.

[0012] The polyolefin residue fractions to be included as starting material in the process according to the invention can be residue fractions from any suitable polyolefin or from mixtures of polyolefins. However, it is preferred if the polyolefin residue fraction is a material which consists predominantly, i.e. at least 75% by weight, preferably at least 80% by weight and particularly preferably at least 90% by weight, of polyolefins of the same base polymer. Base polymers include, inter alia, homopolymers such as polypropylene or polyethylene, but also copolymers of ethylene or propylene with other o-olefin monomers. In the case of polyethylene, the various known modifications such as HDPE, LDPE or LLDPE should also be regarded as independent base polymers.Particularly preferred polyolefins in the context of the present invention are polypropylene and modifications of polyethylene, in particular in the form of LDPE and HDPE, preferably in the form of HDPE.

[0013] Residual material fractions pre-sorted according to their main plastic components, which can be obtained from conventional waste sorting plants, can be used as raw materials for the process. Such pre-sorted residual material fractions are available commercially, for example, in the form of compressed bales, and consist predominantly (approximately 90 to 95%, based on the plastic content) of one or more defined plastic base polymers (e.g., PP, HDPE, or LDPE).

[0014] Within the scope of the inventive process, it is also possible to use separately collected waste materials, such as milk bottles. However, since such separately collected waste materials generally exhibit significantly more uniform contamination, the inventive process cannot fully exploit its advantages in the processing of such waste materials. The waste fraction to be incorporated into the inventive process contains at least polyolefins of various colors. Transparent, white, and black polyolefin articles are also considered colored within the scope of the present invention.

[0015] It is particularly preferred if the proportion of the residual material fraction that constitutes the main color of the residual material fraction does not exceed 40% by weight. Furthermore, the invention provides that the residual material fraction to be included in the process according to the invention contains transparent, white, and residually colored polyolefin articles with a proportion of approximately 20 to 45% by weight of transparent articles, approximately 20 to 45% by weight of white articles, and approximately 20 to 45% by weight of residually colored articles. Furthermore, the invention provides that the residual material fraction comprises packaging from various applications (e.g., shampoo and food packaging), since such residual material fractions are contaminated with a wider range of contaminants, so that the advantages of the process according to the invention are fully utilized.

[0016] In the first step (i), which can also be referred to as cold washing, the polyolefin residue fraction is washed with water to remove surface contaminants, e.g. in the form of food residues, salts or paper labels, from the polyolefins. For this purpose, it is generally not necessary to heat the water before the washing process or to modify it with additives. The temperature at which this washing is carried out depends on the mechanical energy input and the outside temperature, since no thermal energy is added, and is often 30°C or less. Depending on the degree of soiling and the contaminating components present, the cold wash can in individual cases also be replaced by a mechanical dry wash, e.g. by adding abrasive components and then vigorously agitating the mixture. Contaminants can be detached from their surface by impact with the polyolefin components.The abrasive components can then be separated from the polyolefins again, for example using a float / sink process in which the polyolefins float on the water due to their density, while the abrasive components sink.

[0017] For washing in step (i), the invention provides that the starting material is subjected to one or more comminution steps before the cold wash. This is particularly useful when the starting material contains packaging with cavities, since in this case the comminution ensures that the wash water can come into contact with the entire surface of the packaging. The comminution can expediently be carried out in a shredder, a cutting mill or similar comminution devices. The comminution can be carried out both wet (i.e. with the addition of water or moisture) and dry. Furthermore, the comminution can also be carried out in a two- or multi-stage process, in particular a two-stage process, wherein the first stage is preferably designed as a dry process and the second stage as a wet process.The average particle size achieved by comminution should be a maximum of approximately 20 mm, in particular a maximum of 15 mm, but preferably at least 2 mm and especially at least 4 mm. A particularly favorable particle size is in the range of approximately 5 to 10 mm. Particle size refers to the largest spatial dimension of the respective particles.

[0018] The particle size distribution may vary. Ideally, however, at least 80% (± 10%) of the particles should have a particle size within the specified range.

[0019] In addition, it may be useful to subject the feedstock to a step of physically removing loose contaminants prior to treatment in step (i). For example, loose metal or glass components can be removed from the feedstock by pulling magnetic metal components out of the feedstock using magnets, or by exploiting the greater specific gravity of the contaminant. Since polyolefins are lighter than glass or metals, the feedstock can be conveyed, for example, using a conveyor belt over a gap dimensioned so that the contaminants fall into the gap while the lighter polyolefin components are conveyed over the gap. It is also possible to feed the material stream from below with a gas stream, which drives lighter components upwards.Since the heavier components are less buoyant, they can be easily separated from the lighter components using such a device. Finally, a sink / float process can also be used to remove components with a higher specific gravity, which takes advantage of the fact that polyolefins are lighter than water. In such a process, the polyolefin components are therefore obtained as a fraction floating on the water, while components such as glass and metals sink in the water and can be separated as sediment.

[0020] For the separation of components with a higher specific gravity described above, it is advisable to perform this downstream of comminution of the starting material, as this results in a more uniform starting material. Furthermore, upstream comminution has the advantage of also removing impurities that are present in cavities in the polyolefin starting material prior to comminution.

[0021] It may also be useful to roughly sort the raw material by color and / or polymer before shredding, particularly by dividing it into transparent, white, and (residual) colored components and by polymer type. "Rough" color sorting means dividing the raw materials by their primary color, with mixed-color consumer products being assigned to the color fraction that corresponds to their primary color. Similarly, "rough" polymer sorting involves sorting by primary polymer. For example, HDPE bottles often have PP caps; in this case, these bottles would be classified as HDPE polymers.

[0022] In order to avoid carryover of contaminated wash water, it is advisable to mechanically dewater the polyolefin residue fraction obtained from step (i) as completely as possible before it is subjected to the following process steps.

[0023] In the second step (ii), also known as hot washing, the polyolefin residue fraction is treated with an alkaline aqueous solution at elevated temperature. This step dissolves and removes any adhesive residues or printed labels adhering to the source material, and also removes any residual contaminants that could not be separated from the source material during the cold washing process. The term "printed labels" refers, for example, to inks printed directly onto packaging such as drinking or shampoo bottles. For example, non-alcoholic beverage bottles are often printed with epoxy-based inks. Furthermore, alkaline treatment can be used to remove polymer coatings based on acrylates or ethylene-vinyl alcohol (e.g., EVOH films).

[0024] Step (ii) is expediently carried out at a temperature of at least 60°C, in particular at least 70°C, and preferably in the range from 80 to 90°C, most preferably 80 to 85°C. Alternatively or additionally, it is preferred for step (ii) if the alkaline medium is an aqueous alkali solution, in particular an aqueous sodium hydroxide or potassium hydroxide solution, and preferably an aqueous sodium hydroxide solution. The concentration of the sodium hydroxide solution in relation to sodium hydroxide should not exceed 10 wt.%, since this generally places higher demands on the equipment in which step (ii) is carried out. Since it has been found that most impurities can be removed even at lower sodium hydroxide contents, a concentration range of 0.5 to 5 wt.% for the sodium hydroxide solution can be specified as preferred. A particularly preferred concentration range is 1 to 3 wt.%.

[0025] After step (ii) and before the subsequent step (iii), it is advisable to dry the residual fraction, for which known drying processes can be used. Examples of suitable drying devices include fluidized-bed dryers, circulating-air dryers, or adsorption dryers. Before drying, it may also be expedient to wash the polyolefin residual fraction derived from step (ii) with water in order to remove the alkaline medium used in step (ii) as completely as possible. This applies in particular if the alkaline medium contains inorganic constituents that can only be removed from the polyolefin residual fraction with considerable effort in the subsequent process steps.Since drying occurs by evaporation or vaporization of water from the alkaline aqueous solution, it is also advisable to subject the residual fraction to mechanical dewatering before drying in order to minimize the retention and carryover of components dissolved in the water as far as possible.

[0026] After the drying process described above, it may also be useful to subject the polyolefin waste fraction to an air separation step, which allows label residues to be separated. Air separation is particularly useful for waste fractions containing printed or otherwise heavily soiled labels or plastic films. Since these are generally very thin compared to particles from plastic packaging, a significant portion of them can be separated from the main components of the waste fraction using air separation.

[0027] In step (iii) of the process according to the invention, the polyolefin residue fraction is subjected to flake sorting, whereby the material is primarily sorted by color. Thus, during flake sorting, particle mixtures, in particular, can be separated into colorless / transparent particles, white particles, and residual colored particles. Furthermore, it is also possible to further separate the colored particles by color.

[0028] The flake sorting system is designed to effectively remove residual components of materials that do not correspond to the main material of the residual fraction introduced into the flake sorting system. For example, if the residual fraction contains HDPE as its main component, residual components of polypropylene or other polyolefin plastics, as well as remaining residues of other plastics or non-plastics, can be separated during appropriate flake sorting. Furthermore, it is possible to separate heavily contaminated or printed particles, particularly for obtaining transparent or white particles, in order to avoid unwanted discoloration during further processing.

[0029] The device used for flake sorting is preferably a sensor-based sorting system. Sensor-based sorting systems can consist of a belt section for separating and settling the material, one or more detectors arranged below or above a conveyor belt or in the material discharge area, and a nozzle bar for discharging the material component to be positively sorted. Alternatively, the material can be distributed via vibrating chutes onto steeply inclined chutes, at the end of which the particles are guided past the detectors in free fall.

[0030] Particle sorting, particularly for separating particles made of different materials, is best achieved using NIR (near infrared) detectors. Conventional color cameras can also be used to separate particles of different colors. For the colored fractions, it may also be useful to implement a post-sorting step to ensure compliance with a defined color spectrum. In standard operation, a detection unit initially simply measures the color composition and compares it with a color standard without removing any particles. Sorting only begins when the color composition deviates from the color standard beyond a defined tolerance range, with particles of the excess color being removed.

[0031] Suitable devices for flake sorting are sold, for example, by Bühler GmbH under the name SORTEX or by Steinert Global under the name UniSort.

[0032] As stated above, mixed-color starting products that exhibit a relatively homogeneous color distribution can be incorporated into the process according to the invention. Thus, a mixed-color starting product that contains, for example, 20 to 45 wt.% transparent, 20 to 45 wt.% white, and 20 to 45 wt.% residual colored components can be subjected to flake sorting. Since conventional color sorters are optimized for separating relatively small proportions of off-colors (e.g., <5%) from a feed stream, the color purity required for acceptable product quality cannot easily be achieved with such color sorters.

[0033] In the course of the investigations underlying this application, it was surprisingly found that a high level of color purity can be ensured when using starting materials with a strong color mix by connecting several color sorters in series. Therefore, if the starting material contains significant proportions (20 wt. % or more, based on the total weight of the target polymer to be sorted in the starting material) of components that do not correspond to the main color of the starting material (e.g. 20 wt. % residual colored and 80 wt. % white particles), the use of two color sorters connected in series is advantageous in order to increase the color purity of the product obtained from the first color sorter to a reasonable level. If the starting material contains significant proportions (i.e. 10 wt.-% or more, based on the total weight of the target polymer to be sorted in the starting material) of white, transparent and colored components, it is also preferred if, as part of the flake sorting, white and transparent components are separated from residual colored components in a first step and then, in a second step, the white components are separated from the transparent components.

[0034] One problem with currently available color sorters is their coordination, which ensures that desired components remain in the product while undesired components are selectively removed from the mixture. Technically, color sorters cannot be adjusted to produce a product with high yield and high purity (> 95%) in one or more color sorters connected in series. A certain degree of over-sorting, i.e., the incorrect discharge of desired components with undesired components, cannot be technically avoided.

[0035] A particularly favorable separation result in the sense of a product with good color quality (i.e. a proportion of false-colored particles of preferably about 2% or less and in particular about 1% or less) and a high yield can be achieved according to the invention by a unit of three color sorters, in which the first color sorter separates a desired color component (e.g. white / transparent) from an undesired color component (e.g. residual color). Due to the missorting that is unavoidable in conventional color sorters, the fractions of the desired and undesired color components obtained from this color sorter still contain significant residual proportions of undesired and desired color components, respectively. The fraction with predominantly the desired color component is therefore fed to a second color sorter, which re-sorts the product obtained from the first color sorter and there further increases the proportion of the desired color component.Finally, the unit provides a third color sorter to which the fraction with predominantly undesired color component from the first color sorter is fed and in which the proportion of the undesired color component is further increased.

[0036] The enriched, unwanted color component obtained in the third color sorter can then expediently be fed to a further unit, as described above, in which a further color component (e.g., red / yellow) is separated from it according to the same scheme. The sorted fractions obtained in the second and third color sorters, however, each still contain significant proportions of the desired color fraction and are therefore fed back to the first color sorter as starting material. If the color component contains multiple colors (e.g., white / transparent), the enriched, unwanted color component obtained in the second color sorter is expediently fed to a further unit, as described above, in which a further color component (e.g., transparent) is separated from it.

[0037] If the starting material to be separated is a mixture of more than three differently colored components, e.g. a mixture of white / colorless / red / yellow / green / blue components, the separation preferably comprises at least two units, as described above, wherein in the first unit a color pair, e.g. white / colorless, is separated from the remaining colored components and in the second unit the color pair is separated into the individual colored components. The separation of a color pair in the first unit (instead of just material of one color) has the advantage that, with mixtures that are approximately evenly distributed in terms of color, the quantity of particles to be sorted out and the quantity to be left in the mixture is more similar, which enables better quantity management in the overall plant.

[0038] If the residual colored components also contain multiple colors, e.g., red / yellow / green / blue components, it is advantageous to provide a further unit in which a further color pair, e.g., red / yellow components, can be separated from the residual colored components (e.g., green / blue). For mixtures containing white / colorless / red / yellow / green / blue components, it is particularly preferred to separate 1. white / colorless, 2. red / yellow, and 3. green / blue components in this order. Furthermore, for each of the color pairs thus obtained, a further unit of three color sorters, as described above, is preferably provided, in which the color pairs are separated into their individual colored components.

[0039] The described units of color sorters and arrays of several of these units offer the advantage over previously available separation processes that almost uniformly distributed mixtures can be separated into several defined products with high purities. In a comparable arrangement with only color sorters arranged in a linear series, however, either the yield losses or the number of required separation steps would be very high, which would severely impair the cost-effectiveness of the separation.

[0040] In addition to the aforementioned color sorting units, it is possible to incorporate additional individual color sorters into the purification of the polyolefin residue fraction. Such color sorters can be used, for example, to further reduce off-color components in the purified pure-color fractions in order to further improve product quality.

[0041] Following flake sorting in step (iii), the resulting polyolefin residue fractions are subjected to a treatment in step (iv), as described above, at a temperature in the range of 50 to 155°C, with this treatment preferably being carried out for a period of at least 60 minutes. This treatment is intended to remove as much as possible any pollutants, migration products, or contaminants contained in the polyolefin residue fraction that have diffused into the outermost layer of the container.

[0042] The process parameters depend on the inertness and the chemical and physical properties of the respective polymer. For example, it is important to ensure that the treatment temperature is as high as possible above the glass transition temperature, but lower than the melting temperature of the plastic being treated. This ensures, on the one hand, that the molecular chains have sufficient mobility to release migrating substances, but, on the other hand, that they do not melt or soften, which would lead to clumping of the individual particles.

[0043] The following can be specified as suitable temperature ranges for the most common polyolefins HDPE, LDPE and polypropylene: HDPE: 50 to 130 °C, preferably 90 to 122 °C, most preferably 110 to 115 °C LDPE: 50 to 110 °C, preferably 75 to 105 °C Polypropylene: 50 to 155 °C, preferably 100 to 150 °C

[0044] The residence time ensures that the material is cleaned to a minimum. The residence time depends on various criteria, such as the diffusion rate of the migration products in the respective polymer and the softening or melting temperature of the polymer. As stated above, the residence time for the most complete removal of migration products should be at least about 60 minutes. The residence time is preferably at least about 120 minutes, but should not exceed a residence time of about 600 minutes, since with polyolefins, no further improved removal of migration substances is generally observed at residence times of more than 600 minutes. A period of about 180 to 360 minutes and in particular 180 to 240 minutes can be stated as a particularly suitable residence time within the scope of the invention.

[0045] The separation of migrating substances during step (iv) can be positively influenced by applying a vacuum. Applying a vacuum also has the advantage that the migrating substances can be removed from the device in which the heat treatment is carried out via the vacuum, and that the plastics are not exposed to an oxygen-containing atmosphere at the high temperatures, which could cause oxidative damage to the plastics. If the heat treatment is carried out under vacuum, a pressure of ≤ 150 mbar, preferably ≤ 50 mbar, in particular ≤ 20 mbar, and most preferably between 0.1 and 2 mbar, should be used.

[0046] Since oxidative damage can also be suppressed by conducting the heat treatment in an inert gas, the treatment in step (iv) can also be carried out in an inert gas atmosphere. The term "inert gas atmosphere" does not necessarily mean that the inert gas must be present throughout the entire device. Rather, it is sufficient if the inert gas is present in the area of ​​the device directly surrounding the heated particles. Nitrogen and argon are particularly suitable inert gases, although nitrogen is preferred for cost reasons.

[0047] Devices suitable for temperature treatment are marketed, for example, by Erema (AT) under the name VACUREMA.

[0048] Between steps (iii) and (iv), the residual fraction obtained from step (iii) is expediently fed to an extrusion device to produce polyolefin granules. This device can be designed so that the particles obtained from step (iii) are merely plastically deformed into granules, but it is also possible for additives, e.g. in the form of colorants or pigments, to be added during extrusion. In connection with polypropylene, for example, conventional additives for compounding, such as peroxides or talc, can also be added during extrusion. Since the extrusion of polypropylene into which such additives have been incorporated produces odors that can be perceived as unpleasant by the consumer, it is advantageous in this case if the extrusion is carried out before step (iv), since the odors formed can be at least partially removed there.This reduces unpleasant odors even compared to virgin polypropylene compounded with talc.

[0049] During extrusion, the material can also be degassed by applying a vacuum and freed from volatile components in the polyolefin melt. However, it should be noted that such degassing cannot replace the heat treatment in step (iv), because the degassing would have to be carried out for a period that would not allow for economical operation of the extrusion device.

[0050] If the residual fraction obtained from step (iii) is fed to an extrusion process, the extrusion device is advantageously arranged directly upstream of the heat treatment device in step (iv), since the material has already been heated there. Since the heat treatment is also carried out at elevated temperature, less energy is required with such an arrangement than if the material were to first cool after extrusion and then be reheated to the temperature required for the heat treatment. Measures such as transport equipment, insulation, additional vacuum in the transfer area, etc., can be taken to prevent energy losses during transport steps between the extruder and the treatment vessel.

[0051] In individual cases, it may also be possible to perform extrusion into granules only after steps (iii) and (iv). However, this has the disadvantage that the residual fraction prior to granulation usually still contains small particles such as film fluff, which can be removed during heat treatment under vacuum. Such a process would therefore require the installation of filters, which would also have to be cleaned at relatively short intervals. Furthermore, the polyolefin particles have a relatively large volume prior to processing into granules, which limits the throughput through the heat treatment device.

[0052] A further disadvantage of extrusion after step (iv) is that the thermal stress on the material during extrusion can regenerate substances that lead to an unpleasant odor in the product. Such substances can be reduced via step (iv) in extrusion prior to step (iv); however, this is not possible in extrusion after step (iv).

[0053] One would expect that processing into granules prior to heat treatment would have an adverse effect on the product properties and the required heat treatment time. For example, during extrusion, migrating substances can produce decomposition products that are difficult to remove from the granules. For example, migrating substances are generally present on the surface of the particles and should therefore be easier to remove via heat treatment than migrating substances that have become dispersed within the granule particles as a result of extrusion. Surprisingly, however, it was found that these effects have only a minor impact on the product and are more than offset by the advantages of granules for heat treatment.In addition, due to its more compact structure, granules cool down less quickly than the polymer material before granulation, so that when the granules are fed directly into the temperature treatment in step (iv), less energy is required overall for granulation and temperature treatment than when the process is carried out in reverse.

[0054] The investigations underlying the present invention have shown that it is essential for the quality of the resulting product that steps (ii) and (iii) are carried out before step (iv) and that a granulation step, if included, takes place after flake sorting. Furthermore, it is essential for the process that the hot wash is carried out before the heat treatment.

[0055] As stated above, the present invention also relates to a process in which steps (ii) and (iii) are carried out in reverse order. In this case, for example, flake sorting (iii) can be carried out before hot washing (ii), hot washing (ii) before granulation, and granulation before temperature treatment (iv). Likewise, in this embodiment, the present invention relates to a process in which flake sorting (iii) is carried out before hot washing (ii), hot washing (ii) before temperature treatment (iv), and temperature treatment (iv) before granulation.

[0056] However, the latter process is associated with the same disadvantages compared to the former process as described above for a process with heat treatment (iv) prior to granulation. The above statements apply analogously to preferred embodiments of hot washing, flake sorting, heat treatment, and granulation.

[0057] With regard to the sequence of the individual reaction steps, in one embodiment a process comprising the sequence of hot washing (step ii), flake sorting (step iii), granulation and temperature treatment (step iv) is particularly preferred.

[0058] Without the applicant being able to rely on a specific theory, it is suspected that polyolefin residues from consumer products contain impurities, e.g., in the form of imprints, which are initially detached from the polyolefin particles during the hot-washing process. It is also possible that the polyolefin residues contain labels made of other polyolefins, e.g., polypropylene, which are detached from the main product during the hot-washing process. Even if these labels are essentially removed from the pretreated material by air separation, small amounts of the labels may remain in the material.If this material is subsequently subjected to direct thermal treatment, the residues may re-adhere, particularly if the label material has a softening point or glass transition temperature that is below or close to the temperature at which the polyolefin residues are treated in step (iv). Such adhesions may be more difficult to detect in a downstream flake sorting process, resulting in a more contaminated product than in a procedure involving the sequence of hot washing (step ii), flake sorting (step iii), and thermal treatment (step iv).

[0059] In another embodiment, a process sequence comprising flake sorting (step iii), hot washing (step ii), granulation, and heat treatment (step iv) is particularly preferred. This embodiment is particularly advantageous when there are only buyers for some of the products (e.g., white but not residually colored or transparent products). Since hot washing involves a relatively high energy expenditure, it may be expedient to reduce the amount of material to be purified by hot washing via flake sorting in order to further purify only that material via hot washing for which there is a relevant market.

[0060] The process according to the invention can be carried out batchwise or partially batchwise by performing all or some of steps (i) to (iv) with individual batches of the polyolefin residues. However, since this involves greater technical complexity and downtime for individual device components, it is preferred if steps (i) to (iv) are carried out continuously.

[0061] A further aspect of the present invention relates to a polyolefin recyclate obtainable by the process described above. This recyclate is preferably an LDPE, HPDE, or polypropylene recyclate. Short description of the drawings

[0062] Figure 1 describes a unit 1 of three color sorters 2, 3, and 4.Polyolefin residue fraction is fed into the unit via the feed line 5. In the first color sorter 2, the polyolefin residue fraction is separated into a desired color fraction 6 (e.g. white / transparent) and an undesired color fraction 7 (e.g. residual paint) separated. The desired color fraction 6 is then sent to the second color sorter 3 in which residual portions of the unwanted color fraction 9 separated from the mixture and a further purified desired color fraction 8 The unwanted color fraction obtained in the first color sorter 7 is assigned to the third color sorter 4 in which residual parts from this desired colour fraction 11 obtaining a purified fraction of undesired color fraction 10 from the mixture 7 The proportions of the desired color fraction 11 and undesired color fraction9 are then placed in the first color sorter 2 redirected. Figure 2 describes a construction with two units connected in series 1 and 12, where in the first unit 1 with three color sorters 2A, 3A and 4A a color pair (e.g. white / transparent) is separated from the mixture of polyolefin residue fraction. The color pair obtained from the first unit is then fed via the feed line 8 into the second unit 12 in which the color pair is separated into its individual components (ie white on the one hand and transparent on the other). The color pair passes through the same process as the first unit 1 three color sorters 2B, 3B and 4B. The product consists of the very pure individual components of the color pair 13 (e.g. transparent) and 14 (e.g. white). The third color sorter 4Athe purified residual fraction produced in the first unit 1 10A is added to another color sorting unit 15 and further purified there, whereby this unit is constructed analogously to the units 1 and 12. Example:

[0063] Separation of a polyolefin residue mixture with a proportion of white / transparent and residual colored flakes of 34%, 34% and 32%, respectively.

[0064] The specified mixture is added to a first unit 1 from three color sorters 2A, 3A and 4A In the first color sorter, residual colored flakes are separated from the mixture, so that a purified fraction of white / transparent flakes 6A with a distribution of white / transparent / residual color of approximately 47.5% / 47.5% / 5%. The sorted mixture 7Aconsists of white / transparent / residual colored flakes with a distribution of approximately 20% / 20% and 60%. The purified white / transparent fraction 6A is sent to the second color sorter 3A where the fraction is further purified. This produces a pure fraction 8 with a distribution of approximately 49.5% / 49.5% / 1% of white / transparent / residual colored flakes. The secondary fraction obtained during the second purification 9A has a distribution of approximately 40% / 40% / 20% white / transparent / residual coloured flakes and is fed into the first colour sorter 2A The sorted mixture 7A from the first color sorter 2A is in the third color sorter 4A and there into a fraction of predominantly residual colored flakes 10A (Distribution white / transparent / residual colour 2.5% / 2.5% / 95%) and one fraction 11A,in which transparent and white flakes are enriched (distribution white / transparent / residual color 32.5% / 32.5% / 35%). This enriched fraction 11A is also in the first color sorter 2A redirected.

[0065] The mixture 8 of transparent / white flakes obtained in the first unit is sent to a second separation unit 12 with three color sorters 2B, 3B and 4B In the first color sorter 2B white flakes are separated from transparent flakes, whereby a fraction enriched in transparent flakes 6B (Distribution white / transparent / residual colour 6% / 93% / 1%) and a fraction enriched in white 7B (Distribution white / transparent / residual color 66% / 33% / 1%). The fraction enriched in transparent flakes 68 is in the second color sorter 3B to obtain a mixture 13white / transparent / residual coloured flakes 6% / 93.5% / 0.4% and a residual fraction 9B further purified with a distribution of white / transparent / residual color 6% / 88% / 6%.

[0066] The fraction enriched in white flakes 7B is a third color sorter 4B in which a white color fraction 14 with a distribution of 95% / 3.5% / 1.5% white / transparent / residual coloured flakes and a residual fraction 11B with a distribution of 39% / 60.5% / 0.5% white / transparent / residual colored flakes. The residual fractions 9B and 11B from the second and third color sorter 3B and 4B are in the first color sorter 2B the second unit. If necessary, the color sorter can 4B Another color sorter can also be installed downstream to reduce the proportion of residual colored flakes in the white color fraction to below 1%.

Claims

1. A method for producing a polyolefin recyclate, suitable for production of consumer products, from mixed-color, polyolefin-containing wastes, comprising the steps of (i) treating a mixed-color polyolefin waste fraction with water, without supplying thermal energy, (ii) treating the polyolefin waste fraction obtained from (i) by washing with an alkaline medium at a temperature of at least 60°C, (iii) flake-sorting the polyolefin waste fraction obtained from (ii) to obtain one or more single-color polyolefin waste fractions, each comprising a polyolefin in concentrated form, wherein steps (ii) and (iii) may also be carried out in the opposite order, (iv) treating the one or more single-color polyolefin waste fractions obtained from the preceding steps, at a temperature in the range from 50 to 155°C, preferably for a period of at least 60 minutes, wherein the waste fraction to be included as a starting material into the inventive process contains white, transparent and residual colored components in a proportion of 20 to 45 wt% in each case, wherein the waste fraction to be included in the method comprises packaging from different applications including shampoo and food packaging and wherein the starting material prior to step (i) is subjected to one or more comminuting steps.

2. The method as claimed in claim 1, characterized in that the one or more single-color polyolefin waste fractions are supplied to an extrusion apparatus for producing polyolefin granules between steps (iii) and (iv) or after step (iv), preferably between steps (iii) and (iv).

3. The method as claimed in claim 1 or 2, characterized in that the proportion of the waste fraction accounting for the main color of the waste fraction is not more than 40 wt%.

4. The method as claimed in claim 3, characterized in that in the flake-sorting in step (iii), the polyolefin waste fraction is subjected to separation using a unit (1) comprising three color sorters, wherein the polyolefin waste fraction is supplied to a first color sorter (2), in which a desired color component (6) is separated off from an unwanted color component (7); the desired color component (6) contained in the first color sorter is supplied to a second color sorter (3), in which the product obtained from the first color sorter is resorted, and the proportion of desired color component therein is increased further; and the unwanted component obtained in the first color sorter is supplied to a third color sorter (4), in which the proportion of the unwanted color component is increased further; and wherein the fractions (9, 11) sorted out in the second and third color sorters are supplied again to the first color sorter as starting material.

5. The method as claimed in claim 4, characterized in that the flake-sorting in step (iii) incorporates a plurality of units comprising three color sorters in accordance with the mandates from claim 4.

6. The method as claimed in either of claims 4 and 5, characterized in that the polyolefin waste fraction contains more than three colors and, via units (1, optionally 15) comprising three color sorters (2, 3, 4), respective color pairs are separated off from the polyolefin waste fraction, and the color pairs are separated into the corresponding color constituents in a respective downstream unit (12).

7. The method as claimed in any of the preceding claims, characterized in that the polyolefin is polyethylene or polypropylene, preferably HD-polyethylene.

8. The method as claimed in any of the preceding claims, characterized in that the treating of the polyolefin waste fraction in step (ii) takes place at a temperature of at least 70°C, preferably in the range from 80 to 90°C.

9. The method as claimed in any of the preceding claims, characterized in that the alkaline medium in step (ii) is aqueous sodium hydroxide solution with a concentration of less than 10 wt%, preferably with a concentration in the range from 0.5 to 5 wt%, and more particularly with a concentration in the range from 1 to 3 wt%.

10. The method as claimed in any of the preceding claims, characterized in that as part of the flake-sorting in step (iii), particles not consisting of polyolefin and particles having color deviations relative to the numerical majority of the particles in the polyolefin waste fraction are separated off.

11. The method as claimed in any of the preceding claims, characterized in that for the treating according to step (iv) a vacuum of ≤ 150 mbar, preferably ≤ 50 mbar, more particularly ≤ 20 mbar, and most preferably between 0.1 and 2 mbar is applied.

12. The method as claimed in any of the preceding claims, characterized in that the treating according to step (iv) is carried out in an inert gas atmosphere, preferably in a nitrogen atmosphere.

13. The method as claimed in any of the preceding claims, characterized in that the treating according to step (iv) is carried out for a period of 120 to 300 minutes and preferably 180 to 240 minutes.

14. The method as claimed in any of the preceding claims, characterized in that the polyolefin-containing wastes are subjected before step (i) to a preliminary sorting by color.

15. The method as claimed in any of the preceding claims, characterized in that the polyolefin waste fraction obtained from step (ii) is subjected to subsequent drying and to treatment in a pneumatic classifier.