HK40004265B - Method for producing polyolefin recyclates - Google Patents

Description

Method for producing polyolefin recycled materials

Technical Field

The present invention relates to an improved method for producing polyolefin regrind, in particular HDPE and PP regrind.

Background Art

Polyolefins are stable, flexible plastics with many uses due to their easy processing and chemical resistance, and are the largest single category of consumer plastics in Europe at around 45%.

By far the largest application area for polyolefin plastics is packaging. The ubiquity of plastic packaging makes it a constant focus of environmental debate. Without an appropriate collection, sorting, and recycling infrastructure, plastic packaging can become a problem, as the debate over marine pollution demonstrates. Over the past 25 years, EU packaging directives and corresponding national legislation have initiated such infrastructure across Europe to varying degrees. In Germany, this involves a collection system for yellow bags/cans and the associated concepts and systems for sorting and recycling. The long-term capacity of this infrastructure and its expansion into other countries clearly depends on industry's demand for recycled plastics; the higher the quality of the recycled material supplied, the better its development.

With PET packaging, this is now possible in a so-called closed loop, in which the packaging plastic is used again to produce the packaging in the next cycle of use. The problem with polyolefins is that they are processed from standard recycling processes with mixed colors, which are also reproduced in the recycled material. Therefore, depending on the composition of the raw materials, the end products produced in this way have different gray tones. Since the recycling methods available to date also leave residual impurities on polyolefin plastics, the resulting products emit a typical recycled material odor, which excludes applications close to the end user. As a result, polyolefin plastics are now mainly associated with "open-loop" applications far from the end user, that is, the recycled material is not used as packaging again, but is processed into durable plastic products, for example in the construction sector.

Foreign substances absorbed in small amounts during the initial use of polyolefin plastics are particularly problematic for the recycling of polyolefin plastics. For example, polyethylene packaging for shampoo can absorb non-polar substances from the shampoo, such as perfume, which cannot be removed by simple washing with water. If such polyolefin regrind is exposed to high thermal loads (such as during extrusion), these migrating substances decompose, which is a significant contributor to the odor of typical regrind.

Furthermore, a particular problem with polyolefin packaging materials is that, compared to, for example, PET beverage packaging, these do not appear as raw materials with a relatively uniform color. This results in products with different gray tones when using conventional sorting methods, as described above.

An exception is the special collection system for uniform packaging, for example in the form of milk bottles, which are collected separately from other beverage packaging in supermarkets, for example in the UK. However, the majority of polyolefin packaging (which usually contains not only polyolefin packaging of different colors, but also significant proportions of other plastics and foreign matter such as metal, wood or paper) is simply sorted by material type (e.g. "PE") and, as mentioned above, is usually pelletized after shredding and washing with cold water and used in applications far from the end user at a profit level that is usually significantly lower than the price of virgin material.

The long-term trend of rising raw material prices and the pressure on the consumer goods industry to adapt to the growing demand for sustainably manufactured products have led to a need for a method by which polyolefin packaging waste, particularly from private households, can be prepared for reuse in packaging for end consumers. To this end, the method should provide a regrind product that is as pure as possible and can be fed back for extrusion without producing unpleasant odorous by-products. Furthermore, the method should be uncomplicated and cost-effective to carry out, even at high throughputs, in order to produce a product that is competitive on the market. The present invention addresses this need.

SUMMARY OF THE INVENTION

In general, the present invention discloses a method for producing polyolefin regrind from mixed color waste containing polyolefins. The disclosed method is particularly suitable for separating polyolefins from contaminants that have become embedded in the polyolefins due to migration processes, but the method can also separate contaminants that adhere to the surface of the polyolefins or are present in mixtures with the polyolefins.

In particular, the present invention relates to a method for producing polyolefin recycled material from mixed color waste containing polyolefin, wherein the polyolefin recycled material is suitable for manufacturing consumer products, the method comprising the following steps:

(i) treating the mixed-color polyolefin residue fraction with water without supplying thermal energy,

(ii) treating the polyolefin residue fraction obtained from (i) within the scope of washing with an alkaline medium at a temperature of at least 60° C.,

(iii) fractionating the polyolefin residue fraction obtained in step (ii) to obtain one or more pure polyolefin residue fractions, in which the polyolefin is present in concentrated form, wherein steps (ii) and (iii) can also be carried out in the reverse order,

(iv) treating the pure polyolefin residue fraction obtained from the above step at a temperature in the range of 50 to 155°C, preferably for a period of at least 60 minutes.

If it is stated above that steps (ii) and (iii) can also be carried out in the reverse order, this is to be understood as meaning that, in the case of water treatment (i) without supply of thermal energy, the polyolefin residue fraction obtained from the water treatment is subjected downstream to fragmentation (to give one or more pure polyolefin residue fractions) and subsequently to treatment within the context of washing with an alkaline medium at a temperature of at least 60° C. The treatment described in (iv) is then downstream of this washing.

The polyolefin residue fraction used as a starting material in the process according to the invention can be a residue fraction from any conceivable polyolefin or polyolefin mixture. However, it is preferred that the polyolefin residue fraction be a material whose predominant proportion, i.e., at least 75% by weight, preferably at least 80% by weight, and particularly preferably at least 90% by weight, consists of polyolefins of the same base polymer. Suitable base polymers are homopolymers such as polypropylene or polyethylene, but also copolymers of ethylene or propylene with other α-olefin monomers. With regard to polyethylene, the various known variants such as HDPE, LDPE, or LLDPE are each considered to be a separate base polymer. Particularly preferred polyolefins within the scope of the present invention are variants of polypropylene and polyethylene, in particular in the form of LDPE and HDPE, preferably HDPE.

Pre-sorted waste fractions according to their main plastic content can advantageously be used as starting material for the method. These pre-sorted waste fractions can be obtained from conventional waste sorting plants. These pre-sorted waste fractions are commercially available, for example, in the form of extruded bales and consist primarily (approximately 90 to 95%, based on the plastic fraction) of one or more defined plastic base polymers (e.g., PP, HDPE, or LDPE).

Within the scope of the method according to the present invention, it is also possible to use separately collected scraps, such as milk bottles. Because these separately collected scraps usually have significantly more uniform pollution, when preparing these scraps, the method according to the present invention cannot fully utilize its advantages. Therefore, the scrap fraction included in the method according to the present invention preferably at least comprises polyolefins of different colors. Within the scope of the present invention, transparent, white and black polyolefin products should also be considered as colored. Particularly preferably, the proportion of the scrap fraction that constitutes the main color of the scrap fraction is no more than 80 weight %, especially no more than 60 weight %, most preferably no more than 40 weight %. In addition, it can be preferred that the scrap fraction included in the method according to the present invention comprises transparent, white and other color (restfarbige) polyolefin products, preferably having a ratio of about 10 to 60 weight % transparent products, about 10 to 60 weight % white products and about 10 to 60 weight % of the other color products, and particularly preferably having a ratio of about 20 to 45 weight % transparent products, about 20 to 45 weight % white products and about 20 to 45 weight % of the other color products.

Furthermore, it is preferred that the waste material comprises packaging from different applications (eg shampoo packaging and food packaging), since these waste material fractions are contaminated with a wider range of contaminants, allowing the advantages of the method according to the invention to be fully exploited.

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 impurities of the polyolefin, for example in the form of food residues, salt or paper labels. For this reason, it is generally not necessary to heat the water or modify it with additives before the washing process. Since there is no thermal energy supply, the temperature at which this washing is carried out depends on the input of mechanical energy and the external temperature and is usually 30°C or lower. However, depending on the degree of contamination and the contaminating components present, cold washing can also be replaced by mechanical dry cleaning in individual cases, for example by adding a grinding component and then subjecting the mixture to vigorous movement. The contaminants can be removed from the surface by collision with the polyolefin component. The grinding component can then be separated from the polyolefin again, for example by means of a float/sink method, in which the polyolefin floats on the water due to its density, while the grinding component sinks.

Washing in step (i) is facilitated by subjecting the raw material to one or more comminution steps before cold washing. This is particularly useful when the raw material comprises packaging with cavities, as comminution ensures that the wash water comes into contact with the entire surface of the packaging. Comminution can conveniently be performed in a pulverizer, cutter mill, or similar comminution equipment. Comminution can be performed wet (i.e., with the addition of water or water vapor) or dry. Furthermore, comminution can be performed in a two-stage or multi-stage process, in particular a two-stage process, preferably with a first stage designed as a dry process and a second stage as a wet process.

The average particle size achieved by comminution should be at most approximately 20 mm, in particular at most 15 mm, but preferably at least 2 mm, and in particular at least 4 mm. Particularly advantageous particle sizes are in the range of approximately 5 to 10 mm. The particle size here refers to the largest spatial dimension of the respective particle.

The particle size distribution may vary. However, ideally, at least 80% (±10%) of the particles should have a particle size within the specified range.

In addition, it may be meaningful to subject the raw materials to a physical step of removing loose contaminating components before the treatment in step (i). For example, loose metal or glass components can be removed from the raw materials by means of a magnet, by sucking out magnetic metal components from the raw materials, or by utilizing the large specific gravity of the contaminants. Since polyolefins are lighter than glass or metal, the raw materials can be transported through the gaps by means of a conveyor belt, the size of which is designed to allow the contaminants to fall into the gaps while simultaneously transporting the lighter polyolefin components across the gaps. The material stream can also be fed from below by means of an airflow, through which the lighter components are driven upward. Since the heavier components are subject to less buoyancy, they can be well separated from the lighter components by such equipment. Finally, the fact that polyolefins are lighter than water can also be utilized to remove components with greater specific gravity using a float/sink method. Therefore, within the scope of this method, the polyolefin component is obtained as a fraction floating on the water, while components such as glass and metal sink in the water and can be separated as sediment.

It is convenient to separate the above-mentioned components with high specific gravity downstream of the raw material comminution, because a more uniform raw material is obtained. In addition, the advantage of comminution upstream is that impurities located in the cavities of the polyolefin raw material before comminution can also be removed.

It may also be convenient to roughly sort the raw materials by color and/or polymer before comminution, with a particular rough division into transparent, white, and (other) colored components, as well as polymer type. "Rough" color sorting should be understood as sorting the raw materials by their primary color, with mixed-color consumer products being assigned to the color fraction corresponding to their primary color. A similar approach applies to "rough" polymer sorting, which involves sorting by primary polymer. For example, HDPE bottles often use PP caps; in this case, these bottles would be classified as HDPE polymer.

In order to avoid entrainment of contaminated wash water, it is expedient to mechanically dewater the polyolefin residue fraction from step (i) as completely as possible before it is subjected to subsequent treatment steps.

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 adhesive residues or printed labels adhering to the raw material, while also removing residual contaminants that cannot be separated from the raw material during cold washing. The term "printed label" refers, for example, to inks printed directly on packaging such as water or shampoo bottles. For example, non-alcoholic beverage bottles are typically printed with epoxy-based inks. Furthermore, the alkaline treatment removes polymer coatings based on acrylates or ethylene vinyl alcohol (e.g., EVOH films).

Step (ii) is conveniently carried out at a temperature of at least 60°C, in particular at least 70°C and preferably in the range of 80 to 90°C, most preferably 80 to 85°C. Alternatively or additionally, it is preferred for step (ii) that the alkaline medium is an aqueous alkali metal solution, in particular an aqueous caustic soda or caustic potash solution, preferably an aqueous caustic soda solution. The concentration of the caustic soda solution, in terms of sodium hydroxide, should not exceed 10% by weight, as this generally places higher demands on the equipment performing step (ii). Since it has been shown that most impurities can be removed at lower sodium hydroxide contents, the concentration range of the caustic soda solution can preferably be 0.5-5% by weight. A particularly preferred concentration range is 1 to 3% by weight.

After step (ii) and before the subsequent step (iii), it is meaningful to dry the residual fraction, for which known drying methods can be used. Examples of suitable drying devices are, for example, fluidized bed dryers, circulating air dryers or adsorption dryers. Before drying, it is also advantageous to wash the polyolefin residual fraction derived from step (ii) with water to completely remove the alkaline medium used in step (ii) as much as possible. This is particularly applicable when the alkaline medium contains inorganic components, which can only be removed from the polyolefin residual fraction at a great expense in subsequent process steps. Since drying is carried out when water is evaporated or gasified from an alkaline aqueous solution, it is also advantageous to subject the residual fraction to mechanical dehydration before drying in order to minimize the retention and entrainment of components dissolved in water as much as possible.

After the aforementioned drying, it may also be useful to subject the polyolefin residue fraction to airflow sorting, which is capable of separating label residues. Airflow sorting is particularly advantageous for residue fractions containing printed or otherwise heavily soiled labels or plastic films. Since these are generally very thin compared to the pellets made from plastic packaging, they can be separated from a significant proportion of the main components of the residue fraction by airflow sorting.

In step (iii) of the method according to the invention, the polyolefin residue fraction is subjected to a chip classification, wherein the material is first classified according to color. Thus, within the scope of the chip classification, in particular, a particle mixture can be separated into colorless/transparent particles, white particles, and particles of other colors. Furthermore, a further separation of the colored particles can be performed according to color.

The chip classification is advantageously designed so that residual components of materials that do not correspond to the main material of the residue fraction introduced into the chip classification can also be removed. If the residue fraction contains, for example, HDPE as its main component, residual portions of polypropylene or other polyolefin plastics, as well as existing residual materials of other plastics or non-plastics, can be separated out in the corresponding chip classification. Furthermore, in particular to obtain transparent or white pellets, heavily contaminated or printed pellets can be separated out to prevent undesirable discoloration during further processing of the pellets.

The device for sorting the fragments is preferably a sensor-based sorting system. This sensor-based sorting system can consist of a belt segment for singulating and settling the material, one or more detectors arranged below or above the conveyor belt or in the material disposal area, and a nozzle track for discharging the material components that are preferably to be sorted. Alternatively, the material can be distributed over a steep slide channel via a vibrating chute, at the end of which the particles fall freely near the detectors.

NIR (near-infrared) detectors are convenient for particle sorting, especially for separating particles of different materials. Conventional color cameras can also be used to separate particles of different colors. Furthermore, for the colored fraction, a subsequent sorting step that ensures adherence to a defined color spectrum is also useful. Here, the color composition is first measured by the detection unit in standard operation and compared to a color standard without rejecting the particles. Only when the color composition deviates from the color standard by more than a fixed tolerance range is it sorted, with particles with excessive color being rejected separately.

Suitable devices for sorting fragments are sold, for example, by the company Bühler GmbH under the name SORTEX or by the company SteinertGlobal under the name UniSort.

As described above, the method according to the present invention can include mixed-color raw material products with a relatively uniform color distribution. Thus, a mixed-color raw material product having, for example, 20 to 45% by weight of transparent, 20 to 45% by weight of white, and 20 to 45% by weight of other color components can be subjected to fragment sorting. Because conventional color sorters are optimized for separating relatively small proportions (e.g., << 5%) of foreign colors from the feed stream, it is not possible to simply achieve the color purity required for acceptable product quality using such color sorters.

Within the scope of the research that forms the basis of this application, it has been surprisingly determined that when using raw materials that will be seriously mixed in color, high color purity can be ensured by connecting a plurality of color sorters one after another. Therefore, if the raw material contains a significant proportion (20% by weight or more based on the total weight of the target polymer to be sorted in the raw material) of particles that do not correspond to the main color of the raw material (for example 20% by weight of the remaining color particles and 80% by weight of white particles), it is convenient to use two color sorters connected one after another to increase the color purity of the product obtained from the first color sorter to a satisfactory range. If the raw material contains a significant proportion (i.e. 10% by weight or more based on the total weight of the target polymer to be sorted in the raw material) of white, transparent and colored components, it is also preferred that within the scope of fragment sorting, the white and transparent components are separated from the remaining color components in a first step and then separated from the white and transparent components in a second step.

A problem with currently available color sorters is their coordination: retaining the desired components in the product while selectively removing undesirable components from the mixture. Technically, it is not possible to adjust the color sorters to achieve a high yield and high purity (>95%) of product in one or more consecutive color sorters. A certain degree of over-sorting, i.e., the erroneous removal of desired components along with undesirable ones, is also technically unavoidable.

According to the present invention, a unit with three color sorters can achieve particularly advantageous separation results, in terms of a product with good color quality (i.e., a proportion of particles with the wrong color, preferably about 2% or less, in particular about 1% or less) and a high yield. In the first color sorter, the desired color component (e.g., white/transparent) is separated from the undesired color components (e.g., the remaining colors). Due to the inevitable misclassification in conventional color sorters, the fractions of the desired and undesired color components obtained from this color sorter still contain a significant residual proportion of the desired or undesired color components. Therefore, the fraction containing predominantly the desired color component is fed to a second color sorter, which further sorts the product obtained from the first color sorter and further increases the proportion of the desired color component there. Finally, a third color sorter is provided in the unit, to which the fraction containing predominantly the undesired color component from the first color sorter is fed and in which the proportion of the undesired color component is further increased.

The undesirable color component obtained in the third color sorter can then be conveniently fed to another unit as described above, wherein another color component (e.g., red/yellow) is separated therefrom by the same scheme. The classified fractions obtained in the second and third color sorters, on the contrary, respectively contain a still significant proportion of the desired color component and are therefore transported to the first color sorter again as raw material. If the color component comprises a variety of colors (e.g., white/transparent), the undesirable color component obtained in the second color sorter is conveniently fed to another unit as described above, wherein another color component (e.g., transparent) is separated therefrom.

If the raw material to be separated is a mixture of more than three different color components, for example 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, for example, a color pair of white/colorless is separated from the remaining color components, and in the second unit, this color pair is separated into the individual color components. Separating the color pair in the first unit (instead of material of only one color) has the advantage that for a mixture with approximately the same distribution of colors, the amount of particles to be sorted and the amount of particles to be left in the mixture are similar, which enables better quantity management in the entire system.

If the remaining color components also contain multiple colors, such as red/yellow/green/blue components, it is advantageous to provide a further unit in which another color pair, such as a red/yellow component, can be separated from the remaining color components (e.g., green/blue). For a mixture containing white/colorless/red/yellow/green/blue components, separation in the following order is particularly preferred: 1. white/colorless, 2. red/yellow, and 3. green/blue components. For each color pair thus obtained, it is further preferred to provide a further unit with three color classifiers, as described above, in which the color pair is separated into the components of the individual colors.

The described unit formed of color sorters and the arrangement of a plurality of such units offer advantages over previously available separation methods in that a mixture having approximately the same distribution can be separated into a plurality of defined products with high purity. In contrast, in similar arrangements having only color sorters connected in a straight line, the yield loss or the number of required separation steps can be very large, which can seriously impair the cost-effectiveness of the separation.

In addition to the color classifier units mentioned above, a separate color classifier can also be included in the purification of the polyolefin residue fraction. Such a color classifier can, for example, be used to further reduce the false color components in the purified pure color fraction to further improve product quality.

After the fractionation in step (iii), the polyolefin residue fraction obtained in step (iv) is subjected to a treatment as described above at a temperature in the range of 50 to 155° C., wherein the treatment should conveniently be carried out for a period of at least 60 minutes. By this treatment, harmful substances, migration products or contaminants contained in the polyolefin residue fraction that have diffused into the outermost layer of the packaging should be precipitated as much as possible.

The process parameters depend on the inertness, chemical, and physical properties of the respective polymer. Therefore, care should be taken to ensure that the processing temperature is as high as possible above the glass transition temperature, but below the melting temperature of the plastic being processed. This ensures that the molecular chains are sufficiently mobile to release the migrating substances, but that they do not melt or soften, which could lead to agglomeration of the individual particles.

The suitable temperature ranges for the most commonly used polyolefins HDPE, LDPE and polypropylene can be as follows:

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

The residence time ensures that the minimum cleaning of the material is carried out. The residence time depends on different standards, for example the diffusion rate of the migration product in the corresponding polymer and the softening or melting temperature of the polymer. As mentioned above, the residence time that is used to remove the migration product fully as far as possible should be at least about 60 minutes. The residence time is preferably at least about 120 minutes, but should not exceed the residence time of about 600 minutes, because under the situation of polyolefin, can not observe further improved migration material removal usually under the residence time that exceeds 600 minutes. Particularly suitable residence time within the scope of the present invention can be about 180 to 360 minutes and especially 180 to 240 minutes time period.

The application of a vacuum can positively influence the separation of the migrating substances within step (iv). Furthermore, the application of a vacuum is associated with the advantage that the migrating substances can be removed by the vacuum of the apparatus in which the temperature treatment is performed, and the plastic is not exposed to any oxygen-containing atmosphere at high temperatures that could cause oxidative damage to the plastic. If the temperature treatment is performed under vacuum, it is convenient to set the pressure to ≤150 mbar, preferably ≤50 mbar, in particular ≤20 mbar, and most preferably between 0.1 and 2 mbar.

Since oxidative damage can also be suppressed by performing the temperature treatment in an inert gas, the treatment in step (iv) can also be performed in an inert gas atmosphere. The term "inert gas atmosphere" does not necessarily mean that the inert gas must be present throughout the entire apparatus. Rather, it is sufficient that the inert gas is present in the area of the apparatus directly surrounding the heated particles. Nitrogen and argon are particularly suitable inert gases, but nitrogen is preferred for cost reasons.

Suitable devices for temperature treatment are sold, for example, by the company Erema (AT) under the name VACUREMA.

Between steps (iii) and (iv), the residual fraction obtained from step (iii) is conveniently added to an extrusion plant to produce polyolefin granules. This can be designed so that the granules obtained from step (iii) are merely plastically deformed into granules, but additives, such as colorants or pigments, can also be added during the extrusion process. Furthermore, in the case of polypropylene, for example, conventional additives such as peroxides or talc are added during the extrusion process for compounding. Since extrusion of polypropylene containing these additives produces odorous substances that may be perceived by consumers as unpleasant, it is advantageous to perform the extrusion before step (iv) so that the odorous substances formed can be at least partially removed again. This reduces the unpleasant odor to a level comparable to that of fresh polypropylene compounded with talc.

During extrusion, the material can also be degassed by applying a vacuum and releasing volatile substances in the polyolefin melt. However, it should be noted that this degassing cannot replace the temperature treatment in step (iv), since the degassing must be carried out for a period of time, which would not allow for an economical operation of the extrusion equipment.

If the residual fraction obtained in step (iii) is fed to the extruder, the extrusion equipment is conveniently located directly before the equipment for the temperature treatment in step (iv), since the material is already heated there. Since the temperature treatment is also carried out at elevated temperatures, this arrangement requires less energy than first cooling the material after extrusion (and then having to be reheated to the temperature set within the temperature treatment range). To avoid energy losses due to the transport step between the extruder and the treatment vessel, measures such as transport equipment, thermal insulation, and additional vacuum in the transfer area can be implemented.

In some cases, extrusion granulation can also be performed only after steps (iii) and (iv). However, this has the disadvantage that the residual material fraction before granulation often still contains small particles, such as film fluff, which can be discharged during the temperature treatment under vacuum. Therefore, in such a process, the installation of filters is unavoidable, and these filters also need to be cleaned at relatively short intervals. In addition, the polyolefin granules have a relatively large volume before granulation, which limits the throughput through the temperature treatment equipment.

Another disadvantage of carrying out the extrusion downstream of step (iv) is that, due to the thermal loading of the material during the extrusion process, substances that cause an unpleasant odor in the product may be regenerated. In the case of extrusion upstream of step (iv), these substances can be reduced by step (iv); in contrast, extrusion downstream of step (iv) is undesirable.

In fact, it is accepted that granulation prior to temperature treatment has a negative impact on product properties and the required temperature treatment time. Thus, on the one hand, decomposition products can be produced during the extrusion process from migrating substances that are difficult to remove from the pellets again. On the other hand, migrating substances are generally present on the surface of the pellets and can therefore be removed more easily by temperature treatment than migrating substances that are distributed in the pellet particles due to extrusion. However, it has surprisingly been determined that these effects have a minimal impact on the product and are overcompensated by the advantages of the pellets for temperature treatment. In addition, due to their more compact structure, the pellets cool more slowly than the polymer material before granulation. Therefore, when the pellets are fed directly to the temperature treatment in step (iv), the total energy required for granulation and temperature treatment is less than if the opposite method were used.

The research on which the present invention is based has shown that it is of great significance for the quality of the resulting product that steps (ii) and (iii) are carried out before step (iv) and that the granulation step (if included) occurs after the classification of the fragments. Furthermore, it is important for this process that a thermal wash is carried out before the thermal treatment.

As described above, the present invention also relates to a method in which steps (ii) and (iii) are performed in the reverse order. In this case, for example, the chip classification (iii) can be performed before the hot washing (ii), the hot washing (ii) can be performed before the granulation, and the granulation can be performed before the heat treatment (iv). In this embodiment, the present invention also relates to a method in which the chip classification (iii) is performed before the hot washing (ii), the hot washing (ii) is performed before the temperature treatment (iv), and the temperature treatment (iv) is performed before the granulation.

However, the latter method has the same disadvantages as the above method direction of temperature treatment (iv) before granulation compared to the previous method. The above remarks apply analogously to the preferred embodiments of heat washing, chip classification, temperature treatment and granulation.

With regard to the sequence of the individual reaction steps, in one embodiment, particular preference is given to a process orientation with the sequence of thermal washing (step ii), fragment classification (step iii), granulation and temperature treatment (step iv).

Without the applicant being able to cite a particular theory, it can be speculated that the polyolefin residues from consumer products have impurities, for example in the form of printed matter, which are first detached from the polyolefin particles during hot washing. It is also possible that the polyolefin residues have labels formed from other polyolefins, for example polypropylene, which are detached from the main product during hot washing. Even if these labels are substantially removed from the pretreated material by the airflow separator, small residual portions of the labels may remain in the material. If the material is then directly subjected to a heat treatment, re-adhesion of the residues may occur, in particular if the softening point or glass transition temperature of the label material is lower than or within the temperature range of the temperature at which the polyolefin residues are treated in step (iv). This adhesion may be more difficult to capture in the downstream fragment sorting, with the result that the resulting product is more severely contaminated than in a sequential working method with hot washing (step ii), fragment sorting (step iii) and temperature treatment (step iv).

In another embodiment, a process direction with a sequence of fragment sorting (step iii), hot washing (step ii), granulation and temperature treatment (step iv) is particularly preferred. This embodiment is particularly advantageous when only a portion of the product (e.g., white and not other colors or transparent products) is available to the consumer.

Since hot washing is associated with a relatively high energy consumption, it may be sensible to reduce the amount of material to be cleaned by hot washing by sorting the fragments so that only those materials for which there is a relevant market are further cleaned by hot washing.

The process according to the invention can be carried out batchwise or partially batchwise by carrying out all or part of steps (i) to (iv) with a separate charge of polyolefin residues. However, since this is associated with greater technical complexity and idle times for individual plant components, it is preferred to carry out steps (i) to (iv) continuously.

Another aspect of the present invention relates to a polyolefin regrind obtained according to the above method, which is preferably LDPE, HPDE or polypropylene regrind.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 illustrates a unit 1 formed by three color sorters 2, 3, and 4. A polyolefin residue fraction is fed into the unit via a 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., remaining colors). The desired color fraction 6 is then fed to the second color sorter 3, where the remaining portion of the undesired color fraction 9 is separated from the mixture, producing a further purified desired color fraction 8. The undesired color fraction 7 obtained in the first color sorter is fed to the third color sorter 4, where the remaining portion of the desired color fraction 11 is produced, while a purified fraction of the undesired color fraction 10 is obtained from the mixture 7. The desired color fraction 11 and a portion of the undesired color fraction 9 are then fed back to the first color sorter 2.

FIG2 depicts a structure with two units 1 and 12 connected in series, wherein in the first unit 1 having three color filters 2A, 3A and 4A, a color pair (e.g., white/transparent) is separated from a mixture of polyolefin residue fractions. The color pair obtained from the first unit is then fed via a feed line 8 into a second unit 12, where it is separated into individual components (i.e., white on the one hand and transparent on the other hand). Here, the color pair passes through three color sorters 2B, 3B and 4B in a manner similar to the first unit 1. As products, very pure individual components of the color pairs 13 (e.g., transparent) and 14 (e.g., white) are obtained. The purified residual fraction 10A produced in the third color sorter 4A of the first unit 1 is fed to a further color sorter unit 15, where it is further purified, the construction of which is similar to that of units 1 and 12.

Examples

A polyolefin residue mixture was isolated having white/clear and other color fragments in proportions of 34%, 34%, and 32%, respectively.

A given mixture is fed into a first unit 1, formed by three color sorters 2A, 3A, and 4A. In the first color sorter, the remaining color fragments are separated from the mixture, yielding a purified fraction of white/transparent fragments 6A with a white/transparent/remaining color distribution of approximately 47.5%/47.5%/5%. The sorted mixture 7A consists of white/transparent/remaining color fragments with a distribution of approximately 20%/20% and 60% respectively. The purified white/transparent fraction 6A is fed into a second color sorter 3A, where it is subsequently cleaned. This yields a pure fraction 8 with a distribution of approximately 49.5%/49.5%/1% white/transparent/remaining color fragments. The secondary fraction 9A obtained in this second cleaning step has a white/transparent/remaining color fragment distribution of approximately 40%/40%/20% and is fed back to the first color sorter 2A. The sorted mixture 7A from the first color sorter 2A is fed to the third color sorter 4A and separated there into: a fraction 10A consisting primarily of other color fragments (distribution: white/transparent/other colors 2.5%/2.5%/95%), and a fraction 11A enriched in transparent and white fragments (distribution: white/transparent/other colors 32.5%/32.5%/35%). This enriched fraction 11A is also fed back to the first color sorter 2A.

The mixture 8 of transparent/white chips obtained in the first unit is fed to a second separation unit 12 having three color sorters 2B, 3B, and 4B. The white and transparent chips are separated in the first color sorter 2B, yielding a fraction 6B enriched in transparent chips (with a distribution of white/transparent/other colors 6%/93%/1%) and a fraction 7B enriched in white chips (with a distribution of white/transparent/other colors 66%/33%/1%). Fraction 6B enriched in transparent chips is further purified in the second color sorter 3B, yielding a mixture 13 (white/transparent/other colors 6%/93.5%/0.4%) and a remaining fraction 9B (with a distribution of white/transparent/other colors 6%/88%/6%).

The white fragment-enriched fraction 7B is fed to a third color sorter 4B, which produces a white fraction 14 with a white/transparent/other color fragment distribution of 95%/3.5%/1.5% and a residual fraction 11B with a white/transparent/other color fragment distribution of 39%/60.5%/0.5%. The residual fractions 9B and 11B from the second and third color sorters 3B and 4B are fed back to the first color sorter 2B of the second unit. If desired, another color sorter can be added downstream of color sorter 4B to, for example, reduce the proportion of other colors in the white fraction to less than 1%.

List of Reference Numerals

1 First color classifier unit

2, 2A, 2B First color classifier

3, 3A, 3B Second color classifier

4, 4A, 4B Third color classifier

5 Feeding line for the polyolefin residue fraction to the first color sorter unit

6, 6A, 6B Desired color fraction enriched in the first color classifier

7, 7A, 7B Undesirable color fractions enriched in the first color classifier

8 The desired color fraction purified in the first color sorter unit

9, 9A, 9B Undesirable color fractions enriched in the second color classifier

10,10A Undesirable color fraction enriched in the third color classifier

11, 11A, 11B Desired color fraction enriched in the third color classifier

12 Second color classifier unit

13 pure color single ingredients from 8

14 pure color single ingredients from 8

15 Third color classifier unit

Claims (14)

1. A method for manufacturing recycled polyolefin material from polyolefin-containing mixed-color residues, the recycled polyolefin material being suitable for manufacturing consumer products, the method comprising the following steps: (i) Water treatment of mixed-color polyolefin residue fractions in the absence of a heat supply. (ii) The polyolefin residue fraction obtained from (i) is treated within the range of washing with an alkaline medium at a temperature of at least 60°C. (iii) The polyolefin residue fraction obtained from (ii) is further classified into fragments to obtain one or more solid-color polyolefin residue fractions, wherein the polyolefins exist in a concentrated form, and steps (ii) and (iii) can also be performed in reverse order. (iv) Process the one or more solid-color polyolefin residue fractions obtained from the above steps at a temperature range of 50 to 155°C. In this process, a unit (1) consisting of three color classifiers is used to separate the polyolefin residue fractions in the fragment sorting in step (iii). The polyolefin residue fractions are fed into a first color classifier (2), where the desired color component (6) is separated from the undesirable color component (7). The desired color component (6) obtained in the first color classifier is fed into a second color classifier (3), where the product obtained from the first color classifier is further sorted and the proportion of the desired color component is further increased. The undesirable component obtained in the first color classifier is fed into a third color classifier (4), where the proportion of the undesirable color component is further increased. The fractions (9, 11) sorted in the second and third color classifiers are fed back into the first color classifier as raw materials. 2. The method according to claim 1, characterized in that, between or after step (iii) and (iv), one or more solid-color polyolefin residue fractions for manufacturing polyolefin particles are added to the extrusion equipment. 3. The method according to claim 1 or 2, wherein the proportion of the residual fraction constituting the main color of the residual fraction is not greater than 80% by weight. 4. The method according to claim 1, wherein the fragment classification in step (iii) comprises a plurality of the units formed by the three color classifiers. 5. The method according to claim 1 or 4, characterized in that the polyolefin residue fraction contains more than three colors and color pairs are separated from the polyolefin residue fraction by units (1, 15) formed by three color classifiers (2, 3, 4), and these color pairs are separated into corresponding color components in units (12) located downstream respectively. 6. The method according to claim 1 or 2, wherein the polyolefin is polyethylene or polypropylene. 7. The method according to claim 1 or 2, characterized in that the polyolefin residue fraction in step (ii) is processed at a temperature of at least 70°C. 8. The method according to claim 1 or 2, wherein the alkaline medium in step (ii) is an aqueous solution of sodium hydroxide with a concentration of less than 10% by weight. 9. The method according to claim 1 or 2, characterized in that, within the scope of fragment classification in step (iii), particles not composed of polyolefins and particles that have a color deviation from most of the particles in the polyolefin residue fraction are separated. 10. The method according to claim 1 or 2, characterized in that, for the processing according to step (iv), a vacuum of <150 mbar is applied. 11. The method according to claim 1 or 2, characterized in that the treatment according to step (iv) is carried out in an inert gas atmosphere. 12. The method according to claim 1 or 2, characterized in that the processing according to step (iv) lasts for a period of 120 to 300 minutes. 13. The method according to claim 1 or 2, characterized in that, prior to step (i), the polyolefin-containing residue is subjected to pre-sorting based on color. 14. The method according to claim 1 or 2, characterized in that the polyolefin residue fraction from step (ii) is subjected to subsequent drying and treatment in an air classifier.