Process for producing polyolefin recyclates

Abstract

The invention relates to a process for recycling mixed-colour polyolefin residues in order to produce PCR (post consumer recyclate) granulate, the process comprising the following process steps: (a) colour sorting the residues; (b) comminuting the residues to form flakes; (c) a step of washing the flakes using an alkaline liquid at a temperature T> 60°C; (d) removing the washing lye and dewatering the flakes; (e) sorting the flakes to remove colour impurities and extraneous polymers and to obtain one or more pure-colour polyolefin fractions, in each of which there is one type of polyolefin in a concentrated form; (f) granulating the flakes to form pellets in an extruder; (g) decontaminating the polyolefin fractions; and (h) providing the pellets for further use. The decontamination step (g) lasts between 800 and 3000 min, and preferably between 1500 and 2400 min.

Description

[0001] Process for the production of polyolefin recyclates

[0002] Field of the invention

[0003] The invention relates to a process for recycling color-mixed polyolefin residues for producing PCR (post-consumer recyclate) granules according to the preamble of claim 1.

[0004] State of the art

[0005] Over time, polyolefins absorb contaminants that penetrate deeply into the material and are difficult to remove. These include components of the contents that penetrate the polyolefin packaging, but also contaminants that are only later absorbed by the material through contact, for example, with contaminated water, or contaminants already present in the material, such as POSH and POAH, as well as contaminants resulting from degradation reactions of the material and additives, such as degraded lubricants and demolding aids.

[0006] Aliphatic, but also cyclic or polycyclic hydrocarbons such as benzene and toluene often dissolve better in the packaging wall than in the contents themselves, thus leading to an accumulation of contaminants in the packaging material. Even components of food, detergents, and cosmetics that initially appear uncritical migrate into the packaging material and can harm consumers in the form of intolerance, intolerance, or even allergy in even the smallest quantities. Due to the steadily growing number of people with allergic reactions, consumers must be assured that the substances relevant to the allergy are removed from the material during recycling, so deodorization alone is not sufficient.

[0007] During recycling, substances that could be mutagenic, carcinogenic, reproductively toxic, or otherwise toxic, or have hormonal effects, or that could have allergenic effects, must be removed from the material.

[0008] State-of-the-art processes primarily focus on deodorizing the polyolefin material using air, nitrogen, vacuum, or steam. Previous technical approaches to deodorization focus on easily perceptible and typical odors such as limonene, nonanal, nonenal, diphenyl ether, eucalyptol, butyric acid, or valeric acid. Often, the deodorized material is only evaluated using sensory panels.

[0009] For deodorization, air is usually blown through the flakes before the extruder or later through the granules after granulation.

[0010] Even if the inherent odor of the recyclates is greatly reduced and typical odors such as limonene are not perceptible or are only measurable in very small concentrations below 10 ppm, further contaminants (in the sense of toxicology or allergens) are still present in the recyclate.

[0011] There are known processes that deodorize the material with hot air or agitation under vacuum for less than 600 minutes. Extending the residence time beyond 600 minutes does not improve deodorization. Processes are also used that use very large air volumes of more than 5m 3 / kg polyolefins can be deodorized without stirring for less than 3 hours. Processes that decontaminate polyolefins using solvents (e.g., extraction agents such as steam, CO2, or organic solvents) are also known.

[0012] Object of the invention

[0013] The disadvantages of the described state of the art give rise to the task of proposing a decontamination process that provides recycled pellets with an allergen load below the specified limit values ​​and additionally removes cyclic and polycyclic aromatics from the material.

[0014] Description

[0015] The stated problem is solved in a process for recycling color-mixed polyolefin residues to produce PCR (Post-Consumer Recyclate) granules by the features stated in the characterizing portion of patent claim 1. Further developments and / or advantageous embodiments are the subject of the dependent patent claims.

[0016] The invention is preferably characterized in that the decontamination step (g) lasts between 800 and 3000 minutes and preferably between 1500 and 2400 minutes. The effectiveness of extending the treatment time is extremely surprising and not obvious to the person skilled in the art, since it is known from the prior art that the deodorization of polyolefin material (e.g., the depletion of limonene) can no longer be improved by extending the treatment after 600 minutes (see, for example, WO 2011 / 068717 A1). By extending the treatment time, the decontamination of unwanted allergenic aroma substances present in the polyolefin material can be massively improved. For example, alpha-hexyl cinnamaldehyde can be removed from the polyolefin flakes or pellets by 90% by the extended treatment time. With conventional treatment times, the initial value can only be reduced by 50%.

[0017] Decontamination is preferably applied to the flakes and / or pellets, as these are easy to handle as bulk materials and have a large surface area that can come into contact with the cleaning medium, especially air. It is therefore also possible to provide a decontamination step for both the flakes and the pellets.

[0018] In a preferred embodiment of the invention, the decontamination step is carried out at 100 to 125°C, and preferably at 113 to 118°C. In this temperature range, the decontaminants have increased volatility from the pellets, the gaseous medium has good absorption capacity for the decontaminants, and the flakes or pellets do not stick together.

[0019] In a further preferred embodiment of the invention, the decontamination step is carried out in at least one decontamination reactor, which is perfused with a gaseous and preheated medium, preferably air, when filled with flakes or pellets. The treatment time corresponds to the residence time of the flakes or pellets in the decontamination reactor.

[0020] In a particularly preferred embodiment of the invention, the high residence time of 800 to 3000 min is achieved by adjusting the reactor volume or by providing several reactors connected in parallel or in series in order to achieve the usual throughput of a deodorization process. As a result, the output of recycled polyolefin pellets in the decontamination process remains unchanged, even though the residence time is increased by up to five times.

[0021] It proves expedient if the decontamination reactor is heated or the pellets or flakes are preheated before they are introduced into the decontamination reactor. This prevents cold spots where contaminants can accumulate or even condense and are not removed with the cleaning air. In a further preferred embodiment of the invention, the at least one decontamination reactor is operated continuously, and the air flow is between 3 and 5 Nm. 3 / kg. Continuous operation ensures consistent flow conditions, which ensures uniform decontaminating of the flakes or pellets. The continuous feed and discharge of the flakes ensures uninterrupted operation.

[0022] Because the flakes or pellets are preferably fed in and out through a first or second rotary valve, as little hot air as possible is lost and the flow conditions are not changed by the feed into and discharge from the reactor.

[0023] The at least one decontamination reactor can also preferably be operated discontinuously, wherein the air flow rate is between 1 and 4 Nm 3 / kg. The reduced air throughput compared to a continuous process allows for more economical use of air. With discontinuous flow, contaminants can be removed from the flake and granule surfaces at higher flow velocities than in a continuous process, and during periods without flow, the contaminants can migrate back to the surface of the granules or flakes. Overall, smaller air volumes are required in discontinuous operation than in continuous operation.

[0024] It is advantageous if the decontamination reactor is flushed with an inert gas. Depending on the aroma substance to be removed, an inert gas can provide improved absorption of the decontaminants or aroma substances and can also be regenerated more easily.

[0025] It is advantageous if the gaseous medium flows through the flakes or pellets in the decontamination reactor from bottom to top. This flow direction takes advantage of the fact that hot gases, such as air, rise, and the flow through the decontamination reactor is more evenly distributed in a natural direction.

[0026] The gaseous medium is expediently passed through a first or second filter system at the outlet from the decontamination reactor in order to remove particles between 0.1 pm and 1000 pm, and preferably between 10 pm and 100 pm, from the gaseous medium. In this filter area, dust, abrasion of the flakes or pellets, pigments (titanium oxide), or fillers (calcium carbonate) are primarily retained. This protects employees and residents from microplastic particles and other dust. In another particularly preferred embodiment of the invention, the laden gaseous medium is passed through a purification system in order to purify the gaseous medium of the decontaminants transferred from the flakes or pellets. The provision of a purification system avoids odor emissions and also allows purified exhaust air to be recirculated. It is essential that a driving concentration gradient is present. This meansThe concentration of contaminated polyolefin material to be cleaned must be greater than the concentration of contaminants in the air as it enters the reactor. Condensate traps, adsorption filters (carbon), solvent filters, or washing the air with water or spray (absorption), as well as oxidative, thermal, or catalytic cleaning processes, can be used to clean the air.

[0027] It is advantageous if the flakes or pellets are stirred in the decontamination reactor. This allows the flakes or pellets to be homogenized in the reactor and minimizes dead zones that the gaseous medium cannot reach.

[0028] Preferably, the washing step € is carried out at a temperature T> 60 °C. At a temperature T> 60 °C, printing ink is removed from the flakes particularly efficiently.

[0029] Advantageously, the polyolefin is essentially polypropylene or polyethylene, or blends or copolymers of the two, preferably HD polyethylene and LD polyethylene, which are petroleum-based, bio-based, or carbon dioxide-based and may contain catalysts, colors, fillers, or other additives. These polyolefins are increasingly used in the cosmetics industry as packaging and require particularly high quality, for example, recycled HDPE, to prevent allergens from migrating from the packaging into the contents.

[0030] Further advantages and features will become apparent from the following description of an embodiment of the invention with reference to the schematic representations. These are not to scale:

[0031] Figure 1: a flow diagram of a process for recycling color-mixed polyolefin residues to produce PCR (post-consumer recyclate) granules in a first embodiment; Figure 2: a flow diagram of the process in a second embodiment;

[0032] Figure 3: a flow diagram of the process in a third embodiment and

[0033] Figure 4: a flow diagram of the process in a fourth embodiment;

[0034] For high-quality applications of recycled high-density polyethylene (rHDPE), e.g., for cosmetic packaging, residual contamination with flavorings that can have allergenic effects has recently become a relevant issue. These flavorings are aromatic hydrocarbons with molecular weights of 250 g / mol and more, which, due to their diffusion behavior, cannot be removed or can only be removed inadequately (depletion) under the conditions specified in the state of the art. Conventional post-consumer rHDPE grades can therefore not be used at all or only to a very limited extent for the packaging of certain cosmetic products, especially those products that are applied to the skin and remain there, so-called leave-on products, even if they have been "odor-treated" using standard processes, for example, in a deodorization reactor.

[0035] Surprisingly, it has been found that with treatment times significantly longer than 600 minutes (up to 3000 minutes), these substances can be depleted to a degree that allows the recyclates to be used in the aforementioned applications. Embodiments of this inventive process are shown in Figures 1 to 4.

[0036] The process for recycling color-mixed polyolefin residues to produce PCR (Post Consumer Recyclate) granules basically comprises the same process steps as are required for deodorizing the polyolefin residues: After color sorting (a) of the residues, they are comminuted into flakes (b). In a washing step (c) of the flakes with an alkaline liquid at a temperature T> 60 °C, printing ink is removed from the flakes. After drying or removing the wash liquor and dewatering the flakes (d), the flakes are sorted (e) to remove color impurities and foreign polymers and to obtain one or more color-pure polyolefin fractions, each containing a polyolefin type in concentrated form. In a process step (f), the flakes are degassed in an extruder 11 and granulated into pellets.

[0037] The decontamination (g) of the polyolefin fractions preferably takes place in a decontamination reactor 13. As shown in Figures 3 and 4, a first and second decontamination reactor 13a, 13b may also be present, which may be arranged in series (Figure 3) or in parallel (Figure 4). The decontaminated pellets are made available for further use (h), for example, in a silo or big bags. The sequence of process steps (a) to (h) does not necessarily have to be carried out in the described order, but can also be performed in a different order. This allows the recycling process to be adapted to different residual materials.

[0038] The at least one decontamination reactor 13 can be used to decontaminate the flakes or pellets. Accordingly, it can be arranged before (Figure 2 and Figure 4) or after (Figure 1 and Figure 3) the extruder 11. The residence time in the at least one reactor is between 800 and 3000 min and preferably between 1500 and 2400 min. The temperatures in the reactor 13 are between 110 and 125°C and preferably between 113 and 118°C. This allows allergens, which are only inadequately removed during conventional deodorization, to be almost completely removed from the flakes or pellets. For example, with conventional treatment times, a depletion of the substances alpha-hexyl cinnamaldehyde and n-hexyl salicylate to 40-60% of the initial value is achieved. If the treatment time is tripled, approximately 10% of the initial value is achieved.Because up to 90% of the flavorings can be removed from the granules, PCR polyolefin granules can be produced that meet the high requirements of the cosmetics industry regarding cosmetic packaging, especially for the "leave-on" sector.

[0039] Preheated air 15 is blown into the reactor 13 at the bottom, which "releases" the allergens from the flakes or pellets. After the preheated air 15 rises, it is advisable to direct the air from bottom to top. It goes without saying that this process also serves as a deodorization process, removing odorous substances in the first 600 minutes. The additional residence time serves to decontaminate allergens, for example, or more specifically, substances with low diffusion coefficients that cannot be removed or can only be removed inadequately within the usual timeframe, such as some flavorings with allergenic effects.

[0040] To achieve the typical throughput of deodorization processes despite the long residence time, the reactor volume must be increased. This can be achieved by enlarging reactor 13 (Figure 1 and Figure 2) or by providing a first and second reactor 13a, 13b (Figure 3 and Figure 4) or even more reactors, which can be arranged in series or in parallel and can be used before or after extrusion.

[0041] The reactors can be operated continuously. In this case, it is advisable to feed and discharge the flakes or pellets using rotary valves to avoid interrupting operation and to avoid changing the flow conditions.

[0042] Cold flakes or pellets, and generally cold areas, should be avoided, as contaminants can accumulate and even condense there. Therefore, it is advisable to preheat the flakes or pellets and / or heat the reactor.

[0043] The air 15 discharged from the reactor 13 is filtered at the outlet to remove mainly dust, abrasion of the flakes or pellets, pigments (titanium oxide) or fillers (calcium carbonate).

[0044] To separate the contaminant-laden air 15 from the contaminants, it must be passed through a purification system. The purified air can then also be recirculated. It is essential that a driving concentration gradient exists. This means that the concentration to be purified in the contaminated polyolefin material must be greater than the concentration of contaminants in the air as it enters the reactor. Condensate traps, adsorption filters (carbon), solvent filters, or washing the air with water or spray mist (absorption) can be used to purify the air.

[0045] To illustrate the effect of the increased residence time and the difference between deodorization and decontamination, the following three examples or diagrams are disclosed:

[0046] Example 1: Diphenyl ether is a typical contaminant in HDPE from the contents. Diphenyl ether is a popular fragrance. In small amounts, it is non-toxic, non-mutagenic, and non-allergenic. The sole purpose of this substance is to remove odors. After 10 hours (600 minutes), the odor is significantly reduced. The diagram clearly shows that a longer residence time is pointless. Deodorization reactors are used to reduce (deodorize) such substances.

[0047] Example 2: A typical HDPE contamination from the contents is alpha-hexyl cinnamaldehyde (a flavoring). The contents themselves often contain borderline levels of the product; any additional migration from the packaging material carries the risk of exceeding the limits or at least reaching concentrations that require declaration. The target migration values ​​are below 1000 ppb. After 600 minutes and 10 hours of decontamination, the limit is not yet reached, and a deodorization reactor is not advisable. Alpha-hexyl cinnamaldehyde is just one of the typical allergens that the decontamination process must remove. For most of the allergens listed in the EU allergen list, 10 hours of deodorization are insufficient, and further removal is advisable. Example 3: PAH (Polycyclic Aromatic Hydrocarbons) and MOAH (Mineral Oil

[0048] Aromatic hydrocarbons) are a problem in polyolefin regranulates and are

[0049] REVISED SHEET (RULE 91) ISA / EP 10h insufficient purification. The required limits are reached after 2000 min. Tripling the residence time further reduces the concentrations to less than a third of the 10h value.

[0050] REVISED SHEET (RULE 91) ISA / EP Key:

[0051] 11 extruders

[0052] 13a First decontamination reactor

[0053] 13b Second decontamination reactor

[0054] 15 Preheated gaseous medium, air

Claims

1 . Process for recycling colour-mixed polyolefin residues for the production of PCR (Post Consumer Recyclate) granules comprising the following process steps (a) Color sorting of the residues, (b) crushing the residues into flakes, (c) Washing step of the flakes with an alkaline liquid, (d) removing the wash liquor and dewatering the flakes, (e) sorting the flakes to remove color impurities and foreign polymers and to obtain one or more color-pure polyolefin fractions, each containing one type of polyolefin in concentrated form, (f) granulating the flakes into pellets in an extruder, (g) decontaminating the polyolefin fractions and (h) providing the pellets for further use, characterized in that the decontamination step (g) lasts between 800 and 3000 min and preferably between 1500 and 2400 min.

2. Process according to claim 1, characterized in that step (g) is applied to the flakes and / or the pellets.

3. Process according to claim 1 or 2, characterized in that step (g) is carried out at 100 to 125°C and preferably at 113 to 118°C.

4. Method according to one of the preceding claims, characterized in that step (g) is carried out in at least one decontamination reactor (13) through which a gaseous, preheated medium (15), preferably air, flows when it is filled with flakes or pellets, the treatment time of step (g) being the residence time of the flakes or pellets in the decontamination reactor (13).

5. Process according to claim 4, characterized in that the high residence time of 800 to 3000 min is achieved by adjusting the volume of the reactor (13) or by providing several reactors (13a, 13b) connected in parallel or in series in order to achieve the usual throughput of a deodorization process.

6. Method according to claim 4 or 5, characterized in that the decontamination reactor (13) is heated or the pellets or flakes are preheated before they are introduced into the decontamination reactor (13).

7. Method according to one of claims 4 to 6, characterized in that the at least one decontamination reactor (13) is operated continuously and the air flow rate is between 3 and 5 Nm 3 / kg.

8. Method according to one of claims 4 to 7, characterized in that the introduction and discharge of the flakes or pellets takes place through a first or a second rotary valve.

9. Method according to one of claims 4 to 6, characterized in that the at least one decontamination reactor (13) is operated discontinuously and the air flow rate is between 1 and 4 Nm 3 / kg.

10. Method according to one of claims 4 to 9, characterized in that the decontamination reactor (13) is flowed through with an inert gas.

11. Method according to one of claims 4 to 10, characterized in that the gaseous medium (15) flows through the flakes or pellets in the decontamination reactor (13) from bottom to top.

12. Method according to one of claims 4 to 11, characterized in that the gaseous medium is passed through a first or a second filter system at the outlet from the decontamination reactor (13) in order to remove particles between 0.1 pm and 1000 pm and preferably between 10 pm and 100 pm from the gaseous medium.

13. Method according to one of claims 4 to 12, characterized in that the loaded gaseous medium (15) is passed through a cleaning system in order to clean the gaseous medium (15) of the decontaminants transferred from the flakes or the pellets.

14. Method according to one of claims 4 to 13, characterized in that the flakes or pellets are stirred in the decontamination reactor (13).

15. Process according to one of the preceding claims, characterized in that the washing step (c) is carried out at a temperature T> 60 °C.

16. Process according to one of the preceding claims, characterized in that the polyolefin is essentially polypropylene or polyethylene or mixtures or copolymers of the two, preferably HD polyethylene and LD polyethylene, which are produced from petroleum-based, bio-based or carbon dioxide-based materials and may contain catalysts, dyes, fillers or other additives.

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