Process for recycling at least one polyolefin containing impurities

Abstract

The invention relates to a process for recycling at least one polyolefin containing impurities in which polymer-containing waste containing the at least one polyolefin is provided and the at least one polyolefin is selectively dissolved in at least one solvent. At least one precipitating agent is then added to the polyolefin solution, wherein before, during or after this addition a temperature of the mixture is established which leads to melting of a portion of the at least one polyolefin and to formation of a melt phase and a liquid phase having a higher proportion (based on the total polyolefin mass in the polyolefin solution), i.e. a higher mass, of polyolefin than the melt phase. This is followed by a mechanical separation of the melt phase from the liquid phase and a drying of the liquid phase and / or the melt phase to obtain a low-impurity polyolefin fraction, and a polyolefin fraction enriched with impurities, as solids.

Description

[0001] Method for recycling at least one polyolefin containing impurities

[0002] The invention relates to a process for recycling at least one polyolefin containing impurities, in which polymer-containing waste containing the at least one polyolefin is provided and the at least one polyolefin is selectively dissolved in at least one solvent. Subsequently, at least one precipitating agent is added to the polyolefin solution, wherein, before, during, or after this addition, a temperature of the mixture is set which leads to the melting of a portion of the at least one polyolefin and to the formation of a melt phase and a liquid phase with a higher proportion (relative to the total polyolefin mass in the polyolefin solution) compared to the melt phase, i.e., a higher mass of polyolefin.Subsequently, the melt phase is mechanically separated from the liquid phase, and the liquid phase and / or the melt phase is dried, yielding a low-impact polyolefin fraction and an impurity-rich polyolefin fraction as solids.

[0003] Plastic waste often contains contaminants that were introduced to the plastic products during manufacturing (e.g., printing inks, processing aids), during use (e.g., from contact materials, the environment), or during disposal (e.g., cross-contamination from other waste). Even with solvent-based recycling, these contaminants can often only be insufficiently removed through pretreatment or filtration processes and thus remain in the recycled material. This leads to undesirable discoloration and odors in the material and can also negatively affect its processability and mechanical properties.

[0004] To date, solvent-based recycling processes for separating coarser contaminants after solid-liquid separation utilize extraction processes (WO 2022 / 029318 Al) or liquid filtration processes (WO 2018 / 068973 Al) with the addition of a solvent immiscible with the primary solvent for further purification of dyes, pigments, or degradation products. Nevertheless, fine particles, such as soot, often remain in the recyclate, which cannot be separated by these processes and impair the color of the recyclate, resulting in an undesirable gray tone.

[0005] Another method for purifying polymer solutions is to precipitate the polymer from the solution by cooling or adding a precipitating agent. In one case, the target polymer can be completely precipitated, while the impurities remain in the solvent and are removed together from the polymer by solid-liquid separation (EP 1 888 677 Bl). However, this method also has limited effectiveness, as fine dirt particles often remain trapped in the precipitating polymer and are therefore not separated.

[0006] In another case (WO 03 / 018679), only a portion of the polymer precipitates, encapsulating the fine dirt particles, and is subsequently removed from the remaining precipitate solution by solid-liquid separation. The remaining dissolved polymer can then be recovered from the purified precipitate solution. However, this method results in a significant loss of the target polymer and involves a technically complex solid-liquid separation of the polymer and the precipitate solution.

[0007] Based on this, the object of the present invention was to provide a process for recycling polyolefins that enables improved separation of impurities and at the same time allows the process to be carried out as economically and ecologically as possible, e.g. with the lowest possible solvent usage.

[0008] This problem is solved by the method with the features of claim 1 and the recycled polyolefin with the features of claim 12. The further dependent claims describe advantageous embodiments of the invention.

[0009] According to the invention, a process for recycling at least one polyolefin containing impurities is provided, comprising the following steps: a) providing polymer-containing waste containing the at least one polyolefin, b) selectively dissolving the at least one polyolefin in at least one solvent, c) adding at least one precipitating agent to the polyolefin solution from step b), wherein, before, during and / or after the addition in step c), a temperature of the mixture is set which leads to the melting of part of the at least one polyolefin and to the formation of a melt phase and a liquid phase, d) mechanically separating the melt phase from the liquid phase, and e) drying the liquid phase and / or the melt phase to obtain a low-impact polyolefin fraction and an impurity-enriched polyolefin fraction as solids.The process according to the invention allows impurities to be removed from a polymer solution by partial precipitation using a precipitating agent. The process is particularly suitable for polymer solutions made of polyethylene and polypropylene. These can, for example, originate from the solvent-based recycling of mixed waste fractions.

[0010] After solid-liquid separation of the solution and undissolved residue, and possibly a further purification step, a dark gray, highly viscous solution is obtained. Suitable solvents and precipitants can be identified using Hansen's solubility parameters.

[0011] Preferably, the at least one solvent has a value for the hydrogen bond strength ΔH of the Hansen solubility parameter of 0 to 10.0 MPa. 0 5 preferably from 0.1 to 6.0 MPa 0 - 5 , especially preferably from 0.2 to 3.0 MPa 0 - 5and / or preferably a value for the polar bond strength 6P of the Hansen solubility parameter from 0 to 8.0 MPa 0 - 5 preferably from 0.1 to 5.0 MPa 0 - 5 , especially preferably from 0.2 to 3.0 MPa 0 - 5 on.

[0012] Preferably, the at least one solvent contains hydrocarbon compounds, preferably aliphatic hydrocarbon compounds, particularly preferably cycloaliphatic linear or branched hydrocarbon compounds, especially cycloaliphatic linear or branched hydrocarbon compounds with 5 to 18 carbon atoms and mixtures thereof, or consists thereof.

[0013] Preferably, the at least one precipitating agent has a value for the hydrogen bond strength 6H of the Hansen solubility parameter of at least 5.0 MPa. 0 - 5 preferably in the range of 8.0 to 15.0 MPa 0 - 5, especially preferred from 12.0 to 22.0 MPa 0 - 5 and / or preferably a value for the polar bond strength 6P of the Hansen solubility parameter of 4.0 to 20.0 MPa 0 - 5 preferably from 4.0 to 17.0 MPa 0 - 5 , especially preferably from 6.0 to 15.0 MPa 0 - 5 on.

[0014] The at least one precipitating agent preferably contains an alkyl ester, preferably a dicarboxylic acid dialkyl ester, particularly preferably dimethyl ester or diethyl ester of oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid and mixtures thereof, or consists thereof.

[0015] The polymer content in the polymer solution can preferably be from 1 to 20 wt.%, preferably from 2 to 15 wt.%, and particularly preferably from 4 to 10 wt.%.

[0016] The temperature during precipitation in step c) is essentially the same as, or above, the dissolution temperature. Preferably, the precipitation temperature and the dissolution temperature are in the range of 115 °C to 190 °C, and particularly preferably in the range of 130 °C to 160 °C.

[0017] The ratio between the amount of solvent and the amount of precipitating agent required to achieve partial precipitation of the polymer depends on the temperature of the solution and is preferably in the range of 3:1 to 1:5, more preferably in the range of 3:1 to 1:4, and particularly preferably in the range of 2.5:1 to 1:3.

[0018] It is preferred that the mixture of solvent and precipitant has a density greater than that of the melt phase. Preferably, the mixture of solvent and precipitant has a density of < 1 g / cm³. 3 preferably < 0.9 g / cm³ 3 , preferably < 0.8 g / cm³ 3 , and especially preferably < 0.75 g / cm³ 3 .

[0019] The precipitation process is initiated by adding the precipitating agent at the required process temperature. Alternatively, the precipitating agent can be added at a higher or lower temperature, followed by cooling or heating the mixture to the process temperature. Under these process conditions, a portion of the polymer precipitates as a polymer-rich liquid melt phase, while the remainder stays as a second liquid phase in a polymer-poor precipitating solution. Less than 50% of the polymer precipitates in the liquid melt phase.

[0020] The fine particulate impurities in the solution, i.e., dyes, pigments, and degradation products such as soot and titanium dioxide, are essentially bound in the melt phase, thus purifying the precipitate. Due to the concentration of impurities, the melt phase has a dark gray to black color, while the remaining precipitate is whitish to light green.

[0021] The process conditions are chosen so that as little polymer as possible enters the melt phase, but as many impurities as possible are bound in it.

[0022] Due to its lower density, the melt phase collects on the surface of the precipitation solution and can be easily separated there using process technology. This can preferably be achieved by filtration or decantation of the precipitation solution. This removes impurities such as dyes, pigments, fine particles, or cross-linked regions in the polymer. Since the described process also results in size separation of the polymer molecules into the two phases, partial precipitation can also be used to adjust the molar mass. Similarly, in conjunction with molar mass fractionation (the high-molecular-weight polymer chains preferentially aggregate in the melt phase), targeted adjustments of the rheological product properties (molecular weight, melt viscosities during processing, and optimized extrusion and processing temperatures) can also be achieved.This allows for more uniform and quality-assured product properties to be achieved even with very inhomogeneous waste compositions.

[0023] It is preferred that the drying in step e) is carried out at a temperature preferably of 25 to 275 °C, preferably of 100 to 265 °C, particularly preferably of 150 to 250 °C.

[0024] A preferred embodiment provides that the drying in step e) is carried out by evaporation of the solvent or precipitation of the polyolefin by adding a precipitating agent or lowering the temperature, followed by mechanical separation and subsequent evaporation of the solvent. The dried product is colorless to slightly greenish.

[0025] The process according to the invention offers the advantage that even the smallest impurities, which cannot be separated from the polymer by other processes, collect there by precipitating a sub-fraction and can thus be selectively and effectively removed from polymer solutions. In contrast to processes known from the prior art, precipitation in the form of a melt achieves a significantly higher purification efficiency with less material loss. At the same time, the form of a coherent melt phase and its buoyancy due to its lower density enable a significantly easier separation of the precipitated sub-fraction.

[0026] A further advantage of the process according to the invention is that precipitation results in a significantly lower proportion of solvent being bound in the polymer fractions. This considerably reduces the energy required for drying these fractions. Additionally, separation by molar mass can be achieved by precipitating a sub-fraction. The precipitated polymer contains significantly longer polymer chains than the remaining solution. Separation of different types of the same plastic from a mixed solution is also possible.

[0027] Specifically, HDPE and LDPE types can be fractionated, and polyolefinic homopolymers can be separated from copolymers. The inventive process also enables the separation of different polyolefins, such as the enrichment or fractionation (up to complete recovery as a purified fraction) of a polyolefin (especially PP) from a mixed polyolefin solution containing a mixture of different polyolefins, such as LLDPE, LDPE, HDPE, and PP. Thus, for example, purified PP can be recovered from a waste mixture containing both PE and PP.

[0028] According to the invention, a polyolefin recyclate is also provided, which can be produced according to the previously described process. The polyolefin recyclate contains at least one solvent in the range of a maximum of 1000 ppm and at least one precipitating agent in the range of a maximum of 1000 ppm.

[0029] It is preferred that the proportion in the polyolefin recyclate of the at least one solvent is in the range of 50 to 500 ppm and / or of the at least one precipitating agent is in the range of 50 to 500 ppm.

[0030] The following examples and figures are intended to describe the method according to the invention in more detail, without limiting it to the specific embodiments described here.

[0031] Fig. 1 shows a photographic image of recycled material samples according to the invention compared to non-inventive samples.

[0032] Figure 1 shows photographic images of 500 pm thick press films. The following are shown:

[0033] • one LDPE virgin material sample (1),

[0034] • a polymer recycled according to the state of the art from the comparison example without precipitation (2),

[0035] • a low-impact fraction of the polymer recycled according to the invention (3),

[0036] • a fraction of the polymer recycled according to the invention (4) enriched with impurities,

[0037] • a polymer purified according to the state of the art from the comparative example (5) and

[0038] • a recycled polymer (6) precipitated according to the state of the art from the comparison example.

[0039] Example

[0040] A waste fraction containing polyethylene (PE), polypropylene (PP), and polyethylene terephthalate (PET) is dissolved in the solvent mixture CreaSolv® PO63 Hl at 115 °C. After separating the undissolved components, a dark gray solution (sample 2) is obtained, rich in PE and containing fine particulate impurities in addition to the plastic. By adding the precipitating agent CreaSolv® FR1 in a 1:1 ratio to the solvent and increasing the temperature to 148 °C, a small portion of the polymer precipitates from the solution, while the majority remains dissolved. The precipitated polymer appears as a highly viscous, polymer-rich melt, is dark gray-black in color, and collects on the surface of the solution. The solution undergoes a significant lightening to a light green color. The two phases are separated by skimming off the floating melt or by draining the solution.The polymer remaining in solution (sample 3) is subsequently dried. After drying, it has a light green color and is largely particle-free (Fig. 1). Drying the polymer in the melt phase (sample 4) additionally yields a black-colored product with a high proportion of fine particles. To evaluate the color, a color value determination can be performed in the LAB color space. For comparability of different recyclates, the recyclate samples are pressed into round films with a thickness of 500 µm using a hydraulic hot press. The LAB color value is determined according to DIN EN ISO / CIE 11664-4 using a DigiEye-700 mm Cube color measurement system from the manufacturer VeriVedi with DigiEye software version 2.8.0.3. For comparison of LAB color values, the CIEDE2000 color difference can be calculated according to DIN EN ISO / CIE 11664-6. (See Table 1.)l are the LAB color values ​​of the dried samples and their CIEDE2000 color difference to a reference sample of natural (transparent) LDPE virgin material of type Lupolen 1800H (sample 1).

[0041] Table 1

[0042] Table 1 shows the high purification of the solution through precipitation, resulting in a color difference of 11 between the dried solution with precipitation (sample 3) and virgin material (sample 1). Without precipitation (sample 2), a significantly higher color difference of 33 to virgin material is observed. The accumulation of the removed contaminants in the filtered precipitated polymer (sample 4) is evident from the high color difference of 43 to virgin material (sample 1).

[0043] Comparative example

[0044] For comparison, a reference sample was produced according to the procedure described in W003 / 018679.

[0045] A waste fraction containing PE, PP, and PET was dissolved in the solvent mixture CreaSolv® PO63 Hl at 115 °C. After separating the undissolved components, a dark gray PE solution (sample 2) rich in PE and containing fine particulate impurities in addition to the plastic was obtained. Lowering the temperature to 97 °C caused partial precipitation of the solution. The precipitated polymer appeared as dark gray-black flakes in the solution. The two phases were separated by filtration. The polymer remaining in solution (sample 5) was then dried and, after drying, had a dark greenish-gray color (Fig. 1). Drying the filtered-off polymer (sample 6) yielded an additional dark gray product. The ratio of polymer remaining in solution to precipitated polymer was 1:5.To evaluate the color, a color value determination in the LAB color space and a calculation of the CIEDE2000 color difference between the dried samples 5 and 6 and the virgin material can be performed. Table 1 shows that only a slight purification is achieved by precipitation, resulting in a high color difference of 31 between the dried solution with precipitation (sample 5) and the virgin material (sample 1), only slightly below the color difference of 33 of the reference sample without precipitation (sample 2). A slight enrichment of the removed contaminants in the filtered precipitated polymer (sample 6) is indicated by the color difference of 38 compared to the virgin material (sample 1).

Claims

Patent claims 1. A method for recycling at least one impurity-containing polyolefin comprising the following steps: a) providing polymer-containing waste containing at least one polyolefin, b) selectively dissolving the at least one polyolefin in at least one solvent, c) adding at least one precipitating agent to the polyolefin solution from step b), wherein, before, during and / or after the addition in step c), a temperature of the mixture is adjusted to melt a portion of the at least one polyolefin and to form a melt phase and a liquid phase, d) mechanically separating the melt phase from the liquid phase, and e) drying the liquid phase and / or the melt phase to obtain a low-impact polyolefin fraction and an impurity-enriched polyolefin fraction as solids.

2. The method according to claim 1, characterized in that the at least one solvent has a value for the hydrogen bond strength ΔH of the Hansen solubility parameter of 0 to 10.0 MPa. 0 - 5 preferably from 0.1 to 6.0 MPa 0 - 5 , especially preferably from 0.2 to 3.0 MPa 0 - 5 and / or a Value for the polar binding strength εp of the Hansen solubility parameter from 0.0 to 8.0 MPa 0 - 5 preferably from 0.1 to 5.0 MPa 0 - 5 , especially preferably from 0.2 to 3.0 MPa 0 5 exhibits.

3. A method according to one of claims 1 or 2, characterized in that the at least one solvent contains or consists of hydrocarbon compounds, preferably aliphatic hydrocarbon compounds, particularly preferably cycloaliphatic linear or branched hydrocarbon compounds, in particular cycloaliphatic linear or branched hydrocarbon compounds with 5 to 18 carbon atoms and mixtures thereof.

4. Method according to one of claims 1 to 3, characterized in that the at least one precipitating agent has a value for the hydrogen bond strength ΔH of the Hansen solubility parameter of at least 5.0 MPa. 0 - 5 preferably in the range of 8.0 to 15 MPa 0 - 5 , especially preferably from 12 to 22 MPa 0 - 5 and / or a value for the polar bond strength öp of the Hansen solubility parameter from 4.0 to 20.0 MPa 0 - 5preferably from 4.0 to 17.0 MPa 0 - 5 , especially preferably from 6.0 to 15.0 MPa 05 exhibits.

5. Method according to one of the preceding claims, characterized in that the at least one precipitating agent contains or consists of alkyl esters, preferably a dicarboxylic acid dialkyl ester, particularly preferably dimethyl esters or diethyl esters of oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid and mixtures thereof.

6. Method according to one of the preceding claims, characterized in that the polymer content in the polymer solution is 1 to 20 wt.%, preferably 2 to 15 wt.%, particularly preferably 4 and 10 wt.%.

7. Method according to one of the preceding claims, characterized in that the temperature during precipitation in step c) is essentially equal to or greater than the dissolution temperature, wherein it is preferred that the precipitation temperature and the dissolution temperature are in the range of 115 °C to 190 °C, particularly preferably in the range of 130 °C to 160 °C.

8. Method according to one of the preceding claims, characterized in that the ratio of solvent quantity to precipitating agent quantity is in the range of 3:1 to 1:5, preferably 2.5:1 to 1:4, particularly preferably 2:1 to 1:

3.

9. A method according to any of the preceding claims, characterized in that the mixture of solvent and precipitant has a density greater than the density of the melt phase, wherein it is preferred that the mixture of solvent and precipitant has a density < 1 g / cm³ 3 preferably < 0.9 g / cm³ 3 , preferably < 0.8 g / cm³ 3, and especially preferably < 0.75 g / cm³ 3 exhibits.

10. Method according to one of the preceding claims, characterized in that the mechanical separation in step d) is carried out by density separation, in particular sedimentation, decantation, centrifugation, filtration or combinations thereof.

11. Method according to one of the preceding claims, characterized in that the drying in step e) is carried out by evaporation of the solvent and / or by the addition of a precipitating agent and mechanical separation of the polyolefin with subsequent evaporation of the solvent.

12. Polyolefin recyclate producible according to the method of any one of claims 1 to 11, wherein the polyolefin recyclate has proportions of the at least one solvent in the range of a maximum of 1000 ppm and proportions of the at least one precipitating agent of a maximum of 1000 ppm.

13. Polyolefin recyclate according to claim 12, characterized in that the proportion in the polyolefin recyclate of the at least one solvent is in the range of 50 to 500 ppm and / or of the at least one precipitating agent is in the range of 50 to 500 ppm.

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