Recycling method for contaminated plastics
The sponge-like polymer structure formation through controlled cooling and pressure separation addresses the inefficiency in removing low-molecular-weight impurities, achieving high-purity recycled polymers suitable for contact-sensitive applications.
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- ALPLA WERKE ALWIN LEHNER
- Filing Date
- 2026-01-02
- Publication Date
- 2026-07-09
AI Technical Summary
Existing plastic recycling processes fail to effectively separate low-molecular-weight impurities such as flavorings and degraded stabilizers from recycled polymers due to their low volatility, which prevents their use in contact-sensitive applications.
A recycling process that forms a sponge-like polymer structure by cooling a polymer mixture, allowing the solvent and impurities to separate mechanically from the polymer, with controlled temperature and pressure conditions to prevent solvent evaporation and plasticization.
Achieves high purity of the target polymer by effectively removing low-molecular-weight impurities, with a residual solvent content of less than 3% by mass and impurities below 100 ppm, suitable for contact-sensitive applications.
Smart Images
Figure EP2026050013_09072026_PF_FP_ABST
Abstract
Description
[0001] 1040-27163 1 02.01.2026
[0002] Recycling processes for contaminated plastics
[0003] Field of invention
[0004] The invention relates to a recycling process for contaminated plastics according to the preamble of claim 1.
[0005] State of the art
[0006] Plastic recycling processes that utilize the possibility of dissolving and reprecipitating plastics have historically been used primarily for recycling composite materials. These processes employ a highly selective solvent to dissolve the target polymer, thereby separating unwanted undissolved components of the composite material from the solution. In a subsequent process step, the target polymer is precipitated and separated from the solvent in the resulting suspension. Separation of the solvent and target polymer is typically achieved by evaporating the solvent, preceded by solid-liquid separation. The focus of the purification process is on the most complete possible removal of the insoluble components before reprecipitation.
[0007] Soluble, mostly low-molecular-weight impurities such as flavorings, degraded stabilizers, and other undesirable substances with a molecular weight above 200 g / mol ("semi-volatiles"), which prevent the use of the recycled materials in contact-sensitive applications, are often less volatile than the solvent used and are therefore not separated, or only insufficiently separated, in this way because they remain in the polymer matrix when the solvent evaporates. The separation of these impurities is achieved using the swelling process registered under WO 2018 / 091356 A1. The pressing of the swollen polymer matrix described therein removes the dissolved impurities to the extent that the residual solvent content achieved by pressing can be reduced. High purities can be achieved by repeated swelling and pressing, which involves corresponding technical effort. 1040-27163 2 02.01.2026
[0008] Object of the invention
[0009] The disadvantages of the described state of the art necessitate the improvement of the described source process for the separation of low molecular weight impurities.
[0010] Description
[0011] The problem is solved in a recycling process for contaminated plastics by the features listed in the characterizing section of claim 1. Further developments and / or advantageous embodiments are the subject of the dependent claims.
[0012] The invention is characterized in that the polymer mixture is cooled until it acquires a sponge-like, squeezeable structure in the form of a polymer sponge as a solid phase, in which the target polymer is present separately from the solvent and impurities, the solvent and impurities forming a liquid phase, and that the sponge-like structure is mechanically squeezed, thereby separating the solvent and impurities from the sponge-like structure. In other words, cooling the polymer mixture yields a sponge-like, squeezeable structure in the form of a polymer sponge, the pore volume of which is filled with solvent. The solvent, along with the impurities dissolved therein, is mechanically separated from the polymer by squeezing the sponge-like structure.The formation of a solid and a liquid phase facilitates the pressing of the polymer sponge and significantly improves the purity of the "solidified" target polymer with regard to low molecular weight impurities.
[0013] According to the invention, the target polymer is preferably a polyolefin. Preferred polyolefins are polypropylene (PP) and / or polyethylene (PE), in particular HDPE. Exemplary impurities that can be separated from the target polymer using the process according to the invention are pyrene, hexadecanal, diethylhexyl phthalate, Irganox 1076, Irgafos 168 and / or Irganox 1010.
[0014] During the cooling step of the polymer mixture, preferably in a cooling section, the solvent, along with the dissolved impurities, and the polymer sponge exist as two phases, since the target polymer solidifies into a solid polymer sponge. At the end of the cooling section, the solvent is finely dispersed within the polymer sponge. The cooling of the polymer mixture can be carried out either in batches in cooling tanks or continuously in a cooling section. Temperature and 1040-27163 3 02.01.2026
[0015] Pressure must be set so that as little solvent as possible evaporates during pressing and the drainage of the solvent is not hindered by plasticization of the polymer. Pressing is relatively simple, but it is essential that the temperature does not become too high during the process. If the material did not pass through the cooling section or was too hot after the cooling section, separation of the polymer, solvent, and impurities would not be possible in the press. This is because, without cooling, the polymer and solvent form a liquid, viscous polymer mixture that cannot be mechanically separated by a press. Only when the polymer precipitates from the solution and is separated from the polymer and solvent can the polymer be pressed out and thus separated from the solvent and the dissolved impurities.
[0016] If, after cooling, the material were not processed by a press but the solvent were removed by evaporation (e.g., by temperature, an externally applied gas stream, or vacuum), the impurities in the desired molecular size range of 200–1,000 g / mol, preferably 300–1,000 g / mol, and particularly preferably 400–1,000 g / mol, would remain in the material. During mechanical pressing, the liquid solvent, including the impurities dissolved in it, is removed from the polymer matrix. When the solvent evaporates, it changes from a liquid to a gaseous state. However, the impurities remain in the solid polymer matrix because they are less volatile than the solvent.
[0017] Solvents that can be used in the process according to the invention are aliphatic saturated and / or unsaturated hydrocarbons, preferably open-chain and / or cyclic aliphatic saturated and / or unsaturated hydrocarbons, and particularly preferably open-chain and / or cyclic aliphatic saturated and / or unsaturated hydrocarbons with C6-C10 carbon atoms. It is self-evident to those skilled in the art that aliphatic saturated and / or unsaturated hydrocarbons, as well as the preferred embodiments mentioned above, include branched and unbranched representatives.
[0018] It has proven advantageous to cool the polymer mixture to a temperature lower than the boiling point of the solvent, preferably lower than 60°C and particularly preferably lower than 50°C. This prevents excessive evaporation of the solvent during cooling. 1040-27163 4 02.01.2026
[0019] Advantageously, the vapor pressure of the solvent during cooling is less than 0.5 bar, preferably less than or equal to 0.3 bar, and particularly preferably less than or equal to 0.2 bar. In combination with the low temperature, the low vapor pressure of the solvent prevents unwanted evaporation. This ensures that sufficient solvent remains in the polymer sponge for effective squeezing. Furthermore, the impurities are better dispersed in a sufficient quantity of solvent.
[0020] Surprisingly, it has been found that temperature and pressure control during the cooling and pressing process significantly influences the efficiency and effectiveness of the cleaning process. Molecular contaminants in solution are generally less volatile than the solvent. The more completely the solvent in the liquid phase (including dissolved contaminants) is separated from the polymer sponge, or is present separately, the better the molecular contaminants can be removed. If the solvent evaporates directly from the swollen structure, the less volatile contaminants remain in the polymer sponge. Prerequisites for separation in the liquid phase are, firstly, process conditions (pressure and temperature) that are sufficiently different from the solvent's evaporation conditions, and secondly, preventing plasticization of the polymer during the pressing process to ensure solvent drainage.Appropriately configured conditions enable high purification rates even with a single swelling and pressing.
[0021] The invention is also preferably characterized in that the polymer sponge is formed in which the polymer mixture flows through a cooling section. According to the invention, the cooling section is preferably a tube-in-tube heat exchanger or a cooling screw. A tube-in-tube heat exchanger is, for example, a double-tube heat exchanger with a straight or spiral design. A coaxial heat exchanger represents an exemplary spiral design for a double-tube heat exchanger. This enables a continuous cooling process, which increases the throughput. The cooling section can also be divided into two or more segments, with these segments having different temperature settings. This makes it possible to coordinate the material flow and cooling particularly advantageously in order to prevent pressure losses as much as possible on the one hand, and to achieve optimal cooling effect on the other. 1040-27163 5 02.01.2026
[0022] As explained above, it is preferred that the cooled polymer sponge is fed into a press, and the solvent, along with the impurities, is forced out of the polymer sponge within the press. The temperature at the press inlet corresponds to the temperature at the outlet of the cooling section. The solvent is thus finely dispersed within the polymer sponge. Screw presses, calender presses, and roller mills have proven particularly suitable as presses. It is essential that the press chamber can be cooled.
[0023] In a further preferred embodiment of the invention, the press is cooled so that the temperature of the polymer sponge is less than 80°C, preferably less than 70°C and particularly preferably less than 60°C, so that as little solvent as possible evaporates in the press and plasticization of the polymer sponge is prevented.
[0024] It is preferred that the vapor pressure of the solvent in the press is less than or equal to 0.6 bar, preferably less than or equal to 0.4 bar, and particularly preferably less than or equal to 0.3 bar. This low vapor pressure prevents unwanted evaporation of the solvent. At the temperatures specified in the preceding paragraph, the vapor pressure of the solvent is a consequence of the temperature. By precisely adjusting the operating parameters such as temperature, vapor pressure, ratio of polymer sponge to solvent, and pressure in the press, a residual solvent content in the purified polymer sponge after pressing of less than 5% by mass (for example, 50 kg solvent to 950 kg HDPE), preferably less than 4% by mass (for example, 40 kg solvent to 960 kg HDPE), and particularly preferably less than 3% by mass (for example, 30 kg solvent to 970 kg HDPE) can be achieved.Accordingly, only gentle pressing leads to this low residual solvent content.
[0025] It is advantageous to shred the polymer sponge, for example by a cutting device comprising one or more rotating blades, granulators or guillotine blades, before feeding it into the press. This ensures non-destructive feeding to the press.
[0026] In another preferred embodiment of the invention, the target polymer is swollen or dissolved in the polymer mixture and is preferably precipitated and filtered after dissolution. The form in which the target polymer is present is of secondary importance. The essential factor is the formation of the polymer sponge. 1040-27163 6 02.01.2026
[0027] through cooling, for example in a cooling section. Filtration makes it possible to remove undissolved components and / or color pigments from the polymer mixture.
[0028] In another preferred embodiment of the invention, the residual solvent content in the pressed polymer sponge is reduced after pressing by a post-treatment.
[0029] The post-treatment preferably consists of gas flushing through the extruded polymer sponge at a maximum of 115°C, preferably between 95°C and 115°C, or vacuum treatment of the extruded polymer sponge, which has been preheated to 30 to 70°C, preferably between 40°C and 60°C, particularly preferably between 40°C and 50°C, and / or degassing during extrusion of the extruded polymer sponge. Gas flushing can be achieved using an inert gas such as nitrogen or argon. This leaves residual solvents of less than 100 ppm in the extruded material.
[0030] It is preferred that the solvent is separated from the impurities in a solvent recovery process, in particular by means of a membrane separation process and / or distillation, and that the recovered solvent is then brought back into contact with a target polymer. This makes the recycling process sustainable because only a small amount of solvent is lost through evaporation and, consequently, little fresh solvent is required.
[0031] In a further preferred embodiment of the invention, the temperature of the target polymer upon contact or mixing with the solvent is up to 20°C below or above its melting point, and preferably lies between its melting point and 20°C below. This ensures reliable dissolution of the target polymer before the polymer slurry is cooled.
[0032] In a further embodiment, the target polymer undergoes washing, at least a cold wash, and sorting, in particular dyeing and polymer sorting, before being brought into contact with the solvent. This ensures that the target polymer is already free of larger surface impurities greater than 1000 g / mol before mixing with the solvent, and that the solvent can selectively extract the low molecular weight impurities ("semi-volatiles").
[0033] Further advantages and features will become apparent from the following description of an embodiment of the invention with reference to a schematic flow diagram. 1040-27163 7 02.01.2026
[0034] Figure 1: Flowchart of a recycling process for contaminated plastics
[0035] Figure 1 shows a block flow diagram illustrating a recycling process for contaminated plastics. Generally, the plastic material to be recycled is delivered to a recycling plant in bales. This usually consists of collected mixed plastics, particularly plastic containers and / or plastic bottles, which are processed into recyclable plastics. The different plastics are sorted and preferably shredded into flakes. In process step 11, the flakes are washed, at least in a cold wash, and in process step 13, they are sorted. The sorting usually includes color sorting and polymer sorting. This separates different target polymers, which are already pre-cleaned. A target polymer could be, for example, HDPE or PP. The process steps described above are generally known from the prior art.
[0036] In process step 15 (dissolution process), the target polymer, which is present as flakes, is brought into contact with or mixed with a solvent. Alternatively, a product extruded from the flakes (e.g., a melt strand or solidified granules) can first be brought into contact with the solvent. Adding melt to a solvent container or solvent reactor is preferred over adding flakes. The solvent and the target polymer interact to form a polymer mixture known as a "polymer slurry." The term "polymer slurry" refers to this polymer mixture and is a technical term. Depending on the solvent content, either a swollen or a dissolved target polymer is formed. It is preferred that the temperature during mixing is up to 20°C below the melting point of the target polymer.For HDPE, which has a melting point of 135°C, a dissolution temperature between 115°C and 135°C is preferred. The pressure during the dissolution process must be at least equal to the vapor pressure of the solvent at the selected process temperature to prevent unintended solvent evaporation. The term "process temperature" refers to the material temperature of the polymer slurry. Aliphatic hydrocarbons have proven to be well-suited as solvents.
[0037] According to the invention, the polymer slurry is cooled. This can take place in a cooling section 17. Through cooling, the polymer slurry forms a solid, sponge-like structure. 1040-27163 8 02.01.2026
[0038] The resulting structure is a polymer sponge, which can be squeezed out. This polymer sponge consists of the target polymer in which the solvent is finely dispersed. Impurities with low molecular weights between 200 g / mol and 1000 g / mol are dissolved in the solvent and can therefore be removed or extracted from the target polymer. These impurities may be components of previous fillers that have migrated into the target polymer. Other removable impurities may include functional additives added to the target polymer, such as color pigments, stabilizers, or antioxidants. Examples of impurities that can be separated include pyrene (202.25 g / mol), hexadecanal (240.42 g / mol), Irganox 1076 (530 g / mol), and Irgafos 168 (646.9 g / mol).
[0039] In order for the polymer sponge to form, cooling is necessary in the exemplary embodiment using n-heptane as the solvent. This cooling must be at least 40°C below the boiling point of n-heptane at ambient pressure. Temperatures below 50°C with a solvent vapor pressure of less than or equal to 0.2 bar are preferred. This prevents excessive evaporation of the solvent during cooling.
[0040] Basically, the formation of the polymer sponge is an optimized combination of the thermal properties of the target polymer and its solubility in a given solvent.
[0041] Optionally, the polymer sponge can be comminuted in a comminution device 19, for example, in the form of a cutting device 19, and then fed to a press 21. In the case of continuous sponge production, a continuous strand is fed to the press 21. The temperature at the inlet of the press 21 corresponds to the temperature at the outlet of the cooling section 17. The solvent is finely dispersed within the polymer sponge. The contaminated solvent can be very effectively mechanically pressed out of the polymer sponge. Thermal removal of the solvent is not intended. Perforations are provided in the press chamber to retain the polymer sponge and allow the solvent to escape from the press area. The temperature in the press 21 must be controlled or explicitly cooled to minimize solvent evaporation and prevent plasticization of the polymer.Preferably, the temperature of the polymer sponge is less than 60°C and the vapor pressure of the solvent is less than or equal to 0.3 bar. These process parameters enable the residual-1040-27163 9 02.01.2026.
[0042] The solvent content in the extruded polymer sponge is less than 3% by mass. For example, in a 1000 kg extruded polymer sponge containing the target polymer HDPE, 970 kg of HDPE is followed by 30 kg of solvent. Suitable presses include screw presses, calender presses, and roller mills that can be cooled.
[0043] The boiling point of the solvent is selected such that the residual solvent content after pressing 21 can be further reduced by a post-treatment 23. This allows the residual solvent content to be reduced to less than 100 ppm. The post-treatment can be carried out as a thermal post-treatment of the pressed polymer sponge in an (inert) gas stream at a maximum temperature of 115°C. Alternatively, a vacuum treatment of the pressed, preheated polymer sponge in the temperature range of 30–70°C or degassing of the pressed material during extrusion into pellets is also conceivable.
[0044] The purified target polymer can be fed to an extrusion 25 for pellet production. The solvent pressed out in the press 21 and the solvent evaporated in the post-treatment 23 are fed to a solvent recovery unit 27, where the impurities are separated from the solvent. The solvent recovery unit 27 can be implemented using a membrane separation process. The recovered solvent can be brought back into contact with contaminated target polymer in process step 15. If necessary, the recovered solvent can be replenished with fresh solvent. 1040-27163 10 02.01.2026
[0045] Legend:
[0046] 11 Flake Laundry
[0047] 13 Flake sorting
[0048] 15 Contacting target polymer and solvent 17 Cooling section
[0049] 19. Shredding, cutting device
[0050] 21 Press
[0051] 23 Aftercare
[0052] 25 Extrusion
[0053] 27 Solvent processing
Claims
1040-27163 11 02.01.2026 1. Recycling process for contaminated plastics for the separation of low molecular weight contaminants with molecular weights between 200 g / mol and 1000 g / mol comprising the following process steps: - Contacting (15) the target polymer with a solvent to produce a polymer mixture in order to separate low molecular weight impurities present in the target polymer from the target polymer and - Separation of the solvent and the impurities dissolved in the solvent from the target polymer, characterized by that the polymer mixture is cooled until it acquires a sponge-like, squeezeable structure in the form of a polymer sponge as a solid phase, in which the target polymer is separated from the solvent and impurities, with the solvent and impurities forming a liquid phase, and that the sponge-like structure is mechanically squeezed, thereby separating the solvent along with the impurities from the sponge-like structure.
2. Recycling process according to claim 1, characterized in that the polymer mixture is cooled to a temperature which is lower than the boiling point of the solvent, preferably lower than 60°C and particularly preferably lower than 50°C.
3. Recycling process according to claim 1 or 2, characterized in that the vapor pressure of the solvent during cooling is less than 0.5 bar, preferably less than or equal to 0.3 bar and particularly preferably less than or equal to 0.2 bar.
4. Recycling process according to one of the preceding claims, characterized in that the polymer sponge is formed in which the polymer mixture flows through a cooling section (17). 1040-27163 12 02.01.2026 5. Recycling process according to one of the preceding claims, characterized in that the cooled polymer sponge is fed into a press (21) and the solvent with the impurities is pressed out of the polymer sponge in the press (21).
6. Recycling process according to claim 5, characterized in that the press (21) is cooled so that the temperature of the polymer sponge is less than 80°C, preferably less than 70°C and particularly preferably less than 60°C.
7. Recycling process according to claim 5, characterized in that the vapor pressure of the solvent in the press is less than 0.6 bar, preferably less than 0.4 bar and particularly preferably less than 0.3 bar.
8. Recycling process according to one of the preceding claims, characterized in that the polymer sponge is shredded, for example by a cutting device (19), before being fed to the press (21).
9. Recycling process according to one of the preceding claims, characterized in that the target polymer is swollen or dissolved in the polymer mixture and is preferably recrystallized and filtered after dissolution.
10. Recycling process according to one of the preceding claims, characterized in that the residual solvent content in the squeezed polymer sponge is reduced after pressing by a post-treatment (23).
11. Recycling process according to claim 10, characterized in that the post-treatment (23) takes place in the form of a gas flow through the squeezed polymer sponge at max. 115°C or a vacuum treatment of the squeezed polymer sponge preheated to 30 to 70°C and / or degassing during an extrusion of the squeezed polymer sponge.
12. Recycling process according to one of the preceding claims, characterized in that the solvent is separated from the impurities in a solvent recovery unit (27), in particular by means of a membrane separation process, and the recovered solvent is brought back into contact with a target polymer. 1040-27163 13 02.01.2026 13. Recycling process according to one of the preceding claims, characterized in that the temperature of the target polymer when brought into contact (15) or when mixed with the solvent is up to 20°C below or above the melting point of the target polymer and preferably between the melting point and 20°C below it.
14. Recycling process according to one of the preceding claims, characterized in that the pressure during mixing of the target polymer with the solvent corresponds at least to the vapor pressure of the selected solvent at process temperature.
15. Recycling process according to one of the preceding claims, characterized in that the target polymer has undergone a washing (11), at least a cold washing and a sorting (13), in particular a dyeing and a polymer sorting, before being brought into contact (15) with the solvent.