METHOD AND PLANT FOR THE DEPOLYMERIZATION OF PLASTIC MATERIAL

Description

[0001] The invention relates to a method for the depolymerization of plastic material. It further relates to a system for the depolymerization of plastic material.

[0002] Worldwide, over 300 million tons of plastic packaging waste are generated every year. Only a small proportion of this is recycled. In 2018, Germany generated approximately 3.25 million tons of plastic packaging waste. Despite intensive efforts by the German waste management industry and numerous regulatory measures, the rate of material recycling of plastic waste in Germany has stagnated at around 46% for the past 10 years. This is because packaging waste is not generated as pure polymers, but rather as mixed plastics containing a wide variety of contaminants. Sorting and cleaning these materials is neither technologically feasible nor economically viable.

[0003] To ensure that plastic waste can still be meaningfully recycled, a variety of chemical recycling processes have been developed over the past twenty years. Regardless of whether these processes are called pyrolysis, thermolysis, oleation, or depolymerization, the operating principle is almost identical in all known methods: The feed material is heated in a reactor under exclusion of air to temperatures of 400 °C to 600 °C. In the reactor, the polymer chains are broken down into monomers and hydrocarbons of varying lengths and structures. The product exits the reactor as oil vapor and is then either condensed in a heat exchanger or separated into several fractions with different boiling points in a distillation column.

[0004] The hydrocarbons produced in this way can either be used as raw materials in the petrochemical industry or further processed into fuel in a refinery. Most processes yield approximately 10 to 15% short-chain hydrocarbons (low-boiling hydrocarbons) and gases, which are typically used to generate the required process energy. This is done either by means of burners that directly heat the reactors or via diesel generators for on-site power generation.

[0005] Many processes use catalysts and other additives to accelerate the reaction, neutralize acids, and influence the composition of the final product.

[0006] Most of the processes developed so far are characterized by a very high level of technological complexity, which generally entails very high investment and operating costs and consequently presents substantial obstacles to wider commercial application. Other processes, on the other hand, can be operated reliably on a laboratory or pilot plant scale, but fail when attempts are made to scale up economically.

[0007] WO 2005 / 087897 A1 discloses a process and a plant for converting a plastic material derived from plastic waste into diesel fuel. The plant includes a pyrolysis chamber from which atmospheric oxygen is to be removed by means of a purge gas. The purge gas, which can be nitrogen or helium, is provided in a storage container. Purging the pyrolysis chamber with the purge gas is to be carried out with each batch change in order to minimize the unintentional entry of atmospheric oxygen into the pyrolysis chamber and to reduce the oxygen concentration within it as much as possible. This approach requires very high investment and operating costs as well as the storage of the purge gas in large tanks. The process described in WO 2005 / 087897 A1 is operated batch by batch.

[0008] A process for liquefying a plastic material using continuous operation is known from DE 695 32 712 T2. The continuous operation is intended to enable the use of several twin-screw extruders arranged in a cascade. The permanent movement of the extruder screws is intended to prevent coking, which represents a significant advantage over the commonly used stirred-tank reactors or rotary kilns. However, sealing the twin-screw extruders against the ingress of atmospheric oxygen and the escape of gases from the extruder is technically challenging.

[0009] Processes for obtaining fuels from plastic waste are known from US 2016 / 0130505 A1 and WO 2020 / 008050 A1, which require a catalytic converter. In these processes, a gaseous material obtained from the plastic waste in a pyrolysis chamber is fed to the catalytic converter to modify its structure. The use of extruders for the depolymerization of plastic material is known without the use of a planetary roller extruder or by heating using induction methods (JP H11 106758 A, BE 884 302 A, US 5 631 346 A). An inductively heated extruder is known in connection with the depolymerization of plastic material, but not with a planetary roller extruder (WO 2017 / 064211 A1, EP 2 233 547 B1, JP H11 302663 A).The use of a planetary roller extruder for the treatment of plastic material is known, but not in combination with induction heating agents for carrying out depolymerization (DE 10 2010 006476 A1, US 9 556 319 B1, US 2013 / 023639 A1, US 2015 / 191578 A1, EPS 257 644 B1, JP 4 609947 B2).

[0010] The throughput of a plastic waste depolymerization process depends essentially on how quickly, reliably, and efficiently the required process heat can be transferred into the reactor's interior. In other words, the higher the maximum heat flux density (heat flux per m² < heat exchange surface area), the more efficient the process.

[0011] Many existing processes use electric resistance heating to generate process heat. However, the electrical insulation required for the heating elements inevitably limits the heat flow considerably. Another disadvantage of electric resistance heating is the very limited lifespan of the heating elements, resulting in high maintenance costs and frequent operational interruptions.

[0012] In some processes, the process heat is generated via gas or oil firing. Even with this approach, the heat flux density is limited. Furthermore, the depolymerization temperature cannot be precisely controlled with direct firing. While the heat flux can be increased with significantly higher temperatures at the reactor wall, this inevitably leads to increased coking inside the reactor.

[0013] There is therefore a need for a technologically reliable and commercially viable process for the depolymerization of mixed plastics.

[0014] The object of the invention is to eliminate the disadvantages of the prior art. In particular, a process for the depolymerization of plastic materials, especially composite plastics, is to be provided, which exhibits lower technological effort, higher technological reliability, and lower energy consumption. Furthermore, a plant for the depolymerization of plastic materials, especially composite plastics, which can be used to carry out the process, is to be provided.

[0015] This problem is solved by the features of claims 1 and 10. Advantageous embodiments of the inventions result from the features of the dependent claims.

[0016] According to the invention, a process for the depolymerization of plastic material, in particular of mixed plastics, is provided, comprising the following steps: (a) Melting the plastic material to obtain a molten material; (b) Feeding the molten material into a planetary roller extruder; (c) Heating the molten material in the planetary roller extruder to obtain oil vapor; and (d) Cooling the oil vapor.

[0017] The process according to the invention enables the depolymerization of plastic material. The process can be a continuous process. The planetary roller extruder is a reactor in which the depolymerization takes place. The depolymerization can be carried out continuously in the planetary roller extruder.

[0018] The plastic material can be a composite plastic, for example, a composite plastic made from waste plastics. In one embodiment, a composite plastic is understood to be a mixture containing at least two types of plastic. One type of plastic differs from another if it has at least one different repeating unit. A type of plastic can be a homopolymer or a copolymer. Examples of types of plastic include polyamide, polycarbonate, polyethylene, polyethylene terephthalate, polypropylene, polystyrene, polyurethanes, polyvinyl chloride, epoxy resins, phenolic resins, and polyester resins, although this list is not exhaustive.

[0019] The term "depolymerization" refers to the breakdown of polymers into compounds with lower molecular weights. The polymer can be broken down into its monomers, although this is not strictly necessary according to the invention. It may be possible to obtain a middle distillate from the polymer material through depolymerization. A middle distillate is understood to be a hydrocarbon mixture with a boiling range of 180 °C to 360 °C. The meaning of the term "middle distillate" can correspond to its meaning in connection with the refining of crude oil.

[0020] It may be necessary to grind the plastic material before carrying out step (a). This is required if the plastic material is not already available in a ground state. The ground plastic material preferably has a particle size of no more than 50 mm. The grinding can be carried out, for example, mechanically.

[0021] It may be necessary for the shredded plastic material to be free of contaminants, or for contaminants to be largely removed before step (a) is carried out. Ideally, all contaminants should be removed, although complete removal is not achievable in practice. Contaminants are non-plastic materials. Examples include metals, ceramics, glass, minerals, and soil, but this list is not exhaustive. Contaminants can be removed from the plastic material using methods known from recycling technology. Removing contaminants from the shredded plastic material is advantageous to protect the planetary roller extruder from excessive wear.

[0022] Step (a) involves melting the plastic material to obtain a molten material. The plastic material can be a comminuted plastic material. To melt the plastic material, it is preferably heated to a temperature in the range of 200 to 250 °C, more preferably in the range of 230 to 250 °C, and most preferably to 250 °C. This temperature is hereinafter also referred to as the pre-melting temperature. The melting of the plastic material can be carried out in a melting device, which is hereinafter referred to as the melting device. The melting device can, for example, be a melt extruder. The plastic material can be fed to the melting device, for example, via a feed hopper and a metering screw.Melting the plastic material removes residual moisture and / or volatile components. These residual moisture and / or volatile components can escape from the melt extruder via atmospheric degassing. A "volatile component" is defined as a component whose boiling point is at or below the pre-melting temperature. These "volatile components" can include organic compounds such as short-chain hydrocarbons.

[0023] In the melting unit, the plastic material can thus be pre-melted and heated to a pre-melting temperature of up to 250 °C. Residual moisture contained in the shredded plastic material can escape as water vapor, air, and other volatile components via atmospheric degassing, even before the plastic material enters the planetary roller extruder, which serves as the reactor.

[0024] It may be provided that one or more catalysts are added to the plastic material before step (a). The plastic material may be a comminuted plastic material. It may also be provided that one or more additives are added to the plastic material before step (a). The plastic material may be a comminuted plastic material. The term "additive" here refers to an additive that is not a catalyst. Catalysts and additives are collectively referred to as additives in the following. If the plastic material melted in step (a) contains one or more additives, the additive(s) will be homogeneously distributed in the melting plastic material in step (a).In particular, a homogeneous distribution of the additive(s) in the melting plastic material can be achieved using the melting device, for example the melt extruder.

[0025] It may be possible to separate any contaminants still contained in the molten material obtained in step (a). These contaminants may be those mentioned above. In practice, the contaminants separated from the molten material are metal parts, particularly smaller metal parts, and / or mineral impurities. A small metal part is defined as a metal part whose size does not exceed the size of the particles of the pulverized plastic material. Separating the contaminants from the molten material is advantageous to protect the planetary roller extruder from excessive wear.

[0026] For example, the molten material can be directed to a melt filter to remove impurities. The melt filter can be a continuously operating melt filter. The molten material can be introduced into the melt filter via a pipeline. The pipeline can extend from the outlet of the melting unit, where the molten material exits, to the inlet of the melt filter. The molten material can be introduced into the melt filter at a temperature corresponding to the pre-melting temperature. The molten material can be maintained in the melt filter at a temperature corresponding to the pre-melting temperature.

[0027] Step (b) involves feeding the molten material into a planetary roller extruder. The molten material can be fed into the planetary roller extruder via a pipeline. If no melt filter is provided, the pipeline can extend from the outlet of the melting unit, where the molten material exits, to the inlet of the planetary roller extruder. If a melt filter is provided, the pipeline can extend from the outlet of the melt filter, where the molten material exits, to the inlet of the planetary roller extruder. The molten material can be introduced into the planetary roller extruder at a temperature corresponding to the pre-melting temperature.

[0028] Step (c) involves heating the molten material in the planetary roller extruder, generating oil vapor. The molten material is heated to a temperature above the pre-melting temperature. This temperature is referred to as the depolymerization temperature. For example, the molten material in the planetary roller extruder can be heated to a temperature in the range of 380 to 600 °C, preferably 450 to 480 °C. Raising the temperature to the depolymerization temperature causes the molten material to depolymerize, producing oil vapor. This oil vapor can be a mixture of hydrocarbon molecules of varying sizes and structures.

[0029] Heating can be achieved by inductive heating of the planetary roller extruder. At least one inductor can be provided to transfer energy to the material inside the planetary roller extruder. For example, the inductor can transfer a heat flow of 10 to 100 kW to the reactor wall of the planetary roller extruder. This very high heat flow, generated by inductive heating, makes it possible to heat the molten material fed into the planetary roller extruder very quickly to the depolymerization temperature. The inductor can have one or more induction coils. The induction coil(s) can be wound concentrically around the outer wall of the planetary roller extruder or designed as sleeves, for example, as split sleeves.

[0030] The use of a planetary roller extruder enables thorough mixing of the molten material introduced into it. Furthermore, the planetary roller extruder allows for the continuous transport of the molten material. The planetary roller extruder provided according to the invention enables continuous operation of the process according to the invention. The process according to the invention is therefore a continuous process.

[0031] In the planetary roller extruder provided according to the invention, the oil vapor can be generated as part of a mixture. This mixture contains, in addition to the oil vapor, another component. This other component is predominantly solid or pasty. This component typically constitutes only a small proportion by weight of the mixture. Typically, the proportion of the other component is no more than 10 wt.%, based on the mixture; generally, the proportion is between 5 and 10 wt.%, based on the mixture exiting the planetary roller extruder. The other component can be a slag containing, for example, unvaporized solids and / or bitumen, or consisting thereof. It can be provided that the mixture is fed into a separation device for separating the oil vapor from the mixture after step (c) and before step (d). The separation device can be a separation chamber.The separation chamber can be located directly at the outlet of the planetary roller extruder, so that the mixture exiting the extruder enters the separation chamber immediately. In the separation chamber, the other component is separated from the oil vapor. The separated component can be discharged from the separation chamber by means of a conveying device, for example, a cooled screw. Phase separation is achieved in the separation chamber because the oil vapor is present as a gas phase, while the other components of the mixture are present as a solid / liquid phase, which is predominantly solid. Alternatively or additionally, the gas phase, or a portion thereof, can be discharged through one or more outlets located along the outer cylinder of the planetary roller extruder.

[0032] With regard to the depolymerization temperature, it is essential for plant and operational safety that both the unintentional ingress of atmospheric oxygen into the planetary roller extruder and the escape of flammable liquids and gases are reliably prevented. Unlike conventional reactors used for the depolymerization of plastic materials, sealing the drive shaft of the planetary roller extruder does not present a particular technological challenge. This is because the material entering the planetary roller extruder is conveyed away from the shaft seal towards the discharge. Unlike many agitator reactors, the shaft seal is not exposed to high pressures or high temperatures. If a separation chamber is provided, the transition from the planetary roller extruder to the separation chamber is inherently open by design. There are no moving parts that require external sealing.The discharge of the small amount of slag is expediently carried out in the lower area of ​​the separation chamber, preferably via a cooled screw conveyor.

[0033] The common problem of coking on the reactor wall, which occurs in all known processes for the depolymerization of plastic waste, is avoided when using a planetary roller extruder. Coking results in reduced heat transfer, high maintenance costs, and frequent plant downtime. The use of a planetary roller extruder as a reactor for the depolymerization of plastic material, as described in the invention, offers significant advantages over all other extruder types, particularly with regard to preventing coking.

[0034] The planetary roller extruder was invented in the early 1950s and is now used as a continuous mixer and / or reactor in a wide variety of industries, including the chemical industry, rubber mixing plants, paint and coatings manufacturing, and the food industry. A planetary roller extruder has an outer cylinder containing a central spindle and at least three planetary spindles. These components are helically geared and mesh together. The mechanical drive is provided by the central spindle, also known as the drive spindle, which drives the planetary spindles. The planetary spindles, in turn, rotate on their own axis and move uniformly along the inner wall of the cylinder (see also Fig. 2 (below). The outer wall of the cylinder forms the outer wall of the planetary roller extruder. The planetary roller extruder preferably has three to twelve planetary spindles. It can have more than twelve planetary spindles, but this is not preferred. Preferably, the planetary roller extruder has 3 to 9, more preferably 4 to 8, and most preferably 5 to 7 planetary spindles. In one embodiment, it has six planetary spindles.

[0035] The continuous rotation of the planetary spindles not only reliably prevents any coking on the inner wall of the cylinder, but also ensures exceptionally rapid transfer of process heat from the outer wall of the cylinder to the interior of the planetary roller extruder. Thanks to the continuous and intensive mixing of the molten material fed into the planetary roller extruder, very high heat flows can be transported from the outer wall of the cylinder to the interior. Furthermore, this continuous mixing of the molten material promotes consistent and uniform gas formation within the extruder. This constant and uniform gas flow is a significant advantage for the stable operation of the entire system.The molten material fed into the planetary roller extruder can be intensively mixed by means of the helically toothed planetary spindles and continuously transported forward, i.e. towards the exit from the planetary roller extruder.

[0036] The planetary roller extruder may be designed to have two or more reaction zones. These reaction zones may include one, several, or all of the following: (i) Heating zone. The heating zone is a reaction zone in which the feed material is heated to the depolymerization temperature. Vacuum degassing may also be provided in the heating zone. Furthermore, one or more lateral inlets for additives, preferably for other additives, may be provided in the heating zone. (ii) Depolymerization zone. The depolymerization zone is a reaction zone in which the polymer chains are cleaved into shorter molecules. This reaction is endothermic; the required reaction energy is supplied via inductors. The depolymerization temperature prevails in the depolymerization zone. A shorter molecule is understood to be a molecule that has fewer carbon atoms than the cleaved polymer chain. The shorter molecules may, in particular, be hydrocarbon molecules. (iii) Evaporation zone.The evaporation zone is a reaction zone in which the shorter hydrocarbon molecules obtained in the depolymerization zone evaporate into oil vapor. The depolymerization temperature prevails in the depolymerization zone. (iv) Discharge zone. The discharge zone is a reaction zone in which the material introduced into this reaction zone is mostly oil vapor. If one or more separation chambers are provided, the oil vapor can flow towards the separation chamber(s) due to the vapor pressure. The small proportion of solids or slag is also transported towards the separation chamber(s) due to the continuous rotation of the central spindle and the planetary spindles.

[0037] Preferably, when the molten material enters the planetary roller extruder in step (c), it passes into the heating zone, where it is heated to the depolymerization temperature, resulting in heated molten material. From the heating zone, the heated molten material enters the depolymerization zone, where it is split and liquefied, yielding split and liquefied material. From the depolymerization zone, the split and liquefied material enters the evaporation zone, where it evaporates into oil vapor. From the evaporation zone, the oil vapor enters the discharge zone. Via the discharge zone, the oil vapor can exit the planetary roller extruder or be directed to a separation chamber.

[0038] The planetary roller extruder can have two or more segments, with four segments being a possible configuration. It can be configured to have a heating zone, a depolymerization zone adjacent to the heating zone, an evaporation zone adjacent to the depolymerization zone, and a discharge zone adjacent to the evaporation zone. The planetary roller extruder can have one segment for each reaction zone. For example, the planetary roller extruder can have a first segment for the heating zone, a second segment for the depolymerization zone, a third segment for the evaporation zone, and a fourth segment for the discharge zone. The second segment's first end face is adjacent to an end face of the first segment. The third segment's first end face is adjacent to the second end face of the second segment. The fourth segment's first end face is adjacent to the second end face of the third segment.The segments can have the same or different numbers of planetary spindles. The segments can share a common central spindle. If a separation chamber is provided, it can adjoin the second end face of the fourth segment.

[0039] The processing characteristics can be influenced by adjusting the number of planetary spindles. A minimal number of planetary spindles increases the filling volume of the planetary roller extruder and thus the residence time of the material within the extruder. Conversely, six or more spindles maximize both the mixing intensity and the heat and mass transfer. The planetary roller extruder can be designed modularly, allowing the number of planetary spindles to be adapted to the requirements of the respective reaction zone.

[0040] It is known that the addition of one or more catalysts can reduce the reaction temperature and / or increase the reaction rate of depolymerization in a planetary roller extruder. Zeolite is one example of a catalyst. Alkali formers can bind and inertize halogen and sulfur compounds released during depolymerization. The addition of hydrogen donors can significantly influence the composition of the hydrocarbons produced in the planetary roller extruder. Alkali formers and hydrogen donors are examples of additives. Due to the very intensive mixing action of the planetary roller extruder, the catalyst(s) and / or additive(s) are distributed quickly and evenly throughout the extruder's interior. Therefore, even very small quantities can exert their intended effect.Due to the permanent rotational movement, all components of the planetary roller extruder are self-cleaning and always have a metallically clean and catalytically active surface.

[0041] The cylinder wall is preferably made of a heat-resistant, high-alloy steel. One or more planetary spindles may be made of a catalytically active material. All planetary spindles may be made of a catalytically active material. Unlike the processes known from US 2016 / 0130505 A1 and WO 2020 / 008050 A1, no downstream catalyst is required; rather, the planetary roller extruder itself acts catalytically.

[0042] According to the invention, inductive heating can be provided in step (c). This allows the high thermal energy demand required for the depolymerization of plastic material, particularly composite plastics, to be met. The inductive heating can be achieved by inductively heating the outer wall of the planetary roller extruder cylinder. It can be provided that separate inductive heating is supplied for each segment of the planetary roller extruder. For example, an induction coil or sleeve can be provided for each segment.

[0043] The principle of inductive heat generation has been known for many years and is already used in a variety of applications, such as household stoves, kitchen appliances, heat treatment of metals, soldering, and welding. Due to its cylindrical design, the planetary roller extruder is particularly well-suited for inductive heating. Unlike reactors with complex geometries, the planetary roller extruder according to the invention allows for one or more induction coils to be wound concentrically around the outer wall of the extruder. The induction coils can also be designed as one or more sleeves, for example, as split sleeves.

[0044] With inductive heating of the planetary roller extruder, heat flux densities of up to 70 kW / m² can be achieved, many times greater than any other heating method used to date. The only limiting factor for the heat flux density is the temperature difference between the outer wall of the planetary roller extruder cylinder and the depolymerization temperature, as well as the thermal conductivity of the steel from which the cylinder is made.

[0045] Unlike other methods for generating process heat, inductive heating is virtually maintenance-free. This eliminates the frequent downtime and considerable maintenance costs associated with other methods. An inductively heated planetary roller extruder thus enables safe and economical operation with exceptionally high heat flux densities and throughput rates.

[0046] Step (d) involves cooling the oil vapor. Step (d) can also serve to condense the oil vapor. By cooling and condensing the oil vapor, an oil can be obtained. This oil can be the middle distillate. A cooling device can be provided for this purpose. The cooling device could be, for example, a heat exchanger, a condenser, a distillation column, or a quench condenser. The condenser could be an immersion condenser. In step (d), the oil vapor is cooled to a temperature below the depolymerization temperature. The temperature to which the oil vapor is cooled in step (d) is also referred to as the cooling temperature. The cooling temperature may depend on the subsequent use of the oil vapor or the oil. It may be provided that the oil vapor is cooled to room temperature in step (d).Alternatively, it can be provided that the oil vapor in step (d) is cooled to a temperature in the range of 250 to 300 °C.

[0047] The portion of the oil vapor that does not condense upon cooling can consist of a gas and / or vapor of low-boiling hydrocarbons. The gas consists of very short-chain hydrocarbons (C1 to C4). Low-boiling hydrocarbons are defined as mixtures of hydrocarbons in the C5 to C10 range with a boiling point of 35 °C to 210 °C. The mixture of gas and low-boiling hydrocarbons exiting the cooling system can, for example, be used for on-site power generation in a diesel generator.

[0048] The cooling temperature defines the separation point between the oil and the lighter-boiling substances. Substances that boil above the cooling temperature belong to the middle distillate. Substances that boil below or at the cooling temperature are lighter-boiling substances.

[0049] According to the invention, a system for the depolymerization of plastic material is also provided. The system according to the invention is particularly suitable for carrying out the process according to the invention. The system according to the invention can be operated continuously.

[0050] The system comprises a planetary roller extruder for heating the plastic material while generating oil vapor. Preferably, the plastic material heated in the planetary roller extruder while generating oil vapor is a molten material. As already described in connection with the process according to the invention, the molten material is obtained by melting the plastic material at the pre-melting temperature. The plastic material is preferably a granulated plastic material. Preferably, a molten material obtained by melting granulated plastic material at the pre-melting temperature while generating the molten material is introduced into the planetary roller extruder.

[0051] The planetary roller extruder can have inductive heating. For this purpose, the system according to the invention can include at least one inductor. The planetary roller extruder can have a cylinder in which a central spindle and at least three planetary spindles are arranged. One or more induction coils or sleeves can be arranged on the outer wall of the cylinder for inductive heating of the planetary roller extruder.

[0052] The system according to the invention can include a device for melting the plastic material before it enters the planetary roller extruder. This device is also referred to as a melting device. The melting device can, for example, be a melt extruder. The system according to the invention can further include a cooling device for cooling the oil vapor. The cooling device can, for example, be a heat exchanger, a condenser, a distillation column, or a quench cooler.

[0053] Further details of the apparatus according to the invention have already been described in connection with the method according to the invention. Reference is therefore made to the description of the method according to the invention.

[0054] The invention is explained in more detail below with reference to exemplary embodiments, which are not intended to limit the invention, and with reference to the drawings. Fig. 1 a flowchart to illustrate a first embodiment of the method and the system according to the invention; Fig. 2 a schematic sectional view of an embodiment of a planetary roller extruder of a system according to the invention; and Fig. 3 a flowchart to illustrate a second embodiment of the method and the system according to the invention.

[0055] The in Fig. 1 The schematically shown first embodiment of a system 101 according to the invention comprises a planetary roller extruder 106, which has four segments 106a, 106b, 106c, and 106d. The segments 106a, 106b, 106c, and 106d can be modules. The heating zone is formed in the first segment 106a, the depolymerization zone in the second segment 106b, the evaporation zone in the third segment 106c, and the discharge zone in the fourth segment 106d. The first end face of the second segment 106b abuts an end face of the first segment 106a. The first end face of the third segment 106c abuts the second end face of the second segment 106b. The fourth segment 106d abuts the second end face of the third segment 106c. The four segments 106a, 106b, 106c, 106d each have six planetary spindles 108, which are driven by a common central spindle 107 (see Fig. 2 The system 101 has a drive 103 for the central spindle 107. Between adjacent planetary spindles 108 of a segment 106a, 106b, 106c, 106d there is a gap. These gaps together form the interior 110 of the planetary roller extruder 106.

[0056] The interiors of segments 106a, 106b, 106c, and 106d together form the interior 110 of the planetary roller extruder 106. Equipment assigned to a specific segment 106a, 106b, 106c, or 106d is shown in Fig. 1 Identified by a letter corresponding to the letter used to identify the segment. The planetary roller extruder 106 is heated to the depolymerization temperature by inductive heating, which lies in the range of 380 to 600 °C, preferably from 450 to 480 °C.

[0057] The molten material 1 is the feed material. It was pretreated from the shredded plastic material by heating it to the pre-melting temperature in a melting unit (not shown). The molten material 1 is conveyed via a pipe to the first segment 106a of the planetary roller extruder 106, into which it is fed through an inlet 102 formed in the first segment 106a. The first segment 106a of the planetary roller extruder 106 also includes an inlet 104 for additives 2 and a vacuum degassing unit 105 for water vapor and volatile components 3. The inlet 102, the inlet 104, and the vacuum degassing unit 105 are located in the casing of the cylinder 109 of the planetary roller extruder 106. The inlet 104 can be a so-called "side feeder."

[0058] For each segment 106a, 106b, 106c, 106d of the planetary roller extruder 106, an inverter 111 is provided, in which the current frequency required for inductive heating is generated. For each segment 106a, 106b, 106c, 106d of the planetary roller extruder 106, an inductor 112 is also provided, to which the inverter 111 transfers electrical energy 4 and which generates the required heat energy directly into the cylinder 109, which forms the reactor wall of the planetary roller extruder 106. The inductor can have one or more coils wound around the outer cylinder 109. In the first embodiment described, each inductor 112 transfers a power output of 10 to 100 kW of thermal energy to the respective segment 106a, 106b, 106c or 106d of the planetary roller extruder 106. The inverters 111 can be modules. The inductors 112 can also be modules.

[0059] The material conveyed within the interior 110 of the planetary roller extruder 106 by the rotation of the planetary spindles 108 about their axes of rotation from the inlet of the planetary roller extruder 106 to its outlet is converted at the depolymerization temperature into a mixture of oil vapor and the other component, which may be slag. The slag consists essentially of unvaporized solids and bitumen. The mixture of oil vapor and the other component enters a separation chamber 113 directly at the outlet of the planetary roller extruder 106. The separation chamber 113 adjoins the fourth segment 106d.

[0060] In the separation chamber 113, the mixture separates into a gaseous phase, consisting of the oil vapor, and a predominantly solid phase, consisting of the slag. The slag 5 is discharged from the separation chamber 113 via a cooled screw conveyor at a first discharge 120. The oil vapor 6 leaves the separation chamber 113 at a second outlet via a pipe 114, where it is guided to a cooling device 115, which may be, for example, a heat exchanger, a condenser, a distillation column, or a quench cooler. In the cooling device, the oil vapor is cooled to the cooling temperature, thereby separating it into a gaseous phase, consisting of gases and low-boiling substances 7, and a liquid phase, consisting of the middle distillates 8, which are obtained as oil. The middle distillates 8 leave the cooling device 115 via the pipe 118.The gases and light boiling points 7 leave the cooling unit 115 via the pipeline 117, in which they are led to a combined heat and power plant 119.

[0061] The heat generated in the cooling unit 115 is recovered via a cooling circuit 116 which serves as a heat exchanger. The heat can be used, for example, for drying, melting, or hot washing the molten material.

[0062] The in Fig. 3 The second embodiment of a system 101 according to the invention, as shown, comprises a melt extruder 121 with a drive 122. The melt extruder 121 has a feed 123 through which comminuted plastic material 11 is introduced into the melt extruder 121. The comminuted plastic material 11 is the feed material. In the melt extruder 121, the comminuted plastic material 11 is heated to the pre-melting temperature while remaining molten. The molten material 1 exits the melt extruder 121 at a discharge 124 and is conveyed via a pipe 126 to the feed 102 of the planetary roller extruder 106. The melt extruder 121 also has a degassing unit 125 for water vapor and volatile components 3, which are separated from the crushed plastic material in the melt extruder 121 and are carried out of the melt extruder 121 via the degassing unit 125.Degassing 125 can be atmospheric degassing or vacuum degassing.

[0063] The planetary roller extruder 106 of the second embodiment corresponds to the one in Fig. 1 The planetary roller extruder shown is identical, except that no vacuum degassing 105 is provided. The molten material 1 enters the first segment 106a of the planetary roller extruder 106 via the inlet 102. An inverter 111 is provided for each segment 106a, 106b, 106c, 106d of the planetary roller extruder 106, in which the current frequency required for inductive heating is generated. Furthermore, an inductor 112 is provided for each segment 106a, 106b, 106c, 106d of the planetary roller extruder 106. The inverter 111 supplies electrical energy 4 to the inductor, which generates the required heat energy directly in the cylinder 109, which forms the reactor wall of the planetary roller extruder 106. The inductor can have one or more coils wound around the outer cylinder 109.In the described second embodiment, each inductor 112 transmits a power of 10 to 100 kW of thermal energy to the respective segment 106a, 106b, 106c or 106d of the planetary roller extruder 106.

[0064] The material conveyed within the interior 110 of the planetary roller extruder 106 by the rotation of the planetary spindles 108 about their axes of rotation from the inlet of the planetary roller extruder 106 to its outlet is converted at the depolymerization temperature into a mixture of oil vapor and the other component, which may be slag. The slag consists essentially of unvaporized solids and bitumen. The mixture of oil vapor and the other component enters a separation chamber 113 directly at the outlet of the planetary roller extruder 106. The separation chamber 113 adjoins the fourth segment 106d. The separation chamber 113 of the second embodiment also corresponds to the one described in Fig. 1The separation chamber shown is located in the separation chamber 113. Within the separation chamber, the mixture separates into a gaseous phase, consisting of the oil vapor, and a predominantly solid phase, consisting of the slag. The slag 5 is discharged from the separation chamber 113 via a cooled screw conveyor at a first discharge 120. The oil vapor 6 exits the separation chamber 113 at a second outlet via a pipe 114, where it is guided to a cooling device 115, which may, for example, be a heat exchanger. In the cooling device, the oil vapor is cooled to the cooling temperature, thereby separating it into a gaseous phase, consisting of gases and low-boiling substances 7, and a liquid phase, consisting of the middle distillates 8, which are obtained as oil. The middle distillates 8 exit the cooling device 115 via the pipe 118.The gases and light substances 7 leave the cooling unit 115 via the pipeline 117, which carries them to a combined heat and power plant 119. The electrical energy 12 generated in the combined heat and power plant 119 by burning the gases and light substances 7 can be used to supply the inverters 11 1a, 11 1b, 11 1c, 11 1d.

[0065] The second embodiment of the system 101 according to the invention comprises a thermal oil system 128. The liquid condensate in the cooling unit 115 is tempered to the cooling temperature by means of the thermal oil system 128. For this purpose, a pipeline 127 is provided for conveying the thermal oil from the thermal oil system 128 to the cooling unit 115, and a pipeline 129 is provided for conveying the thermal oil from the cooling unit 115 to the thermal oil system 128. The thermal oil system 128 is also used to temper the melt extruder 121 to the pre-melting temperature. For this purpose, a pipeline 130 is provided for conveying the thermal oil from the thermal oil system 128 to the melt extruder 121, and a pipeline 131 is provided for conveying the thermal oil from the melt extruder 121 to the thermal oil system 128. The cooling temperature can be precisely controlled by means of the thermal oil system 128.The thermal oil system 128 enables the use of the process heat generated during depolymerization in the planetary roller extruder 106 to heat the shredded plastic material 11 to the pre-melting temperature. Reference symbol list

[0066] 1 Molten material 2 Additives 3 Water vapor and volatile components 4 Electrical energy 5 Slag 6 Oil vapor 7 Gas and light boiling points 8 Middle distillates 11 Crushed plastic material 12 Electrical energy 101 Plant 102 Input 103 Drive 104 Input 105 Vacuum degassing for water vapor and volatile components 106 Planetary roller extruder, modules a to d 107 Central spindle 108 Planetary spindle 109 Cylinder 110 Interior 111 Inverter, modules a to d 112 Inductor, modules a to d 113 Separation chamber 114 Piping 115 Cooling device 116 Cooling circuit 117 Piping 118 Piping 119 Combined heat and power plant 120 Discharge 121 Melt extruder 122 Drive 123 Feed 124 Discharge 125 Degassing for water vapor and volatile components 126 Pipeline 127 Pipeline 128 Thermal oil system 129 Pipeline 130 Pipeline 131 Pipeline

Claims

1. A method for the depolymerization of a plastic material, the method comprising the steps of: (a) melting the plastic material to obtain a molten material (1); (b) feeding the molten material (1) into a planetary mill extruding machine (106); (c) heating the molten material in the planetary mill extruding machine (106) to obtain oil steam (6); and (d) cooling the oil steam (6).

2. The method according to claim 1, characterized in that in step (c) heating is performed by means of induction-heating the planetary mill extruding machine (106).

3. The method according to claim 1 or claim 2, characterized in that the plastic material is a grinded plastic material (11).

4. The method according to any of the preceding claims, characterized in that step (a) is carried out in a melting facility (121).

5. The method according to any of the preceding claims, characterized in that in step (c) the molten material (1) is heated to a temperature of 380 to 600°C.

6. The method according to any of the preceding claims, characterized in that in step (c) the molten material (1) is intermixed by means of the planetary mill extruding machine (106).

7. The method according to any of the preceding claims, characterized in that in step (c) the molten material is continuously transported by means of the planetary mill extruding machine (106).

8. The method according to any of the preceding claims, characterized in that in step (c) a mixture is obtained that contains oil steam (6), wherein the mixture subsequently to step (c) and before step (d) is transferred into a separating facility (113) for separating the oil steam (6) from the mixture.

9. The method according to any of the preceding claims, characterized in that step (d) is carried out in a cooling facility (115).

10. A plant for the depolymerization of a plastic material, wherein the plant (101) has a planetary mill extruding machine (106) for heating the plastic material to obtain oil steam (6) and wherein the planetary mill extruding machine (106) has an induction heater.

11. The plant according to claim 10, characterized in that the planetary mill extruding machine (106) has a cylinder (109), in which one central spindle (107) and at least three planetary spindles (108) are arranged, wherein one or more induction coils are arranged on the outer wall of the cylinder (109).

12. The plant according to claim 10 or claim 11, characterized in that the planetary mill extruding machine (106) has two or more reaction zones.

13. The plant according to claim 12, characterized in that it has the following reaction zones: (i) a heating zone for heating the molten material (1); (ii) a depolymerization zone for cleaving polymer chains of the molten material (1) to obtain shorter molecules; (iii) an evaporation zone for evaporating the shorter molecules obtained in the depolymerization zone to an oil steam (6); and (iv) a discharging zone for discharging the oil steam (6) from the planetary mill extruding machine (106).

14. The plant according to any of claims 10 to 13, characterized in that is has a cooling facility (115) for cooling the oil steam to obtain an oil.

15. The plant according to any of claims 10 to 14, characterized in that is has a facility (121) for melting the plastic material before it enters the planetary mill extruding machine (106).