Conversion of polyurethane in an extruder

Abstract

Method for converting a polyurethane-containing plastic material in an extruder designed as a twin-screw extruder, comprising the following steps: Providing a reaction mixture, wherein the reaction mixture - a plastic material in solid form containing polyurethane, - Water, and - at least one reaction additive selected from nitric acid, a carboxylic acid, a dicarboxylic acid, in particular adipic acid, a tricarboxylic acid, in particular citric acid, urea and / or a biological material includes Transporting the reaction mixture through the transport zone of the extruder, in which two extruder screws are located, wherein the process is carried out under ambient pressure, wherein momentary local pressure increases within the extruder due to kneading processes cannot be excluded, but a pressure of 3 bar, in particular 2 bar, is not exceeded, wherein the transport zone comprises a reaction zone in which a temperature of 225 °C to 260 °C, in particular 230 °C to 250 °C, is present, and the transport zone further comprises at least one degassing zone after the reaction zone in which at least the same temperature as in the reaction zone is present and in which components of the reaction mixture transported from the reaction zone, which are gaseous at these temperatures, can be removed from the extruder via at least one degassing point.

Description

[0001] The invention relates to a method for converting a polyurethane-containing plastic material in an extruder.

[0002] Polyurethanes, due to their many adjustable properties, are widely used in products for both industrial and household applications. Examples of such products include foams, paints, adhesives, potting compounds, hoses, seals, floor coverings, mattresses, automotive parts, sports equipment components, shoe parts, and the like.

[0003] Therefore, a high proportion of polyurethane waste is generated when the corresponding products are damaged or have reached the end of their service life.

[0004] In the past, attempts have therefore been made to recycle polyurethanes. For example, European patent 01976719 B1 describes a process in which a polyurethane resin is hydrolyzed by contact with water only at high temperatures. German patent application 24 42 387 A1 describes a process for the hydrolytic breakdown of plastic waste, requiring pressures of at least five bar. German patent application 694 15 631 T2 describes a process for the reuse of synthetic resin waste, using pressures of at least 9.8 bar.

[0005] The object of the invention is to provide an improved method.

[0006] The invention results from the features of method claim 1. Advantageous further developments and embodiments are the subject of the dependent claims.

[0007] Within the scope of the invention, "plastic material" is understood to mean a material comprising plastics, ranging from pure plastics to plastic-containing mixtures. The term "plastic" is used in its usual sense and refers to a synthetically produced substance, for example, a substance produced in the course of organic synthesis, such as a polymer produced from one or more different monomers by polymerization, polyaddition, and / or polycondensation. Plastics are classified according to a conventional classification into thermosets, thermoplastics, elastomers, and thermoplastic elastomers.Well-known examples of plastics are polyethylene, polycarbonate, polyacrylic, polymethacrylic, polyacrylamide, polystyrene, acrylonitrile butadiene rubber, styrene butadiene rubber, chloroprene rubber, butadiene rubber, and ethylene propylene diene monomer rubber, as well as polyurethane. In particular embodiments, the plastic material comprises only hydrolyzable plastics, for example, in addition to polyurethanes, also polyesters, polyamides, and / or polycarbonates. Natural rubber previously used for a technical purpose, for example, byproducts of mattress manufacturing or chemically processed, such as vulcanized natural rubber, is also considered a plastic within the scope of the invention; however, lignin, i.e., wood, is not.Depending on their original intended use, plastics may contain other substances such as plasticizers, microbicidal agents, antioxidants, stabilizers (e.g., against UV light), flame retardants, dyes, or residues of polymerization initiators. Plastics also include those not derived from petroleum-based raw materials, but produced from renewable resources within a sustainable and renewable framework, either through chemical synthesis or biotechnological or microbiological processes using appropriately designed enzymes or production organisms. The aforementioned plastic-containing mixtures are either mixtures of pure plastics or mixtures that also include one or more non-plastics such as metal, ceramic, or glass.Preferably, the plastic(s) in such mixtures, which also include non-plastics, constitute the largest relative proportion by mass or volume, for example at least 67%, at least 75%, at least 80%, at least 90%, at least 95%, at least 98%, or at least 99%. Preferably, the plastic material contains no non-plastics, particularly to avoid damage to the extruder screws. Methods for reducing the non-plastic content are known to those skilled in the art and include, for example, manual removal of non-plastics, magnetic removal of magnetic metals or metal alloys, or the separation of plastics and, optionally, other materials of similar density based on density differences between materials of different densities, for example, by means of air classification or shaking or vibration devices.Within the plastic material, polyurethane makes up the largest mass fraction, preferably more than 60%, for example at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, or at least 95%, thus constituting the predominant main component. For example, discarded polyurethane mattresses often contain corresponding small amounts of polyethylene or polypropylene, which usually originate from the cover fabrics.

[0008] The plastic material used in the process contains polyurethane and optionally one or more hydrolyzable plastics selected from polyesters, polyamides, or polycarbonates, or consists of polyurethanes and optionally also polyesters, polyamides, or polycarbonates and / or a mixture thereof. According to a particular embodiment, the plastic material consists of polyurethane or a polyurethane mixture, or consists of polyurethane and polyester or a polyester mixture, for example, polyethylene terephthalate or a polyethylene terephthalate mixture, or consists of a polyurethane / polyolefin composite material, wherein the polyurethane preferably comprises at least 50% by weight in the composite.Within hydrolyzable plastics, polyurethane occupies the largest mass fraction, preferably more than 60%, for example at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, or at least 95%, thus constituting the predominant main component. For example, the plastic material consists of mattresses or waste from mattress manufacturing, where the raw material contains polyurethane as a hydrolyzable component.The polyurethane can be in the form of a foam, and the process offers the particular advantage that a high-volume starting material (namely, a foam which, while compressible to a certain extent, always tends to expand and therefore requires correspondingly sized initial lines and reaction vessels) is reacted in the presence of a comparatively small volume of reaction medium. After appropriate pressure and heat treatment, a significantly smaller volume results. Essentially, a bulky solid, namely a foam, is transformed into a more manageable form with a significantly higher liquid content and a smaller volume, thus solving a major problem in the polyurethane waste and recycling industry.

[0009] The invention relates to a process for converting a polyurethane-containing plastic material in an extruder designed as a twin-screw extruder, comprising the following steps: providing a reaction mixture, wherein the reaction mixture comprises a solid-state polyurethane-containing plastic material, water, and at least one reaction additive selected from nitric acid, a carboxylic acid, a dicarboxylic acid, in particular adipic acid, a tricarboxylic acid, in particular citric acid, urea, and / or a biological material; transporting the reaction mixture through the transport zone of the extruder, in which two extruder screws are located, wherein the transport zone comprises a conversion zone – preferably consisting of at least three kneading zones and a recirculation element – ​​in which a temperature of 225 °C to 260 °C, in particular 230 °C to 250 °C, is maintained.such as 235 °C to 250 °C, 240 °C to 250 °C, or 240 °C to 255 °C, and the transport zone further comprises at least one degassing zone downstream of the reaction zone, in which at least the same temperature as in the reaction zone is present and in which components of the reaction mixture transported from the reaction zone, which are gaseous at these temperatures, can be removed from the extruder via at least one degassing point. During the execution of the process, there is essentially no overpressure in the extruder. According to the invention, the process is carried out under ambient pressure. No special pressure-building or pressure-maintaining devices are provided on the extruder. Momentary local pressure increases within the extruder due to the kneading processes cannot be ruled out; however, it is assumed that a pressure of three bar, and in particular two bar, will not be exceeded.

[0010] The reaction mixture can be supplied outside the extruder or when feeding it into the extruder, optionally with an upstream mixing device.

[0011] For improved implementation, the plastic material can preferably be used in a pre-comminuted state, especially if it comprises non-water-swellable plastics. Standard comminution methods can be used; for example, the plastic material can be cut, torn, shredded into flakes, granulated, ground, or pulverized, optionally after prior temperature reduction to increase brittleness. Non-limiting examples for the size of the plastic particles used are approximately 0.5 cm. 3 up to 10 cm 3 (0.5 ml to 10 ml), such as about 1 cm 3 up to 5 cm 3, especially for porous or large surface area plastic material, or plastic particles with a diameter, measured at their largest point, of a maximum of approximately 10, 5, 2, 1, 0.5, 0.1, 0.05 or 0.01 millimeters.

[0012] The reaction mixture is transported via the two extruder screws, compacted, and subjected to shear forces in preferably at least three kneading zones. Preferably, a recirculation element is located at the end of a second kneading zone, which significantly controls the fill level and residence time in the extruder. The duration of transport from one end to the other of the extruder can depend on the length of the extruder, the set rotational speed of the extruder screws, and the consistency of the reaction mixture. Examples of durations are 10 minutes to 2 hours, particularly 0.4 to 1 hour. If necessary, the rotational speed of the extruder screws can be adjusted to increase the residence time in the reaction zone if sampling indicates insufficient reaction, or to decrease it if sufficient reaction is determined.

[0013] The extruder has a transport zone in which the extruder screws run. Within the transport zone are a reaction zone – preferably consisting of at least three kneading zones and a recirculation element – ​​and, directly or indirectly connected to the reaction zone, with respect to the transport direction, at least one degassing zone. The temperature in the reaction zone is between 225 °C and 260 °C, particularly between 230 °C and 250 °C. The reaction mixture is transported, compacted, and kneaded by the extruder screws. The kneading process introduces mechanical energy into the reaction mixture, some of which is converted into heat energy. However, the heat generated is insufficient, so the extruder is equipped with heating elements to provide and maintain a desired temperature. Within the reaction zone, the polyurethane undergoes at least partial or complete conversion.

[0014] The reaction zone is directly or indirectly connected to at least one degassing zone, in which the temperature is at least equal to or higher than that in the reaction zone. At least one degassing point is provided in the at least one degassing zone, allowing components of the reaction mixture transported through the reaction zone that are gaseous at the prevailing temperatures to be extracted as gas. If necessary, known cold traps or vacuum traps can be used at the degassing points. The extracted gaseous components can be used separately.

[0015] After being transported through the extruder, the reaction mixture has a significantly lower volume fraction of solids compared to the initial reaction mixture, and may even contain no solids at all. Instead, the treated reaction mixture is a liquid or a liquid containing solids. Advantageously, this process achieves a reduction in the volume of the solid material used, consisting of the solid plastic material and any other solid components. For example, reductions of up to 95%, up to 90%, or 4 to 50%, such as 5 to 30%, 7 to 25%, or 10 to 15% are possible, based on the volume of the solid material used. A significant reduction is particularly achievable with foam materials.

[0016] To support the reaction, the reaction mixture includes at least one reaction additive. Non-restrictive examples of reaction additives are nitric acid, carboxylic acids, urea, and / or biological material. Good reaction can be achieved with nitric acid. However, if a reaction product with a low proportion of nitrogenous components is desired, other reaction additives are preferred, since nitric acid introduces additional nitrogen. In general, mineral acids such as hydrochloric acid or phosphoric acid, or mineral bases such as sodium hydroxide, are less preferred because they would introduce chlorine, phosphorus, and sodium components into the reaction product, which could have adverse effects in the case of subsequent pyrolysis or later uses of the resulting pyrolysis products.Alternative reaction additives that achieve good conversion include carboxylic acids, for example, linear, saturated monocarboxylic acids such as formic acid, acetic acid, propionic acid, butyric acid, pentanoic acid, hexanoic acid, and heptanoic acid; dicarboxylic acids such as oxalic acid (ethanedioic acid), malonic acid (propanedioic acid), succinic acid (butanedioic acid), glutaric acid (pentanedioic acid), adipic acid (hexanedioic acid), malic acid (2-hydroxybutanedioic acid), and tartaric acid (2,3-dihydroxybutanedioic acid); and tricarboxylic acids such as 3-carboxy-2-oxo-pentanedicarboxylic acid (oxalsuccinic acid), propane-1,2,3-tricarboxylic acid, citric acid (2-hydroxypropane-1,2,3-tricarboxylic acid), and isocitric acid (1-hydroxypropane-1,2,3-tricarboxylic acid). Urea is another possible reaction additive.Based on the total mass of the aqueous medium, the proportion of urea in the aqueous medium is, for example, 1 to 45% by mass, particularly 1 to 20% by mass, for example, 1 to 10% by mass, such as 1 to 7% by mass, for example, 1.5 to 5% by mass, 1.5 to 4% by mass, 2 to 4% by mass, 2.5 to 3.5% by mass, or 3% by mass. Examples of other ranges or concentrations are 5 to 10% by mass, 1% by mass, 5% by mass, 7.5% by mass, and 10% by mass. A range between 1% by mass and 10% by mass is preferred with regard to the ratio between the amount of urea used and the degree of polyurethane degradation achieved, for example, 2.5 to 10% by mass, 2% by mass to 7.5% by mass, such as 3% by mass to 5% by mass.

[0017] The reaction mixture can contain, in particular, 2.5 to 10% by mass of urea. The ratio between urea-containing water and polyurethane-containing plastic material can be, for example, 0.2 ml / g to 5 ml / g, in particular 0.4 ml / g to 5 ml / g.

[0018] The reaction additive can also be a biological material. For the purposes of this invention, biological material is understood to mean plant, animal, or microorganism material, for example, complete plants or plant parts such as wood, leaves, stems, roots, or seeds, such as horticultural waste or clippings. Preferably, the biological material is plant material. According to a particular embodiment, the biological material is wood, in particular shredded wood, for example, in the form of sawdust, wood chips, or crushed wood.

[0019] The aforementioned reaction additives can be used individually or in any mixture of two or more of the respective aforementioned representatives.

[0020] Examples of mixing ratios of the plastic material with water and at least one reaction additive are 2 to 25 liters of plastic material moistened with 0.08 to 1 liter of water / reaction additive. The water used can contain 3 to 50% by mass, in particular 4 to 40% by mass, for example 4 to 20% by mass of nitric acid, carboxylic acid, a dicarboxylic acid, a tricarboxylic acid, and / or urea. In the case of the addition of a biological material, it can be provided that the plastic material comprises 55 to 95% by volume, in particular 67 to 95% by volume, and the biological material accordingly 5 to 45% by volume, in particular 5 to 33% by volume.The biological material can be mixed with the plastic material and then added to the water / reaction additive, or first mixed with water / reaction additive and then with the plastic material, or all three components can be mixed at the same time.

[0021] If the plastic material and / or the hydrolyzable plastic contained therein is a compressible plastic, in particular a polyurethane foam, the specified volumes refer to the uncompressed plastic.

[0022] Given the temperature in at least one degassing zone, which is at least equal to the temperature of the reaction zone, at least water can be withdrawn as a gas phase at at least one degassing point. Accordingly, the reaction product, i.e., the reaction mixture transported through the reaction zone and the at least one degassing zone, has a reduced water content or is anhydrous.

[0023] The reaction product, i.e., the reaction mixture transported through the transport zone and through at least one degassing zone, can optionally be separated from the liquid phase and the solids it contains, for example by centrifugation or filtration, and optionally the resulting solids can be dried.

[0024] In one embodiment, the temperature in at least one degassing zone is the same as in the reaction zone. In this case, essentially gaseous water is drawn off via the at least one degassing point. The reaction product in this case contains nitrogenous components and products with higher boiling points. The nitrogenous components are typically diamines or their degradation products or reaction products.

[0025] In one embodiment, the temperature in at least one degassing zone is in the range of 265 °C to 300 °C, particularly 265 °C to 280 °C, and components of the reaction mixture transported through the reaction zone, which are gaseous at these temperatures, can be withdrawn from the extruder via a degassing port. At these temperatures, gaseous water can be withdrawn from the reaction mixture transported through the reaction zone. Along with this, nitrogenous components, which are essentially attributable to the diisocyanates used for polyurethane production, can also be withdrawn. In particular, it was found that at a temperature in the degassing zone of 265 °C to 280 °C, diaminotoluenes could be withdrawn from the reaction mixture in gaseous form via the degassing port.Reducing the nitrogen content is advantageous if the reaction product, i.e., the reaction mixture transported through the reaction zone and the at least one degassing zone, is subsequently to be subjected to, for example, pyrolysis, and the pyrolysis oils obtained from the pyrolysis are to be subjected to chemical cracking processes in later applications. Without committing to a specific theory, it is assumed that the components remaining in the reaction mixture with higher boiling points, given the polyurethane present in the initial reaction mixture, are polyols and their degradation and / or transformation products.

[0026] In one embodiment, a first degassing zone is present where the temperature is in the range of 225 °C to 260 °C and where components of the reaction mixture transported through the reaction zone, which are gaseous at these temperatures, can be extracted from the extruder via a first degassing point. Furthermore, a second degassing zone is present downstream of the first degassing zone where the temperature is in the range of 265 °C to 300 °C, particularly 265 °C to 280 °C, and where components of the reaction mixture additionally transported through the first degassing zone can be extracted via a second degassing point. In this case, gaseous water can be extracted from the first degassing zone, whereas nitrogenous components can be extracted as a gas phase from the second degassing zone. Consequently, the water content and the nitrogenous components can be removed separately as a gas phase.This makes later reuse easier.

[0027] It can be stipulated that the mass ratio between water on the one hand and polyurethane or polyurethane-containing plastic material on the other in the reaction mixture is no more than 0.6 to 1, in particular no more than 0.5 to 1, for example 0.45 to 1, so that polyurethane or polyurethane-containing plastic material is present in a significant excess in terms of mass. Larger quantities of water are possible, but also lead to a more water-rich reaction product. Accordingly, it is not necessary for the plastic material to be suspended in a continuous aqueous medium, but only to be moistened with it. With the goal of a resource-conserving circular economy, the reduction of water consumption represents a significant advantage.

[0028] According to one embodiment, the volume ratio between solid and aqueous medium in the reaction mixture for the extruder is 100:1 to 5:1, for example 75:1 to 10:1, 30:1 to 20:1, such as 25:1. It is therefore evident that the medium is not predominantly aqueous, in which the plastic material (and possibly other solids) is suspended as a solid, but rather that the majority of the volume is comprised of the plastic material, which is merely moistened with a significantly smaller volume of aqueous medium. For example, it may be provided that 0.05 to 0.2 volume parts of aqueous medium are provided for each volume part of polyurethane foam or for each volume part of solid.Accordingly, at the beginning of the reaction, only a plastic material moistened with aqueous medium is present in the reaction mixture, i.e., essentially a solid moistened with the reaction medium, whereby, as transport progresses in the direction of transport, the solid with a high volume requirement is converted into a liquid phase with a lower volume requirement.

[0029] In a particular embodiment, the reaction additive is a biological material, especially plant material. It has been found that with an increasing amount of plant material, for example wood, and after appropriate removal of water in the at least one degassing zone, the reaction product develops into a free-flowing solid, which is, for example, well suited for transport via screw conveyors. This significantly facilitates subsequent use, such as transport to and introduction into pyrolysis plants. The presence of plant material in the reaction mixture thus leads to a substantial improvement. The mass ratio of plastic material to biological material, especially plant material, can be, for example, 3:1 to 1:1, such as 3:1 to 1.5:1, or, for example, 2:1.Especially at mass fractions of one third or more, based on the total mass of plastic material and biological material, for example 33 to 50 percent by mass, especially 33 to 45 percent by mass, such as 34 to 40 percent by mass, free-flowing solids are available.

[0030] The reaction mixture obtained at the end of the extruder, having previously passed through the reaction zone and the at least one degassing zone, can be directly or indirectly subjected to pyrolysis. The principle of pyrolysis itself is known and is based on a thermochemical conversion of substances in the absence of external oxygen, typically within a temperature range of 150°C to 800°C. In the process described herein, the lower limit of the temperature range is preferably the highest temperature present in the reaction zone or the at least one degassing zone, such as a temperature range of 265°C to 800°C. For example, a temperature range of 265°C to 500°C or 300°C to 500°C is possible.Another example of a suitable temperature range is 700 °C to 800 °C, particularly 750 °C to 800 °C, which is advantageously suited to decomposing calcium carbonate present in the plastic material into calcium oxide and carbon dioxide, thus providing a calcium carbonate-poor or calcium carbonate-free pyrolysis coke as the pyrolysis product. Pyrolysis treatment is preferred over using the resulting pressure- and heat-treated reaction medium. Assuming that it contains essentially polyols and, optionally, transformation products, additional purification or separation steps are required to ensure sufficient quality for further use. In contrast, pyrolysis can advantageously yield monomers of the polyols, which are assumed to have a higher qualitative purity compared to the polyols themselves.

[0031] According to a preferred embodiment, the reaction product, i.e., the reaction mixture transported through the reaction zone and the at least one degassing zone, which is introduced directly or indirectly into a pyrolysis plant, is a reaction mixture from which gaseous components with a boiling point below the temperature prevailing in a degassing zone of 265 °C to 300 °C, in particular 265 °C to 280 °C, have been partially or completely removed. In particular, according to the embodiments described herein, it is possible to feed such a reaction mixture to a pyrolysis process that has a lower proportion of nitrogenous components or is free of such components. This makes it possible to provide pyrolysis products that can, in turn, be advantageously used further. In particular, liquid, gaseous, and solid pyrolysis products can be obtained during pyrolysis.The liquid products are pyrolysis oils, which can be subjected to chemical cracking, although high proportions of nitrogenous components would be detrimental in this process. Pyrolysis gas can be used for power generation, with low proportions of nitrogenous components reducing the problem of nitrogen oxides. Solid pyrolysis products, which represent a type of pyrolysis coke, can be used in various ways, for example as a substitute for carbon black or as petroleum coke for power generation, so here too, lower or no proportions of nitrogenous components are advantageous.

[0032] Not the subject of the invention is an extruder designed as a twin-screw extruder for carrying out a process as described herein, wherein the extruder has a transport zone comprising a conversion zone - preferably consisting of at least three kneading zones and a recirculation element - and at least one degassing zone after the conversion zone, wherein a temperature of 225 °C to 260 °C, in particular 230 °C to 250 °C, can be specified in the conversion zone, and a temperature can be specified in the at least one degassing zone which corresponds at least to the temperature in the conversion zone.

[0033] According to a variant not covered by the invention, the extruder has a degassing zone in which the same temperature is present as in the conversion zone.

[0034] According to a variant not part of the invention, the extruder has a degassing zone in which a temperature in the range of 260 °C to 300 °C, in particular 265 °C to 280 °C, is present, wherein components of the reaction mixture transported through the reaction zone, which are gaseous at these temperatures, can be removed from the extruder via at least one degassing point.

[0035] According to a variant not part of the invention, a first degassing zone is present in the extruder, in which the temperature is in the range of 225 °C to 260 °C and in which components of the reaction mixture transported through the reaction zone, which are gaseous at these temperatures, can be removed from the extruder via a first degassing point, wherein a second degassing zone is present after the first degassing zone, in which the temperature is in the range of 265 °C to 300 °C, in particular 265 °C to 280 °C, and in which components of the reaction mixture additionally transported through the first degassing zone can be removed via a second degassing point.

[0036] Further advantages, features, and details will become apparent from the following description, in which – possibly with reference to the figures – at least one embodiment is described in detail. Identical, similar, and / or functionally equivalent parts are marked with the same reference numerals.

[0037] They show: Fig. 1: A schematic cross-sectional view of an extruder with a degassing zone, Fig. 2: A schematic representation of an extruder with two degassing zones.

[0038] The representations in the figures are schematic, not necessarily to scale, and only show essential components. Examples Example 1: Extruder

[0039] In a pilot test, a laboratory extruder was used, designed as a twin-screw extruder with three kneading blocks of varying lengths. The closely meshing extruder screws had a diameter of 24 mm and a length of 1.2 m. The extruder featured a cooling zone followed by nine heating zones evenly distributed along its length. A vacuum extraction port was located near the exit point in the last zone. Condensate was collected in a cold trap. Example 2: Preparation of a reaction mixture

[0040] A polyurethane mattress, including its cover, was shredded, and the shredded material was compacted into small granules. One kilogram of this polyurethane-containing plastic material was sprayed and moistened with 200 ml of water and 200 ml of 53% nitric acid. This moistened mixture was fed into a metering unit (a rotary valve) above the extruder feed, with a dosage set at 1 kg / h. Example 3: Implementation 1

[0041] The temperature zones were set to the following values: cooled; 180; 230; 230; 230; 230; 230; 250; 250; 250°C.

[0042] Initially, mainly undegraded brown foam flakes were expelled. Example 4: Implementation 2

[0043] The temperature zones were set to the following values: Chilled; 180; 250; 250; 250; 230; 230; 250; 250; 250 °C

[0044] This resulted in a soft, black, pasty mass that was very soft. Example 5: Reaction with adipic acid as a reaction additive in water

[0045] One kilogram of polyurethane-containing plastic material was mixed with 50 g of powdered adipic acid and then sprayed and moistened with 200 ml of water. This moistened mixture was fed into a metering unit (a rotary valve) above the extruder feed, with a metering rate of 1 kg / h set. The temperature zones were set to the following values: cooled; 180; 250; 250; 250; 250; 265; 265; 265; 265; °C.

[0046] The twin-screw motor rotated at 120 rpm. The heat-treated, degassed, and dehydrated reaction product at the end of the screw was creamy brown. Brown deposits were collected in the cold trap, which were identified as diamines upon analytical examination. Example 6: Reaction with 3% water-urea solution

[0047] One kilogram of the polyurethane-containing plastic material was sprayed and moistened with 400 g of a 3% water-urea solution. This moistened mixture was fed into a metering unit (a rotary valve) above the extruder feed, with a metering rate of 1 kg / h set.

[0048] The temperature zones were set to the following values: cooled; 180; 250; 250; 250; 250; 265; 265; 265; 265; °C.

[0049] The rotational speed of the twin screw was 110 rpm.

[0050] The heat-treated, degassed, and dehydrated reaction product at the end of the screw was greyish-brown and creamy.

[0051] Brown deposits were collected in the cold trap, which, after analytical examination, turned out to be diamines. Character description

[0052] Fig. Figure 1 shows a schematic longitudinal section through an extruder 10, which is designed as a twin-screw extruder and accordingly has an extruder screw 14a and an extruder screw 14b. The extruder 10 has a transport zone 12, which the Fig. 1 is indicated by a dotted bracket. Extruder screws 14a and 14b run through transport zone 12, by means of which a reaction mixture, which can be introduced into the extruder 10 via a filling device not specified in detail and without reference numerals, can be transported. Within transport zone 12, there is a reaction zone 16 and a degassing zone 18. In the reaction zone 16, where the temperature is between 220 °C and 260 °C, the transported reaction mixture is reacted. A degassing zone 18 adjoins the reaction zone 16. This zone has a degassing point 20 through which components of the reaction mixture transported from the reaction zone, which are gaseous at the temperatures present in the degassing point 20, can be removed.

[0053] Fig. Figure 2 also shows a schematic longitudinal section through an extruder 10, which, however, differs from the one in Fig. The extruder shown in Figure 1 has a first degassing zone 18a with an associated first degassing point 20a and a second degassing zone 18b with an associated second degassing point 20b. The temperatures in the first degassing zone 20a are equal to or higher than the temperatures in the reaction zone 16, preferably in the range of 225 °C to 260 °C. Preferably, the temperatures are sufficient to remove gaseous water. The temperature in the second degassing zone 20b is higher than the temperature of the first degassing zone 20a, preferably in the range of 265 °C to 300 °C, particularly 265 °C to 280 °C, and is preferably sufficient to remove nitrogenous components in gaseous form. Reference symbol list 10 extruders 12 Transport Zone 14a, b Extruder screw 16 Implementation Zone 18 Degassing zone 18a first degassing zone 18b second degassing zone 20 Degassing point 20a first degassing point 20b second degassing point

Claims

[1] Method for converting a polyurethane-containing plastic material in an extruder designed as a twin-screw extruder, comprising the following steps: Providing a reaction mixture, wherein the reaction mixture - a plastic material in solid form containing polyurethane, - Water, and - at least one reaction additive selected from nitric acid, a carboxylic acid, a dicarboxylic acid, in particular adipic acid, a tricarboxylic acid, in particular citric acid, urea and / or a biological material includes Transporting the reaction mixture through the transport zone of the extruder, in which two extruder screws are located, wherein the process is carried out under ambient pressure, wherein momentary local pressure increases within the extruder due to kneading processes cannot be excluded, but a pressure of 3 bar, in particular 2 bar, is not exceeded, wherein the transport zone comprises a reaction zone in which a temperature of 225 °C to 260 °C, in particular 230 °C to 250 °C, is present, and the transport zone further comprises at least one degassing zone after the reaction zone in which at least the same temperature as in the reaction zone is present and in which components of the reaction mixture transported from the reaction zone, which are gaseous at these temperatures, can be removed from the extruder via at least one degassing point. [2] Method according to claim 1, characterized bythat the temperature in at least one degassing zone is the same as in the reaction zone. [3] Method according to claim 1, characterized by , that in at least one degassing zone a temperature in the range of 265 °C to 300 °C, in particular 265 °C to 280 °C, is present and that components of the reaction mixture transported through the reaction zone, which are gaseous at these temperatures, can be removed from the extruder via at least one degassing point. [4] Method according to claim 1, characterized by, that a first degassing zone is present in which the temperature is in the range of 225 °C to 260 °C and in which components of the reaction mixture transported through the conversion zone, which are gaseous at these temperatures, can be extracted from the extruder via a first degassing point, and that after the first degassing zone a second degassing zone is present in which the temperature is in the range of 265 °C to 300 °C, in particular 265 °C to 280 °C, and in which components of the reaction mixture additionally transported through the first degassing zone can be extracted via a second degassing point. [5] Method according to any one of the preceding claims, characterized by that in the reaction mixture the mass ratio between water on the one hand and polyurethane or polyurethane-containing plastic material on the other hand is no more than 0.6 to 1. [6] Method according to any one of the preceding claims, characterized by, that the volume ratio between solid and liquid is 100:1 to 5:

1. [7] Method according to any one of the preceding claims, characterized by that the reaction additive is a biological material, in particular a plant material. [8] Method according to any one of the preceding claims, characterized by that the reaction mixture obtained at the end of the extruder and previously transported through the reaction zone and at least one degassing zone is directly or indirectly subjected to pyrolysis.

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