Method, device and use for reprocessing substantially polyalkylene terephthalate

Abstract

The invention aims to provide a method and a device for reprocessing waste material, containing substantially polyalkylene terephthalate, more particularly polyethylene terephthalate and / or polybutylene terephthalate, in a continuous process by means of depolymerization, wherein a preferably solid alkali metal hydroxide and / or alkaline earth hydroxide, in particular sodium hydroxide, is added to the waste material to produce a reaction mixture, said method being suitable for recycling, at a high throughput, even multi-layer systems and coloured materials almost completely chemically into their starting materials with a high quality in order to allow unlimited production of new polyalkylene terephthalate products from the recycling products. To achieve this aim, an alkylene glycol is also added, as a starting material, to the reaction mixture, said alkylene glycol being an alkylene glycol that can be produced by the desired depolymerization, in particular being monoethylene glycol, and no further reactive constituents are added to the reaction mixture.

Description

[0001] METHOD, DEVICE AND USE FOR REPROCESSING ESSENTIALLY POLYALKYL TEREPHTHALATE

[0002] The present invention relates to a process for the reprocessing of essentially polyalkylene terephthalate, in particular

[0003] Waste containing polyalkylene terephthalate and / or polyalkylene terephthalate is processed in a continuous process by means of depolymerization, wherein a, preferably solid, alkali and / or alkaline earth hydroxide, in particular sodium hydroxide, is added to the waste to produce a reaction mixture.

[0004] The present invention relates equally to a device for carrying out such a method.

[0005] Finally, the present invention relates to the use of such a device for carrying out such a method.

[0006] The invention relates in particular to a continuous process for recycling waste containing polyalkylene terephthalate, in which the waste is suitably prepared, mixed with alkali metal or alkaline earth metal hydroxide in an extruder or kneading reactor and heated.

[0007] The main advantage of the process according to the invention is that it enables the continuous processing of polyalkylene terephthalate.

[0008] Waste containing polyalkylene terephthalate, as well as multilayer waste containing polyalkylene terephthalate, is permitted. Continuous processing enables the continuous recovery of an alkali metal or

[0009] alkaline earth metal terephthalate-containing waste stream as well as the

[0010] Separation and recovery of the formed and used

[0011] Alkylene glycol. The alkali metal or alkaline earth metal terephthalate

[0012] The resulting material stream can then be dissolved in a suitable solvent, for example water, purified and, if necessary, converted into terephthalic acid (TPA) or a terephthalic acid ester.

[0013] Several processes are known for producing TPA or a TPA intermediate from polyalkylene terephthalate, and in particular polyethylene terephthalate (PET), in the form of waste. However, these processes do not handle multilayer PET waste and are neither efficient nor economically advantageous. These processes are briefly described below.

[0014] US patent 4542239 describes a process for obtaining TPA from PET waste using aqueous ammonium hydroxide. The process requires both elevated pressure and elevated temperature. Furthermore, extensive [requirements / provisions] are necessary.

[0015] To meet safety requirements when using ammonium hydroxide. In US patents 3120561 and 4578502, the depolymerization of PET in the presence of water or methanol is achieved by hydrolysis. This requires high temperature and high pressure for several hours, followed by cooling to obtain TPA. In US patent 4355175, PET waste is hydrolyzed with dilute sulfuric acid. The solution is then mixed with an alkaline solution to allow for the separation of precipitated impurities by filtration. TPA is obtained by adding sulfuric acid. US patent 3952053 describes a process for treating

[0016] Polyester production waste is described. First, sulfuric acid is added to remove dyes and additives. This purified intermediate product is then treated with

[0017] Sodium hydroxide was added, causing TPA to precipitate. The contained

[0018] Monoethylene glycol (MEG) is recovered by distillation.

[0019] German patent 69714614 describes an aqueous, slightly alkaline solution being prepared at elevated temperature and pressure for

[0020] Depolymerization of PET is used. For the alkaline solution, reagents from the group of bicarbonates of ammonia and...

[0021] Alkali metals, ammonium carbamate, and urea are used. The released carbon dioxide is recycled.

[0022] In German patent 69522479, depolymerization is carried out with a solvent (for example, water) and a

[0023] Wetting agent in the presence of an alkali metal or

[0024] Alkaline earth metal hydroxide at elevated temperature and pressure. After filtration of the dissolved alkali metal or

[0025] An alkaline earth metal terephthalate and the precipitation of TPA using an acid are used to perform a crystallization process in order to enlarge the TPA particles.

[0026] US patent 5395858 describes the depolymerization of PET waste and silver-containing PET waste (photographic and X-ray films) in a sodium hydroxide solution. Subsequent evaporation of the

[0027] Disodium terephthalate remains after the solvent is dissolved in water and reacted with an acid to form TPA.

[0028] US patent 3544622 describes the saponification of PET with sodium hydroxide and ethylene glycol at atmospheric pressure and at least 150°C. This depolymerization takes place batchwise in a

[0029] Stirred tank reactor during simultaneous evaporation of ethylene glycol. The resulting disodium terephthalate is also reacted with an acid to form TPA. In US patent 6720448 B2, PET is reacted at elevated temperature with an anhydrous solution, for example in ethylene glycol, with a salt that is a weaker acid than TPA. Various bases and mixtures thereof are used. Subsequently, the

[0030] The intermediate product is dissolved in water, filtered, and the TPA is obtained by adding a strong acid.

[0031] US patent 2017 / 0152203 A1 describes the depolymerization of PET at temperatures between 20 and 60°C in

[0032] The process involves dichloromethane / methanol mixtures. The use of various other solvents to subsequently recover TPA and ethylene glycol is also mentioned. Furthermore, the swelling of the polymer by, for example, nonpolar solvents is described. The depolymerization is carried out batchwise, sometimes over many hours.

[0033] German patent 69316545 T2 describes a method for

[0034] Depolymerization of uncoated PET using an alkali metal or alkaline earth metal hydroxide in a kneaded extruder is described. No solvent is added. The mixture is then heated in the kneaded extruder and at least partially melted. Subsequently, the resulting alkali metal or alkaline earth metal terephthalate is dissolved in water and filtered to obtain the TPA using sulfuric acid.

[0035] Bergmann et al. beschreiben in„On-Line Monitoring of Molecular Weight Using NIR Spectroscopy in Reactive Extrusion Process“ in

[0036] Macromolecular Symposia 2013 presented the glycolysis of PET in an extruder at a temperature of 320°C. Ethylene glycol is used to depolymerize the PET. However, no TPA is obtained. In the previously described processes, PET conversion predominantly takes place at high temperatures and high pressures. This has the disadvantage that the equipment and energy costs are very high, thus reducing the economic viability of the processes. Furthermore, most of the described processes are only carried out batchwise. Given the high temperatures and pressures, the batchwise processing inherent in the prior art results in considerable costs for heating and pressure build-up, which is a disadvantage. In particular, recycling for multilayer polymer-based composite materials presents a challenge due to the material combination.

[0037] Different materials containing polyalkylene terephthalate have very high process requirements. Such composite systems are

[0038] They are used particularly as multi-layer packaging in the food sector to provide both mechanically stable packaging and the necessary protective functions for the food product. To meet these packaging requirements, the use of two- or

[0039] Multilayer packaging is used. This packaging consists of several layers of different polymers or materials and / or inorganic coatings, each typically having at least one function. For example, ethylene-vinyl acetate copolymer is used in food packaging as an oxygen barrier.

[0040] used. The structure of the multilayer packaging.

[0041] (Multi-layer system packaging) is used, for example, in the

[0042] Patents US9475251 B2, US6610392B1, and EP1036813A1 describe such multilayer packaging. A widely used food packaging, for example, consists of a PET tray coated with a thin layer of polyethylene (PE) or polyamide (PA). These and other multilayer packagings form a solid composite of the various polymers or materials. According to the current state of the art, multilayer materials are difficult or impossible to recycle. Patent W02003104315A1 describes an approach that provides a method for separating these materials.

[0043] This describes a multilayer system in which no depolymerization, dissolution, or oxidation of the material used occurs. However, the process uses environmentally hazardous solvents and, to the authors' knowledge, has not yet been implemented economically. The approach described in patent W02003070376A1 allows coated plastic molded parts consisting of a PET mold body, a barrier layer of polyvinyl alcohol, and a top layer to be separated using water. Here, the barrier and intermediate layers of polyvinyl alcohol are dissolved, allowing the molded part to be separated from the top layer. This disadvantageous limitation of the process is to very specific three-layer systems.

[0044] Due to the difficulty of separating the different layers from each other, such multilayer systems or

[0045] Multilayer materials, according to current technological standards, are only thermally recycled or landfilled on a large scale after their use. Both thermal recycling and landfill disposal are problematic.

[0046] When waste is deposited in landfills, the material is removed from the

[0047] Material cycle lost. An overview of the various

[0048] Packaging used in the food industry is described by Kaiser et al. in “Recycling of Polymer-Based Multilayer Packaging: A Review” in Recycling 2018.

[0049] Against the background described above, the present invention is based on the objective of providing a method, a device, and a

[0050] To specify the use of the aforementioned type for the reprocessing of waste containing essentially polyalkylene terephthalate, in particular polyethylene terephthalate and / or polybutylene terephthalate, in a continuous process by means of depolymerization, which is suitable for the high-throughput, almost complete chemical recycling of multilayer systems and colored materials into high-quality starting materials, in order to obtain from the

[0051] Recycled products without restrictions new

[0052] To be able to manufacture polyalkylene terephthalate products.

[0053] According to the invention, the problem is solved by the combination of features in the independent patent claims.

[0054] In particular, the task directed towards a procedure is solved in a procedure of the type mentioned at the outset by the fact that the

[0055] In the reaction mixture, an alkylene glycol is additionally added as a reactant, wherein the alkylene glycol acts as a product of the desired reaction.

[0056] The invention uses alkylene glycol, particularly MEG, which can be produced by depolymerization, and wherein no further reactive components are added to the reaction mixture. It has been shown within the scope of the invention that the addition of this component as a starting material for the subsequent depolymerization

[0057] optimized process control for the resulting alkylene glycol

[0058] with regard to recycling rates and recycling quality.

[0059] In particular, according to the invention, MEG is added to, for example, sodium hydroxide during the reprocessing of PET waste.

[0060] In a further advantageous embodiment of the process according to the invention, the waste is comminuted to a size of no more than 3 mm before the reaction mixture is prepared. This measure ensures that the waste, particularly multilayer systems, is mechanically ground and broken up during the preparation of the reaction mixture, i.e., even before the actual depolymerization takes place, in order to provide the largest possible surface area for the saponification reaction. The mechanical comminution damages the material bond between the different layers as well as the layers themselves, so that

[0061] According to the invention, a reaction can take place on the waste, in particular PET, from all or from different sides.

[0062] In a preferred embodiment of the process according to the invention, the alkylene glycol is added with a mass flow rate selected such that the mass flow ratio of waste to alkylene glycol is at least 3, in particular 3.3. This ratio has proven suitable within the scope of the invention for achieving high throughput rates and high quality of the recycled products obtained.

[0063] In a further advantageous embodiment of the process according to the invention, the alkali and / or alkaline earth hydroxide is added in such a mass flow rate that the stoichiometric ratio of alkali and / or alkaline earth hydroxide to polyalkylene terephthalate is based on a

[0064] The constitutional repeating unit is at least 2, in particular approximately 2.4. In particular, a mass flow of 3.33 kg / h of sodium hydroxide can be used to process a mass flow of 6.66 kg / h of PET-containing waste.

[0065] In a further advantageous embodiment of the process according to the invention, the reaction mixture for depolymerization is continuously conveyed through a reactor vessel. Continuous operation advantageously allows for a high throughput. Furthermore, a continuous throughput through a reactor vessel enables

[0066] This is an energy-efficient process, as the reactor vessel can be regulated to constant temperature values. In particular, it is advantageous within the scope of the invention if an extruder, especially a twin-screw extruder, is used for conveying, with the screws preferably rotating in the same direction. The use of a twin-screw extruder rotating in the same direction with closely meshing screw elements advantageously provides good

[0067] Thorough mixing of the reaction mixture is ensured, especially when sodium hydroxide, for example in bead form, is used as the alkali or alkaline earth hydroxide. High mechanical action is required.

[0068] The aim is to stress the solids.

[0069] Furthermore, in an advantageous embodiment of the process according to the invention, it is beneficial if the depolymerization is carried out at a temperature below the decomposition point of the polyalkylene terephthalate and / or below the boiling point of MEG, particularly at 160°C. Compared to conventional processes, which operate at temperatures between 180°C and 250°C and above the boiling point of the resulting alkylene glycol, i.e., above 197°C in the case of PET waste, this represents an energy-saving advantage.

[0070] This procedure is possible, as only low pressures are involved.

[0071] No reactor containers are required for carrying out the process according to the invention, which are necessary for

[0072] High pressure is suitable. In particular, according to the invention, extruders can be used as reactor vessels. The main advantage of an extruder, according to the invention, is the continuous process and the thorough mixing of the product.

[0073] In the process according to the invention, it is advantageous to introduce inert gas, preferably nitrogen, into the reactor vessel. Instead of nitrogen, a noble gas or a mixture of noble gases and / or nitrogen can also be introduced according to the invention. This measure prevents the inflow of oxygen or atmospheric moisture into the reactor vessel in order to ensure a constant dosage. Furthermore, an inert gas overlay is used.

[0074] According to the invention, it is advantageously prevented that the highly hygroscopic sodium hydroxide clumps together and, by blocking, brings the reaction process to a standstill.

[0075] To ensure a high recycling rate at high throughput, in an embodiment of the invention, the reaction mixture is kneaded and / or mixed and / or conveyed and / or recirculated during depolymerization. In particular, a sequence of different kneading, mixing, conveying, and recirculation treatments can be carried out in temporal and / or spatial succession to ensure homogeneous mixing of the solids and to mechanically grind the PET material and the multilayer systems.

[0076] to break up, in order to create as large a surface area as possible for the

[0077] To provide a saponification reaction. The mechanical stress damages the material bond between the different layers as well as the layers themselves, so this method advantageously allows the reaction to take place from different sides of the PET. Furthermore, by appropriately selecting the sequence of treatments of the reaction mixture, a desired average residence time of the waste in the reaction vessel can be set, for example, 2 minutes.

[0078] In a preferred embodiment of the process according to the invention, alkylene glycol is obtained from a reaction discharge, preferably by

[0079] Evaporation, removed. According to the invention, both the alkylene glycol used as a starting material, for example MEG, and the alkylene glycol formed can be recovered by condensation. This enables a particularly efficient process. For further processing of the product obtained after depolymerization

[0080] In a preferred embodiment of the reaction discharge

[0081] In the process according to the invention, water is added to the reaction discharge to dissolve solid components. This can be done in a

[0082] This process takes place in a stirred tank or a mixing screw. The

[0083] Dissolution of the TPA salt obtained during depolymerization is achieved. When processing PET-containing waste with the addition of sodium hydroxide, the disodium terephthalate formed during depolymerization is dissolved by the addition of water. In a further preferred embodiment of the

[0084] According to the inventive process, solids are extracted from the

[0085] Reaction residues are filtered out. These are primarily insoluble residues, such as PET residues, polyethylene, polypropylene, metals, cardboard, or polystyrene. Subsequently, in a further advantageous embodiment of the

[0086] In the process according to the invention, an acid is added to the reaction discharge in order to neutralize substances contained in the reaction discharge.

[0087] To convert the carboxylate ions formed during depolymerization into acid.

[0088] For this to happen, the acid must be stronger than the TPA formed, according to the invention. In this context, the following is suitable according to the invention:

[0089] especially sulfuric acid with a concentration of 25% (w / w).

[0090] The problem underlying the invention is solved equally well by a device of the type mentioned at the outset for carrying out a reprocessing method according to any one of claims 1 to 13, comprising a reactor vessel which includes conveying means, and comprising

[0091] The device comprises means for supplying an alkali and / or alkaline earth hydroxide, preferably solid, and means for supplying an alkylene glycol into the reactor vessel. Because the device according to the invention includes a reactor vessel with conveying means, continuous process operation is possible.

[0092] If the reactor vessel is temperature-controlled in an embodiment of the invention, a desired residence time in the vessel is achieved using the conveying media.

[0093] The reactor vessel enables high throughput rates with high recycling rates.

[0094] The measure according to the invention, whereby means for supplying an alkylene glycol, for example MEG, are provided, enables the implementation of the process according to the invention, which has proven to be particularly suitable for the reprocessing of multilayer waste.

[0095] The means for supplying an alkali hydroxide can include a gravimetric dosing device with a forced feeder, for example, to add solid sodium hydroxide in bead form. The means for supplying the hydroxide can be designed as a solid feeder. Furthermore, the means for supplying an alkylene glycol, for example MEG, can include a gravimetric dosing unit.

[0096] In an embodiment of the device according to the invention, the

[0097] The reactor vessel is shaped as an extruder, in particular a twin-screw extruder, preferably rotating in the same direction. This ensures homogeneous mixing during the process.

[0098] Solids are ensured and the material to be reprocessed, especially with multi-layer systems, can be mechanically ground and broken up to provide the largest possible surface area for the

[0099] to provide a saponification reaction.

[0100] In a preferred embodiment of the device according to the invention, the conveying means have at least one screw assembly with at least one screw element whose outer diameter is in a ratio of approximately 1.7, in particular 1.66, to its inner diameter. This ratio has proven advantageous with regard to the quality of the

[0101] Reprocessing on the one hand and throughput on the other hand have proven suitable within the scope of the invention.

[0102] Furthermore, it has proven advantageous if, in the embodiment of the device according to the invention, the length of the screw arrangement is in a ratio of approximately 60 to the outer diameter.

[0103] This allows dwell times of only 2 minutes to be set, during which a very high conversion rate is still achieved.

[0104] In particular, further development of the invention can

[0105] The device comprises conveying elements arranged in series, including conveying, conveying-neutral, and / or return-conveying screw elements, to convey, knead, or return the reaction mixture in the reactor section by section. With a suitable sequence of

[0106] According to the invention, various kneading, mixing, conveying, and return conveying elements ensure homogeneous mixing of the solids, and the polyalkylene terephthalate material to be processed and the multilayer systems are mechanically ground and broken up. This allows for the largest possible surface area for the saponification reaction. The mechanical stress damages the material bond between the different layers, and the

[0107] Layers themselves, so that a reaction from all sides occurs at the

[0108] Polyethylene terephthalate can be processed. According to the invention, by suitable combination of screw elements, the average residence time of the waste in the extruder can be reduced to only about 2 minutes, achieving a depolymerization conversion of 92-97% within this short reaction time. The screw elements can have a length of approximately one to two times their diameter, according to the invention.

[0109] According to the invention, the worm elements used can be threaded onto a shaft in a desired sequence. This allows for changes in the number of threads of the worm elements.

[0110] Spacers or transition elements can be used. These can be used to achieve the highest possible mechanical strength.

[0111] To ensure a consistent residence time of approximately 2 minutes, both conveying and conveying-neutral kneading elements are used. According to the invention, the use of kneading elements advantageously introduces energy into the reaction mixture, which can accelerate the reaction. Furthermore, according to the invention, the

[0112] Kneading elements for good dispersion of the base in the reaction mixture. The use of a return-conveying element leads to a build-up of the reaction mixture. According to the invention, a narrow gap between the return-conveying elements forces the retention of the

[0113] Reaction mixture until the waste residue passes through the gap between

[0114] elements and the cylinder wall can be pressed. If, according to the invention, some screw elements are used as conveying elements

[0115] When mixing elements are designed, very good mixing is achieved with low shear, which puts less mechanical stress on the reaction product than kneading elements.

[0116] In an advantageous further development of the device according to the invention, the reactor vessel is provided with means for section-by-section temperature control adapted to the screw elements. Within the scope of the invention, this measure advantageously enables a temperature control tailored to the respective section.

[0117] To select a temperature control adapted to the mechanical treatment. For this purpose, individual housing sections of the reaction vessel can each be designed with an individually controllable electric heater and a water cooling system according to the invention.

[0118] Finally, the invention underlying the invention is solved by using a device according to one of claims 14 to 19 to carry out a method according to one of claims 1 to 13.

[0119] Preferably, waste from polyalkylene terephthalate is used in the process according to the invention as duo- and / or multi-layer systems with one or several different polymers and / or natural fibers and / or metal coatings. Preferably, the

[0120] waste containing polyalkylene terephthalate forms a layer of

[0121] Polyethylene terephthalate. These are, for example, the commercially available PET bottles or food packaging.

[0122] In contrast to the solvent-free processing of pure polyalkylene terephthalate waste or waste mixed with other polymers according to DE 69316545 T2, the process according to the invention makes it possible to process coated polyalkylene terephthalate waste and multilayer systems containing polyalkylene terephthalate. For certain

[0123] Within the scope of the invention, it is advantageous in applications if a solvent or a

[0124] A solvent mixture is added. The solvent is preferably selected from the group of alcohols.

[0125] Solvent treatment of the material and the addition of solvent during the depolymerization process in the extruder or kneading reactor ensure better mixing, better phase contact, and increased mass transfer.

[0126] Depolymerization efficiency is increased. According to the invention, the waste containing polyalkylene terephthalate, which consists, for example, of bottle, film, fiber, tray, automotive interior trim, and other packaging waste, is crushed prior to treatment and continuously mixed in a reactor with an alkali metal or alkaline earth metal hydroxide. The reagents are fed in such a way that the alkali metal or

[0127] Alkaline earth metal hydroxide in a stoichiometric or a slight stoichiometric excess relative to the constitutional amount

[0128] A repeating unit of polyalkylene terephthalate is present. In the case of

[0129] According to the invention, the reactor used can be a continuously operating extruder or kneading reactor.

[0130] In the process according to the invention, it can be advantageous to cover or overflow all supplied reagents and the comminuted waste containing polyalkylene terephthalate with an inert gas atmosphere before and during processing in the extruder or kneading reactor. This inert gas atmosphere can consist of nitrogen, noble gases, or mixtures thereof, and in certain processes, of dry or synthetic air.

[0131] To ensure thorough mixing of the materials, an embodiment of the invention may utilize a co-rotating or counter-rotating, closely meshing twin-screw extruder or a multi-screw extruder, as well as a

[0132] A kneading reactor with, preferably, self-cleaning blades is used. The arrangement of the extrusion screw elements and the arrangement of the blades is advantageously designed to be self-cleaning and can be adapted to the process by using various mixing, conveying, re-conveying, and kneading elements.

[0133] The extrusion screw elements can be used in the process in

[0134] The invention is designed such that the resulting alkylene glycol can be removed at reduced pressure or by passing it over an inert gas. The solvent and

[0135] In a preferred embodiment of the invention, alkylene glycol vapors can be removed outside the reactor by suitable methods, such as e.g.

[0136] Condense, be obtained.

[0137] In another variant of the process according to the invention, the paddles of the kneading mixer can be arranged in such a way that they self-clean, homogenize the mixture in a manner that prevents the saponification of the polyalkylene terephthalate components in the waste within 1-60 minutes.

[0138] can be carried out. The reactor can also be operated in this manner.

[0139] In the variant according to the invention, an inert gas is used to flow through the reactor, which carries the alkylene glycol vapors out of the reactor. These vapors can be recovered outside the reactor using suitable equipment. According to the process, the reaction yields an alkali metal or alkaline earth metal terephthalate, an alkylene glycol, and the optionally used solvent. In the next process step, the alkali metal or alkaline earth metal terephthalate is dissolved in a suitable solvent, preferably water, filtered, and purified. During filtration, the

[0140] Coatings that emerge partially unchanged during the process are recovered from the multilayer systems. In a specific example according to the invention, these can be RE or other polyolefin components that have ended up as waste in a PE / PET or PP / PET multilayer system used as food packaging.

[0141] In contrast to prior art processes which lead to the formation of alkali metal or alkaline earth metal terephthalates from uncoated PET waste, the process according to the invention allows the processing of coated and multilayer PET.

[0142] Waste and mixtures of various polymers and polyalkylene terephthalate containing polyalkylene terephthalate and waste, and the production of valuable alkali metal or

[0143] Alkaline earth metal terephthalates. From the obtained alkali metal or alkaline earth metal terephthalates, the TPA can be recovered in aqueous solution by adding an acid stronger than TPA.

[0144] Developments over the last decade have shown that a recycling method for the large quantities of packaging material is urgently needed. The method according to the invention can offer a solution to a significant part of this problem, since the inventive method can be used to recycle, in particular, single- and multi-layer polyethylene terephthalate-containing bottles or other packaging materials.

[0145] Liquid containers, packaging trays and films can be recycled, which is not possible according to the current state of the art as soon as there is a direct material bond between two or more different materials.

[0146] It consists of materials.

[0147] In addition to direct material bonding, the process according to the invention advantageously tolerates impurities such as additives, fillers, dyes, pigments, coatings, labels, metals and metal coatings, and the like in the waste containing polyalkylene terephthalate. Within the scope of the invention, these impurities can be separated by filtration and / or other process steps after the reaction discharge, alkali metal, or

[0148] Alkaline earth metal terephthalates have been dissolved in water.

[0149] The target product, TPA, is obtained after a purification step by lowering the pH value with a stronger acid than TPA. Application examples are described below to further illustrate the recycling process, without, however, referring to them.

[0150] restrict.

[0151] Example 1

[0152] In a co-rotating twin-screw extruder with a

[0153] A screw with a diameter of 18 mm is continuously fed under an inert gas atmosphere using two dosing devices at a rate of 0.8 kg / h of PE-coated PET flakes and 0.4 kg / h of sodium hydroxide.

[0154] Addition streams allow the maintenance of a constant

[0155] PET / NaOH weight ratio of approximately 2, based on the

[0156] Constitutional repeating unit for PET. The extruder housing temperature is set between 160-180°C. The rotational speed of the

[0157] The twin screw operates at 500 rpm. A sample of the product shows a PET saponification level of >80%.

[0158] In a twin-screw extruder, the resulting MEG is removed by distillation. The solid obtained in this way consists essentially of mono- and disodium terephthalate as well as unreacted PE components.

[0159] Extruder discharge is dissolved in water and then subjected to solid-liquid separation before the solution is purified and the TPA is precipitated using a strong acid.

[0160] Example 2

[0161] In the same apparatus as in Example 1, using a similar process, a heterogeneous input stream of waste is processed, containing, among other things, PE-coated PET and other polymers, particularly polyolefins such as PP. The input stream contains approximately 0.8 kg / h of PP / PE-coated PET flakes, and 0.4 kg / h of sodium hydroxide, with the addition of 0.9 kg / h of MEG, are each dosed separately into the extruder. These addition streams allow for the maintenance of a constant PET / NaOH weight ratio of approximately 2. The entire apparatus is blanketed with inert gas. The extruder housing temperature is set between 140 and 160°C. The twin-screw speed is 400 rpm. A sample of the product shows a PET saponification level of >90%. In the twin-screw extruder, the input material and the resulting MEG are removed under reduced pressure.The resulting solid consists essentially of mono- and disodium terephthalate as well as unreacted polyolefin components, in particular PP and PE components.

[0162] Example 3

[0163] In a device similar to the one in Example 1, with a

[0164] Using a screw with a diameter of 27 mm and a similar process, 5 kg / h of PE-coated PET flakes are treated with 2.5 kg / h of sodium hydroxide with the addition of 5.7 kg / h of MEG.

[0165] Addition streams allow the maintenance of a constant

[0166] The PET / NaOH weight ratio is approximately 2. The extruder housing temperature is set between 140-160°C. The twin-screw speed is 270 rpm. A sample of the product shows a PET saponification level of >90%.

[0167] In twin-screw extruders, the input material and the resulting MEG are removed by distillation. The solid obtained in this way consists of

[0168] Essentially consisting of mono- and disodium terephthalate as well as unreacted PE components.

[0169] Example 4

[0170] In a twin-shaft kneading reactor, 0.8 kg / h of PE-coated PET flakes and 0.4 kg / h of sodium hydroxide are continuously added via three dosing devices, along with 0.9 kg / h of MEG. These quantities are dosed separately into the twin-shaft kneading reactor to ensure a constant stoichiometric concentration.

[0171] A NaOH / PET ratio of approximately 2.4 is permitted, based on the constitutional repeating unit of PET. The housing temperature of the kneading reactor is set between 160 and 180°C. The kneading shaft speed is 500 rpm. A sample of the product shows a PET saponification degree of >80%. In the twin-shaft kneading reactor, the input and the resulting MEG are removed by distillation. The solid obtained in this way consists essentially of mono- and

[0172] Disodium terephthalate and unreacted PE components.

[0173] Further features of the invention are listed below.

[0174] Feature 1. Method for recycling waste containing polyalkylene terephthalate comprising the following steps:

[0175] Shredding the waste,

[0176] Feeding the shredded waste and an alkali metal or alkaline earth metal hydroxide into an extruder or kneading reactor,

[0177] Mixing and heating the shredded waste with the

[0178] Alkali metal or alkaline earth metal hydroxide in the extruder or kneading reactor to form a saponification and

[0179] Discharge of an alkali metal or

[0180] alkaline earth metal terephthalate-containing intermediate product.

[0181] Merlmal 2. Method according to feature 1, characterized in that the waste containing polyalkylene terephthalate is duo- and / or

[0182] These are multilayer systems with one polymer or several different polymers.

[0183] Feature 3. Process according to feature 1 or 2, characterized in that the waste containing polyalkylene terephthalate contains other polymers and / or mixtures of other polymers and / or natural substances and / or

[0184] Contains metals.

[0185] Feature 4. Method according to feature 1, 2 or 3, characterized in that the polyalkylene terephthalate-containing waste comprises one or more layers of ethylene vinyl alcohol copolymer (EVOH), cardboard, ethylene vinyl acetate copolymer (EVA), polyvinyl alcohol (PVOH), polyamide (PA), polyethylene (PE), polypropylene (PP), polystyrene (PS) or their derivatives.

[0186] Contains copolymers as well as metals and mixtures thereof.

[0187] Feature 5. Method according to one of the preceding features 1 to 4, characterized in that the waste containing polyalkylene terephthalate has a layer of polyethylene terephthalate.

[0188] Feature 6. Method according to one of the preceding features, characterized in that a

[0189] Solvent or a solvent mixture is added.

[0190] Feature 7. Method according to feature 6, characterized in that the solvent is from the group of alcohols, or that the

[0191] The solvent is a nonpolar, halogenated solvent.

[0192] especially dichloromethane, chloroform, tetrachloromethane, 1 ,2

[0193] Dichloroethane, or that the solvent is a non-halogenated one

[0194] solvent is, in particular dimethyl sulfoxide, or that the

[0195] The solvent is 1,4-dioxane or tetrahydrofuran.

[0196] Feature 8. Process according to one of the preceding features, characterized in that zinc acetate, sodium carbonate, sodium bicarbonate, zinc chloride and / or lead acetate are used for saponification.

[0197] Catalysts are added.

[0198] Feature 9. Method according to one of the preceding features, characterized in that the reactive extrusion or kneading reaction is carried out at temperatures of 100°C to 180°C, preferably from 140°C to 160°C.

[0199] Feature 10. Method according to one of the preceding features, characterized in that the reactive extrusion or kneading reaction is carried out continuously and under the influence of an inert gas, in particular argon / nitrogen, for a dry and oxygen-free atmosphere.

[0200] Feature 11. Process according to one of the preceding features, characterized in that the alkylene glycol produced during saponification is separated by distillation.

[0201] The invention is described in a preferred embodiment under

[0202] Reference is made to a drawing as an example, whereby further advantageous details can be found in the figures of the drawing.

[0203] Functionally identical parts are marked with the same reference symbols.

[0204] The single figure in the drawing shows in detail:

[0205] Figure 1: Block diagram illustrating the process steps of an embodiment of the invention

[0206] Method. The preferred method described with reference to Fig. 1.

[0207] An embodiment of the inventive method enables the recycling of materials that were previously not recyclable – or only recyclable thermally.

[0208] Polyethylene terephthalate (PET) waste. The process can also be used for the recycling of other polyalkylene terephthalates such as, for example,

[0209] Polybutylene terephthalate is used. PET-containing waste, including multilayer systems, such as...

[0210] Beverage bottles, detergent bottles (opaque, clear, or black), or other types of food packaging, e.g., salad bowls, sausage and cheese packaging, or PET-containing production waste, are washed in a first step 1 and shredded to a size of less than 3 mm. The waste is then optionally pre-dried in a second step 2 to reduce the water content of the PET material. Alternatively, the material to be processed can be pre-dried according to the inventive method. In this case, step 2 of drying following step 1 of shredding can be omitted. However, in certain applications according to the invention, a further step 2 may be necessary.

[0211] More intensive drying would be advantageous.

[0212] In a further process step, "depolymerization," the waste is fed into a co-rotating twin-screw extruder with closely meshing screw elements. The saponification or depolymerization reaction of the PET is carried out continuously in the extruder. In the system described as an example with reference to Fig. 1, 6.66 kg / h of PET-containing waste and 3.33 kg / h of other materials are processed.

[0213] Sodium hydroxide and 2 kg / h MEG are processed in the extruder. According to the invention, the ratio of sodium hydroxide to PET waste is adjusted during the process such that a constant stoichiometric ratio of approximately 2.4, based on the constitutional repeating unit of PET, is established. The reaction discharge from the extruder consists of disodium terephthalate, MEG, and unreacted fractions of the

[0214] Sodium hydroxide and PET waste, such as PET residues, dyes, degradation products of PA and dyes, other polymers such as...

[0215] PE, PP and PS.

[0216] The twin-screw extruder has a modular design and consists of 14 temperature zones. Each housing is equipped with an individually controllable electric heater and water cooling system.

[0217] Ratio of the outer screw diameter Da to the inner diameter

[0218] Screw diameter Di is a parameter indicating the possible free screw volume. In the extruder used, the Da / Di ratio of the screw elements is 1.66. The ratio of the screw length L to the screw diameter D describes the process length of the extruder.

[0219] The extruder's screw geometry is 60 mm. It is modular and can be adapted to the process and the PET material. The extruder consists of the following individually temperature-controlled cylinders:

[0220] Cylinder 1: Main intake, Cylinder 2: Top injector, Cylinder 3:

[0221] Side degassing with recirculation, cylinder 4: side feed of sodium hydroxide, cylinder 5: top spray nozzle, cylinder 6:

[0222] Venting port at the top, cylinder 7: closed, cylinder 8:

[0223] Top spray nozzle, cylinder 9: side degassing with recirculation, cylinder 10: closed, cylinder 11: degassing, cylinder 12:

[0224] Closed, cylinder 13: degassing, cylinder 14: spray nozzle,

[0225] Cylinder 15: Conveying, discharge downstream of cylinder 15. In cylinders 1 to 15, the raw materials are first drawn into the extruder and mechanically processed within the machine as they pass through all zones. In the last, fifteenth, cylinder, the product is discharged from the extruder.

[0226] The product is conveyed out. The discharge is designed as an opening through which the product is conveyed out of the device.

[0227] The unit is equipped with up to three pressure sensors inserted into the cylinder opening of the spray nozzle. Cylinders 2 to 15 are temperature-controlled at 160°C. Cylinder 1 is not temperature-controlled. The speed of the co-rotating twin screw is set to 100 rpm. The screw configuration is selected to ensure thorough mixing of the two solids during the process.

[0228] The screw elements used can be in any

[0229] The order is threaded onto the shaft. In the case of a

[0230] Spacers or transition elements are used to change the number of threads of the screw elements. To achieve the highest possible deformation / mechanical stress and a relatively long average residence time of approximately 2 minutes for the multilayer PET waste, conveying and conveying-neutral kneading elements are used in the screw configuration design. Furthermore, the use of kneading elements introduces energy into the reaction mixture.

[0231] The mixture is entered, which can thus accelerate the reaction. Furthermore, kneading elements ensure good dispersion of the base in the mixture.

[0232] Reaction mixture. The use of a return element leads to a build-up of the reaction mixture. The narrow gap between the return elements forces the retention of the

[0233] The reaction mixture is pumped until the PET waste residue can be forced through the gap between the elements and the cylinder wall. In the degassing and atmospheric vent area, screw elements with a high free screw volume are used. This allows for the continuous removal of solvent from the reaction mixture. Furthermore, the screw configuration incorporates a number of conveying mixing elements, which, due to their low shear,

[0234] The reaction product is subjected to less mechanical stress than kneading elements, but ensures very good mixing.

[0235] In cylinder 1, the PET is gravimetrically dosed via a solids feeder. The material is transported into the extruder via the feeder and screw elements with a large free screw volume, where it is heated. Within cylinder 1 itself, only transport occurs; no temperature control takes place. In cylinder 2, MEG is added via the top feed opening using gravimetric dosing. Solid material is added via the side feeder in cylinder 4.

[0236] Sodium hydroxide in bead form gravimetrically via a second

[0237] The dosing unit adds the material using a forced feeder. Cylinder 4 also has an atmospheric vent. Both the solid feeder for PET and the solid feeder for sodium hydroxide are covered with inert gas to prevent the ingress of oxygen and (atmospheric) moisture and to ensure constant dosing. Without an inert gas vent, the highly hygroscopic sodium hydroxide would very quickly clump and block, which would bring the process to a standstill. The MEG used and the MEG formed can be recovered by condensation via an atmospheric vent in cylinders 6 and 10.

[0238] The screw configuration is shown in Table 1. The angle values ​​given in degrees indicate the angle between the discs of the kneading elements. A sequence of different kneading, mixing, conveying, and return conveying elements is used to produce a homogeneous mixture.

[0239] Thorough mixing of the solids is ensured, and the PET material and multilayer systems are mechanically ground and broken up to provide the largest possible surface area for the saponification reaction. This mechanical stress damages the material bond between the different layers as well as the layers themselves, allowing the reaction to occur from all / different sides of the PET. In contrast, without mechanical stress on the single- or multi-sided coated PET flakes, the base would only attack the exposed PET surfaces and edges. By selecting the

[0240] In the screw configuration shown, the average residence time of the RET waste in the extruder is set to approximately 2 minutes. During this reaction time, a conversion of 92-97% of the PET content in the PET-containing waste takes place.

[0241] Table 1: Screw configuration PET depolymerization

[0242]

[0243] The pasty reaction discharge is processed in the following step

[0244] "Post-treatment" 4: Granulated, crushed, and spread onto a temperature-controlled conveyor belt with extraction. The MEG vapors are condensed at a cooler and collected.

[0245] In the following process step “Dissolving” 5, the reaction discharge is dissolved in water (55 kg / h, 133 g / L solubility of disodium terephthalate) in a stirred tank or mixing screw. The insoluble residues (PET residues, PE, PP, metals, PS, cardboard) are separated by filtration 6.

[0246] Following filtration 6, impurities and byproducts of the process are separated in a process step called "purification" 11. Various methods are conceivable within the scope of the invention, each of which is known to those skilled in the art.

[0247] In the subsequent process step “TPA precipitation” 7, the solution is treated with sulfuric acid (9.6 kg / h, 25% w / w). The precipitated TPA is recovered by filtration 8 and washed with water 9 and filtered off. The TPA is washed with water to remove residual sulfuric acid and sodium sulfate formed during precipitation. Following washing 10, a solid-liquid separation 10 takes place. » to the fixed TPA » which is insoluble in water » to separate from the wash water.

[0248] Using the method according to the invention » the invention

[0249] The device, as well as the use according to the invention, can be used to process, in particular, multilayer PET-containing waste with high

[0250] throughput and high quality efficiently converted into polymerization feedstocks » which without restriction

[0251] Recycling, i.e., the production of polyalkylene terephthalates, is available. A portion of the alkylene glycol produced in this process can be reused in the effluent of the process according to the invention.

[0252] Depolymerization can be used.

Claims

A method for reprocessing waste products comprising polyalkylene terephthalate, in a continuous process by means of depolymerizing, a solid alkali hydroxide or alkali earth hydroxide, being added to the waste products for producing a reaction mixture, characterized in that an alkylene glycol is additionally added to the reaction mixture as a reactant, wherein the alkylene glycol is an alkylene glycol produced as a product of the intended depolymerizing, and wherein no further reactive components are added to the reaction mixture, wherein a twin-screw extruder is used for transporting, wherein the screws are co-rotating.The method according to claim 1, characterized in that the waste products are comminuted to a size of no greater than 3 mm prior to producing the reaction mixture.The method according to claim 1, characterized in that the alkylene glycol is added at a mass flow rate selected such that the mass flow rate ratio of the waste products to the alkylene glycol is at least 3.The method according to claim 1, characterized in that the alkali or alkaline earth hydroxide is added at a mass flow rate such that the ratio of alkali or alkaline earth hydroxide to polyalkylene terephthalate is stoichiometric relative to a constitutional repeating unit.The method according to claim 1, characterized in that the reaction mixture for depolymerizing is transported continuously through a reactor vessel.The method according to claim 1, characterized in that the depolymerizing is performed at a temperature below the boiling point of the polyalkylene terephthalate or below the boiling point of monoethylene glycol, or at a pressure in the range from 1 bar to 3 bar.The method according to claim 1, characterized in that inert gas is fed into the reactor vessel.The method according to claim 1, characterized in that the reaction mixture is kneaded or mixed or transported or reverse transported.The method according to claim 1, characterized in that alkylene glycol is removed from a reaction output, by evaporating.The method according to claim 1, characterized in that water is added to the reaction output for dissolving solid components.The method according to claim 1, characterized in that solids are filtered out of the reaction output.The method according to claim 1, characterized in that an acid is added to the reaction output in order to convert carboxylate ions formed by depolymerizing and present in the reaction output into acids.A device for performing the method for reprocessing according to claim 1 , having a reactor vessel comprising conveying means, and having means for feeding a solid alkali or alkaline earth hydroxide, and having means for feeding an alkylene glycol into the reactor vessel, wherein the reactor vessel is implemented as a twin-screw extruder.The device according to claim 13, characterized in that the extruder comprises at least one screw element, the outer diameter thereof having a ratio to the inner diameter of 1.7.The device according to claim 13, characterized in that a ratio of the length of the screw element to the outer diameter thereof is 60.The device according to claim 13, characterized in that the conveying means comprise transporting, transportneutral, or reverse transporting screw elements disposed one after the other in order to intermittently convey, knead, or reverse transport the reaction mixture in the reactor.The device according to claim 16, characterized in that the reactor vessel has means for controlling the temperature in segments adapted to the screw elements.A method of using the device according to any one of claims 13 to 17 for performing the method according to any one of the claims 1 to 12.

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