Acidic hydrolysis of polycaprolactam fragments in automotive shredder residue in presence of glass fibers

Abstract

A method for recycling caprolactam from an automotive shredder residue comprising polycaprolactam and glass fibers comprising: a) dissolving the polycaprolactam by treating the automotive shredder residue with at least one acid, whereby a composition containing dissolved polycaprolactam and glass fibers is obtained; b) separating the composition containing dissolved polycaprolactam and glass fibers from the glass fibers, whereby a solution containing the dissolved polycaprolactam is obtained; and c) depolymerizing the polycaprolactam dissolved in the solution to produce caprolactam; a composition comprising i) a solution of polycaprolactam in an acid, ii) glass fibers, and iii) further insoluble particles of an automotive shredder residue; caprolactam obtainable by the inventive method; and the use of an automotive shredder residue comprising polycaprolactam and glass fibers for recycling caprolactam.

Description

Acidic hydrolysis of polycaprolactam fragments in automotive shredder residue in presence of glass fibersDescriptionThe present invention relates to a method for recycling caprolactam from an automotive shredder residue comprising polycaprolactam and glass fibers comprising: a) dissolving the polycaprolactam by treating the automotive shredder residue with at least one acid, whereby a composition containing dissolved polycaprolactam and glass fibers is obtained; b) separating the composition containing dissolved polycaprolactam and glass fibers from the glass fibers, whereby a solution containing the dissolved polycaprolactam is obtained; and c) depolymerizing the polycaprolactam dissolved in the solution to produce caprolactam; a composition comprising i) a solution of polycaprolactam in an acid, ii) glass fibers, and iii) further insoluble particles of an automotive shredder residue; caprolactam obtainable by the inventive method; and the use of an automotive shredder residue comprising polycaprolactam and glass fibers for recycling caprolactam.Automotive shredder residue (ASR) holds significant relevance in the context of recycling due to its composition and environmental impact. ASR is a typical byproduct of the shredding process used to recycle end-of-life vehicles, and it consists usually of various materials such as plastics, rubber, glass, textiles, and metals that cannot be easily separated. This complex mixture poses challenges for traditional recycling methods. However, ASR has gained attention as an alternative energy source through technologies like thermal treatment. By converting ASR into energy, it reduces the reliance on fossil fuels and contributes to a more sustainable future. Additionally, efforts are being made to improve the recycling efficiency of ASR by developing advanced sorting and separation techniques, which would enhance the recovery of valuable materials and minimize its environmental impact. Overall, the relevance of ASR recycling lies in its potential to promote resource conservation, reduce landfill waste, and support the development of innovative recycling solutions.EP0692356 A1 suggests to recycle automotive shredder residue by preparing a composite material comprising ASR and a virgin polymer.Vijayan, S.K.; Kibria, M.A.; Uddin, M.H.; Bhattacharya, S. “Pretreatment of Automotive Shredder Residues, Their Chemical Characterisation, and Pyrolysis Kinetics.” Sustainability 2021 , 13, 10549 suggests to recycle automotive shredder residue by pyrolysis.Ezzat El Halabi, Mike Third, and Matthew Doolan “Machine-based dismantling of end of life vehicles: A life cycle perspective” Procedia, 29 (2015) 651-655 suggest to recycle automotive shredder residue by machine based dismantling.Juliana Argente Caetano, Valdir Schalch, Javier Mazariegos Pablos “Characterization and recycling of the fine fraction of automotive shredder residue (ASR) for concrete paving blocks production” Clean Technologies and Environmental Policy (2020) 22:835-847 suggest to recycle ASR by solidification with cement, gravel and sand for paving blocks production.Won-Seok Yang et al. “Utilization of automobile shredder residue (ASR) as a reducing agent for the recovery of black copper” Korean J. Chem. Eng., 33(4), 1267-1277 (2016) suggests to recycle ASR by using it instead of lump coal as a reducing agent in the copper production.It is an object of the present invention to find an effective and inexpensive method for recycling automotive shredder residue (ASR), especially for recycling the polymers comprising glass fibers, more especially polycaprolactam comprising glass fibers in ASR.The object is achieved by a method for recycling caprolactam from an automotive shredder residue comprising polycaprolactam and glass fibers comprising: a) dissolving the polycaprolactam by treating the automotive shredder residue with at least one acid, whereby a composition containing dissolved polycaprolactam and glass fibers is obtained; b) separating the composition containing dissolved polycaprolactam and glass fibers from the glass fibers, whereby a solution containing the dissolved polycaprolactam is obtained; and c) depolymerizing the polycaprolactam dissolved in the solution to produce caprolactam.The object is further achieved by a composition comprising i) a solution of polycaprolactam in an acid, ii) glass fibers, and iii) further insoluble particles of an automotive shredder residue; preferably obtainable by step a) of the method according to the present invention; caprolactam obtainable by the method according to the present invention and the use of an automotive shredder residue comprising polycaprolactam and glass fibers for recycling caprolactam, preferably by carrying out the method according to the present invention.It has been found by the inventors that the value product caprolactam can be recycled from polycaprolactam comprising ASR by the inventive process. It has especially been found that acid can be used as both, as solvent as well as as depolymerization catalyst. By said process an effective and inexpensive method for recycling automotive shredder residue is therefore provided.The automotive shredder residue may be obtainable, preferably is obtained, by shredding vehicles. Preferably, the automotive shredder residue is obtainable by depollution of the vehicles, dismantling the vehicles, shredding the vehicles, and separating metal particles from the shredded vehicles.The vehicles are typically end-of-life vehicles (also called “ELV”), which are typically at least 15 years old. The vehicles can be passenger cars, light-duty or heavy-duty trucks, motorbikes, a utility vehicle, an agricultural vehicle, or recreational vehicles. The vehicle can be an electric vehicle, such as a fully electric vehicle or a hybrid electric vehicle.In depollution of vehicles hazardous liquids such as fuel, lubricating oil, coolants, brake fluids and batteries can be removed from the vehicles prior to shredding.The dismantling of vehicles may comprise selective removal of parts, such as engines, gearboxes, tires, glass and plastics, for being reused as spare parts for the second-hand market. The dismantling may also comprise the removal of larger plastic components, such as bumpers, dashboard, fluid containers for recycling the plastics separately.The ASR may comprise further waste from other sources. For examples, garbage from the last owners may remain in the trunk or interior of the vehicles. The advantage of the present process is that it can handle broadly varying compositions of the ASR.The shredding can be made with a vehicle shredder machine. Vehicle shredder machines are manufactured in different sizes. Typically, a vehicle shredder machine comprises a heavy fastturning rotor, which may revolve in a vertical or a horizontal plane and is often equipped with swinging hammers. The vehicle shredder machine tears and shreds the car hulk until its parts are reduced to fragments with a desired fragment size, such as up to 30 cm, preferably 1 mm to 15 cm. Then the fragments may pass through grids and leave the rotor housing.After shredding, the metal fragments such as ferrous and non-ferrous metal fragments can be separated from the shredded vehicles. The ferrous metal fragments can be removed by magnetic separators. The non-ferrous metal fragments can be separated from the shredded vehicles by eddy current separators, by heavy media sink / float units which separate on the basis of density, or by manual sorting. Typically, 60 - 90 wt% of the vehicle weight is metal, which can be separated from the shredded vehicle.The automotive shredder residue may represent about 10 - 40 wt%, preferably from 15 - 35, and in particular from 20 - 30 wt% of the original vehicle weight.The automotive shredder residue may comprise fragments of various polymeric vehicle parts, such as fragments of bumpers, interior panels, dashboard, cable insulation, fuel tank, electrical insulation, flexible foam seating, foam insulation panels, automotive suspension bushings, electrical potting compounds, car body parts, pillar coverings, spoilers polymer parts coated with automotive paint, wheel covers, gears, bushes, cams, bearings, weatherproof coatings, interior and exterior trims, fuel systems, gear housings, headlamp retainer, engine cover, connector housings, door handles, carburetor components, exterior mirror components, windscreen wiper components, windscreen wiper protective housings, decorative grilles, cover strips, roof rails, window frames, sliding roof frames, antenna cladding covers, front and rear lights, radiator grilland body exterior parts, engine covers, cylinder head covers, intake pipes, cylinder head covers, engine covers, housings for charge air coolers, charge air cooler valves.The automotive shredder residue may comprise fragments of various polymeric vehicle parts, such as fragments of- bumpers, interior panels, dashboard, cable insulation, where these fragments are often made of polypropylene;- fuel tank, electrical insulation, where these fragments are often made of polyethylene;- flexible foam seating, foam insulation panels, automotive suspension bushings, electrical potting compounds, hard plastic parts, transmission mounts, motor mounts, seals, impact foam parts, where these fragments are often made of polyurethane;- body parts, dashboards, wheel covers, where these fragments are often made of acryloni- trile-butadiene-styrene;- gears, bushes, cams, bearings, charge air coolers, cylinder head covers, oil pans, engine cooling systems, thermostat and heater housings, exhaust systems including mufflers and housings for catalytic converters, air intake manifolds, timing chain belt front covers, where these fragments are often made of nylon 6 or nylon 6.6.;- interior and exterior trims, fuel systems, small gears, where these fragments are often made of polyoxymethylene;- wiper arm and gear housings, headlamp retainer, connector housings, where these fragments are often made of polyethylene terephthalate; and- door handles, bumpers, carburetor components, where these fragments are often made of polybutylene terephthalate.The automotive shredder residue may comprise at least 30 wt%, preferably at least 40 wt%, and in particular at least 50 wt% of the fragments of the polymeric vehicle parts. In another form the automotive shredder residue may comprise at least 70 wt%, preferably at least 80 wt%, and in particular at least 90 wt% of the fragments of the polymeric vehicle parts.The automotive shredder residue may comprise at least 20 wt%, preferably at least 30 wt%, and in particular at least 40 wt% of the fragments of the polymeric vehicle parts, which are black polymeric vehicle parts. In another form the automotive shredder residue may comprise at least 70 wt%, preferably at least 80 wt%, and in particular at least 90 wt% of the fragments of the polymeric vehicle parts, which are black polymeric vehicle parts. The black polymeric vehicle parts usually comprise carbon black pigments.The automotive shredder residue may comprise up to 15 wt%, preferably up to 10 wt%, and in particular up to 5 wt% of metal fragments, such as ferrous and non-ferrous metal particles.The automotive shredder residue may comprise up to 15 wt%, preferably up to 10 wt%, and in particular up to 5 wt% of wood and cardboard.The automotive shredder residue may comprise up to 15 wt%, preferably up to 10 wt%, and in particular up to 5 wt% of glass fragments, e.g. broken window glass fragments.The automotive shredder residue can be separated into a shredder light fraction (also called SLF) and a shredder heavy fraction (also called SHF). The separation of the SLF and the SHF can be achieved by air classification. Another air classification can be made by the rotary movement of the vehicle shredder machine may create a fanning action that can blow out the shredder light fraction, and the shredder heavy fraction may leave the vehicle shredder machine through a grid.The SLF can be present in an amount of 55 - 90 wt%, preferably 65 - 85 wt%, and in particular at 70 - 80 wt% of the automotive shredder residue. The SHF may represent the remaining amount to 100 wt%.The SHF can be present in an amount of 10 - 45 wt%, preferably 15 - 35 wt%, and in particular at 20 - 30 wt% of the automotive shredder residue. The SLF may represent the remaining amount to 100 wt%.The SLF usually contains a lower weight percentage of rubber particles than the SHF. The SLF usually contains a lower weight percentage of glass particles than the SHF. The SLF usually contains a lower weight percentage of metal particles than the SHF.The SLF usually contains a higher weight percentage of polyurethane foam particles than the SHF.The SLF usually contains a lower weight percentage of solid and sand than the SHF.Figure 1 shows a possible flow scheme with a suitable process sequence for obtaining the automotive shredder residue. Starting from the vehicles, followed by optional depollution, followed by optional dismantling, followed by shredding the vehicles, followed by optional separating the metal fragments from the shredded vehicle, then the ASR is obtained, followed by optional separation of the ASR in shredder light fraction and shredder heavy fraction.Preferably, the ASR employed in the method of the present invention comprises at least 1 wt%, preferably 1 .5 to 20 wt%, in particular 2 to 15 wt% polycaprolactam, calculated on polycaprolactam without glass fibers. In another preferred form, the ASR employed in the method of the present invention comprises at least 40 wt%, preferably at least 60 wt%, and in particular at least 70 wt% polycaprolactam, calculated on polycaprolactam without glass fibers.Further preferably, the ASR comprises at least 1 wt%, preferably 1.5 to 15 wt% glass fibers.Further preferably, the automotive shredder residue comprises at most 97 wt%, preferably 96 to 65 wt% total sum of rubber, glass, wood, paper, wire, polyurethane foam, and cardboard.The ASR that is used in step a) has been obtained by the steps mentioned above, generally known in the art.Step a)The step a) comprises dissolving the polycaprolactam by treating the automotive shredder residue with an acid, whereby a composition containing dissolved polycaprolactam and glass fibers is obtained.The automotive shredder residue (ASR) is known in the art and defined above. In the inventive method it is generally possible to employ the complete ASR, a shredder light fraction (SLF) and / or a shredder heavy fraction (SHF). It is further possible to employ ASR (complete, SLF and / or SHF) which is pre-treated, for example as mentioned above.The polycaprolactam (also described as polyamide 6, PA6, nylon 6, poly-e-caproamide) is any polycaprolactam present in ASR. Generally, the polycaprolactam in step a) has a viscosity number of 90 to 350 ml / g, preferably from 100 to 240 ml / g. The viscosity number (VN) of the polyamides and polyamide compositions according to the present invention is determined according to EN ISO 307:2019 in sulphuric acid (0.5% [m / v] of polycaprolactam in 96 wt.-% [m / m] sulphuric acid at 25 °C), unless indicated otherwise.The polycaprolactam in the automotive shredder residue is generally reinforced polycaprolactam comprising at least partly the glass fibers mentioned above. Generally, the reinforced caprolactam comprises 5 to 50 wt%, preferably 10 to 40 wt%, more preferably 15 to 35 wt% of glass fibers, based on the total amount of polycaprolactam and glass fibers.The glass fibers are generally chopped fibers, also called short fibers, having a length in the range from 0.1 to 1 mm, long fibers having a length in the range from 1 to 50 mm, and continuous fibers having a length l>50 mm. Continuous fibers are used in the form of rovings or fabric in fiber-reinforced plastics.Also available are ground glass fibers, the length of which after grinding is typically in the range from 70 to 200 pm.Particular preference being given to glass fibers in the form of rovings or in the forms of chopped glass as described above.Preferred examples of glass fibers are chopped long glass fibers having an average starting length to be determined by laser diffraction-particle size analysis (laser granulometry / laser diffractometry) according to ISO 13320:2009 in the range from 1 to 50 mm, more preferably in the range from 1 to 10 mm, most preferably in the range from 2 to 7 mm. Most preferred glass fibers have an average fiber diameter to be determined by laser diffractometry according to ISO 13320:2009 in the range from 7 to 18 pm, more preferably in the range from 9 to 15 pm.The glass fibers may be modified with a suitable size system or an adhesion promoter / adhesion promoter system. Preference is given to using a size system or an adhesion promoter based on silane, to improve compatibility with the thermoplastic. Suitable size systems and adhesion promoter / adhesion promoter systems are known by a person skilled in the art.The glass fibers present in the ASR, as a result of the processing, may be shorter in the composition than the glass fibers originally used and described above. Thus, the arithmetic average of the glass fiber length after processing, to be determined by high-resolution X-ray computed tomography, is frequently only in the range from 150 pm to 300 pm.Generally, any type of glass fibers may be present (e.g. E, A, C, D, ECR, AR, R, S-2). Particular preference being given to glass fibers in the form of E glass.Generally, the automotive shredder residue is agitated or shaked, preferably agitated, with the at least one acid, generally in a mixer. Suitable mixer are known in the art.The treating, preferably agitating, can be carried out for a time sufficient to dissolve substantially all of the polycaprolactam. Typically, the treating, preferably agitating, is carried out for at least 10 min, 30 min, 1 , 2, 3, 4, 5, 6, 7, 8, 9, or 10 hours and it may take up to 72, 48, or 24 hours.The treating, preferably agitating, time will depend on the size of the automotive shredder residue and the polycaprolactam present.The treating, preferably agitating, can be carried out at ordinary temperature (e.g. at 15-30 °C) and ordinary (atmospheric) pressure (e.g. at 1 bar (1.01325 bar)) or at elevated temperature (e.g. >30 °C, such as 50 - 200 °C) and ordinary pressure. If the required temperature is above a solvent's boiling point, the treating, preferably agitating, may be carried out at elevated pressure (e.g. > 1 bar, such as > 1 bar to 3 bar).The treating in step a) is therefore carried out at a temperature from 15 to 200°C, preferably 15 to 50°C, more preferably 15 to 30°C. The pressure is preferably 1 bar to 3 bar, more preferably atmospheric pressure.Preferably, the treating, preferably agitating, is carried out at ordinary temperature (e.g. 15 to 30°C) and ordinary pressure (e.g. 1 bar).Suitable acids are organic acids, inorganic acids or mixtures thereof. Lewis acids, Bronsted acids or mixtures thereof may be used, preferably Bronsted acids.The acids or mixtures of acids are generally strong acids or acid mixtures having a pKs value of -10 to 4, medium acids or acid mixtures having a pKs value of >4 to 8 or weak acids or acid mixtures having a pKs value of >8 to <14, preferably strong acids or acid mixtures.Further, the acids or acid mixtures are concentrated or diluted, whereby the concentration of the concentrated acids or acid mixtures depends on the acid as known by a person skilled in the art. Preferably, the acids or acid mixtures are concentrated acids.Suitable acids include formic acid, sulfuric acid, hydrochloric acid, acetic acid, phosphoric acid or mixtures thereof as well as other acids which do not degrade polycaprolactam while dissolving polycaprolactam, preferably, the acid is selected from formic acid, sulfuric acid, hydrochloric acid, acetic acid, phosphoric acid and mixtures thereof.Preferably, the acids or acid mixtures are employed in concentrated form, i.e. in the following concentrations: at least 70wt% formic acid in water, preferably 70wt% to 85wt% formic acid in water, at least 70wt% sulfuric acid in water, preferably 70wt% to 98wt% sulfuric acid in water, at least 30wt% hydrochloric acid in water, preferably 30wt% to 36wt% hydrochloric acid in water, at least 70wt% acetic acid in water, preferably 70wt% to 100wt% acetic acid in water (or in the case of 100 wt% water free acetic acid), at least 70wt% phosphoric acid in water, preferably 70wt% to 90wt% phosphoric acid in water.Preferably, the acid is selected from formic acid, sulfuric acid, hydrochloric acid, acetic acid, phosphoric acid and mixtures thereof, more preferably in their concentrated forms.Most preferably, concentrated phosphoric acid is employed, i.e. at least 70wt% phosphoric acid in water, preferably 70wt% to 90wt% phosphoric acid in water.Medium or weak acids can also be used, preferably together with ionic strength enhancers. For example, ethanol and CaCI2dissolves polycaprolactam. Other suitable ionic strength enhancers include LiCI, Na3PO4, Na2HPO4, NaH2PO4, Li3PO4, Li2HPO4, LiH2PO4, lithium acetate, and lithium formate.The amount of acid used should be sufficient to dissolve the polycaprolactam. This will depend on the amount of waste and the fraction of waste comprising polycaprolactam.Step a) can be operated in a batch mode, in a semi-continuous mode or in a continuous mode, all of which are known to the skilled person. Preferably, step a) is operated in a batch mode.Suitable devices for carrying out step a) (dissolution vessels) are known by a person skilled in the art.Step b)Following step a), the composition containing dissolved polycaprolactam and glass fibers is separated from the glass fibers, which are generally insoluble in the acid or acid mixture employed in step a), whereby a solution containing the dissolved polycaprolactam is obtained.The separation may take place according to any known procedure for separating solids from liquids. The solid-liquid separation is generally based on two principal modes of separation: i) filtration (e.g. gravity, vacuum, pressure and centrifugal), in which the solid-liquid mixture is directed towards a filter medium (e.g. screen, woven cloth, membrane). The liquid phase flows through the filter medium while solids are retained, either on the surface or within the medium and ii) sedimentation or settling in a forces field (gravitational and centrifugal) whereby advantage is taken of differences in phase densities between the solid and the liquid, the solid-free liquid is then decanted. The solids are allowed to sink in the fluid under controlled conditions. In the reverse process of flotation, the particles rise through the liquid, by virtue of a natural or induced low solids densities.Preferably, the separation in step b) is carried out by filtration, more preferably filtration by gravity or pressure.Suitable filtration devices are known by a person skilled in the art, and the type of filtration device will depend on the size of the undissolved waste particles. It may consist, for example, of a perforated bottom or a wire screen. In any event, it should be sufficient to prevent a significant portion of the solids from passing through. A significant portion is any portion that will interfere with recovering substantially pure caprolactam.After filtration, the solids may be routed for further recovery of the materials contained therein.In case that the separation is carried out by filtration, the filtration device may be located at or near the bottom of the dissolution vessel used in step a).Step b) is operated in a batch mode, in a semi-continuous mode or in a continuous mode, all of which are known to the skilled person. Preferably, step b) is operated in a batch mode.It is also possible to repeat the separating step b) one or more times in case that one separation step is not sufficient. In this case, the identical or a different separation technique as in the first separation step can be carried out. Preferably, separating step b) is carried out one time.Step c)Step c) comprises depolymerizing the polycaprolactam dissolved in the solution to produce caprolactam.Processes for depolymerization of polycaprolactam are known.Generally, the depolymerization of polycaprolactam into caprolactam monomers comprises a hydrolytic degradation step, usually at elevated temperature, generally in the presence of water and a recovery step of the formed monomer by steam distillation. The hydrolytic degradation step can be performed in both the presence and the absence of a catalyst. As catalyst acidic compounds, such as, e.g., phosphoric acid and boric acid, can be used.In step c) of the inventive process the dissolved polycaprolactam is depolymerized by heating with steam, preferably superheated steam, generally with a nominal temperature of 250°C to 600°C, in the presence of an acid as catalyst to produce caprolactam.It has been found by the inventors that the acid useful as catalyst in the depolymerization of polycaprolactam in step c) of the inventive process can at the same time be used as solvent in the dissolution step a) of the inventive process. The inventive process is therefore extremely convenient and efficient.Suitable and preferred acids and acid mixtures used in the depolymerization step c) are therefore the acids and acid mixtures mentioned in step a).It is generally possible to add an acid or acid mixture in step c) in addition to the acid already present (i.e. derived from step a)), however, this is not necessary. In case that an additional acid or acid mixture is added in step c), said acid may be the same as or different from the acid used in step a), preferably the acid is the same.Preferably, no acid or acid mixture in addition to the acid already present (i.e. derived from step a)) is added in process step c).Most preferably, concentrated phosphoric acid is employed, i.e. at least 70wt% phosphoric acid in water, preferably 70wt% to 90wt% phosphoric acid in water.The depolymerization in step c) is generally carried out at a temperature of 180 °C to 400 °C, preferably 200 °C to 350 °C, more preferably 200°C to 300°C.The pressure in the depolymerization in step c) is generally from 0.1 bar to 10 bar, preferably from 0.5 bar bar to 5 bar, more preferably from 1 bar to 3 bar, most preferably at autogeneous pressure.The depolymerization in step c) is generally carried out for 0.1 hour to 24 hours, preferably 0.5 hour to 8 hours, more preferably 2 hours to 6 hours.Suitable devices (depolymerization reactors) for carrying out the depolymerization step c) are known by a person skilled in the art.Feeding steam to the depolymerization reactor according to step c) of the present invention allows, optionally without further heating, to obtain a vapor stream comprising caprolactam and water. The weight to weight ratio of caprolactam to water in said vapor stream can be adjusted by modifying the amount of steam used in step c).During the depolymerization in step c) typically at least 60 wt% of the polycaprolactam, preferably 60-90 wt%, are depolymerized into caprolactam.The vapor stream comprising caprolactam can be processed for obtaining pure caprolactam using methods known to the skilled person. Oils and by-products can be removed for example by distillation or filtration as known by a person skilled in the art. The caprolactam can be concentrated, or rectified with lime and distilled.Following the depolymerization, in general substantially pure caprolactam is obtained. The recovered caprolactam can be used in all applications, wherein virgin caprolactam is used. The recovered caprolactam may be useful for preparing polycaprolactam and other uses requiring the use of substantially pure caprolactam.Step c) is operated in a batch mode, in a semi-continuous mode or in a continuous mode, all of which are known to the skilled person. Preferably, step c) is operated in a batch mode.In one embodiment, the process of the present invention is performed in the batch mode. In the batch mode, the solution containing the dissolved polycaprolactam obtained in step b) (feedstock for step c)) is charged to the depolymerization reactor. Subsequently, superheated steam is charged to the depolymerization reactor and caprolactam is discharged from the depolymerization reactor as vapor stream comprising caprolactam and water. Next, charging of the superheated steam to the depolymerization reactor is interrupted. After optionally removing residual material from the depolymerization reactor, a new cycle is started by charging new feedstock to the depolymerization reactor. In a preferred embodiment, optional residual material is not removed in between every cycle.In a further embodiment, the polycaprolactam depolymerization is performed in the continuous mode. In the continuous mode, the solution containing the dissolved polycaprolactam obtained in step b) (feedstock for step c)) is continuously charged to the depolymerization reactor. At the same time, superheated steam is continuously charged to the depolymerization reactor and caprolactam is continuously discharged from the depolymerization reactor as vapor stream comprising caprolactam and water. In addition, any optional residual material is continuously discharged from the depolymerization reactor.In another embodiment, the polycaprolactam depolymerization is performed in the semi-continu- ous mode. In the semi-continuous mode, is intermittently charged to the depolymerization reactor, while superheated steam is continuously charged to the depolymerization reactor and caprolactam is continuously discharged from the depolymerization reactor as a vapor stream comprising caprolactam and water. Optional residual material is intermittently discharged from the depolymerization reactor in the semi-continuous mode of polycaprolactam depolymerization.In another form the method comprises the step:converting the plastic fragment mix obtainable by or obtained by the method according to the invention to obtain a product PRF1.More specifically, the method comprises the additional step of: converting the caprolactam obtainable by or obtained by the method according to the invention to obtain a product PRF1 .The product PRF1 may be selected from: i) building block or monomer; or ii) polymer, preferably polymer A, polymer composition, preferably polymer composition A, or polymer product, preferably polymer product A; or iii) industrial use polymer, industrial use surfactant, descaling compound, industrial use biocide, industrial use solvent, industrial use dispersant, composition thereof or formulation thereof; or iv) agrochemical composition, agrochemical formulation auxiliary or agrochemically active ingredient; or v) active pharmaceutical ingredient or intermediate thereof, pharmaceutical excipient, animal feed additive, human food additive, dietary supplements, aroma chemical or aroma composition; or vi) aqueous polymer dispersion, preferably polyurethane or polyurethane - poly(meth)acry- late hybrid polymer dispersion, emulsion, binder for paper and fiber coatings, UV-curable acrylic polymer for hot melts and coatings polyisocyanates, hyperbranched polyester polyol, polymeric dispersant for inorganic binder compositions, unsaturated polyester polyol or 100% curable composition; or vii) cosmetic surfactant, emollient, wax, cosmetic polymer, UV filter, further cosmetic ingredient or composition or formulation thereof; or viii) polymer B, polymer composition B, coating composition, other functional composition, foil, molded body, coating or coated substrate.The content of the caprolactam obtained by the method according to the invention in the product PRF1 can be 1 weight-% or more, preferably 2 weight-% or more, more preferably 5 weight- % or more, more preferably 15 weight-% or more, more preferably 30 weight-% or more, more preferably 40 weight-% or more, more preferably 60 weight-% or more, more preferably 80 weight-% or more, more preferably 90 weight-% or more, more preferably 95 weight-% or more, based on the total content of caprolactam in the product PRF1 .In further embodiments, the content of the target plastic fragments in the product PRF1 can be 100 weight-% or less, preferably 95 weight-% or less, more preferably 90 weight-% or less, more preferably 50 weight-% or less, more preferably 25 weight-% or less, more preferably 10 weight-% or less, based on the total content of caprolactam in the product PRF1 .Preferably this content is determined based on identity preservation and / or segregation and / or mass balance and / or book and claim chain of custody models, preferably based on mass balance, preferably the International Sustainability and Carbon Certification (ISCC) standard.The publication Prior Art Disclosure; Issue 684; paragraphs

[1000] to

[8005] ; ISSN: 2198-4786; published: February 12, 2024 will be regarded as Reference RF1 , which is incorporated herein by reference in its entirety. Preferably, the product PRF1 is a product as described in Reference RF1 ; paragraphs

[1000] to

[8005] , Preferably, the method described herein is further a method for the production of a product, preferably product PRF1.The converting step to obtain the product PRF1 preferably comprises one or more step(s) as described below and can be performed by conventional methods well known to a person skilled in the art. The converting step preferably comprises one or more step(s) selected from: recycling, preferably depolymerizing, gasifying, pyrolyzing, and / or steam cracking; and / or purifying, preferably crystallizing, (solvent) extracting, distilling, evaporating, hydrotreating, absorbing, adsorbing and / or subjecting to ion exchanger; and / or assembling, preferably foaming, synthesizing, chemical conversion, chemically transforming, polymerizing and / or compounding; and / or forming, preferably foaming, extruding and / or molding; and / or finishing, preferably coating and / or smoothing.In addition, the one or more step(s) are described in detail in Reference RF1 ; paragraphs

[1000] to

[8005] ,The term “building block”, as used herein, comprises compounds, which are in a gaseous or liquid state under standard conditions of 0°C and 0.1 MPa. Building blocks are typically used in chemical industry to form secondary products, which provide a higher structural complexity and / or higher molecular weight than the building block on which the secondary product is based. The building block is preferably selected from the group consisting of hydrogen, carbon monoxide, carbon dioxide, ethylene oxide, ethylene glycols, syngas comprising a mixture of hydrogen and carbon monoxide, alkanes, alkenes, alkynes and aromatic compounds. The alkanes, alkenes, alkynes and aromatic compounds comprise in particular 1 to 12 carbon atoms, respectively.The term “monomer”, as used herein, comprises molecules, which can react with each other to form polymer chains by polymerization. The monomer is preferably selected from the group consisting of (meth)acrylic acid, salts of (meth)acrylic acid; in particular sodium, potassium and zinc salts; (meth)acrolein and (meth)acrylates. (Meth)acrylates comprising 1 to 22 carbon atoms are preferred, in particular comprising 1 to 8 carbon atoms. The terms (meth)acrylic acid, (meth)acrolein or (meth)acrylate relate to acrylic acid, acrolein or acrylate and also to methacrylic acid, methacrolein or methacrylate, where applicable. Further, the monomer can be selected from hexamethylenediamine (HMD) and adipic acid.The building block can further be an intermediate compound. The term “intermediate compound”, as used herein, comprises organic reagents, which are applied for formation of compounds with higher molecular complexity. The intermediate compound can be selected for example from the group consisting of phosgene, polyisocyanates and propylene oxide. The polyisocyanates are in particular aromatic di- and polyisocyanates, preferably toluene diisocyanate (TDI) and / or diphenylmethane diisocyanate (MDI).The building block and the monomer and typical converting step(s) to obtain the building block or monomer are described in more detail in paragraphs

[1000] to

[1012] of Reference RF1 .The term “polymer A”, as used herein, comprises thermoplastic, e.g., polyamide or thermoplastic polyurethane, thermoset, e.g., polyurethane, elastomer, e.g., polybutadiene, or a copolymer or a mixture thereof and is defined in more detail in paragraphs

[2001] to

[2007] of Reference RF1 .The term “polymer composition A”, as used herein, comprises all compositions comprising a polymer as described above and one or more additive(s), e.g. reinforcement, colorant, modifier and / or flame retardant, and is defined in more detail in paragraph

[2008] of Reference RF1. The term “polymer product A”, as used herein, comprises any product comprising the polymer A and / or polymer composition A as described above and is defined in more detail in paragraphs

[2009] and

[2010] of Reference RF1.The step(s) to obtain the polymer, preferably polymer A, polymer composition, preferably polymer composition A or polymer product, preferably polymer product A is / are described in more detail in paragraph

[2011] of Reference RF1 .The term “industrial use polymer”, as used herein, comprises rheology, polycarboxylate, alkox- ylated polyalkylenamine, alkoxylated polyalkylenimine, polyether-based, dye inhibition and soil release cleaning polymers defined in more detail in paragraphs

[3035] to

[3044] of Reference RF1. The term “industrial use surfactant”, as used herein, comprises non-ionic, anionic and amphoteric industrial use surfactants defined in more detail in paragraphs

[3008] to

[3034] of Reference RF1. The term “industrial use descaling compound”, as used herein, comprises nonphosphate based builders (NPB) and phosphonates (CoP) described in more detail in paragraphs

[3001] to

[3005] of Reference RF1 . The term “industrial use biocide”, as used herein, refers to a chemical compound that kills microorganisms or inhibits their growth or reproduction defined in more detail in paragraphs

[3006] to

[3007] of Reference RF1. The term “industrial use solvent”, as used herein, comprises alkyl amides, alkyl lactamides, alkyl esters, lactate esters, alkyl diester, cyclic alkyl diester, cyclic carbonates, aromatic aldehydes and aromatic esters defined in more detail in paragraphs

[3045] to

[3055] of Reference RF1. The term “industrial use dispersant”, as used herein, comprises anionic and non-ionic industrial use dispersants defined in more detail in paragraphs

[3056] to

[3058] of Reference RF1 . The term “composition and / or formulation thereof’ with reference to the industrial use polymers, industrial use surfactants, descaling compounds and / or industrial use biocides refers to industrial use compositions and / or institutional use products and / or fabric and home care products and / or personal care products defined in more detail in paragraph

[3059] of Reference RF1 . The converting step(s) to obtainthe industrial use polymer, industrial use surfactant, descaling compound and / or industrial use biocide are defined in more detail in paragraph

[3060] of Reference RF1. The converting steps to obtain the industrial use composition or formulation of the industrial use polymer, industrial use surfactant, descaling compound and / or industrial use biocide are defined in more detail in paragraph

[3061] of Reference RF1 .The term “agrochemical composition”, as used herein, typically relates to a composition comprising an agrochemically active ingredient and at least one agrochemical formulation auxiliary. Examples of agrochemical compositions, active ingredients and auxiliaries are described in more detail in Reference RF1 , paragraph

[4001] ,The agrochemical composition may take the form of any customary formulation. The agrochemical compositions are prepared in a known manner, e.g. described by Mollet and Grubemann, Formulation technology, Wiley VCH, Weinheim, 2001 ; or Knowles, New developments in crop protection product formulation, Agrow Reports DS243, T&F Informa, London, 2005. The converting step(s) to obtain the agrochemically active ingredients and auxiliaries may be conducted in analogy to the production step(s) of their analogues that are based on petrochemicals or other precursors that are not gained by recycling processes. In addition, conversion to compounds mentioned in sections “Polymer” and “Cosmetic surfactant, emollient, wax, cosmetic polymer, UV filter, further cosmetic ingredient or compositions or formulations thereof’ may be performed as described in these sections as well as the respective paragraphs in Reference RF1.The term active pharmaceutical ingredients and / or intermediates thereof, as used herein, comprises substances that provide pharmacological activity or other direct effect in the diagnosis, cure, mitigation, treatment, or prevention of disease, or to affect the structure or any function of the body. Intermediates thereof are isolated products that are generated during a multi-step route of synthesis of an active pharmaceutical ingredient. The term pharmaceutical excipients, as used herein, comprises compounds or compound mixtures used in compositions for various pharmaceutical applications, which are not substantially pharmaceutically active on itself. Active pharmaceutical ingredients and / or intermediates thereof and pharmaceutical excipients are defined in more detail in paragraph

[5001] of Reference RF1.The converting step(s) to obtain the active pharmaceutical ingredients and / or intermediates thereof and pharmaceutical excipients may comprise one or more synthesis steps and can be performed by conventional synthesis and techniques well known to a person skilled in the art.The terms animal feed additives, human food additives, dietary supplements, as used herein, comprises Vitamins, Pro-Vitamins and active metabolites thereof including intermediates and precursors, especially Vitamin A, B, E, D, K and esters thereof, like acetate, propionate, palmitate esters or alcohols thereof like retinol or salts thereof and any combinations thereof; Tetraterpenes, especially isoprenoids like carotenoids and xanthophylls including their intermediates and precursors as well as mixtures and derivates thereof, especially beta carotene, Canthaxan- thin, Citranaxanthin, Astaxanthin, Zeaxanthin, Lutein, Lycopene, Apo-carotenoids, and anycombinations thereof; organic acids, especially formic acid, propionic acid and salts thereof, such as sodium, calcium or ammonium salts, and any combinations thereof, such as but not limited to mixtures of formic acid and sodium formiate, propionic acid and ammonium propionate, formic acid and propionic acid, formic acid and sodium formiate and propionic acid, propionic acid and sodium propionate and formic acid and sodium formiate; glycerides of carboxylic acids and short and medium chain fatty acids, conjugated linoleic acids, such as omega-6 fatty acid (C18:2) methyl ester and 1 ,2-propandiol and beverage stabilizers, such as polyvinylpyrroli- done-polymer or polyvinylimidazole / polyvinylpyrrolidone-copolymer. Animal feed additives, human food additives and dietary supplements are defined in more detail in paragraph

[5002] of Reference RF1.The converting step(s) to obtain the animal feed additives, human food additives, dietary supplements may comprise one or more synthesis steps and can be performed by conventional synthesis and techniques well known to a person skilled in the art.The terms aroma chemical and aroma composition as used herein, comprise a volatile organic substance with a molecular weight between 70-250 g / mol comprising a functional group with a carbon skeleton of C5-C16 carbon atoms comprising linear, branched, cyclic, for example with a ring size of C5-C18, bicyclic or tricyclic aliphatic chains and but not necessarily one or more unsaturated structural elements like double bonds, triple bonds, aromatics or heteroaromatics and preferably the one or more additional functional groups are selected from alcohol, ether, ester, ketone, aldehyde, acetal, carboxylic acid, nitrile, thiol, amine. In one aspect, the aroma chemical is a terpene-based aroma chemical, for example selected from monoterpenes and monoterpenoids, sesquiterpenes and sesquiterpenoids, diterpenes, triterpenes or tetraterpenes. Aroma chemicals can be combined with further aroma chemicals to give an aroma composition. Aroma chemicals and aroma compositions are defined in more detail in paragraph

[5003] of Reference RF1.The converting step(s) to obtain the aroma chemical and aroma composition may comprise one or more synthesis steps and can be performed by conventional synthesis and techniques well known to a person skilled in the art.The term “aqueous polymer dispersion”, as used herein, comprises aqueous composition(s) comprising dispersed polymer(s) and is defined in more detail in the section

[6001] entitled “aqueous polymer dispersion” of Reference RF1. The dispersed polymer(s) may be selected from acrylic emulsion polymer(s), styrene acrylic emulsion polymer(s), styrene butadiene dispersions), aqueous dispersion(s) comprising composite particles, acrylate alkyd hybrid dispersions), polyurethane(s) (including UV-curable polyurethanes) and polyurethane - poly(meth)acrylate hybrid polymer(s). The term “emulsion polymer”, as used herein, comprises polymer(s) made by free-radical emulsion polymerization. Aqueous polyurethane dispersion(s) are defined in more detail in the section

[6002] entitled “Polyurethane dispersions” of Reference RF1 . UV-curable polyurethane(s) is / are defined in more detail in the section

[6017] of Reference RF1. Polyurethane - poly(meth)acrylate hybrid polymer(s) is / are defined in more detail in the section

[6016] of Reference RF1 .The term “polymeric dispersant”, as used herein, comprises preferably polymer(s) comprising polyether side chain, in particular polycarboxylate ether polymer(s) and polycondensation produces) defined in more detail in paragraph

[6020] entitled “Polymeric dispersant” of Reference RF1.The converting (polymerization) step(s) to obtain the aqueous polymer dispersion(s) comprising emulsion polymer(s) is / are defined in more detail in the section

[6003] entitled “Emulsion polymerization” of Reference RF1.The converting (polymerization) step(s) to obtain the aqueous polyurethane dispersion(s) is / are defined in more detail in the section

[6014] entitled “Process for the preparation of aqueous polyurethane dispersions” and section

[6017] entitled “Aqueous UV-curable polyurethane dispersions, their preparation and use and compositions containing them” of Reference RF1 . Composition(s) and uses of aqueous polymer dispersion(s) and of polymeric dispersant(s) are defined in more detail in the following sections of Reference RF1 : section

[6004] entitled “Uses of aqueous polymer dispersions”, section

[6005] entitled “Binders for architectural and construction coatings” section

[6006] entitled “Binders for paper coating” section

[6007] entitled “Binders for fiber bonding” section

[6008] entitled “Adhesive polymers and adhesive compositions” section

[6015] entitled “Aqueous polyurethane dispersions suitable for use in coating compositions” section

[6016] entitled “Aqueous polyurethane - poly(meth)acrylate hybride polymer dispersions suitable for use in coating compositions” section

[6017] entitled “Aqueous UV-curable polyurethane dispersions, their preparation and use and compositions containing them” section

[6018] entitled “Inorganic binder compositions comprising polymeric dispersants and their use”

[6019] 100% curable coating compositionsUV-crosslinkable poly(meth)acrylate(s) and its / their uses are defined in more detail in section

[6009] entitled “UV-crosslinkable poly(meth)acrylates for use in UV-curable solvent-free hotmelt adhesives and their use for making pressure-sensitive self-adhesive articles” of Reference RF1 .Polyisocyanate(s), composition(s) comprising them and their uses are defined in more detail in section

[6010] entitled “Polyisocyanates” of Reference RF1 .Hyperbranched polyester polyol(s) and its / their uses are defined in more detail in section

[6011] entitled “Organic solvent based hyperbranched polyester polyols suitable for use in coating compositions” of Reference RF1 . The converting step(s) to obtain the hyperbranched polyester polyols is / are defined in more detail in the section

[6012] entitled “Preparation of organic solvent based hyperbranched polyester polyols” of Reference RF1. Coating composition(s) comprising hyperbranched polyester polyol(s), polyisocyanate(s) and additive(s) and substrate(s) coatedtherewith are defined in more detail in section

[6013] entitled “Organic solvent based two component coating compositions comprising hyperbranched polyester polyols and polyisocyanates” of Reference RF1.Unsaturated polyester polyol(s), solvent-based coating composition(s) comprising said unsaturated polyester polyol(s) and substrate(s) for coating with said coating composition(s) are defined in more detail in section

[6018] entitled “Organic solvent based coating composition comprising unsaturated polyester polyols” of Reference RF1 .100% curable coating composition(s) is / are defined in more detail in section

[6019] of Reference RF1 .Polymeric dispersant(s) for inorganic binder compositions is / are defined in more detail in section

[6020] of Reference RF1 . The inorganic binder composition(s) comprising the polymeric dispersants and their use are defined in more detail in section

[6021] of Reference RF1 . The converting step(s) to obtain the polymeric dispersant(s) are defined in more detail in section

[6020] of Reference RF1 . The term “inorganic binder composition” comprising the polymeric dispersants), as used herein, comprises preferably in particular hydraulically setting compositions and compositions comprising calcium sulfate and is defined in more detail in section

[6021] of Reference RF1 entitled “Inorganic binder compositions comprising the polymeric dispersant and their use”. Specific building material formulation(s) comprising polymeric dispersant(s) or building product(s) produced by a building material formulation comprising a polymeric dispersant are disclosed in more detail in section

[6021] of Reference RF1 .The term “cosmetic surfactant”, as used herein, comprises non-ionic, anionic, cationic and amphoteric surfactants and is defined in more detail in paragraph

[7002] of Reference RF1 . The term “emollient”, as used herein, refers to a chemical compound used for protecting, moisturizing, and / or lubricating the skin and is defined in more detail in paragraph

[7003] of Reference RF1 . The term “wax”, as used herein, comprises pearlizers and opacifiers and is defined in more detail in paragraph

[7004] of Reference RF1. The term “cosmetic polymer”, as used herein, comprises any polymer that can be used as an ingredient in a cosmetic formulation and is defined in more detail in paragraph

[7005] of Reference RF1 . The term “UV filter”, as used herein, refers to a chemical compound that blocks or absorbs ultraviolet light and is defined in more detail in paragraph

[7006] of Reference RF1 . The term “further cosmetic ingredient”, as used herein, comprises any ingredient suitable for making a cosmetic formulation. Several sources disclose cosmetically acceptable ingredients. E. g. the database Cosing on the internet pages of the European Commission discloses cosmetic ingredients and the International Cosmetic Ingredient Dictionary and Handbook, edited by the Personal Care Products Council (PCPC), discloses cosmetic ingredients. The term “composition and / or formulation thereof’ with reference to the cosmetic surfactant, emollient, wax, cosmetic polymer, UV filter and / or further cosmetic ingredient refers to personal care and / or cosmetic compositions or formulations defined in more detail in paragraph

[7007] of Reference RF1. The converting step(s) to obtain the cosmetic surfactant, emollient, wax, cosmetic polymer, UV filter or further cosmetic ingredient is / are defined in more detail in paragraph

[7008] of Reference RF1.The terms “polymer B”, “polymer composition B”, “coating composition”, “other functional composition”, “foil”, “molded body”, “coating” and “coated substrate” are well known to the person skilled in the art and are defined in more detail from paragraph

[8000] to

[8005] of Reference RF1.The present invention further relates to composition comprising i) a solution of polycaprolactam in at least one acid, ii) glass fibers, and iii) further insoluble particles of an automotive shredder residue; preferably obtainable by step a) of the inventive method.Suitable acids or acid mixtures and polycaprolactam are mentioned before. Also further insoluble particles of an automotive shredder residue are mentioned before and are for example in addition to the glass fibers mentioned under ii), rubber, glass, wood, paper, wire, polyurethane foam, and cardboard. The glass is glass other than the glass fibers mentioned under ii).The inventive composition preferably comprises i) a solution of 0.05 to 2.5 wt%, preferably 0.1 to 2 wt% of polycaprolactam, based on the total weight of the composition, in at least one acid, ii) 0.03 to 1 .5 wt%, preferably 0.05 to 1 wt% of glass fibers, based on the total weight of the composition, and iii) 10 to 25 wt%, preferably 12 to 20 wt% of further insoluble particles of an automotive shredder residue, based on the total weight of the composition, wherein the amount of acid adds up to 100 wt%.Suitable acids and acid mixtures are mentioned above. The acids generally comprise a certain amount of water as defined above.The present invention further relates to caprolactam obtainable by the method according to the present invention.Further, the present invention relates to the use of an automotive shredder residue comprising polycaprolactam and glass fibers for recycling caprolactam, preferably by carrying out the method according to the present invention.Suitable automotive shredder residue (ASR), polycaprolactam and glass fibers are mentioned before.The invention is further illustrated by the following examples.ExamplesExample 1 - Preparation of ASR SamplesTo prepare the model ASR-1 to ASR-3 the single components are collected from a local ELV collector company (an authorized treatment facility which depollutes ELV) from various about 15 year old passenger cars. For example, glass is the glass from front windshields and rear windows, dirt is collected as attached to the car exterior, PUR foam is collected from the seat foam, and plastic is collected from selected plastic parts of the cars, such as wheel covers, dashboard, wiper arm, door handle, gears, and bushes, where the type of polymer is known.The ASR-1 to ASR-3 samples are prepared in 5 kg batches by weighing in the components and by shredding the components listed in Table 1 first by hand with a hammer and metal scissors, followed by shredding with a four-shaft shredder (like Model “JFS 8080” from Jogindra, India with main blade rotation diameter 245 mm, assistant rotation diameter 270 mm, 42 main blades, 20 assistant blades, 25 rpm main axle rotation speed, 120-200 kg / hr capacity). The maximum fragment size is 10 cm.The amount of polycaprolactam which contains 30 wt% glass fibers in the ASR-1 to ASR-3 is adjusted to 10 wt% based on the weight of the “Plastics” component listed in Table 1.Table 1 : Composition of model ASR (amounts in wt%)Example 2 - Preparation of SLF and SHF SamplesTo prepare the model shredder light fractions SLF-1 to SLF-3 and the shredder heavy fractions SHF-1 to SHF-3 the single components are collected from a local ELV collector company as described in Example 1 .The samples are prepared in 5 kg batches by weighing in the components and by shredding the components listed in Tables 2 and 3 first by hand with a hammer and metal scissors, followed by shredding with a four-shaft shredder. The maximum fragment size is 10 cm.Table 2: Composition of SLF (amounts in wt%)Table 3: Composition of SHF (amounts in wt%)Example 3 - Depolymerizing ASR-1 to ASR-3The ASR-1 to ASR-3 samples from Example 1 are used for depolymerization.The samples comprise 10 wt% polycaprolactam based on the weight of the “Plastics” component listed in Table 1 . For example, a 100 g sample of ASR-3 contains 35 wt% plastics, which is 35 g, of which are 10 wt% polycaprolactam including 30 wt% glass fibers, which is 2,45 g pure polycaprolactam (without glass fibers).An Erlenmeyer flask is charged with 100 g of ASR-1 , ASR-2 or ASR-3 along with 500 mL of 86% by weight phosphoric acid. The mixture is stirred for 5 hours and the solid residue is filtered from the acid solution and discarded. The filtrate contains a solution of polycaprolactam. The polycaprolactam dissolved in phosphoric acid is fed to a depolymerization reactor at a nominal rate equal to 5% by weight H3PO4 based on the amount of nylon present. The polymer is depolymerized and the liberated caprolactam is distilled out by feeding superheated steam with a nominal temperature of 900°F (480°C) to the reactor. Oils are separated from the aqueous distillate. The distillate is then concentrated to approximately 80% by weight caprolactam. Theconcentrated lactam solution is then further concentrated to nominally 99% by weight caprolactam by distilling the solution through two thin-film evaporators in series. The 99% by weight lactam is rectified with 5% by weight lime before being distilled a final time in a thin-film evaporator. The resulting caprolactam 99.7% by weight pure.About 1 ,9 g caprolactam are obtained after distillation, which corresponds to about 78 % of the expected yield of 2,45 g.Example 4 - Depolymerizing SLF-1 to SLF-3The SLF-1 to SLF-3 samples from Example 2 (Table 2) are used for depolymerization.The samples comprise 5 wt% polycaprolactam based on the weight of the “Plastics” component listed in Table 2.For example, a 100 g sample of SLF-3 contains 29 wt% plastics, which is 29 g, of which are 5 wt% polycaprolactam including 30 wt% glass fibers, which is 1 ,02 g pure polycaprolactam (without glass fibers).An Erlenmeyer flask is charged with 100 g of SLF-1 , SLF-2 or SLF-3 along with 500 mL of 86% by weight phosphoric acid. The mixture is stirred for 5 hours and the solid residue is filtered from the acid solution and discarded. The filtrate contains a solution of polycaprolactam.The polycaprolactam dissolved in phosphoric acid is fed to a depolymerization reactor at a nominal rate equal to 5% by weight H3PO4 based on the amount of nylon present. The polymer is depolymerized and the liberated caprolactam is distilled out by feeding superheated steam with a nominal temperature of 900°F (480°C) to the reactor. Oils are separated from the aqueous distillate. The distillate is then concentrated to approximately 80% by weight caprolactam. The concentrated lactam solution is then further concentrated to nominally 99% by weight caprolactam by distilling the solution through two thin-film evaporators in series. The 99% by weight lactam is rectified with 5% by weight lime before being distilled a final time in a thin-film evaporator. The resulting caprolactam 99.7% by weight pure.About 0,8 g caprolactam are obtained after distillation, which corresponds to about 78 % of the expected yield of 1 ,02 g.Example 5 - Depolymerizing SHF-1 to SHF-3The SHF-1 to SHF-3 samples from Example 2 (Table 3) are used for depolymerization.The samples comprise 20 wt% polycaprolactam based on the weight of the “Plastics” component listed in Table 3.For example, a 100 g sample of SHF-3 contains 32 wt% plastics, which is 32 g, of which are 20 wt% polycaprolactam including 30 wt% glass fibers, which is 4,2 g pure polycaprolactam (without glass fibers).An Erlenmeyer flask is charged with 5 g of SLF-1 , SLF-2 or SLF-3 along with 400 mL of 86% by weight phosphoric acid. The mixture is stirred for 5 hours and the solid residue is filtered from the acid solution and discarded. The filtrate contains a solution of polycaprolactam.The polycaprolactam dissolved in phosphoric acid is fed to a depolymerization reactor at a nominal rate equal to 5% by weight H3PO4 based on the amount of nylon present. The polymer is depolymerized and the liberated caprolactam is distilled out by feeding superheated steam with a nominal temperature of 900°F (480°C) to the reactor. Oils are separated from the aqueous distillate. The distillate is then concentrated to approximately 80% by weight caprolactam. The concentrated lactam solution is then further concentrated to nominally 99% by weight caprolactam by distilling the solution through two thin-film evaporators in series. The 99% by weight lactam is rectified with 5% by weight lime before being distilled a final time in a thin-film evaporator. The resulting caprolactam 99.7% by weight pure.About 3,4 g caprolactam are obtained after distillation which corresponds to about 81 % of the expected yield of 4,2 g.

Claims

Claims1 . A method for recycling caprolactam from an automotive shredder residue comprising polycaprolactam and glass fibers comprising: a) dissolving the polycaprolactam by treating the automotive shredder residue with at least one acid, whereby a composition containing dissolved polycaprolactam and glass fibers is obtained; b) separating the composition containing dissolved polycaprolactam and glass fibers from the glass fibers, whereby a solution containing the dissolved polycaprolactam is obtained; and c) depolymerizing the polycaprolactam dissolved in the solution to produce caprolactam.

2. The method of claim 1 , where the polycaprolactam in the automotive shredder residue is reinforced polycaprolactam comprising at least partly the glass fibers.

3. The method of claim 2, where the reinforced polycaprolactam comprises 5 to 50 wt%, preferably 10 to 40 wt%, more preferably 15 to 35 wt% of glass fibers, based on the total amount of polycaprolactam and glass fibers.

4. The method of any one of claims 1 to 3, where the automotive shredder residue comprises at least 1 wt%, preferably 1.5 to 20 wt% polycaprolactam, calculated on polycaprolactam without glass fibers.

5. The method of any one of claims 1 to 4, where the automotive shredder residue comprises at least 1 wt%, preferably 1.5 to 15 wt% glass fibers.

6. The method of any one of claims 1 to 5, where the automotive shredder residue comprises at most 97 wt%, preferably 96 to 65 wt% total sum of rubber, glass, wood, paper, wire, polyurethane foam, and cardboard.

7. The method of any one of claims 1 to 6, where the automotive shredder residue is obtainable by shredding vehicles.

8. The method of any one of claims 1 to 7, where the at least one acid has a pKs value of -10 to 4, preferably selected from formic acid, sulfuric acid, hydrochloric acid, acetic acid, phosphoric acid and mixtures thereof.

9. Method, preferably according to any one of claims 1 to 8, comprising the step: converting the caprolactam obtainable by or obtained by the method according to any one of claims 1 to 8 to obtain a product PRF1 .

10. A composition comprising i) a solution of polycaprolactam in at least one acid, ii) glass fibers, and iii) further insoluble particles of an automotive shredder residue; preferably obtainable by step a) of the method according to any one of claims 1 to 8.11 . Caprolactam obtainable by the method according to any one of claims 1 to 8.

12. Use of an automotive shredder residue comprising polycaprolactam and glass fibers for recycling caprolactam, preferably by carrying out the method according to any one of claims 1 to 8.

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