Method for recycling aromatic polycarbonate

Abstract

The invention relates to a method for recycling aromatic polycarbonate comprising the steps of (IIa) providing a recycle stream of recycled polycarbonate having in its backbone repeating units based on at least one type of bisphenol, (IIb) feeding the recycle stream to an upstream cracking unit wherein said recycle stream is optionally combined with a further stream comprising at least one of bisphenol, diarylcarbonate and polycarbonate oligomers and optionally with a cracking agent to form an upstream cracking mixture, (IIc) cracking the upstream cracking mixture in said upstream cracking unit, thereby forming a stream comprising a hydroxyaryl compound and an upstream cracking residue, (IId) separating the hydroxyaryl compound from the upstream cracking residue in at least one distillation column, (II-1) feeding the separated hydroxyaryl compound recovered in step (IId) to a diarylcarbonate manufacturing unit and / or a bisphenol manufacturing unit and manufacturing diaryl carbonate and / or bisphenol, (II-2) manufacturing polycarbonate using, at least in part, said diarylcarbonate and / or said bisphenol obtained in step (II-1).

Description

24POLY0060 1METHOD FOR RECYCLING AROMATIC POLYCARBONATEThe present invention relates to a method for recycling aromatic polycarbonate.Polycarbonate is useful in the manufacture of articles and components for a wide range of applications, from automotive parts to electronic appliances. However, polycarbonate is not readily biodegradable and can present a significant bulk waste disposal problem. Accordingly, efforts have been made to recover valuable resources from polycarbonate wastes.WO2020257234A1 discloses a process for isolation of bisphenol A from depolymerization of a poly(carbonate). The process comprises depolymerizing a poly(carbonate) in the presence of a base, a C1-6 alcohol, and an organic cosolvent such as toluene to provide a depolymerized reaction mixture comprising bisphenol A and a di(C 1 -6 alkyl) carbonate, separating the di(C1 -6 alkyl) carbonate from the depolymerized reaction mixture, hydrolyzing the di(C1 -6 alkyl) carbonate to a corresponding C1-6 alcohol; and crystallizing bisphenol A from the residual depolymerized reaction mixture to provide a purified bisphenol A. The poly(carbonate) may be a virgin poly(carbonate), a post-consumer recycled poly(carbonate), postindustrial recycled poly(carbonate), or a combination thereof.WO2017093974A1 discloses a method of purifying an aromatic alcohol. The method comprises melt polymerizing a dihydroxy compound and a carbonate compound in the presence of a transesterification catalyst to form the aromatic alcohol and a polycarbonate in a melt polymerization facility; removing the aromatic alcohol in an overhead stream; separating the overhead stream in an aromatic alcohol purification unit into a purified aromatic alcohol stream comprising the aromatic alcohol and a purification unit bottom stream; separating the purification unit bottom stream in a diary carbonate purification unit into a diaryl carbonate stream and a diaryl carbonate purification unit bottom stream; and cracking a compound in the diaryl carbonate purification unit bottom stream in a cracker unit in the presence of a cracking agent to form a resultant stream comprising additional aromatic alcohol.There is a need in the art to provide a new method for using recycled aromatic polycarbonate to recover raw materials for making polycarbonate.24POLY0060 2It is an objective of the present invention to provide a new method for using recycled aromatic polycarbonate to recover raw materials for making polycarbonate.Accordingly, the invention provides a method for recycling aromatic polycarbonate comprising the steps of:(Ila) providing a recycle stream of recycled polycarbonate having in its backbone repeating units based on at least one type of bisphenol,(lib) feeding the recycle stream to an upstream cracking unit wherein said recycle stream is optionally combined with a further stream comprising at least one of bisphenol, diarylcarbonate and polycarbonate oligomers and optionally with a cracking agent to form an upstream cracking mixture,(He) cracking the upstream cracking mixture in said upstream cracking unit, thereby forming a stream comprising a hydroxyaryl compound and an upstream cracking residue,(lid) separating the hydroxyaryl compound from the upstream cracking residue in at least one distillation column,(11-1) feeding the separated hydroxyaryl compound recovered in step (lid) to a diarylcarbonate manufacturing unit and / or a bisphenol manufacturing unit and manufacturing diaryl carbonate and / or bisphenol,(I I-2) manufacturing polycarbonate using, at least in part, said diarylcarbonate and / or said bisphenol obtained in step (11-1).Preferably, the method according to the invention is a method for recycling aromatic polycarbonate comprising the steps of:(Ila) providing a recycle stream of recycled polycarbonate having in its backbone repeating units based on at least one type of bisphenol,(lib) feeding the recycle stream to an upstream cracking unit wherein said recycle stream is optionally combined with a further stream comprising at least one of bisphenol, diarylcarbonate and polycarbonate oligomers and said recycle stream is with a cracking agent to form an upstream cracking mixture,(He) cracking the upstream cracking mixture in said upstream cracking unit, thereby forming a stream comprising a hydroxyaryl compound and an upstream cracking residue, wherein the temperature and pressure in the upstream cracking unit are selected such that the cracking agent remains as liquid,(I Id) separating the hydroxyaryl compound from the upstream cracking residue in at least one distillation column,24POLY0060 3(11-1) feeding the separated hydroxyaryl compound recovered in step (lid) to a diarylcarbonate manufacturing unit and / or a bisphenol manufacturing unit and manufacturing diaryl carbonate and / or bisphenol,(I I-2) manufacturing polycarbonate using, at least in part, said diarylcarbonate and / or said bisphenol obtained in step (11-1), wherein the cracking agent in step (lib) comprises one or more selected from water and alkyl alcohol and when the cracking agent in step (lib) is water, the cracking in step (He) is performed in the presence of an acidic or basic catalyst.The method according to the invention advantageously provides hydroxyaryl compound from recycled polycarbonate by cracking, which hydroxyaryl compound in turn is used to obtain diaryl carbonate and / or bisphenol, which diaryl carbonate and / or bisphenol in turn is used to obtain polycarbonate. Accordingly, the method advantageously provides a new method of using recycled polycarbonate to make polycarbonate. This is further explained in relation to steps (lla)-(lld) and (I I- 1 )-(l I-2).In some preferred embodiments, the method involves further cracking to provide further improve the recycling process. This is explained in relation to optional steps (llla)-(llld) and (lll-1)-(lll-2).In some preferred embodiments, the method further provides alkylcarbonate from recycled polycarbonate. This is explained in relation to optional steps (la)-(ld) and (1-1)- (I-2).(la), (Ila), (Illa) Recycle stream of recycled polycarbonateThe recycled polycarbonate has in its backbone repeating units based on at least one type of bisphenol. Polycarbonates and their methods of manufacture are known in the art. Polycarbonates are generally manufactured from bisphenol compounds such as 2,2-bis(4-hydroxyphenyl) propane (“bisphenol-A” or “BPA” or“4,4’- isopropylidenediphenol”), 3,3-bis(4-hydroxyphenyl) phthalimidine, 1,1-bis(4-hydroxy-3- methylphenyl)cyclohexane, or 1,1-bis(4-hydroxyphenyl)- 3,3,5-trimethylcyclohexane (isophorone), or a combination thereof can also be used.For example, the polycarbonate is a homopolymer derived from bisphenol A; a copolymer derived from bisphenol A and another bisphenol or dihydroxy aromatic compound such as resorcinol; or a copolymer derived from bisphenol A and optionally24POLY0060 4 another bisphenol or dihydroxy aromatic compound, and further comprising noncarbonate units, for example aromatic ester units such as resorcinol terephthalate or isophthalate, aromatic-aliphatic ester units based on C6-20 aliphatic diacids, polysiloxane units such as polydimethylsiloxane units, or a combination thereof. Some illustrative examples of other dihydroxy compounds that can be used in combination with bisphenol A are described, for example, in WO 2013 / 175448 Al, US 2014 / 0295363, and WO 2014 / 072923, incorporated herein by reference in their entirety.The recycled polycarbonate may be post-consumer recycled polycarbonate, postindustrial recycled polycarbonate or their combination.The recycled polycarbonate can be obtained from multiple sources, and can therefore comprise a combination of polycarbonates having slight variances in structure, including different comonomers or end groups. For example, polycarbonates can be produced using various end-capping agents (also referred to as a chain stopper agent or chain terminating agent) which can be included during polymerization to provide particular end groups, for example monocyclic phenols such as phenol, p-cyanophenol, and C1-22 alkyl-substituted phenols such as p-cumyl-phenol, resorcinol monobenzoate, and p-and m-tertiary-butyl phenol, monoethers of diphenols, such as p- methoxyphenol, monoesters of diphenols such as resorcinol monobenzoate, and functionalized chlorides of aliphatic monocarboxylic acids such as acryloyl chloride and methacryloyl chloride.The polycarbonate can have an end group derived from at least one of phenol, p- cumylphenol, p-tert-butylphenol, and p-tert-octylphenol. Combinations of different end groups can be used. Thus the recycled polycarbonate used in the present method can be a combination of bisphenol A- containing polycarbonates having different end groups.Preferably, the recycled polycarbonate is or comprises bisphenol A polycarbonate.The amount of polycarbonate in the recycle stream of step (la), (Ila) or (Illa) is preferably at least 70 wt%, more preferably at least 80 wt%, more preferably at least 90 wt%. The nature of the recycle stream, i.e. the type and amounts of components other than polycarbonate (impurities), is selected based on the ease of the downstream separation.24POLY0060 5The recycle stream of recycled polycarbonate is subjected to alcoholysis in step (Ic) or cracking in step (He) or (I He). The recycle stream of recycled polycarbonate can comprise some amounts of impurities which are inert to alcoholysis and cracking and which remain solid in the reactor effluent. Examples of such impurities are mineral fillers and reinforcing agents such as titanium dioxide and glass fibers as well as (degraded) siloxanes. Coatings applied to polycarbonate or polycarbonate-polysiloxane copolymers (such as LEXAN EXL commercially available from SABIC) may be the source of such (degraded) siloxanes. These impurities can be removed e.g. by mechanical separation, e.g. by a filter or screens with appropriate mesh sizes (500-5 pm) provided between the depolymerization unit or cracking unit and the distillation column used in subsequent separation step.Accordingly, in some embodiments, the recycle stream of recycled polycarbonate of step (la), (Ila) and / or (Illa) comprises 1.0 to 30 wt% of mineral fillers, reinforcing agents and (degraded) siloxanes, for example 1.0 to 10 wt%, 10 to 20 wt% or 20 to 30 wt%.The recycle stream of recycled polycarbonate can comprise some amounts of impurities which are inert to alcoholysis and cracking and which are easy to separate from materials to be recovered. Examples of such impurities are additives such as antioxidants, UV absorbers, UV stabilizers and release agents. These impurities remain in the stream of heavies from distillation columns.Accordingly, in some embodiments, the recycle stream of recycled polycarbonate of step (la), (Ila) and / or (Illa) comprises 0.01 to 1.0 wt% of additives.It is preferred that the recycle stream of recycled polycarbonate comprises no or small amount of impurities inert to alcoholysis and cracking which are not easy to separate from materials to be recovered. Examples of such impurities are impact modifiers such as styrene-butadiene-styrene (SBS), styrene-butadiene rubber (SBR), styrene- ethylene-butadiene-styrene (SEBS), acrylonitrile-butadiene-styrene (ABS), acrylonitrile- ethylene-propylene-diene-styrene (AES), styrene-isoprene-styrene (SIS), methyl methacrylate-butadiene (MB) and methyl methacrylate-butadiene-styrene (MBS) and styrene-acrylonitrile (SAN).Accordingly, in preferred embodiments, the recycle stream of recycled polycarbonate of step (la), (Ila) and / or (Illa) comprises 0 wt% or at most 1.0 wt% of impact modifiers24POLY0060 6 selected from styrene-butadiene-styrene (SBS), styrene-butadiene rubber (SBR), styrene-ethylene-butadiene-styrene (SEBS), acrylonitrile-butadiene-styrene (ABS), acrylonitrile-ethylene-propylene-diene-styrene (AES), styrene-isoprene-styrene (SIS), methyl methacrylate-butadiene (MB) and methyl methacrylate-butadiene-styrene (MBS) and styrene-acrylonitrile (SAN).It is preferred that the majority of the recycle stream of recycled polycarbonate to be reacted or cracked is polycarbonate. Accordingly, the recycle stream of recycled polycarbonate of step (la), (Ila) and / or (Illa) comprises no or small amount of polyesters (e.g. PBT and PET) and polyurethanes. This prevents necessitating downstream separation which is very difficult.Accordingly, in preferred embodiments, the recycle stream of step (la), (Ila) and / or (Illa) comprises 0 wt% or at most 0.5 wt% of polyesters and polyurethanes.(lib) feeding the recycle stream to an upstream cracking unit wherein said recycle stream is optionally combined with a further stream comprising at least one of bisphenol, diarylcarbonate and polycarbonate oligomers and optionally with a cracking agent to form an upstream cracking mixturePreferably, the recycle stream of recycled polycarbonate of step (Ila) is fed to the upstream cracking unit as a melt, e.g. from an extruder.The cracking agent can comprise water.The cracking agent can comprise alkyl alcohol. The alkyl alcohol can comprise; C1-34 alkyl alcohol, specifically, C1-6 alkyl alcohol, more specifically, C1-4 alkyl alcohol. For example, the C1-4 alkyl alcohol can comprise methanol, ethanol, n-propanol, isopropanol, n-butanol, sec-butanol, tert-butanol, or a combination comprising one or more of the foregoing. The C1-6 alkanol can comprise n-pentanol, 1 -methylbutanol, 2- methylbutanol, 3-methylbutanol, neopentanol, 1 -ethylpropanol, cyclohexanol, cyclopentanol, n-hexanol, 1,1- dimethylpropanol, 1 ,2-dimethylpropanol, 1- methylpentanol, 2-methylpentanol, 3- methylpentanol, 4-methylpentanol, 1 ,1- dimethylbutanol, 1 ,2-dimethylbutanol, 1 ,3- dimethylbutanol, 2,2-dimethylbutanol, 2,3- dimethylbutanol, 3,3-dimethylbutanol, 1 -ethylbutanol, 2-ethylbutanol, 1 ,1 ,2- trimethylpropanol, 1 ,2,2-trimethylpropanol, 1-ethyl-1-methylpropanol, 1-ethyl-2- methylpropanol, or a combination comprising one or more of the foregoing. The C1- C34-alkanol can comprise n-heptanol, n-octanol, pinacanol, adamantanol, an isomeric24POLY0060 7 methanol, n-nonanol, n-decanol, n-dodecanol, n-tridecanol, n-tetradecanol, n- hexadecanol, or n-octadecanol, or a combination comprising one or more of the foregoing.The cracking can optionally occur in the presence of an added catalyst. The presence of an added catalyst is preferred both when the cracking agent is water and when the cracking agent is alkyl alcohol. However, particularly when the cracking agent is water, the presence of an added catalyst is preferred and often necessary for achieving a desired level of cracking. The catalyst may be acidic or basic. Suitable catalysts include: an aromatic sulfonic acid, sulfuric acid, phosphoric acid, a base (such as sodium hydroxide), a sulfur containing amine compound, a zeolite, sodium hypophosphite, aluminum isopropylate, a sodium salt of one or both of an organic and a mineral acid, or a combination comprising at least one of the foregoing. The catalyst can comprise an aromatic sulfonic acid (such as dodecylbenzene sulfonic acid (DBSA)), sulfuric acid, phosphoric acid, a base (such as sodium hydroxide), or a combination comprising at least one of the foregoing. Optionally, the catalyst can comprise sodium hydroxide. Optionally, the catalyst can comprise an aromatic sulfonic acid; preferably DBSA.The aromatic sulfonic acid can be represented by the general formula RC6H4SO3H, in which R may be in any position in the phenyl ring. Specifically, the aromatic sulfonic acid can have the Formula (IV)wherein R is a C1-25 hydrocarbon group. The 01-25 hydrocarbon group can be an alkyl group such as methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, undecyl, decyl, dodecyl, octadecyl, nonodecyl, eicosyl, heneicysyl, docosyl, tricosyl, tetracosyl, pentacosyl; an aryl group such as phenyl, tolyl, xylyl, napthyl, biphenyl, tetraphenyl; an aralkyl group such as benzyl, phenethyl, phenpropyl, phenbutyl, phenhexyl, napthoctyl; or a cycloalkyl group such as cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl. The aromatic sulfonic acid of the Formula IV can comprise p-toluenesulfonic acid, dodecylbenzene sulfonic acid, or a combination comprising at least one of the foregoing.24POLY0060 8The sulfur containing amine compound can comprise 2-(4-pyridyl)ethanethiol, 2- mercaptoethylamine, 3-mercaptopropylamine, N,N-dimethyl-3-mercaptopropylamine,N,N-di-n-butyl-4-mercaptobutylamine, and 2,2-dimethylthiazolidine can be used. The sulfur containing amine compound can be used in addition to the aromatic sulfonic acid. The sulfur containing amine compound can be present in an amount of 2 to 30 mol%, specifically, 5 to 20 mol% based on the acid group (sulfonic group) in the aromatic sulfonic acid. The sulfonic acid might be present in the form of an polystyrene sulfonated resin.The catalyst can comprise a zeolite, for example, in a fixed bed reactor or in a reactive tray in a distillation column. As is used herein, the zeolite comprises an aluminum oxide (i.e. , AI2O3) and a silicon oxide (SiCh). A silica to alumina mole ratio can be 2 to 20. The zeolite can be functionalized with a sulfonic group. The zeolite can comprise a metal, for example, cobalt, gallium, copper, zinc, iron, magnesium, manganese, cesium, cerium, or a combination comprising at least one of the foregoing. The metal can be present in one or both of the framework of the zeolite or deposited thereon. The zeolite can be ammonium exchanged. The zeolite can have a pore size of 6 to 15 Angstroms.The zeolite can comprise a Y zeolite, such as a 13Y zeolite having the formula Nas6[(AIO2)56(SiO2)l36]250H2O. The Y zeolite can have an SiC^AhOs mole ratio of 3 to 6. The Y zeolite can comprise 10 to 14 wt% of Na2O based on the total weight of the zeolite. The Y zeolite can comprise an ion-exchanged zeolite, for example, with ammonium to result in a Y zeolite comprising less than 1 wt% of Na2O based on the total weight of the Y zeolite.The zeolite can comprise a ZSM-5 zeolite. The ZSM-5 zeolite can have the formulaO.9±0.2M2 / nO:W203:5-100YC>2:zH20, wherein M is at least one cation; n is the valence thereof; W can comprise aluminum, gallium, or a combination comprising at least one of the foregoing; Y can comprise silicon, germanium, or a combination comprising at least one of the foregoing; and z is 0 to 40. The cation can comprise hydrogen, a rare earth metal, aluminum, a Group II metal, a Group VIII metal, manganese, or a combination comprising at least one of the foregoing. The silica to alumina mole ratio can be 10 to 60.In particularly preferred embodiments, the cracking agent comprises one or more selected from water, alkyl alcohol and the cracking is performed in the presence of a catalyst selected from the group consisting of an aromatic sulfonic acid, sulfuric acid,24POLY0060 9 phosphoric acid, a base (such as sodium hydroxide), a sulfur containing amine compound, a zeolite, sodium hypophosphite, aluminum isopropylate, a sodium salt of one or both of an organic and a mineral acid and combinations thereof.In particularly preferred embodiments, the cracking agent comprises water and / or methanol and the cracking is performed in the presence of a catalyst comprising sodium hydroxide and / or dodecylbenzene sulfonic acid (DBSA).Preferably, when the cracking agent is water, the cracking is performed in the presence of a catalyst comprising sodium hydroxide.The upstream cracking unit may further be fed with a stream comprising at least one of bisphenol, diarylcarbonate and polycarbonate oligomers, wherein said stream is combined with the recycle stream of recycled polycarbonate of step (Ila).This optional stream to be fed to the upstream cracking unit may comprise a stream obtained from a polycarbonate manufacturing process. Overheads from oligomerization reactor(s) and / or polymerization reactor(s) comprising a hydroxyaryl compound, diarylcarbonate, bisphenol and polycarbonate oligomers can be fed to a distillation column to separate out the hydroxyaryl compound. The remainder comprising diarylcarbonate, bisphenol and polycarbonate oligomers can be fed to the upstream cracking unit.Thus, in step (lib), the upstream cracking unit may be fed with the further stream which comprises a stream obtained by- melt polymerizing a dihydroxy compound and a diarylcarbonate in the presence of a transesterification catalyst to form a hydroxyaryl compound and a polycarbonate in a melt polymerization facility;- collecting an overhead stream comprising the hydroxyaryl compound from the melt polymerization facility; and- separating a top stream comprising the hydroxyaryl compound from the overhead stream to obtain said stream to be fed to the upstream cracking unit as a bottom stream.This optional stream to be fed to the upstream cracking unit may comprise bisphenol obtained by steps (la)-(ld) described elsewhere in the description.24POLY0060 10 the mixture in said unitresidueThe temperature and pressure in the upstream cracking unit may be selected such that the cracking agent remains as liquid so that it maintains close contact with the material to be cracked.Preferably, the cracking in step (He) is conducted at a temperature within a range of 40 to 200 °C and a pressure within a range of 1 to 20 bar wherein the temperature and pressure in step (He) are selected such that the cracking agent remains as liquid.In some embodiments, the cracking can e.g. be conducted at a temperature of 40 to 70°C, or 45 to 65°C, or 50 to 60°C, and atmospheric pressure. For example, the reaction can be for a time of 1 to 24 hours, preferably 1 to 18 hours, more preferably 1 to 10 hours, even more preferably 1 to 6 hours.The cracking can be conducted at a higher temperature and a higher pressure, for example at a temperature of 130 to 150 °C and a pressure of 18.5-20 bar. Such high pressure ensures that the cracking agent remains as liquid. In such case, the reaction can be for a short time, e.g. 10 to 20min. thecomfrom theresidue in at least one distillation columnThe hydroxyaryl compound can be obtained as a top stream from the distillation column and the upstream cracking residue can be obtained as a bottom stream from the distillation column. The upstream cracking residue typically comprises bisphenol.to aunit andThe reaction of alkylcarbonate with hydroxyaryl compound to form a diarylcarbonate can occur as well-known in the art. A specific example of a non-phosgene route to synthesize the diarylcarbonate of diphenyl carbonate (DPC) can be achieved with the use of respective catalysts through the transesterification of dimethyl carbonate (DMC) and phenol to produce phenyl methyl carbonate (PMC) as shown in Reaction (1),24POLY0060 11DMC Phenol PMC Methanol(1 ) followed by the subsequent disproportionation of PMC to produce diphenyl carbonate(DPC) as shown in Reaction (2),PMC DPC DMC(2) with an additional formation of small amounts of an alkyl aryl ether (anisole) as the main reaction byproduct.Manufacturing of bisphenol from a hydroxyaryl compound is well-known, e.g. condensation reaction of phenol and acetone.(II-2) manufacturing polycarbonate using, at least in part, said diarylcarbonate and / or said bisphenol obtained in step (11-1).Manufacturing of polycarbonate using diarylcarbonate and bisphenol is well-known in the art, for example as described in WO2017093974A1

[0020] -

[0043] ,In some preferred embodiments, additionally the upstream cracking residue from the upstream cracking unit is processed in an advantageous manner as described below. The upstream cracking residue typically comprises bisphenol.Cracking of upstream cracking residue recovered in step (lid)In some preferred embodiments, the method further comprises(I lib) feeding the upstream cracking residue recovered in step (lid) to a downstream cracking unit wherein said stream is optionally combined with a cracking agent to form a downstream cracking mixture,(I He) cracking the downstream cracking mixture in said downstream cracking unit, thereby forming a stream comprising a hydroxyaryl compound and a downstream cracking residue,(Hid) separating the hydroxyaryl compound from the downstream cracking residue.24POLY0060 12This advantageously allows obtaining a hydroxyaryl compound from the upstream cracking residue, which hydroxyaryl compound can be used for further processes.(I lib) feeding the upstream cracking residue recovered in step (lid) to a downstream cracking unit wherein said stream is optionally combined with a cracking agent to form a downstream cracking mixturePreferably, the upstream cracking residue recovered in step (lid) is combined with a cracking agent. Suitable examples of the cracking agent in step (111 b) are those described in relation to step (lib).The cracking can optionally occur in the presence of an added catalyst. The catalyst can be acidic or basic. The presence of an added catalyst is preferred both when the cracking agent is water and when the cracking agent is alkyl alcohol. However, particularly when the cracking agent is water, the presence of an added catalyst is preferred and often necessary for achieving a desired level of cracking. Suitable examples of the catalyst in step (I I lb) are those described in relation to step (lib).In particularly preferred embodiments, the cracking agent comprises one or more selected from water, alkyl alcohol and the cracking is performed in the presence of a catalyst selected from the group consisting of an aromatic sulfonic acid, sulfuric acid, phosphoric acid, a base (such as sodium hydroxide), a sulfur containing amine compound, a zeolite, sodium hypophosphite, aluminum isopropylate, a sodium salt of one or both of an organic and a mineral acid and combinations thereof.In particularly preferred embodiments, the cracking agent comprises water and / or methanol and the cracking is performed in the presence of a catalyst comprising sodium hydroxide and / or dodecylbenzene sulfonic acid (DBSA).Preferably, when the cracking agent is water, the cracking is performed in the presence of a catalyst comprising sodium hydroxide.mixture in said downstream cracking unit and a downstream24POLY0060 13The cracking in the downstream cracking unit is preferably performed under conditions such that substantially all bisphenol in the downstream cracking mixture is cracked into the hydroxyaryl compound, in particular phenol.The cracking in step (I I Ic) can be conducted at a temperature within a range of 40 to 200 °C and a pressure within a range of 1 to 20 bar wherein the temperature and pressure in step (I I Ic) are selected such that the cracking agent remains as liquid. Preferably, the temperature and pressure in in step (I I Ic) are selected such that the hydroxyaryl compound, in particular phenol, is in a gas phase. The cracking could occur, for example, at a cracking temperature of 100 to 500 °C (e.g., 150 to 250 °C or 180 to 200 °C) at reduced pressure, for example less than 500 mbar or less than 100 mbar. The residence time in the downstream cracking unit can e.g. be 10 to 100 hours or 50 to 75 hours.Preferably, the cracking step (I He) and the separation step (Hid) are performed in different parts of one unit. A distillation unit for separating out the hydroaryl compound can be provided with a boiler for boiling the liquid phase and returning the gas phase to the distillation unit. The cracking step (I He) can be performed in such a boiler.(Hid) separating the hydroxyaryl compound from the downstream cracking residue Separation of the hydroxyaryl compound from the downstream cracking residue may be performed in a distillation column. However, the separation is preferably performed in the downstream cracking unit wherein a top phase comprising the hydroxyaryl compound (e.g. gas phase) and a bottom phase comprising the downstream cracking residue (e.g. liquid phase) are formed.Preferably, the phase comprising the hydroxyaryl compound is fed to at least one distillation column wherein the hydroxyaryl compound is separated out. In preferred embodiments, the at least one distillation column used in this step is the at least one distillation column used in step (Hd).The downstream cracking residue may be fed to a hot oil furnace.In some preferred embodiments, the method further comprises(Illa) providing a further recycle stream of recycled polycarbonate having in its backbone repeating units based on at least one type of bisphenol, wherein said further recycle stream is fed to the downstream cracking unit in step (I I lb).24POLY0060 14This advantageously allows obtaining useful hydroxyaryl compound from a further stream of recycled polycarbonate.Preferably, the recycle stream of recycled polycarbonate of step (Illa) is fed to the downstream cracking unit as a melt, e.g. from an extruder.In some preferred embodiments, the method further comprises(111-1) feeding the separated hydroxyaryl compound recovered in step (Hid) to a diarylcarbonate manufacturing unit and / or a bisphenol manufacturing unit and manufacturing diarylcarbonate and / or bisphenol,(HI-2) manufacturing polycarbonate using, at least in part, said diarylcarbonate and / or said bisphenol obtained in step (HI-1).The diarylcarbonate manufacturing unit used in step (11-1) and the diarylcarbonate manufacturing unit used in step (HI-1) may be the same unit or different units. The bisphenol manufacturing unit used in step (11-1) and the bisphenol manufacturing unit used in step (HI-1) may be the same unit or different units.In some preferred embodiments, alkylcarbonate and bisphenol are formed from a recycle stream of recycled polycarbonate and the alkylcarbonate is used for manufacturing polycarbonate.Obtaining alkyl carbonate from further recycle streamIn some preferred embodiments, the method further comprises(la) providing a further recycle stream of recycled polycarbonate having in its backbone repeating units based on at least one type of bisphenol,(lb) feeding the further recycle stream to a depolymerization unit wherein said further recycle stream is combined with an alkyl alcohol to form a reaction mixture,(lc) reacting the reaction mixture in the depolymerization unit, thereby forming a stream comprising alkylcarbonate and bisphenol,(ld) separating said alkylcarbonate from said bisphenol in at least one distillation column, wherein in step (Hb) the upstream cracking unit is fed with the further stream which comprises said bisphenol.24POLY0060 15This advantageously allows obtaining a hydroxyaryl compound from bisphenol obtained from a further recycle stream of recycled polycarbonate, which hydroxyaryl compound can be used for the manufacture of polycarbonate.(lb) feeding the recycle stream to a depolymerization unit wherein said recycle stream is combined with an alkyl alcohol to form a reaction mixtureThe recycle stream of recycled polycarbonate of step (la) is fed to a depolymerization unit wherein said recycle stream is combined with an alkyl alcohol to form a reaction mixture.Preferably, the recycle stream of recycled polycarbonate of step (la) is fed to the depolymerization unit as a melt, e.g. from an extruder.Preferably, the alkyl alcohol is a C1-6 alkyl alcohol preferably selected from the group consisting of methanol, ethanol, n-propanol, isopropanol, n-butanol, iso-butanol and combinations thereof. More preferably, the alkyl alcohol comprises or is methanol. Most preferably, the alkyl alcohol is methanol.Preferably, in step (lb) the recycle stream of recycled polycarbonate of step (la) is further combined in the depolymerization unit with an organic cosolvent to form the reaction mixture, wherein the organic cosolvent is miscible with the alkyl alcohol. Preferably, the organic cosolvent comprises or is an alkylcarbonate. Preferably, the alkylcarbonate comprises or is dimethylcarbonate (DMC).Preferably, the organic cosolvent is substantially free from toluene. Preferably, the organic cosolvent is substantially free from toluene, chlorobenzene and xylene. The use of the alkylcarbonate, in particular dimethylcarbonate, instead of other solvents such as toluene, chlorobenzene and xylene has an advantage that no later separation of the organic solvent is necessary. Accordingly, preferably, the organic cosolvent comprises 0 wt% of toluene or comprises less than 1.0 wt% of toluene with respect to the total organic cosolvent. Preferably, the organic cosolvent comprises 0 wt% of toluene, chlorobenzene and xylene or the total amount of toluene, chlorobenzene and xylene is less than 1.0 wt% with respect to the total organic cosolvent.Particularly preferably, the recycle stream of recycled polycarbonate of step (la) is combined in the depolymerization unit with an azeotropic mixture of the alkyl alcohol and the alkylcarbonate. The weight ratio between the alkyl alcohol and the24POLY0060 16 alkylcarbonate may e.g. be 60:40 to 80:20, preferably 65:35 to 75:25. Particularly preferably, the fist stream of recycled polycarbonate is combined in the depolymerization unit with an azeotropic mixture of methanol and dimethylcarbonate. The weight ratio between methanol and dimethylcarbonate may e.g. be 60:40 to 80:20, preferably 65:35 to 75:25.Preferably, in step (lb) the recycle stream of recycled polycarbonate of step (la) is further combined in the depolymerization unit with a base.The base can be, for example, an alkoxide or hydroxide. Suitable alkoxides and hydroxides are those that are soluble in the reaction mixture. Exemplary alkoxides can include C1-4 alkoxides, and exemplary hydroxides can include, for example, alkali metal hydroxides, alkaline-earth metal hydroxides, tetra-alkyl ammonium hydroxides, and ammonium hydroxide. In an aspect, the base comprises an alkali metal hydroxide, for example sodium hydroxide. In an aspect, the base can be in the form of an aqueous solution for example an aqueous alkali metal hydroxide, preferably an aqueous sodium hydroxide solution. When provided as an aqueous solution, the base (e.g., the alkali metal hydroxide) can be present in an amount sufficient to provide a 10 to 50 wt% solution of the base in water (based on the total weight of the base and the water), preferably a 20 to 50 wt% solution, more preferably a 30 to 50 wt% solution, even more preferably a 35 to 45 wt% solution.The depolymerization unit may further be fed with a stream obtained from a polycarbonate manufacturing process, wherein said stream is combined with the recycle stream of recycled polycarbonate of step (la). Overheads from oligomerization reactor(s) and / or polymerization reactor(s) comprising a hydroxyaryl compound, diarylcarbonate, bisphenol and polycarbonate oligomers can be fed to a distillation column to separate out the hydroxyaryl compound. The remainder comprising diarylcarbonate, bisphenol and polycarbonate oligomers can be fed to the depolymerization unit.Thus, in step (lb) the depolymerization unit may be fed with a further stream obtained by- melt polymerizing a dihydroxy compound and a diarylcarbonate in the presence of a transesterification catalyst to form a hydroxyaryl compound and a polycarbonate in a melt polymerization facility;24POLY0060 17- collecting an overhead stream comprising the hydroxyaryl compound from the melt polymerization facility; and- separating a top stream comprising the hydroxyaryl compound from the overhead stream to obtain the further stream as a bottom stream.(Ic) reacting the reaction mixture in the depolymerization unit, thereby forming a stream comprising alkylcarbonate and bisphenolIn the depolymerization unit, polycarbonate reacts with the alkyl alcohol to depolymerize and may form polycarbonate oligomers, bisphenol, alkylcarbonate and phenol. Alkylcarbonate and phenol may be formed from diarylcarbonate.The reaction is conducted under conditions which allow depolymerization of polycarbonate and polycarbonate oligomers. The temperature and pressure may be selected such that the alkyl alcohol remains as liquid so that it maintains close contact with the polycarbonate and polycarbonate oligomers.Preferably, the reaction is conducted at a temperature within a range of 40 to 200 °C and a pressure within a range of 1 to 20 bar wherein the alkyl alcohol remains as liquid.In some embodiments, the reaction can e.g. be conducted at a temperature of 40 to 70°C, or 45 to 65°C, or 50 to 60°C, and atmospheric pressure. The reaction can be conducted for a time effective to depolymerize the polycarbonate. For example, the reaction can be for a time of 1 to 24 hours, preferably 1 to 18 hours, more preferably 1 to 10 hours, even more preferably 1 to 6 hours.The reaction can be conducted at a higher temperature and a high pressure, for example at a temperature of 130 to 150 °C and a pressure of 18.5-20 bar. Such high pressure ensures that the alkyl alcohol remains as liquid. In such case, the reaction can be for a short time, e.g. 10 to 20min.The degree of depolymerization can be monitored via laboratory analysis, for example, by ultra-performance liquid chromatography (LIPLC), in which the monomers and endcappers are quantified.The depolymerization unit may be provided with an upstream static mixer for increasing the intimate contact of the alkyl alcohol and the recycle stream of molten recycled polycarbonate.24POLY0060 18The depolymerization unit may have a tubular shape. The inner surface of the tube may or may not be provided with modifications to improve heat exchange.The identity of the alkylcarbonate present in the obtained stream can be dictated by the particular alkyl alcohol selected for the depolymerization reaction. For example, in an aspect, the alkylcarbonate can be dimethyl carbonate when methanol is selected as the alcohol.Preferably, the alkylcarbonate comprises or is dimethylcarbonate.(Id) separating said alkylcarbonate from said bisphenol in at least one distillation column, wherein in step (lib) the upstream cracking unit is fed with the further stream which comprises said bisphenolThe separation can be conducted at, for example, a temperature of greater than 90 to 115°C, or 100 to 110°C at atmospheric or reduced pressure.The separation can provide a top stream comprising the alkylcarbonate, phenol and methanol and a bottom stream comprising bisphenol.In step (lib), the upstream cracking unit may be fed with a further stream comprising at least one of bisphenol, diarylcarbonate and polycarbonate oligomers. The bisphenol recovered in step (Id) may form part of said further stream of step (lib).In some preferred embodiments, the method further comprises(1-1) feeding the separated alkylcarbonate recovered in step (Id) to a diarylcarbonate manufacturing unit and reacting said diarylcarbonate with hydroxyaryl compound thereby forming diarylcarbonate,(I-2) manufacturing polycarbonate using, at least in part, said diarylcarbonate obtained in step (1-1).(1-1) feeding the separated alkylcarbonate recovered in step (Id) to a diarylcarbonate manufacturing unit and reacting said diarylcarbonate with hydroxyaryl compound thereby forming diarylcarbonateManufacturing of a diarylcarbonate from alkylcarbonate is well-known, e.g. as described in relation to step (11-1).24POLY0060 19 at least in said obtained in step (1-1)Manufacturing of polycarbonate using diarylcarbonate and / or bisphenol is well-known in the art, for example as described in relation to step (II-2).It is noted that the invention relates to the subject-matter defined in the independent claims alone or in combination with any possible combinations of features described herein, preferred in particular are those combinations of features that are present in the claims. It will therefore be appreciated that all combinations of features relating to the composition according to the invention; all combinations of features relating to the process according to the invention and all combinations of features relating to the composition according to the invention and features relating to the process according to the invention are described herein.It is further noted that the term ‘comprising’ does not exclude the presence of other elements. However, it is also to be understood that a description on a product / composition comprising certain components also discloses a product / composition consisting of these components. The product / composition consisting of these components may be advantageous in that it offers a simpler, more economical process for the preparation of the product / composition. Similarly, it is also to be understood that a description on a process comprising certain steps also discloses a process consisting of these steps. The process consisting of these steps may be advantageous in that it offers a simpler, more economical process.When values are mentioned for a lower limit and an upper limit for a parameter, ranges made by the combinations of the values of the lower limit and the values of the upper limit are also understood to be disclosed.The invention is now elucidated by way of the following figures, without however being limited thereto.Figure 1 is an illustration of an example of a system for carrying out an embodiment of the method according to the invention;Figure 2 is an illustration of an example of a system for carrying out an embodiment of the method according to the invention;Figure 3 is an illustration of an example of a system for carrying out a method for recycling aromatic polycarbonate comprising steps (la)-(ld).24POLY0060 20Figure 4 is an illustration of an example of a system for treating a stream from an upstream cracking unit.Figure 1 is an illustration of an example of a system for carrying out a method according to the invention.An overhead stream 22 comprising a hydroxyaryl compound, diarylcarbonate, bisphenol and polycarbonate oligomers from a polycarbonate manufacturing system (not shown) is fed to a distillation column 500. The distillation column 500 separates the overhead stream 22 into a top stream 23 comprising hydroxyaryl compound and a bottom stream 24 comprising diarylcarbonate, bisphenol and polycarbonate oligomers.The bottom stream 24 from the distillation column 500 is fed to a distillation column 600 which separates the bottom stream 24 into a top stream 13 comprising diarylcarbonate and a bottom stream 14 comprising bisphenol and polycarbonate oligomers. The top stream 13 from the distillation column 600 is fed to a distillation column 620.The top stream 23 from the distillation column 500 may be fed to a system (not shown) for the preparation for diarylcarbonate by the reaction of hydroxyaryl compound and alkylcarbonate in the presence of suitable catalyst, e.g. titanium-based catalyst such as titanium isopropoxide. A stream comprising diarylcarbonate, phenyl alkyl carbonate, catalyst and unreacted species is obtained. This stream can be separated to obtain a crude diarylcarbonate stream mainly comprising diarylcarbonate and phenyl alkyl carbonate. This crude diarylcarbonate stream can be fed as stream 30 to a distillation column 610 which separates the crude diarylcarbonate stream 30 into a top stream 31 comprising phenyl alkyl carbonate and a bottom stream 32 comprising diarylcarbonate. The bottom stream 32 is fed to the distillation column 620.The distillation column 620 produces a high purity diarylcarbonate as a top stream 33 and a diarylcarbonate-rich bottom stream 34 with traces of heavy species and catalyst. Catalyst stream 36 is separated from the bottom stream 34 to be recycled. The remaining stream 35 is fed to a catalyst purge burner 410.The bottom stream 14 from the distillation column 600 is fed to an upstream cracking unit 200. The upstream cracking unit 200 is further fed with a recycle stream 60 of recycled polycarbonate. The upstream cracking unit 200 is further fed with a cracking agent 15 comprising water and / or methanol, and DBSA and / or NaOH.24POLY0060 21An upstream cracking mixture is formed in the upstream cracking unit 200 and is cracked, forming a stream 16 comprising a hydroxyaryl compound and an upstream cracking residue comprising bisphenol. The stream 16 is fed to a distillation column 700 which separates a top stream 17 comprising the hydroxyaryl compound and a bottom stream 18 comprising the upstream cracking residue.The top stream 17 from the distillation column 700 is fed to a diarylcarbonate manufacturing unit and / or a bisphenol manufacturing unit 900 for forming a diarylcarbonate and / or bisphenol. The diarylcarbonate and / or bisphenol is sent to a polycarbonate manufacturing system (not shown).The bottom stream 18 from the distillation column 700 is fed to a downstream cracking unit 300. The downstream cracking unit 300 is further fed with a recycle stream 70 of recycled polycarbonate. The downstream cracking unit 300 is further fed with a cracking agent 19 comprising water and / or methanol, and DBSA and / or NaOH.A downstream cracking mixture is formed in the downstream cracking unit 300 and is cracked, forming a gas phase comprising a hydroxyaryl compound and a liquid phase comprising a downstream cracking residue comprising tars. The gas phase is fed back to the distillation column 700 as stream 21 and the liquid phase is fed to a hot oil furnace 400 as stream 20.Figure 2 is an illustration of an example of a system for carrying out an embodiment of the method according to the invention.A recycle stream 50 of recycled polycarbonate is fed to a depolymerization unit 100. The depolymerization unit 100 is further fed with an azeotropic mixture 11 of an alkyl alcohol (e.g. methanol) and an alkylcarbonate (e.g. DMC).An overhead stream 22 comprising a hydroxyaryl compound, diarylcarbonate, bisphenol and polycarbonate oligomers from a polycarbonate manufacturing system (not shown) is fed to a distillation column 500. The distillation column 500 separates the overhead stream 22 into a top stream 23 comprising hydroxyaryl compound and a bottom stream 24 comprising diarylcarbonate, bisphenol and polycarbonate oligomers. The bottom stream 24 is fed to the depolymerization unit 100.24POLY0060 22A reaction mixture is formed in the depolymerization unit 100 and is reacted, forming a stream 12 comprising an alkylcarbonate, bisphenol, hydroxyaryl compound and polycarbonate oligomers. The stream 12 is fed to a distillation column 600 which separates the stream 12 into a top stream 13’ comprising alkylcarbonate and hydroxyaryl compound and alkyl alcohol and a bottom stream 14’ comprising bisphenol and polycarbonate oligomers.The top stream 13’ from the distillation column 600 is, optionally after removing components other than alkylcarbonate, fed to a diarylcarbonate manufacturing unit 800 wherein alkylcarbonate is reacted with hydroxyaryl compound to form diarylcarbonate. The diarylcarbonate is sent to a polycarbonate manufacturing system (not shown).The bottom stream 14’ from the distillation column 600 is further treated in the manner as described in relation to Figure 1.Figure 3 is an illustration of an example of a system for carrying out carrying out a method for recycling aromatic polycarbonate comprising steps (la)-(ld).An overhead stream 22 comprising a hydroxyaryl compound, diarylcarbonate, bisphenol and polycarbonate oligomers from a polycarbonate manufacturing system (not shown) is fed to a distillation column 500 which separates a top stream 23 comprising hydroxyaryl compound from a bottom stream 24 comprising diarylcarbonate, bisphenol and polycarbonate oligomers. The bottom stream 24 is fed to a distillation column 610.The top stream 23 from the distillation column 500 may be processed to obtain a crude diarylcarbonate stream 30 mainly comprising diarylcarbonate and phenyl alkyl carbonate in the manner explained in relation to Figure 1. This crude diarylcarbonate stream can be fed as stream 30 to a distillation column 610 which separates the crude diarylcarbonate stream 30 into a top stream 31 comprising phenyl alkyl carbonate and a bottom stream 32 comprising diarylcarbonate. The bottom stream 32 is fed to the distillation column 620.The distillation column 620 produces a high purity diarylcarbonate as a top stream 33 and a diarylcarbonate-rich bottom stream 34’ with traces of heavy species and catalyst.The bottom stream 34’ is fed to the depolymerization unit 100.24POLY0060 23A recycle stream 50 of recycled polycarbonate is fed to a depolymerization unit 100. The depolymerization unit 100 is further fed with an azeotropic mixture 11 of an alkyl alcohol (e.g. methanol) and an alkylcarbonate (e.g. DMC).A reaction mixture is formed in the depolymerization unit 100 and is reacted, forming a stream 12 comprising an alkylcarbonate, bisphenol, hydroxyaryl compound and polycarbonate oligomers. The stream 12 is fed to a distillation column 600 which separates the stream 12 into a top stream 13’ comprising alkylcarbonate and hydroxyaryl compound and alkyl alcohol and a bottom stream 14’ comprising bisphenol and polycarbonate oligomers.The top stream 13’ from the distillation column 600 is fed, optionally after removing components other than alkylcarbonate, to a diarylcarbonate manufacturing unit 800 wherein it is reacted with hydroxyaryl compound to form diarylcarbonate. The diarylcarbonate is sent to a polycarbonate manufacturing system (not shown).The bottom stream 14’ from the distillation column 600 is fed to a catalyst purge burner 410.Figure 4 is a further example of a system for treating a stream from an upstream cracking unit, such as stream 16 from upstream cracking unit 200 of Figures 1 and 2. Herein, the exemplary system is described using the stream 16 comprising a hydroxyaryl compound and an upstream cracking residue comprising bisphenol. The system comprises a distillation column 700’ to which the stream 16 is fed. The distillation column 700’ separates the stream 16 into a top stream 17’ comprising the hydroxyaryl compound and a bottom stream 18’ comprising the upstream cracking residue.The bottom stream 18’ from the distillation column 700’ is fed to a downstream cracking unit 300’ using a bottoms stream pump 70T. Part of the bottom stream 18’ is fed back to the distillation column 700’ by a columns reboiler 702’. The downstream cracking unit 300’ is fed with a cracking agent 19’ comprising water and / or methanol, and DBSA and / or NaOH.A downstream cracking mixture is formed in the downstream cracking unit 300’ and is cracked, forming a gas phase comprising a hydroxyaryl compound and a liquid phase comprising a downstream cracking residue comprising tars. The cracked mixture24POLY0060 24 obtained is transferred by a pump 30T so that the liquid phase is separated out as stream 20’. Part 2T of the gas phase is fed back to the distillation column 700’ and part 25’ of the gas phase is fed back to the downstream cracking unit 300’.

Claims

1. 24POLY0060 25CLAIMS1 . Method for recycling aromatic polycarbonate comprising the steps of(Ila) providing a recycle stream of recycled polycarbonate having in its backbone repeating units based on at least one type of bisphenol,(lib) feeding the recycle stream to an upstream cracking unit wherein said recycle stream is optionally combined with a further stream comprising at least one of bisphenol, diarylcarbonate and polycarbonate oligomers and optionally with a cracking agent to form an upstream cracking mixture,(He) cracking the upstream cracking mixture in said upstream cracking unit, thereby forming a stream comprising a hydroxyaryl compound and an upstream cracking residue,(lid) separating the hydroxyaryl compound from the upstream cracking residue in at least one distillation column,(11-1) feeding the separated hydroxyaryl compound recovered in step (lid) to a diarylcarbonate manufacturing unit and / or a bisphenol manufacturing unit and manufacturing diaryl carbonate and / or bisphenol,(I I-2) manufacturing polycarbonate using, at least in part, said diarylcarbonate and / or said bisphenol obtained in step (11-1).

2. The method according to claim 1 , wherein in step (lib) said recycle stream is combined with the cracking agent, the cracking agent in step (lib) comprises one or more selected from water and alkyl alcohol, when the cracking agent in step (lib) is water, the cracking in step (He) is performed in the presence of an acidic or basic catalyst and wherein the temperature and pressure in the upstream cracking unit are selected such that the cracking agent remains as liquid.

3. The method according to claim 1 , wherein in step (I lb) said recycle stream is combined with the cracking agent, the cracking agent in step (Hb) comprises one or more selected from water and alkyl alcohol and the cracking in step (lib) is performed in the presence of an acidic or basic catalyst and wherein the temperature and pressure in the upstream cracking unit are selected such that the cracking agent remains as liquid.24POLY0060 264. The method according to claim 2 or 3, wherein the cracking in step (He) is conducted at a temperature within a range of 40 to 200 °C and a pressure within a range of 1 to 20 bar.

5. The method according to any one of the preceding claims, wherein the amount of polycarbonate in the recycle stream of step (Ila) is at least 70 wt%, more preferably at least 80 wt%, more preferably at least 90 wt%.

6. The method according to any one of the preceding claims, wherein in step (lib) the upstream cracking unit is fed with the further stream which comprises a stream obtained by- melt polymerizing a dihydroxy compound and a diarylcarbonate in the presence of a transesterification catalyst to form a hydroxyaryl compound and a polycarbonate in a melt polymerization facility;- collecting an overhead stream comprising the hydroxyaryl compound from the melt polymerization facility; and- separating a top stream comprising the hydroxyaryl compound from the overhead stream to obtain said stream to be fed to the upstream cracking unit as a bottom stream.

7. The method according to any one of the preceding claims, wherein the method further comprises the steps of:(lllb) feeding a stream of the upstream cracking residue recovered in step (lid) to a downstream cracking unit wherein said stream is optionally combined with a cracking agent to form a downstream cracking mixture,(I lie) cracking the downstream cracking mixture in said downstream cracking unit, thereby forming a stream comprising a hydroxyaryl compound and a downstream cracking residue,(Hid) separating the hydroxyaryl compound and the downstream cracking residue.

8. The method according to claim 7, wherein in step (lllb) said stream is combined with the cracking agent, the cracking agent in step (lllb) comprises one or more selected from water and alkyl alcohol, when the cracking agent in step (lllb) is water, the cracking in step (I I Ic) is performed in the presence of an acidic or basic catalyst and24POLY0060 27 the cracking in step (I I Ic) is conducted at a temperature within a range of 40 to 200 °C and a pressure within a range of 1 to 20 bar wherein the cracking agent remains as liquid or the cracking in step (II Ic) is conducted at a cracking temperature of 100 to 500 °C at reduced pressure, preferably wherein the temperature and pressure in in step (lllc) are selected such that the hydroxyaryl compound, in particular phenol, is in a gas phase.

9. The method according to claim 7, wherein in step (I I lb) said stream is combined with the cracking agent, the cracking agent in step (111 b) comprises one or more selected from water and alkyl alcohol, the cracking in step (lllc) is performed in the presence of an acidic or basic catalyst and the cracking in step (lllc) is conducted at a temperature within a range of 40 to 200 °C and a pressure within a range of 1 to 20 bar wherein the cracking agent remains as liquid or the cracking in step (lllc) is conducted at a cracking temperature of 100 to 500 °C at reduced pressure, preferably wherein the temperature and pressure in in step (lllc) are selected such that the hydroxyaryl compound, in particular phenol, is in a gas phase.

10. The method according to any one of claims 7-9, wherein the separated hydroxyaryl compound recovered in step (Hid) is fed to the at least one distillation column used in step (lid).

11. The method according to any one of claims 7-10, wherein the method further comprises the steps of:(111-1) feeding the separated hydroxyaryl compound recovered in step (Hid) to a diarylcarbonate manufacturing unit and / or a bisphenol manufacturing unit and manufacturing diaryl carbonate and / or bisphenol,(HI-2) manufacturing polycarbonate using, at least in part, said diarylcarbonate and / or said bisphenol obtained in step (HI-1).

12. The method according to any one of claims 7-11, wherein the method further comprises the steps of:24POLY0060 28(Illa) providing a further recycle stream of recycled polycarbonate having in its backbone repeating units based on at least one type of bisphenol, wherein said further recycle stream is fed to the downstream cracking unit in step (lllb).

13. The method according to any one of the preceding claims, wherein the method further comprises the steps of:(la) providing a further recycle stream of recycled polycarbonate having in its backbone repeating units based on at least one type of bisphenol,(lb) feeding the further recycle stream to a depolymerization unit wherein said further recycle stream is combined with an alkyl alcohol to form a reaction mixture,(lc) reacting the reaction mixture in the depolymerization unit, thereby forming a stream comprising alkylcarbonate and bisphenol,(ld) separating said alkylcarbonate from said bisphenol in at least one distillation column, wherein in step (lib) the upstream cracking unit is fed with the further stream which comprises said bisphenol.

14. The method according to claim 13, wherein the method further comprises the steps of:(1-1) feeding the separated alkylcarbonate recovered in step (Id) to a diarylcarbonate manufacturing unit and reacting said diarylcarbonate with hydroxyaryl compound thereby forming diarylcarbonate,(I-2) manufacturing polycarbonate using, at least in part, said diarylcarbonate obtained in step (1-1).

15. The method according to claim 13 or 14, wherein the alkyl alcohol of step (lb) is a C1-6 alkyl alcohol preferably selected from the group consisting of methanol, ethanol, n-propanol, isopropanol, n-butanol, iso-butanol and combinations thereof, preferably methanol.

16. The method according to any one of claims 13-15, wherein in step (lb) the further recycle stream is combined in the depolymerization unit with the alkyl alcohol and an alkylcarbonate to form the reaction mixture, preferably wherein the further recycle stream is combined in the depolymerization unit with an azeotropic mixture of the alkyl alcohol and the alkylcarbonate.24POLY0060 2917. The method according to any one of claims 13-16, wherein in step (lb) the depolymerization unit is fed with a further stream obtained by- melt polymerizing a dihydroxy compound and a diarylcarbonate in the presence of a transesterification catalyst to form a hydroxyaryl compound and a polycarbonate in a melt polymerization facility;- collecting an overhead stream comprising the hydroxyaryl compound from the melt polymerization facility; and- separating a top stream comprising the hydroxyaryl compound from the overhead stream to obtain the further stream as a bottom stream.

18. The method according to any one of the preceding claims, wherein the cracking agent in step (lib) and / or (I I lb) comprises one or more selected from water and alkyl alcohol and the cracking is performed in the presence of a catalyst selected from the group consisting of an aromatic sulfonic acid, sulfuric acid, phosphoric acid, a base (such as sodium hydroxide), a sulfur containing amine compound, a zeolite, sodium hypophosphite, aluminum isopropylate, a sodium salt of one or both of an organic and a mineral acid and combinations thereof.

19. The method according to claim 18, wherein the alkyl alcohol is selected from the group consisting of methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol and combinations thereof.

20. The method according to any one of the preceding claims, wherein the recycled polycarbonate is or comprises bisphenol A polycarbonate and / or the bisphenol is or comprises bisphenol A (BPA) and / or the diarylcarbonate is or comprises diphenylcarbonate (DPC) and / or the hydroxyaryl compound is or comprises phenol and / or the alkylcarbonate is or comprises dimethylcarbonate (DMC).

Images