Method of separating heterogeneous catalyst from depolymerization reaction products

Abstract

NOT VISIBLE DUE TO STATUS OF PATENT

Description

[0001] METHOD OF SEPARATING HETEROGENEOUS CATALYST FROM DEPOLYMERIZATION REACTION PRODUCTS

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to a process for separating a heterogeneous depolymerization catalyst from monomers and to a separation system for separating a heterogeneous depolymerization catalyst from monomers.

[0004] BACKGROUND OF THE INVENTION

[0005] It has been recognized that recycling of polymers in waste material is necessary to prevent huge landfills and to make efficient use of raw materials. Polymers are used in many applications, such as in packaging, construction materials, textiles and so on. Packaging waste, such as plastic bottles, is nowadays collected separately, sorted in a pre-sorting process and then typically processed to flakes or other pieces with a sufficiently small volume. It has become feasible to provide feed streams that largely comprise one or only two types of polymer. A specific polymer feed stream can then be provided to a factory for processing into new raw material of a specific quality. For condensation polymers, such processing typically involves depolymerisation into monomers and oligomers using a depolymerization catalyst, such as a heterogeneous depolymerization catalyst.

[0006] The inherent property of a depolymerization catalyst is that it is not consumed during the depolymerization reaction. Since heterogeneous depolymerization catalysts may be quite expensive, it is of utmost importance to be able to recover as much of the heterogeneous depolymerization catalyst as possible. If the heterogeneous depolymerization catalyst cannot be efficiently removed and / or cannot be removed in high yield from the reaction products of the depolymerization reaction, it can be considered to be at least partly consumed because part of it cannot be used anymore in a subsequent depolymerization reaction and needs to be replenished, which is disadvantageous from an economic point of view.

[0007] A high purity of the monomers and oligomers, is required in order to reuse them for polymerization. As is well-known, any contaminant may have an impact on the subsequent polymerization reaction from the raw materials. It is known that the quality of the raw material resulting from depolymerisation of condensation polymers, i.e. the monomers and oligomers, strongly depends on the removal of contaminants already present in the waste material. These contaminants typically include colorants and other additives, such as fillers and plasticizers. However, any heterogeneous depolymerization catalyst introduced in the depolymerization reactor and remaining in the monomers and oligomers is also considered an unwanted impurity.

[0008] Hence, for at least these two reasons, it is important to be able to separate heterogeneous depolymerization catalyst with high yield from the monomers and oligomers. W02017 / 111602A1 discloses a process of degrading a condensation polymer chosen from the group of polyesters, polyamides, polyamines and polyethers in a depolymerization reaction catalyzed by a heterogeneous depolymerization catalyst, wherein a carrier liquid, such as an alkanediol, alkanetriol, glycol, glycerol, or propylene glycol, acts as a reactant in the degradation reaction. The depolymerization reaction results in a mixture comprising monomer, oligomers, carrier liquid and heterogeneous depolymerization catalyst. A polar medium, such as water or an aqueous solution, is added to this mixture to obtain a hydrophilic solution comprising monomer and a second phase comprising oligomers and heterogeneous depolymerization catalyst. The hydrophilic solution is then separated from the second phase using a centrifuge. It is described that the addition of the polar medium leads to precipitation of the oligomers. The hydrophilic solution is subsequently treated with an adsorption medium, such as active carbon, to remove pigments and dyes. It is further described that the hydrophilic solution can be purified by membrane filtration, such as nanofiltration or ultrafiltration, downstream of the centrifugation step to remove any remaining solid (nano)particles, particularly upstream of the adsorption step. The monomer is obtained in a crystallization step, downstream of the adsorption step and the optional membrane filtration step.

[0009] W02023 / 008997A2 discloses a method for depolymerizing a polymer comprising the steps of (a) providing the polymer and a solvent in a reactor to obtain a reaction mixture, the solvent being capable of reacting with the polymer to degrade the polymer into its monomers and oligomers; (b) providing a heterogeneous catalyst in the reaction mixture being capable of catalyzing said depolymerization; (c) depolymerizing the polymer in the reaction mixture at depolymerization reaction conditions to obtain a depolymerized mixture comprising monomers and at least light oligomers having from 2 to 4 repeating units; and removing unreacted polymer, solid particles and optionally very heavy oligomers having more than 200 repeating units from the depolymerized mixture after exiting the reactor; (d) recovering at least a part of the heterogeneous catalyst from the depolymerized mixture; and (e) recovering the monomers and optionally the light oligomers from the depolymerized mixture, wherein, during recovery of the heterogeneous catalyst in step (d), the depolymerized mixture further comprises heavy oligomers having at least 5 repeating units and at most 200 repeating units. The reactor system that is used for this process comprises a first filter unit, such as a strainer, arranged downstream of the depolymerization reactor outlet, which is configured for removing unreacted polymer, solid particles and very heavy oligomers having more than 200 repeating units from the depolymerized mixture, such that at least monomers and light oligomers having from 2 to 4 repeating units and heavy oligomers having at least 5 and at most 200 repeating units remain present in the depolymerized mixture. A heat exchanger is provided downstream of the first filter unit or water is added to lower the temperature of the depolymerized mixture causing the heavy oligomers to precipitate along with a substantial amount of the catalyst. The heavy oligomers together with the catalyst can then be removed from the depolymerized mixture by centrifugation, such as in a plurality of centrifuges provided in series. The recovered part of the heterogeneous catalyst can be recycled to the depolymerization reactor. It is described that keeping the molecular weight of the heavy oligomers in the depolymerized mixture during the recovery step (d) between at least 5 repeating units to at most 200 repeating units allows for an improved reuse of the catalyst

[0010] Although the processes disclosed in the prior art may be used to recover heterogeneous depolymerization catalyst to a satisfactory extent in small scale processes, being able to recover substantial amounts of heterogeneous depolymerization catalyst in processes performed at industrial scale remains an important goal. The inventors have found that the capacity of the separation processes of the prior art can only be scaled up by increasing the number of centrifugation units connected in parallel. As will be appreciated by those skilled in the art, a higher number of processing units increases cost of operation and maintenance.

[0011] It is therefore an object of the invention to provide an improved process for separating a heterogeneous depolymerization catalyst from monomers present in a reaction product of a depolymerization reaction of condensation polymers.

[0012] It is another object of the invention to provide a process for separating a heterogeneous depolymerization catalyst from said monomers wherein the heterogeneous depolymerization catalyst is separated in a more efficient way and / or in a higher yield, while retaining the catalyzing activity of the recovered heterogeneous depolymerization catalyst.

[0013] It is yet another object of the invention to provide a more efficient process for separating a heterogeneous depolymerization catalyst from said monomers that can be performed at industrial scale at reasonable capital expenditures (CapEx) and operational expenditures (OpEx).

[0014] It is still another object of the invention to provide a corresponding separation system for separating a heterogeneous depolymerization catalyst from monomers present in a reaction product of a depolymerization reaction of condensation polymers.

[0015] SUMMARY OF THE INVENTION

[0016] The inventors have found that one or more of the objects can be met by subjecting a feed comprising reaction products of a depolymerization reaction wherein condensation polymer is depolymerized into monomers and oligomers, said feed comprising monomers, oligomers, carrier liquid and heterogeneous depolymerization catalyst, to cross-flow membrane filtration before subjecting the resulting retentate to a centrifugation step, if the resulting retentate needs to be subjected to a centrifugation step at all. It was found that cross-flow membrane filtration can be used to efficiently, and in high yield, separate heterogeneous depolymerization catalyst from monomers. Moreover, using cross-flow membrane filtration the feed can be concentrated to a retentate with high volumetric concentration factor (VCF), meaning that the amount of retentate to be processed downstream, e.g. with centrifuges, is considerably limited and less processing units are needed at industrial scale than without cross-flow membrane filtration. Accordingly, in a first aspect a process for separating a heterogeneous depolymerization catalyst from monomers is provided, said process comprising the steps of:

[0017] (a) providing a feed comprising reaction products of a depolymerization reaction wherein condensation polymer is depolymerized into monomers and oligomers, said feed comprising monomers, oligomers, carrier liquid and heterogeneous depolymerization catalyst; and

[0018] (b) subjecting the feed of step (a) to cross-flow membrane filtration resulting in a permeate and a retentate, wherein the permeate has an increased monomer to heterogeneous depolymerization catalyst ratio and the retentate is enriched in heterogeneous depolymerization catalyst and oligomers, as compared to the feed, wherein no centrifugation step is performed prior to step (b).

[0019] In a second aspect, a separation system (1) for separating a heterogeneous depolymerization catalyst from monomers is provided, said separation system (1) comprising:

[0020] (i) a first conduit (2a) configured for supplying a feed comprising reaction products of a depolymerization reaction wherein condensation polymer is depolymerized, said feed comprising monomers, oligomers, carrier liquid and heterogeneous depolymerization catalyst;

[0021] (ii) a cross-flow membrane filtration device (3) configured for separating a feed into a permeate having an increased monomer to heterogeneous depolymerization catalyst ratio and a retentate enriched in heterogeneous depolymerization catalyst and oligomers as compared to the feed, having an inlet (3a) for a feed, a first outlet (3b) for a retentate, a second outlet (3c) for a permeate and a second conduit (2b) configured for discharging a retentate from first outlet (3b);

[0022] (iii) optionally a centrifuge and / or dynamic cross-flow filtration unit (4) configured for separating a retentate into a light phase depleted in heterogeneous depolymerization catalyst and a heavy phase enriched in heterogeneous depolymerization catalyst and oligomer as compared to the retentate, having an inlet (4a) for a retentate, a first outlet (4b) for a heavy phase and a second outlet (4c) for a light phase, a second conduit (2b) configured for supplying a retentate from first outlet (3b) of the cross-flow membrane filtration device (3) to inlet (4a) of the centrifuge and / or dynamic cross-flow filtration unit (4), a third conduit (2c) for discharging a light phase from the centrifuge and / or dynamic cross-flow filtration unit (4) via second outlet (4c), and a fourth conduit (2d) for discharging a heavy phase from the centrifuge and / or dynamic crossflow filtration unit (4) via first outlet (4b);

[0023] (iv) optionally a coarse filter unit (5) downstream of the cross-flow membrane filtration device (3) having an inlet (5a) and an outlet (5b), and a fifth conduit (2e) configured for supplying a permeate from second outlet (3c) of the cross-flow membrane filtration device (3) to inlet (5a) of the coarse filter unit (5);

[0024] (v) an adsorption column (6) downstream of the cross-flow membrane filtration device (3) and the optional coarse filter unit (5) having an inlet (6a) and an outlet (6b); (vi) a crystallization vessel (7) downstream of the adsorption column (6) having an inlet (7a) and an outlet (7b); and

[0025] (vii) if coarse filter unit (5) is present, a sixth conduit (2f) configured for supplying a permeate from outlet (5b) of the coarse filter unit (5) to inlet (6a) of the adsorption column (6); or if coarse filter unit (5) is not present, a sixth conduit (2f) configured for supplying a permeate from second outlet (3c) of the cross-flow membrane filtration device (3) to inlet (6a) of the adsorption column (6); and

[0026] (viii) a seventh conduit (2g) configured for supplying a permeate from outlet (6b) of the adsorption column (6) to inlet (7a) of the crystallization vessel (7).

[0027] DEFINITIONS

[0028] The term ‘heterogeneous catalyst'' and ‘heterogeneous depolymerization catalyst' as used herein are used interchangeably and concern catalysts in the form of solid particles. The heterogeneous catalyst is a catalyst that catalyzes the depolymerization of condensation polymers.

[0029] In the context of the present application, monomers are defined as molecules that contain one repeating unit of the polymer, whereas oligomers comprise molecules that contain at least 2 repeating units, such as dimers, trimers and tetramers.

[0030] BRIEF DESCRIPTION OF THE FIGURES

[0031] Figure 1 depicts a flow scheme of the process according to the invention. Figures 2 to 11 depict flow schemes of embodiments of the process according to the invention.

[0032] Figure 7 depicts a separation system according to the invention. Figures 8 to 11 further depict embodiments of the separation system of the invention.

[0033] Figures 12, 13 and 15 show experimental results for membrane retentions and volumetric concentration factors (VCFs).

[0034] Figure 14 shows experimental results for fluxes across different membranes.

[0035] DETAILED DESCRIPTION

[0036] Process for separating heterogeneous catalyst from monomers

[0037] In a first aspect, the invention concerns a process for separating a heterogeneous depolymerization catalyst from monomers, said process comprising the steps of:

[0038] (a) providing a feed comprising reaction products of a depolymerization reaction wherein condensation polymer is depolymerized into monomers and oligomers, said feed comprising monomers, oligomers, carrier liquid and heterogeneous depolymerization catalyst; and

[0039] (b) subjecting the feed of step (a) to cross-flow membrane filtration resulting in a permeate and a retentate, wherein the permeate has an increased monomer to heterogeneous depolymerization catalyst ratio and the retentate is enriched in heterogeneous depolymerization catalyst and oligomers, as compared to the feed, wherein no centrifugation step is performed prior to step (b).

[0040] See Figure 1 for a flow scheme of the process of the first aspect, wherein a feed comprising reaction products of a depolymerization reaction is supplied to cross-flow membrane filtration unit (3) via inlet (3a) and subjected to cross-flow membrane filtration resulting in a permeate having an increased monomer to heterogeneous depolymerization catalyst ratio leaving cross-flow membrane filtration unit (3) via outlet (3c) and a retentate enriched in heterogeneous depolymerization catalyst and oligomers leaving cross-flow membrane filtration unit (3) via outlet (3b).

[0041] The retentate obtained in step (b) typically still contains some monomer and heterogeneous depolymerization catalyst. By recycling the retentate to cross-flow membrane filtration step (b), improved overall separation of monomer and heterogeneous depolymerization catalyst can be obtained.

[0042] Accordingly, in a preferred embodiment, the process according to the first aspect comprises the steps of:

[0043] (a) providing a feed comprising reaction products of a depolymerization reaction wherein condensation polymer is depolymerized into monomers and oligomers, said feed comprising monomers, oligomers, carrier liquid and heterogeneous depolymerization catalyst; and

[0044] (b) subjecting the feed of step (a) to cross-flow membrane filtration resulting in a permeate and a retentate, wherein the permeate has an increased monomer to heterogeneous depolymerization catalyst ratio and the retentate is enriched in heterogeneous depolymerization catalyst and oligomers, as compared to the feed, and subjecting the retentate again to said cross-flow membrane filtration, wherein no centrifugation step is performed prior to step (b).

[0045] Part of the retentate obtained in step (b) can be continuously removed from the process and can for example be recycled to a depolymerization reactor, or the whole retentate obtained in step (b) can after some time be recycled to a depolymerization reactor.

[0046] See Figure 2 for a flow scheme of an embodiment of the process of the first aspect, wherein the retentate is recycled and again subjected to cross-flow membrane filtration. As shown in Figure 2, part of the retentate obtained in step (b) can be continuously removed from the process and can for example be recycled to a depolymerization reactor, or the whole retentate obtained in step (b) can after some time be recycled to a depolymerization reactor via part of conduit (2b). Cross-flow membrane filtration step (b) separates monomer from heterogeneous depolymerization catalyst and oligomer. Typically, the monomers can cross the membrane and end up in the permeate, whereas the oligomers and the heterogeneous depolymerization catalyst do not cross the membrane and are maintained in the retentate. Nevertheless, as will be appreciated by those skilled in the art, some oligomers and tiny amounts of the heterogeneous depolymerization catalyst may pass the membrane and monomer may be maintained in the retentate. The larger part of the carrier liquid crosses the membrane into the permeate, whereas a smaller part of the carrier liquid maintains in the retentate. The retentate is thus not only enriched in heterogeneous depolymerization catalyst and oligomers, as compared to the feed, but also has a decreased monomer to heterogeneous depolymerization catalyst ratio. Moreover, the retentate is more concentrated as compared to the feed. Likewise, the permeate not only has an increased monomer to heterogeneous depolymerization catalyst ratio, as compared to the feed, but is also depleted in heterogeneous depolymerization catalyst and oligomers.

[0047] The process according to the first aspect can be performed batch- wise or in a continuous way.

[0048] As will be appreciated by those skilled in the art, the process can be performed batchwise by first subjecting the feed provided in step (a) to cross-flow membrane filtration and by subsequently subjecting the collected retentate to cross-flow membrane filtration for a certain period of time or until a certain volumetric concentration factor has been obtained.

[0049] Alternatively, the process can be performed continuously, by continuously supplying the feed of step (a) and by continuously adding the retentate obtained in step (b) to this feed to provide a combined feed that is continuously subjected to cross-flow membrane filtration. In this embodiment, part of the retentate obtained in step (b) is continuously removed from the process and can for example be recycled to a depolymerization reactor. The skilled person understands that in this embodiment the volumetric flow of the feed provided in step (a) equals the sum of the volumetric flows of the permeate crossing the membrane and the part of the retentate obtained in step (b) that is continuously removed from the process.

[0050] In an embodiment, the process according to the first aspect comprises a further step (c) of subjecting the retentate of step (b) to centrifugation and / or dynamic cross-flow filtration, resulting in a heavy phase and a light phase, wherein the heavy phase is enriched in the heterogeneous depolymerization catalyst and the oligomers and the light phase is depleted in the heterogeneous depolymerization catalyst, as compared to the retentate.

[0051] Dynamic cross-flow filtration is performed in a membrane cross-flow unit equipped with a rotating element that creates additional turbulence at the retentate side. This aids achievement of high- solids content in the retentate phase, and consequently enables higher volumetric concentration factors of the feed stream.

[0052] Step (c) is preferably performed if the volumetric concentration factor (VCF) that can be reached by the cross-flow filtration step (b) is too low for the process to be economically feasible. If the VCF of the cross-flow filtration step (b) that can be reached is too low, too much monomer is lost and / or too much monomer is recycled back to the depolymerization step, resulting in an unwanted shift of the equilibrium of the depolymerization reaction to lower conversions.

[0053] In Figure 3, the retentate obtained in step (b) is fed via conduit (2b) and inlet (4a) to centrifugation and / or dynamic cross-flow filtration unit (4) where the retentate is separated into a light phase depleted in heterogeneous depolymerization catalyst leaving unit (4) via outlet (4c) and a heavy phase enriched in heterogeneous depolymerization catalyst and oligomers leaving unit (4) via outlet (4b).

[0054] The heavy phase enriched in heterogeneous depolymerization catalyst and oligomers further typically comprises unwanted impurities that were already present during the depolymerization reaction or that were formed during the depolymerization reaction. In order to be able to recycle heterogeneous depolymerization catalyst, oligomer and / or one or more carrier liquids to a depolymerization reactor, the heavy phase may be subjected to a separation process wherein components are separated. The process according to the first aspect may thus further comprise a separation step downstream of the centrifuge and / or dynamic cross-flow filtration unit-wherein the heavy phase is separated into one or more fractions.

[0055] The light phase obtained in step (c) typically still contains some monomer, oligomer and heterogeneous depolymerization catalyst. By recycling the light phase to cross-flow membrane filtration step (b), improved overall separation of monomer and heterogeneous depolymerization catalyst can be obtained. Since the light phase mainly contains carrier liquid, mixing the light phase with the feed comprising the reaction products of a depolymerization reaction of step (a) before supplying the combined feed to the cross-flow membrane filtration step in fact amounts to applying cross-flow membrane filtration step (b) in diafiltration mode.

[0056] Accordingly, in a preferred embodiment, the process according to the first aspect comprises the steps of:

[0057] (a) providing a feed comprising reaction products of a depolymerization reaction wherein condensation polymer is depolymerized into monomers and oligomers, said feed comprising monomers, oligomers, carrier liquid and heterogeneous depolymerization catalyst; (b) subjecting the feed of step (a) to cross-flow membrane filtration resulting in a permeate and a retentate, wherein the permeate has an increased monomer to heterogeneous depolymerization catalyst ratio and the retentate is enriched in heterogeneous depolymerization catalyst and oligomers, as compared to the feed; and

[0058] (c) subjecting the retentate of step (b) to centrifugation and / or dynamic cross-flow filtration resulting in a heavy phase and a light phase, wherein the heavy phase is enriched in the heterogeneous depolymerization catalyst and the oligomers and the light phase is depleted in the heterogeneous depolymerization catalyst, as compared to the retentate, and subjecting the light phase again to said cross-flow membrane filtration, wherein no centrifugation step is performed prior to step (b).

[0059] As will be appreciated by those skilled in the art, the wording ‘wherein no centrifugation step is performed prior to step (bf in embodiments comprising step (c), means that the feed provided in step (a) has not been subjected to centrifugation before step (b). This does not exclude that any light phase provided in step (c) can be subsequently subjected to cross-flow membrane filtration.

[0060] As will further be appreciated by those skilled in the art, this process can be performed batchwise, by first subjecting the feed provided in step (a) to cross-flow membrane filtration, by subjecting the retentate of step (b) to centrifugation and / or dynamic cross-flow filtration and by subsequently subjecting the light phase obtained in step (c) to cross-flow membrane filtration followed by centrifugation and / or dynamic cross-flow filtration for a certain period of time or until a certain volumetric concentration factor has been obtained.

[0061] Alternatively, this process can be performed continuously, by continuously supplying the feed of step (a) and by continuously adding the light phase obtained in step (c) to this feed to provide a combined feed that is continuously subjected to cross-flow membrane filtration followed by centrifugation and / or dynamic cross-flow filtration. The skilled person understands that in this embodiment the volumetric flow of the feed provided in step (a) equals the combined volumetric flows of the permeate crossing the membrane and of the heavy phase formed in step (c).

[0062] See Figure 4 for a flow scheme of an embodiment of the process of the first aspect, wherein the light phase obtained in step (c) is recycled to a cross-flow membrane filtration unit (3).

[0063] In a preferred embodiment, the process according to the first aspect is performed as a batch process comprising:

[0064] (a) providing a batch of the feed comprising reaction products of a depolymerization reaction and supplying this batch of the feed to a collection vessel, continuously supplying the retentate obtained in step (b) to the collection vessel, and mixing the feed and the retentate in the collection vessel to obtain a combined feed; and

[0065] (b) continuously discharging a stream of the combined feed from the collection vessel, for example until a specific VCF is reached, and continuously subjecting this stream of the combined feed to cross-flow membrane filtration resulting in a permeate and a retentate, wherein the permeate has an increased monomer to heterogeneous depolymerization catalyst ratio and the retentate is enriched in heterogeneous depolymerization catalyst and oligomers, as compared to the combined feed, and supplying the retentate to the collection vessel, wherein no centrifugation step is performed prior to step (b) .

[0066] Part of the retentate obtained in step (b) can be continuously removed from the process and can for example be recycled to a depolymerization reactor, or the whole retentate obtained in step (b) can after some time be recycled to a depolymerization reactor.

[0067] In another preferred embodiment, the process according to the first aspect is performed as a batch process comprising:

[0068] (a) providing a batch of the feed comprising reaction products of a depolymerization reaction and supplying this batch of the feed to a collection vessel, continuously supplying the light phase obtained in step (c) to the collection vessel, and mixing the feed and the light phase in the collection vessel to obtain a combined feed;

[0069] (b) continuously discharging a stream of the combined feed from the collection vessel, for example until a specific VCF is reached, and continuously subjecting this stream of the combined feed to cross-flow membrane filtration resulting in a permeate and a retentate, wherein the permeate has an increased monomer to heterogeneous depolymerization catalyst ratio and the retentate is enriched in heterogeneous depolymerization catalyst and oligomers, as compared to the combined feed; and

[0070] (c) subjecting the retentate of step (b) to centrifugation and / or dynamic cross-flow filtration resulting in a heavy phase and a light phase, wherein the heavy phase is enriched in the heterogeneous depolymerization catalyst and the oligomers and the light phase is depleted in the heterogeneous depolymerization catalyst, as compared to the retentate, and supplying the light phase to the collection vessel, wherein no centrifugation step is performed prior to step (b).

[0071] As will be appreciated by those skilled in the art, on startup of this batch process no retentate or light phase is available yet, meaning that the collection vessel only contains the batch of the feed comprising reaction products of a depolymerization reaction. If some cross-flow membrane filtration has taken place and resulting retentate has optionally been subjected to a step of centrifugation and / or dynamic cross-flow filtration, retentate and optionally light phase formed is recycled to the collection vessel where it is mixed with the remaining part of the batch of the feed already present to form a combined feed. A stream of this combined feed is continuously discharged from the collection vessel and subjected to cross-flow membrane filtration and any retentate / light phase formed is continuously recycled to the collection vessel.

[0072] In a more preferred embodiment, the process according to the first aspect is performed as a continuous process comprising:

[0073] (a) continuously providing a stream of the feed comprising reaction products of a depolymerization reaction and continuously supplying this stream of the feed to a collection vessel, continuously supplying the retentate obtained in step (b) to the collection vessel, and mixing the feed and the retentate in the collection vessel to obtain a combined feed;

[0074] (b) continuously discharging a stream of the combined feed from the collection vessel and continuously subjecting this stream of the combined feed to cross-flow membrane filtration resulting in a permeate and a retentate, wherein the permeate has an increased monomer to heterogeneous depolymerization catalyst ratio and the retentate is enriched in heterogeneous depolymerization catalyst and oligomers, as compared to the combined feed, and continuously supplying the retentate to the collection vessel, wherein part of the retentate is continuously or after regular time intervals removed from the process and is for example recycled to a depolymerization reactor, and wherein no centrifugation step is performed prior to step (b).

[0075] As will be understood by those skilled in the art, at some point in time, cleaning of the membranes, such as cleaning in place, needs to take place to remove fouling on the membranes.

[0076] In another more preferred embodiment, the process according to the first aspect is performed as a continuous process comprising:

[0077] (a) continuously providing a stream of the feed comprising reaction products of a depolymerization reaction and continuously supplying this stream of the feed to a collection vessel, continuously supplying the light phase obtained in step (c) to the collection vessel, and mixing the feed and the light phase in the collection vessel to obtain a combined feed;

[0078] (b) continuously discharging a stream of the combined feed from the collection vessel and continuously subjecting this stream of the combined feed to cross-flow membrane filtration resulting in a permeate and a retentate, wherein the permeate has an increased monomer to heterogeneous depolymerization catalyst ratio and the retentate is enriched in heterogeneous depolymerization catalyst and oligomers, as compared to the combined feed; and (c) continuously subjecting the retentate of step (b) to centrifugation and / or dynamic cross-flow filtration resulting in a heavy phase and a light phase, wherein the heavy phase is enriched in the heterogeneous depolymerization catalyst and the oligomers and the light phase is depleted in the heterogeneous depolymerization catalyst, as compared to the retentate, and continuously supplying the light phase to the collection vessel, wherein no centrifugation step is performed prior to step (b).

[0079] As will be appreciated by those skilled in the art, also on startup of this continuous process no retentate / light phase is available yet, meaning that the collection vessel only contains the feed comprising reaction products of a depolymerization reaction. If some cross-flow membrane filtration has taken place and the retentate / light phase has been formed, the retentate / light phase formed is recycled to the collection vessel where it is mixed with the feed already present which is continuously supplied with a stream of fresh feed to form a combined feed. A stream of this combined feed is continuously discharged from the collection vessel and subjected to cross-flow membrane filtration and any retentate / light phase formed is continuously recycled to the collection vessel.

[0080] In an embodiment, the collection vessel is provided with a direct or indirect heating means, preferably with a heat exchanger, to maintain the temperature of the combined feed to be within a certain range to keep the monomers in solution or molecularly dispersed in the carrier liquid when applying cross-flow membrane filtration.

[0081] In a preferred embodiment, the collection vessel is provided with a means for agitating the contents, such as to obtain a homogeneous mixture.

[0082] See Figures 5 and 6 for embodiments of the process according to the first aspect wherein a combined feed is obtained in a collection vessel (8) equipped with a stirring means (8d) and with a heat exchanger (8e).

[0083] In an embodiment, the process according to the first aspect further comprises a step of subjecting the permeate having an increased monomer to heterogeneous depolymerization catalyst ratio downstream of cross-flow membrane filtration step (b) to adsorption treatment, such as adsorption with active carbon, to remove for example pigments and dyes.

[0084] Preferably, oligomers do not pass the membrane in the cross-flow membrane filtration step and stay in the retentate. If, however, too much oligomers pass the membrane during the cross-flow membrane filtration step, these oligomers may result in early blocking of a downstream adsorption column. Hence, in certain embodiments, a coarse filtration step to filter off oligomers is applied in between the cross-flow membrane filtration step and the adsorption treatment. The term ‘coarse filtration step' as used herein concerns a filtration step with a filter with larger pore sizes than the membrane used in cross-flow membrane filtration step (b). In order to be able to improve filtering off oligomers, it may be needed to slightly cool the permeate, for example using a heat exchanger, causing precipitation of the oligomers before the permeate enters the coarse filtration step. The coarse filtration step can for example be performed with a depth filter or with membrane filtration, preferably with a depth filter such as a candle filter.

[0085] Hence, in certain embodiments, the process according to the first aspect further comprises a step of cooling the permeate of cross-flow membrane filtration step (b) to precipitate oligomers, followed by a coarse filtration step to filter off oligomers and subjecting the filtered permeate to adsorption treatment. As will be appreciated by those skilled in the art, this cooling step should only precipitate oligomers whereas monomers should be kept in solution or molecularly dispersed in the permeate.

[0086] In an embodiment, the process according to the first aspect further comprises a step of subjecting the monomer in the permeate leaving the adsorption step to crystallization to obtain crystalline monomer.

[0087] Figures 7-9 show flow schemes of embodiments of the process of the first aspect wherein a permeate leaving the cross-flow membrane filtration step performed in unit (3) is subsequently subjected to adsorption treatment in unit (6) and to crystallization in unit (7).

[0088] Figures 10 and 11 show flow schemes of embodiments of the process of the first aspect wherein a permeate leaving the cross-flow membrane filtration step performed in unit (3) is subsequently subjected to cooling in heat exchanger (9), coarse filtration in unit (5), adsorption treatment in unit (6) and crystallization in unit (7).

[0089] In an embodiment, the process according to the first aspect comprises a coarse filtration step, for example using a strainer, filter basket, sieve bend, and / or filter bag, prior to step (b) to remove solids, such as metal, glass and unreacted condensation polymer particles, from the feed comprising reaction products of a depolymerization reaction provided in step (a).

[0090] Feed comprising reaction products of a depolymerization reaction

[0091] In step (a) of the process of the first aspect, a feed comprising reaction products of a depolymerization reaction is provided. It is specified that in the depolymerization reaction a condensation polymer is depolymerized into monomers and oligomers. Said feed comprises monomers, oligomers, carrier liquid and heterogeneous depolymerization catalyst. The heterogeneous depolymerization catalyst is thus a heterogeneous catalyst that catalyzes depolymerization of condensation polymers into monomers and oligomers. The condensation polymer may be selected from natural polymers, biobased polymers, biodegradable polymers, polymers formed (directly or indirectly) from fossil fuels, and combinations thereof.

[0092] In preferred embodiments, the feed comprises reaction products of a depolymerization reaction wherein a condensation polymer is depolymerized chosen from the group consisting of polyesters, polycarbonates, polyamides, polyurethanes, polyethers and combinations thereof, wherein polyethers also include starch and cellulose-based polymers.

[0093] In a more preferred embodiment, the feed comprises reaction products of a depolymerization reaction wherein a condensation polymer is depolymerized chosen from the group consisting of polyesters; poly ethers, such as poly-oxymethylene (POM), polyethylene glycol (PEG), polypropylene glycol (PPG), poly tetramethyleneglycol (PTMG), poly tetrahydrofuran (PTHF), and polytetramethyleneetherglycol (PTMEG); polypeptides, polyamides; and poly amines.

[0094] In an even more preferred embodiment, the feed comprises reaction products of a depolymerization reaction wherein the condensation polymer that is depolymerized is a polyester chosen from the group consisting of polyethylene terephthalate (PET), polyethylene furanoate (PEF), polybutylene terephthalate (PBT), polytrimethylene terephthalate (PTT), polyglycolic acid (PGA), polylactic acid (PL A), polycaprolactone (PCL), polyethylene adipate (PEA), polyhydroxy alkanoate (PHA), polyhydroxybutyrate (PHB), polyethylene naphthalate (PEN), poly(3-hydroxybutyrate-co-3- hydroxy valerate) (PHBV), a poly condensate of 4-hydroxybenzoic acid and 6-hydroxynaphthalene-2- carboxylic acid (VECTRAN), and combinations thereof.

[0095] Most preferably, the feed comprises reaction products of a depolymerization reaction wherein the condensation polymer that is depolymerized is polyethylene terephthalate (PET). PET may include further comonomers, such as isophthalic acid, diethylene glycol (DEG), polyethylene naphthalate (PEN) and cyclohexane dimethanol (CHDM), to improve its properties, as is known in the art.

[0096] The depolymerization reaction is typically performed in a reactive solvent. This reactive solvent can be water, resulting in hydrolysis of the condensation polymer. Depolymerization of condensation polymers in a reactive solvent other than water is called solvolysis. The reactive solvent is typically selected to be a solvent for the condensation polymer and / or for the monomers and oligomers obtained from said condensation polymer by depolymerisation. Such reactive solvents are known to the person skilled in the art. In the context of the invention, the term ‘reactive solvent' also encompasses mixtures of a solvent that is reactive per se and a non-reactive solvent. Depolymerisation of polyesters by solvolysis is typically performed in alkanols, alkanediols, alkanetriols or in combinations thereof. For the depolymerisation of PET, the use of ethylene glycol as reactive solvent ‘glycolysis') leads to the monomer bis(2-hydroxyethyl) terephthalate (BHET) as primary depolymerisation product. Dimers, trimers and further oligomers are typically also obtained. For the depolymerisation of PET, the use of methanol as reactive solvent leads to the formation of ethylene glycol and the monomer dimethyl terephthalate (DMT) as primary depolymerisation products.

[0097] As will be appreciated by those skilled in the art, any reactive solvent remaining after the depolymerization reaction and any solvent formed during the depolymerization reaction, such as ethylene glycol during methanolysis, forms the carrier liquid in the feed comprising reaction products of a depolymerization reaction as provided in step (a) of the process according to the first aspect. This does, however, not mean that the carrier liquid in the feed comprising reaction products of a depolymerization reaction provided in step (a) can only comprise liquids already present during the depolymerization reaction. As explained in for example W02023 / 008997A2, water can be added to the depolymerization reaction mixture comprising ethylene glycol as reactive solvent to improve downstream separation of heterogeneous depolymerization catalyst from monomers and oligomers.

[0098] In an embodiment, the carrier liquid comprises water, alkanols, alkanediols, alkanetriols or combinations thereof, preferably water, methanol, ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, 1 ,4-butanediol, 1,5-pentanediol, glycerol or combinations thereof, more preferably water, ethylene glycol or a combination thereof. Ethylene glycol has been found suitable in view of its physical properties.

[0099] In a preferred embodiment, the carrier liquid comprises ethylene glycol and water, wherein the weight ratio of ethylene glycol to water is preferably between 90: 10 and 10:90, more preferably between 70:30 and 30:70, even more preferably between 65:35 and 35:65.

[0100] In another preferred embodiment, the carrier liquid comprises ethylene glycol and less than 10 wt.% of water, based on the combined weight of water and ethylene glycol, more preferably less than 5 wt.%, such as less than 2.5 wt.%, less than 1 wt.% or less than 0.5 wt.%.

[0101] In a preferred embodiment, the feed comprising reaction products of a depolymerization reaction provided in step (a) results from depolymerization of PET, the monomer is BHET and the carrier liquid comprises ethylene glycol and water, wherein the weight ratio of ethylene glycol to water is preferably between 90: 10 and 10:90, more preferably between 70:30 and 30:70, even more preferably between 65:35 and 35:65.

[0102] In another preferred embodiment, the feed comprising reaction products of a depolymerization reaction provided in step (a) results from depolymerization of PET, the monomer is BHET and the carrier liquid comprises ethylene glycol and less than 10 wt.% of water, based on the combined weight of water and ethylene glycol, more preferably less than 5 wt.%, such as less than 2.5 wt.%, less than 1 wt.% or less than 0.5 wt.%.

[0103] In a preferred embodiment, the weight ratio of monomers and oligomers to carrier liquid in the feed comprising reaction products of a depolymerization reaction provided in step (a) is from 20:10 to 100:10, more preferably from 40:10 to 90:10.

[0104] In a preferred embodiment, the weight ratio of heterogeneous depolymerization catalyst to monomers and oligomers in the feed comprising reaction products of a depolymerization reaction provided in step (a) ranges from 0.001:10 to 1:10, more preferably from 0.005:10 to 0.3:10, and even more preferably from 0.008:10 to 0.015:10.

[0105] Depolymerization catalysts for depolymerization of polycondensation polymers are well- known in the art. In this respect, reference is made to S. Thiyagarajan et al., RSC Adv., 2022, 12, pp 947-970 (DOI: 10.1039 / dlra08217e), which is hereby incorporated by reference in its entirety.

[0106] Preferred heterogeneous depolymerization catalysts are chosen from the group consisting of metal particles and oxides thereof, solid metal salts, magnetic particles that are optionally functionalized, particles based on earth alkali metals and hydrotalcites.

[0107] Examples of magnetic particles include particles based on ferromagnetic materials, ferrimagnetic materials, anti-ferromagnetic materials, synthetic magnetic materials, paramagnetic materials, superpar amagnetic materials and combinations thereof.

[0108] In a preferred embodiment, the heterogeneous depolymerization catalyst comprises transition metal particles, such as particles comprising transition metals chosen from the first series of transition metals, also known as the 3d orbital transition metals, more preferably transition metals chosen from iron, nickel, cobalt and combinations thereof, even more preferably transition metals chosen from iron, nickel and combinations thereof.

[0109] In a very preferred embodiment, the heterogeneous depolymerization catalyst comprises iron- containing particles.

[0110] If a heterogeneous depolymerization catalyst is made of metal, it may be provided with an oxide surface, which may further enhance catalysis. The oxide surface may be formed by itself, in contact with air, in contact with water, or the oxide surface may be applied deliberately.

[0111] In another embodiment, the heterogeneous depolymerization catalyst comprises earth alkali metal particles, such as particles comprising earth alkali metals chosen from the group consisting of beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr) barium (Ba), their oxides and combinations thereof. A preferred earth alkali metal oxide is magnesium oxide (MgO).

[0112] In yet another embodiment, the heterogeneous depolymerization catalyst comprises (nonmagnetic) metal particles and oxides thereof, such as particles comprising metals chosen from the group consisting of titanium (Ti), zirconium (Zr), manganese (Mn), zinc (Zn), aluminum (Al), germanium (Ge), antimony (Sb), their oxides, and combinations thereof.

[0113] The heterogeneous depolymerization catalyst material is substantially insoluble in the carrier liquid, also at temperatures of more than 100°C. The heterogeneous depolymerization catalyst preferably has an average particle size of between 5 nm and 200 pm, more preferably between 10 nm and 5 pm, even more preferably between 25 nm and 500 nm, still more preferably between 30 and 450 nm.

[0114] The term ‘particle' as used herein includes both single particles and agglomerates and aggregates thereof if present in the heterogeneous depolymerization catalyst. The average particle size as defined herein thus concerns an average size of single particles and agglomerates and aggregates thereof, if present.

[0115] In the size range between 5 nm and 1 pm, the average particle size is measured by Dynamic Light Scattering (DLS), for instance using a Malvern DLS apparatus, such as a NS500 series. Average particle size is then expressed as the Z-average diameter (intensity weighted mean hydrodynamic size derived from the Cumulants analysis of the correlation curve). As particles larger than a few micrometers do no longer display Brownian motion, they can no longer be measured by DLS. Therefore, in the size range between larger than 1 pm and 200 pm, the average particle size is measured by Laser Diffraction, for instance using a Malvern Mastersizer Series apparatus. Particle size is then expressed as a median particle size (D50 from a volume size distribution derived from a Mie or Fraunhofer approximation).

[0116] In a very preferred embodiment, the heterogeneous depolymerization catalyst comprises functionalized magnetic particles comprising a catalyst complex (ABC), said functionalized magnetic particles having an average particle size of between 25 and 500 nm, as measured with DLS, more preferably between 30 and 450 nm, wherein the catalyst complex comprises three distinguishable elements: (nano)particle (A), bridging moiety / linking group (B) chemically attached to the particle (A), such as by a covalent bond, or physically, such as by adsorption, and catalyst entity (C) that is associated with the particles (A), such as by being chemically bonded, for instance covalently bonded, to the linking group. The linking group preferably does not fully cover the (nano)particle surface, such as in a core-shell particle. The (nano)particles of this catalyst complex are preferably based on ferromagnetic and / or ferrimagnetic materials. Also anti-ferromagnetic materials, synthetic magnetic materials, paramagnetic materials, superparamagnetic materials, such as materials comprising at least one of Fe, Co, Ni, Gd, Dy, Mn, Nd, Sm, and preferably at least one of O, B, C, N, such as iron oxide, such as ferrite, such as magnetite, hematite, and maghemite can be used.

[0117] The functional groups of the bridging moiety (B) are for instance weak organic acids, such as a carboxylic acid or a dicarboxylic acid, but preferably silanols, including silanediols and silanetriols. The bridging moiety may be introduced as a reactant in the form of a silyl comprising group, such as silyl ethers, such as triethoxy silylpropylhalide. The linking group is for instance an alkylene chain, with the alkylene typically between C2 and C10, preferably C3-C5, i.e. propylene, butylene, pentylene. Propylene is preferred. The bridging moiety is suitably provided as a reactant in which the linking group is functionalized for chemical reaction with the catalyst entity, whereas the functional group may be protected. For instance, a suitable functionalization of the linking group is the provision as a substituted alkyl halide. A suitable protection of the functional group may be in the form of an ester or alkoxysilane. The alkoxy-group is preferably ethoxy, though methoxy or propoxy are not excluded.

[0118] In an embodiment, the alkoxysilane is provided as a trialkoxysilane, having one alkylene group that constitutes the linking group. In an alternative embodiment, use is made of dialkyl-dialkoxy silanes, with one of the alkyl groups being the linking group. In again another embodiment, use is made of monoalkoxy-trialkylsilanes, with one of the alkyl groups being the linking group. In the latter cases, the alkyl groups are preferably lower alkyl, such as C1-C4 alkyl, thus methyl, ethyl, propyl, / / -butyl and isobutyl. At least one of the alkyls is then functionalized, for instance with a halide, as specified above. Linear alkyls appear preferable to limit steric hindrance.

[0119] The use of a dialkyl-dialkoxysilane and / or a monoalkoxy-trialkylsilane is understood to be beneficial to create a better separation when the carrier liquid comprises ethylene glycol and water. It is believed that not all alkoxy-groups of the trialkoxysilanes bond to the surface of the nanoparticle aggregate. Some of the alkoxygroups may even remain protected. The protective groups may however be removed upon addition of water to the complex. As a result, the hydrophilicity of the complex may increase. By using silanes with less alkoxy-groups, the remaining groups are inherently non-polar and cannot become unprotected. The entire complex thus becomes more hydrophobic. Rather than merely one type of bridging moiety (B), also known as a silane coupling agent, a mixture of those may be used, for instance a mixture of alkyltrialkoxysilane and dialkyl-dialkoxysilane, wherein one of the alkylgroups is functionalized as a halide to react to the catalytic entity, and subsequently - after the reaction of both - carries the catalytic entity. The addition of dialkyldialkoxysilanes may well reduce the size of the layer of groups bonded to the surface. This is not deemed a disadvantage.

[0120] The catalyst entity (C) may be aromatic or aliphatic, and heterocyclic. An aromatic heterocyclic moiety suitably comprises a heterocycle having at least one, preferably at least two nitrogen atoms. The heterocycle may have 5 or 6 atoms, preferably 5 atoms. Suitable aromatic heterocycles are pyrimidines, imidazoles, piperidines, pyrrolidine, pyridine, pyrazol, oxazol, triazol, thiazol, methimazol, benzotriazol, isoquinol and viologen-type compounds (having for instance two coupled pyridine -ring structures). Particularly preferred is an imidazole structure, which results in an imidazolium ion. The negatively charged moiety may relate to an anionic complex, but alternatively a simple ion, such as a halide. Preferably, the reaction of the alkylhalide of the bridging moiety with an uncharged aromatic heterocyclic moiety including at least one nitrogen atom generates the positive charge on the aromatic moiety, particularly on the nitrogen atom therein, as well as the creation of the negative halide. The negatively charged halide may thereafter be strengthened by addition of a Lewis acid to form a metal salt complex. One example is the conversion of chloride to FeCl4. The aromatic moiety has in one example at least one tail. The at least one tail preferably has a length of C1-C10, such as C2-C4, the at least one tail suitably being attached to a nitrogen atom. This tail is more particularly a tail extending into the carrier liquid and away from the bridging moiety. A longer tail is deemed beneficial to increase the hydrophobicity of the complex. This may counteract tendencies of complex to enter a hydrophilic phase.

[0121] The bridging moiety (B) and the catalyst entity (C) bonded thereto are preferably present in an amount of (mole bridging moiety / gr magnetic particle) 5406-0.1, more preferably in an amount of 1-105-0.01, even more preferably in an amount of 2-105-103, such as in an amount 4-105-104. It is preferred to have a relatively large amount available in terms of an effective optional recovery of the catalyst complex, whereas, in terms of amount of catalyst and costs thereof, a somewhat smaller amount may be more preferred.

[0122] It has been found that limited coverage of the surface of the (nano)particles, or aggregates of such (nano)particles, with the catalyst entity (C) is sufficient to obtain an effective catalyst.

[0123] Membrane filtration

[0124] In step (b) of the process according to the first aspect, cross-flow membrane filtration is performed. Cross-flow configuration means that the stream that is subjected to filtration tangentially flows across the surface of the membrane. The advantage of this type of filtration is that any filter cake deposited onto the membrane is substantially washed away during the filtration process, increasing the length of time that the filtration unit can be operational.

[0125] Membrane filtration is a separation process, driven by a pressure gradient over the membrane, in which the membrane fractionates dissolved and dispersed components as a function of their (solvated) size and structure.

[0126] In a preferred embodiment, the cross-flow membrane filtration of step (b) is selected from microfiltration and ultrafiltration, preferably ultrafiltration.

[0127] In a preferred embodiment, the cross-flow membrane filtration of step (b) results in a volumetric concentration factor of the feed or combined feed provided in step (a) of between 3 and 18, more preferably between 6 and 16, even more preferably between 9 and 15.

[0128] In another preferred embodiment, the cross-flow membrane filtration of step (b) results in a retention of the heterogeneous depolymerization catalyst of at least 80%, more preferably at least 85%, even more preferably at least 90%, yet more preferably at least 95%, still more preferably at least 99%. The membrane retention of the heterogeneous depolymerization catalyst is defined as (1 - Concentrationpeime!ite[wt.%] / ConcentrationieleM!ite[wt.%])*100%.

[0129] Microfiltration as used herein refers to filtration over a membrane with a pore size of between 0.1 and 10 pm, i.e. between 100 nm and 10000 nm. In an embodiment, the pore size of the microfiltration membrane is between 0.1 and 8 pm, such as between 0.1 and 5 pm, or between 0.1 and 3 pm. In another embodiment, the pore size of the microfiltration membrane is between 0.5 and 10 pm, such as between 1 and 10 pm, or between 3 and 10 pm.

[0130] Ultrafiltration as used herein refers to filtration over a membrane with a pore size of between 0.01 and less than 0.1 pm or over a membrane having a molecular size cut-off of between 5 and 150 kDa.

[0131] In a preferred embodiment, the molecular size cut-off of the ultrafiltration membrane is between 5 and 150 kDa, more preferably between 7 and 125 kDa, even more preferably between 8 and 100 kDa, still more preferably between 10 and 80 kDa, yet more preferably between 12 and 60 kDa, such as between 13 and 50 kDa, between 14 and 45 kDa, or between 15 and 40 kDa.

[0132] In an embodiment, the molecular size cut-off of the ultrafiltration membrane is between 5 and 100 kDa, such as between 5 and 80 kDa, between 5 and 50 kDa, between 5 and 30 kDa, or between 5 and 20 kDa. In another embodiment, the molecular size cut-off of the ultrafiltration membrane is between 10 and 150 kDa, such as between 15 and 150 kDa, between 25 and 150 kDa, between 40 and 150 kDa, or between 60 and 150 kDa.

[0133] In an embodiment, the carrier liquid comprises ethylene glycol and water, wherein the weight ratio of ethylene glycol to water is between 90:10 and 10:90, preferably between 70:30 and 30:70, more preferably between 65:35 and 35:65, and the molecular size cut-off of the ultrafiltration membrane is between 5 and 150 kDa, preferably between 7 and 125 kDa, more preferably between 8 and 100 kDa, still more preferably between 10 and 80 kDa.

[0134] In another embodiment, the carrier liquid comprises ethylene glycol and less than 10 wt.% of water, preferably less than 5 wt.% of water, such as less than 2.5 wt.% of water, less than 1 wt.% of water, or less than 0.5 wt.% of water, based on the combined weight of water and ethylene glycol, and the molecular size cut-off of the ultrafiltration membrane is between 5 and 60 kDa, preferably between 8 and 50 kDa, more preferably between 10 and 40 kDa, still more preferably between 15 and 30 kDa.

[0135] Examples of membranes that can be applied in the cross-flow membrane filtration step (b) are polysulfone membranes, polyethersulfon membranes, cellulose acetate membranes, modified or polar- functionalized membranes, and ceramic membranes, preferably ceramic membranes. In a preferred embodiment the membrane configuration is chosen from flat sheet membranes, such as disc membranes, flat plate membranes or spiral wound membranes, or tubular membranes, such as multichannel membranes, hollow fiber membranes or honeycomb membranes. In a very preferred embodiment, the membrane configuration is chosen from tubular membranes.

[0136] As will be appreciated by those skilled in the art, two or more, such as 3, 4 or 5 cross-flow membrane filtration units connected in parallel, connected serially or a combination thereof, can be applied instead of a single cross-flow membrane filtration unit. Two or more cross-flow membrane filtration units connected serially can have different pore sizes within the ranges defined herein, with decreasing pore size for cross-flow membrane filtration units positioned downstream.

[0137] Cross-flow membrane filtration in step (b) is preferably performed at a temperature between 60 and 200 °C, more preferably at a temperature between 80 and 110 °C, such as between 90 and 100 °C. It is relevant that the (combined) feed subjected to cross-flow membrane filtration in step (b) has a temperature that is sufficiently high to keep the monomers in solution or molecularly dispersed in the carrier liquid, to enable the monomers to cross the membrane. If the feed has a temperature that is insufficient, heating of the feed may need to be performed.

[0138] If the feed comprising reaction products of a depolymerization reaction provided in step (a) results from depolymerization of PET, the monomer is BHET, the carrier liquid comprises ethylene glycol and water and the weight ratio of ethylene glycol to water is between 90: 10 and 10:90, preferably between 70:30 and 30:70, more preferably between 65:35 and 35:65, the cross-flow membrane filtration in step (b) is preferably performed at a temperature between 60 and 130 °C, more preferably at a temperature between 80 and 100 °C.

[0139] If the feed comprising reaction products of a depolymerization reaction provided in step (a) results from depolymerization of PET, the monomer is BHET and the carrier liquid comprises ethylene glycol and less than 10 wt.% of water, preferably less than 5 wt.% of water, such as less than 2.5 wt.% of water, less than 1 wt.% of water, or less than 0.5 wt.% of water, based on the combined weight of water and ethylene glycol, the cross-flow membrane filtration is preferably performed at a temperature between 90 and 200 °C, more preferably at a temperature between 90 and 110 °C.

[0140] Separation system

[0141] In a second aspect, the invention concerns a separation system (1) for separating a heterogeneous depolymerization catalyst from monomers, said separation system (1) comprising:

[0142] (i) a first conduit (2a) configured for supplying a feed comprising reaction products of a depolymerization reaction wherein condensation polymer is depolymerized, said feed comprising monomers, oligomers, carrier liquid and heterogeneous depolymerization catalyst;

[0143] (ii) a cross-flow membrane filtration device (3) configured for separating a feed into a permeate having an increased monomer to heterogeneous depolymerization catalyst ratio and a retentate enriched in heterogeneous depolymerization catalyst and oligomers as compared to the feed, having an inlet (3a) for a feed, a first outlet (3b) for a retentate, a second outlet (3c) for a permeate and a second conduit (2b) configured for discharging a retentate from first outlet (3b);

[0144] (iii) optionally a centrifuge and / or dynamic cross-flow filtration unit (4) configured for separating a retentate into a light phase depleted in heterogeneous depolymerization catalyst and a heavy phase enriched in heterogeneous depolymerization catalyst and oligomer as compared to the retentate, having an inlet (4a) for a retentate, a first outlet (4b) for a heavy phase and a second outlet (4c) for a light phase, a second conduit (2b) configured for supplying a retentate from first outlet (3b) of the cross-flow membrane filtration device (3) to inlet (4a) of the centrifuge and / or dynamic cross-flow filtration unit (4), a third conduit (2c) for discharging a light phase from the centrifuge and / or dynamic cross-flow filtration unit (4) via second outlet (4c), and a fourth conduit (2d) for discharging a heavy phase from the centrifuge and / or dynamic crossflow filtration unit (4) via first outlet (4b);

[0145] (iv) optionally a coarse filter unit (5) downstream of the cross-flow membrane filtration device (3) having an inlet (5a) and an outlet (5b), and a fifth conduit (2e) configured for supplying a permeate from second outlet (3c) of the cross-flow membrane filtration device (3) to inlet (5a) of the coarse filter unit (5);

[0146] (v) an adsorption column (6) downstream of the cross-flow membrane filtration device (3) and the optional coarse filter unit (5) having an inlet (6a) and an outlet (6b);

[0147] (vi) a crystallization vessel (7) downstream of the adsorption column (6) having an inlet (7a) and an outlet (7b); and

[0148] (vii) if coarse filter unit (5) is present, a sixth conduit (2f) configured for supplying a permeate from outlet (5b) of the coarse filter unit (5) to inlet (6a) of the adsorption column (6); or if coarse filter unit (5) is not present, a sixth conduit (2f) configured for supplying a permeate from second outlet (3c) of the cross-flow membrane filtration device (3) to inlet (6a) of the adsorption column (6); and

[0149] (viii) a seventh conduit (2g) configured for supplying a permeate from outlet (6b) of the adsorption column (6) to inlet (7a) of the crystallization vessel (7).

[0150] Preferred embodiments related to the cross-flow membrane filtration step (b) of the process according to the first aspect equally apply to the cross-flow membrane filtration device (3) of the separation system according to the second aspect, unless specified otherwise. A preferred example of a coarse filter unit (5) is a depth filter such as a candle filter. A preferred example of an adsorption column (6) is an active carbon column.

[0151] The cross-flow membrane filtration device (3) may comprise two or more cross-flow membrane filtration devices in series, in parallel or a combination thereof. Two or more cross-flow membrane filtration devices connected serially can have different pore sizes within the ranges defined herein, with decreasing pore size in downstream direction. Likewise, the centrifuge and / or dynamic cross-flow filtration unit (4), coarse filter unit (5) and adsorption column (6) may comprise two or more units in series, in parallel or a combination thereof. In a preferred embodiment, the separation system (1) does not comprise a coarse filter unit (5). If it turns out, however, that too many oligomers pass the membrane of the cross-flow membrane filtration device (3) into the permeate, these oligomers may result in early blocking of the downstream adsorption column (6). Hence, in certain embodiments, the separation system (1) does comprise the coarse filter unit (5) to filter off oligomers. In order to be able to improve filtering off oligomers, it may be needed to slightly cool the permeate, for example using a heat exchanger, causing precipitation of the oligomers before the permeate enters the coarse filter unit (5). Hence, in certain embodiments, the separation system (1) comprises a cooling means (9), such as a heat exchanger, downstream of the cross-flow membrane filtration device (3) and upstream of the coarse filter unit (5). See Figures 8 and 9 for a separation system (1) without coarse filter unit (5) and Figures 10 and 11 for a separation system (1) with a coarse filter unit (5) and heat exchanger (9).

[0152] In a very preferred embodiment, the separation system (1) according to the second aspect further comprises a collection vessel (8) configured for mixing a feed comprising the reaction products of a depolymerization reaction and either a retentate coming from the cross-flow membrane filtration device (3) or a light phase depleted in heterogeneous depolymerization catalyst coming from the centrifuge and / or dynamic cross-flow filtration unit (4), wherein said collection vessel (8) has a first inlet (8a) for supplying a feed comprising the reaction products of a depolymerization reaction to the collection vessel (8) via a first part of conduit (2a), a second inlet (8b) for supplying either a retentate coming from the cross-flow membrane filtration device (3) or a light phase depleted in heterogeneous depolymerization catalyst to the collection vessel (8) via second conduit (2b) or third conduit (2c), respectively, and an outlet (8c) for supplying a combined feed to the cross-flow membrane filtration device (3) via a second part of conduit (2a).

[0153] If the collection vessel (8) is configured for mixing a feed comprising the reaction products of a depolymerization reaction and a retentate coming from the cross-flow membrane filtration device (3) via second conduit (2b), second conduit (2b) preferably has an outlet configured for removing part of the retentate, for example configured for recycling part of the retentate to a depolymerization reactor.

[0154] In a preferred embodiment, the collection vessel (8) has a means (8d) for agitating the contents, such as to obtain a homogeneous mixture.

[0155] It is relevant that the (combined) feed entering the cross-flow membrane filtration device (3) via first conduit (2a) has a temperature that is sufficiently high to keep the monomers in solution or molecularly dispersed in the carrier liquid, to enable the monomer to cross the membrane of the crossflow membrane filtration device (3), and pass through the optional coarse filter unit (5) and through the adsorption column (6). If the feed supplied via conduit (2a) has a temperature that is insufficient, a direct or indirect heating means can be provided upstream of the cross-flow membrane filtration device (3). In an embodiment, the collection vessel (8) is provided with a direct or indirect heating means (8e). Embodiments wherein direct or indirect heating means downstream of the cross-flow membrane filtration device (3) are provided are also within the scope of the second aspect. A preferred heating means is a heat exchanger.

[0156] The separation system (1) may further comprise a separation unit downstream of the centrifuge and / or dynamic cross-flow filtration unit (4) configured to receive the heavy phase enriched in heterogeneous depolymerization catalyst and oligomers via fourth conduit (2d) and further configured to separate the heavy phase into one or more fractions.

[0157] As will be appreciated by those skilled in the art, the separation system (1) may further be provided with one or more pumps, one or more valves and a controller that interfaces with the hardware and that is configured to control fluid flow therethrough.

[0158] In a preferred embodiment, the separation system (1) according to the second aspect is used in or configured for performing the process according to the first aspect.

[0159] Thus, the invention has been described by reference to certain embodiments discussed above. It will be recognized that these embodiments are susceptible to various modifications and alternative forms well known to those of skill in the art.

[0160] Furthermore, for a proper understanding of this document and its claims, it is to be understood that the verb ‘to comprise' and its conjugations are used in their non-limiting sense to mean that items following the word are included, but items not specifically mentioned are not excluded. In addition, reference to an element by the indefinite article ‘a' or ‘an' does not exclude the possibility that more than one of the element is present, unless the context clearly requires that there be one and only one of the elements. The indefinite article ‘a' or ‘an' thus usually means ‘at least one' .

[0161] EXAMPLES

[0162] Example 1: cross-flow membrane filtration with reaction mixture based on fresh catalyst

[0163] PET flakes from packaging waste (plastic bottles) were depolymerized in a depolymerization reactor using glycolysis in ethylene glycol (EG) and using a heterogeneous depolymerization catalyst being an iron-based catalyst complex (ABC) consisting of magnetite (nano)particles (A), with chemically attached alkylsilane bridging moieties (B) on their surface, linking ionic liquid cationic groups (C) to the particles at a density of 2 wt% (BC) with respect to (A). The particle average diameter was 380 nm, as determined by DLS. The resulting reaction mixture had a BHET content of 16.7 wt.%, an oligomer (dimer) content of 1.2 wt.%, a water content of < 1 wt.%, a heterogeneous depolymerization catalyst content of 175 ppm, and the remainder being ethylene glycol content, based on the total weight of the reaction mixture. Since fresh heterogeneous depolymerization catalyst was used, the resulting mixture was called ‘fresh’ .

[0164] Water was added to the reaction mixture to achieve an EG:water weight ratio of 65:35. The resulting mixture was fed batchwise to a 20 liter collection vessel and was heated to a temperature of 85 °C. A stream of the mixture was then continuously fed from the collection vessel to a cross-flow membrane benchtop separation unit using a pump where it was separated into a permeate and a retentate. The retentate was recycled to the collection vessel. The process was continued until a predetermined minimum level in the collection vessel was reached.

[0165] Subsequently, both the retentate and the permeate were continuously recycled to the collection vessel and the cross-flow membrane filtration was continued for about 1.5 hours to assess the development of membrane fouling over time. The temperature during the whole process was maintained at about 85 °C.

[0166] The experimental setup used is indicated in Figure 5. Permeate and retentate samples were collected and membrane retentions for the heterogeneous depolymerization catalyst were determined. The membrane retention of the heterogeneous depolymerization catalyst is defined as (1 - Concentrationpermenie [wt.%] / Concentration^,,t.,i [wt.%])*100%. Moreover, volumetric concentration factors (VCFs) were determined, wherein the VCF after a specific amount of time is defined as the volume of the mixture initially fed to the collection vessel divided by the difference between the volume of the mixture initially fed to the collection vessel and the volume of the permeate that was collected after said specific amount of time.

[0167] Different ceramic membranes were tested: (1) a microfiltration membrane with a pore size of 100 nm, (2) an ultrafiltration membrane with a pore size of 25 kDa, (3) an ultrafiltration membrane with a pore size of 100 kDa and (4) an ultrafiltration membrane with a pore size of 150 kDa.

[0168] It was observed that sufficient cross-membrane fluxes could be obtained up to high VCFs although the fluxes across the membrane decreased with increasing VCF due to fouling of the membrane. It was observed that the more open membranes (larger pore size) were more prone to fouling than the membranes with the tighter pores. Without wishing to be bound by any theory, the inventors believe that the more open membranes are more prone to fouling because the various foulants (mainly but not limited to those of organic nature) accumulate in, or in the vicinity of, the pores and block them. The obtained flux profile curves, where flux declines sharply with the increase of VCF, support this explanation. Volumetric concentration factors and membrane retentions were determined just before the start (‘start'') of recycling of permeate to the collection vessel and after about 1.5 hours of recycling permeate ‘end' . Results for the membranes with a pore size of 100 kDa and 150 kDa are shown in Figure 12. It can be observed in Figure 12 that the membrane retentions of the heterogeneous depolymerization catalyst particles are >95% in all cases at VCFs of > 5.

[0169] Example 2: cross-flow membrane filtration with reaction mixture based on recycled catalyst

[0170] Example 1 was repeated three times with a depolymerization reaction mixture that was prepared using heterogeneous depolymerization catalyst that had been used in more than one depolymerization reaction. Since recycled heterogeneous depolymerization catalyst was used during the depolymerization reaction, the resulting mixture was called ‘recycled' .

[0171] Volumetric concentration factors and membrane retentions were again determined just before the start of recycling of the permeate to the collection vessel (‘start') and after about 1.5 hours of recycling permeate (‘end'). Results for the membrane with a pore size of 100 kDa are shown in Figure 13. It can be observed in Figure 13 that the membrane retentions of the heterogeneous depolymerization catalyst are >95% at VCFs of >5.4. The measured retentions were reproducible. The membrane retentions are similar to those obtained in Example 1.

[0172] It was observed that cross-membrane fluxes were higher in Example 2 than in Example 1 (see Figure 14). Without wishing to be bound by any theory, it is hypothesized that the reaction mixture prepared with recycled catalyst has a higher BHET concentration than the reaction mixture based on that prepared with fresh catalyst and that higher BHET concentration increases solubility of oligomers causing less precipitation and fouling of oligomers on the membrane.

[0173] Example 3: cross-flow membrane filtration with reaction mixture based on fresh catalyst

[0174] A mixture of -200 ppm fresh ABC heterogeneous depolymerization catalyst as defined in Example 1 in EG was prepared. So, no water, BHET and oligomers were present in this mixture. The mixture was fed batchwise to a 20 liter collection vessel and was heated to a temperature of 85 °C. A stream of the mixture was then continuously fed from the collection vessel to a cross-flow membrane benchtop separation unit using a pump where it was separated into a permeate and a retentate. The retentate was recycled to the collection vessel. The process was continued until a predetermined minimum level in the collection vessel was reached. The temperature during the whole process was maintained at about 85 °C. The experimental setup used is indicated in Figure 5.

[0175] Permeate and retentate samples were collected and the membrane retention of the heterogeneous depolymerization catalyst particles was determined. The membrane applied was a ceramic ultrafiltration membrane with a pore size of 15 kDa. It was concluded that the membrane retention of the heterogeneous depolymerization catalyst particles was >99% at a VCF of about 6.7.

[0176] Example 4: cross-flow membrane filtration with reaction mixture based on recycled catalyst Example 2 was repeated without the addition of water and with two different ceramic ultrafiltration membranes with a pore size of 15 kDa and 25 kDa. It was observed that the membrane with the smaller pore size resulted in a lower cross-membrane flux.

[0177] Volumetric concentration factors and membrane retentions were again determined just before the start of recycling the permeate to the collection vessel {‘start') and after about 1.5 hours of recycling permeate ‘end' . Results are shown in Figure 15. It can be observed in Figure 15 that the membrane retentions of the heterogeneous depolymerization catalyst particles are >85% at VCFs of >7.

Claims

CLAIMS1. Process for separating a heterogeneous depolymerization catalyst from monomers, comprising the steps of:(a) providing a feed comprising reaction products of a depolymerization reaction wherein condensation polymer is depolymerized into monomers and oligomers, said feed comprising monomers, oligomers, carrier liquid and heterogeneous depolymerization catalyst; and(b) subjecting the feed of step (a) to cross-flow membrane filtration resulting in a permeate and a retentate, wherein the permeate has an increased monomer to heterogeneous depolymerization catalyst ratio and the retentate is enriched in heterogeneous depolymerization catalyst and oligomers, as compared to the feed, wherein no centrifugation step is performed prior to step (b).

2. Process according to claim 1, further comprising the step: of(c) subjecting the retentate of step (b) to centrifugation and / or dynamic cross-flow filtration resulting in a heavy phase and a light phase, wherein the heavy phase is enriched in the heterogeneous depolymerization catalyst and the oligomers and the light phase is depleted in the heterogeneous depolymerization catalyst, as compared to the retentate.

3. Process according to claim 1, which is performed as a continuous process comprising:(a) continuously providing a stream of the feed comprising reaction products of a depolymerization reaction and continuously supplying this stream of the feed to a collection vessel, continuously supplying the retentate obtained in step (b) to the collection vessel, and mixing the feed and the retentate in the collection vessel to obtain a combined feed;(b) continuously discharging a stream of the combined feed from the collection vessel and continuously subjecting this stream of the combined feed to cross-flow membrane filtration resulting in a permeate and a retentate, wherein the permeate has an increased monomer to heterogeneous depolymerization catalyst ratio and the retentate is enriched in heterogeneous depolymerization catalyst and oligomers, as compared to the combined feed, and continuously supplying the retentate to the collection vessel, wherein part of the retentate is continuously or after regular time intervals removed from the process and is for example recycled to a depolymerization reactor, and wherein no centrifugation step is performed prior to step (b).

4. Process according to claim 2, which is performed as a continuous process comprising:(a) continuously providing a stream of the feed comprising reaction products of a depolymerization reaction and continuously supplying this stream of the feed to a collection vessel, continuously supplying the light phase obtained in step (c) to the collection vessel, and mixing the feed and the light phase in the collection vessel to obtain a combined feed;(b) continuously discharging a stream of the combined feed from the collection vessel and continuously subjecting this stream of the combined feed to cross-flow membrane filtration resulting in a permeate and a retentate, wherein the permeate has an increased monomer to heterogeneous depolymerization catalyst ratio and the retentate is enriched in heterogeneous depolymerization catalyst and oligomers, as compared to the combined feed; and(c) continuously subjecting the retentate of step (b) to centrifugation and / or dynamic crossflow filtration resulting in a heavy phase and a light phase, wherein the heavy phase is enriched in the heterogeneous depolymerization catalyst and the oligomers and the light phase is depleted in the heterogeneous depolymerization catalyst, as compared to the retentate, and continuously supplying the light phase to the collection vessel, wherein no centrifugation step is performed prior to step (b).

5. Process according to any one of claims 1 to 4, wherein the carrier liquid comprises water, alkanols, alkanediols, alkane triols or combinations thereof, preferably comprising water, methanol, ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, 1,4- butanediol, 1,5 -pentanediol, glycerol or combinations thereof, more preferably comprising water, ethylene glycol or a combination thereof.

6. Process according to any one of claims 1 to 5, wherein the feed provided in step (a) comprises reaction products of a depolymerization reaction wherein a condensation polymer is depolymerized chosen from the group consisting of polyesters, polycarbonates, polyamides, polyurethanes, polyethers and combinations thereof, preferably polyesters, most preferably polyethylene terephthalate (PET).

7. Process according to any one of claims 1 to 6, wherein the cross-flow membrane filtration of step (b) is ultrafiltration and wherein the molecular size cut-off of the ultrafiltration membrane is between 5 and 150 kDa, preferably between 7 and 125 kDa, more preferably between 8 and 100 kDa, still more preferably between 10 and 80 kDa, yet more preferably between 12 and 60 kDa.

8. Process according to any one of claims 1 to 7, wherein the cross-flow membrane filtration of step (b) is performed at temperature between 60 and 200 °C.

9. Process according to any one of claims 1 to 8, wherein the cross-flow membrane filtration of step (b) results in a volumetric concentration factor of the feed or combined feed provided in step (a) of between 3 and 18, preferably between 6 and 16, more preferably between 9 and 15.

10. Process according to any one of claims 1 to 9, wherein the cross-flow membrane filtration of step (b) results in a retention of the heterogeneous depolymerization catalyst of at least 80%, preferably at least 85%, more preferably at least 90%, yet more preferably at least 95%, still more preferably at least 99%.

11. Process according to any one of claims 1 to 10, wherein the feed comprising reaction products of a depolymerization reaction provided in step (a) results from depolymerization of PET, the monomer is BHET and the carrier liquid comprises ethylene glycol and water, wherein the weight ratio of ethylene glycol to water is preferably between 90: 10 and 10:90, more preferably between 70:30 and 30:70, even more preferably between 65:35 and 35:65.

12. Process according to claim 11, wherein the cross-flow membrane filtration of step (b) is performed at a temperature between 60 and 130 °C, preferably at a temperature between 80 and 100 °C.

13. Process according to any one of claims 1 to 10, wherein the feed comprising reaction products of a depolymerization reaction provided in step (a) results from depolymerization of PET, the monomer is BHET and the carrier liquid comprises ethylene glycol and less than 10 wt.% of water, based on the combined weight of water and ethylene glycol, preferably less than 5 wt.%, such as less than 2.5 wt.%, less than 1 wt.% or less than 0.5 wt.%.

14. Process according to claim 13, wherein the cross-flow membrane filtration of step (b) is performed at a temperature between 90 and 200 °C, preferably at a temperature between 90 and 110 °C.

15. Process according to any one of claims 1 to 14, wherein the weight ratio of monomers and oligomers to carrier liquid in the feed comprising reaction products of a depolymerization reaction provided in step (a) is from 20:10 to 100:10, preferably from 40:10 to 90:10.

16. Process according to any one of claims 1 to 15, wherein the weight ratio of heterogeneous depolymerization catalyst to monomers and oligomers in the feed comprising reaction products of a depolymerization reaction provided in step (a) ranges from 0.001:10 to 1:10, preferably from 0.005:10 to 0.3:10, and more preferably from 0.008:10 to 0.015:10.

17. Process according to any one of claims 1 to 16, wherein the heterogeneous depolymerization catalyst has an average particle size of between 5 nm and 200 pm, preferably between 10 nm and 5 pm, more preferably between 25 nm and 500 nm, still more preferably between 30 and 450 nm.

18. Process according to any one of claims 1 to 17, wherein the heterogeneous depolymerization catalyst comprises functionalized magnetic particles comprising a catalyst complex (ABC), said functionalized magnetic particles having an average particle size of between 25 and 500 nm, as measured with Dynamic Light Scattering, more preferably between 30 and 450 nm, wherein the catalyst complex comprises three distinguishable elements: (nano)particle (A), bridging moiety or linking group (B) chemically or physically attached to the particle, and catalyst entity (C) that is associated with the particles (A), such as by being chemically bonded, for instance covalently bonded, to the linking group.

19. A separation system (1) for separating a heterogeneous depolymerization catalyst from monomers, said separation system (1) comprising:(i) a first conduit (2a) configured for supplying a feed comprising reaction products of a depolymerization reaction wherein condensation polymer is depolymerized, said feed comprising monomers, oligomers, carrier liquid and heterogeneous depolymerization catalyst;(ii) a cross-flow membrane filtration device (3) configured for separating a feed into a permeate having an increased monomer to heterogeneous depolymerization catalyst ratio and a retentate enriched in heterogeneous depolymerization catalyst and oligomers as compared to the feed, having an inlet (3a) for the feed, a first outlet (3b) for a retentate, a second outlet (3c) for a permeate and a second conduit (2b) configured for discharging a retentate from first outlet (3b);(iii) optionally a centrifuge and / or dynamic cross-flow filtration unit (4) configured for separating a retentate into a light phase depleted in heterogeneous depolymerization catalyst and a heavy phase enriched in heterogeneous depolymerization catalyst and oligomer as compared to the retentate, having an inlet (4a) for a retentate, a first outlet (4b) for a heavy phase and a second outlet (4c) for a light phase, a second conduit (2b) configured for supplying a retentate from first outlet (3b) of the cross-flow membranefiltration device (3) to inlet (4a) of the centrifuge and / or dynamic cross-flow filtration unit (4), a third conduit (2c) for discharging a light phase from the centrifuge and / or dynamic cross-flow filtration unit (4) via second outlet (4c), and a fourth conduit (2d) for discharging a heavy phase from the centrifuge and / or dynamic cross-flow filtration unit (4) via first outlet (4b);(iv) optionally a coarse filter unit (5) downstream of the cross-flow membrane filtration device (3) having an inlet (5a) and an outlet (5b), and a fifth conduit (2e) configured for supplying a permeate from second outlet (3c) of the cross-flow membrane filtration device (3) to inlet (5a) of the coarse filter unit (5);(v) an adsorption column (6) downstream of the cross-flow membrane filtration device (3) and the optional coarse filter unit (5) having an inlet (6a) and an outlet (6b);(vi) a crystallization vessel (7) downstream of the adsorption column (6) having an inlet (7a) and an outlet (7b);(vii) if coarse filter unit (5) is present, a sixth conduit (2f) configured for supplying a permeate from outlet (5b) of the coarse filter unit (5) to inlet (6a) of the adsorption column (6); or if coarse filter unit (5) is not present, a sixth conduit (2f) configured for supplying a permeate from second outlet (3c) of the cross-flow membrane filtration device (3) to inlet (6a) of the adsorption column (6); and(viii) a seventh conduit (2g) configured for supplying a permeate from outlet (6b) of the adsorption column (6) to inlet (7a) of the crystallization vessel (7).

20. Separation system (1) according to claim 19, comprising the centrifuge and / or dynamic crossflow filtration unit (4), the second conduit (2b), the third conduit (2c), and the fourth conduit (2d), and further comprising a collection vessel (8) configured for mixing a feed comprising the reaction products of a depolymerization reaction and a light phase depleted in heterogeneous depolymerization catalyst coming from the centrifuge and / or dynamic crossflow filtration unit (4), wherein said collection vessel (8) has a first inlet (8a) for supplying a feed comprising the reaction products of a depolymerization reaction to the collection vessel (8) via a first part of conduit (2a), a second inlet (8b) for supplying a light phase depleted in heterogeneous depolymerization catalyst to the collection vessel (8) via third conduit (2c), and an outlet (8c) for supplying a combined feed to the cross-flow membrane filtration device (3) via a second part of conduit (2a).

21. Separation system (1) according to claim 19, not comprising the centrifuge and / or dynamic cross-flow filtration unit (4), the second conduit (2b), the third conduit (2c), and the fourth conduit (2d), and further comprising a collection vessel (8) configured for mixing a feed comprising the reaction products of a depolymerization reaction and a retentate coming fromthe cross-flow membrane filtration device (3), wherein said collection vessel (8) has a first inlet (8a) for supplying a feed comprising the reaction products of a depolymerization reaction to the collection vessel (8) via a first part of conduit (2a), a second inlet (8b) for supplying a retentate coming from the cross-flow membrane filtration device (3) to the collection vessel (8) via second conduit (2b), and an outlet (8c) for supplying a combined feed to the cross-flow membrane filtration device (3) via a second part of conduit (2a).

22. Separation system (1) according to any one of claims 19 to 21, comprising the coarse filter unit (5) and further comprising a cooling means (9) downstream of the cross-flow membrane filtration device (3) and upstream of the coarse filter unit (5).

23. Separation system (1) according to any one of claims 19 to 22, further comprising a direct or indirect heating means upstream of the cross-flow membrane filtration device (3).