Process for separating heterogeneous catalyst from depolymerization reaction product

Abstract

The invention relates to a method for separating a heterogeneous depolymerization catalyst from monomers, comprising the steps of: (a) providing a feed comprising the reaction product of a depolymerization reaction, wherein a polycondensate is depolymerized into monomers and oligomers, said feed comprising monomers, oligomers, a carrier liquid and a 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 ratio of monomers to heterogeneous depolymerization catalyst compared to the feed, and the retentate is enriched in heterogeneous depolymerization catalyst and oligomers, wherein no centrifugation step is performed prior to step (b). The invention further relates to a separation system for separating a heterogeneous depolymerization catalyst from monomers.

Description

Technical Field

[0001] The present invention relates to a method for separating heterogeneous depolymerization catalysts from monomers and a separation system for separating heterogeneous depolymerization catalysts from monomers. Background Technology

[0002] It has been recognized that polymer recycling in waste is essential for preventing massive landfill waste and for the efficient use of raw materials. Polymers are used in many applications, such as packaging, building materials, and textiles. Packaging waste, such as plastic bottles, is now collected separately, sorted in a pre-sorting process, and then typically processed into flakes or other pieces of sufficiently small volume. Providing large feed streams containing one or only two types of polymers has become feasible. Specific polymer feed streams can then be supplied to plants for processing into new feedstocks of a specific quality. For condensation polymers, this processing typically involves the use of depolymerization catalysts, such as heterogeneous depolymerization catalysts, to depolymerize them into monomers and oligomers.

[0003] An inherent property of depolymerization catalysts is that they are not consumed during the depolymerization reaction. Since heterogeneous depolymerization catalysts can be quite expensive, it is crucial to recover as much of them as possible. If a heterogeneous depolymerization catalyst cannot be effectively and / or cannot be removed from the reaction products of the depolymerization reaction in high yield, it can be considered at least partially consumed, as a portion of it cannot be reused in subsequent depolymerization reactions and needs to be replenished, which is economically disadvantageous.

[0004] High-purity monomers and oligomers are required for reuse in polymerization. It is well known that any contaminants can affect subsequent polymerization reactions from the feedstock. The quality of the feedstocks, namely monomers and oligomers, obtained from the depolymerization of condensation polymers is known to be strongly dependent on the removal of contaminants already present in the waste. These contaminants typically include colorants and other additives such as fillers and plasticizers. However, any heterogeneous depolymerization catalyst introduced into the depolymerization reactor and retained in the monomers and oligomers is also considered an undesirable impurity.

[0005] Therefore, for at least these two reasons, it is important to be able to isolate heterogeneous depolymerization catalysts with high yields from monomers and oligomers.

[0006] WO2017 / 111602A1 discloses a method for degrading condensation polymers selected from polyesters, polyamides, polyamines, and polyethers in a depolymerization reaction catalyzed by a heterogeneous depolymerization catalyst, wherein a carrier liquid such as alkyl glycol, alkyltriol, glycol, glycerol, or propylene glycol acts as a reactant in the degradation reaction. The depolymerization reaction produces a mixture comprising monomers, oligomers, a carrier liquid, and a heterogeneous depolymerization catalyst. A polar medium, such as water or an aqueous solution, is added to this mixture to obtain a hydrophilic solution comprising monomers and a second phase comprising oligomers and a heterogeneous depolymerization catalyst. The hydrophilic solution is then separated from the second phase using a centrifuge. The addition of the polar medium is described as leading to precipitation of the oligomers. The hydrophilic solution is subsequently treated with an adsorption medium such as activated carbon to remove pigments and dyes. It is further described that the hydrophilic solution can be purified by membrane filtration (e.g., nanofiltration or ultrafiltration) downstream of the centrifugation step to remove any remaining solid (nano) particles, particularly upstream of the adsorption step. The monomers are obtained in a crystallization step downstream of the adsorption step and optionally the membrane filtration step.

[0007] WO2023 / 008997A2 discloses a method for depolymerizing a polymer, the method comprising the steps of: (a) providing a 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 capable of catalyzing the depolymerization in the reaction mixture; (c) depolymerizing the polymer in the reaction mixture under depolymerization reaction conditions to obtain a depolymerized mixture comprising monomers and light oligomers having at least 2 to 4 repeating units; and, after leaving the reactor, removing unreacted polymer, solid particles, and optionally very heavy oligomers having more than 200 repeating units from the depolymerized mixture; (d) recovering at least a portion of the heterogeneous catalyst from the depolymerized mixture; and (e) recovering the monomers and optionally light oligomers from the depolymerized mixture, wherein, during the recovery of the heterogeneous catalyst in step (d), the depolymerized mixture also comprises heavy oligomers having at least 5 repeating units and up to 200 repeating units. The reactor system used in this method includes a first filtration unit, such as a strainer, arranged downstream of the outlet of the depolymerization reactor. This strainer is configured to remove unreacted polymers, 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 2 to 4 repeating units, and heavy oligomers having at least 5 and up to 200 repeating units, remain present in the depolymerized mixture. A heat exchanger is provided downstream of the first filtration unit, or water is added to lower the temperature of the depolymerized mixture, causing the heavy oligomers to precipitate along with a large amount of catalyst. The heavy oligomers, along with the catalyst, can then be removed from the depolymerized mixture by centrifugation, for example, in multiple centrifuges provided in series. A portion of the heterogeneous catalyst can be recycled back to the depolymerization reactor. Maintaining the molecular weight of the heavy oligomers in the depolymerized mixture at at least 5 to up to 200 repeating units during the recovery step (d) allows for improved catalyst reuse.

[0008] While methods disclosed in the prior art can be used to recover heterogeneous depolymerization catalysts to a satisfactory extent in small-scale processes, the ability to recover large quantities of heterogeneous depolymerization catalysts in industrial-scale processes remains an important objective. The inventors have discovered that the capacity of prior art separation methods can only be increased by increasing the number of centrifuge units connected in parallel. As those skilled in the art will understand, a greater number of processing units increases operating and maintenance costs.

[0009] Therefore, one object of the present invention is to provide an improved method for separating heterogeneous depolymerization catalysts from monomers present in the reaction products of the depolymerization reaction of condensation polymers.

[0010] Another object of the present invention is to provide a method for separating heterogeneous depolymerization catalysts from said monomers, wherein the heterogeneous depolymerization catalysts are separated in a more efficient manner and / or in a higher yield, while maintaining the catalytic activity of the recovered heterogeneous depolymerization catalysts.

[0011] Another object of the present invention is to provide a more efficient method for separating heterogeneous depolymerization catalysts from said monomers, which can be carried out on an industrial scale with reasonable capital expenditures (CapEx) and operational expenditures (OpEx).

[0012] Another object of the present invention is to provide a corresponding separation system for separating heterogeneous depolymerization catalysts from monomers present in the reaction products of the depolymerization reaction of condensation polymers. Summary of the Invention

[0013] The inventors have discovered that one or more objectives can be achieved by subjecting a feed containing reaction products from a depolymerization reaction to cross-flow membrane filtration, wherein the condensation polymer is depolymerized into monomers and oligomers, the feed comprising monomers, oligomers, a carrier liquid, and a heterogeneous depolymerization catalyst, and then subjecting the resulting retentate to a centrifugation step if the resulting retentate is deemed necessary to undergo centrifugation. It has been found that cross-flow membrane filtration can be used to efficiently and in high yield separate the heterogeneous depolymerization catalyst from the monomers. Furthermore, using cross-flow membrane filtration, the feed can be concentrated into a retentate with a high volumetric concentration factor (VCF), meaning that the amount of retentate to be processed downstream, for example, by centrifugation, is considerably limited, and fewer processing units are required on an industrial scale than without cross-flow membrane filtration.

[0014] Therefore, in a first aspect, a method for separating heterogeneous depolymerization catalysts from monomers is provided, the method comprising the following steps: (a) Providing a feed comprising reaction products of a depolymerization reaction, wherein the condensation polymer is depolymerized into monomers and oligomers, said feed comprising monomers, oligomers, a carrier liquid, and a heterogeneous depolymerization catalyst; and (b) The feed from step (a) is subjected to cross-flow membrane filtration to obtain permeate and retentate, wherein the permeate has an increased monomer to heterogeneous depolymerization catalyst ratio compared to the feed, and the retentate is rich in heterogeneous depolymerization catalyst and oligomers. No centrifugation step is performed before step (b).

[0015] In a second aspect, a separation system (1) is provided for separating heterogeneous depolymerization catalysts from monomers, the separation system (1) comprising: (i) A first conduit (2a) configured to supply a feed comprising reaction products of a depolymerization reaction, wherein the condensation polymer is depolymerized, the feed comprising monomers, oligomers, a carrier liquid and a heterogeneous depolymerization catalyst; (ii) A cross-flow membrane filtration device (3) configured to separate the feed into a permeate having an increased ratio of monomers to heterogeneous depolymerization catalyst compared to the feed, and a retentate rich in heterogeneous depolymerization catalyst and oligomers, the cross-flow membrane filtration device (3) having an inlet (3a) for the feed, a first outlet (3b) for the retentate, a second outlet (3c) for the permeate, and a second conduit (2b) configured to discharge the retentate from the first outlet (3b); (iii) An optional centrifuge and / or dynamic cross-flow filtration unit (4) configured to separate the retentate into a light phase that is depleted of heterogeneous depolymerization catalyst compared to the retentate and a heavy phase that is rich in heterogeneous depolymerization catalyst and oligomers, the optional centrifuge and / or dynamic cross-flow filtration unit (4) having an inlet (4a) for the retentate, a first outlet (4b) for the heavy phase and a second outlet (4c) for the light phase, a second conduit (2b) configured to supply the retentate from the first outlet (3b) of the cross-flow membrane filtration device (3) to the inlet (4a) of the centrifuge and / or dynamic cross-flow filtration unit (4), a third conduit (2c) for discharging the light phase from the centrifuge and / or dynamic cross-flow filtration unit (4) via the second outlet (4c), and a fourth conduit (2d) for discharging the heavy phase from the centrifuge and / or dynamic cross-flow filtration unit (4) via the first outlet (4b); (iv) Optionally, a coarse filter unit (5) downstream of the cross-flow membrane filter (3) having an inlet (5a) and an outlet (5b), and a fifth conduit (2e) configured to supply permeate from the second outlet (3c) of the cross-flow membrane filter (3) to the inlet (5a) of the coarse filter unit (5). (v) The adsorption tower (6) downstream of the cross-flow membrane filtration device (3) and the optional coarse filter unit (5) has an inlet (6a) and an outlet (6b); (vi) A crystallization container (7) downstream of the adsorption tower (6), having an inlet (7a) and an outlet (7b); and (vii) The sixth conduit (2f), when a coarse filter unit (5) is present, is configured to supply permeate from the outlet (5b) of the coarse filter unit (5) to the inlet (6a) of the adsorption tower (6); or The sixth conduit (2f), when the coarse filter unit (5) is absent, is configured to supply permeate from the second outlet (3c) of the cross-flow membrane filter (3) to the inlet (6a) of the adsorption tower (6); and (viii) A seventh conduit (2g) is configured to supply permeate from the outlet (6b) of the adsorption tower (6) to the inlet (7a) of the crystallization container (7).

[0016] definition

[0017] As used in this article, the term " Heterogeneous catalysts "and" Heterogeneous depolymerization catalyst "They are interchangeable and involve catalysts in solid particulate form. Heterogeneous catalysts are catalysts that catalyze the depolymerization of condensation polymers."

[0018] In the context of this application, a monomer is defined as a molecule containing one repeating unit of a polymer, while an oligomer includes molecules containing at least two repeating units, such as dimers, trimers, and tetramers. Attached Figure Description

[0019] Figure 1 A flowchart illustrating the method according to the present invention is provided. Figures 2 to 11 A flowchart illustrating an embodiment of the method according to the present invention is provided.

[0020] Figure 7 A separation system according to the present invention is described. Figures 8 to 11 Embodiments of the separation system of the present invention are further described.

[0021] Figure 12 , Figure 13 and Figure 15 Experimental results for membrane rejection rate and volumetric concentration factor (VCF) are shown.

[0022] Figure 14 Experimental results on flux on different membranes are shown. Detailed Implementation

[0023] Methods for separating heterogeneous catalysts from monomers

[0024] In a first aspect, the present invention relates to a method for separating heterogeneous depolymerization catalysts from monomers, the method comprising the steps of: (a) Providing a feed comprising reaction products of a depolymerization reaction, wherein the condensation polymer is depolymerized into monomers and oligomers, said feed comprising monomers, oligomers, a carrier liquid, and a heterogeneous depolymerization catalyst; and (b) The feed from step (a) is subjected to cross-flow membrane filtration to obtain permeate and retentate, wherein the permeate has an increased monomer to heterogeneous depolymerization catalyst ratio compared to the feed, and the retentate is rich in heterogeneous depolymerization catalyst and oligomers. No centrifugation step is performed before step (b).

[0025] See Figure 1 A flowchart of the first aspect of the method includes a feed of the depolymerization reaction product being supplied via inlet (3a) to a cross-flow membrane filtration unit (3) and subjected to cross-flow membrane filtration to obtain a permeate with an increased ratio of monomer to heterogeneous depolymerization catalyst exiting the cross-flow membrane filtration unit (3) via outlet (3c) and a retentate rich in heterogeneous depolymerization catalyst and oligomers exiting the cross-flow membrane filtration unit (3) via outlet (3b).

[0026] The retentate obtained in step (b) typically still contains some monomers and heterogeneous depolymerization catalyst. Improved overall separation of monomers and heterogeneous depolymerization catalyst can be achieved by recycling the retentate to the cross-flow membrane filtration step (b).

[0027] Therefore, in a preferred embodiment, the method according to the first aspect includes the following steps: (a) Providing a feed comprising reaction products of a depolymerization reaction, wherein the condensation polymer is depolymerized into monomers and oligomers, said feed comprising monomers, oligomers, a carrier liquid, and a heterogeneous depolymerization catalyst; and (b) The feed from step (a) is subjected to cross-flow membrane filtration to obtain permeate and retentate, wherein the permeate has an increased monomer to heterogeneous depolymerization catalyst ratio compared to the feed, and the retentate is rich in heterogeneous depolymerization catalyst and oligomers, and the retentate is subjected to cross-flow membrane filtration again. No centrifugation step is performed before step (b).

[0028] Some of the retentate obtained in step (b) can be continuously removed from the process and can be recycled, for example, to the depolymerization reactor, or all of the retentate obtained in step (b) can be recycled to the depolymerization reactor after a period of time.

[0029] See Figure 2 A flowchart of an implementation of the first aspect of the method, wherein the retentate is recycled and subjected to cross-flow membrane filtration again. For example... Figure 2 As shown, some of the retentate obtained in step (b) can be continuously removed from the process and can be recycled, for example, to the depolymerization reactor, or all of the retentate obtained in step (b) can be recycled to the depolymerization reactor via a portion of the conduit (2b) after a period of time.

[0030] The cross-flow membrane filtration step (b) separates monomers from the heterogeneous depolymerization catalyst and oligomers. Typically, monomers can permeate the membrane and terminate in the permeate, while oligomers and heterogeneous depolymerization catalyst do not permeate the membrane and remain in the retentate. However, as those skilled in the art will understand, some oligomers and trace amounts of heterogeneous depolymerization catalyst can permeate the membrane and monomers can remain in the retentate. A larger portion of the carrier liquid permeates the membrane into the permeate, while a smaller portion remains in the retentate. Therefore, compared to the feed, the retentate is not only rich in heterogeneous depolymerization catalyst and oligomers but also has a reduced monomer to heterogeneous depolymerization catalyst ratio. Furthermore, the retentate is more concentrated than the feed. Similarly, compared to the feed, the permeate not only has an increased monomer to heterogeneous depolymerization catalyst ratio but is also leaner in heterogeneous depolymerization catalyst and oligomers.

[0031] The method described in the first aspect can be carried out in batches or continuously.

[0032] As those skilled in the art will understand, the method can be carried out in batches by first subjecting the feed provided in step (a) to cross-flow membrane filtration and then subjecting the collected retentate to cross-flow membrane filtration for a certain period of time or until a certain volume concentration factor is obtained.

[0033] Alternatively, the method can be carried out continuously by continuously supplying the feed from step (a) and continuously adding the retentate obtained in step (b) to the feed to provide a combined feed continuously subjected to cross-flow membrane filtration. In this embodiment, a portion of the retentate obtained in step (b) is continuously removed from the process and may be recycled, for example, to the depolymerization reactor. Those skilled in the art will understand that in this embodiment, the volumetric flow rate of the feed provided in step (a) is equal to the sum of the volumetric flow rate of the permeate passing through the membrane and a portion of the retentate obtained in step (b) that is continuously removed from the process.

[0034] In one embodiment, the method according to the first aspect includes a further step (c): subjecting the retentate from step (b) to centrifugation and / or dynamic cross-flow filtration to obtain a heavy phase and a light phase, wherein the heavy phase is rich in heterogeneous depolymerization catalyst and oligomers compared to the retentate, and the light phase is poor in heterogeneous depolymerization catalyst.

[0035] Dynamic cross-flow filtration is carried out in a membrane cross-flow unit equipped with a rotating element that generates additional turbulence on the retentate side. This helps to achieve a high solids content in the retentate phase and thus a higher volumetric concentration factor for the feed stream.

[0036] If the volumetric concentration factor (VCF) achievable in the cross-flow filtration step (b) is too low to make the method economically infeasible, then step (c) is preferred. If the VCF achievable in the cross-flow filtration step (b) is too low, too much monomer is lost and / or too much monomer is recycled back to the depolymerization step, resulting in an undesirable shift in the equilibrium of the depolymerization reaction and a reduction in conversion.

[0037] exist Figure 3 In this process, the retentate obtained in step (b) is fed into a centrifugal and / or dynamic cross-flow filtration unit (4) via a conduit (2b) and an inlet (4a), wherein the retentate is separated into a light phase of a catalyst-poor heterogeneous depolymerization catalyst leaving the unit (4) via an outlet (4c) and a heavy phase of a catalyst-poor heterogeneous depolymerization catalyst and oligomers leaving the unit (4) via an outlet (4b).

[0038] The heavy phase, rich in heterogeneous depolymerization catalyst and oligomers, typically also contains undesirable impurities that were present during or formed during the depolymerization reaction. To enable the recycling of the heterogeneous depolymerization catalyst, oligomers, and / or one or more carrier liquids to the depolymerization reactor, the heavy phase can be subjected to a separation process in which the components are separated. Therefore, the method according to the first aspect can further include a separation step downstream of a centrifuge and / or dynamic cross-flow filtration unit, wherein the heavy phase is separated into one or more fractions.

[0039] The light phase obtained in step (c) typically still contains some monomers, oligomers, and heterogeneous depolymerization catalyst. Improved overall separation of monomers and heterogeneous depolymerization catalyst can be achieved by recycling the light phase to the cross-flow membrane filtration step (b). Since the light phase primarily contains the carrier liquid, mixing the light phase with the feed containing the reaction products of the depolymerization reaction in step (a) before supplying the combined feed to the cross-flow membrane filtration step is effectively equivalent to applying the cross-flow membrane filtration step (b) in percolation mode.

[0040] Therefore, in a preferred embodiment, the method according to the first aspect includes the following steps: (a) Providing a feed comprising reaction products of a depolymerization reaction, wherein the condensation polymer is depolymerized into monomers and oligomers, said feed comprising monomers, oligomers, a carrier liquid, and a heterogeneous depolymerization catalyst; (b) The feed from step (a) is subjected to cross-flow membrane filtration to obtain permeate and retentate, wherein the permeate has an increased monomer to heterogeneous depolymerization catalyst ratio compared to the feed, and the retentate is rich in heterogeneous depolymerization catalyst and oligomers; and (c) subjecting the residue from step (b) to centrifugation and / or dynamic cross-flow filtration to obtain a heavy phase and a light phase, wherein the heavy phase is rich in the heterogeneous depolymerization catalyst and the oligomers compared to the residue, and the light phase is poor in the heterogeneous depolymerization catalyst, and subjecting the light phase to cross-flow membrane filtration again. No centrifugation step is performed before step (b).

[0041] As those skilled in the art will understand, in embodiments including step (c), ' Before step (b) No centrifugation step The expression ' means that the feed provided in step (a) has not been centrifuged before step (b). This does not preclude any light phase provided in step (c) from subsequently undergoing cross-flow membrane filtration.

[0042] As those skilled in the art will further understand, the method can be carried out in batches 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 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 volume concentration factor is obtained.

[0043] Alternatively, the method can be carried out continuously by continuously supplying the feed from step (a) and continuously adding the light phase obtained in step (c) to the feed to provide a combined feed that continuously undergoes cross-flow membrane filtration followed by centrifugation and / or dynamic cross-flow filtration. Those skilled in the art will understand that, in this embodiment, the volumetric flow rate of the feed provided in step (a) is equal to the combined volumetric flow rate of the permeate passing through the membrane and the heavy phase formed in step (c).

[0044] See Figure 4 A flowchart of an implementation of the first aspect of the method, wherein the light phase obtained in step (c) is recycled to the cross-flow membrane filtration unit (3).

[0045] In a preferred embodiment, the method according to the first aspect is performed as an intermittent process, which includes: (a) Providing a batch of feed containing the reaction products of the depolymerization reaction and supplying the batch of feed to a collection container, continuously supplying the retentate obtained in step (b) to the collection container, and mixing the feed and retentate in the collection container to obtain a combined feed; and (b) The combined feed stream is continuously discharged from a collection container, e.g., until a specific VCF is reached, and the combined feed stream is continuously subjected to cross-flow membrane filtration to obtain permeate and retentate, wherein the permeate has an increased monomer to heterogeneous depolymerization catalyst ratio compared to the combined feed, and the retentate is rich in heterogeneous depolymerization catalyst and oligomers, and the retentate is supplied to the collection container. No centrifugation step is performed before step (b).

[0046] Some of the retentate obtained in step (b) can be continuously removed from the process and can be recycled, for example, to the depolymerization reactor, or all of the retentate obtained in step (b) can be recycled to the depolymerization reactor after a period of time.

[0047] In another preferred embodiment, the method according to the first aspect is carried out as an intermittent process, which includes: (a) Provide a batch of feed containing the reaction products of the depolymerization reaction and supply the batch of feed to a collection container, continuously supply the light phase obtained in step (c) to the collection container, and mix the feed and the light phase in the collection container to obtain a combined feed; (b) The combined feed stream is continuously discharged from a collection container, e.g., until a specific VCF is reached, and the combined feed stream is continuously subjected to cross-flow membrane filtration to obtain permeate and retentate, wherein the permeate has an increased monomer to heterogeneous depolymerization catalyst ratio compared to the combined feed, and the retentate is rich in heterogeneous depolymerization catalyst and oligomers; and (c) subjecting the retentate from step (b) to centrifugation and / or dynamic cross-flow filtration to obtain a heavy phase and a light phase, wherein the heavy phase is rich in the heterogeneous depolymerization catalyst and the oligomers compared to the retentate, and the light phase is lean towards the heterogeneous depolymerization catalyst, and the light phase is supplied to a collection container. No centrifugation step is performed before step (b).

[0048] As those skilled in the art will understand, at the start of this batch process, no retentate or light phase is available, meaning the collection container contains only the feed batch including the reaction products of the depolymerization reaction. If some cross-flow membrane filtration has occurred and the resulting retentate has optionally undergone centrifugation and / or dynamic cross-flow filtration steps, the resulting retentate and optional light phase are recycled to the collection container, where they are mixed with the remainder of the existing feed batch to form a combined feed. The stream of this combined feed is continuously discharged from the collection container and subjected to cross-flow membrane filtration, with any retentate / light phase formed continuously recycled back to the collection container.

[0049] In a more preferred embodiment, the method according to the first aspect is performed as a continuous process, the method comprising: (a) A continuous feed stream containing the reaction products of the depolymerization reaction is provided and the feed stream is continuously supplied to a collection container, the retentate obtained in step (b) is continuously supplied to the collection container, and the feed and retentate are mixed in the collection container to obtain a combined feed; (b) The combined feed stream is continuously discharged from the collection container and continuously subjected to cross-flow membrane filtration to obtain permeate and retentate, wherein the permeate has an increased monomer to heterogeneous depolymerization catalyst ratio compared to the combined feed, and the retentate is rich in heterogeneous depolymerization catalyst and oligomers, and the retentate is continuously supplied to the collection container. A portion of the retentate is continuously or after regular time intervals of removal from the process, and is recycled, for example, to the depolymerization reactor, wherein no centrifugation step is performed prior to step (b).

[0050] As those skilled in the art will understand, at some point in time, membrane cleaning, such as in-situ cleaning, is required to remove fouling from the membrane.

[0051] In another, more preferred embodiment, the method according to the first aspect is carried out as a continuous process, the method comprising: (a) A feed stream containing the reaction products of the depolymerization reaction is continuously supplied and the feed stream is continuously supplied to a collection container, the light phase obtained in step (c) is continuously supplied to the collection container, and the feed and the light phase are mixed in the collection container to obtain a combined feed; (b) The combined feed stream is continuously discharged from a collection container and continuously subjected to cross-flow membrane filtration to obtain permeate and retentate, wherein the permeate has an increased monomer to heterogeneous depolymerization catalyst ratio compared to the combined feed, and the retentate is rich in heterogeneous depolymerization catalyst and oligomers; and (c) The residue from step (b) is continuously subjected to centrifugation and / or dynamic cross-flow filtration to obtain a heavy phase and a light phase, wherein the heavy phase is rich in the heterogeneous depolymerization catalyst and the oligomers compared to the residue, and the light phase is lean towards the heterogeneous depolymerization catalyst, and the light phase is continuously supplied to a collection container. No centrifugation step is performed before step (b).

[0052] As those skilled in the art will understand, at the start of this continuous process, no retentate / light phase is available, meaning the collection container contains only the feed including the reaction products of the depolymerization reaction. If some cross-flow membrane filtration has occurred and a retentate / light phase has formed, the formed retentate / light phase is recycled back to the collection container, where it is mixed with the existing feed that is continuously supplied with fresh feed to form a combined feed. The combined feed stream is continuously discharged from the collection container and subjected to cross-flow membrane filtration, with any retentate / light phase formed continuously recycled back to the collection container.

[0053] In one embodiment, the collection container is provided with a direct or indirect heating device, preferably with a heat exchanger, thereby maintaining the temperature of the combined feed within a certain range to retain monomers in solution or disperse molecules in a carrier liquid when cross-flow membrane filtration is applied.

[0054] In a preferred embodiment, the collection container is provided with means for agitating the contents, for example, to obtain a homogeneous mixture.

[0055] See Figure 5 and Figure 6 According to the implementation of the method of the first aspect, combined feed is obtained in a collection container (8) equipped with a stirring device (8d) and a heat exchanger (8e).

[0056] In one embodiment, the method according to the first aspect further includes the step of subjecting the permeate having an increased ratio of monomer to heterogeneous depolymerization catalyst to adsorption treatment downstream of the cross-flow membrane filtration step (b), for example, with activated carbon adsorption, to remove, for example, pigments and dyes.

[0057] Preferably, the oligomers do not pass through the membrane during the cross-flow membrane filtration step and remain in the retentate. However, if too many oligomers pass through the membrane during the cross-flow membrane filtration step, these oligomers may cause premature clogging of the downstream adsorption tower. Therefore, in some embodiments, a coarse filtration step is applied between the cross-flow membrane filtration step and the adsorption treatment to filter out the oligomers. As used herein, the term " Coarse filtration step "This involves a filtration step with a filter having a larger pore size than the membrane used in the cross-flow membrane filtration step (b). In order to improve the filtration of oligomers, it may be necessary to slightly cool the permeate, for example, by using a heat exchanger, causing the oligomers to settle before the permeate enters the coarse filtration step. The coarse filtration step can be carried out, for example, with a depth filter or with membrane filtration, preferably with a depth filter such as a candle filter."

[0058] Therefore, in some embodiments, the method according to the first aspect further includes the following steps: cooling the permeate from the cross-flow membrane filtration step (b) to precipitate oligomers, followed by a coarse filtration step to filter out the oligomers and subject the filtered permeate to adsorption treatment. As those skilled in the art will understand, the cooling step should only precipitate oligomers, while the monomers should remain in solution or be molecularly dispersed in the permeate.

[0059] In one embodiment, the method according to the first aspect further includes the step of: subjecting the monomer in the permeate leaving the adsorption step to crystallization to obtain crystalline monomer.

[0060] Figures 7-9 A flowchart of an embodiment of the method of the first aspect is shown, wherein the permeate leaving the cross-flow membrane filtration step in unit (3) is subsequently subjected to adsorption treatment in unit (6) and crystallization in unit (7).

[0061] Figure 10 and Figure 11 A flowchart of an implementation of the method of the first aspect is shown, wherein the permeate leaving the cross-flow membrane filtration step in unit (3) is subsequently cooled in heat exchanger (9), subjected to coarse filtration in unit (5), subjected to adsorption treatment in unit (6), and subjected to crystallization in unit (7).

[0062] In one embodiment, the method according to the first aspect includes a coarse filtration step, such as using a strainer, filter basket, sieve bend and / or filter bag prior to step (b) to remove solids, such as metals, glass and unreacted condensate particles, from the feed containing the reaction products of the depolymerization reaction provided in step (a).

[0063] Feed containing reaction products of depolymerization reaction

[0064] In step (a) of the method of the first aspect, a feed comprising the reaction products of the depolymerization reaction is provided. Specifically, in the depolymerization reaction, the condensation polymer is depolymerized into monomers and oligomers. The feed comprises monomers, oligomers, a carrier liquid, and a heterogeneous depolymerization catalyst. Therefore, the heterogeneous depolymerization catalyst is a heterogeneous catalyst that catalyzes the depolymerization of condensation polymers into monomers and oligomers.

[0065] Condensation polymers can be selected from natural polymers, bio-based polymers, biodegradable polymers, polymers formed directly or indirectly from fossil fuels, and combinations thereof.

[0066] In a preferred embodiment, the feed comprises the reaction products of the depolymerization reaction, wherein the condensate is depolymerized, the condensate being selected from polyesters, polycarbonates, polyamides, polyurethanes, polyethers, and combinations thereof, wherein the polyethers also include starch and cellulose-based polymers.

[0067] In a more preferred embodiment, the feed comprises the reaction product of the depolymerization reaction, wherein the condensate is depolymerized, said condensate being selected from polyesters; polyethers, such as polyoxymethylene (POM), polyethylene glycol (PEG), polypropylene glycol (PPG), polytetramethylene glycol (PTMG), polytetrahydrofuran (PTHF), and polytetramethylene ether glycol (PTMEG); peptides, polyamides; and polyamines.

[0068] In even more preferred embodiments, the feed comprises the reaction product of the depolymerization reaction, wherein the depolymerized condensate is a polyester selected from polyethylene terephthalate (PET), polyethylene furanate (PEF), polybutylene terephthalate (PBT), polypropylene terephthalate (PTT), polyglycolic acid (PGA), polylactic acid (PLA), polycaprolactone (PCL), polyethylene adipate (PEA), polyhydroxyalkanoate (PHA), polyhydroxybutyrate (PHB), polyethylene naphthalate (PEN), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), condensate of 4-hydroxybenzoic acid and 6-hydroxynaphthalene-2-carboxylic acid (VECTRAN), and combinations thereof.

[0069] Most preferably, the feed contains the reaction products of the depolymerization reaction, wherein the depolymerized condensate is polyethylene terephthalate (PET). As is known in the art, PET may include other comonomers, such as isophthalic acid, diethylene glycol (DEG), polyethylene naphthalate (PEN), and cyclohexanediol (CHDM), to improve its properties.

[0070] Depolymerization reactions typically occur in reactive solvents. This reactive solvent can be water, leading to the hydrolysis of the condensate. Depolymerization of condensates in reactive solvents other than water is referred to as solvent depolymerization. Reactive solvents are typically chosen for use with the condensate and / or for use with the monomers and oligomers obtained from said condensate via depolymerization. Such reactive solvents are known to those skilled in the art. In the context of this invention, the term 'reactive solvent' also encompasses mixtures of solvents that are reactive themselves and non-reactive solvents. Depolymerization of polyesters via solvent depolymerization typically occurs in alkanols, alkyl glycols, alkyltriols, or combinations thereof. For the depolymerization of PET, ethylene glycol is used as the reactive solvent. Glycolysis The depolymerization process results in bis(2-hydroxyethyl) terephthalate (BHET) as the major depolymerization product. Dimers, trimers, and other oligomers are also typically obtained. For the depolymerization of PET, using methanol as a reactive solvent results in the formation of ethylene glycol and dimethyl terephthalate (DMT) as the major depolymerization products.

[0071] As those skilled in the art will understand, any reactive solvent remaining after the depolymerization reaction and any solvent formed during the depolymerization reaction, such as ethylene glycol during methanol decomposition, form a carrier liquid in the feed containing the reaction products of the depolymerization reaction as provided in step (a) of the method according to the first aspect. However, this does not mean that the carrier liquid in the feed containing the reaction products of the depolymerization reaction provided in step (a) can only contain liquids already present during the depolymerization reaction. As explained, for example, in WO2023 / 008997A2, water can be added to the depolymerization reaction mixture containing ethylene glycol as a reactive solvent to improve the downstream separation of the heterogeneous depolymerization catalyst from the monomers and oligomers.

[0072] In one embodiment, the carrier fluid comprises water, alkanols, alkyldiols, alkyltriols, 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 combinations thereof. Ethylene glycol has been found to be suitable due to its physical properties.

[0073] In a preferred embodiment, the carrier liquid comprises ethylene glycol and water, wherein the weight ratio of ethylene glycol to water is preferably 90:10 to 10:90, more preferably 70:30 to 30:70, and even more preferably 65:35 to 35:65.

[0074] In another preferred embodiment, the carrier liquid comprises ethylene glycol and less than 10% by weight of water based on the total weight of water and ethylene glycol, more preferably less than 5% by weight, for example less than 2.5% by weight, less than 1% by weight, or less than 0.5% by weight of water.

[0075] In a preferred embodiment, the feed containing the reaction product of the depolymerization reaction provided in step (a) is generated by the depolymerization of PET, the monomer is BHET, and the carrier liquid contains ethylene glycol and water, wherein the weight ratio of ethylene glycol to water is preferably 90:10 to 10:90, more preferably 70:30 to 30:70, and even more preferably 65:35 to 35:65.

[0076] In another preferred embodiment, the feed containing the reaction product of the depolymerization reaction provided in step (a) is generated by the depolymerization of PET, the monomer is BHET, and the carrier liquid contains ethylene glycol and water based on the total weight of water and ethylene glycol less than 10% by weight, more preferably less than 5% by weight, for example less than 2.5% by weight, less than 1% by weight, or less than 0.5% by weight.

[0077] In a preferred embodiment, the weight ratio of monomers and oligomers to carrier liquid in the feed containing the reaction products of the depolymerization reaction provided in step (a) is 20:10 to 100:10, more preferably 40:10 to 90:10.

[0078] In a preferred embodiment, the weight ratio of the heterogeneous depolymerization catalyst to the monomer and oligomer in the feed containing the reaction product of the depolymerization reaction provided in step (a) is 0.001:10 to 1:10, more preferably 0.005:10 to 0.3:10, and even more preferably 0.008:10 to 0.015:10.

[0079] Depolymerization catalysts used for the depolymerization of condensation polymers are well known in the art. In this regard, see S. Thiyagarajan et al., RSC Adv. , 2022, 12, pp 947-970 (DOI: 10.1039 / d1ra08217e), the entire contents of which are incorporated herein by reference.

[0080] Preferred heterogeneous depolymerization catalysts are selected from metal particles and their oxides, solid metal salts, optionally functionalized magnetic particles, alkaline earth metal-based particles, and hydrotalcite.

[0081] Examples of magnetic particles include particles based on ferromagnetic materials, subferromagnetic materials, antiferromagnetic materials, synthetic magnetic materials, paramagnetic materials, superparamagnetic materials, and combinations thereof.

[0082] In a preferred embodiment, the heterogeneous depolymerization catalyst comprises transition metal particles, such as particles of transition metals selected from the first series of transition metals (also known as 3d orbital transition metals), more preferably transition metals selected from iron, nickel, cobalt and combinations thereof, and even more preferably transition metals selected from iron, nickel and combinations thereof.

[0083] In a highly preferred embodiment, the heterogeneous depolymerization catalyst comprises iron-containing particles.

[0084] When heterogeneous depolymerization catalysts are made of metal, an oxide surface can be provided to further enhance the catalytic effect. The oxide surface can form spontaneously, be in contact with air or water, or can be intentionally applied.

[0085] In another embodiment, the heterogeneous depolymerization catalyst comprises alkaline earth metal particles, such as particles of alkaline earth metals selected from beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), their oxides, and combinations thereof. A preferred alkaline earth metal oxide is magnesium oxide (MgO).

[0086] In yet another embodiment, the heterogeneous depolymerization catalyst comprises (non-magnetic) metal particles and their oxides, such as particles of metals selected from titanium (Ti), zirconium (Zr), manganese (Mn), zinc (Zn), aluminum (Al), germanium (Ge), antimony (Sb), their oxides, and combinations thereof.

[0087] Heterogeneous depolymerization catalysts are essentially insoluble in the carrier liquid, even at temperatures above 100°C.

[0088] The heterogeneous depolymerization catalyst preferably has an average particle size of 5 nm to 200 μm, more preferably 10 nm to 5 μm, even more preferably 25 nm to 500 nm, and even more preferably 30 nm to 450 nm.

[0089] When present in heterogeneous depolymerization catalysts, the term ' Particles This includes individual particles and their aggregates and clusters. Therefore, the average particle size, as defined herein, refers to the average size of individual particles and their aggregates and clusters (if present).

[0090] In the size range of 5 nm to 1 μm, the average particle size is measured by dynamic light scattering (DLS), for example using a Malvern DLS device, such as the NS500 series. The average particle size is then expressed as the Z-mean diameter (an intensity-weighted average hydrodynamic size obtained from the cumulative analysis of the correlation curve). Since particles larger than a few micrometers no longer exhibit Brownian motion, they can no longer be measured by DLS. Therefore, in the size range of 1 μm to 200 μm, the average particle size is measured by laser diffraction, for example using a Malvern Mastersizer series device. The particle size is then expressed as the median particle size (D). 50 (From the volume size distribution derived from the Mie or Fraunhofer approximation).

[0091] In a highly preferred embodiment, the heterogeneous depolymerization catalyst comprises functionalized magnetic particles containing a catalyst complex (ABC). The functionalized magnetic particles have an average particle size of 25 to 500 nm, more preferably 30 to 450 nm, as measured by DLS. The catalyst complex comprises three distinguishable elements: (nano)particles (A); bridging portions / linking groups (B), which are chemically linked to the particles (A) via, for example, covalent bonds or, for example, adsorption; and a catalyst entity (C) associated with the particles (A), for example, via chemical bonding, such as covalent bonding, to the linking groups. The linking groups preferably do not completely cover the surface of the (nano)particles, for example, in core-shell particles. The (nano)particles of the catalyst complex are preferably based on ferromagnetic and / or ferrimagnetic materials. Antiferromagnetic materials, synthetic magnetic materials, paramagnetic materials, and superparamagnetic materials can also be used, such as materials including at least one of Fe, Co, Ni, Gd, Dy, Mn, Nd, and Sm, preferably materials including at least one of O, B, C, and N, such as iron oxide, ferrite, magnetite, hematite, and maghematite.

[0092] The functional group of the bridging moiety (B) is, for example, a weak organic acid, such as a carboxylic acid or dicarboxylic acid, but preferably a silanol, including silanediols and silanetriols. The bridging moiety can be introduced as a reactant in the form of a silyl group, such as a silyl ether, for example, a triethoxysilylpropyl halide. The linking group is, for example, an alkylene chain, typically at C2 and C3. 10 The components are preferably C3-C5, i.e., propylene, butene, and pentene. Propylene is preferred. The bridging portion is suitably provided as a reactant, wherein the linking group is functionalized to react chemically with the catalyst entity, and the functional group can be protected. For example, suitable functionalization of the linking group is a substituted alkyl halide. Suitable protection of the functional group can be in the form of an ester or an alkoxysilane. The alkoxy group is preferably ethoxy, although methoxy or propoxy is not excluded.

[0093] In one embodiment, the alkoxysilane is provided as a trialkoxysilane having an alkylene group constituting a linking group. In an alternative embodiment, a dialkyl-dialkoxysilane is used, wherein one of its alkyl groups is a linking group. In another embodiment, a monoalkoxy-trialkylsilane is used, wherein one of its alkyl groups is a linking group. In the latter case, the alkyl group is preferably a lower alkyl group, such as a C1-C4 alkyl group, and thus methyl, ethyl, propyl, n-butyl, and isobutyl. At least one alkyl group is then functionalized, for example, with a halogen as described above. Straight-chain alkyl groups appear to be preferred to limit steric hindrance.

[0094] When the carrier liquid contains ethylene glycol and water, the use of dialkyl-dialkoxysilanes and / or monoalkoxy-trialkylsilanes is understood to favor better separation. It is thought that not all alkoxy groups in a trialkoxysilane are bonded to the surface of the nanoparticle aggregates. Some alkoxy groups may even remain protected. However, the protecting groups can be removed when water is added to the complex. As a result, the hydrophilicity of the complex can increase. By using a silane with fewer alkoxy groups, the remaining groups are inherently nonpolar and cannot become unprotected. Therefore, the entire complex becomes more hydrophobic. Not only the bridging portion (B), also known as a silane coupling agent, can be used, but mixtures such as those of alkyltrialkoxysilanes and dialkyl-dialkoxysilanes can be used, where one of the alkyl groups is functionalized to a halide to react with the catalytic entity and subsequently carries the catalytic entity after the reaction of both. The addition of dialkyldialkoxysilanes effectively reduces the size of the layer of groups bound to the surface. This is not considered a disadvantage.

[0095] The catalyst entity (C) can be aromatic or aliphatic and heterocyclic. The aromatic heterocyclic moiety suitably comprises a heterocycle having at least one, preferably at least two, nitrogen atoms. The heterocycle can have 5 or 6 atoms, preferably 5. Suitable aromatic heterocycles are pyrimidines, imidazoles, piperidines, pyrrolidines, pyridines, pyrazoles, oxazoles, triazoles, thiazoles, methimazoles, benzotriazoles, isoquinolines, and viologen-type compounds (having, for example, two coupled pyridine ring structures). Imidazole structures are particularly preferred, which generate imidazole-onium ions. The negatively charged moiety may involve anionic complexes, but alternatively may involve simple ions, such as halide ions. Preferably, the reaction of the alkyl halide of the bridging moiety with the uncharged aromatic heterocyclic moiety comprising at least one nitrogen atom generates a positive charge on the aromatic moiety, particularly on the nitrogen atom therein, and generates an anionic halide ion. The negatively charged halide ion can then be reinforced by adding a Lewis acid to form a metal salt complex. An example is the conversion of chlorine to FeCl₂. 4- The aromatic portion has at least one tail in one example. The at least one tail preferably has C1-C... 10 The length of the tail, for example, the length of C2-C4, is such that at least one tail is suitably attached to a nitrogen atom. More specifically, this tail extends into the carrier liquid and away from the bridging portion. A longer tail is considered advantageous for increasing the hydrophobicity of the complex. This counteracts the tendency of the complex to enter the hydrophilic phase.

[0096] The bridging portion (B) and the catalyst entity (C) bonded thereto are preferably in a ratio of (moles of bridging portion / grams of magnetic particles) 5. 10 -6 It exists in amounts up to 0.1, more preferably in amounts of 1. 10 -5 It exists in amounts up to 0.01, or even more preferably in amounts of 2. 10 -5 Up to 10 -3 The quantity exists, for example, in 4 10 -5 Up to 10 -4 The amount present. For the efficient and optional recovery of the catalyst complex, a relatively large available amount is preferred, while for the amount of catalyst and its cost, a slightly smaller amount may be more preferable.

[0097] It has been found that it is sufficient to obtain an effective catalyst by finitely covering the surface of (nano)particles or aggregates of such (nano)particles with catalyst entities (C).

[0098] Membrane filtration

[0099] In step (b) of the method according to the first aspect, cross-flow membrane filtration is performed. Cross-flow configuration refers to the filtration flow flowing tangentially across the surface of the membrane. The advantage of this type of filtration is that any filter cake deposited on the membrane is substantially washed away during the filtration process, thereby increasing the length of time the filtration unit can be operated.

[0100] Membrane filtration is a separation process driven by a pressure gradient across a membrane, in which the membranes classify and disperse components according to their (solventized) size and structure.

[0101] In a preferred embodiment, the cross-flow membrane filtration in step (b) is selected from microfiltration and ultrafiltration, with ultrafiltration being preferred.

[0102] In a preferred embodiment, the cross-flow membrane filtration in step (b) results in a volume concentration factor of 3 to 18, more preferably 6 to 16, and even more preferably 9 to 15 for the feed or combined feed provided in step (a).

[0103] In another preferred embodiment, the cross-flow membrane filtration in step (b) results in a retention rate of at least 80%, more preferably at least 85%, even more preferably at least 90%, still more preferably at least 95%, and even more preferably at least 99% for the heterogeneous depolymerization catalyst. The membrane retention rate of the heterogeneous depolymerization catalyst is defined as (1 - concentration) / (concentration). 渗透物 [weight%] / concentration 截留物 [weight%]) 100%.

[0104] As used herein, microfiltration refers to filtration on a membrane with a pore size of 0.1 to 10 μm, or 100 nm to 10000 nm. In one embodiment, the pore size of the microfiltration membrane is 0.1 to 8 μm, for example, 0.1 to 5 μm, or 0.1 to 3 μm. In another embodiment, the pore size of the microfiltration membrane is 0.5 to 10 μm, for example, 1 to 10 μm, or 3 to 10 μm.

[0105] The ultrafiltration referred to in this article is filtration on membranes with pore sizes of 0.01 to less than 0.1 μm or on membranes with a molecular weight cutoff of 5 to 150 kDa.

[0106] In a preferred embodiment, the ultrafiltration membrane has a molecular weight cutoff of 5 to 150 kDa, more preferably 7 to 125 kDa, even more preferably 8 to 100 kDa, even more preferably 10 to 80 kDa, and even more preferably 12 to 60 kDa, for example 13 to 50 kDa, 14 to 45 kDa, or 15 to 40 kDa.

[0107] In one embodiment, the ultrafiltration membrane has a molecular weight cutoff of 5 to 100 kDa, such as 5 to 80 kDa, 5 to 50 kDa, 5 to 30 kDa, or 5 to 20 kDa. In another embodiment, the ultrafiltration membrane has a molecular weight cutoff of 10 to 150 kDa, such as 15 to 150 kDa, 25 to 150 kDa, 40 to 150 kDa, or 60 to 150 kDa.

[0108] In one embodiment, the carrier fluid comprises ethylene glycol and water, wherein the weight ratio of ethylene glycol to water is 90:10 to 10:90, preferably 70:30 to 30:70, more preferably 65:35 to 35:65, and the ultrafiltration membrane has a molecular weight cutoff of 5 to 150 kDa, preferably 7 to 125 kDa, more preferably 8 to 100 kDa, and even more preferably 10 to 80 kDa.

[0109] In another embodiment, the carrier fluid comprises ethylene glycol and water based on a combination of water and ethylene glycol, less than 10% by weight, preferably less than 5% by weight, for example less than 2.5% by weight, less than 1% by weight, or less than 0.5% by weight, and the ultrafiltration membrane has a molecular weight cutoff of 5 to 60 kDa, preferably 8 to 50 kDa, more preferably 10 to 40 kDa, and even more preferably 15 to 30 kDa.

[0110] Examples of membranes that can be used in the cross-flow membrane filtration step (b) are polysulfone membranes, polyethersulfone membranes, cellulose acetate membranes, modified or polar functionalized membranes, and ceramic membranes, preferably ceramic membranes. In a preferred embodiment, the membrane structure is selected from flat sheet membranes, such as disc membranes, flat sheet 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 structure is selected from tubular membranes.

[0111] As those skilled in the art will understand, two or more, such as three, four, or five cross-flow membrane filter units, connected in parallel, in series, or in combination thereof, can be used instead of a single cross-flow membrane filter unit. Two or more cross-flow membrane filter units connected in series can have different pore sizes within the scope defined herein, wherein the pore size is smaller for the downstream cross-flow membrane filter unit.

[0112] The cross-flow membrane filtration in step (b) is preferably carried out at a temperature of 60 to 200°C, more preferably at a temperature of 80 to 110°C, for example at a temperature of 90 to 100°C. Relatedly, the (combined) feed undergoing cross-flow membrane filtration in step (b) has a sufficiently high temperature to maintain the monomers in solution or molecularly dispersed in the carrier liquid, allowing the monomers to pass through the membrane. If the feed temperature is insufficient, heating of the feed may be necessary.

[0113] When the feed containing the reaction product of the depolymerization reaction provided in step (a) is generated by the depolymerization of PET, the monomer is BHET, and the carrier liquid contains ethylene glycol and water, with the weight ratio of ethylene glycol to water being 90:10 to 10:90, preferably 70:30 to 30:70, more preferably 65:35 to 35:65, the cross-flow membrane filtration in step (b) is preferably carried out at a temperature of 60 to 130°C, more preferably at a temperature of 80 to 100°C.

[0114] When the feed containing the reaction product of the depolymerization reaction provided in step (a) is generated by the depolymerization of PET, the monomer is BHET, the carrier liquid contains ethylene glycol and water based on a combination of water and ethylene glycol, less than 10% by weight, preferably less than 5% by weight, for example less than 2.5% by weight, less than 1% by weight, or less than 0.5% by weight, and the cross-flow membrane filtration is preferably carried out at a temperature of 90 to 200°C, more preferably at a temperature of 90 to 110°C.

[0115] Separation system

[0116] In a second aspect, the present invention relates to a separation system (1) for separating heterogeneous depolymerization catalysts from monomers, said separation system (1) comprising: (i) A first conduit (2a) configured to supply a feed comprising reaction products of a depolymerization reaction, wherein the condensation polymer is depolymerized, the feed comprising monomers, oligomers, a carrier liquid and a heterogeneous depolymerization catalyst; (ii) A cross-flow membrane filtration device (3) configured to separate the feed into a permeate having an increased ratio of monomers to heterogeneous depolymerization catalyst compared to the feed and a retentate rich in heterogeneous depolymerization catalyst and oligomers, the cross-flow membrane filtration device (3) having an inlet (3a) for the feed, a first outlet (3b) for the retentate, a second outlet (3c) for the permeate and a second conduit (2b) configured to discharge the retentate from the first outlet (3b); (iii) An optional centrifuge and / or dynamic cross-flow filtration unit (4) configured to separate the retentate into a light phase that is depleted of heterogeneous depolymerization catalyst and a heavy phase that is rich in heterogeneous depolymerization catalyst and oligomers compared to the retentate, the optional centrifuge and / or dynamic cross-flow filtration unit (4) having an inlet (4a) for the retentate, a first outlet (4b) for the heavy phase and a second outlet (4c) for the light phase, a second conduit (2b) configured to supply the retentate from the first outlet (3b) of the cross-flow membrane filtration device (3) to the inlet (4a) of the centrifuge and / or dynamic cross-flow filtration unit (4), a third conduit (2c) for discharging the light phase from the centrifuge and / or dynamic cross-flow filtration unit (4) via the second outlet (4c), and a fourth conduit (2d) for discharging the heavy phase from the centrifuge and / or dynamic cross-flow filtration unit (4) via the first outlet (4b); (iv) Optionally, a coarse filter unit (5) downstream of the cross-flow membrane filter (3) having an inlet (5a) and an outlet (5b), and a fifth conduit (2e) configured to supply permeate from the second outlet (3c) of the cross-flow membrane filter (3) to the inlet (5a) of the coarse filter unit (5). (v) The adsorption tower (6) downstream of the cross-flow membrane filtration device (3) and the optional coarse filter unit (5) has an inlet (6a) and an outlet (6b); (vi) A crystallization container (7) downstream of the adsorption tower (6), having an inlet (7a) and an outlet (7b); and (vii) The sixth conduit (2f), when a coarse filter unit (5) is present, is configured to supply permeate from the outlet (5b) of the coarse filter unit (5) to the inlet (6a) of the adsorption tower (6); or The sixth conduit (2f), when the coarse filter unit (5) is absent, is configured to supply permeate from the second outlet (3c) of the cross-flow membrane filter (3) to the inlet (6a) of the adsorption tower (6); and (viii) A seventh conduit (2g) is configured to supply permeate from the outlet (6b) of the adsorption tower (6) to the inlet (7a) of the crystallization container (7).

[0117] Unless otherwise stated, the preferred embodiments relating to the cross-flow membrane filtration step (b) of the method according to the first aspect are also applicable to the cross-flow membrane filtration apparatus (3) of the separation system according to the second aspect. A preferred example of the coarse filter unit (5) is a depth filter such as a candle filter. A preferred example of the adsorption tower (6) is an activated carbon tower.

[0118] Cross-flow membrane filtration unit (3) may include two or more cross-flow membrane filtration units connected in series, in parallel, or in combination thereof. Two or more cross-flow membrane filtration units connected in series may have different pore sizes as defined herein, wherein the pore size is smaller in the downstream direction. Similarly, centrifuges and / or dynamic cross-flow filtration units (4), coarse filter units (5), and adsorption towers (6) may include two or more units connected in series, in parallel, or in combination thereof.

[0119] In a preferred embodiment, the separation system (1) does not include a coarse filter unit (5). However, if too many oligomers pass through the membrane of the cross-flow membrane filter (3) into the permeate, these oligomers may cause premature clogging of the downstream adsorption tower (6). Therefore, in some embodiments, the separation system (1) includes a coarse filter unit (5) to filter out the oligomers. To improve the filtration of oligomers, it may be necessary to slightly cool the permeate, for example, using a heat exchanger, causing the oligomers to settle before the permeate enters the coarse filter unit (5). Therefore, in some embodiments, the separation system (1) includes a cooling device (9), such as a heat exchanger, downstream of the cross-flow membrane filter (3) and upstream of the coarse filter unit (5). See also Figure 8 and Figure 9 The separation system (1) without the coarse filter unit (5), and Figure 10 and Figure 11 A separation system (1) having a coarse filter unit (5) and a heat exchanger (9).

[0120] In a highly preferred embodiment, the separation system (1) according to the second aspect further includes a collection container (8) configured to mix the feed and the retentate from the cross-flow membrane filter (3) or the light phase of the lean heterogeneous depolymerization catalyst from the centrifuge and / or the dynamic cross-flow filter unit (4), the feed containing the reaction products of the depolymerization reaction, wherein the collection container (8) has a first inlet (8a), a second inlet (8b) and an outlet (8c), the first inlet (8a) for supplying the feed containing the reaction products of the depolymerization reaction to the collection container (8) via a first portion of a conduit (2a), the second inlet (8b) for supplying the retentate from the cross-flow membrane filter (3) or the light phase of the lean heterogeneous depolymerization catalyst to the collection container (8) via a second conduit (2b) or a third conduit (2c) respectively, and the outlet (8c) for supplying the combined feed to the cross-flow membrane filter (3) via a second portion of a conduit (2a).

[0121] When the collection container (8) is configured to mix the feed containing the reaction products of the depolymerization reaction and the retentate from the cross-flow membrane filter (3) via the second conduit (2b), the second conduit (2b) preferably has an outlet configured to remove a portion of the retentate, for example, configured to recycle a portion of the retentate back to the depolymerization reactor.

[0122] In a preferred embodiment, the collection container (8) is provided with a means (8d) for agitating the contents, for example, to obtain a homogeneous mixture.

[0123] Relatedly, the (combined) feed entering the cross-flow membrane filter (3) via the first conduit (2a) has a sufficiently high temperature to keep the monomers in solution or the molecules dispersed in the carrier liquid, so that the monomers can pass through the membrane of the cross-flow membrane filter (3), through the optional coarse filter unit (5), and through the adsorption tower (6). If the feed supplied via the conduit (2a) has an insufficient temperature, a direct or indirect heating device can be provided upstream of the cross-flow membrane filter (3). In one embodiment, the collection container (8) is provided with a direct or indirect heating device (8e). Embodiments in which a direct or indirect heating device is provided downstream of the cross-flow membrane filter (3) are also within the scope of the second aspect. A preferred heating device is a heat exchanger.

[0124] The separation system (1) may also include a separation unit downstream of a centrifuge and / or a dynamic cross-flow filtration unit (4), which is configured to receive a heavy phase rich in heterogeneous depolymerization catalyst and oligomers via a fourth conduit (2d) and is further configured to separate the heavy phase into one or more portions.

[0125] As those skilled in the art will understand, the separation system (1) may also be provided with one or more pumps, one or more valves and a controller that interfaces with the hardware and is configured to control the flow of fluid through it.

[0126] In a preferred embodiment, the separation system (1) according to the second aspect is used or configured to perform the method according to the first aspect.

[0127] Therefore, the invention has been described with reference to certain embodiments discussed above. It will be appreciated that these embodiments are readily adaptable to various modifications and alternatives known to those skilled in the art.

[0128] Furthermore, in order to properly understand this document and its claims, it should be understood that the verb " Includes (contains) The indefinite article “” and its variations are used in their non-restrictive sense to indicate items that follow the word, but do not exclude items not specifically mentioned. Additionally, unless the context clearly requires the presence of one and only one element, the indefinite article “” is used. one "or" one"A reference to an element does not preclude the possibility that there may be more than one element. Therefore, the indefinite article..." one "or" one "Usually means" At least one ".

[0129] Example

[0130] Example 1: Cross-flow membrane filtration using a reaction mixture based on a fresh catalyst

[0131] PET sheets from packaging waste (plastic bottles) were subjected to glycololysis in ethylene glycol (EG) in a depolymerization reactor and depolymerized using a heterogeneous depolymerization catalyst, which was an iron-based catalyst complex (ABC) consisting of magnetite (nano) particles (A) and alkylsilane bridging portions (B) chemically linked on their surfaces, with ionic liquid cationic groups (C) attached to the particles at a density of 2 wt% (BC) relative to (A). The average particle diameter was determined by DLS to be 380 nm. Based on the total weight of the reaction mixture, 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 balance being ethylene glycol content. Because a fresh heterogeneous depolymerization catalyst was used, the resulting mixture was referred to as '...' fresh '.

[0132] Water is added to the reaction mixture to achieve an EG:water weight ratio of 65:35. The resulting mixture is fed in batches into a 20-liter collection vessel and heated to 85°C. The mixture is then continuously fed from the collection vessel to a cross-flow membrane benchtop separator using a pump, separating it into permeate and retentate. The retentate is recycled back to the collection vessel. This process continues until a predetermined minimum level is reached in the collection vessel.

[0133] Subsequently, both the retained and permeate were continuously recycled back into the collection container, and cross-flow membrane filtration continued for approximately 1.5 hours to assess the development of membrane fouling over time. The temperature was maintained at approximately 85°C throughout the process.

[0134] The experimental setup used Figure 5 As shown in the figure. Permeate and retentate samples were collected, and the membrane rejection rate of the heterogeneous depolymerization catalyst was determined. The membrane rejection rate of the heterogeneous depolymerization catalyst was defined as (1 - concentration) / ... 渗透物 [weight%] / concentration 截留物 [weight%]) 100%. In addition, the volume concentration factor (VCF) is determined, wherein the VCF after a specific time amount is defined as the difference between the volume of the mixture initially fed into the collection container and the volume of the permeate collected after the specific time amount.

[0135] 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.

[0136] Sufficient transmembrane flux was observed up to high VCF, although the flux decreased with increasing VCF due to membrane fouling. More open membranes (larger pore sizes) were observed to be more prone to fouling than membranes with denser pores. Not wishing to be bound by any theory, the inventors believe that more open membranes are more prone to fouling because various fouling substances (primarily, but not limited to, organic fouling substances) accumulate in or near the pores and block them. The obtained flux profile supports this interpretation, where the flux decreases sharply with increasing VCF.

[0137] Just at the beginning of the permeate recycling to the collection container (' start ') before and approximately 1.5 hours after recirculation of permeate (') Finish Then the volume concentration factor and membrane rejection rate were measured. Figure 12 The results for membranes with pore sizes of 100 kDa and 150 kDa are shown. Figure 12 It can be observed that, in all cases of VCF > 5, the membrane retention rate of heterogeneous depolymerization catalyst particles is > 95%.

[0138] Example 2: Cross-flow membrane filtration using a reaction mixture with a recycled catalyst

[0139] The depolymerization reaction mixture prepared using a heterogeneous depolymerization catalyst that has been used in more than one depolymerization reaction was repeated three times in Example 1. Because a recycled heterogeneous depolymerization catalyst was used during the depolymerization reaction, the resulting mixture was referred to as '...' Recycled '.

[0140] Again, just at the beginning of the permeate recycling to the collection container (' start ') before and approximately 1.5 hours after recirculation of permeate (') Finish Then the volume concentration factor and membrane rejection rate were measured. Figure 13 The results for a membrane with a pore size of 100 kDa are shown in the figure. Figure 13 It can be observed that at VCF > 5.4, the membrane rejection rate of the heterogeneous depolymerization catalyst is > 95%. The measured rejection rate is reproducible. The membrane rejection rate is similar to that obtained in Example 1.

[0141] The transmembrane flux observed in Example 2 was higher than that in Example 1 (see Example 1). Figure 14 Without being bound by any theory, it is assumed that the reaction mixture prepared with recycled catalyst has a higher BHET concentration than the reaction mixture prepared with fresh catalyst, and that the higher BHET concentration increases the solubility of oligomers, resulting in less oligomer precipitation and fouling on the membrane.

[0142] Example 3: Cross-flow membrane filtration using a reaction mixture based on a fresh catalyst

[0143] A mixture of ~200 ppm fresh ABC heterogeneous depolymerization catalyst in EG was prepared as defined in Example 1. Therefore, water, BHET, and oligomers were absent from this mixture. The mixture was fed in batches into a 20-liter collection vessel and heated to 85°C. The stream of the mixture was then continuously fed from the collection vessel to a cross-flow membrane benchtop separator using a pump, separating it into permeate and retentate. The retentate was recycled back to the collection vessel. This process was continued until a predetermined minimum level was reached in the collection vessel. The temperature was maintained at approximately 85°C throughout the process. The experimental setup used was... Figure 5 As shown in the image.

[0144] Permeate and retentate samples were collected, and the membrane rejection rate of the heterogeneous depolymerization catalyst particles was determined. The membrane used was a ceramic ultrafiltration membrane with a pore size of 15 kDa. The conclusion was that the membrane rejection rate of the heterogeneous depolymerization catalyst particles was >99% at a VCF of approximately 6.7.

[0145] Example 4: Cross-flow membrane filtration using a reaction mixture with a recycled catalyst

[0146] Example 2 was repeated without adding water and using two different ceramic ultrafiltration membranes with pore sizes of 15 kDa and 25 kDa. It was observed that the membrane with the smaller pore size resulted in a lower transmembrane flux.

[0147] Again, just at the beginning of the permeate recycling to the collection container (' start ') before and approximately 1.5 hours after recirculation of permeate (') Finish The volume concentration factor and membrane rejection were then measured. The results are shown in... Figure 15 In. Figure 15 It can be observed that at VCF >7, the membrane retention rate of heterogeneous depolymerization catalyst particles is >85%.

Claims

1. A method for separating heterogeneous depolymerization catalysts from monomers, comprising the following steps: (a) Providing a feed comprising reaction products of a depolymerization reaction, wherein the condensation polymer is depolymerized into monomers and oligomers, said feed comprising monomers, oligomers, a carrier liquid, and a heterogeneous depolymerization catalyst; and (b) The feed from step (a) is subjected to cross-flow membrane filtration to obtain permeate and retentate, wherein the permeate has an increased monomer to heterogeneous depolymerization catalyst ratio compared to the feed, and the retentate is rich in heterogeneous depolymerization catalyst and oligomers. No centrifugation step is performed before step (b).

2. The method according to claim 1, further comprising the following steps: (c) subjecting the retentate from step (b) to centrifugation and / or dynamic cross-flow filtration to obtain a heavy phase and a light phase, wherein the heavy phase is rich in the heterogeneous depolymerization catalyst and the oligomers compared to the retentate, and the light phase is poor in the heterogeneous depolymerization catalyst.

3. The method according to claim 1, wherein it is performed as a continuous method, the method comprising: (a) A continuous feed stream containing the reaction products of the depolymerization reaction is provided and the feed stream is continuously supplied to a collection container, the retentate obtained in step (b) is continuously supplied to the collection container, and the feed and retentate are mixed in the collection container to obtain a combined feed; (b) The combined feed stream is continuously discharged from the collection container and continuously subjected to cross-flow membrane filtration to obtain permeate and retentate, wherein the permeate has an increased monomer to heterogeneous depolymerization catalyst ratio compared to the combined feed, and the retentate is rich in heterogeneous depolymerization catalyst and oligomers, and the retentate is continuously supplied to the collection container. A portion of the retentate is continuously or after a regular time interval from being removed from the process, and is recycled, for example, to the depolymerization reactor, wherein no centrifugation step is performed prior to step (b).

4. The method according to claim 2, wherein it is performed as a continuous method, the method comprising: (a) A feed stream containing the reaction products of the depolymerization reaction is continuously supplied and the feed stream is continuously supplied to a collection container, the light phase obtained in step (c) is continuously supplied to the collection container, and the feed and the light phase are mixed in the collection container to obtain a combined feed; (b) The combined feed stream is continuously discharged from the collection container and continuously filtered through a cross-flow membrane to obtain permeate and retentate, wherein the permeate has an increased monomer to heterogeneous depolymerization catalyst ratio compared to the combined feed, and the retentate is rich in heterogeneous depolymerization catalyst and oligomers. and (c) The residue from step (b) is continuously subjected to centrifugation and / or dynamic cross-flow filtration to obtain a heavy phase and a light phase, wherein the heavy phase is rich in the heterogeneous depolymerization catalyst and the oligomers compared to the residue, and the light phase is lean towards the heterogeneous depolymerization catalyst, and the light phase is continuously supplied to a collection container. No centrifugation step is performed before step (b).

5. The method according to any one of claims 1 to 4, wherein the carrier liquid comprises water, alkanol, alkyldiol, alkyltriol or a combination thereof, preferably comprising water, methanol, ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, 1,4-butanediol, 1,5-pentanediol, glycerol or a combination thereof, more preferably comprising water, ethylene glycol or a combination thereof.

6. The method according to any one of claims 1 to 5, wherein the feed provided in step (a) comprises the reaction product of the depolymerization reaction, wherein the condensate is depolymerized, said condensate being selected from the group consisting of polyester, polycarbonate, polyamide, polyurethane, polyether and combinations thereof, preferably polyester, most preferably polyethylene terephthalate (PET).

7. The method according to any one of claims 1 to 6, wherein the cross-flow membrane filtration in step (b) is ultrafiltration, and wherein the molecular weight cutoff of the ultrafiltration membrane is 5 to 150 kDa, preferably 7 to 125 kDa, more preferably 8 to 100 kDa, even more preferably 10 to 80 kDa, and even more preferably 12 to 60 kDa.

8. The method according to any one of claims 1 to 7, wherein the cross-flow membrane filtration in step (b) is carried out at a temperature of 60 to 200°C.

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

10. The method according to any one of claims 1 to 9, wherein the cross-flow membrane filtration in step (b) results in a rejection rate of at least 80% for the heterogeneous depolymerization catalyst, preferably at least 85%, more preferably at least 90%, even more preferably at least 95%, and even more preferably at least 99%.

11. The method according to any one of claims 1 to 10, wherein the feed containing the reaction product of the depolymerization reaction provided in step (a) is generated by the depolymerization of PET, the monomer is BHET, and the carrier liquid contains ethylene glycol and water, wherein the weight ratio of ethylene glycol to water is preferably 90:10 to 10:90, more preferably 70:30 to 30:70, and even more preferably 65:35 to 35:

65.

12. The method according to claim 11, wherein the cross-flow membrane filtration in step (b) is carried out at a temperature of 60 to 130°C, preferably at a temperature of 80 to 100°C.

13. The method according to any one of claims 1 to 10, wherein the feed containing the reaction product of the depolymerization reaction provided in step (a) is generated by the depolymerization of PET, the monomer is BHET, and the carrier liquid contains ethylene glycol and water based on the total weight of water and ethylene glycol less than 10% by weight, preferably less than 5% by weight, for example less than 2.5% by weight, less than 1% by weight, or less than 0.5% by weight.

14. The method according to claim 13, wherein the cross-flow membrane filtration in step (b) is carried out at a temperature of 90 to 200°C, preferably at a temperature of 90 to 110°C.

15. The method according to any one of claims 1 to 14, wherein the weight ratio of monomer and oligomer to carrier liquid in the feed containing the reaction product of the depolymerization reaction provided in step (a) is 20:10 to 100:10, preferably 40:10 to 90:

10.

16. The method according to any one of claims 1 to 15, wherein the weight ratio of the heterogeneous depolymerization catalyst to the monomer and oligomer in the feed containing the reaction product of the depolymerization reaction provided in step (a) ranges from 0.001:10 to 1:10, preferably from 0.005:10 to 0.3:10, more preferably from 0.008:10 to 0.015:

10.

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

18. The method according to any one of claims 1 to 17, wherein the heterogeneous depolymerization catalyst comprises functionalized magnetic particles, the functionalized magnetic particles comprising a catalyst complex (ABC), the functionalized magnetic particles having an average particle size of 25 to 500 nm, more preferably 30 to 450 nm, as measured by dynamic light scattering, wherein the catalyst complex comprises three distinguishable elements: (nano)particles (A); bridging portions or linking groups (B) chemically or physically attached to the particles; and a catalyst entity (C) associated with the particles (A), for example by chemical bonding, such as covalent bonding to the linking groups.

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

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

21. The separation system (1) according to claim 19, excluding 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 including a collection container (8) configured to mix the feed and the retentate from the cross-flow membrane filter (3), the feed containing reaction products of the depolymerization reaction, wherein the collection container (8) has a first inlet (8a), a second inlet (8b) and an outlet (8c), the first inlet (8a) for supplying the feed containing the reaction products of the depolymerization reaction to the collection container (8) via a first portion of the conduit (2a), the second inlet (8b) for supplying the retentate from the cross-flow membrane filter (3) to the collection container (8) via the second conduit (2b), and the outlet (8c) for supplying the combined feed to the cross-flow membrane filter (3) via a second portion of the conduit (2a).

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

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

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