Processes for the depolymerisation of polyurethane materials

Abstract

The invention relates to a process for the depolymerisation of a polyurethane material comprising the following steps: a) reacting the polyurethane material with a dialkylcarbonate or a diarylcarbonate or an alkylarylcarboante to produce i) at least one polyol and / or at least one carbonate-functionalised polyol, and ii) at least one polycarbamate; b) separating i) the at least one polyol and / or at least one carbonate-functionalised polyol, and ii) the at least one polycarbamate; and c) converting the at least one polycarbamate into at least one polyisocyanate. The resultant constituents of the depolymerised polyurethane material may subsequently be recycled for the purpose of making new polyurethanes or other useful materials.

Description

[0001] SP3060 - 1 - PROCESSES FOR THE DEPOLYMERISATION OF POLYURETHANE MATERIALS Field of the Invention This invention relates to the depolymerisation of polyurethane materials for the purpose of waste management and of recycling of said materials. The polyurethane 5 material, typically a polyurethane foam, is broken down into its monomeric component parts which may subsequently be recycled for the purpose of making new polyurethanes or other useful materials. 10 Background of the Invention Polyurethanes are found in many forms, including flexible foams, rigid foams and elastomeric fibres. Flexible polyurethane foams have found extensive use in a multitude of industrial and consumer applications. The 15 main sectors of application are the automotive and aircraft industry, upholstered furniture and technical articles. For instance, full foam seats, top pads for the seats and restraints for back and head, all made from flexible polyurethane foam, are widely used in cars and 20 aeroplanes. Other applications include the use of flexible polyurethane foam as carpet backings, bedding and mattresses, textile lamination, packaging, foamed seat saddles for motorbikes, gaskets between a car body and its lights, lip seals of air filters for engines and 25 insulating layers on car parts and engine parts to reduce sound and vibration. However, such foams are challenging to fully recycle due to their cross-linked nature and high number of inherently stable carbamate bond linkages. Common chemical pathways including standard 30 hydrolysis, acidolysis, alcoholysis (glycolysis) and aminolysis are known for the depolymerisation of polyurethane materials but are still underdeveloped and are not apt for their full recycling and valorisation. Split phase glycolysis currently represents the most 5 promising method for polyurethane recycling by using excess diethylene glycol to shift the equilibrium of the depolymerisation reaction toward the polyol product and allows the purification and recycling of said polyols. However, such methods are inefficient as a result of 10 incomplete depolymerisation of the polyurethane. Polyurethane contains carbamate bonds (formed by the reaction of an alcohol group with an isocyanate group when producing the polyurethane) and urea bonds (created when hydrolysing excess isocyanates for the liberation of 15 carbon dioxide for foam blowing during cross-linking). Alcoholysis of the carbamate bonds leads to new carbamate components while the alcoholysis of urea bonds leads to a mixture of carbamate and amine components, which makes the overall product generally difficult to upgrade to 20 isocyanates and so is often discarded. Such upgrading of the mixture would require the separation and dedicated processing of the carbamate and amine components. Further, the direct conversion of isolated amines into isocyanates requires the use of phosgene, which is both highly toxic 25 and corrosive. Therefore, there is a need to provide safer, simpler, cheaper and more efficient methods for the depolymerisation and subsequent recycling of polyurethane materials, in particular polyurethane foams. These and 30 other objectives will become apparent from the disclosure provided herein. Summary of the Invention The present invention provides a process for the depolymerisation of a polyurethane material, comprising the following steps: 5 a) reacting the polyurethane material with a dialkylcarbonate or a diarylcarbonate or an alkylarylcarbonate to produce i) at least one polyol and / or at least one carbonate-functionalised polyol, and ii) at least one polycarbamate; 10 b) separating i) the at least one polyol and / or at least one carbonate-functionalised polyol, and ii) the at least one polycarbamate; and c) converting the at least one polycarbamate into at least one polyisocyanate. 15 Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and / or in the following description and drawings, and in particular the individual features 20 thereof, may be taken independently or in any combination. That is, all embodiments and / or features of any described embodiment can be combined with other embodiments in any way and / or combination, unless such features are incompatible. 25 Brief Description of the Drawings Figure 1 illustrates a schematic representation of a polyurethane material depolymerisation and recycling process according to an embodiment of the invention; 30 Figure 2 illustrates a chemical scheme according to an embodiment of the invention for a first step in the depolymerisation of a polyurethane foam, using at least diethylcarbonate, into its polyol / polyol precursor and polyalkylcarbamate component parts; Figure 3 illustrates a chemical scheme according to an embodiment of the invention for a first step in the depolymerisation of a polyurethane foam, using at least diphenylcarbonate, into its polyol / polyol precursor and polyarylcarbamate component parts; Figure 4 illustrates a chemical scheme according to an embodiment of the invention for a first step in the depolymerisation of a polyurethane foam, using at least ethylphenylcarbonate, into its polyol / polyol precursor and polycarbamate component parts; Figure 5 illustrates the aliphatic region of a1H NMR (DMSO-d6) spectrum of the product stream of the depolymerisation of PU foam in diphenylcarbonate using an additional zinc acetate catalyst, according to Example 6; Figure 6 illustrates the aromatic region of a1H NMR (DMSO-d6) spectrum of the product stream of the depolymerisation of PU foam in diphenylcarbonate using an additional zinc acetate catalyst, according to Example 6. Detailed Description of the Invention In general terms the present invention provides methods for the depolymerisation of carbamate bond- containing materials, particularly polyurethane materials, including polyurethane foams, and the optional subsequent recycling of the constituent component monomers suitably for the purpose of making new polyurethanes or other useful materials. For the purpose of the following disclosure, the term “depolymerisation” refers to the process whereby a polymeric material is broken down into its component parts, or precursors to its component parts. A polymeric material may be defined as a material that is constituted of repeating units, also called monomers, which are connected by a particular type of chemical bond, such as a carbamate bond, targeted for the depolymerisation process. Depolymerisation may comprise a first process step wherein at least one type of bond is broken. Additionally, depolymerisation may further comprise subsequent steps to 5 isolate and / or purify the component parts, or precursors to its component parts, which may be further chemically modified as necessary. Where “depolymerisation” generates precursors to the component parts, the process may further comprise steps to convert said precursors to said 10 component parts in their pure forms as necessary. The methods comprise reacting the polyurethane material with a dialkylcarbonate or a diarylcarbonate or an alkylarylcarbonate to produce at least one polyol and / or at least one polyol precursor and at least one 15 polycarbamate (a precursor for the polyisocyanate used to make the original polyurethane). The polyol precursor may comprise a polyol wherein at least one alcohol group is terminated with a carbonate group, for example an ethylcarbonate group or a phenylcarbonate group, i.e. the 20 polyol precursor may be a carbonate-functionalised polyol. The at least one carbonate-functionalised polyol may be converted to a polyol by any suitable means, including, for example, alcoholysis. Reaction of the dialkylcarbonate or the diarylcarbonate or the alkylarylcarbonate as used 25 in the method may also liberate an alcohol from the dialkylcarbonate or the diarylcarbonate or the alkylarylcarbonate (herein also referred to as a dicarbonate-liberated alcohol). For example, where a dialkylcarbonate is used, the dicarbonate-liberated 30 alcohol is an alkylalcohol. Where the dialkylcarbonate is diethylcarbonate, the dicarbonate-liberated alcohol is ethanol. Where a diarylcarbonate is used, the dicarbonate- liberated alcohol is an arylalcohol. Where the diarylcarbonate is diphenylcarbonate, the dicarbonate- liberated alcohol is phenol. Where an alkylarylcarbonate is used, the dicarbonate-liberated alcohol alkylalcohol and / or an arylalcohol. Where the alkylarylcarbonate is ethylphenylcarbonate, the dicarbonate-liberated alcohol 5 ethanol and / or phenol. The at least one polyol and / or polyol precursor and the at least one polycarbamate (and optionally also the dicarbonate-liberated alcohol) may be separated from each other (for example by boiling point, melting point, 10 molecular size or molecular affinity) and optionally purified using standard chemical protocols. The at least one polycarbamate produced by the methods disclosed herein may be converted directly into at least one polyisocyanate, which may be a diisocyanate, 15 using relatively facile chemical conditions, including but not limited to pyrolysis. The polyisocyanate may be purified using standard protocols, which may include (vacuum) distillation, crystallization, extraction or micro / nanofiltration. 20 The purified or unpurified polyol and / or polyisocyanate may then be recycled for use in any subsequent suitable method or procedure, suitably in the production of new polyurethane materials or indeed any other new useful material. 25 An advantage of the process of the disclosed invention over the state of the art lies in the use of at least a dialkylcarbonate or at least a diarylcarbonate or at least an alkylarylcarbonate in the depolymerisation of a polyurethane material, which directly generates a 30 polycarbamate, which may be a dicarbamate, which may be a dialkylcarbamate or a diarylcarbamate or an alkylarylcarbamate, as one of the direct depolymerisation products with low-to-zero production of a polyamine by- product, as per conventional polyurethane depolymerisation methods. Whereas amines require the use of phosgene, which is toxic and corrosive, for their direct conversion into isocyanates, polycarbamates may be converted directly into polyisocyanates in a single step without the need for such 5 toxic and / or corrosive reagents, for example by pyrolysis. The generated polyisocyanate may then be recycled for use in the production of new polyurethane materials, and / or other useful materials. Thus, the process of the invention also allows for 10 the simple and efficient recovery of polyisocyanates, which would otherwise typically go to waste, as well as polyols, and both components may be circularly recycled. For the purposes of promoting an understanding of the principles of the invention, reference will now be 15 made to the embodiments illustrated in the accompanying drawings, which are described in more detail below. The embodiments disclosed herein are not intended to be exhaustive or limit the invention to the precise form disclosed in the following detailed description. The 20 invention includes any alterations and further modifications in the described methods and further applications of the principles of the invention as set forth in the claims. Figure 1 shows a schematic illustration according to 25 embodiments of the present invention showing a process (100) of depolymerising and recycling a polyurethane material. Step 1 (101) of the process involves combining starting reagents, which may include at least a 30 polyurethane material (e.g. a polyurethane foam) and a dialkylcarbonate or a diarylcarbonate or an alkylarylcarbonate, required for the depolymerisation of the polyurethane material in a suitable reaction setup and cleavage of the carbamate bonds contained within the polyurethane material. The reagents may be combined once at the beginning of the step or fed continuously or by parts in a reaction setup. As such, a suitable reaction vessel may comprise a batch reactor, which may include an 5 autoclave, with or without stirring, such that the process may be performed at or above atmospheric pressure, or a continuous reactor that may be continuously fed with starting reagents, or any other suitable reaction vessel. The continuous reactor may comprise, for example, a 10 stirred tank, a pipe or an extruder. The individual starting reagents may be fed at different points in the reactor and / or at different times. The dialkylcarbonate or the diarylcarbonate or the alkylarylcarbonate may additionally serve as the reaction 15 solvent for the process and may be any suitable dialkylcarbonate or any suitable diarylcarbonate or any suitable alkylarylcarbonate. The dialkylcarbonate may be a C1-C12 dialkylcarbonate, preferably dimethylcarbonate or diethylcarbonate. The diarylcarbonate may be an 20 optionally-substituted diarylcarbonate, preferably diphenylcarbonate or bis(4-methylphenyl)carbonate. The alkylarylcarbonate may be a substituted alkylarylcarbonate, preferably ethyl-phenylcarbonate, or methyl-phenylcarbonate, or ethyl-(4-methyl- 25 phenyl)carbonate, or methyl-(4-methyl-phenyl)carbonate. The dialkylcarbonate or the diarylcarbonate or the alkylarylcarbonate is preferably used in a molar excess relative to the nitrogen contained in the polyurethane material. 30 Optionally, a catalyst may be added to the reaction vessel. The catalyst may be a Lewis acid catalyst. The catalyst may comprise a metal element including, but not limited to, zinc (Zn), tin (Sn) or titanium (Ti). The Lewis acid catalyst may be in the form of a salt, including an acetate salt or an octanoate salt. The Lewis acid catalyst may be in the form of zinc acetate, titanium acetate or tin octanoate. 5 The catalyst may be a Bronsted base catalyst. The catalyst may comprise a hydroxide ion, an alkoxide ion or a phenoxide ion. The catalyst may comprise an alkali component, a zinc (Zn) component, a tin (Sn) component or a titanium (Ti) component. The alkali component may 10 comprise a lithium ion, a sodium ion or a potassium ion. The catalyst may be lithium hydroxide, sodium hydroxide or potassium hydroxide. The catalyst may be zinc phenoxide or a titanium alkoxide, such as titanium ethoxide, or titanium phenoxide. The base may be an aprotic organic 15 base. The base may be selected from the group consisting of, but not limited to, pyridine, 1,8- diazabicyclo(5.4.0)undec-7-ene (DBU), tetramethylethylenediamine (TMEDA), and triethylenediamine (TEDA / DABCO). 20 The catalyst may be added in any suitable amount, which may be at least about 0.1 wt.%, at least about 0.5 wt.%, at least about 1 wt.%, at least about 2 wt.%, at least about 3 wt.%, at least about 4 wt.%, at least about 5 wt.%, at least about 6 wt.%, at least about 7 wt.%, at 25 least about 10 wt.%, or at least about 15 wt.%, relative to the polyurethane material. The catalyst may be added in an amount of at most about 20 wt.%, at most about 25 wt.%, at most about 30 wt.%, at most about 35 wt.%, at most about 40 wt.%, or at most about 50 wt.% relative to the 30 polyurethane material. Optionally, an alcohol may be added to the reaction vessel. The alcohol may be present in addition to or instead of the catalyst. The alcohol may be any suitable alcohol or mixture of any suitable alcohols. The alcohol may be any suitable alkylalcohol or any suitable arylalcohol or any suitable mixture of an alkylalcohol and an arylalcohol. Suitably, the alcohol may be an alkylalcohol. The alkylalcohol may be a linear, branched or cyclic alkylalcohol. The alkylalcohol may be saturated or unsaturated. The alkylalcohol may be any C1-C12 alkylalcohol. Suitably, the alkylalcohol is selected from the group consisting of methanol, ethanol, propanol, and butanol. Preferably, the alkylalcohol is methanol or ethanol. Suitably, the alcohol may be an arylalcohol. The arylalcohol may be a substituted arylalcohol. The substituted arylalcohol may be an alkyl-substituted arylalcohol. The arylalcohol may be phenol or m-cresol. Optionally, an additional organic solvent may be added to the reaction vessel. The organic solvent is preferably polar and aprotic. For instance, it may contain an ether, ester, lactone, ketone, sulfone or sulfoxide group. The solvent may be selected from the group consisting of dioxane, tetrahydrofuran, dimethoxyethane, bis(methoxyethyl)ether), caprolactone, gamma- valerolactone, acetone, butanone and sulfolane. The depolymerisation process may be performed at any suitable temperature, which may be at least about 100oC, at least about 120oC, at least about 140oC, at least about 160oC, at least about 180oC, at least about 200oC, at least about 210oC, at least about 220oC, or at least about 240 and at most about 250oC, at most about 280oC, at most about 300oC, at most about 320oC or at most about 350oC, and for any suitable length of time. The depolymerisation process may be performed for any suitable length of time, which may be at least about 10 minutes, at least about 20 minutes, at least about 30 minutes, at least about 45 minutes, at least about 1 hour, at least about 1.5 h, at least about 2 h, at least about 2.5 h, at least about 3 h, at least about 3.5 h; and at most about 4 h, at most about 4.5 h, at most about 5 h, at most about 10 h, at most about 15 h or at most about 20 h, so as to achieve depolymerisation of the polyurethane 5 material into at least one polyol and / or polyol precursor and at least one polycarbamate. It is conceivable that the polyurethane material may be depolymerised into more than one type of polyol and / or polyol precursor and / or more than one type of polycarbamate, depending on the 10 composition of the polyurethane. The polycarbamate may be a polyalkylcarbamate or a polyarylcarbamate or a polyalkylarylcarbamate. The polycarbamate may be a polyethylcarbamate, suitably a diethylcarbamate. The polycarbamate may be a polyarylcarbamate, suitably a 15 diphenylcarbamate. Suitably, the polycarbamate may be a polyalkylarylcarbamate, suitably an ethyl-phenylcarbamate or methyl-phenylcarbamate. Step 2 (102) of the process involves separating the components of the product stream generated by the 20 depolymerisation of the polyurethane material from each other and optionally purifying one or more of these components. The separation process may be performed by exploiting differences in the boiling point, melting point, molecular size, chemical affinity, or combination 25 thereof of the components. Where the process generates a polyol and one or more precursors of said polyol, the polyol and the one or more polyol precursors may be isolated as a single product fraction before conversion of the one or more polyol precursors to the polyol (e.g. by 30 alcoholysis) to generate a single polyol fraction. The product stream can be separated into, for example: (1) unreacted depolymerisation solvent which may comprise unreacted dialkylcarbonate or unreacted diarylcarbonate or unreacted alkylarylcarbonate, the optional additional alcohol(s) and / or the optional additional organic solvent, which may be recycled to the depolymerisation reactor; (2) at least one polyol and / or at least one polyol precursor, which may be used for 5 producing new polyurethane materials, optionally after finishing the process or upgrading; (3) an aromatic fraction, which may comprise at least one aromatic compound including the at least one polycarbamate, which may be upgraded to a polyisocyanate and subsequently used 10 for producing new polyurethane materials or other useful materials; (4) dicarbonate-liberated alcohol which may be recycled to the depolymerisation reactor and (5) eventual solid residue, which may be discarded, eventually after further work up to recover and recycle catalysts and / or 15 incompletely depolymerised polyurethane material. If necessary, Step 2 (102) may first comprise recovering the eventual solid residue components by means of any of filtration, (hydro)cyclonation, centrifugation or any other appropriate technique. Further work up could 20 take various forms, some of which are described below. In one preferred example, the product stream may be separated by consecutive distillations, if possible based on the relative boiling points of the various components of the product stream which would depend on the 25 composition of the PU foam for recycling. A first distillation may be run at atmospheric pressure to recover unreacted solvent, which may be diethylcarbonate (DEC) (Tb = 126°C at 1 atm.) and optionally ethanol (Tb = 78°C at 1 atm.) as top product(s). The remaining components may then 30 be subjected to distillation under high vacuum to recover the aromatic components as top product(s)(the aromatic components may have boiling point temperatures within the range, Tb = 250 °C to 300 °C at 1 atm.) and the polyol / polyol precursors (the polyol may have a boiling point temperature, Tb> 300°C at 1 atm) as a bottom product. Vacuum distillation may be required to avoid chemical degradation of the polyol. In another preferred example, the products may be 5 recovered by crystallisation techniques or by combining crystallisation techniques and distillation techniques. All solid components may first be removed from the product stream which may then be cooled to selectively crystallise the aromatic components out of the supernatant liquid. The 10 aromatic components may be characterised by high melting point temperatures that vary between 70 °C and 230 °C. The supernatant liquid may then be subjected to vacuum distillation to recover the dicarbonate / alcohol solvent and optional added solvent as top products and the polyol 15 as bottom product. In another example, the aromatic components with high polarity (such as with, logP < 3.2; where logP is defined as the octanol-water partition coefficient) may be separated from the polyol and / or polyol precursor(s) with 20 low polarity (such as with LogP > 7) by means of liquid / liquid extraction. In a first option, the depolymerisation product may be subjected to atmospheric distillation to recover the solvent as top product. The remaining bottom product may be then subjected to liquid 25 extraction by adding an apolar solvent to selectively extract the polyol and / or polyol precursor(s) and / or adding a polar solvent to selectively extract the aromatic components and / or the dialkylcarbonate, the diarylcarbonate or the dialkylarylcarbonate. In a second 30 option, the depolymerisation mixture containing depolymerisation solvent, aromatic components and polyols / polyol precursor(s) may be contacted with an apolar solvent to extract the polyol / polyol precursor(s). The resulting two streams generated by solvent extraction may then be subjected to distillation to recover the extraction solvent from the aromatic components and unconverted dicarbonate, or from the polyol / polyol precursor(s). In another example, a polar antisolvent may 5 be added to the depolymerisation mixture to push the polyol out of solution. In another example, the depolymerisation mixture may be subjected to nanofiltration to recover the polar and low-molecular weight component as a polyol-lean / polyol 10 precursor-lean permeate from a polyol-rich / polyol precursor-rich retentate. The polyol-rich / polyol precursor-rich retentate may then be further separated into aromatic, polyol / polyol precursor and solvent streams according to any of the examples mentioned above. The 15 polyol-lean / polyol precursor-lean permeate can be separated into a solvent stream and an aromatic stream by means of distillation and / or crystallisation. The above-described examples of step 2 (102) are not intended to limit the invention by any means and any 20 process of separation derivable from the state of the art may be used, including by combining elements of the above examples in any suitable manner and / or with any other suitable process. Step 3 (103) of the process involves conversion of 25 the at least one polycarbamate into at least one polyisocyanate. Suitably, the at least one polycarbamate is converted into at least one polyisocyanate by pyrolysis. Suitably, the polyisocyanate is a diisocyanate. A polycarbamate-liberated alcohol may also be produced. 30 The polycarbamate-liberated alcohol may be an alkylalcohol, suitably ethanol or methanol, and / or an arylalcohol, suitably phenol or m-cresol. Where pyrolysis is suitably used to generate the at least one polyisocyanate from the at least one polycarbamate, any suitable elevated temperature may be used. For example, a temperature of at least about 140oC, at least about 150oC, at least about 160oC, at least about 170oC, at least about 180oC, at least about 190oC, at least about 200oC, at least about 210oC, at least about 220oC or at least about 250oC; and at most about 300oC, at most about 320oC, at most about 340oC, at most about 360oC, at most about 380oC or at most about 400oC may be used. Any suitable reaction time may be used. For example a reaction time of at least about 0.01 seconds, at least about 0.1 seconds, at least about 0.2 seconds, at least about 0.5 seconds, at least about 1 second, at least about 2 seconds, at least about 3 seconds, at least about 5 seconds; and at most about 6 seconds, at most about 10 seconds, at most about 20 seconds, at most about 30 seconds, at most about 40 seconds, at most about 50 seconds, and at most about 60 seconds may be used. Additionally, a solvent may be used, wherein the solvent is preferably an aprotic, polar solvent. The solvent may be dichlorobenzene. The process may be performed under an inert atmosphere, which may be a nitrogen atmosphere. Optionally, step 3 (103) also comprises separation and purification of the polyisocyanate and the polycarbamate-liberated alcohol. Where the process generates at least one polyol precursor, step 3 (103) may additionally, and optionally, involve conversion of the at least one polyol precursor into at least one polyol by any suitable means, for example by alcoholysis. Step 3 (103) may be performed using a mixture of different polyol precursors to generate at least one polyol. Step 4 (104) of the process is optional and involves the use of the at least one polyol output from step 2 (102) and / or the at least one polyisocyanate output from step 3 (103) in the production of a new polyurethane material and / or any other new useful material, such that circular recycling of the original polyurethane material is achieved. 5 Optionally, the dicarbonate-liberated alcohol output from step 2 (102) and / or the polycarbamate-liberated alcohol output from step 3 (103) may be regenerated into carbonates via reaction of the alcohol groups with, for example, a cyclic carbonate, such as ethylene carbonate or 10 propylene carbonate or by reaction of the alcohol groups with carbon monoxide in the presence of oxygen and a catalyst (oxidative carbonylation). Figures 2, 3 and 4 show multiple embodiments of the depolymerisation reaction referred to in step 1 (101) of 15 Figure 1. Figure 2 illustrates the specific example of the depolymerisation of a polyurethane foam, here PU-1, (formed by the polymerisation of Polyol A (a trifunctional copolyether polyol) with 2,4-toluene diisocyanate (2,4- TDI) and 2,6-toluene diisocyanate (2,6-TDI)) with a 20 dialkylcarbonate, here diethylcarbonate (DEC), optionally in the presence of a catalyst, here zinc acetate, and / or optionally in the presence of an alcohol, here ethanol. Figure 3 illustrates the specific example of the depolymerisation of a polyurethane foam, here PU-1, 25 (formed by the polymerisation of Polyol A (a trifunctional copolyether polyol) with 2,4-toluene diisocyanate (2,4- TDI) and 2,6-toluene diisocyanate (2,6-TDI)) with a diarylcarbonate, here diphenylcarbonate (DPC), optionally in the presence of a catalyst, here zinc acetate, and / or 30 optionally in the presence of an alcohol, here phenol. Figure 4 illustrates the specific example of the depolymerisation of a polyurethane foam, here PU-1, (formed by the polymerisation of Polyol A (a trifunctional copolyether polyol) with 2,4-toluene diisocyanate (2,4- TDI) and 2,6-toluene diisocyanate (2,6-TDI)) with an alkylarylcarbonate, here ethyl-phenylcarbonate (EPC), optionally in the presence of a catalyst, here zinc acetate, and / or optionally in the presence of an alcohol, 5 here ethanol. The PU-1 depolymerises into the components, Polyol A and Polyol A precursors (where the polyol A precursors comprise one, two or three ethylcarbonate-substituted alcohol groups, as per Figure 2; where the polyol A10 precursors comprise one, two or three phenylcarbonate- substituted alcohol groups, as per Figure 3; and where the polyol A precursors comprise one, two or three phenylcarbonate-substituted alcohol groups and / or ethylcarbonate-substituted alcohol groups, as per Figure15 4), and 2,4-toluene(dicarbamate) (2,4-TDC) and 2,6- toluene(dicarbamate) (2,6-TDC), wherein the carbamate groups of both the 2,4-TDC and 2,6-TDC may be ethylcarbamates (Figure 2) or phenylcarbamates (Figure 3) or a mixture of ethylcarbamates and phenylcarbamates 20 (Figure 4). Advantageously, 2,4-TDC and 2,6-TDC may be converted directly into their corresponding diisocyanates, 2,4-TDI and 2,6-TDI, using pyrolysis, without the need for toxic or corrosive reagents, such that the polyurethane foam is easily depolymerised and converted into its 25 starting materials for optional circular recycling. This advantageous effect applies broadly to all polyurethanes and carbamate bond-containing materials containing other process-compatible functional groups, such that it is conceivable that the method may be used to depolymerise 30 any compatible polyurethane material, derived from any other component polyol(s) and polyisocyanate(s), into its component parts, or component part precursors, for optional circular recycling. Depolymerisation by-products, 2,4-toluene diamine (2,4-TDA) and 2,6-toluene diamine (2,6-TDA), and mixed- products, 2,6-toluene amine ethylcarbamate (2,6-TAC), isomers of 2,4-toluene amine ethylcarbamate (2,4-TAC), 5 2,6-toluene amine phenylcarbamate (2,6-TAC) and isomers of 2,4-toluene amine phenylcarbamate (2,4-TAC) may also be formed as part of the method. However, optimisation of the method, as demonstrated in the Examples, reduces the amount of these diamines and mixed-products formed, and 10 selectively generates polycarbamates as depolymerisation products. The invention is further exemplified in the following non-limiting examples. 15 EXAMPLES EXAMPLE 1 – Chemicals and polyurethane foam depolymerisation method 20 The chemicals and polyurethane foam depolymerisation method used in the following Examples are set out below. Virgin polyol A and polyurethane (PU) foam were supplied by Shell. Polyol A is a trifunctional copolyether polyol consisting of PO and EO repeating units, with a 25 composition as shown below in Table 1. It has a hydroxyl number of 48 mg KOH g-1and a molar mass of 3.5 kg mol-1. The PU foam sample was composed of polyol A, an isomer mixture of 2,4- and 2,6-toluene diisocyanate (TDI) with isomer ratio of 80 / 20 (TDI index of 107), and water as a 30 foaming agent to chemically produce CO2. Diethylcarbonate (DEC), Diphenylcarbonate (DPC) ethanol, dipropylene glycol, trifluoro acetic acid (TFA), 3- (Trimethylsilyl)propanoic acid (TSP), and zinc acetate Zn(OAc)2 were purchased from Sigma-Aldrich. Table 1: Composition of PU foam and its constituting 5 trifunctional co-polyether polyol (Polyol A) PU Composition wt.% Polyol A 73 % TDI 26 % Additives 1 % Polyol A wt.% Monomer unit Glycerol 2.6 % 1 PO 87.6 % 53 EO 9.7 % 8 PO / EO 6.8 mol / mol - The reaction mixture for the depolymerisation Examples that follow comprised pieces of the PU foam discussed above, together with diethylcarbonate (DEC) or 10 diphenylcarbonate (DPC), optionally ethanol and / or a catalyst (zinc acetate) as appropriate. Unless otherwise stated, the reaction mixture was added to a 95 mL stainless steel Berghof BR-100 High Pressure Reactor with PTFE insert, thermowell, manometer and magnetic stirrer. 15 The autoclave was sealed, purged with argon and placed in a pre-heated aluminium block at 200oC to 210oC for the specified number of hours at 800 rpm stirring rate. Afterwards, the reactor was cooled to room temperature for 1 h, and pressure was slowly released. The reactor was 20 opened, the thermowell was washed with 20 mL acetone and the content of the reactor was transferred to a beaker. The solid precipitate was filtered through a filter paper and the reaction solvent was evaporated from the liquid product and the filtered solid under reduced pressure. The oily liquid left in the flask was dissolved in 2 mL of 10 mM of TSP solution in DMSO-d6 and 0.5 mL of CDCl3 for the quantitative1H NMR analysis.1H NMR spectra were recorded at room temperature using a Bruker 14.1 T magnet operating at 600.16 MHz for1H, equipped with an AVANCE NEO spectrometer and a 5 mm BBO probe. EXAMPLE 2 – Catalytic depolymerisation of PU foam in DEC 400 mg of polyurethane (PU) foam was depolymerised at 210 °C for 4 h with 20 mL DEC and 20 mg zinc acetate. The residual solid amounted to 31 mg (dry), which corresponds to a dissolution degree of 92 wt.%. The solid residue extracted from the filter paper contained a complex mixture of unidentified aromatic products, characterised by a broad1H NMR spectrum. According to Tables 2 and 3, the monomeric aromatics (TDC / TDA / TAC), total aromatics and polyol recovered in the liquid product amounted to 74.5 mol%, 99.5 mol% and 89 mol%, respectively. Notably, there was no TDA identified. The difference between monomeric and total aromatics is assigned to oligomeric aromatics. The polyol appeared to be terminated by carbonate groups. Elemental analysis showed that the solid residue contained 6% of zinc and the liquid 0.1% of zinc. Final proportions of products obtained after the process is shown in Table 3. The dissolution performance is also summarised in Table 3. Table 2: TDA, TAC, and TDC content in liquid after depolymerisation of 400 mg PU foam determined by1H NMR spectroscopy. Initial TDI in PU foam: 0.597 mmol (80:20 2,4:2,6-isomers), initial mmol of PO of polyol in PU foam: 4.410 mmol. NQ: Not quantifiable. Monomers n (mmol) TDX or polyol Recovered (mol%) 2,4-TDC 0.353 59.13 2,6-TDC 0.092 15.41 2,4-TDA NQ NQ 2,6-TDA NQ NQ 2,4-TAC NQ NQ 2,6-TAC NQ NQ Polyol 3.927 89.05 Table 3: Final proportions of products obtained after 5 depolymerisation with DEC. Recovery of polyol 89 (calculated) (mol%) Recovery of aromatics 99.5 (mol%) Dissolution (wt.%) 92 Solid product mass (mg) 31 Liquid product mass (mg) 401 Amine : carbamate ratio 0:100 Example 3 - Thermal depolymerisation of PU foam in DEC (for 4h) 10 Depolymerisation of 400 mg PU foam for 4h at 210°C in 20 mL DEC without catalyst led to 40 mg of residual solid, which corresponds to a degree of dissolution of 90 wt.% (Table 4). The aromatic and polyol recovered in the 15 liquid product amounted to 60 mol% and 83 mol%, respectively. The aromatic region of the1H NMR spectrum shows many poorly resolved peaks, which suggests that the liquid product still contain oligomeric TDX materials that result from incomplete depolymerisation. This still allows to determine an aromatic recovery but no TDC, TAC and TDA recovery. 5 Table 4: Final proportions of products obtained after depolymerisation with DEC without catalyst. Recovery of polyol 83 (calculated) (mol%) Recovery of aromatics 60 (mol%) Dissolution (wt.%) 90 Solid product mass (mg) 40 Liquid product mass (mg) 420 Example 4 - Thermal depolymerisation of PU foam in DEC 10 (for 16 h) Depolymerisation of 400 mg PU foam for 16h at 210 °C in 20 mL DEC without catalyst led to 38 mg of residual solid, which corresponds to a degree of dissolution of 90 15 wt.% (Table 5). The aromatic and polyol recovered in the liquid product amounted to 98 mol% and 91 mol%, respectively. The longer experiment resulted more non identifiable aromatic monomers with similar polyol recovery. 20 Table 5: Final proportions of products obtained after depolymerisation with DEC without catalyst for 16 hours. Recovery of polyol 91 (calculated) (mol%) Recovery of aromatics 98 (mol%) Dissolution (wt.%) 90 Solid product mass (mg) 38 Liquid product mass (mg) 500 Example 5 - Thermal depolymerisation of PU foam in DEC and ethanol (60 / 40 vol / vol) 5 200 mg PU foam was depolymerised for 4h at 210°C in 10 mL DEC / ethanol (60 / 40 vol / vol), in absence of catalyst, and led to full dissolution, with no residual solid being measured. According to Tables 6-7, the monomeric aromatic, 10 total aromatic and polyol recovered in the liquid product amounted to 88 mol%, ~100 mol% and 84 mol%, respectively. Notably, the aromatics consisted of TDC, TDA and TAC with an overall amine:carbamate molar ratio of 43:57. Accordingly, the addition of alcohol to the 15 dialkylcarbonate solvent results in significant aromatic amine by-products. Table 6: TDA, TAC, and TDC content in liquid after depolymerisation of 200 mg PU determined by1H NMR 20 spectroscopy. Initial TDI in PU foam: 0.299 mmol, initial mmol PO of polyol in PU foam: 2.20 mmol. Monomers n (mmol) TDX or polyol Recovered (mol%) 2,4-TDC 0.081 27.09 2,6-TDC 0.019 6.35 2,4-TDA 0.054 18.06 2,6-TDA 0.009 3.01 2,4-TAC 0.040 13.37 2,6-TAC 0.059 19.73 Polyol 1.852 84.18 Table 7: Final proportions of products obtained after depolymerisation with DEC / EtOH. Recovery of polyol 84.2 (calculated) (mol%) Recovery of aromatics 101.7* (mol%) Dissolution (wt.%) 100 Solid product mass (mg) None Amine : carbamate ratio 43:57 * >100% is assigned to experimental errors 5 Comparative Example 1 - Thermal depolymerisation of PU foam in ethanol 100 mg PU foam was depolymerised for 4h at 200°C in 5 mL ethanol, in absence of catalyst, and left 17 mg of 10 residual solid, which corresponds to a degree of dissolution of 83 wt.%. According to Tables 8-9, the monomeric aromatic, total aromatic and polyol recovered in the liquid product amounted to 59 mol%, 69 mol% and 77 mol%, respectively. Notably, the aromatics consisted of 15 TDC, TDA and TAC with an overall amine:carbamate molar ratio of 58:42. Accordingly, the use of alcohol as solvent results in significant aromatic amine by-products. 20 Table 8: TDA, TAC, and TDC content in liquid after depolymerisation of 100 mg PU determined by1H NMR spectroscopy. Initial TDI in PU foam: 0.149 mmol, initial mmol of PO polyol in PU foam: 1.10 mmol. Monomers n (mmol) TDX or polyol Recovered (mol%) 2,4-TDC 0.029 19.46 2,6-TDC 0.0055 3.69 2,4-TDA 0.017 11.41 2,6-TDA 0.004 2.68 2,4-TAC 0.010 6.71 2,6-TAC 0.023 15.44 Polyol 0.846 76.90 Table 9: Final proportions of products obtained after depolymerisation with ethanol. Recovery of polyol (mol%) 77 Recovery of aromatics 69 (mol%) Dissolution (wt.%) 83 Solid product mass (mg) 17 Amine : carbamate ratio 58:42 5 Summary of Depolymerisation Results from Examples 2 to 5 and Comparative Example 1 The results of the Examples discussed above are 10 summarised in Table 10. As shown, PU foam can be depolymerised to polyol A and TDC in the presence of DEC and a depolymerisation catalyst such as Zn(OAc)2(Example 2). The absence of catalyst requires higher severity (Examples 3 and 4) (e.g. longer depolymerisation time or 15 higher temperature) although the depolymerisation of the aromatics components to TDC is still incomplete after 16h (Example 4). The use of EtOH alone as depolymerisation solvent leads to significant formation of amines (Comparative Example 1). 20 In conclusion, DEC allows selective depolymerisation of polyurethanes to their polyol and polycarbamate components with or without a catalyst. Alcohols can be added to the depolymerisation medium to accelerate the reaction. However, this generally leads to the formation of at least some amines (43 mol% at 40:60 EtOH:DEC volume ratio). Pure alcohol leads to excessive amine formation 5 (58 mol%).

[0002] Table 10: Comparison of Examples. NQ: not quantifiable Ex. 2 Ex. 3 Ex. 4 Ex. 5 Comp. Ex. 1 Solvent DEC DEC DEC DEC / EtOH EtOH (20 ml) (20 (20 (60 / 40) (5 ml) ml) (10 ml) mL) Catalyst Zn(OAc)2 - - - - (20 mg) PU (mg) 400 400 400 200 100 Temperature 210 210 210 210 200 (oC) Time (h) 4 4 16 4 4 Liquid product 401 420 500 170 150 (mg) Solid product 31 40 36 0 17 (mg) Dissolution 92 90 90 100 83 (wt.%) Recovery of 89 83 91 84.2 77 polyol (mol%) Recovery of 99.5 60 98 101.7 69 aromatics (mol%) TDC Recovery 75 NQ NQ 33 23 (mol%) TDA Recovery NQ NQ NQ 21 14 (mol%) TAC Recovery NQ NQ NQ 32 22 (mol%) Amine:carbamate 0:100 - - 43:57 58:42 molar ratio EXAMPLE 6 – Catalytic depolymerisation of PU foam in DPC 1g of polyurethane (PU) foam and 5g diphenylcarbonate (DPC) (1:5 molar excess on urethane + urea groups in PU) were loaded in a 100 ml round bottomed flask and 40 mg zinc acetate was added under nitrogen atmosphere. The mixture was refluxed for 4 hours at 210°C. The crude solid product was scrapped from the flask, melted at 80°C and filtered through a filter paper kept at 80°C. The product left on the filter paper amounted to 0.1 g after drying for 1h under vacuum, which indicates deep depolymerisation / dissolution of the PU. A sample of 0.1 ml of hot liquid filtrate was taken and diluted with 0.5 ml DMSO-d6for quantitative1H NMR analysis. The DMSO solution was clear and visibly free of suspected solid, which confirms the deep depolymerization / dissolution of the PU. The1H-NMR spectrum showed clear presence of dissolved polyol and TDI- derivatives, as evidenced by the signal of their respective -CH3 groups at δ 1.04 ppm and δ 1.80 ppm- 2.40 ppm (see Figure 5). These -CH3 groups came in a molar ratio of 4.8:1, which is lower than the 7.4:1 present in the PU and, thereby, suggest better dissolution of the polar TDI derivatives than the apolar polyol in the reaction solvent (DPC) and / or in the analysis solvent (DMSO). The N-bound protons suggest the monomeric aromatic product consists of TDC:TDA in a 5.33:1 molar ratio. The aminocarbamate TAC could not be quantified as N-bound H disappears under the aromatic H of the abundant unreacted DPC. These results show that PU can be deeply depolymerized to its constituting polyol and TDI- derivatives when reacted with DPC. Example 7 - Catalyst screening Catalyst screening experiments were conducted to study the depolymerisation of PU foam under three different catalysts with the same DEC / foam concentration: 5 zinc acetate (0.1 mmol, 20 mg), zinc chloride (0.1 mmol, 15 mg), and zinc triflate (0.1 mmol, 40 mg). PU foam pieces, solvent (diethyl carbonate) and the catalyst were added to a 95 mL stainless steel Berghof BR-100 High Pressure Reactor with PTFE insert, thermowell, manometer 10 and magnetic stirrer. The autoclave was sealed, purged with argon and placed in a pre-heated aluminium block at 210oC for 4 h at 800 rpm stirring rate. Afterwards, the reactor was cooled to room temperature for 1 h, and the pressure was slowly released. The reactor was opened, the 15 thermowell was washed with 20 mL acetone and the content of the reactor was transferred to a beaker. The solid precipitate was filtered through a filter paper and the reaction solvent was evaporated from the liquid product and filtered solid under reduced pressure. The oily 20 liquid left in the flask was dissolved in 2 mL of 10 mM of TSP solution in DMSO-d6 and 0.5 mL of CDCl3 for the quantitative1H NMR analysis. The results are shown in Table 11. In conclusion, catalysts are demonstrated to improve 25 both the recovery of polyols and aromatics in addition to reducing the yield of amines and reducing process severity (such as time and temperature). The results show that different catalysts perform with variable efficiency for a specific polyurethane indicating that each 30 individual system would require standard optimisation as to which catalyst works best for selective recovery of carbamate aromatics in favour of amine aromatics. Table 11: Recovery of polyol and aromatics in liquid after depolymerisation of 400 mg PU with different catalysts determined by1H NMR spectroscopy. Initial TDI in PU foam: 0.597 mmol, initial mmol of PO polyol in PU foam: 4.410 mmol. Experiment Catalyst Recovery Recovery Recovery (0.1 of Polyol of of TDC mmol) (mol%) Aromatics (wt.%) (mol%) 1 Thermal 83 60 NQ 2 Zn(OAc)289 99.5 75 3 Zn(OTf)2 91 91 NQ 4 ZnCl2 79 66 22 Example 8 - Separation (Step 2) by selective crystallisation of components of the product stream generated by the depolymerisation of PU foam (in Step 1) 1.1 g of Polyol A were mixed with 0.49 gram of 2,4- toluene dimethylcarbamate (Obtucarbamate A, CAS: 6935-99- 5), (i.e. in weight ratio of 70:30 that is similar to the ratio present in PU foam). The mixture was loaded into a vial and heated to 180 °C, a typical temperature for PU depolymerisation. Once the liquid was homogenized to a single liquid phase, the vial was opened, loaded with 1 ml of diethylcarbonate without substantial cooling, closed again and shaken for further homogenization. The mixture was then cooled to room temperature, loaded into centrifuge vials and centrifuged for 10 minutes at 4000 rpm. Following centrifugation, the vials consisted of two phases, one heavy carbamate-rich solid phase and a light polyol-rich liquid phase in a weight ratio of about 40:60. Example 9 - Separation (Step 2) by solvent extraction of components of the product stream generated by the depolymerisation of PU foam (in Step 1) 200 mg PU foam was depolymerized in 10 ml diethylcarbonate at 200°C in the presence of 10 mg zinc acetate as catalyst (NB: analogous conditions to Example 2) for 4 hours. The reactor was then cooled to room temperature and opened. The thermowell was washed with 20 mL acetone and the contents of the reactor were transferred to a beaker. The solid precipitate was filtered through a filter paper and filtrate reduced in volume under reduced pressure. The oily liquid residue (400-450 mg) was dissolved in 2 mL of deuterated DMSO that contained 10 mM of TSP as internal standard, which lead to a spontaneous separation of the sample into two liquid phases.1H NMR analysis of the upper phase showed mainly the aliphatic -CHx- peaks of the ethylcarbonate- functionalised polyol precursor and the ethyl protons of its ethylcarbonate chain-ends (1-1.5 and 3.0-4.0 ppm). Minimal amounts of aromatic =CH- and aromatic-bound CH3- (7.0-8.0 and ~2.0 ppm) were observed. In contrast,1H-NMR analysis of the combined top and bottom phases redissolved in CDCl3showed the presence of both polyol and aromatic components. Example 10 - Pyrolysis of alkylcarbamates to isocyanates (Step 3) Methyl N-phenyl carbamate (MPC) was selected as the model compound. Pyrolysis of MPC was evaluated in a tubular reactor (OD=6mm, ID=4mm, length=6m). The tube was coiled around an aluminium heating block which was equipped with a 1000 watts heating element located at the centre of the block. The feed (10 wt.% MPC in o-dichlorobenzene) was pumped through the reactor using an HPLC pump. Prior to 5 the start of the experiment, the tube was heated to the reaction temperature and continuously purged with a flow of nitrogen gas. Once the reaction temperature was reached the flow of nitrogen was stopped and the feed was then pumped through the reactor at flow rates varying 10 from 1-4 ml / min. The reactor products were then passed through a condenser operating at 20ºC. The product was then collected as a liquid. For sampling, a known quantity of the products was extracted from the product line and the isocyanate was 15 immediately stabilized by derivatization by mixing the products with a derivatization solution containing 1-(2- Pyridyl)piperazine (PP) in dimethyl sulfoxide (DMSO). The derivatized samples were then treated and analysed using liquid chromatography (LC) equipped with a UV detector. 20 At the end of the experiment the tube was purged with nitrogen and subsequently with air at 400ºC to remove any contamination and residue from the surface of the tube. Liquid chromatography (LC) was used to quantify the amounts of MPC, phenyl isocyanate (as PP-derivative), 25 diphenylurea (DPU), and aniline in the reaction mixture. LC-UV was performed on the ThermoFisher Ultimate 3000 series with an Ascentis® Express RP-Amide (15cm*2.1mm, 2.7 µm) HPLC column accompanied by an Ascentis® Express 90Å RP-Amide guard column at room temperature. 30 A gradient mobile phase (0.2 ml / min) consisting of [A] 5 mM ammonium acetate with deionized water (0.1%v Formic acid) and [B] Acetonitrile (0.1%v Formic acid) was used. The UV detector was set to measure at 254 nm and 310 nm. All the components were visible at 254 nm, and 310 nm was used to verify some of the components (e.g., PI). Standard solutions for the aniline, diphenylurea (DPU), phenyl isocyanate (PI) (as PP-derivative), and methyl n-phenylcarbamate (MPC) were created with a concentration of 1 mg / ml in DMSO and then further diluted using a mixture of water: acetonitrile (1:1 v) to create calibration samples. Once the extracts from the reaction were neutralized, they were prepared for analysis in LC-UV. The samples were first filtered (Whatman 0.2 µm filter) and then diluted with equal volumes of water and acetonitrile. The stability and reproducibility of the analysis done via LC-UV were evaluated at regular intervals to maintain a reliable method. Conversion, yield, selectivity and mole balance were expressed in mol% relative to the phenyl group fed as MPC into the reactor. As illustrated in Table 12, isocyanates were obtained in high yield at different conversion levels of carbamates during a thermal depolymerisation reaction. Table 12: Depolymerisation of carbamate and the selectivity toward phenyl isocyanate (PI) in the range of experiments performed with 95% confidence intervals. Experiments were performed at atmospheric pressure and no aniline was observed within the products. Flow Temperature Conversion PI DPU Mole Rate (oC) (%) Selectivity Selectivity Balance (ml / min) (%) (%) (mol%) 2 300 68.2 97.7 3.9 99.6 ± 2.9 ± 1.5 ± 0.3 ± 1.1 2 350 79.1 91.7 4.3 96.8 ± 0.7 ± 0.5 ± 0.3 ± 0.5

Claims

SP3060 - 34 - C L A I M S 1. A process for the depolymerisation of a polyurethane material, comprising the following steps: a) reacting the polyurethane material with a dialkylcarbonate or a diarylcarbonate or an 5 alkylarylcarbonate to produce i) at least one polyol and / or at least one carbonate-functionalised polyol, and ii) at least one polycarbamate; b) separating i) the at least one polyol and / or at least one carbonate-functionalised polyol, and ii) the at 10 least one polycarbamate; and c) converting the at least one polycarbamate into at least one polyisocyanate.

2. The process of claim 1, wherein in step a) the 15 polyurethane material is reacted with the dialkylcarbonate or the diarylcarbonate or the alkylarylcarbonate in the presence of an alcohol.

3. The process of claim 2, wherein the polyurethane 20 material is reacted with the dialkylcarbonate and the alcohol is an alkylalcohol.

4. The process of claim 3, wherein the alkylalcohol is a C1-C12 alkylalcohol, preferably wherein the alkylalcohol 25 is methanol or ethanol.

5. The process of any preceding claim, wherein the dialkylcarbonate is a C1-C12 dialkylcarbonate, preferably wherein the dialkylcarbonate is dimethylcarbonate or 30 diethylcarbonate.

6. The process of claim 2, wherein the polyurethane material is reacted with the diarylcarbonate and the alcohol is an arylalcohol. 5 7. The process of claim 6, wherein the arylalcohol is a phenylalcohol, preferably wherein the phenylalcohol is phenol or m-cresol.

8. The process of any of claims 1, 2, 6 or 7, wherein10 the diarylcarbonate is diphenylcarbonate or bis(4- methylphenyl)carbonate or bis(4-ethylphenyl)carbonate.

9. The process of claim 2, wherein the polyurethane material is reacted with the alkylarylcarbonate and the 15 alcohol is an alkylalcohol or an arylalcohol or a combination thereof.

10. The process of claim 9, wherein the alkylalcohol is a C1-C12 alkylalcohol, preferably wherein the alkylalcohol 20 is methanol or ethanol, and / or the arylalcohol is a phenylalcohol, preferably wherein the phenylalcohol is phenol or m-cresol.

11. The process of any of claims 1, 2, 9 or 10, wherein25 the alkylarylcarbonate is ethyl-phenylcarbonate, methyl- phenylcarbonate, ethyl-(4-methyl-phenyl)carbonate, or methyl-(4-methyl-phenyl)carbonate.

12. The process of any preceding claim, wherein in step 30 a) the polyurethane material is reacted with the dialkylcarbonate or the diarylcarbonate or the alkylarylcarbonate in the presence of a catalyst.

13. The process of claim 12, wherein the catalyst is selected from the group consisting of a Lewis acid catalyst and a Bronsted base catalyst. 5 14. The process of claim 12 or claim 13, wherein the catalyst is a zinc-, tin- or titanium-based Lewis acid catalyst, preferably a zinc acetate catalyst, a titanium acetate catalyst or a tin octanoate catalyst. 10 15. The process of any preceding claim, further comprising, after step b) and before step c), purifying i) the at least one polyol and / or at least one carbonate- functionalised polyol, and / or ii) the at least one 15 polycarbamate.

16. The process of any preceding claim, wherein step c) is performed by pyrolysis. 20 17. The process of any preceding claim, further comprising purifying the at least one polyisocyanate of step c).

18. The process of any preceding claim, wherein the 25 process further comprises converting the at least one carbonate-functionalised polyol to at least one polyol by alcoholysis.

19. The process of any preceding claim, wherein the at 30 least one polyol and / or the at least one polyisocyanate are recycled for use in the production of a new polyurethane material and / or any other new useful material.

20. The process of any preceding claim, wherein the polyurethane material is a polyurethane foam.

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