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 an alcohol to produce i) at least one polyol and ii) an aromatic mixture comprising at least one polycarbamate and at least one amine-containing compound; b) separating the at least one polyol and the aromatic mixture; c) converting the aromatic mixture into a polycarbamate aromatic fraction by reaction of the aromatic mixture with a carbonate; and d) converting the polycarbamate aromatic fraction into a polyisocyanate aromatic fraction by converting the polycarbamate compounds of the polycarbamate aromatic fraction into polyisocyanate compounds.

Description

[0001] SP3142 - 1 - PROCESSES FOR THE 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 hydrolysis, acidolysis, (glycolysis) and aminolysis are known for the depolymerisation of polyurethane materials but are still underdeveloped and 5 are not apt for their full recycling and valorisation. Split phase glycolysis currently represents the most promising method for polyurethane recycling by using excess diethylene glycol to shift the equilibrium of the depolymerisation reaction toward the polyol product and 10 allows the purification and recycling of said polyols. However, such methods are inefficient as a result of incomplete depolymerisation of the polyurethane. Polyurethane contains carbamate bonds (formed by the reaction of an alcohol group with an isocyanate group when 15 producing the polyurethane) and urea bonds (created when hydrolysing excess isocyanates for the liberation of carbon dioxide for foam blowing during cross-linking). Alcoholysis (glycolysis) of the carbamate bonds leads to new carbamate components while the alcoholysis of urea 20 bonds leads to a mixture of carbamate and amine components. The presence of amines makes the overall product generally difficult to upgrade to isocyanates and so is often discarded. Such upgrading of the mixture would require the separation and dedicated processing of the 25 carbamate and amine components. Further, the direct conversion of isolated amines into isocyanates requires the use of phosgene, which is both highly toxic and corrosive. Therefore, there is a need to provide safer, 30 simpler, cheaper and more efficient methods for the depolymerisation and subsequent recycling of polyurethane materials, in particular polyurethane foams. These and 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 5 the following steps: a) reacting the polyurethane material with an alcohol to produce i) at least one polyol and ii) an aromatic mixture comprising at least one polycarbamate and at least one amine-containing compound; 10 b) separating the at least one polyol and the aromatic mixture; c) converting the aromatic mixture into a polycarbamate aromatic fraction by reaction of the aromatic mixture with a carbonate; and 15 d) converting the polycarbamate aromatic fraction into a polyisocyanate aromatic fraction by converting the polycarbamate compounds of the polycarbamate aromatic fraction into polyisocyanate compounds. Within the scope of this application it is expressly 20 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 thereof, may be taken independently or in any combination. 25 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. 30 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; Figure 2 illustrates a chemical scheme according to an embodiment of the for a first step in the depolymerisation of a polyurethane foam, by alcoholysis, into its polyol and aromatic mixture component parts. 5 Figure 3 illustrates a chemical scheme according to an embodiment of the invention for a subsequent step in the depolymerisation process using at least diethylcarbonate to convert amines in the aromatic mixture to polyalkylcarbamates. 10 Detailed Description of the Invention In general terms the present invention provides methods for the depolymerisation of carbamate bond- containing materials, particularly polyurethane materials, 15 including polyurethane foams, and the optional subsequent recycling of the constituent component monomers or component monomer precursors suitably for the purpose of making new polyurethanes or other useful materials. For the purpose of the following disclosure, the 20 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 which contains at least two, more commonly many, of a particular type of 25 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 isolate and / or purify the 30 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 component parts in their pure forms as necessary. The methods comprise reacting the polyurethane material with an alcohol, wherein the alcohol may be an 5 alkylalcohol or an arylalcohol, to produce at least one polyol and an aromatic mixture comprising at least one polycarbamate and at least one amine-containing compound. The at least one amine-containing compound may comprise at least one polyamine and / or at least one mixed amine-10 carbamate compound, wherein the at least one amine- carbamate compound may comprise at least one amine functional group and at least one carbamate functional group. The at least one polyol, which is one of the 15 component parts of a polyurethane, may be separated from the aromatic mixture, which comprises precursors to the other component parts (for example by boiling point, melting point, molecular size or molecular affinity) and optionally purified using standard chemical protocols. 20 The aromatic mixture, comprising at least one polycarbamate and at least one amine-containing compound, may be converted into a polycarbamate aromatic fraction wherein the amine-containing components / compounds of the aromatic mixture are converted into carbamate components 25 by reaction of the aromatic mixture with a carbonate. The carbonate may be a C1-C12 dialkylcarbonate, such as dimethylcarbonate, diethylcarbonate or dipropylcarbonate. The carbonate may be a diarylcarbonate, such as diphenylcarbonate or a phenyl-substituted 30 diphenylcarbonate. The carbonate may be a mixed alkylarylcarbonate, such as ethyl-phenylcarbonate, methyl- phenylcarbonate or tert-butyl-phenylcarbonate. The polyalkylcarbamate aromatic fraction may be purified using standard protocols, which may include (vacuum) distillation, crystallization, extraction or micro / nanofiltration. Optionally, if the polyalkylcarbamate aromatic fraction contains more than one type of polyalkylcarbamate 5 component, the different components may be separated from each other to yield multiple polycarbamate aromatic fractions, or the polycarbamate aromatic fraction may be used as a mixture of multiple different polycarbamate components. 10 The polycarbamate aromatic fraction may be converted into a polyisocyanate aromatic fraction by conversion of the carbamate functional groups into polyisocyanate functional groups by any suitable method, for example by pyrolysis. Optionally, if the polyisocyanate aromatic 15 fraction contains more than one type of polyisocyanate component, the different components may be separated from each other before any further use thereof. The polyisocyanate aromatic fraction, or differing components thereof, may be purified using standard protocols, which 20 may include (vacuum) distillation, crystallization, extraction or micro / nanofiltration. The purified or unpurified polyol and / or polyisocyanate aromatic fraction and / or at least one polyisocyanate compound of the polyisocyanate fraction may 25 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. An advantage of the process of the disclosed 30 invention over the state of the art lies in the use of a carbonate to treat the aromatic mixture derived from the depolymerisation of a polyurethane material. Amine- containing compounds and polycarbamates require different chemistries for their conversion into polyisocyanates, wherein polyisocyanates comprise one of the component parts of a polyurethane typically necessitating the separation of said amine-containing compounds and polycarbamates prior to such conversion to 5 polyisocyanates. Separation and upgrading of the amine- containing compounds and polycarbamate components of the aromatic mixture can be difficult to achieve and may be economically unfeasible, often leading to the entire aromatic mixture being disposed of and not recycled. 10 Further, the direct conversion of isolated amines into isocyanates typically requires the use of phosgene, which is both highly toxic and corrosive. The present methods described herein allow for the amine-containing components of the aromatic mixture to be easily converted into 15 polycarbamates, which can then in turn be converted to polyisocyanates. 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 20 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 25 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 30 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 an embodiment of the invention showing a process (100) of depolymerising and recycling a polyurethane material. 5 Step 1 (101) of the process involves combining starting reagents, which may include at least a polyurethane material (e.g. a polyurethane foam) and an alcohol, required for the depolymerisation of the polyurethane material in a suitable reaction setup and 10 cleavage of the carbamate bonds and / or the urea 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, 15 which may include an 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 20 comprise, for example, a 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 alcohol may be any suitable alkylalcohol or arylalcohol. The alcohol may be a linear, branched or 25 cyclic alkylalcohol. The alcohol may be a saturated or unsaturated alkylalcohol. The alcohol may be any C1-C12 alkylalcohol. Suitably, the alcohol is selected from the group consisting of methanol, ethanol, propanol, and butanol. Preferably, the alcohol is methanol or ethanol. 30 More preferably, the alcohol is ethanol. The arylalcohol may be a substituted arylalcohol. The substituted arylalcohol may be an alkyl-substituted arylalcohol. Suitably, the arylalcohol may be phenol or m-cresol. Optionally, an additional organic solvent may be added to the reaction 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 least 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. It is conceivable that the polyurethane material may be depolymerised into more than one type of polyol and / or more than one type of polycarbamate and / or amine-containing compound, depending on the composition of the polyurethane. Suitably, the polycarbamate may be a polyalkylcarbamate, suitably a polyethylcarbamate, suitably a diethylcarbamate. The polycarbamate may be a polyarylcarbamate, suitably a polyphenylcarbamate, suitably a diphenylcarbamate. The polycarbamate may be a mixed alkylarylcarbamate, such as an ethyl-phenylcarbamate, containing at least an ethylcarbamate group and least a phenylcarbamate group. Suitably, the amine-containing compound may be a diamine or amino-ethylcarbamate compound, containing at least an 5 amino group and an ethylcarbamate group. Step 2 (102) of the process involves separating the components of the product stream generated by the depolymerisation of the polyurethane material from each other and optionally purifying one or more of these 10 components. The separation process may be performed by exploiting differences in the boiling point, melting point, molecular size, chemical affinity, or combination thereof of the components. The product stream can be separated into, for 15 example: (1) unreacted depolymerisation solvent which may comprise unreacted alkylalcohol and / or unreacted arylalcohol and / or the optional additional organic solvent, which may be recycled to the depolymerisation reactor; (2) at least one polyol, which may be used for 20 producing new polyurethane materials, optionally after finishing the process or upgrading; (3) an aromatic mixture, which may comprise at least one polycarbamate aromatic compound and at least one amine-containing compound, which may eventually be upgraded to at least one 25 polyisocyanate and subsequently used for producing new polyurethane materials or other useful materials; and (4) eventual solid residue, which may be discarded, eventually after further work up to recover incompletely depolymerised polyurethane material. 30 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 take various forms, some of which are described below. In one preferred example, the product stream may be separated by consecutive if possible based on the relative boiling points of the various components of the product stream which would depend on the 5 composition of a PU foam for recycling. A first distillation may be run at atmospheric pressure to recover unreacted solvent, which may be ethanol (Tb= 78°C at 1 atm.) as top product(s). The remaining components may then be subjected to distillation under high vacuum to recover 10 the aromatic components of the aromatic mixture 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 (the polyol may have a boiling point temperature, Tb > 300°C at 1 atm) as a bottom product. 15 Vacuum distillation may be required to avoid chemical degradation of the polyol. In another preferred example, the products may be recovered by crystallisation techniques or combining crystallisation techniques and distillation techniques. 20 All solid components may first be removed from the product stream which may then be cooled to selectively crystallise the aromatic components, possibly including unreacted dicarbonate, out of the supernatant liquid. The aromatic components of the aromatic mixture may be characterised by 25 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 optional solvent as top product and the polyol as bottom product. In another example, the aromatic components of the 30 aromatic fraction 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 with 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 The remaining bottom product may be then subjected to liquid extraction by adding an apolar solvent to selectively extract the polyol 5 and / or adding a polar solvent to selectively extract the aromatic mixture comprising aromatic components and / or dicarbonate. In a second option, for instance, the polar depolymerisation mixture containing optional depolymerisation solvent, aromatic components and polyols 10 may be contacted with an apolar solvent to extract the polyol. The resulting two streams generated by solvent extraction may then be subjected to distillation or crystallisation to recover the extraction solvent from the aromatic components and unconverted dicarbonate, or from 15 the polyol. In another example, a polar antisolvent may be added to the depolymerization mixture to push the polyol out of solution. In another example, the depolymerisation mixture, optionally hot depolymerisation mixture, may be subjected 20 to nanofiltration to recover the polar and low-molecular weight component as a polyol-lean permeate from a polyol- rich retentate. The polyol-rich retentate may then be further separated into aromatic, polyol and solvent streams according to any of the examples mentioned above. 25 The polyol-lean permeate can be separated into a solvent stream and an aromatic stream by means of distillation and / or crystallisation. Optionally, trace amine by- products may be separated from the aromatic stream by water washing. 30 The above-described examples of step 2 (102) are not intended to limit the invention by any means and any 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 the aromatic mixture comprising at least one polycarbamate 5 and at least one amine-containing compound into a polycarbamate aromatic fraction containing at least one polycarbamate aromatic compound. Suitably the aromatic mixture is converted to the polycarbamate aromatic fraction by reaction with at least a carbonate. 10 Suitably, the carbonate is a dialkylcarbonate, which may be any suitable dialkylcarbonate, which may be a C1- C12 dialkylcarbonate, preferably dimethylcarbonate or diethylcarbonate. Alternatively, the carbonate may be a diarylcarbonate, such as diphenylcarbonate or an alkyl- 15 substituted diphenylcarbonate. Further alternatively, the carbonate may be a mixed alkylarylcarbonate, such as ethyl-phenylcarbonate, methyl-phenylcarbonate or tert- butyl-phenylcarbonate. The carbonate is preferably used in a molar excess relative to the nitrogen contained in the 20 aromatic mixture. Optionally, a catalyst may also be used in the reaction. The catalyst may be a Lewis acid catalyst. The catalyst may comprise a metal element including, but not limited to, zinc (Zn), tin (Sn) and titanium (Ti). The 25 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. The catalyst be a Bronsted base catalyst. The 30 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 comprise a lithium ion, a sodium ion or a potassium ion. The catalyst may be lithium hydroxide, sodium hydroxide or potassium hydroxide. The may be zinc phenoxide or a titanium alkoxide, such as titanium ethoxide, or titanium phenoxide. The catalyst may be an aprotic organic base. The aprotic organic 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). 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 least about 10 wt.%, or at least about 15 wt.% relative to the aromatic mixture. 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 aromatic mixture. The conversion of the aromatic mixture to the polycarbamate aromatic fraction 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, at most about 350oC, at most about 370oC, or at most about 400oC. The conversion of the aromatic mixture to the polycarbamate aromatic fraction 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 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. Optionally, an organic solvent may also be used. The organic solvent is preferably polar and aprotic. For instance, it may contain an ether, ester, lactone, ketone, sulfone, sulfoxide. The solvent may be selected from the group consisting of dioxane, tetrahydrofuran, dimethoxyethane, bis(methoxyethyl)ether), caprolactone, gamma-valerolactone, acetone, butanone, and sulfolane. Step 4 (104) of the process involves conversion of the polycarbamate aromatic fraction into a polyisocyanate aromatic fraction. Suitably the polyalkylcarbamate aromatic fraction is converted to the polyisocyanate aromatic fraction by pyrolysis. Suitably, the polyisocyanate(s) of the polyisocyanate aromatic fraction is a diisocyanate(s). Where pyrolysis is suitably used to generate the polyisocyanate aromatic fraction from the polycarbamate aromatic fraction, 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 at most about 50 seconds, and at most about 60 seconds may be used. Additionally, a solvent may be used, wherein the 5 solvent is preferably an aprotic, polar solvent. The solvent may suitably be dichlorobenzene. The process may be performed under an inert atmosphere, which may be a nitrogen atmosphere. An alcohol may be liberated from the polycarbamate 10 aromatic fraction upon conversion to the polyisocyanate aromatic fraction. Optionally, the alcohol may be separated from the polyisocyanate aromatic fraction. Optionally, if the polyisocyanate aromatic fraction comprises more than one type of polyisocyanate, Step 4 15 (104) may further involve separation and further optional purification of the different polyisocyanates by any suitable means. Step 5 (105) of the process is optional and involves the use of the at least one polyol output from Step 2 20 (102) and / or the at least one polyisocyanate output from step 4 (104) 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. The at least one polyol output from Step 2 25 (102) and / or the at least one polyisocyanate output from step 4 (104) can optionally be blended with virgin polyols and / or virgin polyisocyanates prior to use in the production of a new polyurethane material and / or any other new useful material. 30 Optionally, the alcohol output from step 3 and step 4 (103 and 104) may be regenerated into carbonates via reaction of the alcohol groups with, for example, a cyclic carbonate, such as ethylene carbonate or propylene carbonate or by reaction of the alcohol groups with carbon monoxide in the presence of oxygen and a catalyst (oxidative carbonylation). Figure 2 shows multiple embodiments of the depolymerisation reaction referred to in step 1 (101) of 5 Figure 1, illustrated by 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 10 alcohol, here ethanol (EtOH). The PU-1 depolymerises into the components, Polyol A, and 2,4-toluene(diethylcarbamate) (2,4-TDC) and 2,6- toluene(diethylcarbamate) (2,6-TDC), 2,4-toluene(diamine) (2,4-TDA), 2,6-toluene(diamine) (2,6-TDA), (2-amino-4-15 ethylcarbamate)toluene (2,4-TAC), (4-amino-2- ethylcarbamate)toluene (4,2-TAC) and (2-amino-6- ethylcarbamate)toluene (2,6-TAC). Advantageously, 2,4-TDA, 2,6-TDA, 2,4-TAC 4,2-TAC and 2,6-TAC may be converted into their corresponding dialkylcarbamates, 2,4-TDC and 2,6- 20 TDC, by reaction with diethylcarbonate and optionally, zinc acetate, avoiding the necessity of separating the amine-containing components (2,4-TDA, 2,6-TDA, 2,4-TAC, 4,2-TDA, and 2,6-TAC) from the polycarbamate components (2,4-TDC and 2,6-TDC) of the aromatic mixture or disposing25 of the aromatic mixture altogether. As such, amine- containing compounds of the aromatic mixture may be converted into a polyalkylcarbamate aromatic fraction, which may be converted into a polyisocyanate fraction comprising at least one polyisocyanate compound, using 30 pyrolysis. The advantage of this method is two-fold. First, the need to separate out the amine components from the carbamate components in the aromatic mixture resulting from depolymerisation of the polyurethane foam in order to achieve recycling of the aromatic mixture, which may be costly, is avoided. the amine components of the aromatic mixture may be easily consumed within the recycling process such that the components of the aromatic 5 mixture may be converted into a polyisocyanate aromatic fraction without the need for toxic or corrosive reagents, such as phosgene which is usually used to convert amines into isocyanates, such that the polyurethane foam is easily depolymerised and converted into its starting 10 materials for 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 any compatible 15 polyurethane material, derived from any other component polyol(s) and polyisocyanate(s), into its component parts, or component part precursors, for optional circular recycling. The invention is further exemplified in the 20 following non-limiting examples. EXAMPLES EXAMPLE 1 – Chemicals and polyurethane foam 25 The chemicals and polyurethane foam 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 30 polyol consisting of PO and EO repeating units, with a 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 foaming agent to produce CO2. Diethyl carbonate (DEC), ethanol, dipropylene glycol, trifluoro acetic acid (TFA), 3-(Trimethylsilyl)propanoic acid (TSP), and zinc 5 acetate Zn(OAc)2 were purchased from Sigma-Aldrich. Table 1: Composition of PU foam and its constituting 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 10 Example 2 - Polyurethane foam alcoholysis 108.2 mg of PU foam pieces and 5 mL ethanol were added to a 95 mL stainless steel Berghof BR-100 High Pressure Reactor with PTFE insert, thermowell, manometer 15 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 pressure was slowly released. The reactor was opened, the 20 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 the reaction solvent was evaporated from the liquid product and the filtered solid under reduced pressure. The oily liquid left in the flask 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 in DMSO-d6using a Bruker 14.1 T magnet operating at 600.16 MHz for1H, equipped with an AVANCE NEO spectrometer and a 5 mm BBO probe. 17 mg of residual solid was left, which corresponds to a degree of dissolution of 84 wt%. According to Tables 2-3, the aromatic and polyol recovered in the liquid product amounted to 61 mol% and 72 mol%, respectively. Notably, the aromatics consisted of TDC, TDA and TAC. The use of alcohol as solvent results in significant aromatic amine by-products. Table 2: TDA, TAC, and TDC content in liquid after depolymerization of 108.2 mg PU determined by1H NMR spectroscopy. Initial TDI in PU foam: 0.164 mmol, initial mmol of PO polyol in PU foam: 1.186 mmol Monomers n (mmol) TDX or polyol Recovery (mol%) 2,4-TDC 0.029 17.68 2,6-TDC 0.0046 2.80 2,4-TDA 0.017 10.38 2,6-TDA 0.0038 2.31 2,4-TAC 0.010 6.10 2,6-TAC 0.023 14.02 Polyol 0.85 71.66

[0002] Table 3: Final proportions of products obtained after depolymerization with Recovery of polyol 72 (mol%) Recovery of aromatics 61 (mol%) Recovery of monomeric 53 aromatics (mol%) Dissolution (wt%) 84 Solid product mass (mg) 17 Liquid product mass 150 (mg) This Example shows that polyurethane foam can be 5 converted to polyol and a mixture of aromatic dicarbamate, aminocarbamate and diamine products. EXAMPLE 3 – Converting aniline to ethyl-N-phenylcarbamate (EPC) at 125°C under reflux 10 Aniline (0.9 ml, 10 mmol) and diethylcarbonate (DEC) (12 ml, 99 mmol) were loaded in a 50 ml round bottomed flask and various catalysts (2-13 mol% on aniline) were added under nitrogen atmosphere. The mixture was refluxed 15 for 18 hours at 125°C (boiling temperature of DEC). The solid precipitate was filtered over a filter paper and the DEC was evaporated from the solid under reduced pressure. The crude product was dissolved in CDCl3 for quantitative 1H NMR analysis.

[0003] Table 4: Converting aniline to ethyl-N-phenylcarbamate (EPC) (Molar ratio of = 1:10 ,125oC, time = 18 hours) Catalyst mol % Conversion of Yield of EPC (on aniline) Aniline none - 20% 18% Zn(OAc)2 2.2 58% 55% Zn(OAc)24.4 89% 85% Zn(OAc)28.7 93% 90% Zn(OAc)2 13 100% 100% Cu(OAc)2 5 6% 6% Co(OAc)25 6% 6% NaOAc 5 0 0 KOAc 5 80% 70% MK10 * 5 30% 30% * Montmorrilonite K10 clay This example shows that amines can be upgraded to a dicarbamate product by reaction with a dialkylcarbonate. EXAMPLE 4 – Converting aniline to ethyl-N-phenylcarbamate (EPC) at 180°C in autoclave Aniline (0.9 ml, 10 mmol) and diethylcarbonate (DEC) (12 ml, 99 mmol) were loaded in a 45 ml autoclave and various Zn(OAc)2catalysts (5 mol% on aniline) were added under nitrogen atmosphere. The mixture was heated for 2 hours at 180°C. The solid precipitate was filtered over a filter paper and the DEC was evaporated from the solid under reduced pressure. The crude product was dissolved in CDCl3 for the quantitative1H NMR analysis.

[0004] Table 5: Converting aniline to ethyl-N-phenylcarbamate (EPC), in presence of Zn 2 (5 mol% on aniline) at 180oC for 2 h) Aniline:DEC Conversion of Yield of Aniline EPC 1:10 99% 99% 1:1 <5% <5% This example shows that the amine resulting from the alcoholysis step can be upgraded to a dicarbamate product by reaction with dialkylcarbonate. EXAMPLE 5 – Converting diphenylurea (DPU) to ethyl-N- phenylcarbamate (EPC) at 180°C in autoclave Diphenylurea (250 mg, 1.18 mmol) and diethylcarbonate (DEC) (4 ml, 35 mmol) were loaded in a 45 ml autoclave and various catalysts (20 mol% on diphenylurea) were added under nitrogen atmosphere. The mixture was heated for 2 hours at 180°C. The solid precipitate was filtered over a filter paper and the DEC was evaporated from the solid under reduced pressure. The crude product was dissolved in CDCl3for the quantitative 1H NMR analysis. The molar yields are defined per mole of phenyl, meaning to 100% yield of EPC represents two mole of EPC being produced from 1 mole of DPU. Table 6: converting DPU to ethyl-N-phenyl carbamate (180oC, DPU:DEC:Zn(OAc)2 molar ratio 1:30:0.2) Experiment Reaction Conversion of Yield of EPC Yield of time DPU Aniline 1 0.5 h 24% 11% 12% 2 1 h 41% 27% 14% 3 2 h 78% 73% 5% 4 4 h 99% 99% <1% 5 6 h 99% 99% <1% This Example shows that residual urea products (e.g. diphenylurea) that would from incomplete depolymerisation of the polyurethane foam can also be converted to carbamate product by reaction with 5 dialkylcarbonate. EXAMPLE 6 – Pyrolysis of carbamates to isocyanates (step 4) Methyl N-phenyl carbamate (MPC) was selected as the 10 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- 15 dichlorobenzene) was pumped through the reactor using an HPLC pump. Prior to 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 20 and the feed was then pumped through the reactor at flow rates varying 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 25 extracted from the product line and the isocyanate was 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 30 liquid chromatography (LC) equipped with a UV detector. 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 (as PP-derivative), diphenylurea (DPU), and aniline in the reaction mixture. LC-UV was performed on the ThermoFisher Ultimate 3000 5 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. A gradient mobile phase (0.2 ml / min) consisting of [A] 5 mM ammonium acetate with deionized water (0.1%v 10 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, DPU, phenyl isocyanate 15 (PI) (as PP-derivative), and 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 20 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 25 reliable method. Conversion, yield, selectivity and mole balance were expressed in mol% relative to the phenyl group fed into the reactor. As illustrated in Table 7, isocyanates were obtained in high yield at different conversion levels of carbamates 30 during a thermal depolymerisation reaction. Table 7: 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 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

SP3142 - 27 - 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 an alcohol to produce i) at least one polyol and ii) an 5 aromatic mixture comprising at least one polycarbamate and at least one amine-containing compound; b) separating the at least one polyol and the aromatic mixture; c) converting the aromatic mixture into a 10 polycarbamate aromatic fraction by reaction of the aromatic mixture with a carbonate; and d) converting the polycarbamate aromatic fraction into a polyisocyanate aromatic fraction by converting the polycarbamate compounds of the polycarbamate aromatic 15 fraction into polyisocyanate compounds.

2. The process of claim 1, wherein the alcohol is an alkylalcohol, preferably wherein the alkylalcohol is a C1- C12 alkylalcohol, preferably wherein the alkylalcohol is 20 methanol or ethanol.

3. The process of claim 1, wherein the alcohol is an arylalcohol, preferably wherein the arylalcohol is phenol. 25 4. The process of any preceding claim, wherein the carbonate is a C1-C12 dialkylcarbonate, preferably wherein the dialkylcarbonate is dimethylcarbonate or diethylcarbonate. 30 5. The process of any of claims 1 to 3, wherein the carbonate is a diarylcarbonate, preferably wherein the diarylcarbonate is diphenylcarbonate.

6. The process of any claims 1 to 3, wherein the carbonate is an alkylarylcarbonate, preferably wherein the alkylarylcarbonate is methyl-phenylcarbonate, ethyl- 5 phenylcarbonate, or tert-butyl-phenylcarbonate.

7. The process of any preceding claim, wherein in step c) the aromatic mixture is reacted with the carbonate in the presence of a catalyst. 10 8. The process of claim 7, wherein the catalyst is selected from the group consisting of a Lewis acid catalyst and a Bronsted base catalyst. 15 9. The process of claim 7 or claim 8, 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. 20 10. The process of any preceding claim, further comprising purifying the separated at least one polyol from step b).

11. The process of any preceding claim, wherein step d) 25 is performed by pyrolysis.

12. The process of any preceding claim, further comprising separating different components of the polyisocyanate aromatic fraction. 30 13. The process of any preceding claim, further comprising purifying the polyisocyanate aromatic fraction or purifying the different components of the polyisocyanate aromatic fraction.

14. The process of any claim, wherein the at least one polyol and / or the polyisocyanate aromatic fraction and / or at least one polyisocyanate compound of 5 the polyisocyanate aromatic fraction are recycled for use in the production of a new polyurethane material and / or any other new useful material.

15. The process of any preceding claim, wherein the10 polyurethane material is a polyurethane foam.

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