Method for polyurethane depolymerization

Abstract

The present invention relates to a method for the depolymerization of polyurethane materials, preferably thermosetting polyurethanes. The method comprises four main steps: i) mixing the polyurethane material with a depolymerization reaction medium comprising an ionic liquid in a proportion of 50 w / w% or more relative to the total weight of the medium, a superbase as a catalyst, and a nucleophile in a proportion of 15 w / w% or less relative to the total weight of the medium, and subjecting the mixture to a temperature between 50 and 100 °C over a time period including between 2 minutes and 10 hours; ii) adding a protonic molecular solvent in an amount between 4 and 40 times greater than the weight of the depolymerization reaction medium; iii) subjecting the mixture of step ii) to a temperature between 20 and 60 °C over at least 1 hour; and iv) separating the fractions obtained in step iii); namely, a semi-solid fraction comprising at least a polyol material for reuse in the synthesis of new polyurethanes, and a single-phase liquid fraction comprising at least an ionic liquid and a basic catalyst for reuse in a new process for polyurethane depolymerization.

Description

Technical Field

[0001] The present invention lies in the technical field of chemical recycling of polymers. More specifically, the present invention is based on the use of mild reaction conditions and an active reaction medium that is stable over time and completely recyclable and reusable, whereby a polyol material that is easily separable from the reaction medium and does not require subsequent purification steps for reuse in the synthesis of new polyurethanes is obtained, and relates to a method for polyurethane depolymerization.

Background Art

[0002] Polyurethane is a polymer obtained by the reaction between a polyol and a diisocyanate. When polymerization is carried out in the presence of a controlled amount of water, the formation of urethane (-NH-CO-O-) and urea (-NH-CO-NH-) bonds is induced. By FT-IR spectroscopy, the urethane bond is selectively and unambiguously identified by a band between 1700 and 1740 cm -1 -1 [L.Zhao, V.Semetey. ACS Omega, 2021, 6, p.4175-4183]. Polyurethanes are classified into two large groups according to their chemical structure and distinguished by their behavior with respect to temperature: thermoplastic, which can be melted and flowed by temperature before degradation; and thermosetting, which maintain their shape and strength under high pressure and temperature conditions. Due to the excellent properties of the latter group, including foamed polyurethanes, polyurethanes have become one of the most widely used polymers for manufacturing insulation materials and consumer products such as mattresses, seats, furniture, or cleaning sponges. In 2017, 22.9 million tons of said polymer were manufactured and have since been increasing at an annual rate of 4.5%.

[0003] As a result of this increasing demand, 10% of total polyurethane production is estimated to correspond to post-production products and post-production waste that are removed, and these are disposed of in landfills or by incineration because they lack useful and easy-to-implement recycling methods. This is largely due to the fact that thermoset polyurethanes cannot be melted and remade into other products. However, in addition to the constant need for space to deposit waste and the increasing costs of landfills, the strengthening of environmental regulations and the higher awareness of society to improve the sustainability of current lifestyles determine the need to develop and implement alternatives for the disposal of polyurethane waste, preferably by reincorporating it into the consumption chain.

[0004] The molecular depolymerization of polyurethane waste is one of the strategies that currently attracts greater interest for the implementation of industrial processes based on the circular economy. In said process, polyurethane wastes are converted into the compounds that caused their synthesis; that is, they are converted into polyols and diamines derived from diisocyanates for the purpose of being reincorporated into the synthesis process of new polyurethanes, thereby promoting economic and environmental advantages characteristic of sustainable development and the circular economy [Kemona, A., Piotrowska, M. Polymers, 2020, 12(8), p. 1752].

[0005] Strategies that combine both have also been defined [Gerlock J. et al. (1984). Ind. Eng. Chem. Process Des. Dev., 23(3), p. 545 - 552], but the most common chemical methods in the depolymerization of polyurethanes are hydrolysis and glycolysis. In the depolymerization by hydrolysis, water is the compound that is used as both a cleavage agent and a solvent for urethane bonds; while in the case of depolymerization by glycolysis, an alcohol (e.g., methanol) or a glycol (e.g., ethylene glycol, propylene glycol, diethylene glycol) is used for both functions in an amount by weight greater than the weight of the polyurethane being treated (typically 1.5:1 or more).

[0006] So far, all methods for polyurethane depolymerization described in the prior art are based on suspensions of polyurethane materials in excess protonic molecular solvents; that is, water, glycols, alcohols, or mixtures thereof, with or without unstable volatile organic co-solvents (typically toluene or tetrahydrofuran, THF), and carbene-type organic catalysts, quaternary ammonium salts, or conventional bases such as sodium hydroxide, potassium hydroxide, etc. (at concentrations above 4N) act as nucleophiles, have low catalytic activity, and the method needs to be carried out at high temperatures (130 - 250 °C) and long reaction times (> 12 hours), with yields of less than 85% obtained and unnecessary side reactions promoted [see, for example, EP0011662B1, US5208379A, WO2010 / 130652A2; US2004127720A1; EP1693409A1; WO2022 / 042909 A1; Gadhave, R.V., et al. Open J. Polym. Chem., 2019, 9(2), p. 39 - 51].

[0007] Alternatively, the depolymerization of foamed polyurethane by glycolysis using diols (e.g., ethylene glycol) is a widely described process that also requires extreme reaction conditions [Simon, D. et al. Waste Management, 2018, 16, p. 147 - 171]. By this strategy, polyurethane waste is suspended in excess polyol (e.g., ethylene glycol) in the presence of a catalyst (e.g., naphthenic acid, potassium acetate, titanium butoxide, stannous octoate, etc.) over a period of 6 - 48 hours and at temperatures ranging from 150 - 280 °C. The process produces a two-phase system, where the denser lower layer contains the polyurethane glycolysis products, while the upper layer contains the excess polyol used as the reaction medium. Furthermore, a subsequent expensive step is required to remove the excess polyol by vacuum distillation (100 mbar, 170 - 180 °C) after the catalytic reaction to achieve a product with a potassium hydroxide value suitable for possible reuse in the synthesis of new polyurethanes [see EP1693409A1, JP2003064218A].

[0008] In the same sense, the process of glycolysis using diethanolamine or ethanolamine and the process of efficient depolymerization of polyurethane catalyzed by tin salts (such as dibutyltin dilaurate, etc.) at a temperature close to 200 °C were also described [dos Santos, L.M. et al. Polimeros: Ciencia e Tecnologia, 2013, 23, 608 - 613; Jehanno, C. et al. Polymer Chemistry, 2019, 10, 172 - 186].

Prior Art Documents

Patent Documents

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Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Patent Document 6

Patent Document 7

Non - Patent Documents

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Non - Patent Document 1

Non - Patent Document 2

Non - Patent Document 3

Non-Patent Document 4

Non-Patent Document 5

Non-Patent Document 6

Summary of the Invention

Problems to be Solved by the Invention

[0011] Based on the prior art, there is a need to develop a rapid and efficient method for the depolymerization of polyurethane based on mild reaction conditions and the use of an active reaction medium that is stable over time and completely renewable and recyclable, whereby a recycled polyol material that can be easily separated from the reaction medium is obtained, and which does not require a subsequent purification step for reuse in the synthesis of new polyurethanes.

Means for Solving the Problems

[0012] The object of the present invention relates to a method for depolymerizing a polyurethane material, a) a step of mixing the polyurethane material with a depolymerization reaction medium, wherein the depolymerization reaction medium comprises an ionic liquid, a basic catalyst and a nucleophile; and b) two immiscible fractions of the mixture obtained in step a), - a first fraction comprising at least a polyol material, and - a second fraction comprising at least an ionic liquid and a basic catalyst; includes performing

[0013] Advantageously, in the method of the present invention, - the depolymerization reaction medium comprises ■ an ionic liquid in a proportion of 50 w / w% or more based on the total weight of the depolymerization reaction medium; ■ a superbase as a basic catalyst; and ■ a nucleophile in a proportion of 15 w / w% or less based on the total weight of the depolymerization reaction medium; - step a) is carried out at a temperature between 50 and 100 °C over a time period including between 2 minutes and 10 hours; and - step b) comprises i. adding a protic molecular solvent in an amount between 4 and 40 times greater than the weight of the depolymerization reaction medium to the mixture of step a); ii. subjecting the mixture of step i) to a temperature between 20 and 60 °C over at least 1 hour; and iii. separating the resulting fraction as a sub-step.

[0014] Within the scope of the interpretation of the present invention, "ionic liquid" is understood as any chemical substance formed only by ions and having a melting point below 100°C. Among the physicochemical properties, its substantially zero volatility stands out, converting this type of compound into a non-polluting and reusable alternative to volatile organic solvents. Furthermore, they have excellent thermal stability, a large capacity to dissolve various molecular compounds including gases, and density, melting point, polarity, and miscibility with water or other molecular solvents, which can be adjusted by the types of anions and cations forming the same. Similarly, "superbase" is understood as any organic compound containing two or more basic functional groups and one or more nitrogen atoms (N) forming C-N, C=N, C=N-C, -N-H, and / or =N-H bonds (where C represents the element symbol for carbon and H represents hydrogen), and having a high proton affinity that increases their reaction rate when added to a reaction. More preferably, "superbase" means any amidine, amidine derivative, guanidine, or guanidine derivative, and even more preferably, bicyclic amidine, bicyclic amidine derivative, guanidine, or a guanidine derivative having a pK a of 12 or more is understood to be meant. The term "nucleophile" is understood to mean any chemical compound that interacts or reacts with the carbon of the carbonyl group of the urethane bond, causing cleavage of said bond. More preferably, "nucleophile" is understood to mean water, alcohol, primary amine, secondary amine, or any possible combination thereof. Finally, the term "protic molecular solvent" is understood as any polar solvent composed of a single molecule that forms hydrogen bonds with other electronegative molecules and is capable of donating and accepting protons, having a boiling temperature of 100°C or less and in which the polyol material regenerated by the method of the present invention is insoluble.

Advantages of the Invention

[0015] The method of the present invention represents a sustainable alternative to the previously known methods for polyurethane depolymerization. First, the method enables the depolymerization of polyurethane at temperatures below 100 °C and with a reaction time of less than 10 hours, simplifies the operating system, and facilitates process control and safety. Second, the process is characterized by the simultaneous use of an ionic liquid and a superbase to form a depolymerization reaction medium. The ionic liquid is the main component of the reaction medium, and its use in place of volatile organic solvents or glycols not only provides better tuning of the polyurethane for depolymerization but also offers solutions to the issues of solvent emissions (due to their low volatility) and waste generation (due to their easy regeneration and reuse without the need for expensive purification processes). Next, the superbase provides much higher catalytic activity in a non-aqueous reaction medium and / or in a state of low water content, and higher stability over time compared to conventional basic catalysts (e.g., sodium hydroxide, potassium hydroxide, carbenes, amines), enabling easy regeneration for reuse. And finally, since the process is carried out at a temperature below 100 °C, it is possible to carry out the process using a nucleophile with a low boiling point at atmospheric pressure (e.g., water, alcohols such as methanol or ethanol, primary amines such as butylamine), which determines the absence of a subsequent purification step for the polyol material obtained from the depolymerization process. These conditions are clearly different from those occurring in conventional saccharolysis processes, where the use of high reaction temperatures (130 - 280 °C) is determined by the low efficiency of the catalyst. To reduce the risk, the use of glycol is required as it has a boiling point near or above 200 °C, but the separation of excess glycol is required to obtain a polyol that can be reused in the synthesis of new polyurethanes. Furthermore, the use of a nucleophile with a low boiling point at a concentration of 15 w / w% or less in the method of the present invention enables easy and complete removal because the amount is substantially consumed during the depolymerization reaction of the polyurethane material. Their final possible excess may be easily removed by evaporation or washing with a protic molecular solvent, preferably water, to achieve the separation of the polyol material from the reaction medium.

Embodiments for Carrying Out the Invention

[0016] In a preferred embodiment of the present invention, the polyurethane material includes a thermosetting polyurethane and, more preferably, a foamed polyurethane.

[0017] In another preferred embodiment of the present invention, in step a), the polyurethane material is mixed with the depolymerization reaction medium at a mass ratio including between 1:20 and 1:1; more preferably, between 1:15 and 1:3, and even more preferably, between 1:10 and 1:5.

[0018] In another preferred embodiment of the present invention, step a) is carried out at a temperature including between 80 and 100 °C and / or over a time including between 2 and 8 hours. More preferably, at a temperature including between 90 and 98 °C and / or over a time including between 3 and 7 hours.

[0019] In another preferred embodiment of the present invention, step a) is carried out in a depolymerization reaction medium, and the depolymerization reaction medium includes an ionic liquid at a ratio between 50 and 85 w / w% with respect to the total weight of the depolymerization reaction medium. More preferably, between 65 and 80 w / w%.

[0020] In another preferred embodiment of the present invention, step a) is carried out in a depolymerization reaction medium, and the depolymerization reaction medium includes a nucleophile at a ratio between 1 and 15 w / w% with respect to the total weight of the depolymerization reaction medium. More preferably, between 5 and 15 w / w%.

[0021] In another preferred embodiment of the present invention, in step b), a protic molecular solvent with a mass between 5 and 15 times greater than the weight of the depolymerization reaction medium is added.

[0022] In another preferred embodiment of the present invention, step a) is carried out using a nucleophile including water, alcohol, amine, or any possible combination thereof. More preferably, the nucleophile includes at least 80% water due to its higher nucleophilic ability and low boiling point.

[0023] In a preferred embodiment of the present invention, the sub-step i) is carried out using a protic molecular solvent containing water, methanol, ethanol, isopropanol, or any possible combination thereof. More preferably, the protic molecular solvent contains at least 80% water.

[0024] In another preferred embodiment of the present invention, step a) is: - a cation selected from dialkylimidazolium, tetraalkylammonium, dialkylpiperidinium, alkylpyridinium, dialkylpyrrolidonium, and / or tetraalkylphosphonium; and / or - an anion selected from fluoride, chloride, bromide, iodide, acetate, trifluoroacetate, formate, and / or carbonate is carried out using an ionic liquid containing

[0025] More preferably, the ionic liquid is 1-butyl-3-methylimidazolium acetate, 1-ethyl-3-methylimidazolium acetate, 1-butyl-3-methylpyridinium chloride, 1-butyl-3-methylpyridinium bromide, 1-butyl-3-methylpyridinium iodide, 1-butyl-1-methylpiperidinium chloride, 1-butyl-1-methylpiperidinium bromide, 1-butyl-1-methylpiperidinium iodide, 1-butyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium bromide, 1-butyl-3-methylimidazolium iodide, 1-ethyl-3-methylimidazolium chloride, 1-ethyl-3-methylimidazolium bromide, 1-ethyl-3-methylimidazolium iodide, 1-butyl-4-methylpyridinium chloride, 1-butyl-3-methylimidazolium formate, 1-hexyl-3-methylimidazolium chloride, 1-hexyl-3-methylimidazolium bromide, 1-hexyl-3-methylimidazolium iodide, 1-octyl-3-methylimidazolium chloride, 1-octyl-3-methylimidazolium bromide, 1-octyl-3-methylimidazolium iodide, 1-allyl-3-methylimidazolium chloride, 1-butyl-3-methyl-imidazolium acetate, 1-butyl-3-methyl-imidazolium bromide, 1-ethyl-2-methylpyridinium bromide, N-ethylpyridinium bromide, 1-butyl-3-methyl-imidazolium chloride, 1-butyl-1-methylpyrrolidinium chloride, 1-butyl-1-methylpiperidinium iodide, tetrabutylphosphonium bromide, tetrabutylphosphonium chloride, 1-butyl-2-methylpyridinium chloride, 1-ethyl-1-methyl-piperidinium chloride, or any possible combination thereof.

[0026] In another preferred embodiment of the present invention, step a) is carried out using a superbase comprising at least a bicyclic amidine, a bicyclic amidine derivative, guanidine, a guanidine derivative, or any possible combination thereof. More preferably, the superbase used in the method of the present invention comprises 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), 1,5-diazabicyclo[4.3.0]non-5-ene (DBN), 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD), tetramethylguanidine (TMG), or any possible combination thereof.

[0027] In another preferred embodiment of the present invention, the method comprises at least one of the following additional steps: - a step of recycling a first fraction in the synthesis of a new polyurethane; and / or - a step of recycling a second fraction in step a) of a new process for the depolymerization of a polyurethane material is included.

[0028] In another preferred embodiment of the present invention, the method comprises an additional step of drying the first and / or second fraction until the moisture content of the fraction is reduced to a value of less than 1 w / w%. In the scope of the interpretation of the present invention, "drying" is understood as any physical or chemical operation that enables the removal of water; preferably, the process of freeze-drying, vacuum evaporation, heating, distillation, resin adsorption, or any possible combination thereof.

[0029] In addition, the above two preferred embodiments can include a preliminary step of treating the second fraction with a hydrophobic adsorbent, preferably activated carbon or a polystyrene resin.

[0030] In another preferred embodiment of the present invention, sub-step iii) includes a process of centrifugation, decantation, filtration, suction filtration, resin adsorption, or any possible combination thereof.

[0031] In another preferred embodiment of the present invention, the method of the present invention includes an additional step of verifying the progress and completion of step a) and / or step b). Preferably, the additional step includes at least one of the following sub-steps: - During step a), aliquots (e.g., 0.2 mL) of the reaction medium are taken at different time intervals and suspended in an aprotic polar solvent (e.g., acetone, dimethyl sulfoxide (DMSO), or tetrahydrofuran) capable of dissolving a ten-fold larger volume of the polymerized polyol, and a solution free of suspended solids is obtained when step a) is completely finished; - Analysis by attenuated total reflection (ATR-FTIR) combined with Fourier transform infrared spectroscopy of the first dried fraction is performed to observe the absence of the characteristic absorption band of the urethane bond (1700 cm -1 ~1740 cm -1 ); and / or - According to ASTM D-4274-16 (2016) standard, the hydroxyl value (mg KOH / g of sample) is measured by titration of the first dried fraction with phthalic anhydride / pyridine to quantify the presence of hydroxyl groups in the regenerated solid fraction. Since the polyol contains multiple hydroxyl groups, the higher the value, the more polyol is present in the fraction, demonstrating the accurate depolymerization of the polyurethane material in the method of the present invention.

Brief Description of the Drawings

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[0051] Detailed Description of the Invention As described in the preceding paragraphs, the object of the present invention relates to a method for depolymerizing polyurethane materials by hydrolysis reaction, alcoholysis reaction, aminolysis reaction, or any possible combination thereof, at a temperature below 100 °C and in a reaction medium containing an ionic liquid, a basic catalyst, and a nucleophile. Preferably, the polyurethane material includes thermosetting polyurethane and, more preferably, foamed polyurethane derived from generally removed post-production products and post-production waste.

[0052] Ionic liquids contain cations in a highly charge-delocalized state, preferably dialkylimidazolium, tetraalkylammonium, dialkylpiperidinium, alkylpyridinium, dialkylpyrrolidinium, and / or tetraalkylphosphonium, and / or anions that are hydrophilic and not charge-delocalized, preferably fluoride, chloride, bromide, iodide, acetate, trifluoroacetate, formate, and / or carbonate. More preferably, the ionic liquids used in the method of the present invention are 1-butyl-3-methylimidazolium acetate, 1-ethyl-3-methylimidazolium acetate, 1-butyl-3-methylpyridinium chloride, 1-butyl-3-methylpyridinium bromide, 1-butyl-3-methylpyridinium iodide, 1-butyl-1-methylpiperidinium chloride, 1-butyl-1-methylpiperidinium bromide, 1-butyl-1-methylpiperidinium iodide, 1-butyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium bromide, 1-butyl-3-methylimidazolium iodide, 1-ethyl-3-methylimidazolium chloride, 1-ethyl-3-methylimidazolium bromide, 1-ethyl-3-methylimidazolium iodide, 1-butyl-4-methylpyridinium chloride, 1-butyl-3-methylimidazolium formate, 1-hexyl-3-methylimidazolium chloride, 1-hexyl-3-methylimidazolium bromide, 1-hexyl-3-methylimidazolium iodide, 1-octyl-3-methylimidazolium chloride, 1-octyl-3-methylimidazolium bromide, 1-octyl-3-methylimidazolium iodide, 1-allyl-3-methylimidazolium chloride, 1-butyl-3-methyl-imidazolium acetate, 1-butyl-3-methyl-imidazolium bromide, 1-ethyl-2-methylpyridinium bromide, N-ethylpyridinium bromide, 1-butyl-3-methyl-imidazolium chloride, 1-butyl-1-methylpyrrolidinium chloride, 1-butyl-1-methylpiperidinium iodide, tetrabutylphosphonium bromide, tetrabutylphosphonium chloride, 1-butyl-2-methylpyridinium chloride, 1-ethyl-1-methyl-piperidinium chloride, or any possible combination thereof.With respect to its concentration in the reaction medium, the ionic liquid is present in a proportion of 50 w / w% or more, preferably between 50 and 85 w / w%, and more preferably between 65 and 85 w / w%, based on the total weight of the depolymerization reaction medium.

[0053] The basic catalyst preferably comprises a superbase comprising at least a bicyclic amidine, a bicyclic amidine derivative, guanidine, a guanidine derivative, or any possible combination thereof. Catalysts of these types are more active in non-aqueous systems and / or in the presence of low water content and have higher stability over time compared to conventional basic catalysts, such as sodium hydroxide (NaOH) or potassium hydroxide (KOH) which carbonize over time. More preferably, the basic catalyst used in the method of the present invention comprises 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), 1,5-diazabicyclo[4.3.0]non-5-ene (DBN), 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD), tetramethylguanidine (TMG), or any possible combination thereof.

[0054] The nucleophile preferably comprises water (depolymerization reaction by hydrolysis), alcohol (depolymerization reaction by alcoholysis), amine (depolymerization reaction by aminolysis), or any possible combination thereof, and is present in a proportion of 15 w / w% or less based on the total weight of the depolymerization reaction medium. More preferably, the nucleophile contains at least 80% water for its higher nucleophilicity, immiscibility with polyols, and easy removal by evaporation. With respect to its concentration in the depolymerization reaction medium, the nucleophile is preferably in a proportion between 1 and 15 w / w%, more preferably between 5 and 15 w / w%, based on the weight of the medium.

[0055] The mixture of the polyurethane material and the reaction medium is left to stand at a controlled temperature between 50 and 100 °C, preferably between 80 and 100 °C, more preferably between 90 and 98 °C, and even more preferably including 95 °C, for a time including between 2 minutes and 10 hours, preferably between 2 and 8 hours, and even more preferably between 3 and 7 hours, under constant stirring (mechanical, magnetic, etc.).

[0056] Next, the washing of the mixture is carried out by the addition of a mass of a protic molecular solvent in an amount between 4 and 40 times, preferably between 5 and 15 times, more than the weight of the reaction medium. The said washing of the mixture causes the precipitation of the polyol material, which is a component of the polyurethane material, due to its insolubility in the said solvent. Preferably, the protic molecular solvent is water, methanol, ethanol, isopropanol or any possible combination thereof, and, more preferably, contains at least 80% water.

[0057] The heterogeneous mixture or suspension obtained after the addition of the protic molecular solvent is kept under constant stirring (mechanical, magnetic, etc.) at a temperature including between 20 and 60 °C for at least 1 hour, and a time of 2 hours at 40 °C is recommended. The reaction mixture is then subjected to a separation process, typically filtration or centrifugation, making it possible to obtain two fractions: a first fraction or semi-solid fraction, and a second fraction or single-phase liquid fraction.

[0058] The single-phase liquid fraction contains all the elements of the reaction medium soluble in the protic molecular solvent, i.e., the ionic liquid and the catalyst. The said mixture is filtered through a hydrophobic adsorbent, such as activated carbon or polystyrene resin, making it possible to remove any diamine residue and prevent the fraction from darkening. After the filtration process, the said fraction is concentrated to a final concentration of less than 1 w / w% by removing the water present, for example, by evaporation under reduced pressure, and can be directly reused in a new process for chemical polyurethane depolymerization.

[0059] The semi-solid fraction mainly contains the polyol material. To examine its molecular properties, the fraction is subjected to a drying process, preferably freeze-drying or evaporation under reduced pressure, making it possible to reduce the water content to a level lower than 1 w / w%. Thereafter, three different analytical tests can be carried out to verify the complete depolymerization of the polyurethane material; namely, solubility in an organic solvent, attenuated total reflection combined with Fourier transform infrared spectroscopy (ATR-FTIR), and hydroxyl value measurement.

[0060] Unlike polyols, polyurethanes are insoluble in all conventional polar organic solvents, such as acetone or dimethyl sulfoxide (DMSO). This difference makes it possible to examine the properties of the semi-solid fraction obtained after the depolymerization process of the present invention by a simple solubility test. Preferably, 20 mg of the obtained semi-solid fraction is filtered and dried and then resuspended in 2 mL of DMSO. If the depolymerization is complete, the semi-solid fraction will dissolve completely in the organic solvent, demonstrating the loss of polymer integrity.

[0061] Molecular confirmation of the success of the depolymerization reaction can be carried out by ATR-FTIR analysis of the first dried fraction. The absence of the characteristic absorption band of the carbonyl group (CO) forming the urethane bond (-NH-CO-O-) between 1700 and 1740 cm -1 can prove the accurate depolymerization of the polyurethane material.

[0062] Similarly, in accordance with ASTM D-4274-16 (2016), measurement of the hydroxyl value (mg KOH / g of sample) by titration of the first dried fraction with phthalic anhydride / pyridine enables quantification of the presence of hydroxyl groups in the fraction. Since polyols contain multiple hydroxyl groups, the higher the value, the more polyol is present in the fraction, demonstrating the accurate depolymerization of the polyurethane material in the method of the present invention.

Examples

[0063] Various embodiments of the present invention are detailed below, demonstrating that the following are strictly necessary in order to depolymerize the polyurethane material at a temperature between 50 and 100 °C over a period of less than 10 hours (since the regenerated polyol does not require subsequent purification steps): - The depolymerization reaction medium contains an ionic liquid, a superbase, and a nucleophile; - The ionic liquid is a major component of the reaction medium; - The basic catalyst is a superbase; - The concentration of the nucleophile is 15 w / w% or less based on the total weight of the depolymerization reaction medium; - The protonic molecular solvent is used in an amount between 4 and 40 times more in mass than the weight of the depolymerization reaction medium to stop the reaction.

[0064] Therefore, in addition to the visual examples (see Examples 1 to 3), the results of the above analytical tests are for the following depolymerization reaction media: - Using the same superbase and nucleophile, different ionic liquids (see Examples 4, 7 and 10); - Using the same ionic liquid and nucleophile, different superbases (see Examples 4, 8, 9 and 14); - Using the same ionic liquid and superbase, different nucleophiles (see Examples 4, 8, 11, 12, 13, 14 and 15); - Incomplete, without an ionic liquid or superbase (see Example 6); - Using a base as a catalyst instead of a superbase (see Example 20) to verify the complete depolymerization of the polyurethane material when using (i.e., solubility tests, ATR-FTIR spectroscopy, and measurement of the hydroxyl value).

[0065] Similarly, it is demonstrated that the polyol fraction regenerated by the method of the present invention can be reused as a starting material for the synthesis of new polyurethanes by any procedure known in the prior art (see Example 5).

[0066] Finally, the influence of the components of the reaction medium was also evaluated in a simple urethane model: bis(phenylcarbamic acid)oxybis(ethane-2,1-diyl), synthesized and purified by the method described in Motokucho, S. et al. J. Polym. Sci. A Polym. Chem. 2017, 55(12), p. 2004-2010. The use of the said model instead of foamed polyurethane as a starting material makes it possible to monitor the change in the conversion of the carbamate groups by nuclear magnetic resonance (NMR) or high performance liquid chromatography (HPLC) techniques and to provide evidence of the cleavage of the said bonds which are the key to the depolymerization of polyurethanes.

[0067] Tables 1 and 2 include the abbreviations of ionic liquids and superbases used in the depolymerization reaction media of different embodiments of the present invention shown so far.

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Table 1

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Table 2

Example 1

[0070] Depolymerization of a foamed polyurethane (PU) material at 95 °C for 4 hours in a depolymerization reaction medium containing [Bmim][Cl], [Bmim][Br], [Bmim][I], [Emim][Cl], or [Omim][Cl] as the ionic liquid, DBU as the superbase, and water as the nucleophile.

[0071] As an example of the present invention, Figure 1 shows the changes in five different reaction media through the depolymerization process of foamed polyurethane in a preferred embodiment of the method of the present invention. Specifically, a depolymerization reaction medium based on a combination of [Bmim][Cl], [Bmim][Br], [Bmim][I], [Emim][Cl], or [Omim][Cl] (65 w / w%, ionic liquid) and DBU (20 w / w%, superbase) and water (15 w / w%, nucleophile) was used to treat a pulverized foamed polyurethane material (25 w / w%, relative to the total mass of the depolymerization reaction medium). The images show the appearance of the depolymerization reaction mixture at the beginning of the reaction (Figure 1A) and after incubation at 95 °C for 4 hours using magnetic stirring (Figure 1B).

Example 2

[0072] Time-course changes in the depolymerization of a foamed PU material in a depolymerization reaction medium containing [Bmim][Cl] as the ionic liquid, DBU as the superbase, and water as the nucleophile.

[0073] Figure 2 shows the time-dependent change of a foamed polyurethane material (0.2 g) immersed in 3 g of a depolymerization reaction medium based on [Bmim][Cl] (65 w / w%), DBU (20 w / w%) and water (15 w / w%) under stirring at 95°C, as shown by images taken over a period of 2 minutes.

Example 3

[0074] Separation of the polyol regenerated after depolymerization of the foamed PU material at 95°C for 4 hours in a depolymerization reaction medium containing [Bmim][Cl] or [Bmim][Br] as the ionic liquid, DBU as the superbase and water as the nucleophile.

[0075] Figure 3 shows the separation of the polyol regenerated by centrifugation after depolymerization of the ground foamed polyurethane material (25 w / w% based on the total mass of the system) at 95°C for 4 hours in a depolymerization reaction medium containing [Bmim][Cl] or [Bmim][Br] (65 w / w%), DBU (20 w / w%) and water (15 w / w%) under constant stirring. After the passage of time, 20 mL of water was added.

Example 4

[0076] Depolymerization of the foamed PU material at 95°C for 4 hours in a depolymerization reaction medium containing [Bmim][Ac], [Bmim][Cl] or [Emim][Cl] as the ionic liquid, DBU as the superbase and water as the nucleophile.

[0077] 1 g of [Bmim][Ac], [Bmim][Cl] or [Emim][Cl] was added to each of three 50 mL screw cap containers, and in each of them, 0.3 g of DBU, 0.25 g of water, and 0.4 g of crushed foamed polyurethane were mixed. The three containers were sealed and kept under mechanical stirring at 95 °C for 4 hours. After the elapse of the said period, 20 mL of water was added to each container and kept under stirring at room temperature for 1 hour. Then, each of the obtained suspensions was centrifuged at 7000 rpm for 20 minutes. The obtained precipitate was separated by decantation and filtration through a nylon membrane (0.45 micron), and finally dried in a vacuum oven at 80 °C to a constant weight. The dried product was analyzed by the following control tests:

[0078] ■ Control criterion 1 - Solubility test. The addition of 20 mg of each of the obtained dry polyols in 2 mL of dimethyl sulfoxide (DMSO) enabled their complete dissolution, and a clear solution was obtained in all cases. Since polyurethane is not soluble in DMSO and the polyol is soluble, the said results indicate that the depolymerization of the foamed polyurethane material was carried out.

[0079] ■ Control criterion 2 - ATR-FTIR spectroscopic analysis (see Figure 4). Each of the obtained dry polyols was analyzed by ATR-FTIR, and their spectra (3 - 5) were compared with those of the original foamed polyurethane material (1) and those of a commercially available polyol material (2). The characteristic absorption band of the urethane bond (1700 - 1740 cm -1 ) was not detected in any case (see Spectra 3, 4 and 5), and signals similar to those of the commercially available polyol (Spectrum 2) were obtained. From the above, the accurate depolymerization of the foamed polyurethane material in the method of the present invention was confirmed.

[0080] ■ Control criterion 3 - Hydroxyl value measurement. By titration of different dry polyols using phthalic anhydride / pyridine, the following hydroxyl values were obtained based on the ASTM D-4274-16 (2016) standard: - PU standard: 9.45 mg KOH / g polyol - Reaction medium: [Bmim][Ac] + DBU + water: 57.41 mg KOH / g polyol - Reaction medium: [Bmim][Cl] + DBU + water: 52.52 mg KOH / g polyol - Reaction medium: [Emim][Cl] + DBU + water: 55.61 mg KOH / g polyol

[0081] Since the compound has multiple hydroxyl groups, a higher hydroxyl value represents a higher concentration of polyol in the sample. Therefore, the hydroxyl values obtained for different solid fractions are much higher than those of the starting foamed polyurethane material, thus reconfirming the accurate depolymerization in these preferred embodiments of the method of the present invention.

Example 5

[0082] Reuse of the polyol fraction regenerated by the method of the present invention in the synthesis of new polyurethanes.

[0083] Figure 4 shows the ATR-FTIR spectra of (1) ground foamed polyurethane waste; (2) foamed polyurethane synthesized from industrial commercially available polyol material; and (3) foamed polyurethane synthesized from the polyol material regenerated by a preferred embodiment of the method of the present invention. That is, for the regenerated polyol in a preferred embodiment of the method of the present invention, a depolymerization reaction medium containing 65 w / w% [Bmim][Cl], 20 w / w% DBU, and 15 w / w% water was used. The depolymerization reaction was carried out by combining 40% foamed polyurethane waste and 60% depolymerization reaction medium and keeping it under constant stirring at 95 °C for 4 hours. As can be observed, the three polymer products have bands in the characteristic region of the urethane bond (1700 - 1740 cm -1 ), proving that the first fraction obtained by the method of the present invention can be used as a starting material for the synthesis of new polyurethanes by any procedure known in the prior art.

Example 6

[0084] Depolymerization of Foamed PU Material in Incomplete Depolymerization Reaction Medium

[0085] Four incomplete depolymerization reaction media were prepared by adding 0.4 g of DBN, or 0.4 g of TMG, or 2.4 g of [Bmim][Cl], or 2.4 g of [Bmim][Br], each mixed with 2.6 g, 2.6 g, 0.6 g, or 0.6 g of water respectively in four 50 mL screw-cap containers. Finally, 1 g of ground foamed polyurethane was added to each of them. The four containers were sealed and kept at 95 °C for 6 hours under mechanical stirring, and then 20 mL of water was added to stop the reaction. The precipitated products were subjected to the same sample separation, drying, and analysis methods as described in Example 4, showing the following results:

[0086] ■ Control Criterion 1 - Solubility test. The addition of 20 mg of each obtained dry solid in 2 mL of DMSO resulted in insoluble precipitates in all cases, indicating that the depolymerization of the foamed polyurethane material does not occur under these conditions.

[0087] ■ Control Criterion 2 - ATR-FTIR spectroscopic analysis (see Figure 6). Each obtained dry product was analyzed by ATR-FTIR, and their spectra (2 - 5) were compared with that of the original foamed polyurethane material (1). The characteristic absorption band of the urethane bond (1700 - 1740 cm -1 ) was detected in all cases (spectra 2 - 5), enabling them to be identified as non-depolymerized polyurethanes. The above experiment demonstrated the inefficiency of the process at temperatures below 100 °C when ionic liquids or superbases were not present simultaneously in the depolymerization reaction medium.

[0088] ■ Control Criterion 3 - Hydroxyl value measurement. Since the hydroxyl values obtained for different solid fractions were very similar to those of the starting foamed polyurethane material, the inefficiency of the process for depolymerization under these conditions was confirmed again: - PU standard: 9.45 mg KOH / g polyol - Reaction medium [Bmim][Cl] + water: 9.52 mg KOH / g polyol - Reaction medium [Bmim][Br] + water: 9.85 mg KOH / g polyol - Reaction medium DBU + water: 11.25 mg KOH / g polyol - Reaction medium DBN + water: 12.75 mg KOH / g polyol

Example 7

[0089] Depolymerization of foamed PU at 95 °C for 6 h in a depolymerization reaction medium containing [BmPyrr][Cl], [BmPip][I] or [TBP][Br] as ionic liquids, DBU as superbase and water as nucleophile.

[0090] 2 g of [BmPyrr][Cl], [BmPip][I] or [TBP][Br] were added respectively into three 50 mL screw-cap containers, and in each of them were mixed with 0.4 g of DBU, 0.6 g of water, and 1 g of ground foamed polyurethane. The three containers were sealed and kept at 95 °C for 6 h under mechanical stirring, and then 20 mL of water was added to stop the reaction. The precipitated product was subjected to the same sample separation, drying and analysis as described in Example 4, showing the following results:

[0091] ■ Control criterion 1 - Solubility test. Addition of 20 mg of each of the obtained dry polyols in 2 mL of DMSO enabled their complete dissolution, and a clear solution was obtained in all cases. The above indicates that the depolymerization of the foamed polyurethane material was carried out.

[0092] ■ Control criterion 2 - ATR-FTIR spectroscopic analysis (see Figure 7). Each of the obtained dry polyols was analyzed by ATR-FTIR, and their spectra (2 - 4) were compared with that of the original foamed polyurethane material (1). The characteristic absorption band of urethane bond (1700 - 1740 cm -1 ) was not detected in any case: reaction medium [BmPyrr][Cl] + DBU + water (spectrum 2); reaction medium [BmPip][I] + DBU + water (spectrum 3); reaction medium [TBP][Br] + DBU + water (spectrum 4). The above confirmed the exact depolymerization of the foamed polyurethane material in the method of the present invention.

[0093] ■Control standard 3 - Hydroxyl value measurement. Since the hydroxyl values obtained for different solid fractions are much higher than those of the starting foamed polyurethane material, the exact depolymerization in these preferred embodiments of the method of the present invention was reconfirmed: - PU standard: 9.45 mg KOH / g polyol - Reaction medium [BmPyrr][Cl] + DBU + water: 97.04 mg KOH / g polyol - Reaction medium [BmPip][I] + DBU + water: 78.2 mg KOH / g polyol - Reaction medium [TBP][Br] + DBU + water: 58.71 mg KOH / g polyol

Example 8

[0094] Depolymerization of foamed PU material at 95 °C for 6 hours in a depolymerization reaction medium containing [Bmim][Ac], [Bmim][Cl], [Amim][Cl], or [TBP][Br] as ionic liquids, TMG as a superbase, and water as a nucleophile.

[0095] 2 g of [Bmim][Ac], [Bmim][Cl], [Amim][Cl], or [TBP][Br] was added to each of four 50 mL screw - cap containers, and in each of them, 0.4 g of TMG, 0.6 g of water, and 1 g of shredded foamed polyurethane were mixed. The four containers were sealed and kept at 95 °C for 6 hours under mechanical stirring, and then 20 mL of water was added to stop the reaction. The precipitated product was subjected to the same sample separation, drying, and analysis methods as described in Example 4, showing the following results:

[0096] ■Control standard 1 - Solubility test. The addition of 20 mg of each obtained dry polyol in 2 mL of DMSO enabled their complete dissolution, and a clear solution was obtained in all cases. The above indicates that the depolymerization of the foamed polyurethane material was carried out.

[0097] ■Control Standard 2 - ATR-FTIR Spectroscopic Analysis (see Figure 8). Each of the obtained dried polyols was analyzed by ATR-FTIR, and their spectra (2 - 5) were compared with that of the original foamed polyurethane material (1). The characteristic absorption band of the urethane bond (1700 - 1740 cm -1 ) was not detected in any case: reaction medium [Bmim][Ac] + TMG + water (spectrum 2); reaction medium [Bmim][Cl] + TMG + water (spectrum 3); reaction medium [Amim][Cl] + TMG + water (spectrum 4); reaction medium [TBP][Br] + TMG + water (spectrum 5). From the above, the accurate depolymerization of the foamed polyurethane material in the method of the present invention was confirmed.

[0098] ■Control Standard 3 - Hydroxyl Value Measurement. Since the hydroxyl values obtained for different solid fractions were much higher than those of the starting foamed polyurethane material, the accurate depolymerization in these preferred embodiments of the method of the present invention was confirmed again: - PU standard: 9.45 mg KOH / g polyol - Reaction medium [Bmim][Ac] + TMG + water: 66.83 mg KOH / g polyol - Reaction medium [Bmim][Cl] + TMG + water: 57.75 mg KOH / g polyol - Reaction medium [Amim][Cl] + TMG + water: 67.43 mg KOH / g polyol - Reaction medium [TBP][Br] + TMG + water: 58.56 mg KOH / g polyol

Example 9

[0099] Depolymerization of a foamed PU material at 95 °C for 6 hours in a depolymerization reaction medium containing [Bmim][Cl] as an ionic liquid, DBN as a superbase, and water as a nucleophile.

[0100] 2 g of [Bmim][Cl] was added into a 50 mL screw-cap container and mixed with 0.4 g of DBN, 0.6 g of water, and 1 g of shredded foamed polyurethane. The container was sealed and maintained at 95 °C for 6 hours under mechanical stirring, and then 20 mL of water was added to stop the reaction. The precipitated product was subjected to the same sample separation, drying, and analysis methods described in Example 4, showing the following results:

[0101] ■ Control criterion 1 - Solubility test. The addition of 20 mg of the obtained dried polyol in 2 mL of DMSO enabled its complete dissolution, resulting in a clear solution. The above indicates that the depolymerization of the foamed polyurethane material was carried out.

[0102] ■ Control criterion 2 - ATR-FTIR spectroscopic analysis (see Figure 9). The obtained dried polyol was analyzed by ATR-FTIR, and its spectrum (2) was compared with that of the original foamed polyurethane material (1). The characteristic absorption band of the urethane bond (1700 - 1740 cm -1 ) was not detected, confirming the accurate depolymerization of the foamed polyurethane material in the method of the present invention.

[0103] ■ Control criterion 3 - Hydroxyl value measurement. Since the hydroxyl value obtained for the solid fraction was much higher than that of the starting foamed polyurethane material, the accurate depolymerization of it in this preferred embodiment of the method of the present invention was confirmed again: - PU standard: 9.45 mg KOH / g polyol - Reaction medium [Bmim][Cl] + DBN + water: 81.51 mg KOH / g polyol

Example 10

[0104] Depolymerization of a foamed PU material at 95 °C for 6 hours in a depolymerization reaction medium containing [BmPyr][Cl] or [Epyr][Br] as an ionic liquid, DBU as a superbase, and water as a nucleophile.

[0105] 2 g of [BmPyr][Cl] or [Epyr][Br] was added to two 50 mL screw-cap containers, respectively, and in each of them, 0.4 g of DBU, 0.6 g of water, and 1 g of ground polyurethane foam were mixed. The two containers were sealed and kept at 95 °C for 6 hours under mechanical stirring, and then 20 mL of water was added to stop the reaction. The precipitated product was subjected to the same sample separation, drying, and analysis methods as described in Example 4, showing the following results:

[0106] ■ Control criterion 1 - Solubility test. The addition of 20 mg of each of the obtained dry polyols in 2 mL of DMSO enabled their complete dissolution, and a clear solution was obtained in all cases. The above indicates that the depolymerization of the polyurethane foam material was carried out.

[0107] ■ Control criterion 2 - ATR-FTIR spectroscopic analysis (see Figure 10). Each of the obtained dry polyols was analyzed by ATR-FTIR, and their spectra (2, 3) were compared with that of the original polyurethane foam material (1). The characteristic absorption band of the urethane bond (1700 - 1740 cm -1 ) was not detected in any case: reaction medium [BmPyr][Cl] + DBU + water (spectrum 2); reaction medium [Epyr][Br] + DBU + water (spectrum 3). From the above, the accurate depolymerization of the polyurethane foam material in the method of the present invention was confirmed.

[0108] ■ Control criterion 3 - Hydroxyl value measurement. Since the hydroxyl values obtained for different solid fractions were much higher than those of the starting polyurethane foam material, the accurate depolymerization in these preferred embodiments of the method of the present invention was confirmed again: - PU standard: 9.45 mg KOH / g polyol - Reaction medium [BmPyr][Cl] + DBU + water: 66.28 mg KOH / g polyol - Reaction medium [Epyr][Br] + DBU + water: 67.36 mg KOH / g polyol

Example 11

[0109] Depolymerization of foamed PU material at 95 °C for 6 hours in a depolymerization reaction medium containing [Bmim][Ac] as an ionic liquid, DBU as a superbase, and methanol as a nucleophile.

[0110] 2 g of [Bmim][Ac] was added to a 50 mL screw-cap container and mixed with 0.4 g of DBU, 0.6 g of methanol, and 1 g of ground foamed polyurethane. The container was sealed and kept at 95 °C for 6 hours under mechanical stirring, and then 20 mL of water was added to stop the reaction. The precipitated product was subjected to the same sample separation, drying, and analysis methods as described in Example 4, showing the following results:

[0111] ■ Control criterion 1 - Solubility test. Addition of 20 mg of the obtained dry polyol in 2 mL of DMSO enabled its complete dissolution, and a clear solution was obtained. The above indicates that the depolymerization of the foamed polyurethane material was carried out.

[0112] ■ Control criterion 2 - ATR-FTIR spectroscopic analysis (see Figure 11). The obtained dry polyol was analyzed by ATR-FTIR, and its spectrum (2) was compared with that of the original foamed polyurethane material (1). The characteristic absorption band of the urethane bond (1700 - 1740 cm -1 ) was not detected, confirming the accurate depolymerization of the foamed polyurethane material in the method of the present invention.

[0113] ■ Control criterion 3 - Hydroxyl value measurement. Since the hydroxyl value obtained for the solid fraction was much higher than that of the starting foamed polyurethane material, the accurate depolymerization of it in this preferred embodiment of the method of the present invention was confirmed again: - PU standard: 9.45 mg KOH / g polyol - Reaction medium [Bmim][Ac] + DBU + methanol: 62.06 mg KOH / g polyol

Example 12

[0114] Depolymerization of a foamed PU material at 95 °C for 6 hours in a depolymerization reaction medium containing [Bmim][Cl] or [BmPip][I] as the ionic liquid, TMG as the superbase, and ethanol as the nucleophile.

[0115] Into two 50 mL screw-cap containers, 2 g of [Bmim][Cl] or [BmPip][I] were added respectively, and mixed with 0.4 g of TMG, 0.6 g of ethanol, and 1 g of the ground foamed polyurethane material. The two containers were sealed and kept at 95 °C for 6 hours under mechanical stirring, and then 20 mL of water was added to each of them to stop the reaction. The precipitated product was subjected to the same sample separation, drying, and analysis methods as described in Example 4, showing the following results:

[0116] ■ Control criterion 1 - Solubility test. The addition of 20 mg of each of the obtained dry polyols in 2 mL of DMSO enabled their complete dissolution, and a clear solution was obtained in all cases. The above indicates that the depolymerization of the foamed polyurethane material was carried out.

[0117] ■ Control criterion 2 - ATR-FTIR spectroscopic analysis (see Figure 11). Each of the obtained dry polyols was analyzed by ATR-FTIR, and their spectra (3, 4) were compared with that of the original foamed polyurethane material (1). The characteristic absorption band of the urethane bond (1700 - 1740 cm -1 ) was not detected in any case: reaction medium [Bmim][Cl] + TMG + ethanol (spectrum 3); reaction medium [BmPip][I] + TMG + ethanol (spectrum 4). From the above, the accurate depolymerization of the foamed polyurethane material in the method of the present invention was confirmed.

[0118] ■ Control criterion 3 - Hydroxyl value measurement. Since the hydroxyl values obtained for the different solid fractions were much higher than those of the starting foamed polyurethane material, the accurate depolymerization in these preferred embodiments of the method of the present invention was confirmed again: - PU standard: 9.45 mg KOH / g polyol - Reaction medium [Bmim][Cl] + TMG + ethanol: 61.23 mg KOH / g polyol - Reaction medium [BmPip][I] + TMG + ethanol: 54.92 mg KOH / g polyol

Example 13

[0119] Depolymerization of a foamed PU material at 95°C for 6 hours in a depolymerization reaction medium containing 1-butylamine as a nucleophile, [Bmim][Cl] or [TBP][Br] as an ionic liquid, and DBU or DBN as a superbase.

[0120] 2 g of [Bmim][Cl] was added to a 50 mL screw-cap container and mixed with 0.4 g of DBU. In a similar container, 2 g of [TBP][Br] and 0.4 g of DBN were added. Finally, 0.6 g of 1-butylamine and 1 g of ground foamed polyurethane were added to each container, sealed, and kept at 95°C for 6 hours under mechanical stirring. Then, 20 mL of water was added to each container to stop the depolymerization reaction. The precipitated product was subjected to the same sample separation, drying, and analysis methods as described in Example 4, showing the following results:

[0121] ■ Control criterion 1 - Solubility test. The addition of 20 mg of each obtained dry polyol in 2 mL of DMSO enabled their complete dissolution, and a clear solution was obtained in all cases. The above indicates that the depolymerization of the foamed polyurethane material was carried out.

[0122] ■ Control criterion 2 - ATR-FTIR spectroscopic analysis (see Figure 12). Each obtained dry polyol was analyzed by ATR-FTIR, and their spectra (2, 3) were compared with that of the original foamed polyurethane material (1). The characteristic absorption band of the urethane bond (1700 - 1740 cm -1 ) was not detected in any case: reaction medium [Bmim][Cl] + DBU + 1-butylamine (spectrum 2); reaction medium [TBP][Br] + DBN + 1-butylamine (spectrum 3). From the above, the accurate depolymerization of polyurethane in the method of the present invention was confirmed.

[0123] ■Control standard 3 - Hydroxyl value measurement. Since the hydroxyl values obtained for different solid fractions are much higher than those of the starting foamed polyurethane material, the exact depolymerization in these preferred embodiments of the method of the present invention was confirmed again: -PU standard: 9.45 mg KOH / g polyol -Reaction medium [Bmim][Cl] + DBU + 1 - butylamine: 90.04 mg KOH / g polyol -Reaction medium [TBP][Br] + DBN + 1 - butylamine: 85.56 mg KOH / g polyol

Example 14

[0124] Depolymerization of foamed PU material at 95 °C for 6 hours in a depolymerization reaction medium containing [Bmim][Cl], [BmPyrr][Cl], [BmPip][I], [BmPyr][Cl], [TBP][Br], or [EmPyr][Br] as ionic liquids, TBD as a superbase, and water as a nucleophile.

[0125] 2 g of [Bmim][Cl], [BmPyrr][Cl], [BmPip][I], [BmPyr][Cl], [TBP][Br], or [EmPyr][Br] were added to six 50 mL screw - cap containers, respectively. Next, 0.4 g of TBD, 0.6 g of water, and 1 g of crushed foamed polyurethane were added to each of them, sealed, and kept at 95 °C for 6 hours under mechanical stirring. Then, 20 mL of water was added to each container to stop the reaction. The precipitated product was subjected to the same sample separation, drying, and analysis methods as described in Example 4, and the following results are shown:

[0126] ■Control standard 1 - Solubility test. The addition of 20 mg of each obtained dry polyol in 2 mL of DMSO enabled their complete dissolution, and a clear solution was obtained in all cases.

[0127] ■Control Standard 2 - ATR-FTIR Spectroscopic Analysis (see Figure 13). Each of the obtained dried polyols was analyzed by ATR-FTIR, and their spectra (2 - 7) were compared with that of the original foamed polyurethane material (1). The characteristic absorption band of the urethane bond (1700 - 1740 cm -1 ) was not detected in any case: reaction medium [Bmim][Cl] + TBD + water (spectrum 2); reaction medium [BmPyrr][Cl] + TBD + water (spectrum 3); reaction medium [BmPip][I] + TBD + water (spectrum 4); reaction medium [BmPyr][Cl] + TBD + water (spectrum 5); reaction medium [TBP][Br] + TBD + water (spectrum 6); reaction medium [EmPyr][Br] + TBD + water (spectrum 7). From the above, the accurate depolymerization of the foamed polyurethane material in the method of the present invention was confirmed.

[0128] ■Control Standard 3 - Hydroxyl Value Measurement. Since the hydroxyl values obtained for different solid fractions were much higher than those of the starting foamed polyurethane material, the accurate depolymerization in these preferred embodiments of the method of the present invention was confirmed again: - PU standard: 9.45 mg KOH / g polyol - Reaction medium [Bmim][Cl] + TBD + water: 96.61 mg KOH / g polyol - Reaction medium [BmPyrr][Cl] + TBD + water: 79.66 mg KOH / g polyol - Reaction medium [BmPip][I] + TBD + water: 111.46 mg KOH / g polyol - Reaction medium [BmPyr][Cl] + TBD + water: 66.51 mg KOH / g polyol - Reaction medium [TBP][Br] + TBD + water: 89.46 mg KOH / g polyol - Reaction medium [EmPyr][Br] + TBD + water: 67.23 mg KOH / g polyol

Example 15

[0129] Depolymerization of foamed PU materials at 95 °C for 6 hours in a depolymerization reaction medium containing [Bmim][Cl] or [BmPyrr][Cl] as ionic liquids, TBD as a superbase, and 1,2-isopropylidene glycerol (sorbitol ketal) as a nucleophile.

[0130] 2 g of [Bmim][Cl] or [BmPyrr][Cl] was added to each of two 50 mL screw-cap containers. Next, 0.4 g of TMG, 0.6 g of sorbitol ketal, and 1 g of shredded foamed polyurethane were added to each of them, sealed, and kept at 95 °C for 6 hours under mechanical stirring. Then, 20 mL of water was added to each container to stop the reaction. The precipitated product was subjected to the same sample separation, drying, and analysis as described in Example 4, showing the following results:

[0131] ■ Control criterion 1 - Solubility test. The addition of 20 mg of each of the obtained dry polyols in 2 mL of DMSO enabled their complete dissolution, and a clear solution was obtained in all cases. The above indicates that the depolymerization of the foamed polyurethane material was carried out.

[0132] ■ Control criterion 2 - ATR-FTIR spectroscopic analysis (see Figure 14). Each of the obtained dry polyols was analyzed by ATR-FTIR, and their spectra (2, 3) were compared with that of the original foamed polyurethane material (1). The characteristic absorption band of the urethane bond (1700 - 1740 cm -1 ) was not detected in any case: reaction medium [Bmim][Cl] + TBD + sorbitol ketal (spectrum 2); reaction medium [BmPyrr][Cl] + TBD + sorbitol ketal (spectrum 3). The above confirmed the accurate depolymerization of the foamed polyurethane material in the method of the present invention.

[0133] ■ Control criterion 3 - Hydroxyl value measurement. Since the hydroxyl values obtained for different solid fractions were much higher than those of the starting foamed polyurethane material, the accurate depolymerization in these preferred embodiments of the method of the present invention was confirmed again: - PU standard: 9.45 mg KOH / g polyol - Reaction medium [Bmim][Cl] + TBD + solketal: 117.19 mg KOH / g polyol - Reaction medium [BmPyrr][Cl] + TBD + solketal: 65.71 mg KOH / g polyol

Example 16

[0134] Cleavage of the urethane bond of a certain mass of bis(phenylcarbamic acid)oxybis(ethane-2,1-diyl) in a reaction medium containing [Bmim][Cl] as an ionic liquid, DBU, TBD, pyrrolidine, tert-butylamine or triethylamine as a basic catalyst, and water as a nucleophile.

[0135] 1.334 g of [Bmim][Cl] was added to five 50 mL screw-cap containers. Next, the corresponding superbase was added to each of them: 0.267 g of DBU (pK a = 13.5); 0.249 g of TBD (pK a = 15.2); 0.148 g of pyrrolidine (pK a = 11.3); 0.189 g of tert-butylamine (pK a = 10.7) or 0.251 g of triethylamine (pK a = 10.8). And finally, 0.4 g of water and 0.05 g of bis(phenylcarbamic acid)oxybis(ethane-2,1-diyl) were added, the containers were sealed and kept at 95 °C for 4 hours under mechanical stirring. After the elapse of the period, 10 mL of chloroform and 20 mL of water were added to the reaction mixture. The layers were separated, and the organic layer was washed with water (2 × 10 mL). Finally, the organic layer was collected, dried over anhydrous magnesium sulfate and the solvent was evaporated in a rotavapor. The obtained product was analyzed by ATR-FTIR (Figure 15a) and HPLC (Figure 15b).

[0136] As can be observed in Spectra 2 and 3 of Figure 15a, in the reaction carried out in the presence of an ionic liquid, a superbase and a nucleophile, the carbonyl corresponding to the urethane bond completely disappears, and at 1700 - 1740 cm -1It is confirmed by the absence of the band in. However, when the ionic liquid and the nucleophile are combined with a base having a pK of less than 12, the band is present (see Spectra 4, 5, and 6 in Figure 15a). These results are also confirmed in the HPLC chromatogram (Figure 15b), where the peak corresponding to the urethane bond disappears along with the peak associated with the cleavage of the carbamate, and other new peaks appear in relation to the ionic species formed between the superbase (either DBU or TBD) and the hydrolysis products (see Chromatograms 4 - 6 for Chromatograms 2 and 3 in Figure 15b). a When combined with a base having a pK of less than 12, the band is present (see Spectra 4, 5, and 6 in Figure 15a). These results are also confirmed in the HPLC chromatogram (Figure 15b), where the peak corresponding to the urethane bond disappears along with the peak associated with the cleavage of the carbamate, and other new peaks appear in relation to the ionic species formed between the superbase (either DBU or TBD) and the hydrolysis products (see Chromatograms 4 - 6 for Chromatograms 2 and 3 in Figure 15b).

Example 17

[0137] Separation and characterization of the products separated after cleavage of the urethane bond of a certain mass of bis(phenylcarbamic acid)oxybis(ethane - 2,1 - diyl) in a reaction medium containing [Bmim][Cl] as the ionic liquid, DBU as the superbase, and water as the nucleophile.

[0138] After completion of the depolymerization reaction described in Example 16 in which a reaction medium composed of [Bmim][Cl], DBU, and water was used, the main product obtained by a chromatography column was separated using silica gel as the stationary phase and a mixture of dichloromethane / methanol as the mobile phase (changing the ratio from 100 / 0 to 95 / 15 v / v). The pure product was analyzed as follows:

[0139] - 1 1H - NMR (300 MHz, CDCl3): δ 7.88 (s, 2H)|7.34 (dt, J = 8.8, 1.7 Hz, 4H)|7.25 - 7.15 (m, 4H)|7.00 - 6.83 (m, 2H)|6.16 (t, J = 5.9 Hz, 2H)|3.37 (t, J = 6.7 Hz, 4H)|3.24 (dd, J = 10.3, 6.0 Hz, 4H)|3.21 - 3.08 (m, 5H)|2.56 - 2.37 (m, 4H)|1.77 - 1.47 (m, 16H) (see Figure 16A);

[0140] - 1313C-NMR (101 MHz, CDCl3): δ 176.64 | 156.28 | 139.74 | 128.86 | 122.26 | 119.26 | 49.67 | 45.65 | 37.18 | 36.88 | 29.83 | 28.38 | 28.21 | 23.32 (see Figure 16B);

[0141] - ATR-FTIR: ν (cm -1 ) = 3337 | 3336 | 3331 | 2930 | 1690 | 1613 | 1597 | 1548 | 1497 | 1440 | 1368 | 1353 | 1310 | 1227 | 1199 | 1176 | 1153 | 1112 | 1081 | 1031 | 978 | 909 | 853 | 753 | 726 | 693 | 644 (see Figure 16C), and

[0142] - Mass spectrum: m / z: [C 16 H 23 N3O2Na] + Calculated [M + Na] + = 312.1689; Detected: 312.1686.

Example 18

[0143] An HPLC method for monitoring the change in the conversion of carbamate groups through the cleavage of urethane bonds of bis(phenylcarbamic acid)oxybis(ethane-2,1-diyl).

[0144] The conditions of the HPLC-DAD method used were: a 100 mm long C-18 column, a flow rate of 0.5 mL / min, an initial pressure of 43 - 44 bar, a column temperature of 30 °C, a detector temperature of 50 °C, a sample volume of 10 μL, a wavelength of 220 nm, a time of 30 minutes, and a gradient of acetonitrile (ACN)-water (5% ACN from 0 to 5 minutes, 5 - 20% ACN from 5 to 8 minutes, 20 - 60% ACN from 8 to 13 minutes, 60 - 95% ACN from 13 to 18 minutes, maintained at 95% ACN from 18 to 23 minutes, then decreased to 95 - 5% ACN from 23 to 25 minutes and maintained at 5% ACN from 25 to 30 minutes). Under these conditions, the presence of bis(phenylcarbamic acid)oxybis(ethane-2,1-diyl) of the urethane model was identified by the appearance of a signal at a retention time of 18.12 minutes (see chromatogram A in Figure 17b).

[0145] Sampling of the products analyzed in different reactions using bis(phenylcarbamic acid)oxybis(ethane-2,1-diyl) of the urethane model consists of dissolving all the products obtained in 3 mL of methanol (according to the method described in Example 16), and then taking a 50 μL aliquot of the said solution and diluting it in 1 mL of methanol.

Example 19

[0146] Cleavage of the urethane bond of a certain mass of bis(phenylcarbamic acid)oxybis(ethane-2,1-diyl) in a depolymerization reaction medium containing [Bmim][Cl] as an ionic liquid, different amounts of DBU as a superbase, and water as a nucleophile.

[0147] 1.334 g of [Bmim][Cl] was added into three 50 mL screw-cap containers. Next, the corresponding amounts of DBU (0.267 g for the investigation at 12.3 equivalents, 0.108 g for the investigation at 5 equivalents, 0 g for the investigation in the absence of DBU), 0.4 g of water and 0.05 g of bis(phenylcarbamic acid)oxybis(ethane-2,1-diyl) were added, the said containers were sealed and kept at 95 °C for 4 hours under mechanical stirring. After the elapse of the said period, it was subjected to the same method of separation and drying as described in Example 16.

[0148] In each case, the product separated after cleavage of the urethane bond of bis(phenylcarbamic acid)oxybis(ethane-2,1-diyl) 1 was analyzed by 1H-NMR (Figure 17a) and HPLC (Figure 17b). The results obtained show that in the absence of superbase, one of the components of the reaction mixture, the urethane bond does not cleave (compare spectrum E in Figures 17a and 17b with C and D), thus once again demonstrating the regeneration of the starting urethane as such.

Example 20

[0149] Depolymerization of a foamed PU material at 95 °C for 6 h in a depolymerization reaction medium containing [Bmim][Cl] as the ionic liquid, DBU, TBD, pyrrolidine, tert-butylamine or triethylamine as the basic catalyst, and water as the nucleophile.

[0150] 2 g of [Bmim][Cl] is added into five 50 mL screw-cap containers. Next, 0.4 g of the corresponding basic catalyst (DBU, TBD, pyrrolidine, tert-butylamine or triethylamine), 0.6 g of water and 1 g of ground foamed polyurethane are added to each of them, the containers are sealed and kept at 95 °C for 6 h under mechanical stirring. Then, 20 mL of water is added to each container to stop the reaction. The precipitated product is subjected to the same sample separation, drying and analysis as described in Example 3, giving the following results:

[0151] ■ Control reference 1 - Solubility test. Addition of 20 mg of the dry polyol obtained using the superbase DBU or superbase TBD as the basic catalyst in 2 mL of DMSO allowed their complete dissolution, giving a clear solution. In contrast, for the product obtained using a base, i.e., pyrrolidine, tert-butylamine or triethylamine as the basic catalyst, addition of the said product in 2 mL of DMSO gave an insoluble precipitate.

[0152] ■Control Standard 2 - ATR - FTIR Spectroscopic Analysis (see Figure 18). Each of the obtained dry polyols was analyzed by ATR - FTIR, and their spectra (2 - 6) were compared with that of the original foamed polyurethane material (1). The characteristic absorption band of the urethane bond (1700 - 1740 cm -1 ) was not detected when DBU (spectrum 2) or TBD (spectrum 3) was used as the superbase, but was observed when pyrrolidine (spectrum 4), tert - butylamine (spectrum 5), or triethylamine (spectrum 6) was used.

[0153] These results confirmed the same behavior observed in Example 16. Only the use of a reaction medium consisting of a combination of an ionic liquid, a superbase, and a nucleophile leads to the cleavage of the urethane bond and, therefore, the depolymerization of the polyurethane material at temperatures below 100°C.

Example 21

[0154] Cleavage of the urethane bond of a certain mass of bis(phenylcarbamic acid) oxybis(ethane - 2,1 - diyl) in a reaction medium containing [Bmim][Cl], [Bmim][AcO], [TBP][Br], or [BmPyr][Cl] as the ionic liquid, DBU as the superbase, and water as the nucleophile.

[0155] 1.334 g of [Bmim][Cl], 1.666 g of [Bmim][AcO], 2.5917 g of [TBP][Br], or 1.4183 g of [BmPyr][Cl] was added to four 50 - mL screw - cap containers. Next, 0.267 g of DBU, 0.4 g of water, and 0.05 g of the urethane model bis(phenylcarbamic acid) oxybis(ethane - 2,1 - diyl) were added to each of them, sealed, and kept at 95°C for 4 hours under mechanical stirring. After the lapse of the said period, it was subjected to the same separation and drying methods as described in Example 16. The obtained product was analyzed by HPLC (see Figure 19).

[0156] The need for a reaction medium composed of an ionic liquid, a superbase, and a nucleophile to achieve cleavage of the urethane bond was exemplified again according to the above embodiment. Regardless of the type of ionic liquid used, the basis for the effectiveness of the cleavage was shown by the complete disappearance of the peaks associated with the urethane bond.

Claims

1. A method for depolymerizing a polyurethane material, comprising: a) mixing the polyurethane material with a depolymerization reaction medium, wherein the depolymerization reaction medium comprises an ionic liquid, a basic catalyst, and a nucleophile; and b) obtaining two immiscible fractions of the mixture obtained in step a), - a first fraction comprising at least a polyol material, and - a second fraction comprising at least an ionic liquid and a basic catalyst; including performing, - the depolymerization reaction medium is ■ an ionic liquid in a proportion of 50 w / w% or more based on the total weight of the depolymerization reaction medium; ■ a superbase as a basic catalyst; and ■ a nucleophile in a proportion of 15 w / w% or less based on the total weight of the depolymerization reaction medium; - step a) is carried out at a temperature between 50 and 100 °C over a time including between 2 minutes and 10 hours; and - step b) is i. adding a protic molecular solvent in an amount between 4 and 40 times the weight of the depolymerization reaction medium to the mixture of step a); ii. subjecting the mixture of step i) to a temperature between 20 and 60 °C over at least 1 hour; and iii. separating the resulting fractions; characterized in that the method comprises performing the sub-steps.

2. The method according to the preceding claim, wherein the polyurethane material comprises a thermosetting polyurethane.

3. The method according to the preceding claim, wherein the thermosetting polyurethane comprises a foamed polyurethane.

4. The method according to any one of the preceding claims, wherein in step a), the polyurethane material is mixed with the depolymerization reaction medium in a mass ratio including between 1:20 and 1:

1.

5. The method according to the preceding claim, wherein in step a), the polyurethane material is mixed with the depolymerization reaction medium in a mass ratio including between 1:15 and 1:

3.

6. The method according to the preceding claim, wherein in step a), the polyurethane material is mixed with the depolymerization reaction medium in a mass ratio including between 1:10 and 1:

5.

7. The method according to any one of the preceding claims, wherein step a) is carried out at a temperature including between 80 and 100 °C and / or over a time including between 2 and 8 hours.

8. The method according to the preceding claim, wherein step a) is carried out at a temperature including between 90 and 98 °C and / or over a time including between 3 and 7 hours.

9. The step a) is carried out in a depolymerization reaction medium, and the depolymerization reaction medium contains an ionic liquid in a proportion of 50 to 85 w / w% based on the total weight of the depolymerization reaction medium, according to the method of any of the preceding claims.

10. The depolymerization reaction medium contains an ionic liquid in a proportion of 65 to 80 w / w% based on the total weight of the depolymerization reaction medium, according to the method of the preceding claims.

11. The step a) is carried out in a depolymerization reaction medium, and the depolymerization reaction medium contains a nucleophile in a proportion of 1 to 15 w / w% based on the total weight of the depolymerization reaction medium, according to the method of any of the preceding claims.

12. The depolymerization reaction medium contains a nucleophile in a proportion of 5 to 15 w / w% based on the total weight of the depolymerization reaction medium, according to the method of the preceding claims.

13. In step b), a protonic molecular solvent with a mass between 5 and 15 times greater than the weight of the depolymerization reaction medium is added, according to the method of any of the preceding claims.

14. The step a) is carried out using a nucleophile containing water, alcohol, amine, or any possible combination thereof, according to the method of any of the preceding claims.

15. The nucleophile contains at least 80% water, according to the method of the preceding claims.

16. The sub-step i) is carried out using a protonic molecular solvent containing water, methanol, ethanol, isopropanol, or any possible combination thereof, according to the method of any of the preceding claims.

17. The protonic molecular solvent contains at least 80% water, according to the method of the preceding claims.

18. The step a) is: - using an ionic liquid containing a cation selected from dialkylimidazolium, tetraalkylammonium, dialkylpiperidinium, alkylpyridinium, dialkylpyrrolidinium, and / or tetraalkylphosphonium, and / or - an anion selected from fluoride, chloride, bromide, iodide, acetate, trifluoroacetate, formate, and / or carbonate according to the method of any of the preceding claims.

19. The ionic liquid is 1-butyl-3-methylimidazolium acetate, 1-ethyl-3-methylimidazolium acetate, 1-butyl-3-methylpyridinium chloride, 1-butyl-3-methylpyridinium bromide, 1-butyl-3-methylpyridinium iodide, 1-butyl-1-methylpiperidinium chloride, 1-butyl-1-methylpiperidinium bromide, 1-butyl-1-methylpiperidinium iodide, 1-butyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium bromide, 1-butyl-3-methylimidazolium iodide, 1-ethyl-3-methylimidazolium chloride, 1-ethyl-3-methylimidazolium bromide, 1-ethyl-3-methylimidazolium iodide, 1-butyl-4-methylpyridinium chloride, 1-butyl-3-methylimidazolium formate, 1-hexyl-3-methylimidazolium chloride, 1-hexyl-3-methylimidazolium bromide, 1-hexyl-3-methylimidazolium iodide, 1-octyl-3-methylimidazolium chloride, 1-octyl-3-methylimidazolium bromide, 1-octyl-3-methylimidazolium iodide, 1-allyl-3-methylimidazolium chloride, 1-butyl-3-methyl-imidazolium acetate, 1-butyl-3-methyl-imidazolium bromide, 1-ethyl-2-methylpyridinium bromide, N-ethylpyridinium bromide, 1-butyl-3-methyl-imidazolium chloride, 1-butyl-1-methylpyrrolidinium chloride, 1-butyl-1-methylpiperidinium iodide, tetrabutylphosphonium bromide, tetrabutylphosphonium chloride. The method according to the preceding claim, comprising 1-butyl-2-methylpyridinium chloride, 1-ethyl-1-methyl-piperidinium chloride, or any possible combination thereof.

20. The method according to any of the preceding claims, wherein the superbase comprises at least a bicyclic amidine, a bicyclic amidine derivative, guanidine, a guanidine derivative, or any possible combination thereof.

21. The method according to the preceding claim, wherein the superbase comprises 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), 1,5-diazabicyclo[4.3.0]non-5-ene (DBN), 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD), tetramethylguanidine (TMG), or any possible combination thereof. **Claim 22** At least one of the following additional steps: - A step of reusing a first fraction in the synthesis of a new polyurethane; and / or - A step of reusing a second fraction in step a) of a new process for the depolymerization of a polyurethane material The method according to any one of the preceding claims, comprising: **Claim 23** The method according to any one of the preceding claims, further comprising a step of drying the first and / or second fraction until the moisture content of the fraction is reduced to a value of less than 1 w / w%. **Claim 24** The method according to the preceding claim, wherein the drying step comprises a process of freeze-drying, vacuum evaporation, heating, distillation, resin adsorption, or any possible combination thereof. **Claim 25** The method according to claims 22 to 24, comprising in advance a step of treating the second fraction with a hydrophobic adsorbent. **Claim 26** The method according to the preceding claim, wherein the hydrophobic adsorbent comprises activated carbon or polystyrene resin. **Claim 27** The method according to any one of the preceding claims, wherein the sub-step iii) comprises a process of centrifugation, decantation, filtration, suction filtration, resin adsorption, or any possible combination thereof. **Claim 28** The method according to any one of the preceding claims, comprising an additional step of verifying the progress and completion of step a) and / or step b).

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